Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

57 files changed, 13537 insertions, 0 deletions

diff --git a/dom/fetch/BodyExtractor.cpp b/dom/fetch/BodyExtractor.cpp
new file mode 100644
index 0000000000..c4a6e3a399
--- /dev/null
+++ b/dom/fetch/BodyExtractor.cpp
@@ -0,0 +1,182 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "BodyExtractor.h"
+#include "mozilla/dom/File.h"
+#include "mozilla/dom/FormData.h"
+#include "mozilla/dom/TypedArray.h"
+#include "mozilla/dom/URLSearchParams.h"
+#include "mozilla/dom/XMLHttpRequest.h"
+#include "mozilla/UniquePtr.h"
+#include "nsContentUtils.h"
+#include "nsDOMSerializer.h"
+#include "nsIGlobalObject.h"
+#include "nsIInputStream.h"
+#include "nsIOutputStream.h"
+#include "nsIStorageStream.h"
+#include "nsStringStream.h"
+
+namespace mozilla::dom {
+
+static nsresult GetBufferDataAsStream(
+    const uint8_t* aData, uint32_t aDataLength, nsIInputStream** aResult,
+    uint64_t* aContentLength, nsACString& aContentType, nsACString& aCharset) {
+  aContentType.SetIsVoid(true);
+  aCharset.Truncate();
+
+  *aContentLength = aDataLength;
+  const char* data = reinterpret_cast<const char*>(aData);
+
+  nsCOMPtr<nsIInputStream> stream;
+  nsresult rv = NS_NewByteInputStream(
+      getter_AddRefs(stream), Span(data, aDataLength), NS_ASSIGNMENT_COPY);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  stream.forget(aResult);
+
+  return NS_OK;
+}
+
+template <>
+nsresult BodyExtractor<const ArrayBuffer>::GetAsStream(
+    nsIInputStream** aResult, uint64_t* aContentLength,
+    nsACString& aContentTypeWithCharset, nsACString& aCharset) const {
+  mBody->ComputeState();
+  return GetBufferDataAsStream(mBody->Data(), mBody->Length(), aResult,
+                               aContentLength, aContentTypeWithCharset,
+                               aCharset);
+}
+
+template <>
+nsresult BodyExtractor<const ArrayBufferView>::GetAsStream(
+    nsIInputStream** aResult, uint64_t* aContentLength,
+    nsACString& aContentTypeWithCharset, nsACString& aCharset) const {
+  mBody->ComputeState();
+  return GetBufferDataAsStream(mBody->Data(), mBody->Length(), aResult,
+                               aContentLength, aContentTypeWithCharset,
+                               aCharset);
+}
+
+template <>
+nsresult BodyExtractor<Document>::GetAsStream(
+    nsIInputStream** aResult, uint64_t* aContentLength,
+    nsACString& aContentTypeWithCharset, nsACString& aCharset) const {
+  NS_ENSURE_STATE(mBody);
+  aCharset.AssignLiteral("UTF-8");
+
+  nsresult rv;
+  nsCOMPtr<nsIStorageStream> storStream;
+  rv = NS_NewStorageStream(4096, UINT32_MAX, getter_AddRefs(storStream));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsIOutputStream> output;
+  rv = storStream->GetOutputStream(0, getter_AddRefs(output));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (mBody->IsHTMLDocument()) {
+    aContentTypeWithCharset.AssignLiteral("text/html;charset=UTF-8");
+
+    nsString serialized;
+    if (!nsContentUtils::SerializeNodeToMarkup(mBody, true, serialized)) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+
+    nsAutoCString utf8Serialized;
+    if (!AppendUTF16toUTF8(serialized, utf8Serialized, fallible)) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+
+    uint32_t written;
+    rv = output->Write(utf8Serialized.get(), utf8Serialized.Length(), &written);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    MOZ_ASSERT(written == utf8Serialized.Length());
+  } else {
+    aContentTypeWithCharset.AssignLiteral("application/xml;charset=UTF-8");
+
+    auto serializer = MakeUnique<nsDOMSerializer>();
+
+    // Make sure to use the encoding we'll send
+    ErrorResult res;
+    serializer->SerializeToStream(*mBody, output, u"UTF-8"_ns, res);
+    if (NS_WARN_IF(res.Failed())) {
+      return res.StealNSResult();
+    }
+  }
+
+  output->Close();
+
+  uint32_t length;
+  rv = storStream->GetLength(&length);
+  NS_ENSURE_SUCCESS(rv, rv);
+  *aContentLength = length;
+
+  rv = storStream->NewInputStream(0, aResult);
+  NS_ENSURE_SUCCESS(rv, rv);
+  return NS_OK;
+}
+
+template <>
+nsresult BodyExtractor<const nsAString>::GetAsStream(
+    nsIInputStream** aResult, uint64_t* aContentLength,
+    nsACString& aContentTypeWithCharset, nsACString& aCharset) const {
+  nsCString encoded;
+  if (!CopyUTF16toUTF8(*mBody, encoded, fallible)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  uint32_t encodedLength = encoded.Length();
+  nsresult rv = NS_NewCStringInputStream(aResult, std::move(encoded));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  *aContentLength = encodedLength;
+  aContentTypeWithCharset.AssignLiteral("text/plain;charset=UTF-8");
+  aCharset.AssignLiteral("UTF-8");
+  return NS_OK;
+}
+
+template <>
+nsresult BodyExtractor<nsIInputStream>::GetAsStream(
+    nsIInputStream** aResult, uint64_t* aContentLength,
+    nsACString& aContentTypeWithCharset, nsACString& aCharset) const {
+  aContentTypeWithCharset.AssignLiteral("text/plain");
+  aCharset.Truncate();
+
+  nsresult rv = mBody->Available(aContentLength);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsIInputStream> stream(mBody);
+  stream.forget(aResult);
+  return NS_OK;
+}
+
+template <>
+nsresult BodyExtractor<const Blob>::GetAsStream(
+    nsIInputStream** aResult, uint64_t* aContentLength,
+    nsACString& aContentTypeWithCharset, nsACString& aCharset) const {
+  return mBody->GetSendInfo(aResult, aContentLength, aContentTypeWithCharset,
+                            aCharset);
+}
+
+template <>
+nsresult BodyExtractor<const FormData>::GetAsStream(
+    nsIInputStream** aResult, uint64_t* aContentLength,
+    nsACString& aContentTypeWithCharset, nsACString& aCharset) const {
+  return mBody->GetSendInfo(aResult, aContentLength, aContentTypeWithCharset,
+                            aCharset);
+}
+
+template <>
+nsresult BodyExtractor<const URLSearchParams>::GetAsStream(
+    nsIInputStream** aResult, uint64_t* aContentLength,
+    nsACString& aContentTypeWithCharset, nsACString& aCharset) const {
+  return mBody->GetSendInfo(aResult, aContentLength, aContentTypeWithCharset,
+                            aCharset);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/fetch/BodyExtractor.h b/dom/fetch/BodyExtractor.h
new file mode 100644
index 0000000000..08e5210afc
--- /dev/null
+++ b/dom/fetch/BodyExtractor.h
@@ -0,0 +1,42 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_BodyExtractor_h
+#define mozilla_dom_BodyExtractor_h
+
+#include "nsString.h"
+
+class nsIInputStream;
+class nsIGlobalObject;
+
+namespace mozilla::dom {
+
+class BodyExtractorBase {
+ public:
+  virtual nsresult GetAsStream(nsIInputStream** aResult,
+                               uint64_t* aContentLength,
+                               nsACString& aContentTypeWithCharset,
+                               nsACString& aCharset) const = 0;
+};
+
+// The implementation versions of this template are:
+// ArrayBuffer, ArrayBufferView, Blob, FormData,
+// URLSearchParams, nsAString, Document, nsIInputStream.
+template <typename Type>
+class BodyExtractor final : public BodyExtractorBase {
+  Type* mBody;
+
+ public:
+  explicit BodyExtractor(Type* aBody) : mBody(aBody) {}
+
+  nsresult GetAsStream(nsIInputStream** aResult, uint64_t* aContentLength,
+                       nsACString& aContentTypeWithCharset,
+                       nsACString& aCharset) const override;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_BodyExtractor_h
diff --git a/dom/fetch/ChannelInfo.cpp b/dom/fetch/ChannelInfo.cpp
new file mode 100644
index 0000000000..71b9e3277b
--- /dev/null
+++ b/dom/fetch/ChannelInfo.cpp
@@ -0,0 +1,95 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/ChannelInfo.h"
+#include "nsCOMPtr.h"
+#include "nsContentUtils.h"
+#include "nsIChannel.h"
+#include "mozilla/dom/Document.h"
+#include "nsIGlobalObject.h"
+#include "nsIHttpChannel.h"
+#include "nsSerializationHelper.h"
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/net/HttpBaseChannel.h"
+#include "nsNetUtil.h"
+
+using namespace mozilla;
+using namespace mozilla::dom;
+
+void ChannelInfo::InitFromDocument(Document* aDoc) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(!mInited, "Cannot initialize the object twice");
+
+  nsCOMPtr<nsITransportSecurityInfo> securityInfo(aDoc->GetSecurityInfo());
+  if (securityInfo) {
+    SetSecurityInfo(securityInfo);
+  }
+
+  mInited = true;
+}
+
+void ChannelInfo::InitFromChannel(nsIChannel* aChannel) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(!mInited, "Cannot initialize the object twice");
+
+  nsCOMPtr<nsITransportSecurityInfo> securityInfo;
+  aChannel->GetSecurityInfo(getter_AddRefs(securityInfo));
+  if (securityInfo) {
+    SetSecurityInfo(securityInfo);
+  }
+
+  mInited = true;
+}
+
+void ChannelInfo::InitFromChromeGlobal(nsIGlobalObject* aGlobal) {
+  MOZ_ASSERT(!mInited, "Cannot initialize the object twice");
+  MOZ_ASSERT(aGlobal);
+
+  MOZ_RELEASE_ASSERT(aGlobal->PrincipalOrNull()->IsSystemPrincipal());
+
+  mSecurityInfo = nullptr;
+  mInited = true;
+}
+
+void ChannelInfo::InitFromTransportSecurityInfo(
+    nsITransportSecurityInfo* aSecurityInfo) {
+  MOZ_ASSERT(!mInited, "Cannot initialize the object twice");
+
+  mSecurityInfo = aSecurityInfo;
+  mInited = true;
+}
+
+void ChannelInfo::SetSecurityInfo(nsITransportSecurityInfo* aSecurityInfo) {
+  MOZ_ASSERT(!mSecurityInfo, "security info should only be set once");
+  mSecurityInfo = aSecurityInfo;
+}
+
+nsresult ChannelInfo::ResurrectInfoOnChannel(nsIChannel* aChannel) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(mInited);
+
+  if (mSecurityInfo) {
+    nsCOMPtr<nsIHttpChannel> httpChannel = do_QueryInterface(aChannel);
+    MOZ_ASSERT(httpChannel);
+    net::HttpBaseChannel* httpBaseChannel =
+        static_cast<net::HttpBaseChannel*>(httpChannel.get());
+    nsresult rv = httpBaseChannel->OverrideSecurityInfo(mSecurityInfo);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+
+  return NS_OK;
+}
+
+already_AddRefed<nsITransportSecurityInfo> ChannelInfo::SecurityInfo() const {
+  // This may be called when mInited is false, for example if we try to store
+  // a synthesized Response object into the Cache.  Uninitialized and empty
+  // ChannelInfo objects are indistinguishable at the IPC level, so this is
+  // fine.
+  nsCOMPtr<nsITransportSecurityInfo> securityInfo(mSecurityInfo);
+  return securityInfo.forget();
+}
diff --git a/dom/fetch/ChannelInfo.h b/dom/fetch/ChannelInfo.h
new file mode 100644
index 0000000000..7df6c53ec4
--- /dev/null
+++ b/dom/fetch/ChannelInfo.h
@@ -0,0 +1,70 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_ChannelInfo_h
+#define mozilla_dom_ChannelInfo_h
+
+#include "nsCOMPtr.h"
+#include "nsITransportSecurityInfo.h"
+#include "nsString.h"
+
+class nsIChannel;
+class nsIGlobalObject;
+class nsIURI;
+
+namespace mozilla {
+namespace dom {
+
+class Document;
+
+// This class represents the information related to a Response that we
+// retrieve from the corresponding channel that is used to perform the fetch.
+//
+// When adding new members to this object, the following code needs to be
+// updated:
+// * InitFromChannel and InitFromTransportSecurityInfo members
+// * ResurrectInfoOnChannel member
+// * SecurityInfo member
+// * constructors and assignment operators for this class.
+// * DOM Cache schema code (in dom/cache/DBSchema.cpp) to ensure that the newly
+//   added member is saved into the DB and loaded from it properly.
+//
+// Care must be taken when initializing this object, or when calling
+// ResurrectInfoOnChannel().  This object cannot be initialized twice, and
+// ResurrectInfoOnChannel() cannot be called on it before it has been
+// initialized.  There are assertions ensuring these invariants.
+class ChannelInfo final {
+ public:
+  ChannelInfo() : mInited(false) {}
+
+  ChannelInfo(const ChannelInfo& aRHS) = default;
+
+  ChannelInfo& operator=(const ChannelInfo& aRHS) = default;
+
+  void InitFromDocument(Document* aDoc);
+  void InitFromChannel(nsIChannel* aChannel);
+  void InitFromChromeGlobal(nsIGlobalObject* aGlobal);
+  void InitFromTransportSecurityInfo(nsITransportSecurityInfo* aSecurityInfo);
+
+  // This restores every possible information stored from a previous channel
+  // object on a new one.
+  nsresult ResurrectInfoOnChannel(nsIChannel* aChannel);
+
+  bool IsInitialized() const { return mInited; }
+
+  already_AddRefed<nsITransportSecurityInfo> SecurityInfo() const;
+
+ private:
+  void SetSecurityInfo(nsITransportSecurityInfo* aSecurityInfo);
+
+  nsCOMPtr<nsITransportSecurityInfo> mSecurityInfo;
+  bool mInited;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_ChannelInfo_h
diff --git a/dom/fetch/Fetch.cpp b/dom/fetch/Fetch.cpp
new file mode 100644
index 0000000000..c4589bd513
--- /dev/null
+++ b/dom/fetch/Fetch.cpp
@@ -0,0 +1,1683 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "Fetch.h"
+
+#include "js/RootingAPI.h"
+#include "js/Value.h"
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/StaticPrefs_dom.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/ipc/BackgroundChild.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "mozilla/ipc/PBackgroundSharedTypes.h"
+#include "mozilla/ipc/IPCStreamUtils.h"
+#include "nsIGlobalObject.h"
+
+#include "nsDOMString.h"
+#include "nsJSUtils.h"
+#include "nsNetUtil.h"
+#include "nsReadableUtils.h"
+#include "nsStreamUtils.h"
+#include "nsStringStream.h"
+#include "nsProxyRelease.h"
+
+#include "mozilla/ErrorResult.h"
+#include "mozilla/dom/BindingDeclarations.h"
+#include "mozilla/dom/BodyConsumer.h"
+#include "mozilla/dom/Exceptions.h"
+#include "mozilla/dom/DOMException.h"
+#include "mozilla/dom/FetchDriver.h"
+#include "mozilla/dom/File.h"
+#include "mozilla/dom/FormData.h"
+#include "mozilla/dom/Headers.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/PromiseWorkerProxy.h"
+#include "mozilla/dom/ReadableStreamDefaultReader.h"
+#include "mozilla/dom/RemoteWorkerChild.h"
+#include "mozilla/dom/Request.h"
+#include "mozilla/dom/Response.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/dom/URLSearchParams.h"
+#include "mozilla/net/CookieJarSettings.h"
+
+#include "BodyExtractor.h"
+#include "FetchChild.h"
+#include "FetchObserver.h"
+#include "InternalRequest.h"
+#include "InternalResponse.h"
+
+#include "mozilla/dom/WorkerCommon.h"
+#include "mozilla/dom/WorkerRef.h"
+#include "mozilla/dom/WorkerRunnable.h"
+#include "mozilla/dom/WorkerScope.h"
+
+namespace mozilla::dom {
+
+namespace {
+
+// Step 17.2.1.2 and 17.2.2 of
+// https://fetch.spec.whatwg.org/#concept-http-network-fetch
+// If stream is readable, then error stream with ...
+void AbortStream(JSContext* aCx, ReadableStream* aReadableStream,
+                 ErrorResult& aRv, JS::Handle<JS::Value> aReasonDetails) {
+  if (aReadableStream->State() != ReadableStream::ReaderState::Readable) {
+    return;
+  }
+
+  JS::Rooted<JS::Value> value(aCx, aReasonDetails);
+
+  if (aReasonDetails.isUndefined()) {
+    RefPtr<DOMException> e = DOMException::Create(NS_ERROR_DOM_ABORT_ERR);
+    if (!GetOrCreateDOMReflector(aCx, e, &value)) {
+      return;
+    }
+  }
+
+  aReadableStream->ErrorNative(aCx, value, aRv);
+}
+
+}  // namespace
+
+class AbortSignalMainThread final : public AbortSignalImpl {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(AbortSignalMainThread)
+
+  explicit AbortSignalMainThread(bool aAborted)
+      : AbortSignalImpl(aAborted, JS::UndefinedHandleValue) {
+    mozilla::HoldJSObjects(this);
+  }
+
+ private:
+  ~AbortSignalMainThread() { mozilla::DropJSObjects(this); };
+};
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(AbortSignalMainThread)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(AbortSignalMainThread)
+  AbortSignalImpl::Unlink(static_cast<AbortSignalImpl*>(tmp));
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(AbortSignalMainThread)
+  AbortSignalImpl::Traverse(static_cast<AbortSignalImpl*>(tmp), cb);
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(AbortSignalMainThread)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mReason)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(AbortSignalMainThread)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(AbortSignalMainThread)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(AbortSignalMainThread)
+
+class AbortSignalProxy;
+
+// This runnable propagates changes from the AbortSignalImpl on workers to the
+// AbortSignalImpl on main-thread.
+class AbortSignalProxyRunnable final : public Runnable {
+  RefPtr<AbortSignalProxy> mProxy;
+
+ public:
+  explicit AbortSignalProxyRunnable(AbortSignalProxy* aProxy)
+      : Runnable("dom::AbortSignalProxyRunnable"), mProxy(aProxy) {}
+
+  NS_IMETHOD Run() override;
+};
+
+// This class orchestrates the proxying of AbortSignal operations between the
+// main thread and a worker thread.
+class AbortSignalProxy final : public AbortFollower {
+  // This is created and released on the main-thread.
+  RefPtr<AbortSignalImpl> mSignalImplMainThread;
+
+  // The main-thread event target for runnable dispatching.
+  nsCOMPtr<nsIEventTarget> mMainThreadEventTarget;
+
+  // This value is used only when creating mSignalImplMainThread on the main
+  // thread, to create it in already-aborted state if necessary.  It does *not*
+  // reflect the instantaneous is-aborted status of the worker thread's
+  // AbortSignal.
+  const bool mAborted;
+
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+  AbortSignalProxy(AbortSignalImpl* aSignalImpl,
+                   nsIEventTarget* aMainThreadEventTarget)
+      : mMainThreadEventTarget(aMainThreadEventTarget),
+        mAborted(aSignalImpl->Aborted()) {
+    MOZ_ASSERT(!NS_IsMainThread());
+    MOZ_ASSERT(mMainThreadEventTarget);
+    Follow(aSignalImpl);
+  }
+
+  // AbortFollower
+  void RunAbortAlgorithm() override;
+
+  AbortSignalImpl* GetOrCreateSignalImplForMainThread() {
+    MOZ_ASSERT(NS_IsMainThread());
+    if (!mSignalImplMainThread) {
+      mSignalImplMainThread = new AbortSignalMainThread(mAborted);
+    }
+    return mSignalImplMainThread;
+  }
+
+  AbortSignalImpl* GetSignalImplForTargetThread() {
+    MOZ_ASSERT(!NS_IsMainThread());
+    return Signal();
+  }
+
+  nsIEventTarget* MainThreadEventTarget() { return mMainThreadEventTarget; }
+
+  void Shutdown() {
+    MOZ_ASSERT(!NS_IsMainThread());
+    Unfollow();
+  }
+
+ private:
+  ~AbortSignalProxy() {
+    NS_ProxyRelease("AbortSignalProxy::mSignalImplMainThread",
+                    mMainThreadEventTarget, mSignalImplMainThread.forget());
+  }
+};
+
+NS_IMPL_ISUPPORTS0(AbortSignalProxy)
+
+NS_IMETHODIMP AbortSignalProxyRunnable::Run() {
+  MOZ_ASSERT(NS_IsMainThread());
+  AbortSignalImpl* signalImpl = mProxy->GetOrCreateSignalImplForMainThread();
+  signalImpl->SignalAbort(JS::UndefinedHandleValue);
+  return NS_OK;
+}
+
+void AbortSignalProxy::RunAbortAlgorithm() {
+  MOZ_ASSERT(!NS_IsMainThread());
+  RefPtr<AbortSignalProxyRunnable> runnable =
+      new AbortSignalProxyRunnable(this);
+  MainThreadEventTarget()->Dispatch(runnable.forget(), NS_DISPATCH_NORMAL);
+}
+
+class WorkerFetchResolver final : public FetchDriverObserver {
+  // Thread-safe:
+  RefPtr<PromiseWorkerProxy> mPromiseProxy;
+  RefPtr<AbortSignalProxy> mSignalProxy;
+
+  // Touched only on the worker thread.
+  RefPtr<FetchObserver> mFetchObserver;
+  RefPtr<WeakWorkerRef> mWorkerRef;
+  bool mIsShutdown;
+
+  Atomic<bool> mNeedOnDataAvailable;
+
+ public:
+  // Returns null if worker is shutting down.
+  static already_AddRefed<WorkerFetchResolver> Create(
+      WorkerPrivate* aWorkerPrivate, Promise* aPromise,
+      AbortSignalImpl* aSignalImpl, FetchObserver* aObserver) {
+    MOZ_ASSERT(aWorkerPrivate);
+    aWorkerPrivate->AssertIsOnWorkerThread();
+    RefPtr<PromiseWorkerProxy> proxy =
+        PromiseWorkerProxy::Create(aWorkerPrivate, aPromise);
+    if (!proxy) {
+      return nullptr;
+    }
+
+    RefPtr<AbortSignalProxy> signalProxy;
+    if (aSignalImpl) {
+      signalProxy = new AbortSignalProxy(
+          aSignalImpl, aWorkerPrivate->MainThreadEventTarget());
+    }
+
+    RefPtr<WorkerFetchResolver> r =
+        new WorkerFetchResolver(proxy, signalProxy, aObserver);
+
+    RefPtr<WeakWorkerRef> workerRef = WeakWorkerRef::Create(
+        aWorkerPrivate, [r]() { r->Shutdown(r->mWorkerRef->GetPrivate()); });
+    if (NS_WARN_IF(!workerRef)) {
+      return nullptr;
+    }
+
+    r->mWorkerRef = std::move(workerRef);
+
+    return r.forget();
+  }
+
+  AbortSignalImpl* GetAbortSignalForMainThread() {
+    MOZ_ASSERT(NS_IsMainThread());
+
+    if (!mSignalProxy) {
+      return nullptr;
+    }
+
+    return mSignalProxy->GetOrCreateSignalImplForMainThread();
+  }
+
+  AbortSignalImpl* GetAbortSignalForTargetThread() {
+    mPromiseProxy->GetWorkerPrivate()->AssertIsOnWorkerThread();
+
+    if (!mSignalProxy) {
+      return nullptr;
+    }
+
+    return mSignalProxy->GetSignalImplForTargetThread();
+  }
+
+  PromiseWorkerProxy* PromiseProxy() const {
+    MOZ_ASSERT(NS_IsMainThread());
+    return mPromiseProxy;
+  }
+
+  Promise* WorkerPromise(WorkerPrivate* aWorkerPrivate) const {
+    MOZ_ASSERT(aWorkerPrivate);
+    aWorkerPrivate->AssertIsOnWorkerThread();
+    MOZ_ASSERT(!mIsShutdown);
+
+    return mPromiseProxy->WorkerPromise();
+  }
+
+  FetchObserver* GetFetchObserver(WorkerPrivate* aWorkerPrivate) const {
+    MOZ_ASSERT(aWorkerPrivate);
+    aWorkerPrivate->AssertIsOnWorkerThread();
+
+    return mFetchObserver;
+  }
+
+  void OnResponseAvailableInternal(
+      SafeRefPtr<InternalResponse> aResponse) override;
+
+  void OnResponseEnd(FetchDriverObserver::EndReason aReason,
+                     JS::Handle<JS::Value> aReasonDetails) override;
+
+  bool NeedOnDataAvailable() override;
+
+  void OnDataAvailable() override;
+
+  void Shutdown(WorkerPrivate* aWorkerPrivate) {
+    MOZ_ASSERT(aWorkerPrivate);
+    aWorkerPrivate->AssertIsOnWorkerThread();
+
+    mIsShutdown = true;
+    mPromiseProxy->CleanUp();
+
+    mNeedOnDataAvailable = false;
+    mFetchObserver = nullptr;
+
+    if (mSignalProxy) {
+      mSignalProxy->Shutdown();
+    }
+
+    mWorkerRef = nullptr;
+  }
+
+  bool IsShutdown(WorkerPrivate* aWorkerPrivate) const {
+    MOZ_ASSERT(aWorkerPrivate);
+    aWorkerPrivate->AssertIsOnWorkerThread();
+    return mIsShutdown;
+  }
+
+ private:
+  WorkerFetchResolver(PromiseWorkerProxy* aProxy,
+                      AbortSignalProxy* aSignalProxy, FetchObserver* aObserver)
+      : mPromiseProxy(aProxy),
+        mSignalProxy(aSignalProxy),
+        mFetchObserver(aObserver),
+        mIsShutdown(false),
+        mNeedOnDataAvailable(!!aObserver) {
+    MOZ_ASSERT(!NS_IsMainThread());
+    MOZ_ASSERT(mPromiseProxy);
+  }
+
+  ~WorkerFetchResolver() = default;
+
+  virtual void FlushConsoleReport() override;
+};
+
+void FetchDriverObserver::OnResponseAvailable(
+    SafeRefPtr<InternalResponse> aResponse) {
+  MOZ_ASSERT(!mGotResponseAvailable);
+  mGotResponseAvailable = true;
+  OnResponseAvailableInternal(std::move(aResponse));
+}
+
+class MainThreadFetchResolver final : public FetchDriverObserver {
+  RefPtr<Promise> mPromise;
+  RefPtr<Response> mResponse;
+  RefPtr<FetchObserver> mFetchObserver;
+  RefPtr<AbortSignalImpl> mSignalImpl;
+  const bool mMozErrors;
+
+  nsCOMPtr<nsILoadGroup> mLoadGroup;
+
+  NS_DECL_OWNINGTHREAD
+ public:
+  MainThreadFetchResolver(Promise* aPromise, FetchObserver* aObserver,
+                          AbortSignalImpl* aSignalImpl, bool aMozErrors)
+      : mPromise(aPromise),
+        mFetchObserver(aObserver),
+        mSignalImpl(aSignalImpl),
+        mMozErrors(aMozErrors) {}
+
+  void OnResponseAvailableInternal(
+      SafeRefPtr<InternalResponse> aResponse) override;
+
+  void SetLoadGroup(nsILoadGroup* aLoadGroup) { mLoadGroup = aLoadGroup; }
+
+  void OnResponseEnd(FetchDriverObserver::EndReason aReason,
+                     JS::Handle<JS::Value> aReasonDetails) override {
+    if (aReason == eAborted) {
+      if (!aReasonDetails.isUndefined()) {
+        mPromise->MaybeReject(aReasonDetails);
+      } else {
+        mPromise->MaybeReject(NS_ERROR_DOM_ABORT_ERR);
+      }
+    }
+
+    mFetchObserver = nullptr;
+
+    FlushConsoleReport();
+  }
+
+  bool NeedOnDataAvailable() override;
+
+  void OnDataAvailable() override;
+
+ private:
+  ~MainThreadFetchResolver();
+
+  void FlushConsoleReport() override {
+    mReporter->FlushConsoleReports(mLoadGroup);
+  }
+};
+
+class MainThreadFetchRunnable : public Runnable {
+  RefPtr<WorkerFetchResolver> mResolver;
+  const ClientInfo mClientInfo;
+  const Maybe<ServiceWorkerDescriptor> mController;
+  nsCOMPtr<nsICSPEventListener> mCSPEventListener;
+  SafeRefPtr<InternalRequest> mRequest;
+  UniquePtr<SerializedStackHolder> mOriginStack;
+
+ public:
+  MainThreadFetchRunnable(WorkerFetchResolver* aResolver,
+                          const ClientInfo& aClientInfo,
+                          const Maybe<ServiceWorkerDescriptor>& aController,
+                          nsICSPEventListener* aCSPEventListener,
+                          SafeRefPtr<InternalRequest> aRequest,
+                          UniquePtr<SerializedStackHolder>&& aOriginStack)
+      : Runnable("dom::MainThreadFetchRunnable"),
+        mResolver(aResolver),
+        mClientInfo(aClientInfo),
+        mController(aController),
+        mCSPEventListener(aCSPEventListener),
+        mRequest(std::move(aRequest)),
+        mOriginStack(std::move(aOriginStack)) {
+    MOZ_ASSERT(mResolver);
+  }
+
+  NS_IMETHOD
+  Run() override {
+    AssertIsOnMainThread();
+    RefPtr<FetchDriver> fetch;
+    RefPtr<PromiseWorkerProxy> proxy = mResolver->PromiseProxy();
+
+    {
+      // Acquire the proxy mutex while getting data from the WorkerPrivate...
+      MutexAutoLock lock(proxy->Lock());
+      if (proxy->CleanedUp()) {
+        NS_WARNING("Aborting Fetch because worker already shut down");
+        return NS_OK;
+      }
+
+      WorkerPrivate* workerPrivate = proxy->GetWorkerPrivate();
+      MOZ_ASSERT(workerPrivate);
+      nsCOMPtr<nsIPrincipal> principal = workerPrivate->GetPrincipal();
+      MOZ_ASSERT(principal);
+      nsCOMPtr<nsILoadGroup> loadGroup = workerPrivate->GetLoadGroup();
+      MOZ_ASSERT(loadGroup);
+      // We don't track if a worker is spawned from a tracking script for now,
+      // so pass false as the last argument to FetchDriver().
+      fetch = new FetchDriver(mRequest.clonePtr(), principal, loadGroup,
+                              workerPrivate->MainThreadEventTarget(),
+                              workerPrivate->CookieJarSettings(),
+                              workerPrivate->GetPerformanceStorage(), false);
+      nsAutoCString spec;
+      if (proxy->GetWorkerPrivate()->GetBaseURI()) {
+        proxy->GetWorkerPrivate()->GetBaseURI()->GetAsciiSpec(spec);
+      }
+      fetch->SetWorkerScript(spec);
+
+      fetch->SetClientInfo(mClientInfo);
+      fetch->SetController(mController);
+      fetch->SetCSPEventListener(mCSPEventListener);
+    }
+
+    fetch->SetOriginStack(std::move(mOriginStack));
+
+    RefPtr<AbortSignalImpl> signalImpl =
+        mResolver->GetAbortSignalForMainThread();
+
+    // ...but release it before calling Fetch, because mResolver's callback can
+    // be called synchronously and they want the mutex, too.
+    return fetch->Fetch(signalImpl, mResolver);
+  }
+};
+
+already_AddRefed<Promise> FetchRequest(nsIGlobalObject* aGlobal,
+                                       const RequestOrUSVString& aInput,
+                                       const RequestInit& aInit,
+                                       CallerType aCallerType,
+                                       ErrorResult& aRv) {
+  RefPtr<Promise> p = Promise::Create(aGlobal, aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  MOZ_ASSERT(aGlobal);
+
+  // Double check that we have chrome privileges if the Request's content
+  // policy type has been overridden.
+  MOZ_ASSERT_IF(aInput.IsRequest() &&
+                    aInput.GetAsRequest().IsContentPolicyTypeOverridden(),
+                aCallerType == CallerType::System);
+
+  AutoJSAPI jsapi;
+  if (!jsapi.Init(aGlobal)) {
+    aRv.Throw(NS_ERROR_NOT_AVAILABLE);
+    return nullptr;
+  }
+
+  JSContext* cx = jsapi.cx();
+  JS::Rooted<JSObject*> jsGlobal(cx, aGlobal->GetGlobalJSObject());
+  GlobalObject global(cx, jsGlobal);
+
+  SafeRefPtr<Request> request =
+      Request::Constructor(global, aInput, aInit, aRv);
+  if (aRv.Failed()) {
+    return nullptr;
+  }
+
+  SafeRefPtr<InternalRequest> r = request->GetInternalRequest();
+
+  // Restore information of InterceptedHttpChannel if they are passed with the
+  // Request. Since Request::Constructor would not copy these members.
+  if (aInput.IsRequest()) {
+    RefPtr<Request> inputReq = &aInput.GetAsRequest();
+    SafeRefPtr<InternalRequest> inputInReq = inputReq->GetInternalRequest();
+    if (inputInReq->GetInterceptionTriggeringPrincipalInfo()) {
+      r->SetInterceptionContentPolicyType(
+          inputInReq->InterceptionContentPolicyType());
+      r->SetInterceptionTriggeringPrincipalInfo(
+          MakeUnique<mozilla::ipc::PrincipalInfo>(
+              *(inputInReq->GetInterceptionTriggeringPrincipalInfo().get())));
+      if (!inputInReq->InterceptionRedirectChain().IsEmpty()) {
+        r->SetInterceptionRedirectChain(
+            inputInReq->InterceptionRedirectChain());
+      }
+      r->SetInterceptionFromThirdParty(
+          inputInReq->InterceptionFromThirdParty());
+    }
+  }
+
+  RefPtr<AbortSignalImpl> signalImpl = request->GetSignalImpl();
+
+  if (signalImpl && signalImpl->Aborted()) {
+    // Already aborted signal rejects immediately.
+    JS::Rooted<JS::Value> reason(cx, signalImpl->RawReason());
+    if (reason.get().isUndefined()) {
+      aRv.Throw(NS_ERROR_DOM_ABORT_ERR);
+      return nullptr;
+    }
+
+    p->MaybeReject(reason);
+    return p.forget();
+  }
+
+  JS::Realm* realm = JS::GetCurrentRealmOrNull(cx);
+  if (realm && JS::GetDebuggerObservesWasm(realm)) {
+    r->SetSkipWasmCaching();
+  }
+
+  RefPtr<FetchObserver> observer;
+  if (aInit.mObserve.WasPassed()) {
+    observer = new FetchObserver(aGlobal, signalImpl);
+    aInit.mObserve.Value().HandleEvent(*observer);
+  }
+
+  if (NS_IsMainThread()) {
+    nsCOMPtr<nsPIDOMWindowInner> window = do_QueryInterface(aGlobal);
+    nsCOMPtr<Document> doc;
+    nsCOMPtr<nsILoadGroup> loadGroup;
+    nsCOMPtr<nsICookieJarSettings> cookieJarSettings;
+    nsIPrincipal* principal;
+    bool isTrackingFetch = false;
+    if (window) {
+      doc = window->GetExtantDoc();
+      if (!doc) {
+        aRv.Throw(NS_ERROR_FAILURE);
+        return nullptr;
+      }
+      principal = doc->NodePrincipal();
+      loadGroup = doc->GetDocumentLoadGroup();
+      cookieJarSettings = doc->CookieJarSettings();
+
+      isTrackingFetch = doc->IsScriptTracking(cx);
+    } else {
+      principal = aGlobal->PrincipalOrNull();
+      if (NS_WARN_IF(!principal)) {
+        aRv.Throw(NS_ERROR_FAILURE);
+        return nullptr;
+      }
+
+      cookieJarSettings = mozilla::net::CookieJarSettings::Create(principal);
+    }
+
+    if (!loadGroup) {
+      nsresult rv = NS_NewLoadGroup(getter_AddRefs(loadGroup), principal);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        aRv.Throw(rv);
+        return nullptr;
+      }
+    }
+
+    RefPtr<MainThreadFetchResolver> resolver = new MainThreadFetchResolver(
+        p, observer, signalImpl, request->MozErrors());
+    RefPtr<FetchDriver> fetch =
+        new FetchDriver(std::move(r), principal, loadGroup,
+                        aGlobal->EventTargetFor(TaskCategory::Other),
+                        cookieJarSettings, nullptr,  // PerformanceStorage
+                        isTrackingFetch);
+    fetch->SetDocument(doc);
+    resolver->SetLoadGroup(loadGroup);
+    aRv = fetch->Fetch(signalImpl, resolver);
+    if (NS_WARN_IF(aRv.Failed())) {
+      return nullptr;
+    }
+  } else {
+    WorkerPrivate* worker = GetCurrentThreadWorkerPrivate();
+    MOZ_ASSERT(worker);
+
+    if (worker->IsServiceWorker()) {
+      r->SetSkipServiceWorker();
+    }
+
+    // PFetch gives no benefit for the fetch in the parent process.
+    // Dispatch fetch to the parent process main thread directly for that case.
+    // For child process, dispatch fetch op to the parent.
+    if (StaticPrefs::dom_workers_pFetch_enabled() && !XRE_IsParentProcess()) {
+      RefPtr<FetchChild> actor =
+          FetchChild::Create(worker, p, signalImpl, observer);
+      if (!actor) {
+        NS_WARNING("Could not keep the worker alive.");
+        aRv.Throw(NS_ERROR_DOM_ABORT_ERR);
+        return nullptr;
+      }
+
+      Maybe<ClientInfo> clientInfo(worker->GlobalScope()->GetClientInfo());
+      if (clientInfo.isNothing()) {
+        aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
+        return nullptr;
+      }
+
+      auto* backgroundChild =
+          mozilla::ipc::BackgroundChild::GetOrCreateForCurrentThread();
+      Unused << NS_WARN_IF(!backgroundChild->SendPFetchConstructor(actor));
+
+      FetchOpArgs ipcArgs;
+
+      ipcArgs.request() = IPCInternalRequest();
+      r->ToIPCInternalRequest(&(ipcArgs.request()), backgroundChild);
+
+      ipcArgs.principalInfo() = worker->GetPrincipalInfo();
+      ipcArgs.clientInfo() = clientInfo.ref().ToIPC();
+      if (worker->GetBaseURI()) {
+        worker->GetBaseURI()->GetAsciiSpec(ipcArgs.workerScript());
+      }
+      if (worker->GlobalScope()->GetController().isSome()) {
+        ipcArgs.controller() =
+            Some(worker->GlobalScope()->GetController().ref().ToIPC());
+      }
+      if (worker->CookieJarSettings()) {
+        ipcArgs.cookieJarSettings() = Some(worker->CookieJarSettingsArgs());
+      }
+      if (worker->CSPEventListener()) {
+        ipcArgs.hasCSPEventListener() = true;
+        actor->SetCSPEventListener(worker->CSPEventListener());
+      } else {
+        ipcArgs.hasCSPEventListener() = false;
+      }
+
+      ipcArgs.associatedBrowsingContextID() =
+          worker->AssociatedBrowsingContextID();
+
+      if (worker->IsWatchedByDevTools()) {
+        UniquePtr<SerializedStackHolder> stack;
+        stack = GetCurrentStackForNetMonitor(cx);
+        actor->SetOriginStack(std::move(stack));
+      }
+
+      actor->DoFetchOp(ipcArgs);
+
+      return p.forget();
+    }
+
+    RefPtr<WorkerFetchResolver> resolver =
+        WorkerFetchResolver::Create(worker, p, signalImpl, observer);
+    if (!resolver) {
+      NS_WARNING("Could not keep the worker alive.");
+      aRv.Throw(NS_ERROR_DOM_ABORT_ERR);
+      return nullptr;
+    }
+
+    Maybe<ClientInfo> clientInfo(worker->GlobalScope()->GetClientInfo());
+    if (clientInfo.isNothing()) {
+      aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
+      return nullptr;
+    }
+
+    UniquePtr<SerializedStackHolder> stack;
+    if (worker->IsWatchedByDevTools()) {
+      stack = GetCurrentStackForNetMonitor(cx);
+    }
+
+    RefPtr<MainThreadFetchRunnable> run = new MainThreadFetchRunnable(
+        resolver, clientInfo.ref(), worker->GlobalScope()->GetController(),
+        worker->CSPEventListener(), std::move(r), std::move(stack));
+    worker->DispatchToMainThread(run.forget());
+  }
+
+  return p.forget();
+}
+
+class ResolveFetchPromise : public Runnable {
+ public:
+  ResolveFetchPromise(Promise* aPromise, Response* aResponse)
+      : Runnable("ResolveFetchPromise"),
+        mPromise(aPromise),
+        mResponse(aResponse) {}
+
+  NS_IMETHOD Run() override {
+    mPromise->MaybeResolve(mResponse);
+    return NS_OK;
+  }
+  RefPtr<Promise> mPromise;
+  RefPtr<Response> mResponse;
+};
+
+void MainThreadFetchResolver::OnResponseAvailableInternal(
+    SafeRefPtr<InternalResponse> aResponse) {
+  NS_ASSERT_OWNINGTHREAD(MainThreadFetchResolver);
+  AssertIsOnMainThread();
+
+  if (aResponse->Type() != ResponseType::Error) {
+    nsCOMPtr<nsIGlobalObject> go = mPromise->GetParentObject();
+    nsCOMPtr<nsPIDOMWindowInner> inner = do_QueryInterface(go);
+
+    // Notify the document when a fetch completes successfully. This is
+    // used by the password manager as a hint to observe DOM mutations.
+    // Call this prior to setting state to Complete so we can set up the
+    // observer before mutations occurs.
+    Document* doc = inner ? inner->GetExtantDoc() : nullptr;
+    if (doc) {
+      doc->NotifyFetchOrXHRSuccess();
+    }
+
+    if (mFetchObserver) {
+      mFetchObserver->SetState(FetchState::Complete);
+    }
+
+    mResponse = new Response(go, std::move(aResponse), mSignalImpl);
+    // response headers received from the network should be immutable
+    // all response header settings must be done before this point
+    // see Bug 1574174
+    ErrorResult result;
+    mResponse->Headers_()->SetGuard(HeadersGuardEnum::Immutable, result);
+    MOZ_ASSERT(!result.Failed());
+
+    BrowsingContext* bc = inner ? inner->GetBrowsingContext() : nullptr;
+    bc = bc ? bc->Top() : nullptr;
+    if (bc && bc->IsLoading()) {
+      bc->AddDeprioritizedLoadRunner(
+          new ResolveFetchPromise(mPromise, mResponse));
+    } else {
+      mPromise->MaybeResolve(mResponse);
+    }
+  } else {
+    if (mFetchObserver) {
+      mFetchObserver->SetState(FetchState::Errored);
+    }
+
+    if (mMozErrors) {
+      mPromise->MaybeReject(aResponse->GetErrorCode());
+      return;
+    }
+
+    mPromise->MaybeRejectWithTypeError<MSG_FETCH_FAILED>();
+  }
+}
+
+bool MainThreadFetchResolver::NeedOnDataAvailable() {
+  NS_ASSERT_OWNINGTHREAD(MainThreadFetchResolver);
+  return !!mFetchObserver;
+}
+
+void MainThreadFetchResolver::OnDataAvailable() {
+  NS_ASSERT_OWNINGTHREAD(MainThreadFetchResolver);
+  AssertIsOnMainThread();
+
+  if (!mFetchObserver) {
+    return;
+  }
+
+  if (mFetchObserver->State() == FetchState::Requesting) {
+    mFetchObserver->SetState(FetchState::Responding);
+  }
+}
+
+MainThreadFetchResolver::~MainThreadFetchResolver() {
+  NS_ASSERT_OWNINGTHREAD(MainThreadFetchResolver);
+}
+
+class WorkerFetchResponseRunnable final : public MainThreadWorkerRunnable {
+  RefPtr<WorkerFetchResolver> mResolver;
+  // Passed from main thread to worker thread after being initialized.
+  SafeRefPtr<InternalResponse> mInternalResponse;
+
+ public:
+  WorkerFetchResponseRunnable(WorkerPrivate* aWorkerPrivate,
+                              WorkerFetchResolver* aResolver,
+                              SafeRefPtr<InternalResponse> aResponse)
+      : MainThreadWorkerRunnable(aWorkerPrivate),
+        mResolver(aResolver),
+        mInternalResponse(std::move(aResponse)) {
+    MOZ_ASSERT(mResolver);
+  }
+
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override {
+    MOZ_ASSERT(aWorkerPrivate);
+    aWorkerPrivate->AssertIsOnWorkerThread();
+
+    RefPtr<Promise> promise = mResolver->WorkerPromise(aWorkerPrivate);
+    RefPtr<FetchObserver> fetchObserver =
+        mResolver->GetFetchObserver(aWorkerPrivate);
+
+    if (mInternalResponse->Type() != ResponseType::Error) {
+      if (fetchObserver) {
+        fetchObserver->SetState(FetchState::Complete);
+      }
+
+      RefPtr<nsIGlobalObject> global = aWorkerPrivate->GlobalScope();
+      RefPtr<Response> response =
+          new Response(global, mInternalResponse.clonePtr(),
+                       mResolver->GetAbortSignalForTargetThread());
+
+      // response headers received from the network should be immutable,
+      // all response header settings must be done before this point
+      // see Bug 1574174
+      ErrorResult result;
+      response->Headers_()->SetGuard(HeadersGuardEnum::Immutable, result);
+      MOZ_ASSERT(!result.Failed());
+
+      promise->MaybeResolve(response);
+    } else {
+      if (fetchObserver) {
+        fetchObserver->SetState(FetchState::Errored);
+      }
+
+      promise->MaybeRejectWithTypeError<MSG_FETCH_FAILED>();
+    }
+    return true;
+  }
+};
+
+class WorkerDataAvailableRunnable final : public MainThreadWorkerRunnable {
+  RefPtr<WorkerFetchResolver> mResolver;
+
+ public:
+  WorkerDataAvailableRunnable(WorkerPrivate* aWorkerPrivate,
+                              WorkerFetchResolver* aResolver)
+      : MainThreadWorkerRunnable(aWorkerPrivate), mResolver(aResolver) {}
+
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override {
+    MOZ_ASSERT(aWorkerPrivate);
+    aWorkerPrivate->AssertIsOnWorkerThread();
+
+    RefPtr<FetchObserver> fetchObserver =
+        mResolver->GetFetchObserver(aWorkerPrivate);
+
+    if (fetchObserver && fetchObserver->State() == FetchState::Requesting) {
+      fetchObserver->SetState(FetchState::Responding);
+    }
+
+    return true;
+  }
+};
+
+class WorkerFetchResponseEndBase {
+ protected:
+  RefPtr<WorkerFetchResolver> mResolver;
+
+ public:
+  explicit WorkerFetchResponseEndBase(WorkerFetchResolver* aResolver)
+      : mResolver(aResolver) {
+    MOZ_ASSERT(aResolver);
+  }
+
+  void WorkerRunInternal(WorkerPrivate* aWorkerPrivate) {
+    mResolver->Shutdown(aWorkerPrivate);
+  }
+};
+
+class WorkerFetchResponseEndRunnable final : public MainThreadWorkerRunnable,
+                                             public WorkerFetchResponseEndBase {
+  FetchDriverObserver::EndReason mReason;
+
+ public:
+  WorkerFetchResponseEndRunnable(WorkerPrivate* aWorkerPrivate,
+                                 WorkerFetchResolver* aResolver,
+                                 FetchDriverObserver::EndReason aReason)
+      : MainThreadWorkerRunnable(aWorkerPrivate),
+        WorkerFetchResponseEndBase(aResolver),
+        mReason(aReason) {}
+
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override {
+    if (mResolver->IsShutdown(aWorkerPrivate)) {
+      return true;
+    }
+
+    if (mReason == FetchDriverObserver::eAborted) {
+      mResolver->WorkerPromise(aWorkerPrivate)
+          ->MaybeReject(NS_ERROR_DOM_ABORT_ERR);
+    }
+
+    WorkerRunInternal(aWorkerPrivate);
+    return true;
+  }
+
+  nsresult Cancel() override {
+    // We need to check first if cancel is called twice
+    nsresult rv = WorkerRunnable::Cancel();
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    // Execute Run anyway to make sure we cleanup our promise proxy to avoid
+    // leaking the worker thread
+    Run();
+    return NS_OK;
+  }
+};
+
+class WorkerFetchResponseEndControlRunnable final
+    : public MainThreadWorkerControlRunnable,
+      public WorkerFetchResponseEndBase {
+ public:
+  WorkerFetchResponseEndControlRunnable(WorkerPrivate* aWorkerPrivate,
+                                        WorkerFetchResolver* aResolver)
+      : MainThreadWorkerControlRunnable(aWorkerPrivate),
+        WorkerFetchResponseEndBase(aResolver) {}
+
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override {
+    WorkerRunInternal(aWorkerPrivate);
+    return true;
+  }
+
+  // Control runnable cancel already calls Run().
+};
+
+void WorkerFetchResolver::OnResponseAvailableInternal(
+    SafeRefPtr<InternalResponse> aResponse) {
+  AssertIsOnMainThread();
+
+  MutexAutoLock lock(mPromiseProxy->Lock());
+  if (mPromiseProxy->CleanedUp()) {
+    return;
+  }
+
+  RefPtr<WorkerFetchResponseRunnable> r = new WorkerFetchResponseRunnable(
+      mPromiseProxy->GetWorkerPrivate(), this, std::move(aResponse));
+
+  if (!r->Dispatch()) {
+    NS_WARNING("Could not dispatch fetch response");
+  }
+}
+
+bool WorkerFetchResolver::NeedOnDataAvailable() {
+  AssertIsOnMainThread();
+  return mNeedOnDataAvailable;
+}
+
+void WorkerFetchResolver::OnDataAvailable() {
+  AssertIsOnMainThread();
+
+  MutexAutoLock lock(mPromiseProxy->Lock());
+  if (mPromiseProxy->CleanedUp()) {
+    return;
+  }
+
+  RefPtr<WorkerDataAvailableRunnable> r =
+      new WorkerDataAvailableRunnable(mPromiseProxy->GetWorkerPrivate(), this);
+  Unused << r->Dispatch();
+}
+
+void WorkerFetchResolver::OnResponseEnd(FetchDriverObserver::EndReason aReason,
+                                        JS::Handle<JS::Value> aReasonDetails) {
+  AssertIsOnMainThread();
+  MutexAutoLock lock(mPromiseProxy->Lock());
+  if (mPromiseProxy->CleanedUp()) {
+    return;
+  }
+
+  FlushConsoleReport();
+
+  Unused << aReasonDetails;
+
+  RefPtr<WorkerFetchResponseEndRunnable> r = new WorkerFetchResponseEndRunnable(
+      mPromiseProxy->GetWorkerPrivate(), this, aReason);
+
+  if (!r->Dispatch()) {
+    RefPtr<WorkerFetchResponseEndControlRunnable> cr =
+        new WorkerFetchResponseEndControlRunnable(
+            mPromiseProxy->GetWorkerPrivate(), this);
+    // This can fail if the worker thread is canceled or killed causing
+    // the PromiseWorkerProxy to give up its WorkerRef immediately,
+    // allowing the worker thread to become Dead.
+    if (!cr->Dispatch()) {
+      NS_WARNING("Failed to dispatch WorkerFetchResponseEndControlRunnable");
+    }
+  }
+}
+
+void WorkerFetchResolver::FlushConsoleReport() {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(mPromiseProxy);
+
+  if (!mReporter) {
+    return;
+  }
+
+  WorkerPrivate* worker = mPromiseProxy->GetWorkerPrivate();
+  if (!worker) {
+    mReporter->FlushReportsToConsole(0);
+    return;
+  }
+
+  if (worker->IsServiceWorker()) {
+    // Flush to service worker
+    mReporter->FlushReportsToConsoleForServiceWorkerScope(
+        worker->ServiceWorkerScope());
+    return;
+  }
+
+  if (worker->IsSharedWorker()) {
+    // Flush to shared worker
+    worker->GetRemoteWorkerController()->FlushReportsOnMainThread(mReporter);
+    return;
+  }
+
+  // Flush to dedicated worker
+  mReporter->FlushConsoleReports(worker->GetLoadGroup());
+}
+
+nsresult ExtractByteStreamFromBody(const fetch::OwningBodyInit& aBodyInit,
+                                   nsIInputStream** aStream,
+                                   nsCString& aContentTypeWithCharset,
+                                   uint64_t& aContentLength) {
+  MOZ_ASSERT(aStream);
+  nsAutoCString charset;
+  aContentTypeWithCharset.SetIsVoid(true);
+
+  if (aBodyInit.IsArrayBuffer()) {
+    BodyExtractor<const ArrayBuffer> body(&aBodyInit.GetAsArrayBuffer());
+    return body.GetAsStream(aStream, &aContentLength, aContentTypeWithCharset,
+                            charset);
+  }
+
+  if (aBodyInit.IsArrayBufferView()) {
+    BodyExtractor<const ArrayBufferView> body(
+        &aBodyInit.GetAsArrayBufferView());
+    return body.GetAsStream(aStream, &aContentLength, aContentTypeWithCharset,
+                            charset);
+  }
+
+  if (aBodyInit.IsBlob()) {
+    Blob& blob = aBodyInit.GetAsBlob();
+    BodyExtractor<const Blob> body(&blob);
+    return body.GetAsStream(aStream, &aContentLength, aContentTypeWithCharset,
+                            charset);
+  }
+
+  if (aBodyInit.IsFormData()) {
+    FormData& formData = aBodyInit.GetAsFormData();
+    BodyExtractor<const FormData> body(&formData);
+    return body.GetAsStream(aStream, &aContentLength, aContentTypeWithCharset,
+                            charset);
+  }
+
+  if (aBodyInit.IsUSVString()) {
+    BodyExtractor<const nsAString> body(&aBodyInit.GetAsUSVString());
+    return body.GetAsStream(aStream, &aContentLength, aContentTypeWithCharset,
+                            charset);
+  }
+
+  if (aBodyInit.IsURLSearchParams()) {
+    URLSearchParams& usp = aBodyInit.GetAsURLSearchParams();
+    BodyExtractor<const URLSearchParams> body(&usp);
+    return body.GetAsStream(aStream, &aContentLength, aContentTypeWithCharset,
+                            charset);
+  }
+
+  MOZ_ASSERT_UNREACHABLE("Should never reach here");
+  return NS_ERROR_FAILURE;
+}
+
+nsresult ExtractByteStreamFromBody(const fetch::BodyInit& aBodyInit,
+                                   nsIInputStream** aStream,
+                                   nsCString& aContentTypeWithCharset,
+                                   uint64_t& aContentLength) {
+  MOZ_ASSERT(aStream);
+  MOZ_ASSERT(!*aStream);
+
+  nsAutoCString charset;
+  aContentTypeWithCharset.SetIsVoid(true);
+
+  if (aBodyInit.IsArrayBuffer()) {
+    BodyExtractor<const ArrayBuffer> body(&aBodyInit.GetAsArrayBuffer());
+    return body.GetAsStream(aStream, &aContentLength, aContentTypeWithCharset,
+                            charset);
+  }
+
+  if (aBodyInit.IsArrayBufferView()) {
+    BodyExtractor<const ArrayBufferView> body(
+        &aBodyInit.GetAsArrayBufferView());
+    return body.GetAsStream(aStream, &aContentLength, aContentTypeWithCharset,
+                            charset);
+  }
+
+  if (aBodyInit.IsBlob()) {
+    BodyExtractor<const Blob> body(&aBodyInit.GetAsBlob());
+    return body.GetAsStream(aStream, &aContentLength, aContentTypeWithCharset,
+                            charset);
+  }
+
+  if (aBodyInit.IsFormData()) {
+    BodyExtractor<const FormData> body(&aBodyInit.GetAsFormData());
+    return body.GetAsStream(aStream, &aContentLength, aContentTypeWithCharset,
+                            charset);
+  }
+
+  if (aBodyInit.IsUSVString()) {
+    BodyExtractor<const nsAString> body(&aBodyInit.GetAsUSVString());
+    return body.GetAsStream(aStream, &aContentLength, aContentTypeWithCharset,
+                            charset);
+  }
+
+  if (aBodyInit.IsURLSearchParams()) {
+    BodyExtractor<const URLSearchParams> body(
+        &aBodyInit.GetAsURLSearchParams());
+    return body.GetAsStream(aStream, &aContentLength, aContentTypeWithCharset,
+                            charset);
+  }
+
+  MOZ_ASSERT_UNREACHABLE("Should never reach here");
+  return NS_ERROR_FAILURE;
+}
+
+nsresult ExtractByteStreamFromBody(const fetch::ResponseBodyInit& aBodyInit,
+                                   nsIInputStream** aStream,
+                                   nsCString& aContentTypeWithCharset,
+                                   uint64_t& aContentLength) {
+  MOZ_ASSERT(aStream);
+  MOZ_ASSERT(!*aStream);
+
+  // ReadableStreams should be handled by
+  // BodyExtractorReadableStream::GetAsStream.
+  MOZ_ASSERT(!aBodyInit.IsReadableStream());
+
+  nsAutoCString charset;
+  aContentTypeWithCharset.SetIsVoid(true);
+
+  if (aBodyInit.IsArrayBuffer()) {
+    BodyExtractor<const ArrayBuffer> body(&aBodyInit.GetAsArrayBuffer());
+    return body.GetAsStream(aStream, &aContentLength, aContentTypeWithCharset,
+                            charset);
+  }
+
+  if (aBodyInit.IsArrayBufferView()) {
+    BodyExtractor<const ArrayBufferView> body(
+        &aBodyInit.GetAsArrayBufferView());
+    return body.GetAsStream(aStream, &aContentLength, aContentTypeWithCharset,
+                            charset);
+  }
+
+  if (aBodyInit.IsBlob()) {
+    BodyExtractor<const Blob> body(&aBodyInit.GetAsBlob());
+    return body.GetAsStream(aStream, &aContentLength, aContentTypeWithCharset,
+                            charset);
+  }
+
+  if (aBodyInit.IsFormData()) {
+    BodyExtractor<const FormData> body(&aBodyInit.GetAsFormData());
+    return body.GetAsStream(aStream, &aContentLength, aContentTypeWithCharset,
+                            charset);
+  }
+
+  if (aBodyInit.IsUSVString()) {
+    BodyExtractor<const nsAString> body(&aBodyInit.GetAsUSVString());
+    return body.GetAsStream(aStream, &aContentLength, aContentTypeWithCharset,
+                            charset);
+  }
+
+  if (aBodyInit.IsURLSearchParams()) {
+    BodyExtractor<const URLSearchParams> body(
+        &aBodyInit.GetAsURLSearchParams());
+    return body.GetAsStream(aStream, &aContentLength, aContentTypeWithCharset,
+                            charset);
+  }
+
+  MOZ_ASSERT_UNREACHABLE("Should never reach here");
+  return NS_ERROR_FAILURE;
+}
+
+NS_IMPL_CYCLE_COLLECTION(FetchBodyBase, mReadableStreamBody)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(FetchBodyBase)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(FetchBodyBase)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(FetchBodyBase)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+template <class Derived>
+FetchBody<Derived>::FetchBody(nsIGlobalObject* aOwner)
+    : mOwner(aOwner), mBodyUsed(false) {
+  MOZ_ASSERT(aOwner);
+
+  if (!NS_IsMainThread()) {
+    WorkerPrivate* wp = GetCurrentThreadWorkerPrivate();
+    MOZ_ASSERT(wp);
+    mMainThreadEventTarget = wp->MainThreadEventTarget();
+  } else {
+    mMainThreadEventTarget = aOwner->EventTargetFor(TaskCategory::Other);
+  }
+
+  MOZ_ASSERT(mMainThreadEventTarget);
+}
+
+template FetchBody<Request>::FetchBody(nsIGlobalObject* aOwner);
+
+template FetchBody<Response>::FetchBody(nsIGlobalObject* aOwner);
+
+template <class Derived>
+FetchBody<Derived>::~FetchBody() {
+  Unfollow();
+}
+
+template FetchBody<Request>::~FetchBody();
+
+template FetchBody<Response>::~FetchBody();
+
+template <class Derived>
+bool FetchBody<Derived>::BodyUsed() const {
+  if (mBodyUsed) {
+    return true;
+  }
+
+  // If this stream is disturbed, return true.
+  if (mReadableStreamBody) {
+    return mReadableStreamBody->Disturbed();
+  }
+
+  return false;
+}
+
+template bool FetchBody<Request>::BodyUsed() const;
+
+template bool FetchBody<Response>::BodyUsed() const;
+
+template <class Derived>
+void FetchBody<Derived>::SetBodyUsed(JSContext* aCx, ErrorResult& aRv) {
+  MOZ_ASSERT(aCx);
+  MOZ_ASSERT(mOwner->EventTargetFor(TaskCategory::Other)->IsOnCurrentThread());
+
+  MOZ_DIAGNOSTIC_ASSERT(!BodyUsed(), "Consuming already used body?");
+  if (BodyUsed()) {
+    return;
+  }
+
+  mBodyUsed = true;
+
+  // If we already have a ReadableStreamBody and it has been created by DOM, we
+  // have to lock it now because it can have been shared with other objects.
+  if (mReadableStreamBody) {
+    if (mReadableStreamBody->MaybeGetInputStreamIfUnread()) {
+      LockStream(aCx, mReadableStreamBody, aRv);
+      if (NS_WARN_IF(aRv.Failed())) {
+        return;
+      }
+    } else {
+      MOZ_ASSERT(mFetchStreamReader);
+      //  Let's activate the FetchStreamReader.
+      mFetchStreamReader->StartConsuming(aCx, mReadableStreamBody, aRv);
+      if (NS_WARN_IF(aRv.Failed())) {
+        return;
+      }
+    }
+  }
+}
+
+template void FetchBody<Request>::SetBodyUsed(JSContext* aCx, ErrorResult& aRv);
+
+template void FetchBody<Response>::SetBodyUsed(JSContext* aCx,
+                                               ErrorResult& aRv);
+
+template <class Derived>
+already_AddRefed<Promise> FetchBody<Derived>::ConsumeBody(
+    JSContext* aCx, BodyConsumer::ConsumeType aType, ErrorResult& aRv) {
+  aRv.MightThrowJSException();
+
+  RefPtr<AbortSignalImpl> signalImpl =
+      DerivedClass()->GetSignalImplToConsumeBody();
+
+  if (signalImpl && signalImpl->Aborted()) {
+    JS::Rooted<JS::Value> abortReason(aCx, signalImpl->RawReason());
+
+    if (abortReason.get().isUndefined()) {
+      aRv.Throw(NS_ERROR_DOM_ABORT_ERR);
+      return nullptr;
+    }
+
+    nsCOMPtr<nsIGlobalObject> go = DerivedClass()->GetParentObject();
+
+    RefPtr<Promise> promise = Promise::Create(go, aRv);
+    promise->MaybeReject(abortReason);
+    return promise.forget();
+  }
+
+  if (BodyUsed()) {
+    aRv.ThrowTypeError<MSG_FETCH_BODY_CONSUMED_ERROR>();
+    return nullptr;
+  }
+
+  nsAutoCString mimeType;
+  nsAutoCString mixedCaseMimeType;
+  DerivedClass()->GetMimeType(mimeType, mixedCaseMimeType);
+
+  // Null bodies are a special-case in the fetch spec.  The Body mix-in can only
+  // be "disturbed" or "locked" if its associated "body" is non-null.
+  // Additionally, the Body min-in's "consume body" algorithm explicitly creates
+  // a fresh empty ReadableStream object in step 2.  This means that `bodyUsed`
+  // will never return true for a null body.
+  //
+  // To this end, we create a fresh (empty) body every time a request is made
+  // and consume its body here, without marking this FetchBody consumed via
+  // SetBodyUsed.
+  nsCOMPtr<nsIInputStream> bodyStream;
+  DerivedClass()->GetBody(getter_AddRefs(bodyStream));
+  if (!bodyStream) {
+    RefPtr<EmptyBody> emptyBody =
+        EmptyBody::Create(DerivedClass()->GetParentObject(),
+                          DerivedClass()->GetPrincipalInfo().get(), signalImpl,
+                          mimeType, mixedCaseMimeType, aRv);
+    if (NS_WARN_IF(aRv.Failed())) {
+      return nullptr;
+    }
+
+    return emptyBody->ConsumeBody(aCx, aType, aRv);
+  }
+
+  SetBodyUsed(aCx, aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  nsCOMPtr<nsIGlobalObject> global = DerivedClass()->GetParentObject();
+
+  MutableBlobStorage::MutableBlobStorageType blobStorageType =
+      MutableBlobStorage::eOnlyInMemory;
+  const mozilla::UniquePtr<mozilla::ipc::PrincipalInfo>& principalInfo =
+      DerivedClass()->GetPrincipalInfo();
+  // We support temporary file for blobs only if the principal is known and
+  // it's system or content not in private Browsing.
+  if (principalInfo &&
+      (principalInfo->type() ==
+           mozilla::ipc::PrincipalInfo::TSystemPrincipalInfo ||
+       (principalInfo->type() ==
+            mozilla::ipc::PrincipalInfo::TContentPrincipalInfo &&
+        principalInfo->get_ContentPrincipalInfo().attrs().mPrivateBrowsingId ==
+            0))) {
+    blobStorageType = MutableBlobStorage::eCouldBeInTemporaryFile;
+  }
+
+  RefPtr<Promise> promise = BodyConsumer::Create(
+      global, mMainThreadEventTarget, bodyStream, signalImpl, aType,
+      BodyBlobURISpec(), BodyLocalPath(), mimeType, mixedCaseMimeType,
+      blobStorageType, aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  return promise.forget();
+}
+
+template already_AddRefed<Promise> FetchBody<Request>::ConsumeBody(
+    JSContext* aCx, BodyConsumer::ConsumeType aType, ErrorResult& aRv);
+
+template already_AddRefed<Promise> FetchBody<Response>::ConsumeBody(
+    JSContext* aCx, BodyConsumer::ConsumeType aType, ErrorResult& aRv);
+
+template already_AddRefed<Promise> FetchBody<EmptyBody>::ConsumeBody(
+    JSContext* aCx, BodyConsumer::ConsumeType aType, ErrorResult& aRv);
+
+template <class Derived>
+void FetchBody<Derived>::GetMimeType(nsACString& aMimeType,
+                                     nsACString& aMixedCaseMimeType) {
+  // Extract mime type.
+  ErrorResult result;
+  nsCString contentTypeValues;
+  MOZ_ASSERT(DerivedClass()->GetInternalHeaders());
+  DerivedClass()->GetInternalHeaders()->Get("Content-Type"_ns,
+                                            contentTypeValues, result);
+  MOZ_ALWAYS_TRUE(!result.Failed());
+
+  // HTTP ABNF states Content-Type may have only one value.
+  // This is from the "parse a header value" of the fetch spec.
+  if (!contentTypeValues.IsVoid() && contentTypeValues.Find(",") == -1) {
+    // Convert from a bytestring to a UTF8 CString.
+    CopyLatin1toUTF8(contentTypeValues, aMimeType);
+    aMixedCaseMimeType = aMimeType;
+    ToLowerCase(aMimeType);
+  }
+}
+
+template void FetchBody<Request>::GetMimeType(nsACString& aMimeType,
+                                              nsACString& aMixedCaseMimeType);
+template void FetchBody<Response>::GetMimeType(nsACString& aMimeType,
+                                               nsACString& aMixedCaseMimeType);
+
+template <class Derived>
+const nsACString& FetchBody<Derived>::BodyBlobURISpec() const {
+  return DerivedClass()->BodyBlobURISpec();
+}
+
+template const nsACString& FetchBody<Request>::BodyBlobURISpec() const;
+
+template const nsACString& FetchBody<Response>::BodyBlobURISpec() const;
+
+template const nsACString& FetchBody<EmptyBody>::BodyBlobURISpec() const;
+
+template <class Derived>
+const nsAString& FetchBody<Derived>::BodyLocalPath() const {
+  return DerivedClass()->BodyLocalPath();
+}
+
+template const nsAString& FetchBody<Request>::BodyLocalPath() const;
+
+template const nsAString& FetchBody<Response>::BodyLocalPath() const;
+
+template const nsAString& FetchBody<EmptyBody>::BodyLocalPath() const;
+
+template <class Derived>
+void FetchBody<Derived>::SetReadableStreamBody(JSContext* aCx,
+                                               ReadableStream* aBody) {
+  MOZ_ASSERT(!mReadableStreamBody);
+  MOZ_ASSERT(aBody);
+  mReadableStreamBody = aBody;
+
+  RefPtr<AbortSignalImpl> signalImpl = DerivedClass()->GetSignalImpl();
+  if (!signalImpl) {
+    return;
+  }
+
+  bool aborted = signalImpl->Aborted();
+  if (aborted) {
+    IgnoredErrorResult result;
+    JS::Rooted<JS::Value> abortReason(aCx, signalImpl->RawReason());
+    AbortStream(aCx, mReadableStreamBody, result, abortReason);
+    if (NS_WARN_IF(result.Failed())) {
+      return;
+    }
+  } else if (!IsFollowing()) {
+    Follow(signalImpl);
+  }
+}
+
+template void FetchBody<Request>::SetReadableStreamBody(JSContext* aCx,
+                                                        ReadableStream* aBody);
+
+template void FetchBody<Response>::SetReadableStreamBody(JSContext* aCx,
+                                                         ReadableStream* aBody);
+
+template <class Derived>
+already_AddRefed<ReadableStream> FetchBody<Derived>::GetBody(JSContext* aCx,
+                                                             ErrorResult& aRv) {
+  if (mReadableStreamBody) {
+    return do_AddRef(mReadableStreamBody);
+  }
+
+  nsCOMPtr<nsIInputStream> inputStream;
+  DerivedClass()->GetBody(getter_AddRefs(inputStream));
+
+  if (!inputStream) {
+    return nullptr;
+  }
+
+  // The spec immediately creates ReadableStream on Response/Request constructor
+  // via https://fetch.spec.whatwg.org/#concept-bodyinit-extract, but Gecko
+  // creates nsIInputStream there instead and creates ReadableStream only when
+  // .body is accessed. Thus we only follow step 4 of it here.
+  //
+  // Step 4: Otherwise, set stream to a new ReadableStream object, and set up
+  // stream with byte reading support.
+  auto algorithms =
+      MakeRefPtr<NonAsyncInputToReadableStreamAlgorithms>(*inputStream);
+  RefPtr<ReadableStream> body = ReadableStream::CreateByteNative(
+      aCx, DerivedClass()->GetParentObject(), *algorithms, Nothing(), aRv);
+  if (aRv.Failed()) {
+    return nullptr;
+  }
+  mReadableStreamBody = body;
+
+  // If the body has been already consumed, we lock the stream.
+  if (BodyUsed()) {
+    LockStream(aCx, body, aRv);
+    if (NS_WARN_IF(aRv.Failed())) {
+      return nullptr;
+    }
+  }
+
+  RefPtr<AbortSignalImpl> signalImpl = DerivedClass()->GetSignalImpl();
+  if (signalImpl) {
+    if (signalImpl->Aborted()) {
+      JS::Rooted<JS::Value> abortReason(aCx, signalImpl->RawReason());
+      AbortStream(aCx, body, aRv, abortReason);
+      if (NS_WARN_IF(aRv.Failed())) {
+        return nullptr;
+      }
+    } else if (!IsFollowing()) {
+      Follow(signalImpl);
+    }
+  }
+
+  return body.forget();
+}
+
+template already_AddRefed<ReadableStream> FetchBody<Request>::GetBody(
+    JSContext* aCx, ErrorResult& aRv);
+
+template already_AddRefed<ReadableStream> FetchBody<Response>::GetBody(
+    JSContext* aCx, ErrorResult& aRv);
+
+template <class Derived>
+void FetchBody<Derived>::LockStream(JSContext* aCx, ReadableStream* aStream,
+                                    ErrorResult& aRv) {
+  // This is native stream, creating a reader will not execute any JS code.
+  RefPtr<ReadableStreamDefaultReader> reader = aStream->GetReader(aRv);
+  if (aRv.Failed()) {
+    return;
+  }
+}
+
+template void FetchBody<Request>::LockStream(JSContext* aCx,
+                                             ReadableStream* aStream,
+                                             ErrorResult& aRv);
+
+template void FetchBody<Response>::LockStream(JSContext* aCx,
+                                              ReadableStream* aStream,
+                                              ErrorResult& aRv);
+
+template <class Derived>
+void FetchBody<Derived>::MaybeTeeReadableStreamBody(
+    JSContext* aCx, ReadableStream** aBodyOut,
+    FetchStreamReader** aStreamReader, nsIInputStream** aInputStream,
+    ErrorResult& aRv) {
+  MOZ_DIAGNOSTIC_ASSERT(aStreamReader);
+  MOZ_DIAGNOSTIC_ASSERT(aInputStream);
+  MOZ_DIAGNOSTIC_ASSERT(!BodyUsed());
+
+  *aBodyOut = nullptr;
+  *aStreamReader = nullptr;
+  *aInputStream = nullptr;
+
+  if (!mReadableStreamBody) {
+    return;
+  }
+
+  // If this is a ReadableStream with an native source, this has been
+  // generated by a Fetch. In this case, Fetch will be able to recreate it
+  // again when GetBody() is called.
+  if (mReadableStreamBody->MaybeGetInputStreamIfUnread()) {
+    *aBodyOut = nullptr;
+    return;
+  }
+
+  nsTArray<RefPtr<ReadableStream> > branches;
+  MOZ_KnownLive(mReadableStreamBody)->Tee(aCx, branches, aRv);
+  if (aRv.Failed()) {
+    return;
+  }
+
+  mReadableStreamBody = branches[0];
+  branches[1].forget(aBodyOut);
+
+  aRv = FetchStreamReader::Create(aCx, mOwner, aStreamReader, aInputStream);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+}
+
+template void FetchBody<Request>::MaybeTeeReadableStreamBody(
+    JSContext* aCx, ReadableStream** aBodyOut,
+    FetchStreamReader** aStreamReader, nsIInputStream** aInputStream,
+    ErrorResult& aRv);
+
+template void FetchBody<Response>::MaybeTeeReadableStreamBody(
+    JSContext* aCx, ReadableStream** aBodyOut,
+    FetchStreamReader** aStreamReader, nsIInputStream** aInputStream,
+    ErrorResult& aRv);
+
+template <class Derived>
+void FetchBody<Derived>::RunAbortAlgorithm() {
+  if (!mReadableStreamBody) {
+    return;
+  }
+
+  AutoJSAPI jsapi;
+  if (!jsapi.Init(mOwner)) {
+    return;
+  }
+
+  JSContext* cx = jsapi.cx();
+
+  RefPtr<ReadableStream> body(mReadableStreamBody);
+  IgnoredErrorResult result;
+
+  JS::Rooted<JS::Value> abortReason(cx);
+
+  AbortSignalImpl* signalImpl = Signal();
+  if (signalImpl) {
+    abortReason.set(signalImpl->RawReason());
+  }
+
+  AbortStream(cx, body, result, abortReason);
+}
+
+template void FetchBody<Request>::RunAbortAlgorithm();
+
+template void FetchBody<Response>::RunAbortAlgorithm();
+
+NS_IMPL_ADDREF_INHERITED(EmptyBody, FetchBody<EmptyBody>)
+NS_IMPL_RELEASE_INHERITED(EmptyBody, FetchBody<EmptyBody>)
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(EmptyBody)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(EmptyBody, FetchBody<EmptyBody>)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mOwner)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mAbortSignalImpl)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mFetchStreamReader)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(EmptyBody,
+                                                  FetchBody<EmptyBody>)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mOwner)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mAbortSignalImpl)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mFetchStreamReader)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(EmptyBody, FetchBody<EmptyBody>)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(EmptyBody)
+NS_INTERFACE_MAP_END_INHERITING(FetchBody<EmptyBody>)
+
+EmptyBody::EmptyBody(nsIGlobalObject* aGlobal,
+                     mozilla::ipc::PrincipalInfo* aPrincipalInfo,
+                     AbortSignalImpl* aAbortSignalImpl,
+                     const nsACString& aMimeType,
+                     const nsACString& aMixedCaseMimeType,
+                     already_AddRefed<nsIInputStream> aBodyStream)
+    : FetchBody<EmptyBody>(aGlobal),
+      mAbortSignalImpl(aAbortSignalImpl),
+      mMimeType(aMimeType),
+      mMixedCaseMimeType(aMixedCaseMimeType),
+      mBodyStream(std::move(aBodyStream)) {
+  if (aPrincipalInfo) {
+    mPrincipalInfo = MakeUnique<mozilla::ipc::PrincipalInfo>(*aPrincipalInfo);
+  }
+}
+
+EmptyBody::~EmptyBody() = default;
+
+/* static */
+already_AddRefed<EmptyBody> EmptyBody::Create(
+    nsIGlobalObject* aGlobal, mozilla::ipc::PrincipalInfo* aPrincipalInfo,
+    AbortSignalImpl* aAbortSignalImpl, const nsACString& aMimeType,
+    const nsACString& aMixedCaseMimeType, ErrorResult& aRv) {
+  nsCOMPtr<nsIInputStream> bodyStream;
+  aRv = NS_NewCStringInputStream(getter_AddRefs(bodyStream), ""_ns);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  RefPtr<EmptyBody> emptyBody =
+      new EmptyBody(aGlobal, aPrincipalInfo, aAbortSignalImpl, aMimeType,
+                    aMixedCaseMimeType, bodyStream.forget());
+  return emptyBody.forget();
+}
+
+void EmptyBody::GetBody(nsIInputStream** aStream, int64_t* aBodyLength) {
+  MOZ_ASSERT(aStream);
+
+  if (aBodyLength) {
+    *aBodyLength = 0;
+  }
+
+  nsCOMPtr<nsIInputStream> bodyStream = mBodyStream;
+  bodyStream.forget(aStream);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/fetch/Fetch.h b/dom/fetch/Fetch.h
new file mode 100644
index 0000000000..9b9dccd1ee
--- /dev/null
+++ b/dom/fetch/Fetch.h
@@ -0,0 +1,310 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_Fetch_h
+#define mozilla_dom_Fetch_h
+
+#include "mozilla/Attributes.h"
+#include "nsCOMPtr.h"
+#include "nsError.h"
+#include "nsProxyRelease.h"
+#include "nsString.h"
+
+#include "mozilla/DebugOnly.h"
+#include "mozilla/dom/AbortSignal.h"
+#include "mozilla/dom/BodyConsumer.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/FetchStreamReader.h"
+#include "mozilla/dom/ReadableStream.h"
+#include "mozilla/dom/ReadableStreamDefaultReaderBinding.h"
+#include "mozilla/dom/RequestBinding.h"
+#include "mozilla/dom/workerinternals/RuntimeService.h"
+
+class nsIGlobalObject;
+class nsIEventTarget;
+
+namespace mozilla {
+class ErrorResult;
+
+namespace ipc {
+class PrincipalInfo;
+}  // namespace ipc
+
+namespace dom {
+
+class BlobOrArrayBufferViewOrArrayBufferOrFormDataOrURLSearchParamsOrUSVString;
+class
+    BlobOrArrayBufferViewOrArrayBufferOrFormDataOrURLSearchParamsOrReadableStreamOrUSVString;
+class BlobImpl;
+class InternalRequest;
+class
+    OwningBlobOrArrayBufferViewOrArrayBufferOrFormDataOrURLSearchParamsOrUSVString;
+
+class ReadableStreamDefaultReader;
+class RequestOrUSVString;
+class WorkerPrivate;
+
+enum class CallerType : uint32_t;
+
+already_AddRefed<Promise> FetchRequest(nsIGlobalObject* aGlobal,
+                                       const RequestOrUSVString& aInput,
+                                       const RequestInit& aInit,
+                                       CallerType aCallerType,
+                                       ErrorResult& aRv);
+
+nsresult UpdateRequestReferrer(nsIGlobalObject* aGlobal,
+                               InternalRequest* aRequest);
+
+namespace fetch {
+using BodyInit =
+    BlobOrArrayBufferViewOrArrayBufferOrFormDataOrURLSearchParamsOrUSVString;
+using ResponseBodyInit =
+    BlobOrArrayBufferViewOrArrayBufferOrFormDataOrURLSearchParamsOrReadableStreamOrUSVString;
+using OwningBodyInit =
+    OwningBlobOrArrayBufferViewOrArrayBufferOrFormDataOrURLSearchParamsOrUSVString;
+};  // namespace fetch
+
+/*
+ * Creates an nsIInputStream based on the fetch specifications 'extract a byte
+ * stream algorithm' - http://fetch.spec.whatwg.org/#concept-bodyinit-extract.
+ * Stores content type in out param aContentType.
+ */
+nsresult ExtractByteStreamFromBody(const fetch::OwningBodyInit& aBodyInit,
+                                   nsIInputStream** aStream,
+                                   nsCString& aContentType,
+                                   uint64_t& aContentLength);
+
+/*
+ * Non-owning version.
+ */
+nsresult ExtractByteStreamFromBody(const fetch::BodyInit& aBodyInit,
+                                   nsIInputStream** aStream,
+                                   nsCString& aContentType,
+                                   uint64_t& aContentLength);
+
+/*
+ * Non-owning version. This method should go away when BodyInit will contain
+ * ReadableStream.
+ */
+nsresult ExtractByteStreamFromBody(const fetch::ResponseBodyInit& aBodyInit,
+                                   nsIInputStream** aStream,
+                                   nsCString& aContentType,
+                                   uint64_t& aContentLength);
+
+/*
+ * FetchBody's body consumption uses nsIInputStreamPump to read from the
+ * underlying stream to a block of memory, which is then adopted by
+ * ContinueConsumeBody() and converted to the right type based on the JS
+ * function called.
+ *
+ * Use of the nsIInputStreamPump complicates things on the worker thread.
+ * The solution used here is similar to WebSockets.
+ * The difference is that we are only interested in completion and not data
+ * events, and nsIInputStreamPump can only deliver completion on the main
+ * thread.
+ *
+ * Before starting the pump on the main thread, we addref the FetchBody to keep
+ * it alive. Then we add a feature, to track the status of the worker.
+ *
+ * ContinueConsumeBody() is the function that cleans things up in both success
+ * and error conditions and so all callers call it with the appropriate status.
+ *
+ * Once the read is initiated on the main thread there are two possibilities.
+ *
+ * 1) Pump finishes before worker has finished Running.
+ *    In this case we adopt the data and dispatch a runnable to the worker,
+ *    which derefs FetchBody and removes the feature and resolves the Promise.
+ *
+ * 2) Pump still working while worker has stopped Running.
+ *    The feature is Notify()ed and ContinueConsumeBody() is called with
+ *    NS_BINDING_ABORTED. We first Cancel() the pump using a sync runnable to
+ *    ensure that mFetchBody remains alive (since mConsumeBodyPump is strongly
+ *    held by it) until pump->Cancel() is called. OnStreamComplete() will not
+ *    do anything if the error code is NS_BINDING_ABORTED, so we don't have to
+ *    worry about keeping anything alive.
+ *
+ * The pump is always released on the main thread.
+ */
+
+class FetchBodyBase : public nsISupports {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_CLASS(FetchBodyBase)
+
+ protected:
+  virtual ~FetchBodyBase() = default;
+
+  RefPtr<ReadableStream> mReadableStreamBody;
+};
+
+template <class Derived>
+class FetchBody : public FetchBodyBase, public AbortFollower {
+ public:
+  using FetchBodyBase::QueryInterface;
+
+  NS_INLINE_DECL_REFCOUNTING_INHERITED(FetchBody, FetchBodyBase)
+
+  bool BodyUsed() const;
+
+  already_AddRefed<Promise> ArrayBuffer(JSContext* aCx, ErrorResult& aRv) {
+    return ConsumeBody(aCx, BodyConsumer::CONSUME_ARRAYBUFFER, aRv);
+  }
+
+  already_AddRefed<Promise> Blob(JSContext* aCx, ErrorResult& aRv) {
+    return ConsumeBody(aCx, BodyConsumer::CONSUME_BLOB, aRv);
+  }
+
+  already_AddRefed<Promise> FormData(JSContext* aCx, ErrorResult& aRv) {
+    return ConsumeBody(aCx, BodyConsumer::CONSUME_FORMDATA, aRv);
+  }
+
+  already_AddRefed<Promise> Json(JSContext* aCx, ErrorResult& aRv) {
+    return ConsumeBody(aCx, BodyConsumer::CONSUME_JSON, aRv);
+  }
+
+  already_AddRefed<Promise> Text(JSContext* aCx, ErrorResult& aRv) {
+    return ConsumeBody(aCx, BodyConsumer::CONSUME_TEXT, aRv);
+  }
+
+  already_AddRefed<ReadableStream> GetBody(JSContext* aCx, ErrorResult& aRv);
+  void GetMimeType(nsACString& aMimeType, nsACString& aMixedCaseMimeType);
+
+  const nsACString& BodyBlobURISpec() const;
+
+  const nsAString& BodyLocalPath() const;
+
+  // If the body contains a ReadableStream body object, this method produces a
+  // tee() of it.
+  //
+  // This is marked as a script boundary minimize changes required for
+  // annotation while we work out how to correctly annotate this code.
+  // Tracked in Bug 1750650.
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  void MaybeTeeReadableStreamBody(JSContext* aCx, ReadableStream** aBodyOut,
+                                  FetchStreamReader** aStreamReader,
+                                  nsIInputStream** aInputStream,
+                                  ErrorResult& aRv);
+
+  // Utility public methods accessed by various runnables.
+
+  // This method _must_ be called in order to set the body as used. If the body
+  // is a ReadableStream, this method will start reading the stream.
+  // More in details, this method does:
+  // 1) It uses an internal flag to track if the body is used.  This is tracked
+  // separately from the ReadableStream disturbed state due to purely native
+  // streams.
+  // 2) If there is a ReadableStream reflector for the native stream it is
+  // Locked.
+  // 3) If there is a JS ReadableStream then we begin pumping it into the native
+  // body stream.  This effectively locks and disturbs the stream.
+  //
+  // Note that JSContext is used only if there is a ReadableStream (this can
+  // happen because the body is a ReadableStream or because attribute body has
+  // already been used by content). If something goes wrong using
+  // ReadableStream, errors will be reported via ErrorResult and not as JS
+  // exceptions in JSContext. This is done in order to have a centralized error
+  // reporting way.
+  //
+  // Exceptions generated when reading from the ReadableStream are directly sent
+  // to the Console.
+  void SetBodyUsed(JSContext* aCx, ErrorResult& aRv);
+
+  virtual AbortSignalImpl* GetSignalImpl() const = 0;
+
+  virtual AbortSignalImpl* GetSignalImplToConsumeBody() const = 0;
+
+  // AbortFollower
+  void RunAbortAlgorithm() override;
+
+  already_AddRefed<Promise> ConsumeBody(JSContext* aCx,
+                                        BodyConsumer::ConsumeType aType,
+                                        ErrorResult& aRv);
+
+ protected:
+  nsCOMPtr<nsIGlobalObject> mOwner;
+
+  // This is the Reader used to retrieve data from the body. This needs to be
+  // traversed by subclasses.
+  RefPtr<FetchStreamReader> mFetchStreamReader;
+
+  explicit FetchBody(nsIGlobalObject* aOwner);
+
+  virtual ~FetchBody();
+
+  void SetReadableStreamBody(JSContext* aCx, ReadableStream* aBody);
+
+ private:
+  Derived* DerivedClass() const {
+    return static_cast<Derived*>(const_cast<FetchBody*>(this));
+  }
+
+  void LockStream(JSContext* aCx, ReadableStream* aStream, ErrorResult& aRv);
+
+  void AssertIsOnTargetThread() {
+    MOZ_ASSERT(NS_IsMainThread() == !GetCurrentThreadWorkerPrivate());
+  }
+
+  // Only ever set once, always on target thread.
+  bool mBodyUsed;
+
+  // The main-thread event target for runnable dispatching.
+  nsCOMPtr<nsISerialEventTarget> mMainThreadEventTarget;
+};
+
+class EmptyBody final : public FetchBody<EmptyBody> {
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(EmptyBody,
+                                                         FetchBody<EmptyBody>)
+
+ public:
+  static already_AddRefed<EmptyBody> Create(
+      nsIGlobalObject* aGlobal, mozilla::ipc::PrincipalInfo* aPrincipalInfo,
+      AbortSignalImpl* aAbortSignalImpl, const nsACString& aMimeType,
+      const nsACString& aMixedCaseMimeType, ErrorResult& aRv);
+
+  nsIGlobalObject* GetParentObject() const { return mOwner; }
+
+  AbortSignalImpl* GetSignalImpl() const override { return mAbortSignalImpl; }
+  AbortSignalImpl* GetSignalImplToConsumeBody() const final { return nullptr; }
+
+  const UniquePtr<mozilla::ipc::PrincipalInfo>& GetPrincipalInfo() const {
+    return mPrincipalInfo;
+  }
+
+  void GetMimeType(nsACString& aMimeType, nsACString& aMixedCaseMimeType) {
+    aMimeType = mMimeType;
+    aMixedCaseMimeType = mMixedCaseMimeType;
+  }
+
+  void GetBody(nsIInputStream** aStream, int64_t* aBodyLength = nullptr);
+
+  using FetchBody::BodyBlobURISpec;
+
+  const nsACString& BodyBlobURISpec() const { return EmptyCString(); }
+
+  using FetchBody::BodyLocalPath;
+
+  const nsAString& BodyLocalPath() const { return EmptyString(); }
+
+ private:
+  EmptyBody(nsIGlobalObject* aGlobal,
+            mozilla::ipc::PrincipalInfo* aPrincipalInfo,
+            AbortSignalImpl* aAbortSignalImpl, const nsACString& aMimeType,
+            const nsACString& aMixedCaseMimeType,
+            already_AddRefed<nsIInputStream> aBodyStream);
+
+  ~EmptyBody();
+
+  UniquePtr<mozilla::ipc::PrincipalInfo> mPrincipalInfo;
+  RefPtr<AbortSignalImpl> mAbortSignalImpl;
+  nsCString mMimeType;
+  nsCString mMixedCaseMimeType;
+  nsCOMPtr<nsIInputStream> mBodyStream;
+};
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_Fetch_h
diff --git a/dom/fetch/FetchChild.cpp b/dom/fetch/FetchChild.cpp
new file mode 100644
index 0000000000..774eb516e7
--- /dev/null
+++ b/dom/fetch/FetchChild.cpp
@@ -0,0 +1,380 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "FetchChild.h"
+#include "FetchLog.h"
+#include "FetchObserver.h"
+#include "InternalResponse.h"
+#include "Request.h"
+#include "Response.h"
+#include "mozilla/ConsoleReportCollector.h"
+#include "mozilla/SchedulerGroup.h"
+#include "mozilla/dom/PerformanceTiming.h"
+#include "mozilla/dom/PerformanceStorage.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/RemoteWorkerChild.h"
+#include "mozilla/dom/SecurityPolicyViolationEventBinding.h"
+#include "mozilla/dom/WorkerChannelInfo.h"
+#include "mozilla/dom/WorkerPrivate.h"
+#include "mozilla/dom/WorkerRef.h"
+#include "mozilla/dom/WorkerScope.h"
+#include "nsIAsyncInputStream.h"
+#include "nsIGlobalObject.h"
+#include "nsIObserverService.h"
+#include "nsIRunnable.h"
+#include "nsIURI.h"
+#include "nsNetUtil.h"
+#include "nsThreadUtils.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_ISUPPORTS0(FetchChild)
+
+mozilla::ipc::IPCResult FetchChild::Recv__delete__(const nsresult&& aResult) {
+  FETCH_LOG(("FetchChild::Recv__delete__ [%p]", this));
+  if (mIsShutdown) {
+    return IPC_OK();
+  }
+  // Shutdown has not been called, so mWorkerRef->Private() should be still
+  // alive.
+  MOZ_ASSERT(mWorkerRef->Private());
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+
+  if (mPromise->State() == Promise::PromiseState::Pending) {
+    if (NS_FAILED(aResult)) {
+      mPromise->MaybeReject(aResult);
+      if (mFetchObserver) {
+        mFetchObserver->SetState(FetchState::Errored);
+      }
+    } else {
+      mPromise->MaybeResolve(aResult);
+      if (mFetchObserver) {
+        mFetchObserver->SetState(FetchState::Complete);
+      }
+    }
+  }
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult FetchChild::RecvOnResponseAvailableInternal(
+    ParentToChildInternalResponse&& aResponse) {
+  FETCH_LOG(("FetchChild::RecvOnResponseAvailableInternal [%p]", this));
+  if (mIsShutdown) {
+    return IPC_OK();
+  }
+  // Shutdown has not been called, so mWorkerRef->Private() should be still
+  // alive.
+  MOZ_ASSERT(mWorkerRef->Private());
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+  SafeRefPtr<InternalResponse> internalResponse =
+      InternalResponse::FromIPC(aResponse);
+  IgnoredErrorResult result;
+  internalResponse->Headers()->SetGuard(HeadersGuardEnum::Immutable, result);
+  MOZ_ASSERT(internalResponse);
+
+  if (internalResponse->Type() != ResponseType::Error) {
+    if (internalResponse->Type() == ResponseType::Opaque) {
+      internalResponse->GeneratePaddingInfo();
+    }
+
+    if (mFetchObserver) {
+      mFetchObserver->SetState(FetchState::Complete);
+    }
+    nsCOMPtr<nsIGlobalObject> global;
+    global = mWorkerRef->Private()->GlobalScope();
+    RefPtr<Response> response =
+        new Response(global, internalResponse.clonePtr(), mSignalImpl);
+    mPromise->MaybeResolve(response);
+
+    return IPC_OK();
+  }
+
+  FETCH_LOG(
+      ("FetchChild::RecvOnResponseAvailableInternal [%p] response type is "
+       "Error(0x%x)",
+       this, static_cast<int32_t>(internalResponse->GetErrorCode())));
+  if (mFetchObserver) {
+    mFetchObserver->SetState(FetchState::Errored);
+  }
+  mPromise->MaybeRejectWithTypeError<MSG_FETCH_FAILED>();
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult FetchChild::RecvOnResponseEnd(ResponseEndArgs&& aArgs) {
+  FETCH_LOG(("FetchChild::RecvOnResponseEnd [%p]", this));
+  if (mIsShutdown) {
+    return IPC_OK();
+  }
+  // Shutdown has not been called, so mWorkerRef->Private() should be still
+  // alive.
+  MOZ_ASSERT(mWorkerRef->Private());
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+
+  if (aArgs.endReason() == FetchDriverObserver::eAborted) {
+    FETCH_LOG(
+        ("FetchChild::RecvOnResponseEnd [%p] endReason is eAborted", this));
+    if (mFetchObserver) {
+      mFetchObserver->SetState(FetchState::Errored);
+    }
+    mPromise->MaybeReject(NS_ERROR_DOM_ABORT_ERR);
+  }
+
+  Unfollow();
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult FetchChild::RecvOnDataAvailable() {
+  FETCH_LOG(("FetchChild::RecvOnDataAvailable [%p]", this));
+  if (mIsShutdown) {
+    return IPC_OK();
+  }
+  // Shutdown has not been called, so mWorkerRef->Private() should be still
+  // alive.
+  MOZ_ASSERT(mWorkerRef->Private());
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+
+  if (mFetchObserver && mFetchObserver->State() == FetchState::Requesting) {
+    mFetchObserver->SetState(FetchState::Responding);
+  }
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult FetchChild::RecvOnFlushConsoleReport(
+    nsTArray<net::ConsoleReportCollected>&& aReports) {
+  FETCH_LOG(("FetchChild::RecvOnFlushConsoleReport [%p]", this));
+  if (mIsShutdown) {
+    return IPC_OK();
+  }
+  // Shutdown has not been called, so mWorkerRef->Private() should be still
+  // alive.
+  MOZ_ASSERT(mWorkerRef->Private());
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+  MOZ_ASSERT(mReporter);
+
+  RefPtr<ThreadSafeWorkerRef> workerRef = mWorkerRef;
+  nsCOMPtr<nsIConsoleReportCollector> reporter = mReporter;
+
+  nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+      __func__, [reports = std::move(aReports), reporter = std::move(reporter),
+                 workerRef = std::move(workerRef)]() mutable {
+        for (const auto& report : reports) {
+          reporter->AddConsoleReport(
+              report.errorFlags(), report.category(),
+              static_cast<nsContentUtils::PropertiesFile>(
+                  report.propertiesFile()),
+              report.sourceFileURI(), report.lineNumber(),
+              report.columnNumber(), report.messageName(),
+              report.stringParams());
+        }
+
+        if (workerRef->Private()->IsServiceWorker()) {
+          reporter->FlushReportsToConsoleForServiceWorkerScope(
+              workerRef->Private()->ServiceWorkerScope());
+        }
+
+        if (workerRef->Private()->IsSharedWorker()) {
+          workerRef->Private()
+              ->GetRemoteWorkerController()
+              ->FlushReportsOnMainThread(reporter);
+        }
+
+        reporter->FlushConsoleReports(workerRef->Private()->GetLoadGroup());
+      });
+  MOZ_ALWAYS_SUCCEEDS(
+      SchedulerGroup::Dispatch(TaskCategory::Other, r.forget()));
+
+  return IPC_OK();
+}
+
+RefPtr<FetchChild> FetchChild::Create(WorkerPrivate* aWorkerPrivate,
+                                      RefPtr<Promise> aPromise,
+                                      RefPtr<AbortSignalImpl> aSignalImpl,
+                                      RefPtr<FetchObserver> aObserver) {
+  MOZ_DIAGNOSTIC_ASSERT(aWorkerPrivate);
+  aWorkerPrivate->AssertIsOnWorkerThread();
+
+  RefPtr<FetchChild> actor = MakeRefPtr<FetchChild>(
+      std::move(aPromise), std::move(aSignalImpl), std::move(aObserver));
+
+  RefPtr<StrongWorkerRef> workerRef =
+      StrongWorkerRef::Create(aWorkerPrivate, "FetchChild", [actor]() {
+        FETCH_LOG(("StrongWorkerRef callback"));
+        actor->Shutdown();
+      });
+  if (NS_WARN_IF(!workerRef)) {
+    return nullptr;
+  }
+
+  actor->mWorkerRef = new ThreadSafeWorkerRef(workerRef);
+  if (NS_WARN_IF(!actor->mWorkerRef)) {
+    return nullptr;
+  }
+  return actor;
+}
+
+mozilla::ipc::IPCResult FetchChild::RecvOnCSPViolationEvent(
+    const nsAString& aJSON) {
+  FETCH_LOG(("FetchChild::RecvOnCSPViolationEvent [%p] aJSON: %s\n", this,
+             NS_ConvertUTF16toUTF8(aJSON).BeginReading()));
+
+  nsString JSON(aJSON);
+
+  nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(__func__, [JSON]() mutable {
+    SecurityPolicyViolationEventInit violationEventInit;
+    if (NS_WARN_IF(!violationEventInit.Init(JSON))) {
+      return;
+    }
+
+    nsCOMPtr<nsIURI> uri;
+    nsresult rv =
+        NS_NewURI(getter_AddRefs(uri), violationEventInit.mBlockedURI);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return;
+    }
+
+    nsCOMPtr<nsIObserverService> observerService =
+        mozilla::services::GetObserverService();
+    if (!observerService) {
+      return;
+    }
+
+    rv = observerService->NotifyObservers(
+        uri, CSP_VIOLATION_TOPIC, violationEventInit.mViolatedDirective.get());
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return;
+    }
+  });
+  MOZ_ALWAYS_SUCCEEDS(
+      SchedulerGroup::Dispatch(TaskCategory::Other, r.forget()));
+
+  if (mCSPEventListener) {
+    Unused << NS_WARN_IF(
+        NS_FAILED(mCSPEventListener->OnCSPViolationEvent(aJSON)));
+  }
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult FetchChild::RecvOnReportPerformanceTiming(
+    ResponseTiming&& aTiming) {
+  FETCH_LOG(("FetchChild::RecvOnReportPerformanceTiming [%p]", this));
+  if (mIsShutdown) {
+    return IPC_OK();
+  }
+  // Shutdown has not been called, so mWorkerRef->Private() should be still
+  // alive.
+  MOZ_ASSERT(mWorkerRef->Private());
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+
+  RefPtr<PerformanceStorage> performanceStorage =
+      mWorkerRef->Private()->GetPerformanceStorage();
+  if (performanceStorage) {
+    performanceStorage->AddEntry(
+        aTiming.entryName(), aTiming.initiatorType(),
+        MakeUnique<PerformanceTimingData>(aTiming.timingData()));
+  }
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult FetchChild::RecvOnNotifyNetworkMonitorAlternateStack(
+    uint64_t aChannelID) {
+  FETCH_LOG(
+      ("FetchChild::RecvOnNotifyNetworkMonitorAlternateStack [%p]", this));
+  if (mIsShutdown) {
+    return IPC_OK();
+  }
+  // Shutdown has not been called, so mWorkerRef->Private() should be still
+  // alive.
+  MOZ_ASSERT(mWorkerRef->Private());
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+
+  if (!mOriginStack) {
+    return IPC_OK();
+  }
+
+  if (!mWorkerChannelInfo) {
+    mWorkerChannelInfo = MakeRefPtr<WorkerChannelInfo>(
+        aChannelID, mWorkerRef->Private()->AssociatedBrowsingContextID());
+  }
+
+  // Unfortunately, SerializedStackHolder can only be read on the main thread.
+  // However, it doesn't block the fetch execution.
+  nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+      __func__, [channel = mWorkerChannelInfo,
+                 stack = std::move(mOriginStack)]() mutable {
+        NotifyNetworkMonitorAlternateStack(channel, std::move(stack));
+      });
+
+  MOZ_ALWAYS_SUCCEEDS(
+      SchedulerGroup::Dispatch(TaskCategory::Other, r.forget()));
+
+  return IPC_OK();
+}
+
+void FetchChild::SetCSPEventListener(nsICSPEventListener* aListener) {
+  MOZ_ASSERT(aListener && !mCSPEventListener);
+  mCSPEventListener = aListener;
+}
+
+FetchChild::FetchChild(RefPtr<Promise>&& aPromise,
+                       RefPtr<AbortSignalImpl>&& aSignalImpl,
+                       RefPtr<FetchObserver>&& aObserver)
+    : mPromise(std::move(aPromise)),
+      mSignalImpl(std::move(aSignalImpl)),
+      mFetchObserver(std::move(aObserver)),
+      mReporter(new ConsoleReportCollector()) {
+  FETCH_LOG(("FetchChild::FetchChild [%p]", this));
+}
+
+void FetchChild::RunAbortAlgorithm() {
+  FETCH_LOG(("FetchChild::RunAbortAlgorithm [%p]", this));
+  if (mIsShutdown) {
+    return;
+  }
+  if (mWorkerRef) {
+    Unused << SendAbortFetchOp();
+  }
+}
+
+void FetchChild::DoFetchOp(const FetchOpArgs& aArgs) {
+  FETCH_LOG(("FetchChild::DoFetchOp [%p]", this));
+  if (mSignalImpl) {
+    if (mSignalImpl->Aborted()) {
+      Unused << SendAbortFetchOp();
+      return;
+    }
+    Follow(mSignalImpl);
+  }
+  Unused << SendFetchOp(aArgs);
+}
+
+void FetchChild::Shutdown() {
+  FETCH_LOG(("FetchChild::Shutdown [%p]", this));
+  if (mIsShutdown) {
+    return;
+  }
+  mIsShutdown.Flip();
+
+  // If mWorkerRef is nullptr here, that means Recv__delete__() must be called
+  if (!mWorkerRef) {
+    return;
+  }
+  mPromise = nullptr;
+  mFetchObserver = nullptr;
+  Unfollow();
+  mSignalImpl = nullptr;
+  mCSPEventListener = nullptr;
+  Unused << SendAbortFetchOp();
+  mWorkerRef = nullptr;
+}
+
+void FetchChild::ActorDestroy(ActorDestroyReason aReason) {
+  FETCH_LOG(("FetchChild::ActorDestroy [%p]", this));
+  mPromise = nullptr;
+  mFetchObserver = nullptr;
+  mSignalImpl = nullptr;
+  mCSPEventListener = nullptr;
+  mWorkerRef = nullptr;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/fetch/FetchChild.h b/dom/fetch/FetchChild.h
new file mode 100644
index 0000000000..986fc728cb
--- /dev/null
+++ b/dom/fetch/FetchChild.h
@@ -0,0 +1,91 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_fetchChild_h__
+#define mozilla_dom_fetchChild_h__
+
+#include "mozilla/dom/AbortSignal.h"
+#include "mozilla/dom/AbortFollower.h"
+#include "mozilla/dom/FlippedOnce.h"
+#include "mozilla/dom/PFetchChild.h"
+#include "mozilla/dom/SerializedStackHolder.h"
+#include "nsIConsoleReportCollector.h"
+#include "nsIContentSecurityPolicy.h"
+#include "nsISupports.h"
+#include "nsIWorkerChannelInfo.h"
+
+namespace mozilla::dom {
+
+class FetchObserver;
+class ThreadSafeWorkerRef;
+class Promise;
+class WorkerPrivate;
+
+class FetchChild final : public PFetchChild, public AbortFollower {
+  friend class PFetchChild;
+
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+  mozilla::ipc::IPCResult Recv__delete__(const nsresult&& aResult);
+
+  mozilla::ipc::IPCResult RecvOnResponseAvailableInternal(
+      ParentToChildInternalResponse&& aResponse);
+
+  mozilla::ipc::IPCResult RecvOnResponseEnd(ResponseEndArgs&& aArgs);
+
+  mozilla::ipc::IPCResult RecvOnDataAvailable();
+
+  mozilla::ipc::IPCResult RecvOnFlushConsoleReport(
+      nsTArray<net::ConsoleReportCollected>&& aReports);
+
+  mozilla::ipc::IPCResult RecvOnCSPViolationEvent(const nsAString& aJSon);
+
+  mozilla::ipc::IPCResult RecvOnReportPerformanceTiming(
+      ResponseTiming&& aTiming);
+
+  mozilla::ipc::IPCResult RecvOnNotifyNetworkMonitorAlternateStack(
+      uint64_t aChannelID);
+
+  void SetCSPEventListener(nsICSPEventListener* aListener);
+
+  static RefPtr<FetchChild> Create(WorkerPrivate* aWorkerPrivate,
+                                   RefPtr<Promise> aPromise,
+                                   RefPtr<AbortSignalImpl> aSignalImpl,
+                                   RefPtr<FetchObserver> aObserver);
+
+  FetchChild(RefPtr<Promise>&& aPromise, RefPtr<AbortSignalImpl>&& aSignalImpl,
+             RefPtr<FetchObserver>&& aObserver);
+
+  // AbortFollower
+  void RunAbortAlgorithm() override;
+
+  void DoFetchOp(const FetchOpArgs& aArgs);
+
+  void SetOriginStack(UniquePtr<SerializedStackHolder>&& aStack) {
+    MOZ_ASSERT(!mOriginStack);
+    mOriginStack = std::move(aStack);
+  }
+
+ private:
+  ~FetchChild() = default;
+
+  // WorkerPrivate shutdown callback.
+  void Shutdown();
+  void ActorDestroy(ActorDestroyReason aReason) override;
+
+  RefPtr<ThreadSafeWorkerRef> mWorkerRef;
+  RefPtr<Promise> mPromise;
+  RefPtr<AbortSignalImpl> mSignalImpl;
+  RefPtr<FetchObserver> mFetchObserver;
+  UniquePtr<SerializedStackHolder> mOriginStack;
+  nsCOMPtr<nsICSPEventListener> mCSPEventListener;
+  nsCOMPtr<nsIConsoleReportCollector> mReporter;
+  FlippedOnce<false> mIsShutdown;
+  nsCOMPtr<nsIWorkerChannelInfo> mWorkerChannelInfo;
+};
+
+}  // namespace mozilla::dom
+
+#endif
diff --git a/dom/fetch/FetchDriver.cpp b/dom/fetch/FetchDriver.cpp
new file mode 100644
index 0000000000..8c527ffeae
--- /dev/null
+++ b/dom/fetch/FetchDriver.cpp
@@ -0,0 +1,1755 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "js/Value.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/TaskQueue.h"
+#include "mozilla/dom/FetchDriver.h"
+
+#include "mozilla/dom/ReferrerInfo.h"
+#include "nsIAsyncVerifyRedirectCallback.h"
+#include "mozilla/dom/Document.h"
+#include "nsICookieJarSettings.h"
+#include "nsIFile.h"
+#include "nsIInputStream.h"
+#include "nsIInterceptionInfo.h"
+#include "nsIOutputStream.h"
+#include "nsIFileChannel.h"
+#include "nsIHttpChannel.h"
+#include "nsIHttpChannelInternal.h"
+#include "nsISupportsPriority.h"
+#include "nsIThreadRetargetableRequest.h"
+#include "nsIUploadChannel2.h"
+#include "nsIInterfaceRequestorUtils.h"
+#include "nsIPipe.h"
+#include "nsIRedirectHistoryEntry.h"
+
+#include "nsContentPolicyUtils.h"
+#include "nsDataHandler.h"
+#include "nsNetUtil.h"
+#include "nsPrintfCString.h"
+#include "nsProxyRelease.h"
+#include "nsStreamUtils.h"
+#include "nsStringStream.h"
+#include "nsHttpChannel.h"
+
+#include "mozilla/dom/BlobURLProtocolHandler.h"
+#include "mozilla/dom/File.h"
+#include "mozilla/dom/PerformanceStorage.h"
+#include "mozilla/dom/PerformanceTiming.h"
+#include "mozilla/dom/ServiceWorkerInterceptController.h"
+#include "mozilla/dom/UserActivation.h"
+#include "mozilla/dom/WorkerCommon.h"
+#include "mozilla/PreloaderBase.h"
+#include "mozilla/net/InterceptionInfo.h"
+#include "mozilla/net/NeckoChannelParams.h"
+#include "mozilla/ipc/PBackgroundSharedTypes.h"
+#include "mozilla/StaticPrefs_browser.h"
+#include "mozilla/StaticPrefs_network.h"
+#include "mozilla/StaticPrefs_privacy.h"
+#include "mozilla/StaticPrefs_javascript.h"
+#include "mozilla/Unused.h"
+
+#include "Fetch.h"
+#include "FetchUtil.h"
+#include "InternalRequest.h"
+#include "InternalResponse.h"
+
+namespace mozilla::dom {
+
+namespace {
+
+void GetBlobURISpecFromChannel(nsIRequest* aRequest, nsCString& aBlobURISpec) {
+  MOZ_ASSERT(aRequest);
+
+  aBlobURISpec.SetIsVoid(true);
+
+  nsCOMPtr<nsIChannel> channel = do_QueryInterface(aRequest);
+  if (!channel) {
+    return;
+  }
+
+  nsCOMPtr<nsIURI> uri;
+  nsresult rv = NS_GetFinalChannelURI(channel, getter_AddRefs(uri));
+  if (NS_FAILED(rv)) {
+    return;
+  }
+
+  if (!dom::IsBlobURI(uri)) {
+    return;
+  }
+
+  uri->GetSpec(aBlobURISpec);
+}
+
+bool ShouldCheckSRI(const InternalRequest& aRequest,
+                    const InternalResponse& aResponse) {
+  return !aRequest.GetIntegrity().IsEmpty() &&
+         aResponse.Type() != ResponseType::Error;
+}
+
+}  // anonymous namespace
+
+//-----------------------------------------------------------------------------
+// AlternativeDataStreamListener
+//-----------------------------------------------------------------------------
+class AlternativeDataStreamListener final
+    : public nsIStreamListener,
+      public nsIThreadRetargetableStreamListener {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIREQUESTOBSERVER
+  NS_DECL_NSISTREAMLISTENER
+  NS_DECL_NSITHREADRETARGETABLESTREAMLISTENER
+
+  // The status of AlternativeDataStreamListener
+  // LOADING: is the initial status, loading the alternative data
+  // COMPLETED: Alternative data loading is completed
+  // CANCELED: Alternative data loading is canceled, this would make
+  //           AlternativeDataStreamListener ignore all channel callbacks
+  // FALLBACK: fallback the channel callbacks to FetchDriver
+  // Depends on different situaions, the status transition could be followings
+  // 1. LOADING->COMPLETED
+  //    This is the normal status transition for alternative data loading
+  //
+  // 2. LOADING->CANCELED
+  //    LOADING->COMPLETED->CANCELED
+  //    Alternative data loading could be canceled when cacheId from alternative
+  //    data channel does not match with from main data channel(The cacheID
+  //    checking is in FetchDriver::OnStartRequest).
+  //    Notice the alternative data loading could finish before the cacheID
+  //    checking, so the statust transition could be
+  //    LOADING->COMPLETED->CANCELED
+  //
+  // 3. LOADING->FALLBACK
+  //    For the case that alternative data loading could not be initialized,
+  //    i.e. alternative data does not exist or no preferred alternative data
+  //    type is requested. Once the status becomes FALLBACK,
+  //    AlternativeDataStreamListener transits the channel callback request to
+  //    FetchDriver, and the status should not go back to LOADING, COMPLETED, or
+  //    CANCELED anymore.
+  enum eStatus { LOADING = 0, COMPLETED, CANCELED, FALLBACK };
+
+  AlternativeDataStreamListener(FetchDriver* aFetchDriver, nsIChannel* aChannel,
+                                const nsACString& aAlternativeDataType);
+  eStatus Status();
+  void Cancel();
+  uint64_t GetAlternativeDataCacheEntryId();
+  const nsACString& GetAlternativeDataType() const;
+  already_AddRefed<nsICacheInfoChannel> GetCacheInfoChannel();
+  already_AddRefed<nsIInputStream> GetAlternativeInputStream();
+
+ private:
+  ~AlternativeDataStreamListener() = default;
+
+  // This creates a strong reference cycle with FetchDriver and its
+  // mAltDataListener. We need to clear at least one reference of them once the
+  // data loading finishes.
+  RefPtr<FetchDriver> mFetchDriver;
+  nsCString mAlternativeDataType;
+  nsCOMPtr<nsIInputStream> mPipeAlternativeInputStream;
+  nsCOMPtr<nsIOutputStream> mPipeAlternativeOutputStream;
+  uint64_t mAlternativeDataCacheEntryId;
+  nsCOMPtr<nsICacheInfoChannel> mCacheInfoChannel;
+  nsCOMPtr<nsIChannel> mChannel;
+  Atomic<eStatus> mStatus;
+};
+
+NS_IMPL_ISUPPORTS(AlternativeDataStreamListener, nsIStreamListener,
+                  nsIThreadRetargetableStreamListener)
+
+AlternativeDataStreamListener::AlternativeDataStreamListener(
+    FetchDriver* aFetchDriver, nsIChannel* aChannel,
+    const nsACString& aAlternativeDataType)
+    : mFetchDriver(aFetchDriver),
+      mAlternativeDataType(aAlternativeDataType),
+      mAlternativeDataCacheEntryId(0),
+      mChannel(aChannel),
+      mStatus(AlternativeDataStreamListener::LOADING) {
+  MOZ_DIAGNOSTIC_ASSERT(mFetchDriver);
+  MOZ_DIAGNOSTIC_ASSERT(mChannel);
+}
+
+AlternativeDataStreamListener::eStatus AlternativeDataStreamListener::Status() {
+  return mStatus;
+}
+
+void AlternativeDataStreamListener::Cancel() {
+  mAlternativeDataCacheEntryId = 0;
+  mCacheInfoChannel = nullptr;
+  mPipeAlternativeOutputStream = nullptr;
+  mPipeAlternativeInputStream = nullptr;
+  if (mChannel && mStatus != AlternativeDataStreamListener::FALLBACK) {
+    // if mStatus is fallback, we need to keep channel to forward request back
+    // to FetchDriver
+    mChannel->CancelWithReason(NS_BINDING_ABORTED,
+                               "AlternativeDataStreamListener::Cancel"_ns);
+    mChannel = nullptr;
+  }
+  mStatus = AlternativeDataStreamListener::CANCELED;
+}
+
+uint64_t AlternativeDataStreamListener::GetAlternativeDataCacheEntryId() {
+  return mAlternativeDataCacheEntryId;
+}
+
+const nsACString& AlternativeDataStreamListener::GetAlternativeDataType()
+    const {
+  return mAlternativeDataType;
+}
+
+already_AddRefed<nsIInputStream>
+AlternativeDataStreamListener::GetAlternativeInputStream() {
+  nsCOMPtr<nsIInputStream> inputStream = mPipeAlternativeInputStream;
+  return inputStream.forget();
+}
+
+already_AddRefed<nsICacheInfoChannel>
+AlternativeDataStreamListener::GetCacheInfoChannel() {
+  nsCOMPtr<nsICacheInfoChannel> channel = mCacheInfoChannel;
+  return channel.forget();
+}
+
+NS_IMETHODIMP
+AlternativeDataStreamListener::OnStartRequest(nsIRequest* aRequest) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(!mAlternativeDataType.IsEmpty());
+  // Checking the alternative data type is the same between we asked and the
+  // saved in the channel.
+  nsAutoCString alternativeDataType;
+  nsCOMPtr<nsICacheInfoChannel> cic = do_QueryInterface(aRequest);
+  mStatus = AlternativeDataStreamListener::LOADING;
+  if (cic && NS_SUCCEEDED(cic->GetAlternativeDataType(alternativeDataType)) &&
+      mAlternativeDataType.Equals(alternativeDataType) &&
+      NS_SUCCEEDED(cic->GetCacheEntryId(&mAlternativeDataCacheEntryId))) {
+    MOZ_DIAGNOSTIC_ASSERT(!mPipeAlternativeInputStream);
+    MOZ_DIAGNOSTIC_ASSERT(!mPipeAlternativeOutputStream);
+    NS_NewPipe(getter_AddRefs(mPipeAlternativeInputStream),
+               getter_AddRefs(mPipeAlternativeOutputStream),
+               0 /* default segment size */, UINT32_MAX /* infinite pipe */,
+               true /* non-blocking input, otherwise you deadlock */,
+               false /* blocking output, since the pipe is 'in'finite */);
+
+    MOZ_DIAGNOSTIC_ASSERT(!mCacheInfoChannel);
+    mCacheInfoChannel = cic;
+
+    // call FetchDriver::HttpFetch to load main body
+    MOZ_ASSERT(mFetchDriver);
+    return mFetchDriver->HttpFetch();
+  }
+  // Needn't load alternative data, since alternative data does not exist.
+  // Set status to FALLBACK to reuse the opened channel to load main body,
+  // then call FetchDriver::OnStartRequest to continue the work. Unfortunately
+  // can't change the stream listener to mFetchDriver, need to keep
+  // AlternativeDataStreamListener alive to redirect OnDataAvailable and
+  // OnStopRequest to mFetchDriver.
+  MOZ_ASSERT(alternativeDataType.IsEmpty());
+  mStatus = AlternativeDataStreamListener::FALLBACK;
+  mAlternativeDataCacheEntryId = 0;
+  MOZ_ASSERT(mFetchDriver);
+  return mFetchDriver->OnStartRequest(aRequest);
+}
+
+NS_IMETHODIMP
+AlternativeDataStreamListener::OnDataAvailable(nsIRequest* aRequest,
+                                               nsIInputStream* aInputStream,
+                                               uint64_t aOffset,
+                                               uint32_t aCount) {
+  if (mStatus == AlternativeDataStreamListener::LOADING) {
+    MOZ_ASSERT(mPipeAlternativeOutputStream);
+    uint32_t read = 0;
+    return aInputStream->ReadSegments(
+        NS_CopySegmentToStream, mPipeAlternativeOutputStream, aCount, &read);
+  }
+  if (mStatus == AlternativeDataStreamListener::FALLBACK) {
+    MOZ_ASSERT(mFetchDriver);
+    return mFetchDriver->OnDataAvailable(aRequest, aInputStream, aOffset,
+                                         aCount);
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+AlternativeDataStreamListener::OnStopRequest(nsIRequest* aRequest,
+                                             nsresult aStatusCode) {
+  AssertIsOnMainThread();
+
+  // Alternative data loading is going to finish, breaking the reference cycle
+  // here by taking the ownership to a loacl variable.
+  RefPtr<FetchDriver> fetchDriver = std::move(mFetchDriver);
+
+  if (mStatus == AlternativeDataStreamListener::CANCELED) {
+    // do nothing
+    return NS_OK;
+  }
+
+  if (mStatus == AlternativeDataStreamListener::FALLBACK) {
+    MOZ_ASSERT(fetchDriver);
+    return fetchDriver->OnStopRequest(aRequest, aStatusCode);
+  }
+
+  MOZ_DIAGNOSTIC_ASSERT(mStatus == AlternativeDataStreamListener::LOADING);
+
+  MOZ_ASSERT(!mAlternativeDataType.IsEmpty() && mPipeAlternativeOutputStream &&
+             mPipeAlternativeInputStream);
+
+  mPipeAlternativeOutputStream->Close();
+  mPipeAlternativeOutputStream = nullptr;
+
+  // Cleanup the states for alternative data if needed.
+  if (NS_FAILED(aStatusCode)) {
+    mAlternativeDataCacheEntryId = 0;
+    mCacheInfoChannel = nullptr;
+    mPipeAlternativeInputStream = nullptr;
+  }
+  mStatus = AlternativeDataStreamListener::COMPLETED;
+  // alternative data loading finish, call FetchDriver::FinishOnStopRequest to
+  // continue the final step for the case FetchDriver::OnStopRequest is called
+  // earlier than AlternativeDataStreamListener::OnStopRequest
+  MOZ_ASSERT(fetchDriver);
+  fetchDriver->FinishOnStopRequest(this);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+AlternativeDataStreamListener::CheckListenerChain() { return NS_OK; }
+//-----------------------------------------------------------------------------
+// FetchDriver
+//-----------------------------------------------------------------------------
+
+NS_IMPL_ISUPPORTS(FetchDriver, nsIStreamListener, nsIChannelEventSink,
+                  nsIInterfaceRequestor, nsIThreadRetargetableStreamListener,
+                  nsINetworkInterceptController)
+
+FetchDriver::FetchDriver(SafeRefPtr<InternalRequest> aRequest,
+                         nsIPrincipal* aPrincipal, nsILoadGroup* aLoadGroup,
+                         nsIEventTarget* aMainThreadEventTarget,
+                         nsICookieJarSettings* aCookieJarSettings,
+                         PerformanceStorage* aPerformanceStorage,
+                         bool aIsTrackingFetch)
+    : mPrincipal(aPrincipal),
+      mLoadGroup(aLoadGroup),
+      mRequest(std::move(aRequest)),
+      mMainThreadEventTarget(aMainThreadEventTarget),
+      mCookieJarSettings(aCookieJarSettings),
+      mPerformanceStorage(aPerformanceStorage),
+      mNeedToObserveOnDataAvailable(false),
+      mIsTrackingFetch(aIsTrackingFetch),
+      mOnStopRequestCalled(false)
+#ifdef DEBUG
+      ,
+      mResponseAvailableCalled(false),
+      mFetchCalled(false)
+#endif
+{
+  AssertIsOnMainThread();
+
+  MOZ_ASSERT(mRequest);
+  MOZ_ASSERT(aPrincipal);
+  MOZ_ASSERT(aMainThreadEventTarget);
+}
+
+FetchDriver::~FetchDriver() {
+  AssertIsOnMainThread();
+
+  // We assert this since even on failures, we should call
+  // FailWithNetworkError().
+  MOZ_ASSERT(mResponseAvailableCalled);
+  if (mObserver) {
+    mObserver = nullptr;
+  }
+}
+
+already_AddRefed<PreloaderBase> FetchDriver::FindPreload(nsIURI* aURI) {
+  // Decide if we allow reuse of an existing <link rel=preload as=fetch>
+  // response for this request.  First examine this fetch requets itself if it
+  // is 'pure' enough to use the response and then try to find a preload.
+
+  if (!mDocument) {
+    // Preloads are mapped on the document, no document, no preload.
+    return nullptr;
+  }
+  CORSMode cors;
+  switch (mRequest->Mode()) {
+    case RequestMode::No_cors:
+      cors = CORSMode::CORS_NONE;
+      break;
+    case RequestMode::Cors:
+      cors = mRequest->GetCredentialsMode() == RequestCredentials::Include
+                 ? CORSMode::CORS_USE_CREDENTIALS
+                 : CORSMode::CORS_ANONYMOUS;
+      break;
+    default:
+      // Can't be satisfied by a preload because preload cannot define any of
+      // remaining modes.
+      return nullptr;
+  }
+  if (!mRequest->Headers()->HasOnlySimpleHeaders()) {
+    // Preload can't set any headers.
+    return nullptr;
+  }
+  if (!mRequest->GetIntegrity().IsEmpty()) {
+    // There is currently no support for SRI checking in the fetch preloader.
+    return nullptr;
+  }
+  if (mRequest->GetCacheMode() != RequestCache::Default) {
+    // Preload can only go with the default caching mode.
+    return nullptr;
+  }
+  if (mRequest->SkipServiceWorker()) {
+    // Preload can't be forbidden interception.
+    return nullptr;
+  }
+  if (mRequest->GetRedirectMode() != RequestRedirect::Follow) {
+    // Preload always follows redirects.
+    return nullptr;
+  }
+  nsAutoCString method;
+  mRequest->GetMethod(method);
+  if (!method.EqualsLiteral("GET")) {
+    // Preload can only do GET, this also eliminates the case we do upload, so
+    // no need to check if the request has any body to send out.
+    return nullptr;
+  }
+
+  // OK, this request can be satisfied by a preloaded response, try to find one.
+
+  auto preloadKey = PreloadHashKey::CreateAsFetch(aURI, cors);
+  return mDocument->Preloads().LookupPreload(preloadKey);
+}
+
+void FetchDriver::UpdateReferrerInfoFromNewChannel(nsIChannel* aChannel) {
+  nsCOMPtr<nsIHttpChannel> httpChannel = do_QueryInterface(aChannel);
+  if (!httpChannel) {
+    return;
+  }
+
+  nsCOMPtr<nsIReferrerInfo> referrerInfo = httpChannel->GetReferrerInfo();
+  if (!referrerInfo) {
+    return;
+  }
+
+  nsAutoString computedReferrerSpec;
+  mRequest->SetReferrerPolicy(referrerInfo->ReferrerPolicy());
+  Unused << referrerInfo->GetComputedReferrerSpec(computedReferrerSpec);
+  mRequest->SetReferrer(computedReferrerSpec);
+}
+
+nsresult FetchDriver::Fetch(AbortSignalImpl* aSignalImpl,
+                            FetchDriverObserver* aObserver) {
+  AssertIsOnMainThread();
+#ifdef DEBUG
+  MOZ_ASSERT(!mFetchCalled);
+  mFetchCalled = true;
+#endif
+
+  mObserver = aObserver;
+
+  // FIXME(nsm): Deal with HSTS.
+
+  MOZ_RELEASE_ASSERT(!mRequest->IsSynchronous(),
+                     "Synchronous fetch not supported");
+
+  UniquePtr<mozilla::ipc::PrincipalInfo> principalInfo(
+      new mozilla::ipc::PrincipalInfo());
+  nsresult rv = PrincipalToPrincipalInfo(mPrincipal, principalInfo.get());
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  mRequest->SetPrincipalInfo(std::move(principalInfo));
+
+  // If the signal is aborted, it's time to inform the observer and terminate
+  // the operation.
+  if (aSignalImpl) {
+    if (aSignalImpl->Aborted()) {
+      FetchDriverAbortActions(aSignalImpl);
+      return NS_OK;
+    }
+
+    Follow(aSignalImpl);
+  }
+
+  rv = HttpFetch(mRequest->GetPreferredAlternativeDataType());
+  if (NS_FAILED(rv)) {
+    FailWithNetworkError(rv);
+  }
+
+  // Any failure is handled by FailWithNetworkError notifying the aObserver.
+  return NS_OK;
+}
+
+// This function implements the "HTTP Fetch" algorithm from the Fetch spec.
+// Functionality is often split between here, the CORS listener proxy and the
+// Necko HTTP implementation.
+nsresult FetchDriver::HttpFetch(
+    const nsACString& aPreferredAlternativeDataType) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  // Step 1. "Let response be null."
+  mResponse = nullptr;
+  mOnStopRequestCalled = false;
+  nsresult rv;
+
+  nsCOMPtr<nsIIOService> ios = do_GetIOService(&rv);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsAutoCString url;
+  mRequest->GetURL(url);
+  nsCOMPtr<nsIURI> uri;
+  rv = NS_NewURI(getter_AddRefs(uri), url);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Unsafe requests aren't allowed with when using no-core mode.
+  if (mRequest->Mode() == RequestMode::No_cors && mRequest->UnsafeRequest() &&
+      (!mRequest->HasSimpleMethod() ||
+       !mRequest->Headers()->HasOnlySimpleHeaders())) {
+    MOZ_ASSERT(false, "The API should have caught this");
+    return NS_ERROR_DOM_BAD_URI;
+  }
+
+  // non-GET requests aren't allowed for blob.
+  if (IsBlobURI(uri)) {
+    nsAutoCString method;
+    mRequest->GetMethod(method);
+    if (!method.EqualsLiteral("GET")) {
+      return NS_ERROR_DOM_NETWORK_ERR;
+    }
+  }
+
+  RefPtr<PreloaderBase> fetchPreload = FindPreload(uri);
+  if (fetchPreload) {
+    fetchPreload->RemoveSelf(mDocument);
+    fetchPreload->NotifyUsage(mDocument, PreloaderBase::LoadBackground::Keep);
+
+    rv = fetchPreload->AsyncConsume(this);
+    if (NS_SUCCEEDED(rv)) {
+      mFromPreload = true;
+
+      mChannel = fetchPreload->Channel();
+      MOZ_ASSERT(mChannel);
+      mChannel->SetNotificationCallbacks(this);
+
+      // Copied from AsyncOnChannelRedirect.
+      for (const auto& redirect : fetchPreload->Redirects()) {
+        if (redirect.Flags() & nsIChannelEventSink::REDIRECT_INTERNAL) {
+          mRequest->SetURLForInternalRedirect(redirect.Flags(), redirect.Spec(),
+                                              redirect.Fragment());
+        } else {
+          mRequest->AddURL(redirect.Spec(), redirect.Fragment());
+        }
+      }
+
+      return NS_OK;
+    }
+
+    // The preload failed to be consumed.  Behave like there were no preload.
+    fetchPreload = nullptr;
+  }
+
+  // Step 2 deals with letting ServiceWorkers intercept requests. This is
+  // handled by Necko after the channel is opened.
+  // FIXME(nsm): Bug 1119026: The channel's skip service worker flag should be
+  // set based on the Request's flag.
+
+  // Step 3.1 "If the CORS preflight flag is set and one of these conditions is
+  // true..." is handled by the CORS proxy.
+  //
+  // Step 3.2 "Set request's skip service worker flag." This isn't required
+  // since Necko will fall back to the network if the ServiceWorker does not
+  // respond with a valid Response.
+  //
+  // NS_StartCORSPreflight() will automatically kick off the original request
+  // if it succeeds, so we need to have everything setup for the original
+  // request too.
+
+  // Step 3.3 "Let credentials flag be set if one of
+  //  - request's credentials mode is "include"
+  //  - request's credentials mode is "same-origin" and either the CORS flag
+  //    is unset or response tainting is "opaque"
+  // is true, and unset otherwise."
+
+  // Set skip serviceworker flag.
+  // While the spec also gates on the client being a ServiceWorker, we can't
+  // infer that here. Instead we rely on callers to set the flag correctly.
+  const nsLoadFlags bypassFlag = mRequest->SkipServiceWorker()
+                                     ? nsIChannel::LOAD_BYPASS_SERVICE_WORKER
+                                     : 0;
+
+  nsSecurityFlags secFlags = 0;
+  if (mRequest->Mode() == RequestMode::Cors) {
+    secFlags |= nsILoadInfo::SEC_REQUIRE_CORS_INHERITS_SEC_CONTEXT;
+  } else if (mRequest->Mode() == RequestMode::Same_origin ||
+             mRequest->Mode() == RequestMode::Navigate) {
+    secFlags |= nsILoadInfo::SEC_REQUIRE_SAME_ORIGIN_INHERITS_SEC_CONTEXT;
+  } else if (mRequest->Mode() == RequestMode::No_cors) {
+    secFlags |= nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_INHERITS_SEC_CONTEXT;
+  } else {
+    MOZ_ASSERT_UNREACHABLE("Unexpected request mode!");
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  if (mRequest->GetRedirectMode() != RequestRedirect::Follow) {
+    secFlags |= nsILoadInfo::SEC_DONT_FOLLOW_REDIRECTS;
+  }
+
+  // This handles the use credentials flag in "HTTP
+  // network or cache fetch" in the spec and decides whether to transmit
+  // cookies and other identifying information.
+  if (mRequest->GetCredentialsMode() == RequestCredentials::Include) {
+    secFlags |= nsILoadInfo::SEC_COOKIES_INCLUDE;
+  } else if (mRequest->GetCredentialsMode() == RequestCredentials::Omit) {
+    secFlags |= nsILoadInfo::SEC_COOKIES_OMIT;
+  } else if (mRequest->GetCredentialsMode() ==
+             RequestCredentials::Same_origin) {
+    secFlags |= nsILoadInfo::SEC_COOKIES_SAME_ORIGIN;
+  } else {
+    MOZ_ASSERT_UNREACHABLE("Unexpected credentials mode!");
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  // From here on we create a channel and set its properties with the
+  // information from the InternalRequest. This is an implementation detail.
+  MOZ_ASSERT(mLoadGroup);
+  nsCOMPtr<nsIChannel> chan;
+
+  nsLoadFlags loadFlags = nsIRequest::LOAD_BACKGROUND | bypassFlag;
+  if (mDocument) {
+    MOZ_ASSERT(mDocument->NodePrincipal() == mPrincipal);
+    MOZ_ASSERT(mDocument->CookieJarSettings() == mCookieJarSettings);
+    rv = NS_NewChannel(getter_AddRefs(chan), uri, mDocument, secFlags,
+                       mRequest->ContentPolicyType(),
+                       nullptr,             /* aPerformanceStorage */
+                       mLoadGroup, nullptr, /* aCallbacks */
+                       loadFlags, ios);
+  } else if (mClientInfo.isSome()) {
+    rv = NS_NewChannel(getter_AddRefs(chan), uri, mPrincipal, mClientInfo.ref(),
+                       mController, secFlags, mRequest->ContentPolicyType(),
+                       mCookieJarSettings, mPerformanceStorage, mLoadGroup,
+                       nullptr, /* aCallbacks */
+                       loadFlags, ios);
+  } else {
+    rv =
+        NS_NewChannel(getter_AddRefs(chan), uri, mPrincipal, secFlags,
+                      mRequest->ContentPolicyType(), mCookieJarSettings,
+                      mPerformanceStorage, mLoadGroup, nullptr, /* aCallbacks */
+                      loadFlags, ios);
+  }
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (mCSPEventListener) {
+    nsCOMPtr<nsILoadInfo> loadInfo = chan->LoadInfo();
+    rv = loadInfo->SetCspEventListener(mCSPEventListener);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  {
+    nsCOMPtr<nsILoadInfo> loadInfo = chan->LoadInfo();
+    rv = loadInfo->SetLoadingEmbedderPolicy(mRequest->GetEmbedderPolicy());
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  if (mAssociatedBrowsingContextID) {
+    nsCOMPtr<nsILoadInfo> loadInfo = chan->LoadInfo();
+    rv = loadInfo->SetWorkerAssociatedBrowsingContextID(
+        mAssociatedBrowsingContextID);
+  }
+
+  // If the fetch is created by FetchEvent.request or NavigationPreload request,
+  // corresponding InterceptedHttpChannel information need to propagte to the
+  // channel of the fetch.
+  if (mRequest->GetInterceptionTriggeringPrincipalInfo()) {
+    auto principalOrErr = mozilla::ipc::PrincipalInfoToPrincipal(
+        *(mRequest->GetInterceptionTriggeringPrincipalInfo().get()));
+    if (!principalOrErr.isErr()) {
+      nsCOMPtr<nsIPrincipal> principal = principalOrErr.unwrap();
+
+      nsTArray<nsCOMPtr<nsIRedirectHistoryEntry>> redirectChain;
+      if (!mRequest->InterceptionRedirectChain().IsEmpty()) {
+        for (const RedirectHistoryEntryInfo& entryInfo :
+             mRequest->InterceptionRedirectChain()) {
+          nsCOMPtr<nsIRedirectHistoryEntry> entry =
+              mozilla::ipc::RHEntryInfoToRHEntry(entryInfo);
+          redirectChain.AppendElement(entry);
+        }
+      }
+
+      nsCOMPtr<nsILoadInfo> loadInfo = chan->LoadInfo();
+      MOZ_ASSERT(loadInfo);
+      loadInfo->SetInterceptionInfo(new mozilla::net::InterceptionInfo(
+          principal, mRequest->InterceptionContentPolicyType(), redirectChain,
+          mRequest->InterceptionFromThirdParty()));
+    }
+  }
+
+  if (mDocument && mDocument->GetEmbedderElement() &&
+      mDocument->GetEmbedderElement()->IsAnyOfHTMLElements(nsGkAtoms::object,
+                                                           nsGkAtoms::embed)) {
+    nsCOMPtr<nsILoadInfo> loadInfo = chan->LoadInfo();
+    rv = loadInfo->SetIsFromObjectOrEmbed(true);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  // Insert ourselves into the notification callbacks chain so we can set
+  // headers on redirects.
+#ifdef DEBUG
+  {
+    nsCOMPtr<nsIInterfaceRequestor> notificationCallbacks;
+    chan->GetNotificationCallbacks(getter_AddRefs(notificationCallbacks));
+    MOZ_ASSERT(!notificationCallbacks);
+  }
+#endif
+  chan->SetNotificationCallbacks(this);
+
+  nsCOMPtr<nsIClassOfService> cos(do_QueryInterface(chan));
+  // Mark channel as urgent-start if the Fetch is triggered by user input
+  // events.
+  if (cos && UserActivation::IsHandlingUserInput()) {
+    cos->AddClassFlags(nsIClassOfService::UrgentStart);
+  }
+
+  // Step 3.5 begins "HTTP network or cache fetch".
+  // HTTP network or cache fetch
+  // ---------------------------
+  // Step 1 "Let HTTPRequest..." The channel is the HTTPRequest.
+  nsCOMPtr<nsIHttpChannel> httpChan = do_QueryInterface(chan);
+  if (httpChan) {
+    // Copy the method.
+    nsAutoCString method;
+    mRequest->GetMethod(method);
+    rv = httpChan->SetRequestMethod(method);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    // Set the same headers.
+    SetRequestHeaders(httpChan, false, false);
+
+    // Step 5 of https://fetch.spec.whatwg.org/#main-fetch
+    // If request's referrer policy is the empty string and request's client is
+    // non-null, then set request's referrer policy to request's client's
+    // associated referrer policy.
+    // Basically, "client" is not in our implementation, we use
+    // EnvironmentReferrerPolicy of the worker or document context
+    ReferrerPolicy referrerPolicy = mRequest->GetEnvironmentReferrerPolicy();
+    if (mRequest->ReferrerPolicy_() == ReferrerPolicy::_empty) {
+      mRequest->SetReferrerPolicy(referrerPolicy);
+    }
+    // Step 6 of https://fetch.spec.whatwg.org/#main-fetch
+    // If request’s referrer policy is the empty string,
+    // then set request’s referrer policy to the user-set default policy.
+    if (mRequest->ReferrerPolicy_() == ReferrerPolicy::_empty) {
+      nsCOMPtr<nsILoadInfo> loadInfo = httpChan->LoadInfo();
+      bool isPrivate = loadInfo->GetOriginAttributes().mPrivateBrowsingId > 0;
+      referrerPolicy =
+          ReferrerInfo::GetDefaultReferrerPolicy(httpChan, uri, isPrivate);
+      mRequest->SetReferrerPolicy(referrerPolicy);
+    }
+
+    rv = FetchUtil::SetRequestReferrer(mPrincipal, mDocument, httpChan,
+                                       *mRequest);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    // Bug 1120722 - Authorization will be handled later.
+    // Auth may require prompting, we don't support it yet.
+    // The next patch in this same bug prevents this from aborting the request.
+    // Credentials checks for CORS are handled by nsCORSListenerProxy,
+
+    nsCOMPtr<nsIHttpChannelInternal> internalChan = do_QueryInterface(httpChan);
+
+    rv = internalChan->SetRequestMode(mRequest->Mode());
+    MOZ_ASSERT(NS_SUCCEEDED(rv));
+    // Conversion between enumerations is safe due to static asserts in
+    // dom/workers/ServiceWorkerManager.cpp
+    rv = internalChan->SetRedirectMode(
+        static_cast<uint32_t>(mRequest->GetRedirectMode()));
+    MOZ_ASSERT(NS_SUCCEEDED(rv));
+    mRequest->MaybeSkipCacheIfPerformingRevalidation();
+    rv = internalChan->SetFetchCacheMode(
+        static_cast<uint32_t>(mRequest->GetCacheMode()));
+    MOZ_ASSERT(NS_SUCCEEDED(rv));
+    rv = internalChan->SetIntegrityMetadata(mRequest->GetIntegrity());
+    MOZ_ASSERT(NS_SUCCEEDED(rv));
+
+    // Set the initiator type
+    nsCOMPtr<nsITimedChannel> timedChannel(do_QueryInterface(httpChan));
+    if (timedChannel) {
+      timedChannel->SetInitiatorType(u"fetch"_ns);
+    }
+  }
+
+  // Step 5. Proxy authentication will be handled by Necko.
+
+  // Continue setting up 'HTTPRequest'. Content-Type and body data.
+  nsCOMPtr<nsIUploadChannel2> uploadChan = do_QueryInterface(chan);
+  if (uploadChan) {
+    nsAutoCString contentType;
+    ErrorResult result;
+    mRequest->Headers()->GetFirst("content-type"_ns, contentType, result);
+    // We don't actually expect "result" to have failed here: that only happens
+    // for invalid header names.  But if for some reason it did, just propagate
+    // it out.
+    if (result.Failed()) {
+      return result.StealNSResult();
+    }
+
+    // Now contentType is the header that was set in mRequest->Headers(), or a
+    // void string if no header was set.
+#ifdef DEBUG
+    bool hasContentTypeHeader =
+        mRequest->Headers()->Has("content-type"_ns, result);
+    MOZ_ASSERT(!result.Failed());
+    MOZ_ASSERT_IF(!hasContentTypeHeader, contentType.IsVoid());
+#endif  // DEBUG
+
+    int64_t bodyLength;
+    nsCOMPtr<nsIInputStream> bodyStream;
+    mRequest->GetBody(getter_AddRefs(bodyStream), &bodyLength);
+    if (bodyStream) {
+      nsAutoCString method;
+      mRequest->GetMethod(method);
+      rv = uploadChan->ExplicitSetUploadStream(bodyStream, contentType,
+                                               bodyLength, method,
+                                               false /* aStreamHasHeaders */);
+      NS_ENSURE_SUCCESS(rv, rv);
+    }
+  }
+
+  // If preflight is required, start a "CORS preflight fetch"
+  // https://fetch.spec.whatwg.org/#cors-preflight-fetch-0. All the
+  // implementation is handled by the http channel calling into
+  // nsCORSListenerProxy. We just inform it which unsafe headers are included
+  // in the request.
+  if (mRequest->Mode() == RequestMode::Cors) {
+    AutoTArray<nsCString, 5> unsafeHeaders;
+    mRequest->Headers()->GetUnsafeHeaders(unsafeHeaders);
+    nsCOMPtr<nsILoadInfo> loadInfo = chan->LoadInfo();
+    loadInfo->SetCorsPreflightInfo(unsafeHeaders, false);
+  }
+
+  if (mIsTrackingFetch && StaticPrefs::network_http_tailing_enabled() && cos) {
+    cos->AddClassFlags(nsIClassOfService::Throttleable |
+                       nsIClassOfService::Tail);
+  }
+
+  if (mIsTrackingFetch &&
+      StaticPrefs::privacy_trackingprotection_lower_network_priority()) {
+    nsCOMPtr<nsISupportsPriority> p = do_QueryInterface(chan);
+    if (p) {
+      p->SetPriority(nsISupportsPriority::PRIORITY_LOWEST);
+    }
+  }
+
+  NotifyNetworkMonitorAlternateStack(chan, std::move(mOriginStack));
+  if (mObserver && httpChan) {
+    mObserver->OnNotifyNetworkMonitorAlternateStack(httpChan->ChannelId());
+  }
+
+  // if the preferred alternative data type in InternalRequest is not empty, set
+  // the data type on the created channel and also create a
+  // AlternativeDataStreamListener to be the stream listener of the channel.
+  if (!aPreferredAlternativeDataType.IsEmpty()) {
+    nsCOMPtr<nsICacheInfoChannel> cic = do_QueryInterface(chan);
+    if (cic) {
+      cic->PreferAlternativeDataType(
+          aPreferredAlternativeDataType, ""_ns,
+          nsICacheInfoChannel::PreferredAlternativeDataDeliveryType::ASYNC);
+      MOZ_ASSERT(!mAltDataListener);
+      mAltDataListener = new AlternativeDataStreamListener(
+          this, chan, aPreferredAlternativeDataType);
+      rv = chan->AsyncOpen(mAltDataListener);
+    } else {
+      rv = chan->AsyncOpen(this);
+    }
+  } else {
+    // Integrity check cannot be done on alt-data yet.
+    if (mRequest->GetIntegrity().IsEmpty()) {
+      MOZ_ASSERT(!FetchUtil::WasmAltDataType.IsEmpty());
+      nsCOMPtr<nsICacheInfoChannel> cic = do_QueryInterface(chan);
+      if (cic && StaticPrefs::javascript_options_wasm_caching() &&
+          !mRequest->SkipWasmCaching()) {
+        cic->PreferAlternativeDataType(
+            FetchUtil::WasmAltDataType, nsLiteralCString(WASM_CONTENT_TYPE),
+            nsICacheInfoChannel::PreferredAlternativeDataDeliveryType::
+                SERIALIZE);
+      }
+    }
+
+    rv = chan->AsyncOpen(this);
+  }
+
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // Step 4 onwards of "HTTP Fetch" is handled internally by Necko.
+
+  mChannel = chan;
+  return NS_OK;
+}
+
+SafeRefPtr<InternalResponse> FetchDriver::BeginAndGetFilteredResponse(
+    SafeRefPtr<InternalResponse> aResponse, bool aFoundOpaqueRedirect) {
+  MOZ_ASSERT(aResponse);
+  AutoTArray<nsCString, 4> reqURLList;
+  mRequest->GetURLListWithoutFragment(reqURLList);
+  MOZ_ASSERT(!reqURLList.IsEmpty());
+  aResponse->SetURLList(reqURLList);
+  SafeRefPtr<InternalResponse> filteredResponse;
+  if (aFoundOpaqueRedirect) {
+    filteredResponse = aResponse->OpaqueRedirectResponse();
+  } else {
+    switch (mRequest->GetResponseTainting()) {
+      case LoadTainting::Basic:
+        filteredResponse = aResponse->BasicResponse();
+        break;
+      case LoadTainting::CORS:
+        filteredResponse = aResponse->CORSResponse();
+        break;
+      case LoadTainting::Opaque: {
+        filteredResponse = aResponse->OpaqueResponse();
+        nsresult rv = filteredResponse->GeneratePaddingInfo();
+        if (NS_WARN_IF(NS_FAILED(rv))) {
+          return nullptr;
+        }
+        break;
+      }
+      default:
+        MOZ_CRASH("Unexpected case");
+    }
+  }
+
+  MOZ_ASSERT(filteredResponse);
+  MOZ_ASSERT(mObserver);
+  MOZ_ASSERT(filteredResponse);
+  if (!ShouldCheckSRI(*mRequest, *filteredResponse)) {
+    // Need to keep mObserver alive.
+    RefPtr<FetchDriverObserver> observer = mObserver;
+    observer->OnResponseAvailable(filteredResponse.clonePtr());
+#ifdef DEBUG
+    mResponseAvailableCalled = true;
+#endif
+  }
+
+  return filteredResponse;
+}
+
+void FetchDriver::FailWithNetworkError(nsresult rv) {
+  AssertIsOnMainThread();
+  if (mObserver) {
+    // Need to keep mObserver alive.
+    RefPtr<FetchDriverObserver> observer = mObserver;
+    observer->OnResponseAvailable(InternalResponse::NetworkError(rv));
+#ifdef DEBUG
+    mResponseAvailableCalled = true;
+#endif
+  }
+
+  // mObserver could be null after OnResponseAvailable().
+  if (mObserver) {
+    mObserver->OnResponseEnd(FetchDriverObserver::eByNetworking,
+                             JS::UndefinedHandleValue);
+    mObserver = nullptr;
+  }
+
+  mChannel = nullptr;
+  Unfollow();
+}
+
+NS_IMETHODIMP
+FetchDriver::OnStartRequest(nsIRequest* aRequest) {
+  AssertIsOnMainThread();
+
+  // Note, this can be called multiple times if we are doing an opaqueredirect.
+  // In that case we will get a simulated OnStartRequest() and then the real
+  // channel will call in with an errored OnStartRequest().
+
+  if (mFromPreload && mAborted) {
+    aRequest->CancelWithReason(NS_BINDING_ABORTED,
+                               "FetchDriver::OnStartRequest aborted"_ns);
+    return NS_BINDING_ABORTED;
+  }
+
+  if (!mChannel) {
+    // if the request is aborted, we remove the mObserver reference in
+    // OnStopRequest or ~FetchDriver()
+    MOZ_ASSERT_IF(!mAborted, !mObserver);
+    return NS_BINDING_ABORTED;
+  }
+
+  nsresult rv;
+  aRequest->GetStatus(&rv);
+  if (NS_FAILED(rv)) {
+    FailWithNetworkError(rv);
+    return rv;
+  }
+
+  // We should only get to the following code once.
+  MOZ_ASSERT(!mPipeOutputStream);
+
+  if (!mObserver) {
+    MOZ_ASSERT(false, "We should have mObserver here.");
+    FailWithNetworkError(NS_ERROR_UNEXPECTED);
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  mNeedToObserveOnDataAvailable = mObserver->NeedOnDataAvailable();
+
+  SafeRefPtr<InternalResponse> response;
+  nsCOMPtr<nsIChannel> channel = do_QueryInterface(aRequest);
+  nsCOMPtr<nsIHttpChannel> httpChannel = do_QueryInterface(aRequest);
+
+  // On a successful redirect we perform the following substeps of HTTP Fetch,
+  // step 5, "redirect status", step 11.
+
+  bool foundOpaqueRedirect = false;
+
+  nsAutoCString contentType;
+  channel->GetContentType(contentType);
+
+  int64_t contentLength = InternalResponse::UNKNOWN_BODY_SIZE;
+  rv = channel->GetContentLength(&contentLength);
+  MOZ_ASSERT_IF(NS_FAILED(rv),
+                contentLength == InternalResponse::UNKNOWN_BODY_SIZE);
+
+  if (httpChannel) {
+    uint32_t responseStatus = 0;
+    rv = httpChannel->GetResponseStatus(&responseStatus);
+    if (NS_FAILED(rv)) {
+      FailWithNetworkError(rv);
+      return rv;
+    }
+
+    if (mozilla::net::nsHttpChannel::IsRedirectStatus(responseStatus)) {
+      if (mRequest->GetRedirectMode() == RequestRedirect::Error) {
+        FailWithNetworkError(NS_BINDING_ABORTED);
+        return NS_BINDING_FAILED;
+      }
+      if (mRequest->GetRedirectMode() == RequestRedirect::Manual) {
+        foundOpaqueRedirect = true;
+      }
+    }
+
+    nsAutoCString statusText;
+    rv = httpChannel->GetResponseStatusText(statusText);
+    MOZ_ASSERT(NS_SUCCEEDED(rv));
+
+    response = MakeSafeRefPtr<InternalResponse>(responseStatus, statusText,
+                                                mRequest->GetCredentialsMode());
+
+    UniquePtr<mozilla::ipc::PrincipalInfo> principalInfo(
+        new mozilla::ipc::PrincipalInfo());
+    nsresult rv = PrincipalToPrincipalInfo(mPrincipal, principalInfo.get());
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    response->SetPrincipalInfo(std::move(principalInfo));
+
+    response->Headers()->FillResponseHeaders(httpChannel);
+
+    // If Content-Encoding or Transfer-Encoding headers are set, then the actual
+    // Content-Length (which refer to the decoded data) is obscured behind the
+    // encodings.
+    ErrorResult result;
+    if (response->Headers()->Has("content-encoding"_ns, result) ||
+        response->Headers()->Has("transfer-encoding"_ns, result)) {
+      // We cannot trust the content-length when content-encoding or
+      // transfer-encoding are set.  There are many servers which just
+      // get this wrong.
+      contentLength = InternalResponse::UNKNOWN_BODY_SIZE;
+    }
+    MOZ_ASSERT(!result.Failed());
+  } else {
+    response = MakeSafeRefPtr<InternalResponse>(200, "OK"_ns,
+                                                mRequest->GetCredentialsMode());
+
+    if (!contentType.IsEmpty()) {
+      nsAutoCString contentCharset;
+      channel->GetContentCharset(contentCharset);
+      if (NS_SUCCEEDED(rv) && !contentCharset.IsEmpty()) {
+        contentType += ";charset="_ns + contentCharset;
+      }
+    }
+
+    IgnoredErrorResult result;
+    response->Headers()->Append("Content-Type"_ns, contentType, result);
+    MOZ_ASSERT(!result.Failed());
+
+    if (contentLength >= 0) {
+      nsAutoCString contentLenStr;
+      contentLenStr.AppendInt(contentLength);
+
+      IgnoredErrorResult result;
+      response->Headers()->Append("Content-Length"_ns, contentLenStr, result);
+      MOZ_ASSERT(!result.Failed());
+    }
+  }
+
+  nsCOMPtr<nsICacheInfoChannel> cic = do_QueryInterface(aRequest);
+  if (cic) {
+    if (mAltDataListener) {
+      // Skip the case that mAltDataListener->Status() equals to FALLBACK, that
+      // means the opened channel for alternative data loading is reused for
+      // loading the main data.
+      if (mAltDataListener->Status() !=
+          AlternativeDataStreamListener::FALLBACK) {
+        // Verify the cache ID is the same with from alternative data cache.
+        // If the cache ID is different, droping the alternative data loading,
+        // otherwise setup the response's alternative body and cacheInfoChannel.
+        uint64_t cacheEntryId = 0;
+        if (NS_SUCCEEDED(cic->GetCacheEntryId(&cacheEntryId)) &&
+            cacheEntryId !=
+                mAltDataListener->GetAlternativeDataCacheEntryId()) {
+          mAltDataListener->Cancel();
+        } else {
+          // AlternativeDataStreamListener::OnStartRequest had already been
+          // called, the alternative data input stream and cacheInfo channel
+          // must be created.
+          nsCOMPtr<nsICacheInfoChannel> cacheInfo =
+              mAltDataListener->GetCacheInfoChannel();
+          nsCOMPtr<nsIInputStream> altInputStream =
+              mAltDataListener->GetAlternativeInputStream();
+          MOZ_ASSERT(altInputStream && cacheInfo);
+          response->SetAlternativeBody(altInputStream);
+          nsMainThreadPtrHandle<nsICacheInfoChannel> handle(
+              new nsMainThreadPtrHolder<nsICacheInfoChannel>(
+                  "nsICacheInfoChannel", cacheInfo, false));
+          response->SetCacheInfoChannel(handle);
+        }
+      } else if (!mAltDataListener->GetAlternativeDataType().IsEmpty()) {
+        // If the status is FALLBACK and the
+        // mAltDataListener::mAlternativeDataType is not empty, that means the
+        // data need to be saved into cache, setup the response's
+        // nsICacheInfoChannel for caching the data after loading.
+        nsMainThreadPtrHandle<nsICacheInfoChannel> handle(
+            new nsMainThreadPtrHolder<nsICacheInfoChannel>(
+                "nsICacheInfoChannel", cic, false));
+        response->SetCacheInfoChannel(handle);
+      }
+    } else if (!cic->PreferredAlternativeDataTypes().IsEmpty()) {
+      MOZ_ASSERT(cic->PreferredAlternativeDataTypes().Length() == 1);
+      MOZ_ASSERT(cic->PreferredAlternativeDataTypes()[0].type().Equals(
+          FetchUtil::WasmAltDataType));
+      MOZ_ASSERT(
+          cic->PreferredAlternativeDataTypes()[0].contentType().EqualsLiteral(
+              WASM_CONTENT_TYPE));
+
+      if (contentType.EqualsLiteral(WASM_CONTENT_TYPE)) {
+        // We want to attach the CacheInfoChannel to the response object such
+        // that we can track its origin when the Response object is manipulated
+        // by JavaScript code. This is important for WebAssembly, which uses
+        // fetch to query its sources in JavaScript and transfer the Response
+        // object to other function responsible for storing the alternate data
+        // using the CacheInfoChannel.
+        nsMainThreadPtrHandle<nsICacheInfoChannel> handle(
+            new nsMainThreadPtrHolder<nsICacheInfoChannel>(
+                "nsICacheInfoChannel", cic, false));
+        response->SetCacheInfoChannel(handle);
+      }
+    }
+  }
+
+  // We open a pipe so that we can immediately set the pipe's read end as the
+  // response's body. Setting the segment size to UINT32_MAX means that the
+  // pipe has infinite space. The nsIChannel will continue to buffer data in
+  // xpcom events even if we block on a fixed size pipe.  It might be possible
+  // to suspend the channel and then resume when there is space available, but
+  // for now use an infinite pipe to avoid blocking.
+  nsCOMPtr<nsIInputStream> pipeInputStream;
+  NS_NewPipe(getter_AddRefs(pipeInputStream), getter_AddRefs(mPipeOutputStream),
+             0, /* default segment size */
+             UINT32_MAX /* infinite pipe */,
+             true /* non-blocking input, otherwise you deadlock */,
+             false /* blocking output, since the pipe is 'in'finite */);
+  response->SetBody(pipeInputStream, contentLength);
+
+  // If the request is a file channel, then remember the local path to
+  // that file so we can later create File blobs rather than plain ones.
+  nsCOMPtr<nsIFileChannel> fc = do_QueryInterface(aRequest);
+  if (fc) {
+    nsCOMPtr<nsIFile> file;
+    rv = fc->GetFile(getter_AddRefs(file));
+    if (!NS_WARN_IF(NS_FAILED(rv))) {
+      nsAutoString path;
+      file->GetPath(path);
+      response->SetBodyLocalPath(path);
+    }
+  } else {
+    // If the request is a blob URI, then remember that URI so that we
+    // can later just use that blob instance instead of cloning it.
+    nsCString blobURISpec;
+    GetBlobURISpecFromChannel(aRequest, blobURISpec);
+    if (!blobURISpec.IsVoid()) {
+      response->SetBodyBlobURISpec(blobURISpec);
+    }
+  }
+
+  response->InitChannelInfo(channel);
+
+  nsCOMPtr<nsILoadInfo> loadInfo = channel->LoadInfo();
+  // Propagate any tainting from the channel back to our response here.  This
+  // step is not reflected in the spec because the spec is written such that
+  // FetchEvent.respondWith() just passes the already-tainted Response back to
+  // the outer fetch().  In gecko, however, we serialize the Response through
+  // the channel and must regenerate the tainting from the channel in the
+  // interception case.
+  mRequest->MaybeIncreaseResponseTainting(loadInfo->GetTainting());
+
+  // Resolves fetch() promise which may trigger code running in a worker.  Make
+  // sure the Response is fully initialized before calling this.
+  mResponse =
+      BeginAndGetFilteredResponse(std::move(response), foundOpaqueRedirect);
+  if (NS_WARN_IF(!mResponse)) {
+    // Fail to generate a paddingInfo for opaque response.
+    MOZ_DIAGNOSTIC_ASSERT(mRequest->GetResponseTainting() ==
+                              LoadTainting::Opaque &&
+                          !foundOpaqueRedirect);
+    FailWithNetworkError(NS_ERROR_UNEXPECTED);
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  // From "Main Fetch" step 19: SRI-part1.
+  if (ShouldCheckSRI(*mRequest, *mResponse) && mSRIMetadata.IsEmpty()) {
+    nsIConsoleReportCollector* reporter = nullptr;
+    if (mObserver) {
+      reporter = mObserver->GetReporter();
+    }
+
+    nsAutoCString sourceUri;
+    if (mDocument && mDocument->GetDocumentURI()) {
+      mDocument->GetDocumentURI()->GetAsciiSpec(sourceUri);
+    } else if (!mWorkerScript.IsEmpty()) {
+      sourceUri.Assign(mWorkerScript);
+    }
+    SRICheck::IntegrityMetadata(mRequest->GetIntegrity(), sourceUri, reporter,
+                                &mSRIMetadata);
+    mSRIDataVerifier =
+        MakeUnique<SRICheckDataVerifier>(mSRIMetadata, sourceUri, reporter);
+
+    // Do not retarget off main thread when using SRI API.
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsIEventTarget> sts =
+      do_GetService(NS_STREAMTRANSPORTSERVICE_CONTRACTID, &rv);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    FailWithNetworkError(rv);
+    // Cancel request.
+    return rv;
+  }
+
+  // Try to retarget off main thread.
+  if (nsCOMPtr<nsIThreadRetargetableRequest> rr = do_QueryInterface(aRequest)) {
+    RefPtr<TaskQueue> queue =
+        TaskQueue::Create(sts.forget(), "FetchDriver STS Delivery Queue");
+    Unused << NS_WARN_IF(NS_FAILED(rr->RetargetDeliveryTo(queue)));
+  }
+  return NS_OK;
+}
+
+namespace {
+
+// Runnable to call the observer OnDataAvailable on the main-thread.
+class DataAvailableRunnable final : public Runnable {
+  RefPtr<FetchDriverObserver> mObserver;
+
+ public:
+  explicit DataAvailableRunnable(FetchDriverObserver* aObserver)
+      : Runnable("dom::DataAvailableRunnable"), mObserver(aObserver) {
+    MOZ_ASSERT(aObserver);
+  }
+
+  NS_IMETHOD
+  Run() override {
+    mObserver->OnDataAvailable();
+    mObserver = nullptr;
+    return NS_OK;
+  }
+};
+
+struct SRIVerifierAndOutputHolder {
+  SRIVerifierAndOutputHolder(SRICheckDataVerifier* aVerifier,
+                             nsIOutputStream* aOutputStream)
+      : mVerifier(aVerifier), mOutputStream(aOutputStream) {}
+
+  SRICheckDataVerifier* mVerifier;
+  nsIOutputStream* mOutputStream;
+
+ private:
+  SRIVerifierAndOutputHolder() = delete;
+};
+
+// Just like NS_CopySegmentToStream, but also sends the data into an
+// SRICheckDataVerifier.
+nsresult CopySegmentToStreamAndSRI(nsIInputStream* aInStr, void* aClosure,
+                                   const char* aBuffer, uint32_t aOffset,
+                                   uint32_t aCount, uint32_t* aCountWritten) {
+  auto holder = static_cast<SRIVerifierAndOutputHolder*>(aClosure);
+  MOZ_DIAGNOSTIC_ASSERT(holder && holder->mVerifier && holder->mOutputStream,
+                        "Bogus holder");
+  nsresult rv = holder->mVerifier->Update(
+      aCount, reinterpret_cast<const uint8_t*>(aBuffer));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // The rest is just like NS_CopySegmentToStream.
+  *aCountWritten = 0;
+  while (aCount) {
+    uint32_t n = 0;
+    rv = holder->mOutputStream->Write(aBuffer, aCount, &n);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+    aBuffer += n;
+    aCount -= n;
+    *aCountWritten += n;
+  }
+  return NS_OK;
+}
+
+}  // anonymous namespace
+
+NS_IMETHODIMP
+FetchDriver::OnDataAvailable(nsIRequest* aRequest, nsIInputStream* aInputStream,
+                             uint64_t aOffset, uint32_t aCount) {
+  // NB: This can be called on any thread!  But we're guaranteed that it is
+  // called between OnStartRequest and OnStopRequest, so we don't need to worry
+  // about races for accesses in OnStartRequest, OnStopRequest and
+  // member functions accessed before opening the channel.
+  // However, we have a possibility of a race from FetchDriverAbortActions.
+  // Hence, we need to ensure that we are not modifying any members accessed by
+  // FetchDriver::FetchDriverAbortActions
+
+  if (mNeedToObserveOnDataAvailable) {
+    mNeedToObserveOnDataAvailable = false;
+    if (mObserver) {
+      // Need to keep mObserver alive.
+      RefPtr<FetchDriverObserver> observer = mObserver;
+      if (NS_IsMainThread()) {
+        observer->OnDataAvailable();
+      } else {
+        RefPtr<Runnable> runnable = new DataAvailableRunnable(observer);
+        nsresult rv = mMainThreadEventTarget->Dispatch(runnable.forget(),
+                                                       NS_DISPATCH_NORMAL);
+        if (NS_WARN_IF(NS_FAILED(rv))) {
+          return rv;
+        }
+      }
+    }
+  }
+
+  if (!mResponse) {
+    MOZ_ASSERT(false);
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  // Needs to be initialized to 0 because in some cases nsStringInputStream may
+  // not write to aRead.
+  uint32_t aRead = 0;
+  MOZ_ASSERT(mPipeOutputStream);
+
+  // From "Main Fetch" step 19: SRI-part2.
+  // Note: Avoid checking the hidden opaque body.
+  nsresult rv;
+  if (mResponse->Type() != ResponseType::Opaque &&
+      ShouldCheckSRI(*mRequest, *mResponse)) {
+    MOZ_ASSERT(mSRIDataVerifier);
+
+    SRIVerifierAndOutputHolder holder(mSRIDataVerifier.get(),
+                                      mPipeOutputStream);
+    rv = aInputStream->ReadSegments(CopySegmentToStreamAndSRI, &holder, aCount,
+                                    &aRead);
+  } else {
+    rv = aInputStream->ReadSegments(NS_CopySegmentToStream, mPipeOutputStream,
+                                    aCount, &aRead);
+  }
+
+  // If no data was read, it's possible the output stream is closed but the
+  // ReadSegments call followed its contract of returning NS_OK despite write
+  // errors.  Unfortunately, nsIOutputStream has an ill-conceived contract when
+  // taken together with ReadSegments' contract, because the pipe will just
+  // NS_OK if we try and invoke its Write* functions ourselves with a 0 count.
+  // So we must just assume the pipe is broken.
+  if (aRead == 0 && aCount != 0) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+  return rv;
+}
+
+NS_IMETHODIMP
+FetchDriver::OnStopRequest(nsIRequest* aRequest, nsresult aStatusCode) {
+  AssertIsOnMainThread();
+
+  MOZ_DIAGNOSTIC_ASSERT(!mOnStopRequestCalled);
+  mOnStopRequestCalled = true;
+
+  if (mObserver && mAborted) {
+    // fetch request was aborted.
+    // We have already sent the observer
+    // notification that request has been aborted in FetchDriverAbortActions.
+    // Remove the observer reference and don't push anymore notifications.
+    mObserver = nullptr;
+  }
+
+  // main data loading is going to finish, breaking the reference cycle.
+  RefPtr<AlternativeDataStreamListener> altDataListener =
+      std::move(mAltDataListener);
+
+  // For PFetch and ServiceWorker navigationPreload, resource timing should be
+  // reported before the body stream closing.
+  if (mObserver) {
+    mObserver->OnReportPerformanceTiming();
+  }
+
+  // We need to check mObserver, which is nulled by FailWithNetworkError(),
+  // because in the case of "error" redirect mode, aStatusCode may be NS_OK but
+  // mResponse will definitely be null so we must not take the else branch.
+  if (NS_FAILED(aStatusCode) || !mObserver) {
+    nsCOMPtr<nsIAsyncOutputStream> outputStream =
+        do_QueryInterface(mPipeOutputStream);
+    if (outputStream) {
+      outputStream->CloseWithStatus(NS_FAILED(aStatusCode) ? aStatusCode
+                                                           : NS_BINDING_FAILED);
+    }
+    if (altDataListener) {
+      altDataListener->Cancel();
+    }
+
+    // We proceed as usual here, since we've already created a successful
+    // response from OnStartRequest.
+  } else {
+    MOZ_ASSERT(mResponse);
+    MOZ_ASSERT(!mResponse->IsError());
+
+    // From "Main Fetch" step 19: SRI-part3.
+    if (ShouldCheckSRI(*mRequest, *mResponse)) {
+      MOZ_ASSERT(mSRIDataVerifier);
+
+      nsCOMPtr<nsIChannel> channel = do_QueryInterface(aRequest);
+
+      nsIConsoleReportCollector* reporter = nullptr;
+      if (mObserver) {
+        reporter = mObserver->GetReporter();
+      }
+
+      nsAutoCString sourceUri;
+      if (mDocument && mDocument->GetDocumentURI()) {
+        mDocument->GetDocumentURI()->GetAsciiSpec(sourceUri);
+      } else if (!mWorkerScript.IsEmpty()) {
+        sourceUri.Assign(mWorkerScript);
+      }
+      nsresult rv =
+          mSRIDataVerifier->Verify(mSRIMetadata, channel, sourceUri, reporter);
+      if (NS_FAILED(rv)) {
+        if (altDataListener) {
+          altDataListener->Cancel();
+        }
+        FailWithNetworkError(rv);
+        // Cancel request.
+        return rv;
+      }
+    }
+
+    if (mPipeOutputStream) {
+      mPipeOutputStream->Close();
+    }
+  }
+
+  FinishOnStopRequest(altDataListener);
+  return NS_OK;
+}
+
+void FetchDriver::FinishOnStopRequest(
+    AlternativeDataStreamListener* aAltDataListener) {
+  AssertIsOnMainThread();
+  // OnStopRequest is not called from channel, that means the main data loading
+  // does not finish yet. Reaching here since alternative data loading finishes.
+  if (!mOnStopRequestCalled) {
+    return;
+  }
+
+  MOZ_DIAGNOSTIC_ASSERT(!mAltDataListener);
+  // Wait for alternative data loading finish if we needed it.
+  if (aAltDataListener &&
+      aAltDataListener->Status() == AlternativeDataStreamListener::LOADING) {
+    // For LOADING case, channel holds the reference of altDataListener, no need
+    // to restore it to mAltDataListener.
+    return;
+  }
+
+  if (mObserver) {
+    // From "Main Fetch" step 19.1, 19.2: Process response.
+    if (ShouldCheckSRI(*mRequest, *mResponse)) {
+      MOZ_ASSERT(mResponse);
+      // Need to keep mObserver alive.
+      RefPtr<FetchDriverObserver> observer = mObserver;
+      observer->OnResponseAvailable(mResponse.clonePtr());
+#ifdef DEBUG
+      mResponseAvailableCalled = true;
+#endif
+    }
+  }
+
+  if (mObserver) {
+    mObserver->OnResponseEnd(FetchDriverObserver::eByNetworking,
+                             JS::UndefinedHandleValue);
+    mObserver = nullptr;
+  }
+
+  mChannel = nullptr;
+  Unfollow();
+}
+
+NS_IMETHODIMP
+FetchDriver::ShouldPrepareForIntercept(nsIURI* aURI, nsIChannel* aChannel,
+                                       bool* aShouldIntercept) {
+  MOZ_ASSERT(aChannel);
+
+  if (mInterceptController) {
+    MOZ_ASSERT(XRE_IsParentProcess());
+    return mInterceptController->ShouldPrepareForIntercept(aURI, aChannel,
+                                                           aShouldIntercept);
+  }
+
+  nsCOMPtr<nsINetworkInterceptController> controller;
+  NS_QueryNotificationCallbacks(nullptr, mLoadGroup,
+                                NS_GET_IID(nsINetworkInterceptController),
+                                getter_AddRefs(controller));
+  if (controller) {
+    return controller->ShouldPrepareForIntercept(aURI, aChannel,
+                                                 aShouldIntercept);
+  }
+
+  *aShouldIntercept = false;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+FetchDriver::ChannelIntercepted(nsIInterceptedChannel* aChannel) {
+  if (mInterceptController) {
+    MOZ_ASSERT(XRE_IsParentProcess());
+    return mInterceptController->ChannelIntercepted(aChannel);
+  }
+
+  nsCOMPtr<nsINetworkInterceptController> controller;
+  NS_QueryNotificationCallbacks(nullptr, mLoadGroup,
+                                NS_GET_IID(nsINetworkInterceptController),
+                                getter_AddRefs(controller));
+  if (controller) {
+    return controller->ChannelIntercepted(aChannel);
+  }
+
+  return NS_OK;
+}
+
+void FetchDriver::EnableNetworkInterceptControl() {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(!mInterceptController);
+  mInterceptController = new ServiceWorkerInterceptController();
+}
+
+NS_IMETHODIMP
+FetchDriver::AsyncOnChannelRedirect(nsIChannel* aOldChannel,
+                                    nsIChannel* aNewChannel, uint32_t aFlags,
+                                    nsIAsyncVerifyRedirectCallback* aCallback) {
+  nsCOMPtr<nsIHttpChannel> oldHttpChannel = do_QueryInterface(aOldChannel);
+  nsCOMPtr<nsIHttpChannel> newHttpChannel = do_QueryInterface(aNewChannel);
+  if (oldHttpChannel && newHttpChannel) {
+    nsAutoCString method;
+    mRequest->GetMethod(method);
+
+    // Fetch 4.4.11
+    bool rewriteToGET = false;
+    Unused << oldHttpChannel->ShouldStripRequestBodyHeader(method,
+                                                           &rewriteToGET);
+
+    // we need to strip Authentication headers for cross-origin requests
+    // Ref: https://fetch.spec.whatwg.org/#http-redirect-fetch
+    bool skipAuthHeader =
+        (StaticPrefs::network_fetch_redirect_stripAuthHeader() &&
+         NS_ShouldRemoveAuthHeaderOnRedirect(aOldChannel, aNewChannel, aFlags));
+
+    SetRequestHeaders(newHttpChannel, rewriteToGET, skipAuthHeader);
+  }
+
+  // "HTTP-redirect fetch": step 14 "Append locationURL to request's URL list."
+  // However, ignore internal redirects here.  We don't want to flip
+  // Response.redirected to true if an internal redirect occurs.  These
+  // should be transparent to script.
+  nsCOMPtr<nsIURI> uri;
+  MOZ_ALWAYS_SUCCEEDS(NS_GetFinalChannelURI(aNewChannel, getter_AddRefs(uri)));
+
+  nsCOMPtr<nsIURI> uriClone;
+  nsresult rv = NS_GetURIWithoutRef(uri, getter_AddRefs(uriClone));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  nsCString spec;
+  rv = uriClone->GetSpec(spec);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  nsCString fragment;
+  rv = uri->GetRef(fragment);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  if (!(aFlags & nsIChannelEventSink::REDIRECT_INTERNAL)) {
+    mRequest->AddURL(spec, fragment);
+  } else {
+    // Overwrite the URL only when the request is redirected by a service
+    // worker.
+    mRequest->SetURLForInternalRedirect(aFlags, spec, fragment);
+  }
+
+  // In redirect, httpChannel already took referrer-policy into account, so
+  // updates request’s associated referrer policy from channel.
+  UpdateReferrerInfoFromNewChannel(aNewChannel);
+
+  aCallback->OnRedirectVerifyCallback(NS_OK);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+FetchDriver::CheckListenerChain() { return NS_OK; }
+
+NS_IMETHODIMP
+FetchDriver::GetInterface(const nsIID& aIID, void** aResult) {
+  if (aIID.Equals(NS_GET_IID(nsIChannelEventSink))) {
+    *aResult = static_cast<nsIChannelEventSink*>(this);
+    NS_ADDREF_THIS();
+    return NS_OK;
+  }
+  if (aIID.Equals(NS_GET_IID(nsIStreamListener))) {
+    *aResult = static_cast<nsIStreamListener*>(this);
+    NS_ADDREF_THIS();
+    return NS_OK;
+  }
+  if (aIID.Equals(NS_GET_IID(nsIRequestObserver))) {
+    *aResult = static_cast<nsIRequestObserver*>(this);
+    NS_ADDREF_THIS();
+    return NS_OK;
+  }
+
+  return QueryInterface(aIID, aResult);
+}
+
+void FetchDriver::SetDocument(Document* aDocument) {
+  // Cannot set document after Fetch() has been called.
+  MOZ_ASSERT(!mFetchCalled);
+  mDocument = aDocument;
+}
+
+void FetchDriver::SetCSPEventListener(nsICSPEventListener* aCSPEventListener) {
+  MOZ_ASSERT(!mFetchCalled);
+  mCSPEventListener = aCSPEventListener;
+}
+
+void FetchDriver::SetClientInfo(const ClientInfo& aClientInfo) {
+  MOZ_ASSERT(!mFetchCalled);
+  mClientInfo.emplace(aClientInfo);
+}
+
+void FetchDriver::SetController(
+    const Maybe<ServiceWorkerDescriptor>& aController) {
+  MOZ_ASSERT(!mFetchCalled);
+  mController = aController;
+}
+
+PerformanceTimingData* FetchDriver::GetPerformanceTimingData(
+    nsAString& aInitiatorType, nsAString& aEntryName) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  if (!mChannel) {
+    return nullptr;
+  }
+
+  nsCOMPtr<nsITimedChannel> timedChannel = do_QueryInterface(mChannel);
+  if (!timedChannel) {
+    return nullptr;
+  }
+  nsCOMPtr<nsIHttpChannel> httpChannel = do_QueryInterface(mChannel);
+  if (!httpChannel) {
+    return nullptr;
+  }
+  return dom::PerformanceTimingData::Create(timedChannel, httpChannel, 0,
+                                            aInitiatorType, aEntryName);
+}
+
+void FetchDriver::SetRequestHeaders(nsIHttpChannel* aChannel,
+                                    bool aStripRequestBodyHeader,
+                                    bool aStripAuthHeader) const {
+  MOZ_ASSERT(aChannel);
+
+  // nsIHttpChannel has a set of pre-configured headers (Accept,
+  // Accept-Languages, ...) and we don't want to merge the Request's headers
+  // with them. This array is used to know if the current header has been aleady
+  // set, if yes, we ask necko to merge it with the previous one, otherwise, we
+  // don't want the merge.
+  nsTArray<nsCString> headersSet;
+
+  AutoTArray<InternalHeaders::Entry, 5> headers;
+  mRequest->Headers()->GetEntries(headers);
+  for (uint32_t i = 0; i < headers.Length(); ++i) {
+    if (aStripRequestBodyHeader &&
+        (headers[i].mName.LowerCaseEqualsASCII("content-type") ||
+         headers[i].mName.LowerCaseEqualsASCII("content-encoding") ||
+         headers[i].mName.LowerCaseEqualsASCII("content-language") ||
+         headers[i].mName.LowerCaseEqualsASCII("content-location"))) {
+      continue;
+    }
+
+    if (aStripAuthHeader &&
+        headers[i].mName.LowerCaseEqualsASCII("authorization")) {
+      continue;
+    }
+
+    bool alreadySet = headersSet.Contains(headers[i].mName);
+    if (!alreadySet) {
+      headersSet.AppendElement(headers[i].mName);
+    }
+
+    if (headers[i].mValue.IsEmpty()) {
+      DebugOnly<nsresult> rv =
+          aChannel->SetEmptyRequestHeader(headers[i].mName);
+      MOZ_ASSERT(NS_SUCCEEDED(rv));
+    } else {
+      DebugOnly<nsresult> rv = aChannel->SetRequestHeader(
+          headers[i].mName, headers[i].mValue, alreadySet /* merge */);
+      MOZ_ASSERT(NS_SUCCEEDED(rv));
+    }
+  }
+}
+
+void FetchDriver::RunAbortAlgorithm() { FetchDriverAbortActions(Signal()); }
+
+void FetchDriver::FetchDriverAbortActions(AbortSignalImpl* aSignalImpl) {
+  MOZ_DIAGNOSTIC_ASSERT(NS_IsMainThread());
+
+  if (mObserver) {
+#ifdef DEBUG
+    mResponseAvailableCalled = true;
+#endif
+    JS::Rooted<JS::Value> reason(RootingCx());
+    if (aSignalImpl) {
+      reason.set(aSignalImpl->RawReason());
+    }
+    mObserver->OnResponseEnd(FetchDriverObserver::eAborted, reason);
+    // As a part of cleanup, we are not removing the mObserver reference as it
+    // could race with mObserver access in OnDataAvailable when it runs OMT.
+    // We will be removing the reference in the OnStopRequest which guaranteed
+    // to run after cancelling the channel.
+  }
+
+  if (mChannel) {
+    mChannel->CancelWithReason(NS_BINDING_ABORTED,
+                               "FetchDriver::RunAbortAlgorithm"_ns);
+    mChannel = nullptr;
+  }
+
+  mAborted = true;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/fetch/FetchDriver.h b/dom/fetch/FetchDriver.h
new file mode 100644
index 0000000000..84391ef951
--- /dev/null
+++ b/dom/fetch/FetchDriver.h
@@ -0,0 +1,232 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_FetchDriver_h
+#define mozilla_dom_FetchDriver_h
+
+#include "nsIChannelEventSink.h"
+#include "nsIInterfaceRequestor.h"
+#include "nsINetworkInterceptController.h"
+#include "nsIStreamListener.h"
+#include "nsIThreadRetargetableStreamListener.h"
+#include "mozilla/ConsoleReportCollector.h"
+#include "mozilla/dom/AbortSignal.h"
+#include "mozilla/dom/SafeRefPtr.h"
+#include "mozilla/dom/SerializedStackHolder.h"
+#include "mozilla/dom/SRIMetadata.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/UniquePtr.h"
+
+#include "mozilla/DebugOnly.h"
+
+class nsIConsoleReportCollector;
+class nsICookieJarSettings;
+class nsICSPEventListener;
+class nsIEventTarget;
+class nsIOutputStream;
+class nsILoadGroup;
+class nsIPrincipal;
+
+namespace mozilla {
+class PreloaderBase;
+
+namespace dom {
+
+class Document;
+class InternalRequest;
+class InternalResponse;
+class PerformanceStorage;
+class PerformanceTimingData;
+
+/**
+ * Provides callbacks to be called when response is available or on error.
+ * Implemenations usually resolve or reject the promise returned from fetch().
+ * The callbacks can be called synchronously or asynchronously from
+ * FetchDriver::Fetch.
+ */
+class FetchDriverObserver {
+ public:
+  FetchDriverObserver()
+      : mReporter(new ConsoleReportCollector()), mGotResponseAvailable(false) {}
+
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(FetchDriverObserver);
+  void OnResponseAvailable(SafeRefPtr<InternalResponse> aResponse);
+
+  enum EndReason {
+    eAborted,
+    eByNetworking,
+  };
+
+  virtual void OnResponseEnd(EndReason aReason,
+                             JS::Handle<JS::Value> aReasonDetails){};
+
+  nsIConsoleReportCollector* GetReporter() const { return mReporter; }
+
+  virtual void FlushConsoleReport() = 0;
+
+  // Called in OnStartRequest() to determine if the OnDataAvailable() method
+  // needs to be called.  Invoking that method may generate additional main
+  // thread runnables.
+  virtual bool NeedOnDataAvailable() = 0;
+
+  // Called once when the first byte of data is received iff
+  // NeedOnDataAvailable() returned true when called in OnStartRequest().
+  virtual void OnDataAvailable() = 0;
+
+  virtual void OnReportPerformanceTiming() {}
+
+  virtual void OnNotifyNetworkMonitorAlternateStack(uint64_t aChannelID) {}
+
+ protected:
+  virtual ~FetchDriverObserver() = default;
+
+  virtual void OnResponseAvailableInternal(
+      SafeRefPtr<InternalResponse> aResponse) = 0;
+
+  nsCOMPtr<nsIConsoleReportCollector> mReporter;
+
+ private:
+  bool mGotResponseAvailable;
+};
+
+class AlternativeDataStreamListener;
+
+class FetchDriver final : public nsIStreamListener,
+                          public nsIChannelEventSink,
+                          public nsIInterfaceRequestor,
+                          public nsINetworkInterceptController,
+                          public nsIThreadRetargetableStreamListener,
+                          public AbortFollower {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIREQUESTOBSERVER
+  NS_DECL_NSISTREAMLISTENER
+  NS_DECL_NSICHANNELEVENTSINK
+  NS_DECL_NSIINTERFACEREQUESTOR
+  NS_DECL_NSINETWORKINTERCEPTCONTROLLER
+  NS_DECL_NSITHREADRETARGETABLESTREAMLISTENER
+
+  FetchDriver(SafeRefPtr<InternalRequest> aRequest, nsIPrincipal* aPrincipal,
+              nsILoadGroup* aLoadGroup, nsIEventTarget* aMainThreadEventTarget,
+              nsICookieJarSettings* aCookieJarSettings,
+              PerformanceStorage* aPerformanceStorage, bool aIsTrackingFetch);
+
+  nsresult Fetch(AbortSignalImpl* aSignalImpl, FetchDriverObserver* aObserver);
+
+  void SetDocument(Document* aDocument);
+
+  void SetCSPEventListener(nsICSPEventListener* aCSPEventListener);
+
+  void SetClientInfo(const ClientInfo& aClientInfo);
+
+  void SetController(const Maybe<ServiceWorkerDescriptor>& aController);
+
+  void SetWorkerScript(const nsACString& aWorkerScript) {
+    MOZ_ASSERT(!aWorkerScript.IsEmpty());
+    mWorkerScript = aWorkerScript;
+  }
+
+  void SetOriginStack(UniquePtr<SerializedStackHolder>&& aOriginStack) {
+    mOriginStack = std::move(aOriginStack);
+  }
+
+  PerformanceTimingData* GetPerformanceTimingData(nsAString& aInitiatorType,
+                                                  nsAString& aEntryName);
+
+  // AbortFollower
+  void RunAbortAlgorithm() override;
+  void FetchDriverAbortActions(AbortSignalImpl* aSignalImpl);
+
+  void EnableNetworkInterceptControl();
+
+  void SetAssociatedBrowsingContextID(uint64_t aID) {
+    mAssociatedBrowsingContextID = aID;
+  }
+
+ private:
+  nsCOMPtr<nsIPrincipal> mPrincipal;
+  nsCOMPtr<nsILoadGroup> mLoadGroup;
+  SafeRefPtr<InternalRequest> mRequest;
+  SafeRefPtr<InternalResponse> mResponse;
+  nsCOMPtr<nsIOutputStream> mPipeOutputStream;
+  // Access to mObserver can be racy from OnDataAvailable and
+  // FetchAbortActions. This must not be modified
+  // in either of these functions.
+  RefPtr<FetchDriverObserver> mObserver;
+  RefPtr<Document> mDocument;
+  nsCOMPtr<nsICSPEventListener> mCSPEventListener;
+  Maybe<ClientInfo> mClientInfo;
+  Maybe<ServiceWorkerDescriptor> mController;
+  nsCOMPtr<nsIChannel> mChannel;
+  UniquePtr<SRICheckDataVerifier> mSRIDataVerifier;
+  nsCOMPtr<nsIEventTarget> mMainThreadEventTarget;
+
+  nsCOMPtr<nsICookieJarSettings> mCookieJarSettings;
+
+  // This is set only when Fetch is used in workers.
+  RefPtr<PerformanceStorage> mPerformanceStorage;
+
+  SRIMetadata mSRIMetadata;
+  nsCString mWorkerScript;
+  UniquePtr<SerializedStackHolder> mOriginStack;
+
+  // This is written once in OnStartRequest on the main thread and then
+  // written/read in OnDataAvailable() on any thread.  Necko guarantees
+  // that these do not overlap.
+  bool mNeedToObserveOnDataAvailable;
+
+  bool mIsTrackingFetch;
+
+  RefPtr<AlternativeDataStreamListener> mAltDataListener;
+  bool mOnStopRequestCalled;
+
+  // This flag is true when this fetch has found a matching preload and is being
+  // satisfied by a its response.
+  bool mFromPreload = false;
+  // This flag is set in call to Abort() and spans the possible window this
+  // fetch doesn't have mChannel (to be cancelled) between reuse of the matching
+  // preload, that has already finished and dropped reference to its channel,
+  // and OnStartRequest notification.  It let's us cancel the load when we get
+  // the channel in OnStartRequest.
+  bool mAborted = false;
+
+#ifdef DEBUG
+  bool mResponseAvailableCalled;
+  bool mFetchCalled;
+#endif
+  nsCOMPtr<nsINetworkInterceptController> mInterceptController;
+
+  uint64_t mAssociatedBrowsingContextID{0};
+
+  friend class AlternativeDataStreamListener;
+
+  FetchDriver() = delete;
+  FetchDriver(const FetchDriver&) = delete;
+  FetchDriver& operator=(const FetchDriver&) = delete;
+  ~FetchDriver();
+
+  already_AddRefed<PreloaderBase> FindPreload(nsIURI* aURI);
+
+  void UpdateReferrerInfoFromNewChannel(nsIChannel* aChannel);
+
+  nsresult HttpFetch(const nsACString& aPreferredAlternativeDataType = ""_ns);
+  // Returns the filtered response sent to the observer.
+  SafeRefPtr<InternalResponse> BeginAndGetFilteredResponse(
+      SafeRefPtr<InternalResponse> aResponse, bool aFoundOpaqueRedirect);
+  // Utility since not all cases need to do any post processing of the filtered
+  // response.
+  void FailWithNetworkError(nsresult rv);
+
+  void SetRequestHeaders(nsIHttpChannel* aChannel, bool aStripRequestBodyHeader,
+                         bool aStripAuthHeader) const;
+
+  void FinishOnStopRequest(AlternativeDataStreamListener* aAltDataListener);
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_FetchDriver_h
diff --git a/dom/fetch/FetchIPCTypes.h b/dom/fetch/FetchIPCTypes.h
new file mode 100644
index 0000000000..343a5acb3f
--- /dev/null
+++ b/dom/fetch/FetchIPCTypes.h
@@ -0,0 +1,63 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_fetch_IPCUtils_h
+#define mozilla_dom_fetch_IPCUtils_h
+
+#include "ipc/EnumSerializer.h"
+
+#include "mozilla/dom/HeadersBinding.h"
+#include "mozilla/dom/RequestBinding.h"
+#include "mozilla/dom/ResponseBinding.h"
+#include "mozilla/dom/FetchDriver.h"
+
+namespace IPC {
+template <>
+struct ParamTraits<mozilla::dom::HeadersGuardEnum>
+    : public ContiguousEnumSerializer<
+          mozilla::dom::HeadersGuardEnum, mozilla::dom::HeadersGuardEnum::None,
+          mozilla::dom::HeadersGuardEnum::EndGuard_> {};
+template <>
+struct ParamTraits<mozilla::dom::ReferrerPolicy>
+    : public ContiguousEnumSerializer<mozilla::dom::ReferrerPolicy,
+                                      mozilla::dom::ReferrerPolicy::_empty,
+                                      mozilla::dom::ReferrerPolicy::EndGuard_> {
+};
+template <>
+struct ParamTraits<mozilla::dom::RequestMode>
+    : public ContiguousEnumSerializer<mozilla::dom::RequestMode,
+                                      mozilla::dom::RequestMode::Same_origin,
+                                      mozilla::dom::RequestMode::EndGuard_> {};
+template <>
+struct ParamTraits<mozilla::dom::RequestCredentials>
+    : public ContiguousEnumSerializer<
+          mozilla::dom::RequestCredentials,
+          mozilla::dom::RequestCredentials::Omit,
+          mozilla::dom::RequestCredentials::EndGuard_> {};
+template <>
+struct ParamTraits<mozilla::dom::RequestCache>
+    : public ContiguousEnumSerializer<mozilla::dom::RequestCache,
+                                      mozilla::dom::RequestCache::Default,
+                                      mozilla::dom::RequestCache::EndGuard_> {};
+template <>
+struct ParamTraits<mozilla::dom::RequestRedirect>
+    : public ContiguousEnumSerializer<
+          mozilla::dom::RequestRedirect, mozilla::dom::RequestRedirect::Follow,
+          mozilla::dom::RequestRedirect::EndGuard_> {};
+template <>
+struct ParamTraits<mozilla::dom::ResponseType>
+    : public ContiguousEnumSerializer<mozilla::dom::ResponseType,
+                                      mozilla::dom::ResponseType::Basic,
+                                      mozilla::dom::ResponseType::EndGuard_> {};
+template <>
+struct ParamTraits<mozilla::dom::FetchDriverObserver::EndReason>
+    : public ContiguousEnumSerializerInclusive<
+          mozilla::dom::FetchDriverObserver::EndReason,
+          mozilla::dom::FetchDriverObserver::eAborted,
+          mozilla::dom::FetchDriverObserver::eByNetworking> {};
+}  // namespace IPC
+
+#endif  // mozilla_dom_fetch_IPCUtils_h
diff --git a/dom/fetch/FetchLog.h b/dom/fetch/FetchLog.h
new file mode 100644
index 0000000000..37ef66e989
--- /dev/null
+++ b/dom/fetch/FetchLog.h
@@ -0,0 +1,19 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef _mozilla_dom_FetchLog_h
+#define _mozilla_dom_FetchLog_h
+
+#include "mozilla/Logging.h"
+
+namespace mozilla::dom {
+
+extern mozilla::LazyLogModule gFetchLog;
+
+#define FETCH_LOG(args) MOZ_LOG(gFetchLog, LogLevel::Debug, args)
+
+}  // namespace mozilla::dom
+#endif
diff --git a/dom/fetch/FetchObserver.cpp b/dom/fetch/FetchObserver.cpp
new file mode 100644
index 0000000000..0c9d1b9f7a
--- /dev/null
+++ b/dom/fetch/FetchObserver.cpp
@@ -0,0 +1,79 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "FetchObserver.h"
+#include "mozilla/dom/Event.h"
+#include "mozilla/dom/EventBinding.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(FetchObserver)
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(FetchObserver,
+                                                  DOMEventTargetHelper)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(FetchObserver,
+                                                DOMEventTargetHelper)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(FetchObserver)
+NS_INTERFACE_MAP_END_INHERITING(DOMEventTargetHelper)
+
+NS_IMPL_ADDREF_INHERITED(FetchObserver, DOMEventTargetHelper)
+NS_IMPL_RELEASE_INHERITED(FetchObserver, DOMEventTargetHelper)
+
+FetchObserver::FetchObserver(nsIGlobalObject* aGlobal,
+                             AbortSignalImpl* aSignalImpl)
+    : DOMEventTargetHelper(aGlobal), mState(FetchState::Requesting) {
+  if (aSignalImpl) {
+    Follow(aSignalImpl);
+  }
+}
+
+JSObject* FetchObserver::WrapObject(JSContext* aCx,
+                                    JS::Handle<JSObject*> aGivenProto) {
+  return FetchObserver_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+FetchState FetchObserver::State() const { return mState; }
+
+void FetchObserver::RunAbortAlgorithm() { SetState(FetchState::Aborted); }
+
+void FetchObserver::SetState(FetchState aState) {
+  MOZ_ASSERT(mState < aState);
+
+  if (mState == FetchState::Aborted || mState == FetchState::Errored ||
+      mState == FetchState::Complete) {
+    // We are already in a final state.
+    return;
+  }
+
+  // We cannot pass from Requesting to Complete directly.
+  if (mState == FetchState::Requesting && aState == FetchState::Complete) {
+    SetState(FetchState::Responding);
+  }
+
+  mState = aState;
+
+  if (mState == FetchState::Aborted || mState == FetchState::Errored ||
+      mState == FetchState::Complete) {
+    Unfollow();
+  }
+
+  EventInit init;
+  init.mBubbles = false;
+  init.mCancelable = false;
+
+  // TODO which kind of event should we dispatch here?
+
+  RefPtr<Event> event = Event::Constructor(this, u"statechange"_ns, init);
+  event->SetTrusted(true);
+
+  DispatchEvent(*event);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/fetch/FetchObserver.h b/dom/fetch/FetchObserver.h
new file mode 100644
index 0000000000..a80342a2fd
--- /dev/null
+++ b/dom/fetch/FetchObserver.h
@@ -0,0 +1,45 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_FetchObserver_h
+#define mozilla_dom_FetchObserver_h
+
+#include "mozilla/DOMEventTargetHelper.h"
+#include "mozilla/dom/FetchObserverBinding.h"
+#include "mozilla/dom/AbortSignal.h"
+
+namespace mozilla::dom {
+
+class FetchObserver final : public DOMEventTargetHelper, public AbortFollower {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(FetchObserver, DOMEventTargetHelper)
+
+  FetchObserver(nsIGlobalObject* aGlobal, AbortSignalImpl* aSignalImpl);
+
+  JSObject* WrapObject(JSContext* aCx,
+                       JS::Handle<JSObject*> aGivenProto) override;
+
+  FetchState State() const;
+
+  IMPL_EVENT_HANDLER(statechange);
+  IMPL_EVENT_HANDLER(requestprogress);
+  IMPL_EVENT_HANDLER(responseprogress);
+
+  // AbortFollower
+  void RunAbortAlgorithm() override;
+
+  void SetState(FetchState aState);
+
+ private:
+  ~FetchObserver() = default;
+
+  FetchState mState;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_FetchObserver_h
diff --git a/dom/fetch/FetchParent.cpp b/dom/fetch/FetchParent.cpp
new file mode 100644
index 0000000000..93e9b9e43e
--- /dev/null
+++ b/dom/fetch/FetchParent.cpp
@@ -0,0 +1,340 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "FetchLog.h"
+#include "FetchParent.h"
+#include "FetchService.h"
+#include "InternalRequest.h"
+#include "InternalResponse.h"
+#include "mozilla/Unused.h"
+#include "mozilla/dom/ClientInfo.h"
+#include "mozilla/dom/FetchTypes.h"
+#include "mozilla/dom/PerformanceTimingTypes.h"
+#include "mozilla/dom/ServiceWorkerDescriptor.h"
+#include "mozilla/ipc/BackgroundParent.h"
+#include "nsThreadUtils.h"
+
+using namespace mozilla::ipc;
+
+namespace mozilla::dom {
+
+NS_IMPL_ISUPPORTS(FetchParent::FetchParentCSPEventListener, nsICSPEventListener)
+
+FetchParent::FetchParentCSPEventListener::FetchParentCSPEventListener(
+    const nsID& aActorID, nsCOMPtr<nsISerialEventTarget> aEventTarget)
+    : mActorID(aActorID), mEventTarget(aEventTarget) {
+  MOZ_ASSERT(mEventTarget);
+  FETCH_LOG(("FetchParentCSPEventListener [%p] actor ID: %s", this,
+             mActorID.ToString().get()));
+}
+
+NS_IMETHODIMP FetchParent::FetchParentCSPEventListener::OnCSPViolationEvent(
+    const nsAString& aJSON) {
+  AssertIsOnMainThread();
+  FETCH_LOG(("FetchParentCSPEventListener::OnCSPViolationEvent [%p]", this));
+
+  nsAutoString json(aJSON);
+  nsCOMPtr<nsIRunnable> r =
+      NS_NewRunnableFunction(__func__, [actorID = mActorID, json]() mutable {
+        FETCH_LOG(
+            ("FetchParentCSPEventListener::OnCSPViolationEvent, Runnale"));
+        RefPtr<FetchParent> actor = FetchParent::GetActorByID(actorID);
+        if (actor) {
+          actor->OnCSPViolationEvent(json);
+        }
+      });
+
+  MOZ_ALWAYS_SUCCEEDS(mEventTarget->Dispatch(r, nsIThread::DISPATCH_NORMAL));
+  return NS_OK;
+}
+
+nsTHashMap<nsIDHashKey, RefPtr<FetchParent>> FetchParent::sActorTable;
+
+/*static*/
+RefPtr<FetchParent> FetchParent::GetActorByID(const nsID& aID) {
+  AssertIsOnBackgroundThread();
+  auto entry = sActorTable.Lookup(aID);
+  if (entry) {
+    return entry.Data();
+  }
+  return nullptr;
+}
+
+FetchParent::FetchParent() : mID(nsID::GenerateUUID()) {
+  FETCH_LOG(("FetchParent::FetchParent [%p]", this));
+  AssertIsOnBackgroundThread();
+  mBackgroundEventTarget = GetCurrentSerialEventTarget();
+  MOZ_ASSERT(mBackgroundEventTarget);
+  if (!sActorTable.WithEntryHandle(mID, [&](auto&& entry) {
+        if (entry.HasEntry()) {
+          return false;
+        }
+        entry.Insert(this);
+        return true;
+      })) {
+    FETCH_LOG(("FetchParent::FetchParent entry[%p] already exists", this));
+  }
+}
+
+FetchParent::~FetchParent() {
+  FETCH_LOG(("FetchParent::~FetchParent [%p]", this));
+  // MOZ_ASSERT(!mBackgroundEventTarget);
+  MOZ_ASSERT(!mResponsePromises);
+  MOZ_ASSERT(mActorDestroyed && mIsDone);
+}
+
+IPCResult FetchParent::RecvFetchOp(FetchOpArgs&& aArgs) {
+  FETCH_LOG(("FetchParent::RecvFetchOp [%p]", this));
+  AssertIsOnBackgroundThread();
+
+  MOZ_ASSERT(!mIsDone);
+  if (mActorDestroyed) {
+    return IPC_OK();
+  }
+
+  mRequest = MakeSafeRefPtr<InternalRequest>(std::move(aArgs.request()));
+  mPrincipalInfo = std::move(aArgs.principalInfo());
+  mWorkerScript = aArgs.workerScript();
+  mClientInfo = Some(ClientInfo(aArgs.clientInfo()));
+  if (aArgs.controller().isSome()) {
+    mController = Some(ServiceWorkerDescriptor(aArgs.controller().ref()));
+  }
+  mCookieJarSettings = aArgs.cookieJarSettings();
+  mNeedOnDataAvailable = aArgs.needOnDataAvailable();
+  mHasCSPEventListener = aArgs.hasCSPEventListener();
+
+  if (mHasCSPEventListener) {
+    mCSPEventListener =
+        MakeRefPtr<FetchParentCSPEventListener>(mID, mBackgroundEventTarget);
+  }
+  mAssociatedBrowsingContextID = aArgs.associatedBrowsingContextID();
+
+  MOZ_ASSERT(!mPromise);
+  mPromise = new GenericPromise::Private(__func__);
+
+  RefPtr<FetchParent> self = this;
+  mPromise->Then(
+      mBackgroundEventTarget, __func__,
+      [self](const bool&& result) mutable {
+        FETCH_LOG(
+            ("FetchParent::RecvFetchOp [%p] Success Callback", self.get()));
+        AssertIsOnBackgroundThread();
+        self->mPromise = nullptr;
+        if (self->mIsDone) {
+          FETCH_LOG(("FetchParent::RecvFetchOp [%p] Fetch has already aborted",
+                     self.get()));
+          if (!self->mActorDestroyed) {
+            Unused << NS_WARN_IF(
+                !self->Send__delete__(self, NS_ERROR_DOM_ABORT_ERR));
+          }
+          return;
+        }
+        self->mIsDone = true;
+        if (!self->mActorDestroyed && !self->mExtendForCSPEventListener) {
+          FETCH_LOG(("FetchParent::RecvFetchOp [%p] Send__delete__(NS_OK)",
+                     self.get()));
+          Unused << NS_WARN_IF(!self->Send__delete__(self, NS_OK));
+        }
+      },
+      [self](const nsresult&& aErr) mutable {
+        FETCH_LOG(
+            ("FetchParent::RecvFetchOp [%p] Failure Callback", self.get()));
+        AssertIsOnBackgroundThread();
+        self->mIsDone = true;
+        self->mPromise = nullptr;
+        if (!self->mActorDestroyed) {
+          FETCH_LOG(("FetchParent::RecvFetchOp [%p] Send__delete__(aErr)",
+                     self.get()));
+          Unused << NS_WARN_IF(!self->Send__delete__(self, aErr));
+        }
+      });
+
+  RefPtr<nsIRunnable> r = NS_NewRunnableFunction(__func__, [self]() mutable {
+    FETCH_LOG(
+        ("FetchParent::RecvFetchOp [%p], Main Thread Runnable", self.get()));
+    AssertIsOnMainThread();
+    if (self->mIsDone) {
+      MOZ_ASSERT(!self->mResponsePromises);
+      MOZ_ASSERT(self->mPromise);
+      FETCH_LOG(
+          ("FetchParent::RecvFetchOp [%p], Main Thread Runnable, "
+           "already aborted",
+           self.get()));
+      self->mPromise->Reject(NS_ERROR_DOM_ABORT_ERR, __func__);
+      return;
+    }
+    RefPtr<FetchService> fetchService = FetchService::GetInstance();
+    MOZ_ASSERT(fetchService);
+    MOZ_ASSERT(!self->mResponsePromises);
+    self->mResponsePromises =
+        fetchService->Fetch(AsVariant(FetchService::WorkerFetchArgs(
+            {self->mRequest.clonePtr(), self->mPrincipalInfo,
+             self->mWorkerScript, self->mClientInfo, self->mController,
+             self->mCookieJarSettings, self->mNeedOnDataAvailable,
+             self->mCSPEventListener, self->mAssociatedBrowsingContextID,
+             self->mBackgroundEventTarget, self->mID})));
+
+    self->mResponsePromises->GetResponseEndPromise()->Then(
+        GetMainThreadSerialEventTarget(), __func__,
+        [self](ResponseEndArgs&& aArgs) mutable {
+          AssertIsOnMainThread();
+          MOZ_ASSERT(self->mPromise);
+          self->mPromise->Resolve(true, __func__);
+          self->mResponsePromises = nullptr;
+        },
+        [self](CopyableErrorResult&& aErr) mutable {
+          AssertIsOnMainThread();
+          MOZ_ASSERT(self->mPromise);
+          self->mPromise->Reject(aErr.StealNSResult(), __func__);
+          self->mResponsePromises = nullptr;
+        });
+  });
+
+  MOZ_ALWAYS_SUCCEEDS(
+      NS_DispatchToMainThread(r.forget(), nsIThread::DISPATCH_NORMAL));
+
+  return IPC_OK();
+}
+
+IPCResult FetchParent::RecvAbortFetchOp() {
+  FETCH_LOG(("FetchParent::RecvAbortFetchOp [%p]", this));
+  AssertIsOnBackgroundThread();
+
+  if (mIsDone) {
+    FETCH_LOG(("FetchParent::RecvAbortFetchOp [%p], Already aborted", this));
+    return IPC_OK();
+  }
+  mIsDone = true;
+
+  RefPtr<FetchParent> self = this;
+  nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(__func__, [self]() mutable {
+    FETCH_LOG(("FetchParent::RecvAbortFetchOp Runnable"));
+    AssertIsOnMainThread();
+    if (self->mResponsePromises) {
+      RefPtr<FetchService> fetchService = FetchService::GetInstance();
+      MOZ_ASSERT(fetchService);
+      fetchService->CancelFetch(std::move(self->mResponsePromises));
+    }
+  });
+
+  MOZ_ALWAYS_SUCCEEDS(
+      NS_DispatchToMainThread(r.forget(), nsIThread::DISPATCH_NORMAL));
+
+  return IPC_OK();
+}
+
+void FetchParent::OnResponseAvailableInternal(
+    SafeRefPtr<InternalResponse>&& aResponse) {
+  FETCH_LOG(("FetchParent::OnResponseAvailableInternal [%p]", this));
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aResponse);
+  MOZ_ASSERT(!mActorDestroyed);
+
+  if (mIsDone && aResponse->Type() != ResponseType::Error) {
+    FETCH_LOG(
+        ("FetchParent::OnResponseAvailableInternal [%p] "
+         "Fetch has already aborted",
+         this));
+    return;
+  }
+
+  // To monitor the stream status between processes, response's body can not be
+  // serialized as RemoteLazyInputStream. Such that stream close can be
+  // propagated to FetchDriver in the parent process.
+  aResponse->SetSerializeAsLazy(false);
+
+  // CSP violation notification is asynchronous. Extending the FetchParent's
+  // life cycle for the notificaiton.
+  if (aResponse->Type() == ResponseType::Error &&
+      aResponse->GetErrorCode() == NS_ERROR_CONTENT_BLOCKED &&
+      mCSPEventListener) {
+    FETCH_LOG(
+        ("FetchParent::OnResponseAvailableInternal [%p] "
+         "NS_ERROR_CONTENT_BLOCKED",
+         this));
+    mExtendForCSPEventListener = true;
+  }
+
+  Unused << SendOnResponseAvailableInternal(
+      aResponse->ToParentToChildInternalResponse(WrapNotNull(Manager())));
+}
+
+void FetchParent::OnResponseEnd(const ResponseEndArgs& aArgs) {
+  FETCH_LOG(("FetchParent::OnResponseEnd [%p]", this));
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mActorDestroyed);
+
+  if (mIsDone && aArgs.endReason() != FetchDriverObserver::eAborted) {
+    FETCH_LOG(
+        ("FetchParent::OnResponseEnd [%p] "
+         "Fetch has already aborted",
+         this));
+    return;
+  }
+
+  Unused << SendOnResponseEnd(aArgs);
+}
+
+void FetchParent::OnDataAvailable() {
+  FETCH_LOG(("FetchParent::OnDataAvailable [%p]", this));
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mActorDestroyed);
+
+  Unused << SendOnDataAvailable();
+}
+
+void FetchParent::OnFlushConsoleReport(
+    const nsTArray<net::ConsoleReportCollected>& aReports) {
+  FETCH_LOG(("FetchParent::OnFlushConsoleReport [%p]", this));
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mActorDestroyed);
+
+  Unused << SendOnFlushConsoleReport(aReports);
+}
+
+void FetchParent::OnReportPerformanceTiming(const ResponseTiming&& aTiming) {
+  FETCH_LOG(("FetchParent::OnReportPerformanceTiming [%p]", this));
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mActorDestroyed);
+
+  Unused << SendOnReportPerformanceTiming(aTiming);
+}
+
+void FetchParent::OnNotifyNetworkMonitorAlternateStack(uint64_t aChannelID) {
+  FETCH_LOG(("FetchParent::OnNotifyNetworkMonitorAlternateStack [%p]", this));
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mActorDestroyed);
+
+  Unused << SendOnNotifyNetworkMonitorAlternateStack(aChannelID);
+}
+
+void FetchParent::ActorDestroy(ActorDestroyReason aReason) {
+  FETCH_LOG(("FetchParent::ActorDestroy [%p]", this));
+  AssertIsOnBackgroundThread();
+  mActorDestroyed = true;
+  auto entry = sActorTable.Lookup(mID);
+  if (entry) {
+    entry.Remove();
+    FETCH_LOG(("FetchParent::ActorDestroy entry [%p] removed", this));
+  }
+  // Force to abort the existing fetch.
+  // Actor can be destoried by shutdown when still fetching.
+  RecvAbortFetchOp();
+  // mBackgroundEventTarget = nullptr;
+}
+
+nsICSPEventListener* FetchParent::GetCSPEventListener() {
+  return mCSPEventListener;
+}
+
+void FetchParent::OnCSPViolationEvent(const nsAString& aJSON) {
+  FETCH_LOG(("FetchParent::OnCSPViolationEvent [%p]", this));
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mHasCSPEventListener);
+  MOZ_ASSERT(!mActorDestroyed);
+
+  Unused << SendOnCSPViolationEvent(aJSON);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/fetch/FetchParent.h b/dom/fetch/FetchParent.h
new file mode 100644
index 0000000000..e373d93b73
--- /dev/null
+++ b/dom/fetch/FetchParent.h
@@ -0,0 +1,109 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_fetchParent_h__
+#define mozilla_dom_fetchParent_h__
+
+#include "mozilla/Maybe.h"
+#include "mozilla/MozPromise.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/dom/PFetchParent.h"
+#include "mozilla/dom/SafeRefPtr.h"
+#include "mozilla/ipc/PBackgroundSharedTypes.h"
+#include "mozilla/net/NeckoChannelParams.h"
+#include "nsCOMPtr.h"
+#include "nsIContentSecurityPolicy.h"
+#include "nsID.h"
+#include "nsISerialEventTarget.h"
+#include "nsString.h"
+#include "nsTHashMap.h"
+
+namespace mozilla::dom {
+
+class ClientInfo;
+class FetchServicePromises;
+class InternalRequest;
+class InternalResponse;
+class ServiceWorkerDescriptor;
+
+class FetchParent final : public PFetchParent {
+  friend class PFetchParent;
+
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(FetchParent, override);
+
+  mozilla::ipc::IPCResult RecvFetchOp(FetchOpArgs&& aArgs);
+
+  mozilla::ipc::IPCResult RecvAbortFetchOp();
+
+  FetchParent();
+
+  static RefPtr<FetchParent> GetActorByID(const nsID& aID);
+
+  void OnResponseAvailableInternal(SafeRefPtr<InternalResponse>&& aResponse);
+
+  void OnResponseEnd(const ResponseEndArgs& aArgs);
+
+  void OnDataAvailable();
+
+  void OnFlushConsoleReport(
+      const nsTArray<net::ConsoleReportCollected>& aReports);
+
+  class FetchParentCSPEventListener final : public nsICSPEventListener {
+   public:
+    NS_DECL_THREADSAFE_ISUPPORTS
+    NS_DECL_NSICSPEVENTLISTENER
+
+    FetchParentCSPEventListener(const nsID& aActorID,
+                                nsCOMPtr<nsISerialEventTarget> aEventTarget);
+
+   private:
+    ~FetchParentCSPEventListener() = default;
+
+    nsID mActorID;
+    nsCOMPtr<nsISerialEventTarget> mEventTarget;
+  };
+
+  nsICSPEventListener* GetCSPEventListener();
+
+  void OnCSPViolationEvent(const nsAString& aJSON);
+
+  void OnReportPerformanceTiming(const ResponseTiming&& aTiming);
+
+  void OnNotifyNetworkMonitorAlternateStack(uint64_t aChannelID);
+
+ private:
+  ~FetchParent();
+
+  void ActorDestroy(ActorDestroyReason aReason) override;
+
+  // The map of FetchParent and ID. Should only access in background thread.
+  static nsTHashMap<nsIDHashKey, RefPtr<FetchParent>> sActorTable;
+
+  // The unique ID of the FetchParent
+  nsID mID;
+  SafeRefPtr<InternalRequest> mRequest;
+  RefPtr<FetchServicePromises> mResponsePromises;
+  RefPtr<GenericPromise::Private> mPromise;
+  PrincipalInfo mPrincipalInfo;
+  nsCString mWorkerScript;
+  Maybe<ClientInfo> mClientInfo;
+  Maybe<ServiceWorkerDescriptor> mController;
+  Maybe<CookieJarSettingsArgs> mCookieJarSettings;
+  nsCOMPtr<nsICSPEventListener> mCSPEventListener;
+  bool mNeedOnDataAvailable{false};
+  bool mHasCSPEventListener{false};
+  bool mExtendForCSPEventListener{false};
+  uint64_t mAssociatedBrowsingContextID{0};
+
+  Atomic<bool> mIsDone{false};
+  Atomic<bool> mActorDestroyed{false};
+
+  nsCOMPtr<nsISerialEventTarget> mBackgroundEventTarget;
+};
+
+}  // namespace mozilla::dom
+
+#endif
diff --git a/dom/fetch/FetchService.cpp b/dom/fetch/FetchService.cpp
new file mode 100644
index 0000000000..e32d6f178e
--- /dev/null
+++ b/dom/fetch/FetchService.cpp
@@ -0,0 +1,643 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "FetchLog.h"
+#include "FetchParent.h"
+#include "nsContentUtils.h"
+#include "nsIContentSecurityPolicy.h"
+#include "nsICookieJarSettings.h"
+#include "nsILoadGroup.h"
+#include "nsILoadInfo.h"
+#include "nsIIOService.h"
+#include "nsIObserverService.h"
+#include "nsIPrincipal.h"
+#include "nsIScriptSecurityManager.h"
+#include "nsNetUtil.h"
+#include "nsThreadUtils.h"
+#include "nsXULAppAPI.h"
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/SchedulerGroup.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/dom/ClientInfo.h"
+#include "mozilla/dom/FetchService.h"
+#include "mozilla/dom/InternalRequest.h"
+#include "mozilla/dom/InternalResponse.h"
+#include "mozilla/dom/PerformanceStorage.h"
+#include "mozilla/dom/PerformanceTiming.h"
+#include "mozilla/dom/ServiceWorkerDescriptor.h"
+#include "mozilla/ipc/BackgroundUtils.h"
+#include "mozilla/net/CookieJarSettings.h"
+
+namespace mozilla::dom {
+
+mozilla::LazyLogModule gFetchLog("Fetch");
+
+// FetchServicePromises
+
+FetchServicePromises::FetchServicePromises()
+    : mAvailablePromise(
+          MakeRefPtr<FetchServiceResponseAvailablePromise::Private>(__func__)),
+      mTimingPromise(
+          MakeRefPtr<FetchServiceResponseTimingPromise::Private>(__func__)),
+      mEndPromise(
+          MakeRefPtr<FetchServiceResponseEndPromise::Private>(__func__)) {
+  mAvailablePromise->UseSynchronousTaskDispatch(__func__);
+  mTimingPromise->UseSynchronousTaskDispatch(__func__);
+  mEndPromise->UseSynchronousTaskDispatch(__func__);
+}
+
+RefPtr<FetchServiceResponseAvailablePromise>
+FetchServicePromises::GetResponseAvailablePromise() {
+  return mAvailablePromise;
+}
+
+RefPtr<FetchServiceResponseTimingPromise>
+FetchServicePromises::GetResponseTimingPromise() {
+  return mTimingPromise;
+}
+
+RefPtr<FetchServiceResponseEndPromise>
+FetchServicePromises::GetResponseEndPromise() {
+  return mEndPromise;
+}
+
+void FetchServicePromises::ResolveResponseAvailablePromise(
+    FetchServiceResponse&& aResponse, const char* aMethodName) {
+  if (mAvailablePromise) {
+    mAvailablePromise->Resolve(std::move(aResponse), aMethodName);
+  }
+}
+
+void FetchServicePromises::RejectResponseAvailablePromise(
+    const CopyableErrorResult&& aError, const char* aMethodName) {
+  if (mAvailablePromise) {
+    mAvailablePromise->Reject(aError, aMethodName);
+  }
+}
+
+void FetchServicePromises::ResolveResponseTimingPromise(
+    ResponseTiming&& aTiming, const char* aMethodName) {
+  if (mTimingPromise) {
+    mTimingPromise->Resolve(std::move(aTiming), aMethodName);
+  }
+}
+
+void FetchServicePromises::RejectResponseTimingPromise(
+    const CopyableErrorResult&& aError, const char* aMethodName) {
+  if (mTimingPromise) {
+    mTimingPromise->Reject(aError, aMethodName);
+  }
+}
+
+void FetchServicePromises::ResolveResponseEndPromise(ResponseEndArgs&& aArgs,
+                                                     const char* aMethodName) {
+  if (mEndPromise) {
+    mEndPromise->Resolve(std::move(aArgs), aMethodName);
+  }
+}
+
+void FetchServicePromises::RejectResponseEndPromise(
+    const CopyableErrorResult&& aError, const char* aMethodName) {
+  if (mEndPromise) {
+    mEndPromise->Reject(aError, aMethodName);
+  }
+}
+
+// FetchInstance
+
+nsresult FetchService::FetchInstance::Initialize(FetchArgs&& aArgs) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(!aArgs.is<UnknownArgs>() && mArgs.is<UnknownArgs>());
+
+  mArgs = std::move(aArgs);
+
+  // Get needed information for FetchDriver from passed-in channel.
+  if (mArgs.is<NavigationPreloadArgs>()) {
+    mRequest = mArgs.as<NavigationPreloadArgs>().mRequest.clonePtr();
+    nsIChannel* channel = mArgs.as<NavigationPreloadArgs>().mChannel;
+    FETCH_LOG(("FetchInstance::Initialize [%p] request[%p], channel[%p]", this,
+               mRequest.unsafeGetRawPtr(), channel));
+
+    nsresult rv;
+    nsCOMPtr<nsILoadInfo> loadInfo = channel->LoadInfo();
+    MOZ_ASSERT(loadInfo);
+
+    nsCOMPtr<nsIURI> channelURI;
+    rv = channel->GetURI(getter_AddRefs(channelURI));
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    nsIScriptSecurityManager* securityManager =
+        nsContentUtils::GetSecurityManager();
+    if (securityManager) {
+      securityManager->GetChannelResultPrincipal(channel,
+                                                 getter_AddRefs(mPrincipal));
+    }
+
+    if (!mPrincipal) {
+      return NS_ERROR_UNEXPECTED;
+    }
+
+    // Get loadGroup from channel
+    rv = channel->GetLoadGroup(getter_AddRefs(mLoadGroup));
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+    if (!mLoadGroup) {
+      rv = NS_NewLoadGroup(getter_AddRefs(mLoadGroup), mPrincipal);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+    }
+
+    // Get CookieJarSettings from channel
+    rv = loadInfo->GetCookieJarSettings(getter_AddRefs(mCookieJarSettings));
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    // Get PerformanceStorage from channel
+    mPerformanceStorage = loadInfo->GetPerformanceStorage();
+  } else {
+    mIsWorkerFetch = true;
+    mRequest = mArgs.as<WorkerFetchArgs>().mRequest.clonePtr();
+
+    FETCH_LOG(("FetchInstance::Initialize [%p] request[%p]", this,
+               mRequest.unsafeGetRawPtr()));
+
+    auto principalOrErr =
+        PrincipalInfoToPrincipal(mArgs.as<WorkerFetchArgs>().mPrincipalInfo);
+    if (principalOrErr.isErr()) {
+      return principalOrErr.unwrapErr();
+    }
+    mPrincipal = principalOrErr.unwrap();
+    nsresult rv = NS_NewLoadGroup(getter_AddRefs(mLoadGroup), mPrincipal);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    if (mArgs.as<WorkerFetchArgs>().mCookieJarSettings.isSome()) {
+      net::CookieJarSettings::Deserialize(
+          mArgs.as<WorkerFetchArgs>().mCookieJarSettings.ref(),
+          getter_AddRefs(mCookieJarSettings));
+    }
+  }
+
+  return NS_OK;
+}
+
+RefPtr<FetchServicePromises> FetchService::FetchInstance::Fetch() {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  MOZ_ASSERT(NS_IsMainThread());
+
+  MOZ_ASSERT(mPrincipal);
+  MOZ_ASSERT(mLoadGroup);
+
+  nsAutoCString principalSpec;
+  MOZ_ALWAYS_SUCCEEDS(mPrincipal->GetAsciiSpec(principalSpec));
+  nsAutoCString requestURL;
+  mRequest->GetURL(requestURL);
+  FETCH_LOG(("FetchInstance::Fetch [%p], mRequest URL: %s mPrincipal: %s", this,
+             requestURL.BeginReading(), principalSpec.BeginReading()));
+
+  nsresult rv;
+
+  // Create a FetchDriver instance
+  mFetchDriver = MakeRefPtr<FetchDriver>(
+      mRequest.clonePtr(),               // Fetch Request
+      mPrincipal,                        // Principal
+      mLoadGroup,                        // LoadGroup
+      GetMainThreadSerialEventTarget(),  // MainThreadEventTarget
+      mCookieJarSettings,                // CookieJarSettings
+      mPerformanceStorage,               // PerformanceStorage
+      false                              // IsTrackingFetch
+  );
+
+  if (mIsWorkerFetch) {
+    auto& args = mArgs.as<WorkerFetchArgs>();
+    mFetchDriver->SetWorkerScript(args.mWorkerScript);
+    MOZ_ASSERT(args.mClientInfo.isSome());
+    mFetchDriver->SetClientInfo(args.mClientInfo.ref());
+    mFetchDriver->SetController(args.mController);
+    if (args.mCSPEventListener) {
+      mFetchDriver->SetCSPEventListener(args.mCSPEventListener);
+    }
+    mFetchDriver->SetAssociatedBrowsingContextID(
+        args.mAssociatedBrowsingContextID);
+  }
+
+  mFetchDriver->EnableNetworkInterceptControl();
+
+  mPromises = MakeRefPtr<FetchServicePromises>();
+
+  // Call FetchDriver::Fetch to start fetching.
+  // Pass AbortSignalImpl as nullptr since we no need support AbortSignalImpl
+  // with FetchService. AbortSignalImpl related information should be passed
+  // through PFetch or InterceptedHttpChannel, then call
+  // FetchService::CancelFetch() to abort the running fetch.
+  rv = mFetchDriver->Fetch(nullptr, this);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    FETCH_LOG(
+        ("FetchInstance::Fetch FetchDriver::Fetch failed(0x%X)", (uint32_t)rv));
+    return FetchService::NetworkErrorResponse(rv);
+  }
+
+  return mPromises;
+}
+
+void FetchService::FetchInstance::Cancel() {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  MOZ_ASSERT(NS_IsMainThread());
+
+  FETCH_LOG(("FetchInstance::Cancel() [%p]", this));
+
+  if (mFetchDriver) {
+    mFetchDriver->RunAbortAlgorithm();
+  }
+
+  MOZ_ASSERT(mPromises);
+
+  mPromises->ResolveResponseAvailablePromise(
+      InternalResponse::NetworkError(NS_ERROR_DOM_ABORT_ERR), __func__);
+
+  mPromises->ResolveResponseTimingPromise(ResponseTiming(), __func__);
+
+  mPromises->ResolveResponseEndPromise(
+      ResponseEndArgs(FetchDriverObserver::eAborted), __func__);
+}
+
+void FetchService::FetchInstance::OnResponseEnd(
+    FetchDriverObserver::EndReason aReason,
+    JS::Handle<JS::Value> aReasonDetails) {
+  FETCH_LOG(("FetchInstance::OnResponseEnd [%p] %s", this,
+             aReason == eAborted ? "eAborted" : "eNetworking"));
+
+  if (mIsWorkerFetch) {
+    FlushConsoleReport();
+    nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+        __func__, [endArgs = ResponseEndArgs(aReason),
+                   actorID = mArgs.as<WorkerFetchArgs>().mActorID]() {
+          FETCH_LOG(("FetchInstance::OnResponseEnd, Runnable"));
+          RefPtr<FetchParent> actor = FetchParent::GetActorByID(actorID);
+          if (actor) {
+            actor->OnResponseEnd(std::move(endArgs));
+          }
+        });
+    MOZ_ALWAYS_SUCCEEDS(mArgs.as<WorkerFetchArgs>().mEventTarget->Dispatch(
+        r, nsIThread::DISPATCH_NORMAL));
+  }
+
+  MOZ_ASSERT(mPromises);
+
+  // If ResponseTimingPromise is not resolved, it means the fetch is aborted.
+  // Resolving ResponseTimingPromise with an emtpy ResponseTiming.
+  if (!mPromises->GetResponseTimingPromise()->IsResolved()) {
+    mPromises->ResolveResponseTimingPromise(ResponseTiming(), __func__);
+  }
+  // Resolve the ResponseEndPromise
+  mPromises->ResolveResponseEndPromise(ResponseEndArgs(aReason), __func__);
+
+  if (aReason == eAborted) {
+    return;
+  }
+
+  // Remove the FetchInstance from FetchInstanceTable
+  RefPtr<FetchService> fetchService = FetchService::GetInstance();
+  MOZ_ASSERT(fetchService);
+  auto entry = fetchService->mFetchInstanceTable.Lookup(mPromises);
+  if (entry) {
+    entry.Remove();
+    FETCH_LOG(
+        ("FetchInstance::OnResponseEnd entry of responsePromise[%p] is "
+         "removed",
+         mPromises.get()));
+  }
+}
+
+void FetchService::FetchInstance::OnResponseAvailableInternal(
+    SafeRefPtr<InternalResponse> aResponse) {
+  FETCH_LOG(("FetchInstance::OnResponseAvailableInternal [%p]", this));
+  mResponse = std::move(aResponse);
+
+  nsCOMPtr<nsIInputStream> body;
+  mResponse->GetUnfilteredBody(getter_AddRefs(body));
+  FETCH_LOG(
+      ("FetchInstance::OnResponseAvailableInternal [%p] response body: %p",
+       this, body.get()));
+
+  if (mIsWorkerFetch) {
+    nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+        __func__, [response = mResponse.clonePtr(),
+                   actorID = mArgs.as<WorkerFetchArgs>().mActorID]() mutable {
+          FETCH_LOG(("FetchInstance::OnResponseAvailableInternal Runnable"));
+          RefPtr<FetchParent> actor = FetchParent::GetActorByID(actorID);
+          if (actor) {
+            actor->OnResponseAvailableInternal(std::move(response));
+          }
+        });
+    MOZ_ALWAYS_SUCCEEDS(mArgs.as<WorkerFetchArgs>().mEventTarget->Dispatch(
+        r, nsIThread::DISPATCH_NORMAL));
+  }
+
+  MOZ_ASSERT(mPromises);
+
+  // Resolve the ResponseAvailablePromise
+  mPromises->ResolveResponseAvailablePromise(mResponse.clonePtr(), __func__);
+}
+
+bool FetchService::FetchInstance::NeedOnDataAvailable() {
+  if (mArgs.is<WorkerFetchArgs>()) {
+    return mArgs.as<WorkerFetchArgs>().mNeedOnDataAvailable;
+  }
+  return false;
+}
+
+void FetchService::FetchInstance::OnDataAvailable() {
+  FETCH_LOG(("FetchInstance::OnDataAvailable [%p]", this));
+
+  if (!NeedOnDataAvailable()) {
+    return;
+  }
+
+  if (mIsWorkerFetch) {
+    nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+        __func__, [actorID = mArgs.as<WorkerFetchArgs>().mActorID]() {
+          FETCH_LOG(("FetchInstance::OnDataAvailable, Runnable"));
+          RefPtr<FetchParent> actor = FetchParent::GetActorByID(actorID);
+          if (actor) {
+            actor->OnDataAvailable();
+          }
+        });
+    MOZ_ALWAYS_SUCCEEDS(mArgs.as<WorkerFetchArgs>().mEventTarget->Dispatch(
+        r, nsIThread::DISPATCH_NORMAL));
+  }
+}
+
+void FetchService::FetchInstance::FlushConsoleReport() {
+  FETCH_LOG(("FetchInstance::FlushConsoleReport [%p]", this));
+
+  if (mIsWorkerFetch) {
+    if (!mReporter) {
+      return;
+    }
+    nsTArray<net::ConsoleReportCollected> reports;
+    mReporter->StealConsoleReports(reports);
+    nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+        __func__, [actorID = mArgs.as<WorkerFetchArgs>().mActorID,
+                   consoleReports = std::move(reports)]() {
+          FETCH_LOG(("FetchInstance::FlushConsolReport, Runnable"));
+          RefPtr<FetchParent> actor = FetchParent::GetActorByID(actorID);
+          if (actor) {
+            actor->OnFlushConsoleReport(std::move(consoleReports));
+          }
+        });
+    MOZ_ALWAYS_SUCCEEDS(mArgs.as<WorkerFetchArgs>().mEventTarget->Dispatch(
+        r, nsIThread::DISPATCH_NORMAL));
+  }
+}
+
+void FetchService::FetchInstance::OnReportPerformanceTiming() {
+  FETCH_LOG(("FetchInstance::OnReportPerformanceTiming [%p]", this));
+  MOZ_ASSERT(mFetchDriver);
+  MOZ_ASSERT(mPromises);
+
+  if (mPromises->GetResponseTimingPromise()->IsResolved()) {
+    return;
+  }
+
+  ResponseTiming timing;
+  UniquePtr<PerformanceTimingData> performanceTiming(
+      mFetchDriver->GetPerformanceTimingData(timing.initiatorType(),
+                                             timing.entryName()));
+  if (!performanceTiming) {
+    return;
+  }
+  timing.timingData() = performanceTiming->ToIPC();
+  // Force replace initiatorType for ServiceWorkerNavgationPreload.
+  if (!mIsWorkerFetch) {
+    timing.initiatorType() = u"navigation"_ns;
+  } else {
+    nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+        __func__,
+        [actorID = mArgs.as<WorkerFetchArgs>().mActorID, timing = timing]() {
+          FETCH_LOG(("FetchInstance::OnReportPerformanceTiming, Runnable"));
+          RefPtr<FetchParent> actor = FetchParent::GetActorByID(actorID);
+          if (actor) {
+            actor->OnReportPerformanceTiming(std::move(timing));
+          }
+        });
+    MOZ_ALWAYS_SUCCEEDS(mArgs.as<WorkerFetchArgs>().mEventTarget->Dispatch(
+        r, nsIThread::DISPATCH_NORMAL));
+  }
+
+  mPromises->ResolveResponseTimingPromise(std::move(timing), __func__);
+}
+
+void FetchService::FetchInstance::OnNotifyNetworkMonitorAlternateStack(
+    uint64_t aChannelID) {
+  FETCH_LOG(("FetchInstance::OnNotifyNetworkMonitorAlternateStack [%p]", this));
+  MOZ_ASSERT(mFetchDriver);
+  MOZ_ASSERT(mPromises);
+  if (!mIsWorkerFetch) {
+    return;
+  }
+
+  nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+      __func__, [actorID = mArgs.as<WorkerFetchArgs>().mActorID,
+                 channelID = aChannelID]() {
+        FETCH_LOG(
+            ("FetchInstance::NotifyNetworkMonitorAlternateStack, Runnable"));
+        RefPtr<FetchParent> actor = FetchParent::GetActorByID(actorID);
+        if (actor) {
+          actor->OnNotifyNetworkMonitorAlternateStack(channelID);
+        }
+      });
+
+  MOZ_ALWAYS_SUCCEEDS(mArgs.as<WorkerFetchArgs>().mEventTarget->Dispatch(
+      r, nsIThread::DISPATCH_NORMAL));
+}
+
+// FetchService
+
+NS_IMPL_ISUPPORTS(FetchService, nsIObserver)
+
+StaticRefPtr<FetchService> gInstance;
+
+/*static*/
+already_AddRefed<FetchService> FetchService::GetInstance() {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (!gInstance) {
+    gInstance = MakeRefPtr<FetchService>();
+    nsresult rv = gInstance->RegisterNetworkObserver();
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      gInstance = nullptr;
+      return nullptr;
+    }
+    ClearOnShutdown(&gInstance);
+  }
+  RefPtr<FetchService> service = gInstance;
+  return service.forget();
+}
+
+/*static*/
+RefPtr<FetchServicePromises> FetchService::NetworkErrorResponse(nsresult aRv) {
+  RefPtr<FetchServicePromises> promises = MakeRefPtr<FetchServicePromises>();
+  promises->ResolveResponseAvailablePromise(InternalResponse::NetworkError(aRv),
+                                            __func__);
+  promises->ResolveResponseTimingPromise(ResponseTiming(), __func__);
+  promises->ResolveResponseEndPromise(
+      ResponseEndArgs(FetchDriverObserver::eAborted), __func__);
+  return promises;
+}
+
+FetchService::FetchService() {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  MOZ_ASSERT(NS_IsMainThread());
+}
+
+FetchService::~FetchService() {
+  MOZ_ALWAYS_SUCCEEDS(UnregisterNetworkObserver());
+}
+
+nsresult FetchService::RegisterNetworkObserver() {
+  AssertIsOnMainThread();
+  nsCOMPtr<nsIObserverService> observerService = services::GetObserverService();
+  if (!observerService) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  nsCOMPtr<nsIIOService> ioService = services::GetIOService();
+  if (!ioService) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  nsresult rv = observerService->AddObserver(
+      this, NS_IOSERVICE_OFFLINE_STATUS_TOPIC, false);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = observerService->AddObserver(this, "xpcom-shutdown", false);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = ioService->GetOffline(&mOffline);
+  NS_ENSURE_SUCCESS(rv, rv);
+  mObservingNetwork = true;
+
+  return NS_OK;
+}
+
+nsresult FetchService::UnregisterNetworkObserver() {
+  AssertIsOnMainThread();
+  nsresult rv;
+  if (mObservingNetwork) {
+    nsCOMPtr<nsIObserverService> observerService =
+        mozilla::services::GetObserverService();
+    if (observerService) {
+      rv = observerService->RemoveObserver(this,
+                                           NS_IOSERVICE_OFFLINE_STATUS_TOPIC);
+      NS_ENSURE_SUCCESS(rv, rv);
+      rv = observerService->RemoveObserver(this, "xpcom-shutdown");
+      NS_ENSURE_SUCCESS(rv, rv);
+    }
+    mObservingNetwork = false;
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP FetchService::Observe(nsISupports* aSubject, const char* aTopic,
+                                    const char16_t* aData) {
+  FETCH_LOG(("FetchService::Observe topic: %s", aTopic));
+  AssertIsOnMainThread();
+  MOZ_ASSERT(!strcmp(aTopic, NS_IOSERVICE_OFFLINE_STATUS_TOPIC) ||
+             !strcmp(aTopic, "xpcom-shutdown"));
+
+  if (!strcmp(aTopic, "xpcom-shutdown")) {
+    // Going to shutdown, unregister the network status observer to avoid
+    // receiving
+    nsresult rv = UnregisterNetworkObserver();
+    NS_ENSURE_SUCCESS(rv, rv);
+    return NS_OK;
+  }
+
+  if (nsDependentString(aData).EqualsLiteral(NS_IOSERVICE_ONLINE)) {
+    mOffline = false;
+  } else {
+    mOffline = true;
+    // Network is offline, cancel running fetchs.
+    for (auto it = mFetchInstanceTable.begin(), end = mFetchInstanceTable.end();
+         it != end; ++it) {
+      it->GetData()->Cancel();
+    }
+    mFetchInstanceTable.Clear();
+  }
+  return NS_OK;
+}
+
+RefPtr<FetchServicePromises> FetchService::Fetch(FetchArgs&& aArgs) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  MOZ_ASSERT(NS_IsMainThread());
+
+  FETCH_LOG(("FetchService::Fetch (%s)", aArgs.is<NavigationPreloadArgs>()
+                                             ? "NavigationPreload"
+                                             : "WorkerFetch"));
+  if (mOffline) {
+    FETCH_LOG(("FetchService::Fetch network offline"));
+    return NetworkErrorResponse(NS_ERROR_OFFLINE);
+  }
+
+  // Create FetchInstance
+  RefPtr<FetchInstance> fetch = MakeRefPtr<FetchInstance>();
+
+  // Call FetchInstance::Initialize() to get needed information for FetchDriver,
+  nsresult rv = fetch->Initialize(std::move(aArgs));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return NetworkErrorResponse(rv);
+  }
+
+  // Call FetchInstance::Fetch() to start an asynchronous fetching.
+  RefPtr<FetchServicePromises> promises = fetch->Fetch();
+  MOZ_ASSERT(promises);
+
+  if (!promises->GetResponseAvailablePromise()->IsResolved()) {
+    // Insert the created FetchInstance into FetchInstanceTable.
+    if (!mFetchInstanceTable.WithEntryHandle(promises, [&](auto&& entry) {
+          if (entry.HasEntry()) {
+            return false;
+          }
+          entry.Insert(fetch);
+          return true;
+        })) {
+      FETCH_LOG(
+          ("FetchService::Fetch entry[%p] already exists", promises.get()));
+      return NetworkErrorResponse(NS_ERROR_UNEXPECTED);
+    }
+    FETCH_LOG(("FetchService::Fetch entry[%p] of FetchInstance[%p] added",
+               promises.get(), fetch.get()));
+  }
+  return promises;
+}
+
+void FetchService::CancelFetch(const RefPtr<FetchServicePromises>&& aPromises) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aPromises);
+  FETCH_LOG(("FetchService::CancelFetch aPromises[%p]", aPromises.get()));
+
+  auto entry = mFetchInstanceTable.Lookup(aPromises);
+  if (entry) {
+    // Notice any modifications here before entry.Remove() probably should be
+    // reflected to Observe() offline case.
+    entry.Data()->Cancel();
+    entry.Remove();
+    FETCH_LOG(
+        ("FetchService::CancelFetch entry [%p] removed", aPromises.get()));
+  }
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/fetch/FetchService.h b/dom/fetch/FetchService.h
new file mode 100644
index 0000000000..3032c4d2a9
--- /dev/null
+++ b/dom/fetch/FetchService.h
@@ -0,0 +1,186 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+#ifndef _mozilla_dom_FetchService_h
+#define _mozilla_dom_FetchService_h
+
+#include "nsIChannel.h"
+#include "nsIObserver.h"
+#include "nsTHashMap.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/MozPromise.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/dom/FetchDriver.h"
+#include "mozilla/dom/FetchTypes.h"
+#include "mozilla/dom/PerformanceTimingTypes.h"
+#include "mozilla/dom/SafeRefPtr.h"
+#include "mozilla/ipc/PBackgroundSharedTypes.h"
+#include "mozilla/net/NeckoChannelParams.h"
+
+class nsILoadGroup;
+class nsIPrincipal;
+class nsICookieJarSettings;
+class PerformanceStorage;
+
+namespace mozilla::dom {
+
+class InternalRequest;
+class InternalResponse;
+class ClientInfo;
+class ServiceWorkerDescriptor;
+
+using FetchServiceResponse = SafeRefPtr<InternalResponse>;
+using FetchServiceResponseAvailablePromise =
+    MozPromise<FetchServiceResponse, CopyableErrorResult, true>;
+using FetchServiceResponseTimingPromise =
+    MozPromise<ResponseTiming, CopyableErrorResult, true>;
+using FetchServiceResponseEndPromise =
+    MozPromise<ResponseEndArgs, CopyableErrorResult, true>;
+
+class FetchServicePromises final {
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(FetchServicePromises);
+
+ public:
+  FetchServicePromises();
+
+  RefPtr<FetchServiceResponseAvailablePromise> GetResponseAvailablePromise();
+  RefPtr<FetchServiceResponseTimingPromise> GetResponseTimingPromise();
+  RefPtr<FetchServiceResponseEndPromise> GetResponseEndPromise();
+
+  void ResolveResponseAvailablePromise(FetchServiceResponse&& aResponse,
+                                       const char* aMethodName);
+  void RejectResponseAvailablePromise(const CopyableErrorResult&& aError,
+                                      const char* aMethodName);
+  void ResolveResponseTimingPromise(ResponseTiming&& aTiming,
+                                    const char* aMethodName);
+  void RejectResponseTimingPromise(const CopyableErrorResult&& aError,
+                                   const char* aMethodName);
+  void ResolveResponseEndPromise(ResponseEndArgs&& aArgs,
+                                 const char* aMethodName);
+  void RejectResponseEndPromise(const CopyableErrorResult&& aError,
+                                const char* aMethodName);
+
+ private:
+  ~FetchServicePromises() = default;
+
+  RefPtr<FetchServiceResponseAvailablePromise::Private> mAvailablePromise;
+  RefPtr<FetchServiceResponseTimingPromise::Private> mTimingPromise;
+  RefPtr<FetchServiceResponseEndPromise::Private> mEndPromise;
+};
+
+/**
+ * FetchService is a singleton object which designed to be used in parent
+ * process main thread only. It is used to handle the special fetch requests
+ * from ServiceWorkers(by Navigation Preload) and PFetch.
+ *
+ * FetchService creates FetchInstance internally to represent each Fetch
+ * request. It supports an asynchronous fetching, FetchServicePromises is
+ * created when a Fetch starts, once the response is ready or any error happens,
+ * the FetchServicePromises would be resolved or rejected. The promises
+ * consumers can set callbacks to handle the Fetch result.
+ */
+class FetchService final : public nsIObserver {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  struct NavigationPreloadArgs {
+    SafeRefPtr<InternalRequest> mRequest;
+    nsCOMPtr<nsIChannel> mChannel;
+  };
+
+  struct WorkerFetchArgs {
+    SafeRefPtr<InternalRequest> mRequest;
+    mozilla::ipc::PrincipalInfo mPrincipalInfo;
+    nsCString mWorkerScript;
+    Maybe<ClientInfo> mClientInfo;
+    Maybe<ServiceWorkerDescriptor> mController;
+    Maybe<net::CookieJarSettingsArgs> mCookieJarSettings;
+    bool mNeedOnDataAvailable;
+    nsCOMPtr<nsICSPEventListener> mCSPEventListener;
+    uint64_t mAssociatedBrowsingContextID;
+    nsCOMPtr<nsISerialEventTarget> mEventTarget;
+    nsID mActorID;
+  };
+
+  struct UnknownArgs {};
+
+  using FetchArgs =
+      Variant<NavigationPreloadArgs, WorkerFetchArgs, UnknownArgs>;
+
+  static already_AddRefed<FetchService> GetInstance();
+
+  static RefPtr<FetchServicePromises> NetworkErrorResponse(nsresult aRv);
+
+  FetchService();
+
+  // This method creates a FetchInstance to trigger fetch.
+  // The created FetchInstance is saved in mFetchInstanceTable
+  RefPtr<FetchServicePromises> Fetch(FetchArgs&& aArgs);
+
+  void CancelFetch(const RefPtr<FetchServicePromises>&& aPromises);
+
+ private:
+  /**
+   * FetchInstance is an internal representation for each Fetch created by
+   * FetchService.
+   * FetchInstance is also a FetchDriverObserver which has responsibility to
+   * resolve/reject the FetchServicePromises.
+   * FetchInstance triggers fetch by instancing a FetchDriver with proper
+   * initialization. The general usage flow of FetchInstance is as follows
+   *
+   * RefPtr<FetchInstance> fetch = MakeRefPtr<FetchInstance>();
+   * fetch->Initialize(FetchArgs args);
+   * RefPtr<FetchServicePromises> fetch->Fetch();
+   */
+  class FetchInstance final : public FetchDriverObserver {
+   public:
+    FetchInstance() = default;
+
+    nsresult Initialize(FetchArgs&& aArgs);
+
+    RefPtr<FetchServicePromises> Fetch();
+
+    void Cancel();
+
+    /* FetchDriverObserver interface */
+    void OnResponseEnd(FetchDriverObserver::EndReason aReason,
+                       JS::Handle<JS::Value> aReasonDetails) override;
+    void OnResponseAvailableInternal(
+        SafeRefPtr<InternalResponse> aResponse) override;
+    bool NeedOnDataAvailable() override;
+    void OnDataAvailable() override;
+    void FlushConsoleReport() override;
+    void OnReportPerformanceTiming() override;
+    void OnNotifyNetworkMonitorAlternateStack(uint64_t aChannelID) override;
+
+   private:
+    ~FetchInstance() = default;
+
+    SafeRefPtr<InternalRequest> mRequest;
+    nsCOMPtr<nsIPrincipal> mPrincipal;
+    nsCOMPtr<nsILoadGroup> mLoadGroup;
+    nsCOMPtr<nsICookieJarSettings> mCookieJarSettings;
+    RefPtr<PerformanceStorage> mPerformanceStorage;
+    FetchArgs mArgs{AsVariant(FetchService::UnknownArgs())};
+    RefPtr<FetchDriver> mFetchDriver;
+    SafeRefPtr<InternalResponse> mResponse;
+    RefPtr<FetchServicePromises> mPromises;
+    bool mIsWorkerFetch{false};
+  };
+
+  ~FetchService();
+
+  nsresult RegisterNetworkObserver();
+  nsresult UnregisterNetworkObserver();
+
+  // This is a container to manage the generated fetches.
+  nsTHashMap<nsRefPtrHashKey<FetchServicePromises>, RefPtr<FetchInstance> >
+      mFetchInstanceTable;
+  bool mObservingNetwork{false};
+  bool mOffline{false};
+};
+
+}  // namespace mozilla::dom
+
+#endif  // _mozilla_dom_FetchService_h
diff --git a/dom/fetch/FetchStreamReader.cpp b/dom/fetch/FetchStreamReader.cpp
new file mode 100644
index 0000000000..de5a2cfefe
--- /dev/null
+++ b/dom/fetch/FetchStreamReader.cpp
@@ -0,0 +1,441 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "FetchStreamReader.h"
+#include "InternalResponse.h"
+#include "mozilla/ConsoleReportCollector.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/StaticAnalysisFunctions.h"
+#include "mozilla/dom/AutoEntryScript.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/PromiseBinding.h"
+#include "mozilla/dom/ReadableStream.h"
+#include "mozilla/dom/ReadableStreamDefaultController.h"
+#include "mozilla/dom/ReadableStreamDefaultReader.h"
+#include "mozilla/dom/WorkerPrivate.h"
+#include "mozilla/dom/WorkerRef.h"
+#include "mozilla/HoldDropJSObjects.h"
+#include "mozilla/TaskCategory.h"
+#include "nsContentUtils.h"
+#include "nsDebug.h"
+#include "nsIAsyncInputStream.h"
+#include "nsIPipe.h"
+#include "nsIScriptError.h"
+#include "nsPIDOMWindow.h"
+#include "jsapi.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(FetchStreamReader)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(FetchStreamReader)
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(FetchStreamReader)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(FetchStreamReader)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mGlobal)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mReader)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(FetchStreamReader)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mGlobal)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mReader)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(FetchStreamReader)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(FetchStreamReader)
+  NS_INTERFACE_MAP_ENTRY(nsIOutputStreamCallback)
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIOutputStreamCallback)
+NS_INTERFACE_MAP_END
+
+/* static */
+nsresult FetchStreamReader::Create(JSContext* aCx, nsIGlobalObject* aGlobal,
+                                   FetchStreamReader** aStreamReader,
+                                   nsIInputStream** aInputStream) {
+  MOZ_ASSERT(aCx);
+  MOZ_ASSERT(aGlobal);
+  MOZ_ASSERT(aStreamReader);
+  MOZ_ASSERT(aInputStream);
+
+  RefPtr<FetchStreamReader> streamReader = new FetchStreamReader(aGlobal);
+
+  nsCOMPtr<nsIAsyncInputStream> pipeIn;
+
+  NS_NewPipe2(getter_AddRefs(pipeIn), getter_AddRefs(streamReader->mPipeOut),
+              true, true, 0, 0);
+
+  if (!NS_IsMainThread()) {
+    WorkerPrivate* workerPrivate = GetWorkerPrivateFromContext(aCx);
+    MOZ_ASSERT(workerPrivate);
+
+    RefPtr<StrongWorkerRef> workerRef = StrongWorkerRef::Create(
+        workerPrivate, "FetchStreamReader", [streamReader]() {
+          MOZ_ASSERT(streamReader);
+
+          // mAsyncWaitWorkerRef may keep the (same) StrongWorkerRef alive even
+          // when mWorkerRef has already been nulled out by a previous call to
+          // CloseAndRelease, we can just safely ignore this callback then
+          // (as would the CloseAndRelease do on a second call).
+          if (streamReader->mWorkerRef) {
+            streamReader->CloseAndRelease(
+                streamReader->mWorkerRef->Private()->GetJSContext(),
+                NS_ERROR_DOM_INVALID_STATE_ERR);
+          } else {
+            MOZ_DIAGNOSTIC_ASSERT(streamReader->mAsyncWaitWorkerRef);
+          }
+        });
+
+    if (NS_WARN_IF(!workerRef)) {
+      streamReader->mPipeOut->CloseWithStatus(NS_ERROR_DOM_INVALID_STATE_ERR);
+      return NS_ERROR_DOM_INVALID_STATE_ERR;
+    }
+
+    // These 2 objects create a ref-cycle here that is broken when the stream is
+    // closed or the worker shutsdown.
+    streamReader->mWorkerRef = std::move(workerRef);
+  }
+
+  pipeIn.forget(aInputStream);
+  streamReader.forget(aStreamReader);
+  return NS_OK;
+}
+
+FetchStreamReader::FetchStreamReader(nsIGlobalObject* aGlobal)
+    : mGlobal(aGlobal),
+      mOwningEventTarget(mGlobal->EventTargetFor(TaskCategory::Other)) {
+  MOZ_ASSERT(aGlobal);
+
+  mozilla::HoldJSObjects(this);
+}
+
+FetchStreamReader::~FetchStreamReader() {
+  CloseAndRelease(nullptr, NS_BASE_STREAM_CLOSED);
+
+  mozilla::DropJSObjects(this);
+}
+
+// If a context is provided, an attempt will be made to cancel the reader.  The
+// only situation where we don't expect to have a context is when closure is
+// being triggered from the destructor or the WorkerRef is notifying.  If
+// we're at the destructor, it's far too late to cancel anything.  And if the
+// WorkerRef is being notified, the global is going away, so there's also
+// no need to do further JS work.
+void FetchStreamReader::CloseAndRelease(JSContext* aCx, nsresult aStatus) {
+  NS_ASSERT_OWNINGTHREAD(FetchStreamReader);
+
+  if (mStreamClosed) {
+    // Already closed.
+    return;
+  }
+
+  RefPtr<FetchStreamReader> kungFuDeathGrip = this;
+  if (aCx && mReader) {
+    ErrorResult rv;
+    if (aStatus == NS_ERROR_DOM_WRONG_TYPE_ERR) {
+      rv.ThrowTypeError<MSG_FETCH_BODY_WRONG_TYPE>();
+    } else {
+      rv = aStatus;
+    }
+    JS::Rooted<JS::Value> errorValue(aCx);
+    if (ToJSValue(aCx, std::move(rv), &errorValue)) {
+      IgnoredErrorResult ignoredError;
+      // It's currently safe to cancel an already closed reader because, per the
+      // comments in ReadableStream::cancel() conveying the spec, step 2 of
+      // 3.4.3 that specified ReadableStreamCancel is: If stream.[[state]] is
+      // "closed", return a new promise resolved with undefined.
+      RefPtr<Promise> cancelResultPromise =
+          MOZ_KnownLive(mReader)->Cancel(aCx, errorValue, ignoredError);
+      NS_WARNING_ASSERTION(!ignoredError.Failed(),
+                           "Failed to cancel stream during close and release");
+      if (cancelResultPromise) {
+        bool setHandled = cancelResultPromise->SetAnyPromiseIsHandled();
+        NS_WARNING_ASSERTION(setHandled,
+                             "Failed to mark cancel promise as handled.");
+        (void)setHandled;
+      }
+    }
+
+    // We don't want to propagate exceptions during the cleanup.
+    JS_ClearPendingException(aCx);
+  }
+
+  mStreamClosed = true;
+
+  mGlobal = nullptr;
+
+  if (mPipeOut) {
+    mPipeOut->CloseWithStatus(aStatus);
+  }
+  mPipeOut = nullptr;
+
+  mWorkerRef = nullptr;
+
+  mReader = nullptr;
+  mBuffer.Clear();
+}
+
+// https://fetch.spec.whatwg.org/#body-incrementally-read
+void FetchStreamReader::StartConsuming(JSContext* aCx, ReadableStream* aStream,
+                                       ErrorResult& aRv) {
+  MOZ_DIAGNOSTIC_ASSERT(!mReader);
+  MOZ_DIAGNOSTIC_ASSERT(aStream);
+
+  // Step 2: Let reader be the result of getting a reader for body’s stream.
+  RefPtr<ReadableStreamDefaultReader> reader = aStream->GetReader(aRv);
+  if (aRv.Failed()) {
+    CloseAndRelease(aCx, NS_ERROR_DOM_INVALID_STATE_ERR);
+    return;
+  }
+
+  mReader = reader;
+
+  mAsyncWaitWorkerRef = mWorkerRef;
+  aRv = mPipeOut->AsyncWait(this, 0, 0, mOwningEventTarget);
+  if (NS_WARN_IF(aRv.Failed())) {
+    mAsyncWaitWorkerRef = nullptr;
+    CloseAndRelease(aCx, NS_ERROR_DOM_INVALID_STATE_ERR);
+  }
+}
+
+struct FetchReadRequest : public ReadRequest {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(FetchReadRequest, ReadRequest)
+
+  explicit FetchReadRequest(FetchStreamReader* aReader)
+      : mFetchStreamReader(aReader) {}
+
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  void ChunkSteps(JSContext* aCx, JS::Handle<JS::Value> aChunk,
+                  ErrorResult& aRv) override {
+    mFetchStreamReader->ChunkSteps(aCx, aChunk, aRv);
+  }
+
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  void CloseSteps(JSContext* aCx, ErrorResult& aRv) override {
+    mFetchStreamReader->CloseSteps(aCx, aRv);
+  }
+
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  void ErrorSteps(JSContext* aCx, JS::Handle<JS::Value> aError,
+                  ErrorResult& aRv) override {
+    mFetchStreamReader->ErrorSteps(aCx, aError, aRv);
+  }
+
+ protected:
+  virtual ~FetchReadRequest() = default;
+
+  MOZ_KNOWN_LIVE RefPtr<FetchStreamReader> mFetchStreamReader;
+};
+
+NS_IMPL_CYCLE_COLLECTION_INHERITED(FetchReadRequest, ReadRequest,
+                                   mFetchStreamReader)
+NS_IMPL_ADDREF_INHERITED(FetchReadRequest, ReadRequest)
+NS_IMPL_RELEASE_INHERITED(FetchReadRequest, ReadRequest)
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(FetchReadRequest)
+NS_INTERFACE_MAP_END_INHERITING(ReadRequest)
+
+// nsIOutputStreamCallback interface
+MOZ_CAN_RUN_SCRIPT_BOUNDARY
+NS_IMETHODIMP
+FetchStreamReader::OnOutputStreamReady(nsIAsyncOutputStream* aStream) {
+  NS_ASSERT_OWNINGTHREAD(FetchStreamReader);
+  if (mStreamClosed) {
+    mAsyncWaitWorkerRef = nullptr;
+    return NS_OK;
+  }
+
+  AutoEntryScript aes(mGlobal, "ReadableStreamReader.read", !mWorkerRef);
+  if (!Process(aes.cx())) {
+    // We're done processing data, and haven't queued up a new AsyncWait - we
+    // can clear our mAsyncWaitWorkerRef.
+    mAsyncWaitWorkerRef = nullptr;
+  }
+  return NS_OK;
+}
+
+bool FetchStreamReader::Process(JSContext* aCx) {
+  NS_ASSERT_OWNINGTHREAD(FetchStreamReader);
+  MOZ_ASSERT(mReader);
+
+  if (!mBuffer.IsEmpty()) {
+    nsresult rv = WriteBuffer();
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      CloseAndRelease(aCx, NS_ERROR_DOM_ABORT_ERR);
+      return false;
+    }
+    return true;
+  }
+
+  // Check if the output stream has already been closed. This lets us propagate
+  // errors eagerly, and detect output stream closures even when we have no data
+  // to write.
+  if (NS_WARN_IF(NS_FAILED(mPipeOut->StreamStatus()))) {
+    CloseAndRelease(aCx, NS_ERROR_DOM_ABORT_ERR);
+    return false;
+  }
+
+  // We're waiting on new data - set up a WAIT_CLOSURE_ONLY callback so we
+  // notice if the reader closes.
+  nsresult rv = mPipeOut->AsyncWait(
+      this, nsIAsyncOutputStream::WAIT_CLOSURE_ONLY, 0, mOwningEventTarget);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    CloseAndRelease(aCx, NS_ERROR_DOM_INVALID_STATE_ERR);
+    return false;
+  }
+
+  // If we already have an outstanding read request, don't start another one
+  // concurrently.
+  if (!mHasOutstandingReadRequest) {
+    // https://fetch.spec.whatwg.org/#incrementally-read-loop
+    // The below very loosely tries to implement the incrementally-read-loop
+    // from the fetch spec.
+    // Step 2: Read a chunk from reader given readRequest.
+    RefPtr<ReadRequest> readRequest = new FetchReadRequest(this);
+    RefPtr<ReadableStreamDefaultReader> reader = mReader;
+    mHasOutstandingReadRequest = true;
+
+    IgnoredErrorResult err;
+    reader->ReadChunk(aCx, *readRequest, err);
+    if (NS_WARN_IF(err.Failed())) {
+      // Let's close the stream.
+      mHasOutstandingReadRequest = false;
+      CloseAndRelease(aCx, NS_ERROR_DOM_INVALID_STATE_ERR);
+      // Don't return false, as we've already called `AsyncWait`.
+    }
+  }
+  return true;
+}
+
+void FetchStreamReader::ChunkSteps(JSContext* aCx, JS::Handle<JS::Value> aChunk,
+                                   ErrorResult& aRv) {
+  // This roughly implements the chunk steps from
+  // https://fetch.spec.whatwg.org/#incrementally-read-loop.
+
+  mHasOutstandingReadRequest = false;
+
+  // Step 2. If chunk is not a Uint8Array object, then set continueAlgorithm to
+  // this step: run processBodyError given a TypeError.
+  RootedSpiderMonkeyInterface<Uint8Array> chunk(aCx);
+  if (!aChunk.isObject() || !chunk.Init(&aChunk.toObject())) {
+    CloseAndRelease(aCx, NS_ERROR_DOM_WRONG_TYPE_ERR);
+    return;
+  }
+  chunk.ComputeState();
+
+  MOZ_DIAGNOSTIC_ASSERT(mBuffer.IsEmpty());
+
+  // Let's take a copy of the data.
+  // FIXME: We could sometimes avoid this copy by trying to write `chunk`
+  // directly into `mPipeOut` eagerly, and only filling `mBuffer` if there isn't
+  // enough space in the pipe's buffer.
+  if (!mBuffer.AppendElements(chunk.Data(), chunk.Length(), fallible)) {
+    CloseAndRelease(aCx, NS_ERROR_OUT_OF_MEMORY);
+    return;
+  }
+
+  mBufferOffset = 0;
+  mBufferRemaining = chunk.Length();
+
+  nsresult rv = WriteBuffer();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    CloseAndRelease(aCx, NS_ERROR_DOM_ABORT_ERR);
+  }
+}
+
+void FetchStreamReader::CloseSteps(JSContext* aCx, ErrorResult& aRv) {
+  mHasOutstandingReadRequest = false;
+  CloseAndRelease(aCx, NS_BASE_STREAM_CLOSED);
+}
+
+void FetchStreamReader::ErrorSteps(JSContext* aCx, JS::Handle<JS::Value> aError,
+                                   ErrorResult& aRv) {
+  mHasOutstandingReadRequest = false;
+  ReportErrorToConsole(aCx, aError);
+  CloseAndRelease(aCx, NS_ERROR_FAILURE);
+}
+
+nsresult FetchStreamReader::WriteBuffer() {
+  MOZ_ASSERT(mBuffer.Length() == (mBufferOffset + mBufferRemaining));
+
+  char* data = reinterpret_cast<char*>(mBuffer.Elements());
+
+  while (mBufferRemaining > 0) {
+    uint32_t written = 0;
+    nsresult rv =
+        mPipeOut->Write(data + mBufferOffset, mBufferRemaining, &written);
+
+    if (rv == NS_BASE_STREAM_WOULD_BLOCK) {
+      break;
+    }
+
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    MOZ_ASSERT(written <= mBufferRemaining);
+    mBufferRemaining -= written;
+    mBufferOffset += written;
+
+    if (mBufferRemaining == 0) {
+      mBuffer.Clear();
+      break;
+    }
+  }
+
+  nsresult rv = mPipeOut->AsyncWait(this, 0, 0, mOwningEventTarget);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+void FetchStreamReader::ReportErrorToConsole(JSContext* aCx,
+                                             JS::Handle<JS::Value> aValue) {
+  nsCString sourceSpec;
+  uint32_t line = 0;
+  uint32_t column = 0;
+  nsString valueString;
+
+  nsContentUtils::ExtractErrorValues(aCx, aValue, sourceSpec, &line, &column,
+                                     valueString);
+
+  nsTArray<nsString> params;
+  params.AppendElement(valueString);
+
+  RefPtr<ConsoleReportCollector> reporter = new ConsoleReportCollector();
+  reporter->AddConsoleReport(nsIScriptError::errorFlag,
+                             "ReadableStreamReader.read"_ns,
+                             nsContentUtils::eDOM_PROPERTIES, sourceSpec, line,
+                             column, "ReadableStreamReadingFailed"_ns, params);
+
+  uint64_t innerWindowId = 0;
+
+  if (NS_IsMainThread()) {
+    nsCOMPtr<nsPIDOMWindowInner> window = do_QueryInterface(mGlobal);
+    if (window) {
+      innerWindowId = window->WindowID();
+    }
+    reporter->FlushReportsToConsole(innerWindowId);
+    return;
+  }
+
+  WorkerPrivate* workerPrivate = GetWorkerPrivateFromContext(aCx);
+  if (workerPrivate) {
+    innerWindowId = workerPrivate->WindowID();
+  }
+
+  RefPtr<Runnable> r = NS_NewRunnableFunction(
+      "FetchStreamReader::ReportErrorToConsole", [reporter, innerWindowId]() {
+        reporter->FlushReportsToConsole(innerWindowId);
+      });
+
+  workerPrivate->DispatchToMainThread(r.forget());
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/fetch/FetchStreamReader.h b/dom/fetch/FetchStreamReader.h
new file mode 100644
index 0000000000..65d94d8cb0
--- /dev/null
+++ b/dom/fetch/FetchStreamReader.h
@@ -0,0 +1,94 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_FetchStreamReader_h
+#define mozilla_dom_FetchStreamReader_h
+
+#include "js/RootingAPI.h"
+#include "js/TypeDecls.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/dom/FetchBinding.h"
+#include "mozilla/dom/PromiseNativeHandler.h"
+#include "nsIAsyncOutputStream.h"
+#include "nsIGlobalObject.h"
+
+namespace mozilla::dom {
+
+class ReadableStream;
+class ReadableStreamDefaultReader;
+class StrongWorkerRef;
+
+class FetchStreamReader final : public nsIOutputStreamCallback {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_AMBIGUOUS(
+      FetchStreamReader, nsIOutputStreamCallback)
+  NS_DECL_NSIOUTPUTSTREAMCALLBACK
+
+  // This creates a nsIInputStream able to retrieve data from the ReadableStream
+  // object. The reading starts when StartConsuming() is called.
+  static nsresult Create(JSContext* aCx, nsIGlobalObject* aGlobal,
+                         FetchStreamReader** aStreamReader,
+                         nsIInputStream** aInputStream);
+
+  MOZ_CAN_RUN_SCRIPT
+  void ChunkSteps(JSContext* aCx, JS::Handle<JS::Value> aChunk,
+                  ErrorResult& aRv);
+  MOZ_CAN_RUN_SCRIPT
+  void CloseSteps(JSContext* aCx, ErrorResult& aRv);
+  MOZ_CAN_RUN_SCRIPT
+  void ErrorSteps(JSContext* aCx, JS::Handle<JS::Value> aError,
+                  ErrorResult& aRv);
+
+  // Idempotently close the output stream and null out all state. If aCx is
+  // provided, the reader will also be canceled.  aStatus must be a DOM error
+  // as understood by DOMException because it will be provided as the
+  // cancellation reason.
+  //
+  // This is a script boundary minimize annotation changes required while
+  // we figure out how to handle some more tricky annotation cases (for
+  // example, the destructor of this class. Tracking under Bug 1750656)
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  void CloseAndRelease(JSContext* aCx, nsresult aStatus);
+
+  void StartConsuming(JSContext* aCx, ReadableStream* aStream,
+                      ErrorResult& aRv);
+
+ private:
+  explicit FetchStreamReader(nsIGlobalObject* aGlobal);
+  ~FetchStreamReader();
+
+  nsresult WriteBuffer();
+
+  // Attempt to copy data from mBuffer into mPipeOut. Returns `true` if data was
+  // written, and AsyncWait callbacks or FetchReadRequest calls have been set up
+  // to write more data in the future, and `false` otherwise.
+  MOZ_CAN_RUN_SCRIPT
+  bool Process(JSContext* aCx);
+
+  void ReportErrorToConsole(JSContext* aCx, JS::Handle<JS::Value> aValue);
+
+  nsCOMPtr<nsIGlobalObject> mGlobal;
+  nsCOMPtr<nsIEventTarget> mOwningEventTarget;
+
+  nsCOMPtr<nsIAsyncOutputStream> mPipeOut;
+
+  RefPtr<StrongWorkerRef> mWorkerRef;
+  RefPtr<StrongWorkerRef> mAsyncWaitWorkerRef;
+
+  RefPtr<ReadableStreamDefaultReader> mReader;
+
+  nsTArray<uint8_t> mBuffer;
+  uint32_t mBufferRemaining = 0;
+  uint32_t mBufferOffset = 0;
+
+  bool mHasOutstandingReadRequest = false;
+  bool mStreamClosed = false;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_FetchStreamReader_h
diff --git a/dom/fetch/FetchStreamUtils.cpp b/dom/fetch/FetchStreamUtils.cpp
new file mode 100644
index 0000000000..d9cb762526
--- /dev/null
+++ b/dom/fetch/FetchStreamUtils.cpp
@@ -0,0 +1,83 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "FetchStreamUtils.h"
+
+#include "mozilla/NotNull.h"
+#include "mozilla/RemoteLazyInputStreamChild.h"
+#include "mozilla/RemoteLazyInputStreamStorage.h"
+#include "mozilla/dom/FetchTypes.h"
+#include "mozilla/dom/IPCBlob.h"
+#include "mozilla/ipc/IPCStreamUtils.h"
+#include "nsContentUtils.h"
+#include "nsXULAppAPI.h"
+
+namespace mozilla::dom {
+
+namespace {
+
+RefPtr<RemoteLazyInputStreamStorage> GetRemoteLazyInputStreamStorage() {
+  auto storageOrErr = RemoteLazyInputStreamStorage::Get();
+  MOZ_ASSERT(storageOrErr.isOk());
+  return storageOrErr.unwrap();
+}
+
+}  // namespace
+
+NotNull<nsCOMPtr<nsIInputStream>> ToInputStream(
+    const ParentToParentStream& aStream) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  return WrapNotNull(
+      GetRemoteLazyInputStreamStorage()->ForgetStream(aStream.uuid()));
+}
+
+NotNull<nsCOMPtr<nsIInputStream>> ToInputStream(
+    const ParentToChildStream& aStream) {
+  MOZ_ASSERT(XRE_IsContentProcess());
+  nsCOMPtr<nsIInputStream> result;
+  if (aStream.type() == ParentToChildStream::TRemoteLazyInputStream) {
+    result = aStream.get_RemoteLazyInputStream();
+  } else {
+    result = DeserializeIPCStream(aStream.get_IPCStream());
+  }
+  return WrapNotNull(result);
+}
+
+ParentToParentStream ToParentToParentStream(
+    const NotNull<nsCOMPtr<nsIInputStream>>& aStream, int64_t aStreamSize) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+
+  ParentToParentStream stream;
+  stream.uuid() = nsID::GenerateUUID();
+  GetRemoteLazyInputStreamStorage()->AddStream(aStream.get(), stream.uuid());
+  return stream;
+}
+
+ParentToChildStream ToParentToChildStream(
+    const NotNull<nsCOMPtr<nsIInputStream>>& aStream, int64_t aStreamSize,
+    NotNull<mozilla::ipc::PBackgroundParent*> aBackgroundParent,
+    bool aSerializeAsLazy) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+
+  ParentToChildStream result;
+  if (aSerializeAsLazy) {
+    result = RemoteLazyInputStream::WrapStream(aStream.get());
+  } else {
+    nsCOMPtr<nsIInputStream> stream(aStream.get());
+    mozilla::ipc::IPCStream ipcStream;
+    Unused << NS_WARN_IF(
+        !mozilla::ipc::SerializeIPCStream(stream.forget(), ipcStream, false));
+    result = ipcStream;
+  }
+  return result;
+}
+
+ParentToChildStream ToParentToChildStream(
+    const ParentToParentStream& aStream, int64_t aStreamSize,
+    NotNull<mozilla::ipc::PBackgroundParent*> aBackgroundParent) {
+  return ToParentToChildStream(ToInputStream(aStream), aStreamSize,
+                               aBackgroundParent);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/fetch/FetchStreamUtils.h b/dom/fetch/FetchStreamUtils.h
new file mode 100644
index 0000000000..407339df41
--- /dev/null
+++ b/dom/fetch/FetchStreamUtils.h
@@ -0,0 +1,56 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef _mozilla_dom_fetch_FetchStreamUtils_h
+#define _mozilla_dom_fetch_FetchStreamUtils_h
+
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/NotNull.h"
+#include "mozilla/dom/FetchTypes.h"
+
+#include "nsIInputStream.h"
+
+#include <cstdint>
+
+namespace mozilla {
+
+namespace ipc {
+class PBackgroundParent;
+}
+
+namespace dom {
+
+// Convert a ParentToParentStream received over IPC to an nsIInputStream. Can
+// only be called in the parent process.
+NotNull<nsCOMPtr<nsIInputStream>> ToInputStream(
+    const ParentToParentStream& aStream);
+
+// Convert a ParentToChildStream received over IPC to an nsIInputStream. Can
+// only be called in a content process.
+NotNull<nsCOMPtr<nsIInputStream>> ToInputStream(
+    const ParentToChildStream& aStream);
+
+// Serialize an nsIInputStream for IPC inside the parent process. Can only be
+// called in the parent process.
+ParentToParentStream ToParentToParentStream(
+    const NotNull<nsCOMPtr<nsIInputStream>>& aStream, int64_t aStreamSize);
+
+// Serialize an nsIInputStream for IPC from the parent process to a content
+// process. Can only be called in the parent process.
+ParentToChildStream ToParentToChildStream(
+    const NotNull<nsCOMPtr<nsIInputStream>>& aStream, int64_t aStreamSize,
+    NotNull<mozilla::ipc::PBackgroundParent*> aBackgroundParent,
+    bool aSerializeAsLazy = true);
+
+// Convert a ParentToParentStream to a ParentToChildStream. Can only be called
+// in the parent process.
+ParentToChildStream ToParentToChildStream(
+    const ParentToParentStream& aStream, int64_t aStreamSize,
+    NotNull<mozilla::ipc::PBackgroundParent*> aBackgroundParent);
+
+}  // namespace dom
+
+}  // namespace mozilla
+
+#endif  // _mozilla_dom_fetch_FetchStreamUtils_h
diff --git a/dom/fetch/FetchTypes.ipdlh b/dom/fetch/FetchTypes.ipdlh
new file mode 100644
index 0000000000..f8c594bf1a
--- /dev/null
+++ b/dom/fetch/FetchTypes.ipdlh
@@ -0,0 +1,127 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+include IPCStream;
+include PBackgroundSharedTypes;
+include PerformanceTimingTypes;
+include NeckoChannelParams;
+
+include "mozilla/dom/FetchIPCTypes.h";
+include "mozilla/ipc/TransportSecurityInfoUtils.h";
+
+using mozilla::dom::HeadersGuardEnum from "mozilla/dom/HeadersBinding.h";
+using mozilla::dom::ReferrerPolicy from "mozilla/dom/ReferrerPolicyBinding.h";
+using mozilla::dom::RequestCache from "mozilla/dom/RequestBinding.h";
+using mozilla::dom::RequestCredentials from "mozilla/dom/RequestBinding.h";
+using mozilla::dom::RequestRedirect from "mozilla/dom/RequestBinding.h";
+using mozilla::dom::ResponseType from "mozilla/dom/ResponseBinding.h";
+using struct nsID from "nsID.h";
+using mozilla::dom::FetchDriverObserver::EndReason from "mozilla/dom/FetchDriver.h";
+using nsILoadInfo::CrossOriginEmbedderPolicy from "nsILoadInfo.h";
+[RefCounted] using class mozilla::RemoteLazyInputStream from "mozilla/RemoteLazyInputStream.h";
+[RefCounted] using class nsITransportSecurityInfo from "nsITransportSecurityInfo.h";
+
+namespace mozilla {
+namespace dom {
+
+struct HeadersEntry {
+  nsCString name;
+  nsCString value;
+};
+
+struct ParentToParentStream {
+  // Used as a key for RemoteLazyInputStreamStorage
+  nsID uuid;
+};
+
+union ParentToChildStream {
+  nullable RemoteLazyInputStream;
+  IPCStream;
+};
+
+struct ChildToParentStream {
+  IPCStream stream;
+};
+
+union BodyStreamVariant {
+  ParentToParentStream;
+  ParentToChildStream;
+  ChildToParentStream;
+};
+
+struct IPCInternalRequest {
+  nsCString method;
+  nsCString[] urlList;
+  HeadersGuardEnum headersGuard;
+  HeadersEntry[] headers;
+  BodyStreamVariant? body;
+  int64_t bodySize;
+  nsCString preferredAlternativeDataType;
+  uint32_t contentPolicyType;
+  nsString referrer;
+  ReferrerPolicy referrerPolicy;
+  ReferrerPolicy environmentReferrerPolicy;
+  RequestMode requestMode;
+  RequestCredentials requestCredentials;
+  RequestCache cacheMode;
+  RequestRedirect requestRedirect;
+  nsString integrity;
+  nsCString fragment;
+  PrincipalInfo? principalInfo;
+  PrincipalInfo? interceptionTriggeringPrincipalInfo;
+  uint32_t interceptionContentPolicyType;
+  RedirectHistoryEntryInfo[] interceptionRedirectChain;
+  bool interceptionFromThirdParty;
+  CrossOriginEmbedderPolicy embedderPolicy;
+};
+
+struct InternalResponseMetadata {
+  ResponseType type;
+  nsCString[] urlList;
+  uint16_t status;
+  nsCString statusText;
+  HeadersGuardEnum headersGuard;
+  HeadersEntry[] headers;
+  nsresult errorCode;
+  nsCString alternativeDataType;
+  nullable nsITransportSecurityInfo securityInfo;
+  PrincipalInfo? principalInfo;
+  nsCString bodyBlobURISpec;
+  nsString bodyLocalPath;
+  RequestCredentials credentialsMode;
+};
+
+struct ParentToParentInternalResponse {
+  InternalResponseMetadata metadata;
+  ParentToParentStream? body;
+  int64_t bodySize;
+  ParentToParentStream? alternativeBody;
+};
+
+struct ParentToChildInternalResponse {
+  InternalResponseMetadata metadata;
+  ParentToChildStream? body;
+  int64_t bodySize;
+  ParentToChildStream? alternativeBody;
+};
+
+struct ChildToParentInternalResponse {
+  InternalResponseMetadata metadata;
+  ChildToParentStream? body;
+  int64_t bodySize;
+  ChildToParentStream? alternativeBody;
+};
+
+struct ResponseTiming {
+  IPCPerformanceTimingData timingData;
+  nsString initiatorType;
+  nsString entryName;
+};
+
+struct ResponseEndArgs {
+  EndReason endReason;
+};
+
+} // namespace ipc
+} // namespace mozilla
diff --git a/dom/fetch/FetchUtil.cpp b/dom/fetch/FetchUtil.cpp
new file mode 100644
index 0000000000..48281df321
--- /dev/null
+++ b/dom/fetch/FetchUtil.cpp
@@ -0,0 +1,814 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "FetchUtil.h"
+
+#include "zlib.h"
+
+#include "js/friend/ErrorMessages.h"  // JSMSG_*
+#include "nsCRT.h"
+#include "nsError.h"
+#include "nsIAsyncInputStream.h"
+#include "nsICloneableInputStream.h"
+#include "nsIHttpChannel.h"
+#include "nsNetUtil.h"
+#include "nsStreamUtils.h"
+#include "nsString.h"
+#include "js/BuildId.h"
+#include "mozilla/dom/Document.h"
+
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/dom/DOMException.h"
+#include "mozilla/dom/InternalRequest.h"
+#include "mozilla/dom/Response.h"
+#include "mozilla/dom/ReferrerInfo.h"
+#include "mozilla/dom/WorkerRef.h"
+
+namespace mozilla::dom {
+
+// static
+nsresult FetchUtil::GetValidRequestMethod(const nsACString& aMethod,
+                                          nsCString& outMethod) {
+  nsAutoCString upperCaseMethod(aMethod);
+  ToUpperCase(upperCaseMethod);
+  if (!NS_IsValidHTTPToken(aMethod)) {
+    outMethod.SetIsVoid(true);
+    return NS_ERROR_DOM_SYNTAX_ERR;
+  }
+
+  if (upperCaseMethod.EqualsLiteral("CONNECT") ||
+      upperCaseMethod.EqualsLiteral("TRACE") ||
+      upperCaseMethod.EqualsLiteral("TRACK")) {
+    outMethod.SetIsVoid(true);
+    return NS_ERROR_DOM_SECURITY_ERR;
+  }
+
+  if (upperCaseMethod.EqualsLiteral("DELETE") ||
+      upperCaseMethod.EqualsLiteral("GET") ||
+      upperCaseMethod.EqualsLiteral("HEAD") ||
+      upperCaseMethod.EqualsLiteral("OPTIONS") ||
+      upperCaseMethod.EqualsLiteral("POST") ||
+      upperCaseMethod.EqualsLiteral("PUT")) {
+    outMethod = upperCaseMethod;
+  } else {
+    outMethod = aMethod;  // Case unchanged for non-standard methods
+  }
+  return NS_OK;
+}
+
+static bool FindCRLF(nsACString::const_iterator& aStart,
+                     nsACString::const_iterator& aEnd) {
+  nsACString::const_iterator end(aEnd);
+  return FindInReadable("\r\n"_ns, aStart, end);
+}
+
+// Reads over a CRLF and positions start after it.
+static bool PushOverLine(nsACString::const_iterator& aStart,
+                         const nsACString::const_iterator& aEnd) {
+  if (*aStart == nsCRT::CR && (aEnd - aStart > 1) && *(++aStart) == nsCRT::LF) {
+    ++aStart;  // advance to after CRLF
+    return true;
+  }
+
+  return false;
+}
+
+// static
+bool FetchUtil::ExtractHeader(nsACString::const_iterator& aStart,
+                              nsACString::const_iterator& aEnd,
+                              nsCString& aHeaderName, nsCString& aHeaderValue,
+                              bool* aWasEmptyHeader) {
+  MOZ_ASSERT(aWasEmptyHeader);
+  // Set it to a valid value here so we don't forget later.
+  *aWasEmptyHeader = false;
+
+  const char* beginning = aStart.get();
+  nsACString::const_iterator end(aEnd);
+  if (!FindCRLF(aStart, end)) {
+    return false;
+  }
+
+  if (aStart.get() == beginning) {
+    *aWasEmptyHeader = true;
+    return true;
+  }
+
+  nsAutoCString header(beginning, aStart.get() - beginning);
+
+  nsACString::const_iterator headerStart, iter, headerEnd;
+  header.BeginReading(headerStart);
+  header.EndReading(headerEnd);
+  iter = headerStart;
+  if (!FindCharInReadable(':', iter, headerEnd)) {
+    return false;
+  }
+
+  aHeaderName.Assign(StringHead(header, iter - headerStart));
+  aHeaderName.CompressWhitespace();
+  if (!NS_IsValidHTTPToken(aHeaderName)) {
+    return false;
+  }
+
+  aHeaderValue.Assign(Substring(++iter, headerEnd));
+  if (!NS_IsReasonableHTTPHeaderValue(aHeaderValue)) {
+    return false;
+  }
+  aHeaderValue.CompressWhitespace();
+
+  return PushOverLine(aStart, aEnd);
+}
+
+// static
+nsresult FetchUtil::SetRequestReferrer(nsIPrincipal* aPrincipal, Document* aDoc,
+                                       nsIHttpChannel* aChannel,
+                                       InternalRequest& aRequest) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  nsresult rv = NS_OK;
+  nsAutoString referrer;
+  aRequest.GetReferrer(referrer);
+
+  ReferrerPolicy policy = aRequest.ReferrerPolicy_();
+  nsCOMPtr<nsIReferrerInfo> referrerInfo;
+  if (referrer.IsEmpty()) {
+    // This is the case request’s referrer is "no-referrer"
+    referrerInfo = new ReferrerInfo(nullptr, ReferrerPolicy::No_referrer);
+  } else if (referrer.EqualsLiteral(kFETCH_CLIENT_REFERRER_STR)) {
+    referrerInfo = ReferrerInfo::CreateForFetch(aPrincipal, aDoc);
+    // In the first step, we should use referrer info from requetInit
+    referrerInfo = static_cast<ReferrerInfo*>(referrerInfo.get())
+                       ->CloneWithNewPolicy(policy);
+  } else {
+    // From "Determine request's Referrer" step 3
+    // "If request's referrer is a URL, let referrerSource be request's
+    // referrer."
+    nsCOMPtr<nsIURI> referrerURI;
+    rv = NS_NewURI(getter_AddRefs(referrerURI), referrer);
+    NS_ENSURE_SUCCESS(rv, rv);
+    referrerInfo = new ReferrerInfo(referrerURI, policy);
+  }
+
+  rv = aChannel->SetReferrerInfoWithoutClone(referrerInfo);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsAutoString computedReferrerSpec;
+  referrerInfo = aChannel->GetReferrerInfo();
+  if (referrerInfo) {
+    Unused << referrerInfo->GetComputedReferrerSpec(computedReferrerSpec);
+  }
+
+  // Step 8 https://fetch.spec.whatwg.org/#main-fetch
+  // If request’s referrer is not "no-referrer", set request’s referrer to
+  // the result of invoking determine request’s referrer.
+  aRequest.SetReferrer(computedReferrerSpec);
+
+  return NS_OK;
+}
+
+class StoreOptimizedEncodingRunnable final : public Runnable {
+  nsMainThreadPtrHandle<nsICacheInfoChannel> mCache;
+  Vector<uint8_t> mBytes;
+
+ public:
+  StoreOptimizedEncodingRunnable(
+      nsMainThreadPtrHandle<nsICacheInfoChannel>&& aCache,
+      Vector<uint8_t>&& aBytes)
+      : Runnable("StoreOptimizedEncodingRunnable"),
+        mCache(std::move(aCache)),
+        mBytes(std::move(aBytes)) {}
+
+  NS_IMETHOD Run() override {
+    nsresult rv;
+
+    nsCOMPtr<nsIAsyncOutputStream> stream;
+    rv = mCache->OpenAlternativeOutputStream(FetchUtil::WasmAltDataType,
+                                             int64_t(mBytes.length()),
+                                             getter_AddRefs(stream));
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    auto closeStream = MakeScopeExit([&]() { stream->CloseWithStatus(rv); });
+
+    uint32_t written;
+    rv = stream->Write((char*)mBytes.begin(), mBytes.length(), &written);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    MOZ_RELEASE_ASSERT(mBytes.length() == written);
+    return NS_OK;
+  };
+};
+
+class WindowStreamOwner final : public nsIObserver,
+                                public nsSupportsWeakReference {
+  // Read from any thread but only set/cleared on the main thread. The lifecycle
+  // of WindowStreamOwner prevents concurrent read/clear.
+  nsCOMPtr<nsIAsyncInputStream> mStream;
+
+  nsCOMPtr<nsIGlobalObject> mGlobal;
+
+  ~WindowStreamOwner() {
+    MOZ_ASSERT(NS_IsMainThread());
+
+    nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+    if (obs) {
+      obs->RemoveObserver(this, DOM_WINDOW_DESTROYED_TOPIC);
+    }
+  }
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  WindowStreamOwner(nsIAsyncInputStream* aStream, nsIGlobalObject* aGlobal)
+      : mStream(aStream), mGlobal(aGlobal) {
+    MOZ_DIAGNOSTIC_ASSERT(mGlobal);
+    MOZ_ASSERT(NS_IsMainThread());
+  }
+
+  static already_AddRefed<WindowStreamOwner> Create(
+      nsIAsyncInputStream* aStream, nsIGlobalObject* aGlobal) {
+    nsCOMPtr<nsIObserverService> os = mozilla::services::GetObserverService();
+    if (NS_WARN_IF(!os)) {
+      return nullptr;
+    }
+
+    RefPtr<WindowStreamOwner> self = new WindowStreamOwner(aStream, aGlobal);
+
+    // Holds nsIWeakReference to self.
+    nsresult rv = os->AddObserver(self, DOM_WINDOW_DESTROYED_TOPIC, true);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return nullptr;
+    }
+
+    return self.forget();
+  }
+
+  // nsIObserver:
+
+  NS_IMETHOD
+  Observe(nsISupports* aSubject, const char* aTopic,
+          const char16_t* aData) override {
+    MOZ_ASSERT(NS_IsMainThread());
+    MOZ_DIAGNOSTIC_ASSERT(strcmp(aTopic, DOM_WINDOW_DESTROYED_TOPIC) == 0);
+
+    if (!mStream) {
+      return NS_OK;
+    }
+
+    nsCOMPtr<nsPIDOMWindowInner> window = do_QueryInterface(mGlobal);
+    if (!SameCOMIdentity(aSubject, window)) {
+      return NS_OK;
+    }
+
+    // mStream->Close() will call JSStreamConsumer::OnInputStreamReady which may
+    // then destory itself, dropping the last reference to 'this'.
+    RefPtr<WindowStreamOwner> keepAlive(this);
+
+    mStream->Close();
+    mStream = nullptr;
+    mGlobal = nullptr;
+    return NS_OK;
+  }
+};
+
+NS_IMPL_ISUPPORTS(WindowStreamOwner, nsIObserver, nsISupportsWeakReference)
+
+inline nsISupports* ToSupports(WindowStreamOwner* aObj) {
+  return static_cast<nsIObserver*>(aObj);
+}
+
+class WorkerStreamOwner final {
+ public:
+  NS_INLINE_DECL_REFCOUNTING(WorkerStreamOwner)
+
+  explicit WorkerStreamOwner(nsIAsyncInputStream* aStream,
+                             nsCOMPtr<nsIEventTarget>&& target)
+      : mStream(aStream), mOwningEventTarget(std::move(target)) {}
+
+  static already_AddRefed<WorkerStreamOwner> Create(
+      nsIAsyncInputStream* aStream, WorkerPrivate* aWorker,
+      nsCOMPtr<nsIEventTarget>&& target) {
+    RefPtr<WorkerStreamOwner> self =
+        new WorkerStreamOwner(aStream, std::move(target));
+
+    self->mWorkerRef =
+        StrongWorkerRef::Create(aWorker, "JSStreamConsumer", [self]() {
+          if (self->mStream) {
+            // If this Close() calls JSStreamConsumer::OnInputStreamReady and
+            // drops the last reference to the JSStreamConsumer, 'this' will not
+            // be destroyed since ~JSStreamConsumer() only enqueues a release
+            // proxy.
+            self->mStream->Close();
+            self->mStream = nullptr;
+          }
+        });
+
+    if (!self->mWorkerRef) {
+      return nullptr;
+    }
+
+    return self.forget();
+  }
+
+  static void ProxyRelease(already_AddRefed<WorkerStreamOwner> aDoomed) {
+    RefPtr<WorkerStreamOwner> doomed = aDoomed;
+    nsIEventTarget* target = doomed->mOwningEventTarget;
+    NS_ProxyRelease("WorkerStreamOwner", target, doomed.forget(),
+                    /* aAlwaysProxy = */ true);
+  }
+
+ private:
+  ~WorkerStreamOwner() = default;
+
+  // Read from any thread but only set/cleared on the worker thread. The
+  // lifecycle of WorkerStreamOwner prevents concurrent read/clear.
+  nsCOMPtr<nsIAsyncInputStream> mStream;
+  RefPtr<StrongWorkerRef> mWorkerRef;
+  nsCOMPtr<nsIEventTarget> mOwningEventTarget;
+};
+
+class JSStreamConsumer final : public nsIInputStreamCallback,
+                               public JS::OptimizedEncodingListener {
+  // A LengthPrefixType is stored at the start of the compressed optimized
+  // encoding, allowing the decompressed buffer to be allocated to exactly
+  // the right size.
+  using LengthPrefixType = uint32_t;
+  static const unsigned PrefixBytes = sizeof(LengthPrefixType);
+
+  RefPtr<WindowStreamOwner> mWindowStreamOwner;
+  RefPtr<WorkerStreamOwner> mWorkerStreamOwner;
+  nsMainThreadPtrHandle<nsICacheInfoChannel> mCache;
+  const bool mOptimizedEncoding;
+  z_stream mZStream;
+  bool mZStreamInitialized;
+  Vector<uint8_t> mOptimizedEncodingBytes;
+  JS::StreamConsumer* mConsumer;
+  bool mConsumerAborted;
+
+  JSStreamConsumer(already_AddRefed<WindowStreamOwner> aWindowStreamOwner,
+                   nsIGlobalObject* aGlobal, JS::StreamConsumer* aConsumer,
+                   nsMainThreadPtrHandle<nsICacheInfoChannel>&& aCache,
+                   bool aOptimizedEncoding)
+      : mWindowStreamOwner(aWindowStreamOwner),
+        mCache(std::move(aCache)),
+        mOptimizedEncoding(aOptimizedEncoding),
+        mZStreamInitialized(false),
+        mConsumer(aConsumer),
+        mConsumerAborted(false) {
+    MOZ_DIAGNOSTIC_ASSERT(mWindowStreamOwner);
+    MOZ_DIAGNOSTIC_ASSERT(mConsumer);
+  }
+
+  JSStreamConsumer(RefPtr<WorkerStreamOwner> aWorkerStreamOwner,
+                   nsIGlobalObject* aGlobal, JS::StreamConsumer* aConsumer,
+                   nsMainThreadPtrHandle<nsICacheInfoChannel>&& aCache,
+                   bool aOptimizedEncoding)
+      : mWorkerStreamOwner(std::move(aWorkerStreamOwner)),
+        mCache(std::move(aCache)),
+        mOptimizedEncoding(aOptimizedEncoding),
+        mZStreamInitialized(false),
+        mConsumer(aConsumer),
+        mConsumerAborted(false) {
+    MOZ_DIAGNOSTIC_ASSERT(mWorkerStreamOwner);
+    MOZ_DIAGNOSTIC_ASSERT(mConsumer);
+  }
+
+  ~JSStreamConsumer() {
+    if (mZStreamInitialized) {
+      inflateEnd(&mZStream);
+    }
+
+    // Both WindowStreamOwner and WorkerStreamOwner need to be destroyed on
+    // their global's event target thread.
+
+    if (mWindowStreamOwner) {
+      MOZ_DIAGNOSTIC_ASSERT(!mWorkerStreamOwner);
+      NS_ReleaseOnMainThread("JSStreamConsumer::mWindowStreamOwner",
+                             mWindowStreamOwner.forget(),
+                             /* aAlwaysProxy = */ true);
+    } else {
+      MOZ_DIAGNOSTIC_ASSERT(mWorkerStreamOwner);
+      WorkerStreamOwner::ProxyRelease(mWorkerStreamOwner.forget());
+    }
+
+    // Bug 1733674: these annotations currently do nothing, because they are
+    // member variables and the annotation mechanism only applies to locals. But
+    // the analysis could be extended so that these could replace the big-hammer
+    // ~JSStreamConsumer annotation and thus the analysis could check that
+    // nothing is added that might GC for a different reason.
+    JS_HAZ_VALUE_IS_GC_SAFE(mWindowStreamOwner);
+    JS_HAZ_VALUE_IS_GC_SAFE(mWorkerStreamOwner);
+  }
+
+  static nsresult WriteSegment(nsIInputStream* aStream, void* aClosure,
+                               const char* aFromSegment, uint32_t aToOffset,
+                               uint32_t aCount, uint32_t* aWriteCount) {
+    JSStreamConsumer* self = reinterpret_cast<JSStreamConsumer*>(aClosure);
+    MOZ_DIAGNOSTIC_ASSERT(!self->mConsumerAborted);
+
+    if (self->mOptimizedEncoding) {
+      if (!self->mZStreamInitialized) {
+        // mOptimizedEncodingBytes is used as temporary storage until we have
+        // the full prefix.
+        MOZ_ASSERT(self->mOptimizedEncodingBytes.length() < PrefixBytes);
+        uint32_t remain = PrefixBytes - self->mOptimizedEncodingBytes.length();
+        uint32_t consume = std::min(remain, aCount);
+
+        if (!self->mOptimizedEncodingBytes.append(aFromSegment, consume)) {
+          return NS_ERROR_UNEXPECTED;
+        }
+
+        if (consume == remain) {
+          // Initialize zlib once all prefix bytes are loaded.
+          LengthPrefixType length;
+          memcpy(&length, self->mOptimizedEncodingBytes.begin(), PrefixBytes);
+
+          if (!self->mOptimizedEncodingBytes.resizeUninitialized(length)) {
+            return NS_ERROR_UNEXPECTED;
+          }
+
+          memset(&self->mZStream, 0, sizeof(self->mZStream));
+          self->mZStream.avail_out = length;
+          self->mZStream.next_out = self->mOptimizedEncodingBytes.begin();
+
+          if (inflateInit(&self->mZStream) != Z_OK) {
+            return NS_ERROR_UNEXPECTED;
+          }
+          self->mZStreamInitialized = true;
+        }
+
+        *aWriteCount = consume;
+        return NS_OK;
+      }
+
+      // Zlib is initialized, overwrite the prefix with the inflated data.
+
+      MOZ_DIAGNOSTIC_ASSERT(aCount > 0);
+      self->mZStream.avail_in = aCount;
+      self->mZStream.next_in = (uint8_t*)aFromSegment;
+
+      int ret = inflate(&self->mZStream, Z_NO_FLUSH);
+
+      MOZ_DIAGNOSTIC_ASSERT(ret == Z_OK || ret == Z_STREAM_END,
+                            "corrupt optimized wasm cache file: data");
+      MOZ_DIAGNOSTIC_ASSERT(self->mZStream.avail_in == 0,
+                            "corrupt optimized wasm cache file: input");
+      MOZ_DIAGNOSTIC_ASSERT_IF(ret == Z_STREAM_END,
+                               self->mZStream.avail_out == 0);
+      // Gracefully handle corruption in release.
+      bool ok =
+          (ret == Z_OK || ret == Z_STREAM_END) && self->mZStream.avail_in == 0;
+      if (!ok) {
+        return NS_ERROR_UNEXPECTED;
+      }
+    } else {
+      // This callback can be called on any thread which is explicitly allowed
+      // by this particular JS API call.
+      if (!self->mConsumer->consumeChunk((const uint8_t*)aFromSegment,
+                                         aCount)) {
+        self->mConsumerAborted = true;
+        return NS_ERROR_UNEXPECTED;
+      }
+    }
+
+    *aWriteCount = aCount;
+    return NS_OK;
+  }
+
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+  static bool Start(nsCOMPtr<nsIInputStream> aStream, nsIGlobalObject* aGlobal,
+                    WorkerPrivate* aMaybeWorker, JS::StreamConsumer* aConsumer,
+                    nsMainThreadPtrHandle<nsICacheInfoChannel>&& aCache,
+                    bool aOptimizedEncoding) {
+    nsCOMPtr<nsIAsyncInputStream> asyncStream;
+    nsresult rv = NS_MakeAsyncNonBlockingInputStream(
+        aStream.forget(), getter_AddRefs(asyncStream));
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return false;
+    }
+
+    RefPtr<JSStreamConsumer> consumer;
+    if (aMaybeWorker) {
+      RefPtr<WorkerStreamOwner> owner = WorkerStreamOwner::Create(
+          asyncStream, aMaybeWorker,
+          aGlobal->EventTargetFor(TaskCategory::Other));
+      if (!owner) {
+        return false;
+      }
+
+      consumer = new JSStreamConsumer(std::move(owner), aGlobal, aConsumer,
+                                      std::move(aCache), aOptimizedEncoding);
+    } else {
+      RefPtr<WindowStreamOwner> owner =
+          WindowStreamOwner::Create(asyncStream, aGlobal);
+      if (!owner) {
+        return false;
+      }
+
+      consumer = new JSStreamConsumer(owner.forget(), aGlobal, aConsumer,
+                                      std::move(aCache), aOptimizedEncoding);
+    }
+
+    // This AsyncWait() creates a ref-cycle between asyncStream and consumer:
+    //
+    //   asyncStream -> consumer -> (Window|Worker)StreamOwner -> asyncStream
+    //
+    // The cycle is broken when the stream completes or errors out and
+    // asyncStream drops its reference to consumer.
+    return NS_SUCCEEDED(asyncStream->AsyncWait(consumer, 0, 0, nullptr));
+  }
+
+  // nsIInputStreamCallback:
+
+  NS_IMETHOD
+  OnInputStreamReady(nsIAsyncInputStream* aStream) override {
+    // Can be called on any stream. The JS API calls made below explicitly
+    // support being called from any thread.
+    MOZ_DIAGNOSTIC_ASSERT(!mConsumerAborted);
+
+    nsresult rv;
+
+    uint64_t available = 0;
+    rv = aStream->Available(&available);
+    if (NS_SUCCEEDED(rv) && available == 0) {
+      rv = NS_BASE_STREAM_CLOSED;
+    }
+
+    if (rv == NS_BASE_STREAM_CLOSED) {
+      if (mOptimizedEncoding) {
+        // Gracefully handle corruption of compressed data stream in release.
+        // From on investigations in bug 1738987, the incomplete data cases
+        // mostly happen during shutdown. Some corruptions in the cache entry
+        // can still happen and will be handled in the WriteSegment above.
+        bool ok = mZStreamInitialized && mZStream.avail_out == 0;
+        if (!ok) {
+          mConsumer->streamError(size_t(NS_ERROR_UNEXPECTED));
+          return NS_OK;
+        }
+
+        mConsumer->consumeOptimizedEncoding(mOptimizedEncodingBytes.begin(),
+                                            mOptimizedEncodingBytes.length());
+      } else {
+        // If there is cache entry associated with this stream, then listen for
+        // an optimized encoding so we can store it in the alt data. By JS API
+        // contract, the compilation process will hold a refcount to 'this'
+        // until it's done, optionally calling storeOptimizedEncoding().
+        mConsumer->streamEnd(mCache ? this : nullptr);
+      }
+      return NS_OK;
+    }
+
+    if (NS_FAILED(rv)) {
+      mConsumer->streamError(size_t(rv));
+      return NS_OK;
+    }
+
+    // Check mConsumerAborted before NS_FAILED to avoid calling streamError()
+    // if consumeChunk() returned false per JS API contract.
+    uint32_t written = 0;
+    rv = aStream->ReadSegments(WriteSegment, this, available, &written);
+    if (mConsumerAborted) {
+      return NS_OK;
+    }
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      mConsumer->streamError(size_t(rv));
+      return NS_OK;
+    }
+
+    rv = aStream->AsyncWait(this, 0, 0, nullptr);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      mConsumer->streamError(size_t(rv));
+      return NS_OK;
+    }
+
+    return NS_OK;
+  }
+
+  // JS::OptimizedEncodingListener
+
+  void storeOptimizedEncoding(const uint8_t* aSrcBytes,
+                              size_t aSrcLength) override {
+    MOZ_ASSERT(mCache, "we only listen if there's a cache entry");
+
+    z_stream zstream;
+    memset(&zstream, 0, sizeof(zstream));
+    zstream.avail_in = aSrcLength;
+    zstream.next_in = (uint8_t*)aSrcBytes;
+
+    // The wins from increasing compression levels are tiny, while the time
+    // to compress increases drastically. For example, for a 148mb alt-data
+    // produced by a 40mb .wasm file, the level 2 takes 2.5s to get a 3.7x size
+    // reduction while level 9 takes 22.5s to get a 4x size reduction. Read-time
+    // wins from smaller compressed cache files are not found to be
+    // significant, thus the fastest compression level is used. (On test
+    // workloads, level 2 actually was faster *and* smaller than level 1.)
+    const int COMPRESSION = 2;
+    if (deflateInit(&zstream, COMPRESSION) != Z_OK) {
+      return;
+    }
+    auto autoDestroy = MakeScopeExit([&]() { deflateEnd(&zstream); });
+
+    Vector<uint8_t> dstBytes;
+    if (!dstBytes.resizeUninitialized(PrefixBytes +
+                                      deflateBound(&zstream, aSrcLength))) {
+      return;
+    }
+
+    MOZ_RELEASE_ASSERT(LengthPrefixType(aSrcLength) == aSrcLength);
+    LengthPrefixType srcLength = aSrcLength;
+    memcpy(dstBytes.begin(), &srcLength, PrefixBytes);
+
+    uint8_t* compressBegin = dstBytes.begin() + PrefixBytes;
+    zstream.next_out = compressBegin;
+    zstream.avail_out = dstBytes.length() - PrefixBytes;
+
+    int ret = deflate(&zstream, Z_FINISH);
+    if (ret == Z_MEM_ERROR) {
+      return;
+    }
+    MOZ_RELEASE_ASSERT(ret == Z_STREAM_END);
+
+    dstBytes.shrinkTo(zstream.next_out - dstBytes.begin());
+
+    NS_DispatchToMainThread(new StoreOptimizedEncodingRunnable(
+        std::move(mCache), std::move(dstBytes)));
+  }
+};
+
+NS_IMPL_ISUPPORTS(JSStreamConsumer, nsIInputStreamCallback)
+
+// static
+const nsCString FetchUtil::WasmAltDataType;
+
+// static
+void FetchUtil::InitWasmAltDataType() {
+  nsCString& type = const_cast<nsCString&>(WasmAltDataType);
+  MOZ_ASSERT(type.IsEmpty());
+
+  RunOnShutdown([]() {
+    // Avoid nsStringBuffer leak tests failures.
+    const_cast<nsCString&>(WasmAltDataType).Truncate();
+  });
+
+  type.Append(nsLiteralCString("wasm-"));
+
+  JS::BuildIdCharVector buildId;
+  if (!JS::GetOptimizedEncodingBuildId(&buildId)) {
+    MOZ_CRASH("build id oom");
+  }
+
+  type.Append(buildId.begin(), buildId.length());
+}
+
+static bool ThrowException(JSContext* aCx, unsigned errorNumber) {
+  JS_ReportErrorNumberASCII(aCx, js::GetErrorMessage, nullptr, errorNumber);
+  return false;
+}
+
+// static
+bool FetchUtil::StreamResponseToJS(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                                   JS::MimeType aMimeType,
+                                   JS::StreamConsumer* aConsumer,
+                                   WorkerPrivate* aMaybeWorker) {
+  MOZ_ASSERT(!WasmAltDataType.IsEmpty());
+  MOZ_ASSERT(!aMaybeWorker == NS_IsMainThread());
+
+  RefPtr<Response> response;
+  nsresult rv = UNWRAP_OBJECT(Response, aObj, response);
+  if (NS_FAILED(rv)) {
+    return ThrowException(aCx, JSMSG_WASM_BAD_RESPONSE_VALUE);
+  }
+
+  const char* requiredMimeType = nullptr;
+  switch (aMimeType) {
+    case JS::MimeType::Wasm:
+      requiredMimeType = WASM_CONTENT_TYPE;
+      break;
+  }
+
+  nsAutoCString mimeType;
+  nsAutoCString mixedCaseMimeType;  // unused
+  response->GetMimeType(mimeType, mixedCaseMimeType);
+
+  if (!mimeType.EqualsASCII(requiredMimeType)) {
+    JS_ReportErrorNumberASCII(aCx, js::GetErrorMessage, nullptr,
+                              JSMSG_WASM_BAD_RESPONSE_MIME_TYPE, mimeType.get(),
+                              requiredMimeType);
+    return false;
+  }
+
+  if (response->Type() != ResponseType::Basic &&
+      response->Type() != ResponseType::Cors &&
+      response->Type() != ResponseType::Default) {
+    return ThrowException(aCx, JSMSG_WASM_BAD_RESPONSE_CORS_SAME_ORIGIN);
+  }
+
+  if (!response->Ok()) {
+    return ThrowException(aCx, JSMSG_WASM_BAD_RESPONSE_STATUS);
+  }
+
+  if (response->BodyUsed()) {
+    return ThrowException(aCx, JSMSG_WASM_RESPONSE_ALREADY_CONSUMED);
+  }
+
+  switch (aMimeType) {
+    case JS::MimeType::Wasm:
+      nsAutoString url;
+      response->GetUrl(url);
+
+      IgnoredErrorResult result;
+      nsCString sourceMapUrl;
+      response->GetInternalHeaders()->Get("SourceMap"_ns, sourceMapUrl, result);
+      if (NS_WARN_IF(result.Failed())) {
+        return ThrowException(aCx, JSMSG_WASM_ERROR_CONSUMING_RESPONSE);
+      }
+      NS_ConvertUTF16toUTF8 urlUTF8(url);
+      aConsumer->noteResponseURLs(
+          urlUTF8.get(), sourceMapUrl.IsVoid() ? nullptr : sourceMapUrl.get());
+      break;
+  }
+
+  SafeRefPtr<InternalResponse> ir = response->GetInternalResponse();
+  if (NS_WARN_IF(!ir)) {
+    return ThrowException(aCx, JSMSG_OUT_OF_MEMORY);
+  }
+
+  nsCOMPtr<nsIInputStream> stream;
+
+  nsMainThreadPtrHandle<nsICacheInfoChannel> cache;
+  bool optimizedEncoding = false;
+  if (ir->HasCacheInfoChannel()) {
+    cache = ir->TakeCacheInfoChannel();
+
+    nsAutoCString altDataType;
+    if (NS_SUCCEEDED(cache->GetAlternativeDataType(altDataType)) &&
+        WasmAltDataType.Equals(altDataType)) {
+      optimizedEncoding = true;
+      rv = cache->GetAlternativeDataInputStream(getter_AddRefs(stream));
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return ThrowException(aCx, JSMSG_OUT_OF_MEMORY);
+      }
+      if (ir->HasBeenCloned()) {
+        // If `Response` is cloned, clone alternative data stream instance.
+        // The cache entry does not clone automatically, and multiple
+        // JSStreamConsumer instances will collide during read if not cloned.
+        nsCOMPtr<nsICloneableInputStream> original = do_QueryInterface(stream);
+        if (NS_WARN_IF(!original)) {
+          return ThrowException(aCx, JSMSG_OUT_OF_MEMORY);
+        }
+        rv = original->Clone(getter_AddRefs(stream));
+        if (NS_WARN_IF(NS_FAILED(rv))) {
+          return ThrowException(aCx, JSMSG_OUT_OF_MEMORY);
+        }
+      }
+    }
+  }
+
+  if (!optimizedEncoding) {
+    ir->GetUnfilteredBody(getter_AddRefs(stream));
+    if (!stream) {
+      aConsumer->streamEnd();
+      return true;
+    }
+  }
+
+  MOZ_ASSERT(stream);
+
+  IgnoredErrorResult error;
+  response->SetBodyUsed(aCx, error);
+  if (NS_WARN_IF(error.Failed())) {
+    return ThrowException(aCx, JSMSG_WASM_ERROR_CONSUMING_RESPONSE);
+  }
+
+  nsIGlobalObject* global = xpc::NativeGlobal(js::UncheckedUnwrap(aObj));
+
+  if (!JSStreamConsumer::Start(stream, global, aMaybeWorker, aConsumer,
+                               std::move(cache), optimizedEncoding)) {
+    return ThrowException(aCx, JSMSG_OUT_OF_MEMORY);
+  }
+
+  return true;
+}
+
+// static
+void FetchUtil::ReportJSStreamError(JSContext* aCx, size_t aErrorCode) {
+  // For now, convert *all* errors into AbortError.
+
+  RefPtr<DOMException> e = DOMException::Create(NS_ERROR_DOM_ABORT_ERR);
+
+  JS::Rooted<JS::Value> value(aCx);
+  if (!GetOrCreateDOMReflector(aCx, e, &value)) {
+    return;
+  }
+
+  JS_SetPendingException(aCx, value);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/fetch/FetchUtil.h b/dom/fetch/FetchUtil.h
new file mode 100644
index 0000000000..c0c9157a43
--- /dev/null
+++ b/dom/fetch/FetchUtil.h
@@ -0,0 +1,82 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_FetchUtil_h
+#define mozilla_dom_FetchUtil_h
+
+#include "nsString.h"
+#include "nsError.h"
+
+#include "mozilla/dom/File.h"
+#include "mozilla/dom/FormData.h"
+
+#define WASM_CONTENT_TYPE "application/wasm"
+
+class nsIPrincipal;
+class nsIHttpChannel;
+
+namespace mozilla::dom {
+
+class Document;
+class InternalRequest;
+class WorkerPrivate;
+
+class FetchUtil final {
+ private:
+  FetchUtil() = delete;
+
+ public:
+  /**
+   * Sets outMethod to a valid HTTP request method string based on an input
+   * method. Implements checks and normalization as specified by the Fetch
+   * specification. Returns NS_ERROR_DOM_SECURITY_ERR if the method is invalid.
+   * Otherwise returns NS_OK and the normalized method via outMethod.
+   */
+  static nsresult GetValidRequestMethod(const nsACString& aMethod,
+                                        nsCString& outMethod);
+  /**
+   * Extracts an HTTP header from a substring range.
+   */
+  static bool ExtractHeader(nsACString::const_iterator& aStart,
+                            nsACString::const_iterator& aEnd,
+                            nsCString& aHeaderName, nsCString& aHeaderValue,
+                            bool* aWasEmptyHeader);
+
+  static nsresult SetRequestReferrer(nsIPrincipal* aPrincipal, Document* aDoc,
+                                     nsIHttpChannel* aChannel,
+                                     InternalRequest& aRequest);
+
+  /**
+   * The WebAssembly alt data type includes build-id, cpu-id and other relevant
+   * state that is necessary to ensure the validity of caching machine code and
+   * metadata in alt data. InitWasmAltDataType() must be called during startup
+   * before the first fetch(), ensuring that !WasmAltDataType.IsEmpty().
+   */
+  static const nsCString WasmAltDataType;
+  static void InitWasmAltDataType();
+
+  /**
+   * Check that the given object is a Response and, if so, stream to the given
+   * JS consumer. On any failure, this function will report an error on the
+   * given JSContext before returning false. If executing in a worker, the
+   * WorkerPrivate must be given.
+   */
+  static bool StreamResponseToJS(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                                 JS::MimeType aMimeType,
+                                 JS::StreamConsumer* aConsumer,
+                                 WorkerPrivate* aMaybeWorker);
+
+  /**
+   * Called by JS to report (i.e., throw) an error that was passed to the
+   * JS::StreamConsumer::streamError() method on a random stream thread.
+   * This method is passed by function pointer to the JS engine hence the
+   * untyped 'size_t' instead of Gecko 'nsresult'.
+   */
+  static void ReportJSStreamError(JSContext* aCx, size_t aErrorCode);
+};
+
+}  // namespace mozilla::dom
+#endif
diff --git a/dom/fetch/Headers.cpp b/dom/fetch/Headers.cpp
new file mode 100644
index 0000000000..b8edbe1ed7
--- /dev/null
+++ b/dom/fetch/Headers.cpp
@@ -0,0 +1,87 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/Headers.h"
+
+#include "mozilla/ErrorResult.h"
+#include "mozilla/dom/WorkerPrivate.h"
+#include "mozilla/Preferences.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(Headers)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(Headers)
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(Headers, mOwner)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(Headers)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+// static
+already_AddRefed<Headers> Headers::Constructor(
+    const GlobalObject& aGlobal,
+    const Optional<ByteStringSequenceSequenceOrByteStringByteStringRecord>&
+        aInit,
+    ErrorResult& aRv) {
+  RefPtr<InternalHeaders> ih = new InternalHeaders();
+  RefPtr<Headers> headers = new Headers(aGlobal.GetAsSupports(), ih);
+
+  if (!aInit.WasPassed()) {
+    return headers.forget();
+  }
+
+  if (aInit.Value().IsByteStringSequenceSequence()) {
+    ih->Fill(aInit.Value().GetAsByteStringSequenceSequence(), aRv);
+  } else if (aInit.Value().IsByteStringByteStringRecord()) {
+    ih->Fill(aInit.Value().GetAsByteStringByteStringRecord(), aRv);
+  }
+
+  if (aRv.Failed()) {
+    return nullptr;
+  }
+
+  return headers.forget();
+}
+
+// static
+already_AddRefed<Headers> Headers::Constructor(
+    const GlobalObject& aGlobal,
+    const OwningByteStringSequenceSequenceOrByteStringByteStringRecord& aInit,
+    ErrorResult& aRv) {
+  nsCOMPtr<nsIGlobalObject> global = do_QueryInterface(aGlobal.GetAsSupports());
+  return Create(global, aInit, aRv);
+}
+
+/* static */
+already_AddRefed<Headers> Headers::Create(
+    nsIGlobalObject* aGlobal,
+    const OwningByteStringSequenceSequenceOrByteStringByteStringRecord& aInit,
+    ErrorResult& aRv) {
+  RefPtr<InternalHeaders> ih = new InternalHeaders();
+  RefPtr<Headers> headers = new Headers(aGlobal, ih);
+
+  if (aInit.IsByteStringSequenceSequence()) {
+    ih->Fill(aInit.GetAsByteStringSequenceSequence(), aRv);
+  } else if (aInit.IsByteStringByteStringRecord()) {
+    ih->Fill(aInit.GetAsByteStringByteStringRecord(), aRv);
+  }
+
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  return headers.forget();
+}
+
+JSObject* Headers::WrapObject(JSContext* aCx,
+                              JS::Handle<JSObject*> aGivenProto) {
+  return mozilla::dom::Headers_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+Headers::~Headers() = default;
+
+}  // namespace mozilla::dom
diff --git a/dom/fetch/Headers.h b/dom/fetch/Headers.h
new file mode 100644
index 0000000000..ea3b24405d
--- /dev/null
+++ b/dom/fetch/Headers.h
@@ -0,0 +1,132 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_Headers_h
+#define mozilla_dom_Headers_h
+
+#include "mozilla/dom/HeadersBinding.h"
+
+#include "nsClassHashtable.h"
+#include "nsWrapperCache.h"
+
+#include "InternalHeaders.h"
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+template <typename K, typename V>
+class Record;
+class ByteStringSequenceSequenceOrByteStringByteStringRecord;
+class OwningByteStringSequenceSequenceOrByteStringByteStringRecord;
+
+/**
+ * This Headers class is only used to represent the content facing Headers
+ * object. It is actually backed by an InternalHeaders implementation. Gecko
+ * code should NEVER use this, except in the Request and Response
+ * implementations, where they must always be created from the backing
+ * InternalHeaders object.
+ */
+class Headers final : public nsISupports, public nsWrapperCache {
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(Headers)
+
+  friend class Request;
+  friend class Response;
+
+ private:
+  nsCOMPtr<nsISupports> mOwner;
+  RefPtr<InternalHeaders> mInternalHeaders;
+
+ public:
+  explicit Headers(nsISupports* aOwner, InternalHeaders* aInternalHeaders)
+      : mOwner(aOwner), mInternalHeaders(aInternalHeaders) {}
+
+  explicit Headers(const Headers& aOther) = delete;
+
+  static bool PrefEnabled(JSContext* cx, JSObject* obj);
+
+  static already_AddRefed<Headers> Constructor(
+      const GlobalObject& aGlobal,
+      const Optional<ByteStringSequenceSequenceOrByteStringByteStringRecord>&
+          aInit,
+      ErrorResult& aRv);
+
+  static already_AddRefed<Headers> Constructor(
+      const GlobalObject& aGlobal,
+      const OwningByteStringSequenceSequenceOrByteStringByteStringRecord& aInit,
+      ErrorResult& aRv);
+
+  static already_AddRefed<Headers> Create(
+      nsIGlobalObject* aGlobalObject,
+      const OwningByteStringSequenceSequenceOrByteStringByteStringRecord& aInit,
+      ErrorResult& aRv);
+
+  void Append(const nsACString& aName, const nsACString& aValue,
+              ErrorResult& aRv) {
+    mInternalHeaders->Append(aName, aValue, aRv);
+  }
+
+  void Delete(const nsACString& aName, ErrorResult& aRv) {
+    mInternalHeaders->Delete(aName, aRv);
+  }
+
+  void Get(const nsACString& aName, nsACString& aValue,
+           ErrorResult& aRv) const {
+    mInternalHeaders->Get(aName, aValue, aRv);
+  }
+
+  void GetSetCookie(nsTArray<nsCString>& aValues) const {
+    mInternalHeaders->GetSetCookie(aValues);
+  }
+
+  void GetFirst(const nsACString& aName, nsACString& aValue,
+                ErrorResult& aRv) const {
+    mInternalHeaders->GetFirst(aName, aValue, aRv);
+  }
+
+  bool Has(const nsACString& aName, ErrorResult& aRv) const {
+    return mInternalHeaders->Has(aName, aRv);
+  }
+
+  void Set(const nsACString& aName, const nsACString& aValue,
+           ErrorResult& aRv) {
+    mInternalHeaders->Set(aName, aValue, aRv);
+  }
+
+  uint32_t GetIterableLength() const {
+    return mInternalHeaders->GetIterableLength();
+  }
+  const nsString GetKeyAtIndex(unsigned aIndex) const {
+    return mInternalHeaders->GetKeyAtIndex(aIndex);
+  }
+  const nsString GetValueAtIndex(unsigned aIndex) const {
+    return mInternalHeaders->GetValueAtIndex(aIndex);
+  }
+
+  // ChromeOnly
+  HeadersGuardEnum Guard() const { return mInternalHeaders->Guard(); }
+
+  void SetGuard(HeadersGuardEnum aGuard, ErrorResult& aRv) {
+    mInternalHeaders->SetGuard(aGuard, aRv);
+  }
+
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+  nsISupports* GetParentObject() const { return mOwner; }
+
+ private:
+  virtual ~Headers();
+
+  InternalHeaders* GetInternalHeaders() const { return mInternalHeaders; }
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_Headers_h
diff --git a/dom/fetch/InternalHeaders.cpp b/dom/fetch/InternalHeaders.cpp
new file mode 100644
index 0000000000..af24432b62
--- /dev/null
+++ b/dom/fetch/InternalHeaders.cpp
@@ -0,0 +1,654 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/InternalHeaders.h"
+
+#include "FetchUtil.h"
+#include "mozilla/dom/FetchTypes.h"
+#include "mozilla/ErrorResult.h"
+
+#include "nsCharSeparatedTokenizer.h"
+#include "nsContentUtils.h"
+#include "nsIHttpChannel.h"
+#include "nsIHttpHeaderVisitor.h"
+#include "nsNetUtil.h"
+#include "nsReadableUtils.h"
+
+namespace mozilla::dom {
+
+InternalHeaders::InternalHeaders(nsTArray<Entry>&& aHeaders,
+                                 HeadersGuardEnum aGuard)
+    : mGuard(aGuard), mList(std::move(aHeaders)), mListDirty(true) {}
+
+InternalHeaders::InternalHeaders(
+    const nsTArray<HeadersEntry>& aHeadersEntryList, HeadersGuardEnum aGuard)
+    : mGuard(aGuard), mListDirty(true) {
+  for (const HeadersEntry& headersEntry : aHeadersEntryList) {
+    mList.AppendElement(Entry(headersEntry.name(), headersEntry.value()));
+  }
+}
+
+void InternalHeaders::ToIPC(nsTArray<HeadersEntry>& aIPCHeaders,
+                            HeadersGuardEnum& aGuard) {
+  aGuard = mGuard;
+
+  aIPCHeaders.Clear();
+  for (Entry& entry : mList) {
+    aIPCHeaders.AppendElement(HeadersEntry(entry.mName, entry.mValue));
+  }
+}
+
+bool InternalHeaders::IsValidHeaderValue(const nsCString& aLowerName,
+                                         const nsCString& aNormalizedValue,
+                                         ErrorResult& aRv) {
+  // Steps 2 to 6 for ::Set() and ::Append() in the spec.
+
+  // Step 2
+  if (IsInvalidName(aLowerName, aRv) || IsInvalidValue(aNormalizedValue, aRv)) {
+    return false;
+  }
+
+  // Step 3
+  if (IsImmutable(aRv)) {
+    return false;
+  }
+
+  // Step 4
+  if (mGuard == HeadersGuardEnum::Request) {
+    if (IsForbiddenRequestHeader(aLowerName, aNormalizedValue)) {
+      return false;
+    }
+  }
+  // Step 5
+  if (mGuard == HeadersGuardEnum::Request_no_cors) {
+    nsAutoCString tempValue;
+    Get(aLowerName, tempValue, aRv);
+
+    if (tempValue.IsVoid()) {
+      tempValue = aNormalizedValue;
+    } else {
+      tempValue.Append(", ");
+      tempValue.Append(aNormalizedValue);
+    }
+
+    if (!nsContentUtils::IsCORSSafelistedRequestHeader(aLowerName, tempValue)) {
+      return false;
+    }
+  }
+
+  // Step 6
+  else if (IsForbiddenResponseHeader(aLowerName)) {
+    return false;
+  }
+
+  return true;
+}
+
+void InternalHeaders::Append(const nsACString& aName, const nsACString& aValue,
+                             ErrorResult& aRv) {
+  // Step 1
+  nsAutoCString trimValue;
+  NS_TrimHTTPWhitespace(aValue, trimValue);
+
+  // Steps 2 to 6
+  nsAutoCString lowerName;
+  ToLowerCase(aName, lowerName);
+  if (!IsValidHeaderValue(lowerName, trimValue, aRv)) {
+    return;
+  }
+
+  // Step 7
+  nsAutoCString name(aName);
+  ReuseExistingNameIfExists(name);
+  SetListDirty();
+  mList.AppendElement(Entry(name, trimValue));
+
+  // Step 8
+  if (mGuard == HeadersGuardEnum::Request_no_cors) {
+    RemovePrivilegedNoCorsRequestHeaders();
+  }
+}
+
+void InternalHeaders::RemovePrivilegedNoCorsRequestHeaders() {
+  bool dirty = false;
+
+  // remove in reverse order to minimize copying
+  for (int32_t i = mList.Length() - 1; i >= 0; --i) {
+    if (IsPrivilegedNoCorsRequestHeaderName(mList[i].mName)) {
+      mList.RemoveElementAt(i);
+      dirty = true;
+    }
+  }
+
+  if (dirty) {
+    SetListDirty();
+  }
+}
+
+bool InternalHeaders::DeleteInternal(const nsCString& aLowerName,
+                                     ErrorResult& aRv) {
+  bool dirty = false;
+
+  // remove in reverse order to minimize copying
+  for (int32_t i = mList.Length() - 1; i >= 0; --i) {
+    if (mList[i].mName.EqualsIgnoreCase(aLowerName.get())) {
+      mList.RemoveElementAt(i);
+      dirty = true;
+    }
+  }
+
+  if (dirty) {
+    SetListDirty();
+  }
+
+  return dirty;
+}
+
+void InternalHeaders::Delete(const nsACString& aName, ErrorResult& aRv) {
+  nsAutoCString lowerName;
+  ToLowerCase(aName, lowerName);
+
+  // Step 1
+  if (IsInvalidName(lowerName, aRv)) {
+    return;
+  }
+
+  // Step 2
+  if (IsImmutable(aRv)) {
+    return;
+  }
+
+  // Step 3
+  nsAutoCString value;
+  GetInternal(lowerName, value, aRv);
+  if (IsForbiddenRequestHeader(lowerName, value)) {
+    return;
+  }
+
+  // Step 4
+  if (mGuard == HeadersGuardEnum::Request_no_cors &&
+      !IsNoCorsSafelistedRequestHeaderName(lowerName) &&
+      !IsPrivilegedNoCorsRequestHeaderName(lowerName)) {
+    return;
+  }
+
+  // Step 5
+  if (IsForbiddenResponseHeader(lowerName)) {
+    return;
+  }
+
+  // Steps 6 and 7
+  if (!DeleteInternal(lowerName, aRv)) {
+    return;
+  }
+
+  // Step 8
+  if (mGuard == HeadersGuardEnum::Request_no_cors) {
+    RemovePrivilegedNoCorsRequestHeaders();
+  }
+}
+
+void InternalHeaders::Get(const nsACString& aName, nsACString& aValue,
+                          ErrorResult& aRv) const {
+  nsAutoCString lowerName;
+  ToLowerCase(aName, lowerName);
+
+  if (IsInvalidName(lowerName, aRv)) {
+    return;
+  }
+
+  GetInternal(lowerName, aValue, aRv);
+}
+
+void InternalHeaders::GetInternal(const nsCString& aLowerName,
+                                  nsACString& aValue, ErrorResult& aRv) const {
+  const char* delimiter = ", ";
+  bool firstValueFound = false;
+
+  for (uint32_t i = 0; i < mList.Length(); ++i) {
+    if (mList[i].mName.EqualsIgnoreCase(aLowerName.get())) {
+      if (firstValueFound) {
+        aValue += delimiter;
+      }
+      aValue += mList[i].mValue;
+      firstValueFound = true;
+    }
+  }
+
+  // No value found, so return null to content
+  if (!firstValueFound) {
+    aValue.SetIsVoid(true);
+  }
+}
+
+void InternalHeaders::GetSetCookie(nsTArray<nsCString>& aValues) const {
+  for (uint32_t i = 0; i < mList.Length(); ++i) {
+    if (mList[i].mName.EqualsIgnoreCase("Set-Cookie")) {
+      aValues.AppendElement(mList[i].mValue);
+    }
+  }
+}
+
+void InternalHeaders::GetFirst(const nsACString& aName, nsACString& aValue,
+                               ErrorResult& aRv) const {
+  nsAutoCString lowerName;
+  ToLowerCase(aName, lowerName);
+
+  if (IsInvalidName(lowerName, aRv)) {
+    return;
+  }
+
+  for (uint32_t i = 0; i < mList.Length(); ++i) {
+    if (mList[i].mName.EqualsIgnoreCase(lowerName.get())) {
+      aValue = mList[i].mValue;
+      return;
+    }
+  }
+
+  // No value found, so return null to content
+  aValue.SetIsVoid(true);
+}
+
+bool InternalHeaders::Has(const nsACString& aName, ErrorResult& aRv) const {
+  nsAutoCString lowerName;
+  ToLowerCase(aName, lowerName);
+
+  if (IsInvalidName(lowerName, aRv)) {
+    return false;
+  }
+
+  for (uint32_t i = 0; i < mList.Length(); ++i) {
+    if (mList[i].mName.EqualsIgnoreCase(lowerName.get())) {
+      return true;
+    }
+  }
+  return false;
+}
+
+void InternalHeaders::Set(const nsACString& aName, const nsACString& aValue,
+                          ErrorResult& aRv) {
+  // Step 1
+  nsAutoCString trimValue;
+  NS_TrimHTTPWhitespace(aValue, trimValue);
+
+  // Steps 2 to 6
+  nsAutoCString lowerName;
+  ToLowerCase(aName, lowerName);
+  if (!IsValidHeaderValue(lowerName, trimValue, aRv)) {
+    return;
+  }
+
+  // Step 7
+  SetListDirty();
+
+  int32_t firstIndex = INT32_MAX;
+
+  // remove in reverse order to minimize copying
+  for (int32_t i = mList.Length() - 1; i >= 0; --i) {
+    if (mList[i].mName.EqualsIgnoreCase(lowerName.get())) {
+      firstIndex = std::min(firstIndex, i);
+      mList.RemoveElementAt(i);
+    }
+  }
+
+  if (firstIndex < INT32_MAX) {
+    Entry* entry = mList.InsertElementAt(firstIndex);
+    entry->mName = aName;
+    entry->mValue = trimValue;
+  } else {
+    mList.AppendElement(Entry(aName, trimValue));
+  }
+
+  // Step 8
+  if (mGuard == HeadersGuardEnum::Request_no_cors) {
+    RemovePrivilegedNoCorsRequestHeaders();
+  }
+}
+
+void InternalHeaders::Clear() {
+  SetListDirty();
+  mList.Clear();
+}
+
+void InternalHeaders::SetGuard(HeadersGuardEnum aGuard, ErrorResult& aRv) {
+  // The guard is only checked during ::Set() and ::Append() in the spec.  It
+  // does not require revalidating headers already set.
+  mGuard = aGuard;
+}
+
+InternalHeaders::~InternalHeaders() = default;
+
+// static
+bool InternalHeaders::IsNoCorsSafelistedRequestHeaderName(
+    const nsCString& aName) {
+  return aName.EqualsIgnoreCase("accept") ||
+         aName.EqualsIgnoreCase("accept-language") ||
+         aName.EqualsIgnoreCase("content-language") ||
+         aName.EqualsIgnoreCase("content-type");
+}
+
+// static
+bool InternalHeaders::IsPrivilegedNoCorsRequestHeaderName(
+    const nsCString& aName) {
+  return aName.EqualsIgnoreCase("range");
+}
+
+// static
+bool InternalHeaders::IsSimpleHeader(const nsCString& aName,
+                                     const nsACString& aValue) {
+  if (aValue.Length() > 128) {
+    return false;
+  }
+  // Note, we must allow a null content-type value here to support
+  // get("content-type"), but the IsInvalidValue() check will prevent null
+  // from being set or appended.
+  return (aName.EqualsIgnoreCase("accept") &&
+          nsContentUtils::IsAllowedNonCorsAccept(aValue)) ||
+         (aName.EqualsIgnoreCase("accept-language") &&
+          nsContentUtils::IsAllowedNonCorsLanguage(aValue)) ||
+         (aName.EqualsIgnoreCase("content-language") &&
+          nsContentUtils::IsAllowedNonCorsLanguage(aValue)) ||
+         (aName.EqualsIgnoreCase("content-type") &&
+          nsContentUtils::IsAllowedNonCorsContentType(aValue));
+}
+
+// static
+bool InternalHeaders::IsRevalidationHeader(const nsCString& aName) {
+  return aName.EqualsIgnoreCase("if-modified-since") ||
+         aName.EqualsIgnoreCase("if-none-match") ||
+         aName.EqualsIgnoreCase("if-unmodified-since") ||
+         aName.EqualsIgnoreCase("if-match") ||
+         aName.EqualsIgnoreCase("if-range");
+}
+
+// static
+bool InternalHeaders::IsInvalidName(const nsACString& aName, ErrorResult& aRv) {
+  if (!NS_IsValidHTTPToken(aName)) {
+    aRv.ThrowTypeError<MSG_INVALID_HEADER_NAME>(aName);
+    return true;
+  }
+
+  return false;
+}
+
+// static
+bool InternalHeaders::IsInvalidValue(const nsACString& aValue,
+                                     ErrorResult& aRv) {
+  if (!NS_IsReasonableHTTPHeaderValue(aValue)) {
+    aRv.ThrowTypeError<MSG_INVALID_HEADER_VALUE>(aValue);
+    return true;
+  }
+  return false;
+}
+
+bool InternalHeaders::IsImmutable(ErrorResult& aRv) const {
+  if (mGuard == HeadersGuardEnum::Immutable) {
+    aRv.ThrowTypeError("Headers are immutable and cannot be modified.");
+    return true;
+  }
+  return false;
+}
+
+bool InternalHeaders::IsForbiddenRequestHeader(const nsCString& aName,
+                                               const nsACString& aValue) const {
+  return mGuard == HeadersGuardEnum::Request &&
+         nsContentUtils::IsForbiddenRequestHeader(aName, aValue);
+}
+
+bool InternalHeaders::IsForbiddenRequestNoCorsHeader(
+    const nsCString& aName) const {
+  return mGuard == HeadersGuardEnum::Request_no_cors &&
+         !IsSimpleHeader(aName, ""_ns);
+}
+
+bool InternalHeaders::IsForbiddenRequestNoCorsHeader(
+    const nsCString& aName, const nsACString& aValue) const {
+  return mGuard == HeadersGuardEnum::Request_no_cors &&
+         !IsSimpleHeader(aName, aValue);
+}
+
+bool InternalHeaders::IsForbiddenResponseHeader(const nsCString& aName) const {
+  return mGuard == HeadersGuardEnum::Response &&
+         nsContentUtils::IsForbiddenResponseHeader(aName);
+}
+
+void InternalHeaders::Fill(const InternalHeaders& aInit, ErrorResult& aRv) {
+  const nsTArray<Entry>& list = aInit.mList;
+  for (uint32_t i = 0; i < list.Length() && !aRv.Failed(); ++i) {
+    const Entry& entry = list[i];
+    Append(entry.mName, entry.mValue, aRv);
+  }
+}
+
+void InternalHeaders::Fill(const Sequence<Sequence<nsCString>>& aInit,
+                           ErrorResult& aRv) {
+  for (uint32_t i = 0; i < aInit.Length() && !aRv.Failed(); ++i) {
+    const Sequence<nsCString>& tuple = aInit[i];
+    if (tuple.Length() != 2) {
+      aRv.ThrowTypeError(
+          "Headers require name/value tuples when being initialized by a "
+          "sequence.");
+      return;
+    }
+    Append(tuple[0], tuple[1], aRv);
+  }
+}
+
+void InternalHeaders::Fill(const Record<nsCString, nsCString>& aInit,
+                           ErrorResult& aRv) {
+  for (auto& entry : aInit.Entries()) {
+    Append(entry.mKey, entry.mValue, aRv);
+    if (aRv.Failed()) {
+      return;
+    }
+  }
+}
+
+namespace {
+
+class FillHeaders final : public nsIHttpHeaderVisitor {
+  RefPtr<InternalHeaders> mInternalHeaders;
+
+  ~FillHeaders() = default;
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  explicit FillHeaders(InternalHeaders* aInternalHeaders)
+      : mInternalHeaders(aInternalHeaders) {
+    MOZ_DIAGNOSTIC_ASSERT(mInternalHeaders);
+  }
+
+  NS_IMETHOD
+  VisitHeader(const nsACString& aHeader, const nsACString& aValue) override {
+    mInternalHeaders->Append(aHeader, aValue, IgnoreErrors());
+    return NS_OK;
+  }
+};
+
+NS_IMPL_ISUPPORTS(FillHeaders, nsIHttpHeaderVisitor)
+
+}  // namespace
+
+void InternalHeaders::FillResponseHeaders(nsIRequest* aRequest) {
+  nsCOMPtr<nsIHttpChannel> httpChannel = do_QueryInterface(aRequest);
+  if (!httpChannel) {
+    return;
+  }
+
+  RefPtr<FillHeaders> visitor = new FillHeaders(this);
+  nsresult rv = httpChannel->VisitResponseHeaders(visitor);
+  if (NS_FAILED(rv)) {
+    NS_WARNING("failed to fill headers");
+  }
+}
+
+bool InternalHeaders::HasOnlySimpleHeaders() const {
+  for (uint32_t i = 0; i < mList.Length(); ++i) {
+    if (!IsSimpleHeader(mList[i].mName, mList[i].mValue)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+bool InternalHeaders::HasRevalidationHeaders() const {
+  for (uint32_t i = 0; i < mList.Length(); ++i) {
+    if (IsRevalidationHeader(mList[i].mName)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+// static
+already_AddRefed<InternalHeaders> InternalHeaders::BasicHeaders(
+    InternalHeaders* aHeaders) {
+  RefPtr<InternalHeaders> basic = new InternalHeaders(*aHeaders);
+  ErrorResult result;
+  // The Set-Cookie headers cannot be invalid mutable headers, so the Delete
+  // must succeed.
+  basic->Delete("Set-Cookie"_ns, result);
+  MOZ_ASSERT(!result.Failed());
+  basic->Delete("Set-Cookie2"_ns, result);
+  MOZ_ASSERT(!result.Failed());
+  return basic.forget();
+}
+
+// static
+already_AddRefed<InternalHeaders> InternalHeaders::CORSHeaders(
+    InternalHeaders* aHeaders, RequestCredentials aCredentialsMode) {
+  RefPtr<InternalHeaders> cors = new InternalHeaders(aHeaders->mGuard);
+  ErrorResult result;
+
+  nsAutoCString acExposedNames;
+  aHeaders->Get("Access-Control-Expose-Headers"_ns, acExposedNames, result);
+  MOZ_ASSERT(!result.Failed());
+
+  bool allowAllHeaders = false;
+  AutoTArray<nsCString, 5> exposeNamesArray;
+  for (const nsACString& token :
+       nsCCharSeparatedTokenizer(acExposedNames, ',').ToRange()) {
+    if (token.IsEmpty()) {
+      continue;
+    }
+
+    if (!NS_IsValidHTTPToken(token)) {
+      NS_WARNING(
+          "Got invalid HTTP token in Access-Control-Expose-Headers. Header "
+          "value is:");
+      NS_WARNING(acExposedNames.get());
+      exposeNamesArray.Clear();
+      break;
+    }
+
+    if (token.EqualsLiteral("*") &&
+        aCredentialsMode != RequestCredentials::Include) {
+      allowAllHeaders = true;
+    }
+
+    exposeNamesArray.AppendElement(token);
+  }
+
+  nsCaseInsensitiveCStringArrayComparator comp;
+  for (uint32_t i = 0; i < aHeaders->mList.Length(); ++i) {
+    const Entry& entry = aHeaders->mList[i];
+    if (allowAllHeaders) {
+      cors->Append(entry.mName, entry.mValue, result);
+      MOZ_ASSERT(!result.Failed());
+    } else if (entry.mName.EqualsIgnoreCase("cache-control") ||
+               entry.mName.EqualsIgnoreCase("content-language") ||
+               entry.mName.EqualsIgnoreCase("content-type") ||
+               entry.mName.EqualsIgnoreCase("content-length") ||
+               entry.mName.EqualsIgnoreCase("expires") ||
+               entry.mName.EqualsIgnoreCase("last-modified") ||
+               entry.mName.EqualsIgnoreCase("pragma") ||
+               exposeNamesArray.Contains(entry.mName, comp)) {
+      cors->Append(entry.mName, entry.mValue, result);
+      MOZ_ASSERT(!result.Failed());
+    }
+  }
+
+  return cors.forget();
+}
+
+void InternalHeaders::GetEntries(
+    nsTArray<InternalHeaders::Entry>& aEntries) const {
+  MOZ_ASSERT(aEntries.IsEmpty());
+  aEntries.AppendElements(mList);
+}
+
+void InternalHeaders::GetUnsafeHeaders(nsTArray<nsCString>& aNames) const {
+  MOZ_ASSERT(aNames.IsEmpty());
+  for (uint32_t i = 0; i < mList.Length(); ++i) {
+    const Entry& header = mList[i];
+    if (!InternalHeaders::IsSimpleHeader(header.mName, header.mValue)) {
+      aNames.AppendElement(header.mName);
+    }
+  }
+}
+
+void InternalHeaders::MaybeSortList() {
+  class Comparator {
+   public:
+    bool Equals(const Entry& aA, const Entry& aB) const {
+      return aA.mName == aB.mName;
+    }
+
+    bool LessThan(const Entry& aA, const Entry& aB) const {
+      return aA.mName < aB.mName;
+    }
+  };
+
+  if (!mListDirty) {
+    return;
+  }
+
+  mListDirty = false;
+
+  Comparator comparator;
+
+  mSortedList.Clear();
+  for (const Entry& entry : mList) {
+    bool found = false;
+
+    // We combine every header but Set-Cookie.
+    if (!entry.mName.EqualsIgnoreCase("Set-Cookie")) {
+      for (Entry& sortedEntry : mSortedList) {
+        if (sortedEntry.mName.EqualsIgnoreCase(entry.mName.get())) {
+          sortedEntry.mValue += ", ";
+          sortedEntry.mValue += entry.mValue;
+          found = true;
+          break;
+        }
+      }
+    }
+
+    if (!found) {
+      Entry newEntry = entry;
+      ToLowerCase(newEntry.mName);
+      mSortedList.InsertElementSorted(newEntry, comparator);
+    }
+  }
+}
+
+void InternalHeaders::SetListDirty() {
+  mSortedList.Clear();
+  mListDirty = true;
+}
+
+void InternalHeaders::ReuseExistingNameIfExists(nsCString& aName) const {
+  for (const Entry& entry : mList) {
+    if (entry.mName.EqualsIgnoreCase(aName.get())) {
+      aName = entry.mName;
+      break;
+    }
+  }
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/fetch/InternalHeaders.h b/dom/fetch/InternalHeaders.h
new file mode 100644
index 0000000000..258725e32e
--- /dev/null
+++ b/dom/fetch/InternalHeaders.h
@@ -0,0 +1,180 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_InternalHeaders_h
+#define mozilla_dom_InternalHeaders_h
+
+// needed for HeadersGuardEnum.
+#include "mozilla/dom/HeadersBinding.h"
+#include "mozilla/dom/RequestBinding.h"
+#include "mozilla/dom/UnionTypes.h"
+
+#include "nsClassHashtable.h"
+#include "nsWrapperCache.h"
+
+class nsIRequest;
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+template <typename K, typename V>
+class Record;
+class HeadersEntry;
+
+class InternalHeaders final {
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(InternalHeaders)
+
+ public:
+  struct Entry {
+    Entry(const nsACString& aName, const nsACString& aValue)
+        : mName(aName), mValue(aValue) {}
+
+    Entry() = default;
+
+    nsCString mName;
+    nsCString mValue;
+  };
+
+ private:
+  HeadersGuardEnum mGuard;
+  nsTArray<Entry> mList;
+
+  nsTArray<Entry> mSortedList;
+
+  // This boolean is set to true at any writing operation to mList. It's set to
+  // false when mSortedList is regenerated. This happens when the header is
+  // iterated.
+  bool mListDirty;
+
+ public:
+  explicit InternalHeaders(HeadersGuardEnum aGuard = HeadersGuardEnum::None)
+      : mGuard(aGuard), mListDirty(false) {}
+
+  explicit InternalHeaders(const InternalHeaders& aOther)
+      : mGuard(HeadersGuardEnum::None), mListDirty(true) {
+    ErrorResult result;
+    Fill(aOther, result);
+    MOZ_ASSERT(!result.Failed());
+    // Note that it's important to set the guard after Fill(), to make sure
+    // that Fill() doesn't fail if aOther is immutable.
+    mGuard = aOther.mGuard;
+  }
+
+  explicit InternalHeaders(nsTArray<Entry>&& aHeaders,
+                           HeadersGuardEnum aGuard = HeadersGuardEnum::None);
+
+  InternalHeaders(const nsTArray<HeadersEntry>& aHeadersEntryList,
+                  HeadersGuardEnum aGuard);
+
+  void ToIPC(nsTArray<HeadersEntry>& aIPCHeaders, HeadersGuardEnum& aGuard);
+
+  void Append(const nsACString& aName, const nsACString& aValue,
+              ErrorResult& aRv);
+  void Delete(const nsACString& aName, ErrorResult& aRv);
+  void Get(const nsACString& aName, nsACString& aValue, ErrorResult& aRv) const;
+  void GetSetCookie(nsTArray<nsCString>& aValues) const;
+  void GetFirst(const nsACString& aName, nsACString& aValue,
+                ErrorResult& aRv) const;
+  bool Has(const nsACString& aName, ErrorResult& aRv) const;
+  void Set(const nsACString& aName, const nsACString& aValue, ErrorResult& aRv);
+
+  uint32_t GetIterableLength() {
+    MaybeSortList();
+    return mSortedList.Length();
+  }
+  const NS_ConvertASCIItoUTF16 GetKeyAtIndex(unsigned aIndex) {
+    MaybeSortList();
+    MOZ_ASSERT(aIndex < mSortedList.Length());
+    return NS_ConvertASCIItoUTF16(mSortedList[aIndex].mName);
+  }
+  const NS_ConvertASCIItoUTF16 GetValueAtIndex(unsigned aIndex) {
+    MaybeSortList();
+    MOZ_ASSERT(aIndex < mSortedList.Length());
+    return NS_ConvertASCIItoUTF16(mSortedList[aIndex].mValue);
+  }
+
+  void Clear();
+
+  HeadersGuardEnum Guard() const { return mGuard; }
+  void SetGuard(HeadersGuardEnum aGuard, ErrorResult& aRv);
+
+  void Fill(const InternalHeaders& aInit, ErrorResult& aRv);
+  void Fill(const Sequence<Sequence<nsCString>>& aInit, ErrorResult& aRv);
+  void Fill(const Record<nsCString, nsCString>& aInit, ErrorResult& aRv);
+  void FillResponseHeaders(nsIRequest* aRequest);
+
+  bool HasOnlySimpleHeaders() const;
+
+  bool HasRevalidationHeaders() const;
+
+  static already_AddRefed<InternalHeaders> BasicHeaders(
+      InternalHeaders* aHeaders);
+
+  static already_AddRefed<InternalHeaders> CORSHeaders(
+      InternalHeaders* aHeaders,
+      RequestCredentials aCredentialsMode = RequestCredentials::Omit);
+
+  void GetEntries(nsTArray<InternalHeaders::Entry>& aEntries) const;
+
+  void GetUnsafeHeaders(nsTArray<nsCString>& aNames) const;
+
+ private:
+  virtual ~InternalHeaders();
+
+  static bool IsInvalidName(const nsACString& aName, ErrorResult& aRv);
+  static bool IsInvalidValue(const nsACString& aValue, ErrorResult& aRv);
+  bool IsValidHeaderValue(const nsCString& aLowerName,
+                          const nsCString& aNormalizedValue, ErrorResult& aRv);
+  bool IsImmutable(ErrorResult& aRv) const;
+  bool IsForbiddenRequestHeader(const nsCString& aName,
+                                const nsACString& aValue) const;
+  bool IsForbiddenRequestNoCorsHeader(const nsCString& aName) const;
+  bool IsForbiddenRequestNoCorsHeader(const nsCString& aName,
+                                      const nsACString& aValue) const;
+  bool IsForbiddenResponseHeader(const nsCString& aName) const;
+
+  bool IsInvalidMutableHeader(const nsCString& aName, ErrorResult& aRv) const {
+    return IsInvalidMutableHeader(aName, ""_ns, aRv);
+  }
+
+  bool IsInvalidMutableHeader(const nsCString& aName, const nsACString& aValue,
+                              ErrorResult& aRv) const {
+    return IsInvalidName(aName, aRv) || IsInvalidValue(aValue, aRv) ||
+           IsImmutable(aRv) || IsForbiddenRequestHeader(aName, aValue) ||
+           IsForbiddenRequestNoCorsHeader(aName, aValue) ||
+           IsForbiddenResponseHeader(aName);
+  }
+
+  // This method updates the passed name to match the capitalization of a header
+  // with the same name (ignoring case, per the spec).
+  void ReuseExistingNameIfExists(nsCString& aName) const;
+
+  void RemovePrivilegedNoCorsRequestHeaders();
+
+  void GetInternal(const nsCString& aLowerName, nsACString& aValue,
+                   ErrorResult& aRv) const;
+
+  bool DeleteInternal(const nsCString& aLowerName, ErrorResult& aRv);
+
+  static bool IsNoCorsSafelistedRequestHeaderName(const nsCString& aName);
+
+  static bool IsPrivilegedNoCorsRequestHeaderName(const nsCString& aName);
+
+  static bool IsSimpleHeader(const nsCString& aName, const nsACString& aValue);
+
+  static bool IsRevalidationHeader(const nsCString& aName);
+
+  void MaybeSortList();
+  void SetListDirty();
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_InternalHeaders_h
diff --git a/dom/fetch/InternalRequest.cpp b/dom/fetch/InternalRequest.cpp
new file mode 100644
index 0000000000..41797d3e82
--- /dev/null
+++ b/dom/fetch/InternalRequest.cpp
@@ -0,0 +1,478 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "InternalRequest.h"
+
+#include "InternalResponse.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/FetchTypes.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/dom/WorkerCommon.h"
+#include "mozilla/dom/WorkerPrivate.h"
+#include "mozilla/ipc/IPCStreamUtils.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "mozilla/RemoteLazyInputStreamChild.h"
+#include "nsIContentPolicy.h"
+#include "nsStreamUtils.h"
+
+namespace mozilla::dom {
+// The global is used to extract the principal.
+SafeRefPtr<InternalRequest> InternalRequest::GetRequestConstructorCopy(
+    nsIGlobalObject* aGlobal, ErrorResult& aRv) const {
+  MOZ_RELEASE_ASSERT(!mURLList.IsEmpty(),
+                     "Internal Request's urlList should not be empty when "
+                     "copied from constructor.");
+  auto copy =
+      MakeSafeRefPtr<InternalRequest>(mURLList.LastElement(), mFragment);
+  copy->SetMethod(mMethod);
+  copy->mHeaders = new InternalHeaders(*mHeaders);
+  copy->SetUnsafeRequest();
+  copy->mBodyStream = mBodyStream;
+  copy->mBodyLength = mBodyLength;
+  // The "client" is not stored in our implementation. Fetch API users should
+  // use the appropriate window/document/principal and other Gecko security
+  // mechanisms as appropriate.
+  copy->mReferrer = mReferrer;
+  copy->mReferrerPolicy = mReferrerPolicy;
+  copy->mEnvironmentReferrerPolicy = mEnvironmentReferrerPolicy;
+  copy->mIntegrity = mIntegrity;
+  copy->mMozErrors = mMozErrors;
+
+  copy->mContentPolicyType = mContentPolicyTypeOverridden
+                                 ? mContentPolicyType
+                                 : nsIContentPolicy::TYPE_FETCH;
+  copy->mMode = mMode;
+  copy->mCredentialsMode = mCredentialsMode;
+  copy->mCacheMode = mCacheMode;
+  copy->mRedirectMode = mRedirectMode;
+  copy->mContentPolicyTypeOverridden = mContentPolicyTypeOverridden;
+
+  copy->mPreferredAlternativeDataType = mPreferredAlternativeDataType;
+  copy->mSkipWasmCaching = mSkipWasmCaching;
+  copy->mEmbedderPolicy = mEmbedderPolicy;
+  return copy;
+}
+
+SafeRefPtr<InternalRequest> InternalRequest::Clone() {
+  auto clone = MakeSafeRefPtr<InternalRequest>(*this, ConstructorGuard{});
+
+  if (!mBodyStream) {
+    return clone;
+  }
+
+  nsCOMPtr<nsIInputStream> clonedBody;
+  nsCOMPtr<nsIInputStream> replacementBody;
+
+  nsresult rv = NS_CloneInputStream(mBodyStream, getter_AddRefs(clonedBody),
+                                    getter_AddRefs(replacementBody));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return nullptr;
+  }
+
+  clone->mBodyStream.swap(clonedBody);
+  if (replacementBody) {
+    mBodyStream.swap(replacementBody);
+  }
+  return clone;
+}
+InternalRequest::InternalRequest(const nsACString& aURL,
+                                 const nsACString& aFragment)
+    : mMethod("GET"),
+      mHeaders(new InternalHeaders(HeadersGuardEnum::None)),
+      mBodyLength(InternalResponse::UNKNOWN_BODY_SIZE),
+      mContentPolicyType(nsIContentPolicy::TYPE_FETCH),
+      mReferrer(NS_LITERAL_STRING_FROM_CSTRING(kFETCH_CLIENT_REFERRER_STR)),
+      mReferrerPolicy(ReferrerPolicy::_empty),
+      mEnvironmentReferrerPolicy(ReferrerPolicy::_empty),
+      mMode(RequestMode::No_cors),
+      mCredentialsMode(RequestCredentials::Omit),
+      mCacheMode(RequestCache::Default),
+      mRedirectMode(RequestRedirect::Follow) {
+  MOZ_ASSERT(!aURL.IsEmpty());
+  AddURL(aURL, aFragment);
+}
+InternalRequest::InternalRequest(
+    const nsACString& aURL, const nsACString& aFragment,
+    const nsACString& aMethod, already_AddRefed<InternalHeaders> aHeaders,
+    RequestCache aCacheMode, RequestMode aMode,
+    RequestRedirect aRequestRedirect, RequestCredentials aRequestCredentials,
+    const nsAString& aReferrer, ReferrerPolicy aReferrerPolicy,
+    nsContentPolicyType aContentPolicyType, const nsAString& aIntegrity)
+    : mMethod(aMethod),
+      mHeaders(aHeaders),
+      mBodyLength(InternalResponse::UNKNOWN_BODY_SIZE),
+      mContentPolicyType(aContentPolicyType),
+      mReferrer(aReferrer),
+      mReferrerPolicy(aReferrerPolicy),
+      mEnvironmentReferrerPolicy(ReferrerPolicy::_empty),
+      mMode(aMode),
+      mCredentialsMode(aRequestCredentials),
+      mCacheMode(aCacheMode),
+      mRedirectMode(aRequestRedirect),
+      mIntegrity(aIntegrity) {
+  MOZ_ASSERT(!aURL.IsEmpty());
+  AddURL(aURL, aFragment);
+}
+InternalRequest::InternalRequest(const InternalRequest& aOther,
+                                 ConstructorGuard)
+    : mMethod(aOther.mMethod),
+      mURLList(aOther.mURLList.Clone()),
+      mHeaders(new InternalHeaders(*aOther.mHeaders)),
+      mBodyLength(InternalResponse::UNKNOWN_BODY_SIZE),
+      mContentPolicyType(aOther.mContentPolicyType),
+      mReferrer(aOther.mReferrer),
+      mReferrerPolicy(aOther.mReferrerPolicy),
+      mEnvironmentReferrerPolicy(aOther.mEnvironmentReferrerPolicy),
+      mMode(aOther.mMode),
+      mCredentialsMode(aOther.mCredentialsMode),
+      mResponseTainting(aOther.mResponseTainting),
+      mCacheMode(aOther.mCacheMode),
+      mRedirectMode(aOther.mRedirectMode),
+      mIntegrity(aOther.mIntegrity),
+      mMozErrors(aOther.mMozErrors),
+      mFragment(aOther.mFragment),
+      mSkipServiceWorker(aOther.mSkipServiceWorker),
+      mSkipWasmCaching(aOther.mSkipWasmCaching),
+      mSynchronous(aOther.mSynchronous),
+      mUnsafeRequest(aOther.mUnsafeRequest),
+      mUseURLCredentials(aOther.mUseURLCredentials),
+      mContentPolicyTypeOverridden(aOther.mContentPolicyTypeOverridden),
+      mEmbedderPolicy(aOther.mEmbedderPolicy),
+      mInterceptionContentPolicyType(aOther.mInterceptionContentPolicyType),
+      mInterceptionRedirectChain(aOther.mInterceptionRedirectChain),
+      mInterceptionFromThirdParty(aOther.mInterceptionFromThirdParty) {
+  // NOTE: does not copy body stream... use the fallible Clone() for that
+
+  if (aOther.GetInterceptionTriggeringPrincipalInfo()) {
+    mInterceptionTriggeringPrincipalInfo =
+        MakeUnique<mozilla::ipc::PrincipalInfo>(
+            *(aOther.GetInterceptionTriggeringPrincipalInfo().get()));
+  }
+}
+
+InternalRequest::InternalRequest(const IPCInternalRequest& aIPCRequest)
+    : mMethod(aIPCRequest.method()),
+      mURLList(aIPCRequest.urlList().Clone()),
+      mHeaders(new InternalHeaders(aIPCRequest.headers(),
+                                   aIPCRequest.headersGuard())),
+      mBodyLength(aIPCRequest.bodySize()),
+      mPreferredAlternativeDataType(aIPCRequest.preferredAlternativeDataType()),
+      mContentPolicyType(
+          static_cast<nsContentPolicyType>(aIPCRequest.contentPolicyType())),
+      mReferrer(aIPCRequest.referrer()),
+      mReferrerPolicy(aIPCRequest.referrerPolicy()),
+      mEnvironmentReferrerPolicy(aIPCRequest.environmentReferrerPolicy()),
+      mMode(aIPCRequest.requestMode()),
+      mCredentialsMode(aIPCRequest.requestCredentials()),
+      mCacheMode(aIPCRequest.cacheMode()),
+      mRedirectMode(aIPCRequest.requestRedirect()),
+      mIntegrity(aIPCRequest.integrity()),
+      mFragment(aIPCRequest.fragment()),
+      mEmbedderPolicy(aIPCRequest.embedderPolicy()),
+      mInterceptionContentPolicyType(static_cast<nsContentPolicyType>(
+          aIPCRequest.interceptionContentPolicyType())),
+      mInterceptionRedirectChain(aIPCRequest.interceptionRedirectChain()),
+      mInterceptionFromThirdParty(aIPCRequest.interceptionFromThirdParty()) {
+  if (aIPCRequest.principalInfo()) {
+    mPrincipalInfo = MakeUnique<mozilla::ipc::PrincipalInfo>(
+        aIPCRequest.principalInfo().ref());
+  }
+
+  if (aIPCRequest.interceptionTriggeringPrincipalInfo()) {
+    mInterceptionTriggeringPrincipalInfo =
+        MakeUnique<mozilla::ipc::PrincipalInfo>(
+            aIPCRequest.interceptionTriggeringPrincipalInfo().ref());
+  }
+
+  const Maybe<BodyStreamVariant>& body = aIPCRequest.body();
+
+  if (body) {
+    if (body->type() == BodyStreamVariant::TParentToChildStream) {
+      mBodyStream = body->get_ParentToChildStream().get_RemoteLazyInputStream();
+    }
+    if (body->type() == BodyStreamVariant::TChildToParentStream) {
+      mBodyStream =
+          DeserializeIPCStream(body->get_ChildToParentStream().stream());
+    }
+  }
+}
+
+void InternalRequest::ToIPCInternalRequest(
+    IPCInternalRequest* aIPCRequest, mozilla::ipc::PBackgroundChild* aManager) {
+  aIPCRequest->method() = mMethod;
+  for (const auto& url : mURLList) {
+    aIPCRequest->urlList().AppendElement(url);
+  }
+  mHeaders->ToIPC(aIPCRequest->headers(), aIPCRequest->headersGuard());
+  aIPCRequest->bodySize() = mBodyLength;
+  aIPCRequest->preferredAlternativeDataType() = mPreferredAlternativeDataType;
+  aIPCRequest->contentPolicyType() = mContentPolicyType;
+  aIPCRequest->referrer() = mReferrer;
+  aIPCRequest->referrerPolicy() = mReferrerPolicy;
+  aIPCRequest->environmentReferrerPolicy() = mEnvironmentReferrerPolicy;
+  aIPCRequest->requestMode() = mMode;
+  aIPCRequest->requestCredentials() = mCredentialsMode;
+  aIPCRequest->cacheMode() = mCacheMode;
+  aIPCRequest->requestRedirect() = mRedirectMode;
+  aIPCRequest->integrity() = mIntegrity;
+  aIPCRequest->fragment() = mFragment;
+  aIPCRequest->embedderPolicy() = mEmbedderPolicy;
+
+  if (mPrincipalInfo) {
+    aIPCRequest->principalInfo() = Some(*mPrincipalInfo);
+  }
+
+  if (mBodyStream) {
+    nsCOMPtr<nsIInputStream> body = mBodyStream;
+    aIPCRequest->body().emplace(ChildToParentStream());
+    DebugOnly<bool> ok = mozilla::ipc::SerializeIPCStream(
+        body.forget(), aIPCRequest->body()->get_ChildToParentStream().stream(),
+        /* aAllowLazy */ false);
+    MOZ_ASSERT(ok);
+  }
+}
+
+InternalRequest::~InternalRequest() = default;
+
+void InternalRequest::SetContentPolicyType(
+    nsContentPolicyType aContentPolicyType) {
+  mContentPolicyType = aContentPolicyType;
+}
+
+void InternalRequest::OverrideContentPolicyType(
+    nsContentPolicyType aContentPolicyType) {
+  SetContentPolicyType(aContentPolicyType);
+  mContentPolicyTypeOverridden = true;
+}
+
+void InternalRequest::SetInterceptionContentPolicyType(
+    nsContentPolicyType aContentPolicyType) {
+  mInterceptionContentPolicyType = aContentPolicyType;
+}
+
+/* static */
+RequestDestination InternalRequest::MapContentPolicyTypeToRequestDestination(
+    nsContentPolicyType aContentPolicyType) {
+  switch (aContentPolicyType) {
+    case nsIContentPolicy::TYPE_OTHER:
+      return RequestDestination::_empty;
+    case nsIContentPolicy::TYPE_INTERNAL_SCRIPT:
+    case nsIContentPolicy::TYPE_INTERNAL_SCRIPT_PRELOAD:
+    case nsIContentPolicy::TYPE_INTERNAL_MODULE:
+    case nsIContentPolicy::TYPE_INTERNAL_MODULE_PRELOAD:
+    case nsIContentPolicy::TYPE_INTERNAL_SERVICE_WORKER:
+    case nsIContentPolicy::TYPE_INTERNAL_WORKER_IMPORT_SCRIPTS:
+    case nsIContentPolicy::TYPE_INTERNAL_CHROMEUTILS_COMPILED_SCRIPT:
+    case nsIContentPolicy::TYPE_INTERNAL_FRAME_MESSAGEMANAGER_SCRIPT:
+    case nsIContentPolicy::TYPE_SCRIPT:
+      return RequestDestination::Script;
+    case nsIContentPolicy::TYPE_INTERNAL_WORKER:
+    case nsIContentPolicy::TYPE_INTERNAL_WORKER_STATIC_MODULE:
+      return RequestDestination::Worker;
+    case nsIContentPolicy::TYPE_INTERNAL_SHARED_WORKER:
+      return RequestDestination::Sharedworker;
+    case nsIContentPolicy::TYPE_IMAGESET:
+    case nsIContentPolicy::TYPE_INTERNAL_IMAGE:
+    case nsIContentPolicy::TYPE_INTERNAL_IMAGE_PRELOAD:
+    case nsIContentPolicy::TYPE_INTERNAL_IMAGE_FAVICON:
+    case nsIContentPolicy::TYPE_IMAGE:
+      return RequestDestination::Image;
+    case nsIContentPolicy::TYPE_STYLESHEET:
+    case nsIContentPolicy::TYPE_INTERNAL_STYLESHEET:
+    case nsIContentPolicy::TYPE_INTERNAL_STYLESHEET_PRELOAD:
+      return RequestDestination::Style;
+    case nsIContentPolicy::TYPE_OBJECT:
+    case nsIContentPolicy::TYPE_INTERNAL_OBJECT:
+      return RequestDestination::Object;
+    case nsIContentPolicy::TYPE_INTERNAL_EMBED:
+      return RequestDestination::Embed;
+    case nsIContentPolicy::TYPE_DOCUMENT:
+      return RequestDestination::Document;
+    case nsIContentPolicy::TYPE_SUBDOCUMENT:
+    case nsIContentPolicy::TYPE_INTERNAL_IFRAME:
+      return RequestDestination::Iframe;
+    case nsIContentPolicy::TYPE_INTERNAL_FRAME:
+      return RequestDestination::Frame;
+    case nsIContentPolicy::TYPE_PING:
+      return RequestDestination::_empty;
+    case nsIContentPolicy::TYPE_XMLHTTPREQUEST:
+    case nsIContentPolicy::TYPE_INTERNAL_XMLHTTPREQUEST:
+      return RequestDestination::_empty;
+    case nsIContentPolicy::TYPE_INTERNAL_EVENTSOURCE:
+      return RequestDestination::_empty;
+    case nsIContentPolicy::TYPE_OBJECT_SUBREQUEST:
+      return RequestDestination::_empty;
+    case nsIContentPolicy::TYPE_DTD:
+    case nsIContentPolicy::TYPE_INTERNAL_DTD:
+    case nsIContentPolicy::TYPE_INTERNAL_FORCE_ALLOWED_DTD:
+      return RequestDestination::_empty;
+    case nsIContentPolicy::TYPE_FONT:
+    case nsIContentPolicy::TYPE_INTERNAL_FONT_PRELOAD:
+    case nsIContentPolicy::TYPE_UA_FONT:
+      return RequestDestination::Font;
+    case nsIContentPolicy::TYPE_MEDIA:
+      return RequestDestination::_empty;
+    case nsIContentPolicy::TYPE_INTERNAL_AUDIO:
+      return RequestDestination::Audio;
+    case nsIContentPolicy::TYPE_INTERNAL_VIDEO:
+      return RequestDestination::Video;
+    case nsIContentPolicy::TYPE_INTERNAL_TRACK:
+      return RequestDestination::Track;
+    case nsIContentPolicy::TYPE_WEBSOCKET:
+      return RequestDestination::_empty;
+    case nsIContentPolicy::TYPE_CSP_REPORT:
+      return RequestDestination::Report;
+    case nsIContentPolicy::TYPE_XSLT:
+      return RequestDestination::Xslt;
+    case nsIContentPolicy::TYPE_BEACON:
+      return RequestDestination::_empty;
+    case nsIContentPolicy::TYPE_FETCH:
+    case nsIContentPolicy::TYPE_INTERNAL_FETCH_PRELOAD:
+      return RequestDestination::_empty;
+    case nsIContentPolicy::TYPE_WEB_MANIFEST:
+      return RequestDestination::Manifest;
+    case nsIContentPolicy::TYPE_SAVEAS_DOWNLOAD:
+      return RequestDestination::_empty;
+    case nsIContentPolicy::TYPE_SPECULATIVE:
+      return RequestDestination::_empty;
+    case nsIContentPolicy::TYPE_INTERNAL_AUDIOWORKLET:
+      return RequestDestination::Audioworklet;
+    case nsIContentPolicy::TYPE_INTERNAL_PAINTWORKLET:
+      return RequestDestination::Paintworklet;
+    case nsIContentPolicy::TYPE_PROXIED_WEBRTC_MEDIA:
+      return RequestDestination::_empty;
+    case nsIContentPolicy::TYPE_WEB_IDENTITY:
+      return RequestDestination::_empty;
+    case nsIContentPolicy::TYPE_WEB_TRANSPORT:
+      return RequestDestination::_empty;
+    case nsIContentPolicy::TYPE_INVALID:
+    case nsIContentPolicy::TYPE_END:
+      break;
+      // Do not add default: so that compilers can catch the missing case.
+  }
+
+  MOZ_ASSERT(false, "Unhandled nsContentPolicyType value");
+  return RequestDestination::_empty;
+}
+
+// static
+bool InternalRequest::IsNavigationContentPolicy(
+    nsContentPolicyType aContentPolicyType) {
+  // https://fetch.spec.whatwg.org/#navigation-request-context
+  //
+  // A navigation request context is one of "form", "frame", "hyperlink",
+  // "iframe", "internal" (as long as context frame type is not "none"),
+  // "location", "metarefresh", and "prerender".
+  //
+  // Note, all of these request types are effectively initiated by nsDocShell.
+  return aContentPolicyType == nsIContentPolicy::TYPE_DOCUMENT ||
+         aContentPolicyType == nsIContentPolicy::TYPE_SUBDOCUMENT ||
+         aContentPolicyType == nsIContentPolicy::TYPE_INTERNAL_FRAME ||
+         aContentPolicyType == nsIContentPolicy::TYPE_INTERNAL_IFRAME;
+}
+
+// static
+bool InternalRequest::IsWorkerContentPolicy(
+    nsContentPolicyType aContentPolicyType) {
+  // https://fetch.spec.whatwg.org/#worker-request-context
+  //
+  // A worker request context is one of "serviceworker", "sharedworker", and
+  // "worker".
+  //
+  // Note, service workers are not included here because currently there is
+  // no way to generate a Request with a "serviceworker" RequestDestination.
+  // ServiceWorker scripts cannot be intercepted.
+  return aContentPolicyType == nsIContentPolicy::TYPE_INTERNAL_WORKER ||
+         aContentPolicyType == nsIContentPolicy::TYPE_INTERNAL_SHARED_WORKER;
+}
+
+bool InternalRequest::IsNavigationRequest() const {
+  return IsNavigationContentPolicy(mContentPolicyType);
+}
+
+bool InternalRequest::IsWorkerRequest() const {
+  return IsWorkerContentPolicy(mContentPolicyType);
+}
+
+bool InternalRequest::IsClientRequest() const {
+  return IsNavigationRequest() || IsWorkerRequest();
+}
+
+// static
+RequestMode InternalRequest::MapChannelToRequestMode(nsIChannel* aChannel) {
+  MOZ_ASSERT(aChannel);
+
+  nsCOMPtr<nsILoadInfo> loadInfo = aChannel->LoadInfo();
+
+  nsContentPolicyType contentPolicy = loadInfo->InternalContentPolicyType();
+  if (IsNavigationContentPolicy(contentPolicy)) {
+    return RequestMode::Navigate;
+  }
+
+  // TODO: remove the worker override once securityMode is fully implemented
+  // (bug 1189945)
+  if (IsWorkerContentPolicy(contentPolicy)) {
+    return RequestMode::Same_origin;
+  }
+
+  uint32_t securityMode = loadInfo->GetSecurityMode();
+
+  switch (securityMode) {
+    case nsILoadInfo::SEC_REQUIRE_SAME_ORIGIN_INHERITS_SEC_CONTEXT:
+    case nsILoadInfo::SEC_REQUIRE_SAME_ORIGIN_DATA_IS_BLOCKED:
+      return RequestMode::Same_origin;
+    case nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_INHERITS_SEC_CONTEXT:
+    case nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_SEC_CONTEXT_IS_NULL:
+      return RequestMode::No_cors;
+    case nsILoadInfo::SEC_REQUIRE_CORS_INHERITS_SEC_CONTEXT:
+      // TODO: Check additional flag force-preflight after bug 1199693 (bug
+      // 1189945)
+      return RequestMode::Cors;
+    default:
+      MOZ_ASSERT_UNREACHABLE("Unexpected security mode!");
+      return RequestMode::Same_origin;
+  }
+}
+
+// static
+RequestCredentials InternalRequest::MapChannelToRequestCredentials(
+    nsIChannel* aChannel) {
+  MOZ_ASSERT(aChannel);
+
+  nsCOMPtr<nsILoadInfo> loadInfo = aChannel->LoadInfo();
+
+  uint32_t cookiePolicy = loadInfo->GetCookiePolicy();
+
+  if (cookiePolicy == nsILoadInfo::SEC_COOKIES_INCLUDE) {
+    return RequestCredentials::Include;
+  } else if (cookiePolicy == nsILoadInfo::SEC_COOKIES_OMIT) {
+    return RequestCredentials::Omit;
+  } else if (cookiePolicy == nsILoadInfo::SEC_COOKIES_SAME_ORIGIN) {
+    return RequestCredentials::Same_origin;
+  }
+
+  MOZ_ASSERT_UNREACHABLE("Unexpected cookie policy!");
+  return RequestCredentials::Same_origin;
+}
+
+void InternalRequest::MaybeSkipCacheIfPerformingRevalidation() {
+  if (mCacheMode == RequestCache::Default &&
+      mHeaders->HasRevalidationHeaders()) {
+    mCacheMode = RequestCache::No_store;
+  }
+}
+
+void InternalRequest::SetPrincipalInfo(
+    UniquePtr<mozilla::ipc::PrincipalInfo> aPrincipalInfo) {
+  mPrincipalInfo = std::move(aPrincipalInfo);
+}
+
+void InternalRequest::SetInterceptionTriggeringPrincipalInfo(
+    UniquePtr<mozilla::ipc::PrincipalInfo> aPrincipalInfo) {
+  mInterceptionTriggeringPrincipalInfo = std::move(aPrincipalInfo);
+}
+}  // namespace mozilla::dom
diff --git a/dom/fetch/InternalRequest.h b/dom/fetch/InternalRequest.h
new file mode 100644
index 0000000000..3dfbb9284d
--- /dev/null
+++ b/dom/fetch/InternalRequest.h
@@ -0,0 +1,489 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_InternalRequest_h
+#define mozilla_dom_InternalRequest_h
+
+#include "mozilla/dom/HeadersBinding.h"
+#include "mozilla/dom/InternalHeaders.h"
+#include "mozilla/dom/RequestBinding.h"
+#include "mozilla/dom/SafeRefPtr.h"
+#include "mozilla/LoadTainting.h"
+#include "mozilla/UniquePtr.h"
+
+#include "nsIChannelEventSink.h"
+#include "nsIInputStream.h"
+#include "nsISupportsImpl.h"
+#include "mozilla/net/NeckoChannelParams.h"
+#ifdef DEBUG
+#  include "nsIURLParser.h"
+#  include "nsNetCID.h"
+#  include "nsServiceManagerUtils.h"
+#endif
+
+using mozilla::net::RedirectHistoryEntryInfo;
+
+namespace mozilla {
+
+namespace ipc {
+class PBackgroundChild;
+class PrincipalInfo;
+}  // namespace ipc
+
+namespace dom {
+
+/*
+ * The mapping of RequestDestination and nsContentPolicyType is currently as the
+ * following.
+ *
+ * RequestDestination| nsContentPolicyType
+ * ------------------+--------------------
+ * "audio"           | TYPE_INTERNAL_AUDIO
+ * "audioworklet"    | TYPE_INTERNAL_AUDIOWORKLET
+ * "document"        | TYPE_DOCUMENT
+ * "embed"           | TYPE_INTERNAL_EMBED
+ * "font"            | TYPE_FONT, TYPE_INTERNAL_FONT_PRELOAD
+ * "frame"           | TYPE_INTERNAL_FRAME
+ * "iframe"          | TYPE_SUBDOCUMENT, TYPE_INTERNAL_IFRAME
+ * "image"           | TYPE_INTERNAL_IMAGE, TYPE_INTERNAL_IMAGE_PRELOAD,
+ *                   | TYPE_IMAGE, TYPE_INTERNAL_IMAGE_FAVICON, TYPE_IMAGESET
+ * "manifest"        | TYPE_WEB_MANIFEST
+ * "object"          | TYPE_INTERNAL_OBJECT, TYPE_OBJECT
+ * "paintworklet"    | TYPE_INTERNAL_PAINTWORKLET
+ * "report"          | TYPE_CSP_REPORT
+ * "script"          | TYPE_INTERNAL_SCRIPT, TYPE_INTERNAL_SCRIPT_PRELOAD,
+ *                   | TYPE_INTERNAL_MODULE, TYPE_INTERNAL_MODULE_PRELOAD,
+ *                   | TYPE_SCRIPT,
+ *                   | TYPE_INTERNAL_SERVICE_WORKER,
+ *                   | TYPE_INTERNAL_WORKER_IMPORT_SCRIPTS,
+ *                   | TYPE_INTERNAL_CHROMEUTILS_COMPILED_SCRIPT
+ *                   | TYPE_INTERNAL_FRAME_MESSAGEMANAGER_SCRIPT
+ * "sharedworker"    | TYPE_INTERNAL_SHARED_WORKER
+ * "serviceworker"   | The spec lists this as a valid value for the enum,
+ *                   | however it is impossible to observe a request with this
+ *                   | destination value.
+ * "style"           | TYPE_INTERNAL_STYLESHEET,
+ *                   | TYPE_INTERNAL_STYLESHEET_PRELOAD,
+ *                   | TYPE_STYLESHEET
+ * "track"           | TYPE_INTERNAL_TRACK
+ * "video"           | TYPE_INTERNAL_VIDEO
+ * "worker"          | TYPE_INTERNAL_WORKER, TYPE_INTERNAL_WORKER_STATIC_MODULE
+ * "xslt"            | TYPE_XSLT
+ * ""                | Default for everything else.
+ *
+ */
+
+class IPCInternalRequest;
+class Request;
+
+#define kFETCH_CLIENT_REFERRER_STR "about:client"
+class InternalRequest final : public AtomicSafeRefCounted<InternalRequest> {
+  friend class Request;
+
+ public:
+  MOZ_DECLARE_REFCOUNTED_TYPENAME(InternalRequest)
+  InternalRequest(const nsACString& aURL, const nsACString& aFragment);
+  InternalRequest(const nsACString& aURL, const nsACString& aFragment,
+                  const nsACString& aMethod,
+                  already_AddRefed<InternalHeaders> aHeaders,
+                  RequestCache aCacheMode, RequestMode aMode,
+                  RequestRedirect aRequestRedirect,
+                  RequestCredentials aRequestCredentials,
+                  const nsAString& aReferrer, ReferrerPolicy aReferrerPolicy,
+                  nsContentPolicyType aContentPolicyType,
+                  const nsAString& aIntegrity);
+
+  explicit InternalRequest(const IPCInternalRequest& aIPCRequest);
+
+  void ToIPCInternalRequest(IPCInternalRequest* aIPCRequest,
+                            mozilla::ipc::PBackgroundChild* aManager);
+
+  SafeRefPtr<InternalRequest> Clone();
+
+  void GetMethod(nsCString& aMethod) const { aMethod.Assign(mMethod); }
+
+  void SetMethod(const nsACString& aMethod) { mMethod.Assign(aMethod); }
+
+  bool HasSimpleMethod() const {
+    return mMethod.LowerCaseEqualsASCII("get") ||
+           mMethod.LowerCaseEqualsASCII("post") ||
+           mMethod.LowerCaseEqualsASCII("head");
+  }
+  // GetURL should get the request's current url with fragment. A request has
+  // an associated current url. It is a pointer to the last fetch URL in
+  // request's url list.
+  void GetURL(nsACString& aURL) const {
+    aURL.Assign(GetURLWithoutFragment());
+    if (GetFragment().IsEmpty()) {
+      return;
+    }
+    aURL.AppendLiteral("#");
+    aURL.Append(GetFragment());
+  }
+
+  const nsCString& GetURLWithoutFragment() const {
+    MOZ_RELEASE_ASSERT(!mURLList.IsEmpty(),
+                       "Internal Request's urlList should not be empty.");
+
+    return mURLList.LastElement();
+  }
+
+  // A safe guard for ensuring that request's URL is only allowed to be set in a
+  // sw internal redirect.
+  void SetURLForInternalRedirect(const uint32_t aFlag, const nsACString& aURL,
+                                 const nsACString& aFragment) {
+    // Only check in debug build to prevent it from being used unexpectedly.
+    MOZ_ASSERT(aFlag & nsIChannelEventSink::REDIRECT_INTERNAL);
+
+    return SetURL(aURL, aFragment);
+  }
+
+  // AddURL should append the url into url list.
+  // Normally we strip the fragment from the URL in Request::Constructor and
+  // pass the fragment as the second argument into it.
+  // If a fragment is present in the URL it must be stripped and passed in
+  // separately.
+  void AddURL(const nsACString& aURL, const nsACString& aFragment) {
+    MOZ_ASSERT(!aURL.IsEmpty());
+    MOZ_ASSERT(!aURL.Contains('#'));
+
+    mURLList.AppendElement(aURL);
+
+    mFragment.Assign(aFragment);
+  }
+  // Get the URL list without their fragments.
+  void GetURLListWithoutFragment(nsTArray<nsCString>& aURLList) {
+    aURLList.Assign(mURLList);
+  }
+  void GetReferrer(nsAString& aReferrer) const { aReferrer.Assign(mReferrer); }
+
+  void SetReferrer(const nsAString& aReferrer) {
+#ifdef DEBUG
+    bool validReferrer = false;
+    if (aReferrer.IsEmpty() ||
+        aReferrer.EqualsLiteral(kFETCH_CLIENT_REFERRER_STR)) {
+      validReferrer = true;
+    } else {
+      nsCOMPtr<nsIURLParser> parser = do_GetService(NS_STDURLPARSER_CONTRACTID);
+      if (!parser) {
+        NS_WARNING("Could not get parser to validate URL!");
+      } else {
+        uint32_t schemePos;
+        int32_t schemeLen;
+        uint32_t authorityPos;
+        int32_t authorityLen;
+        uint32_t pathPos;
+        int32_t pathLen;
+
+        NS_ConvertUTF16toUTF8 ref(aReferrer);
+        nsresult rv =
+            parser->ParseURL(ref.get(), ref.Length(), &schemePos, &schemeLen,
+                             &authorityPos, &authorityLen, &pathPos, &pathLen);
+        if (NS_FAILED(rv)) {
+          NS_WARNING("Invalid referrer URL!");
+        } else if (schemeLen < 0 || authorityLen < 0) {
+          NS_WARNING("Invalid referrer URL!");
+        } else {
+          validReferrer = true;
+        }
+      }
+    }
+
+    MOZ_ASSERT(validReferrer);
+#endif
+
+    mReferrer.Assign(aReferrer);
+  }
+
+  ReferrerPolicy ReferrerPolicy_() const { return mReferrerPolicy; }
+
+  void SetReferrerPolicy(ReferrerPolicy aReferrerPolicy) {
+    mReferrerPolicy = aReferrerPolicy;
+  }
+
+  ReferrerPolicy GetEnvironmentReferrerPolicy() const {
+    return mEnvironmentReferrerPolicy;
+  }
+
+  void SetEnvironmentReferrerPolicy(ReferrerPolicy aReferrerPolicy) {
+    mEnvironmentReferrerPolicy = aReferrerPolicy;
+  }
+
+  bool SkipServiceWorker() const { return mSkipServiceWorker; }
+
+  void SetSkipServiceWorker() { mSkipServiceWorker = true; }
+
+  bool SkipWasmCaching() const { return mSkipWasmCaching; }
+
+  void SetSkipWasmCaching() { mSkipWasmCaching = true; }
+
+  bool IsSynchronous() const { return mSynchronous; }
+
+  RequestMode Mode() const { return mMode; }
+
+  void SetMode(RequestMode aMode) { mMode = aMode; }
+
+  RequestCredentials GetCredentialsMode() const { return mCredentialsMode; }
+
+  void SetCredentialsMode(RequestCredentials aCredentialsMode) {
+    mCredentialsMode = aCredentialsMode;
+  }
+
+  LoadTainting GetResponseTainting() const { return mResponseTainting; }
+
+  void MaybeIncreaseResponseTainting(LoadTainting aTainting) {
+    if (aTainting > mResponseTainting) {
+      mResponseTainting = aTainting;
+    }
+  }
+
+  RequestCache GetCacheMode() const { return mCacheMode; }
+
+  void SetCacheMode(RequestCache aCacheMode) { mCacheMode = aCacheMode; }
+
+  RequestRedirect GetRedirectMode() const { return mRedirectMode; }
+
+  void SetRedirectMode(RequestRedirect aRedirectMode) {
+    mRedirectMode = aRedirectMode;
+  }
+
+  const nsString& GetIntegrity() const { return mIntegrity; }
+
+  void SetIntegrity(const nsAString& aIntegrity) {
+    mIntegrity.Assign(aIntegrity);
+  }
+
+  bool MozErrors() const { return mMozErrors; }
+
+  void SetMozErrors() { mMozErrors = true; }
+
+  const nsCString& GetFragment() const { return mFragment; }
+
+  nsContentPolicyType ContentPolicyType() const { return mContentPolicyType; }
+  void SetContentPolicyType(nsContentPolicyType aContentPolicyType);
+
+  void OverrideContentPolicyType(nsContentPolicyType aContentPolicyType);
+
+  RequestDestination Destination() const {
+    return MapContentPolicyTypeToRequestDestination(mContentPolicyType);
+  }
+
+  bool UnsafeRequest() const { return mUnsafeRequest; }
+
+  void SetUnsafeRequest() { mUnsafeRequest = true; }
+
+  InternalHeaders* Headers() const { return mHeaders; }
+
+  void SetHeaders(InternalHeaders* aHeaders) {
+    MOZ_ASSERT(aHeaders);
+    mHeaders = aHeaders;
+  }
+
+  void SetBody(nsIInputStream* aStream, int64_t aBodyLength) {
+    // A request's body may not be reset once set.
+    MOZ_ASSERT_IF(aStream, !mBodyStream);
+    mBodyStream = aStream;
+    mBodyLength = aBodyLength;
+  }
+
+  // Will return the original stream!
+  // Use a tee or copy if you don't want to erase the original.
+  void GetBody(nsIInputStream** aStream, int64_t* aBodyLength = nullptr) const {
+    nsCOMPtr<nsIInputStream> s = mBodyStream;
+    s.forget(aStream);
+
+    if (aBodyLength) {
+      *aBodyLength = mBodyLength;
+    }
+  }
+
+  void SetBodyBlobURISpec(nsACString& aBlobURISpec) {
+    mBodyBlobURISpec = aBlobURISpec;
+  }
+
+  const nsACString& BodyBlobURISpec() const { return mBodyBlobURISpec; }
+
+  void SetBodyLocalPath(nsAString& aLocalPath) { mBodyLocalPath = aLocalPath; }
+
+  const nsAString& BodyLocalPath() const { return mBodyLocalPath; }
+
+  // The global is used as the client for the new object.
+  SafeRefPtr<InternalRequest> GetRequestConstructorCopy(
+      nsIGlobalObject* aGlobal, ErrorResult& aRv) const;
+
+  bool IsNavigationRequest() const;
+
+  bool IsWorkerRequest() const;
+
+  bool IsClientRequest() const;
+
+  void MaybeSkipCacheIfPerformingRevalidation();
+
+  bool IsContentPolicyTypeOverridden() const {
+    return mContentPolicyTypeOverridden;
+  }
+
+  static RequestMode MapChannelToRequestMode(nsIChannel* aChannel);
+
+  static RequestCredentials MapChannelToRequestCredentials(
+      nsIChannel* aChannel);
+
+  // Takes ownership of the principal info.
+  void SetPrincipalInfo(UniquePtr<mozilla::ipc::PrincipalInfo> aPrincipalInfo);
+  const UniquePtr<mozilla::ipc::PrincipalInfo>& GetPrincipalInfo() const {
+    return mPrincipalInfo;
+  }
+
+  const nsCString& GetPreferredAlternativeDataType() const {
+    return mPreferredAlternativeDataType;
+  }
+
+  void SetPreferredAlternativeDataType(const nsACString& aDataType) {
+    mPreferredAlternativeDataType = aDataType;
+  }
+
+  ~InternalRequest();
+
+  InternalRequest(const InternalRequest& aOther) = delete;
+
+  void SetEmbedderPolicy(nsILoadInfo::CrossOriginEmbedderPolicy aPolicy) {
+    mEmbedderPolicy = aPolicy;
+  }
+
+  nsILoadInfo::CrossOriginEmbedderPolicy GetEmbedderPolicy() const {
+    return mEmbedderPolicy;
+  }
+
+  void SetInterceptionTriggeringPrincipalInfo(
+      UniquePtr<mozilla::ipc::PrincipalInfo> aPrincipalInfo);
+
+  const UniquePtr<mozilla::ipc::PrincipalInfo>&
+  GetInterceptionTriggeringPrincipalInfo() const {
+    return mInterceptionTriggeringPrincipalInfo;
+  }
+
+  nsContentPolicyType InterceptionContentPolicyType() const {
+    return mInterceptionContentPolicyType;
+  }
+  void SetInterceptionContentPolicyType(nsContentPolicyType aContentPolicyType);
+
+  const nsTArray<RedirectHistoryEntryInfo>& InterceptionRedirectChain() const {
+    return mInterceptionRedirectChain;
+  }
+
+  void SetInterceptionRedirectChain(
+      const nsTArray<RedirectHistoryEntryInfo>& aRedirectChain) {
+    mInterceptionRedirectChain = aRedirectChain;
+  }
+
+  const bool& InterceptionFromThirdParty() const {
+    return mInterceptionFromThirdParty;
+  }
+
+  void SetInterceptionFromThirdParty(bool aFromThirdParty) {
+    mInterceptionFromThirdParty = aFromThirdParty;
+  }
+
+ private:
+  struct ConstructorGuard {};
+
+ public:
+  // Does not copy mBodyStream.  Use fallible Clone() for complete copy.
+  InternalRequest(const InternalRequest& aOther, ConstructorGuard);
+
+ private:
+  // Map the content policy type to the associated fetch destination, as defined
+  // by the spec at https://fetch.spec.whatwg.org/#concept-request-destination.
+  // Note that while the HTML spec for the "Link" element and its "as" attribute
+  // (https://html.spec.whatwg.org/#attr-link-as) reuse fetch's definition of
+  // destination.
+  static RequestDestination MapContentPolicyTypeToRequestDestination(
+      nsContentPolicyType aContentPolicyType);
+
+  static bool IsNavigationContentPolicy(nsContentPolicyType aContentPolicyType);
+
+  static bool IsWorkerContentPolicy(nsContentPolicyType aContentPolicyType);
+
+  // It should only be called while there is a service-worker-internal-redirect.
+  void SetURL(const nsACString& aURL, const nsACString& aFragment) {
+    MOZ_ASSERT(!aURL.IsEmpty());
+    MOZ_ASSERT(!aURL.Contains('#'));
+    MOZ_ASSERT(mURLList.Length() > 0);
+
+    mURLList.LastElement() = aURL;
+    mFragment.Assign(aFragment);
+  }
+
+  nsCString mMethod;
+  // mURLList: a list of one or more fetch URLs
+  nsTArray<nsCString> mURLList;
+  RefPtr<InternalHeaders> mHeaders;
+  nsCString mBodyBlobURISpec;
+  nsString mBodyLocalPath;
+  nsCOMPtr<nsIInputStream> mBodyStream;
+  int64_t mBodyLength;
+
+  nsCString mPreferredAlternativeDataType;
+
+  nsContentPolicyType mContentPolicyType;
+
+  // Empty string: no-referrer
+  // "about:client": client (default)
+  // URL: an URL
+  nsString mReferrer;
+  ReferrerPolicy mReferrerPolicy;
+
+  // This will be used for request created from Window or Worker contexts
+  // In case there's no Referrer Policy in Request, this will be passed to
+  // channel.
+  ReferrerPolicy mEnvironmentReferrerPolicy;
+  RequestMode mMode;
+  RequestCredentials mCredentialsMode;
+  LoadTainting mResponseTainting = LoadTainting::Basic;
+  RequestCache mCacheMode;
+  RequestRedirect mRedirectMode;
+  nsString mIntegrity;
+  bool mMozErrors = false;
+  nsCString mFragment;
+  bool mSkipServiceWorker = false;
+  bool mSkipWasmCaching = false;
+  bool mSynchronous = false;
+  bool mUnsafeRequest = false;
+  bool mUseURLCredentials = false;
+  // This is only set when Request.overrideContentPolicyType() has been set.
+  // It is illegal to pass such a Request object to a fetch() method unless
+  // if the caller has chrome privileges.
+  bool mContentPolicyTypeOverridden = false;
+  nsILoadInfo::CrossOriginEmbedderPolicy mEmbedderPolicy =
+      nsILoadInfo::EMBEDDER_POLICY_NULL;
+
+  UniquePtr<mozilla::ipc::PrincipalInfo> mPrincipalInfo;
+
+  // Following members are specific for the FetchEvent.request or
+  // NavigationPreload request which is extracted from the
+  // InterceptedHttpChannel.
+  // Notice that these members would not be copied when calling
+  // InternalRequest::GetRequestConstructorCopy() since these information should
+  // not be propagated when copying the Request in ServiceWorker script.
+
+  // This is the trigging principalInfo of the InterceptedHttpChannel.
+  UniquePtr<mozilla::ipc::PrincipalInfo> mInterceptionTriggeringPrincipalInfo;
+
+  // This is the contentPolicyType of the InterceptedHttpChannel.
+  nsContentPolicyType mInterceptionContentPolicyType{
+      nsIContentPolicy::TYPE_INVALID};
+
+  // This is the redirect history of the InterceptedHttpChannel.
+  CopyableTArray<RedirectHistoryEntryInfo> mInterceptionRedirectChain;
+
+  // This indicates that the InterceptedHttpChannel is a third party channel.
+  bool mInterceptionFromThirdParty{false};
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_InternalRequest_h
diff --git a/dom/fetch/InternalResponse.cpp b/dom/fetch/InternalResponse.cpp
new file mode 100644
index 0000000000..b54e400941
--- /dev/null
+++ b/dom/fetch/InternalResponse.cpp
@@ -0,0 +1,458 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "InternalResponse.h"
+
+#include "mozilla/Assertions.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/dom/FetchStreamUtils.h"
+#include "mozilla/dom/FetchTypes.h"
+#include "mozilla/dom/InternalHeaders.h"
+#include "mozilla/dom/cache/CacheTypes.h"
+#include "mozilla/ipc/PBackgroundSharedTypes.h"
+#include "mozilla/ipc/IPCStreamUtils.h"
+#include "mozilla/RandomNum.h"
+#include "mozilla/RemoteLazyInputStreamStorage.h"
+#include "nsIRandomGenerator.h"
+#include "nsStreamUtils.h"
+
+namespace mozilla::dom {
+
+namespace {
+
+// Const variable for generate padding size
+// XXX This will be tweaked to something more meaningful in Bug 1383656.
+const uint32_t kMaxRandomNumber = 102400;
+
+}  // namespace
+
+InternalResponse::InternalResponse(uint16_t aStatus,
+                                   const nsACString& aStatusText,
+                                   RequestCredentials aCredentialsMode)
+    : mType(ResponseType::Default),
+      mStatus(aStatus),
+      mStatusText(aStatusText),
+      mHeaders(new InternalHeaders(HeadersGuardEnum::Response)),
+      mBodySize(UNKNOWN_BODY_SIZE),
+      mPaddingSize(UNKNOWN_PADDING_SIZE),
+      mErrorCode(NS_OK),
+      mCredentialsMode(aCredentialsMode),
+      mCloned(false) {}
+
+/* static */ SafeRefPtr<InternalResponse> InternalResponse::FromIPC(
+    const ParentToParentInternalResponse& aIPCResponse) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  return FromIPCTemplate(aIPCResponse);
+}
+
+/* static */ SafeRefPtr<InternalResponse> InternalResponse::FromIPC(
+    const ParentToChildInternalResponse& aIPCResponse) {
+  MOZ_ASSERT(XRE_IsContentProcess());
+  return FromIPCTemplate(aIPCResponse);
+}
+
+template <typename T>
+/* static */ SafeRefPtr<InternalResponse> InternalResponse::FromIPCTemplate(
+    const T& aIPCResponse) {
+  if (aIPCResponse.metadata().type() == ResponseType::Error) {
+    return InternalResponse::NetworkError(aIPCResponse.metadata().errorCode());
+  }
+
+  SafeRefPtr<InternalResponse> response = MakeSafeRefPtr<InternalResponse>(
+      aIPCResponse.metadata().status(), aIPCResponse.metadata().statusText());
+
+  response->SetURLList(aIPCResponse.metadata().urlList());
+  response->mHeaders =
+      new InternalHeaders(aIPCResponse.metadata().headers(),
+                          aIPCResponse.metadata().headersGuard());
+
+  if (aIPCResponse.body()) {
+    auto bodySize = aIPCResponse.bodySize();
+    auto body = ToInputStream(*aIPCResponse.body());
+    response->SetBody(body.get(), bodySize);
+  }
+
+  response->SetAlternativeDataType(
+      aIPCResponse.metadata().alternativeDataType());
+
+  if (aIPCResponse.alternativeBody()) {
+    auto alternativeBody = ToInputStream(*aIPCResponse.alternativeBody());
+    response->SetAlternativeBody(alternativeBody.get());
+  }
+
+  response->InitChannelInfo(aIPCResponse.metadata().securityInfo());
+
+  if (aIPCResponse.metadata().principalInfo()) {
+    response->SetPrincipalInfo(MakeUnique<mozilla::ipc::PrincipalInfo>(
+        aIPCResponse.metadata().principalInfo().ref()));
+  }
+
+  nsAutoCString bodyBlobURISpec(aIPCResponse.metadata().bodyBlobURISpec());
+  response->SetBodyBlobURISpec(bodyBlobURISpec);
+  nsAutoString bodyLocalPath(aIPCResponse.metadata().bodyLocalPath());
+  response->SetBodyLocalPath(bodyLocalPath);
+
+  response->mCredentialsMode = aIPCResponse.metadata().credentialsMode();
+
+  switch (aIPCResponse.metadata().type()) {
+    case ResponseType::Basic:
+      response = response->BasicResponse();
+      break;
+    case ResponseType::Cors:
+      response = response->CORSResponse();
+      break;
+    case ResponseType::Default:
+      break;
+    case ResponseType::Opaque:
+      response = response->OpaqueResponse();
+      break;
+    case ResponseType::Opaqueredirect:
+      response = response->OpaqueRedirectResponse();
+      break;
+    default:
+      MOZ_CRASH("Unexpected ResponseType!");
+  }
+
+  MOZ_ASSERT(response);
+
+  return response;
+}
+
+InternalResponse::~InternalResponse() = default;
+
+InternalResponseMetadata InternalResponse::GetMetadata() {
+  nsTArray<HeadersEntry> headers;
+  HeadersGuardEnum headersGuard;
+  UnfilteredHeaders()->ToIPC(headers, headersGuard);
+
+  Maybe<mozilla::ipc::PrincipalInfo> principalInfo =
+      mPrincipalInfo ? Some(*mPrincipalInfo) : Nothing();
+
+  nsAutoCString bodyBlobURISpec(BodyBlobURISpec());
+  nsAutoString bodyLocalPath(BodyLocalPath());
+
+  // Note: all the arguments are copied rather than moved, which would be more
+  // efficient, because there's no move-friendly constructor generated.
+  nsCOMPtr<nsITransportSecurityInfo> securityInfo(mChannelInfo.SecurityInfo());
+  return InternalResponseMetadata(
+      mType, GetUnfilteredURLList(), GetUnfilteredStatus(),
+      GetUnfilteredStatusText(), headersGuard, headers, mErrorCode,
+      GetAlternativeDataType(), securityInfo, principalInfo, bodyBlobURISpec,
+      bodyLocalPath, GetCredentialsMode());
+}
+
+void InternalResponse::ToChildToParentInternalResponse(
+    ChildToParentInternalResponse* aIPCResponse,
+    mozilla::ipc::PBackgroundChild* aManager) {
+  *aIPCResponse = ChildToParentInternalResponse(GetMetadata(), Nothing(),
+                                                UNKNOWN_BODY_SIZE, Nothing());
+
+  nsCOMPtr<nsIInputStream> body;
+  int64_t bodySize;
+  GetUnfilteredBody(getter_AddRefs(body), &bodySize);
+
+  if (body) {
+    aIPCResponse->body().emplace(ChildToParentStream());
+    aIPCResponse->bodySize() = bodySize;
+
+    DebugOnly<bool> ok = mozilla::ipc::SerializeIPCStream(
+        body.forget(), aIPCResponse->body()->stream(), /* aAllowLazy */ false);
+    MOZ_ASSERT(ok);
+  }
+
+  nsCOMPtr<nsIInputStream> alternativeBody = TakeAlternativeBody();
+  if (alternativeBody) {
+    aIPCResponse->alternativeBody().emplace(ChildToParentStream());
+
+    DebugOnly<bool> ok = mozilla::ipc::SerializeIPCStream(
+        alternativeBody.forget(), aIPCResponse->alternativeBody()->stream(),
+        /* aAllowLazy */ false);
+    MOZ_ASSERT(ok);
+  }
+}
+
+ParentToParentInternalResponse
+InternalResponse::ToParentToParentInternalResponse() {
+  ParentToParentInternalResponse result(GetMetadata(), Nothing(),
+                                        UNKNOWN_BODY_SIZE, Nothing());
+
+  nsCOMPtr<nsIInputStream> body;
+  int64_t bodySize;
+  GetUnfilteredBody(getter_AddRefs(body), &bodySize);
+
+  if (body) {
+    result.body() = Some(ToParentToParentStream(WrapNotNull(body), bodySize));
+    result.bodySize() = bodySize;
+  }
+
+  nsCOMPtr<nsIInputStream> alternativeBody = TakeAlternativeBody();
+  if (alternativeBody) {
+    result.alternativeBody() = Some(ToParentToParentStream(
+        WrapNotNull(alternativeBody), UNKNOWN_BODY_SIZE));
+  }
+
+  return result;
+}
+
+ParentToChildInternalResponse InternalResponse::ToParentToChildInternalResponse(
+    NotNull<mozilla::ipc::PBackgroundParent*> aBackgroundParent) {
+  ParentToChildInternalResponse result(GetMetadata(), Nothing(),
+                                       UNKNOWN_BODY_SIZE, Nothing());
+
+  nsCOMPtr<nsIInputStream> body;
+  int64_t bodySize;
+  GetUnfilteredBody(getter_AddRefs(body), &bodySize);
+
+  if (body) {
+    ParentToChildStream bodyStream = ToParentToChildStream(
+        WrapNotNull(body), bodySize, aBackgroundParent, mSerializeAsLazy);
+    // The body stream can fail to serialize as an IPCStream. In the case, the
+    // IPCStream's type would be T__None. Don't set up IPCInternalResponse's
+    // body with the failed IPCStream.
+    if (mSerializeAsLazy || bodyStream.get_IPCStream().stream().type() !=
+                                mozilla::ipc::InputStreamParams::T__None) {
+      result.body() = Some(bodyStream);
+      result.bodySize() = bodySize;
+    }
+  }
+
+  nsCOMPtr<nsIInputStream> alternativeBody = TakeAlternativeBody();
+  if (alternativeBody) {
+    ParentToChildStream alterBodyStream =
+        ToParentToChildStream(WrapNotNull(alternativeBody), UNKNOWN_BODY_SIZE,
+                              aBackgroundParent, mSerializeAsLazy);
+    // The body stream can fail to serialize as an IPCStream. In the case, the
+    // IPCStream's type would be T__None. Don't set up IPCInternalResponse's
+    // body with the failed IPCStream.
+    if (mSerializeAsLazy || alterBodyStream.get_IPCStream().stream().type() !=
+                                mozilla::ipc::InputStreamParams::T__None) {
+      result.alternativeBody() = Some(alterBodyStream);
+    }
+  }
+
+  return result;
+}
+
+SafeRefPtr<InternalResponse> InternalResponse::Clone(CloneType aCloneType) {
+  SafeRefPtr<InternalResponse> clone = CreateIncompleteCopy();
+  clone->mCloned = (mCloned = true);
+
+  clone->mHeaders = new InternalHeaders(*mHeaders);
+
+  // Make sure the clone response will have the same padding size.
+  clone->mPaddingInfo = mPaddingInfo;
+  clone->mPaddingSize = mPaddingSize;
+
+  clone->mCacheInfoChannel = mCacheInfoChannel;
+  clone->mCredentialsMode = mCredentialsMode;
+
+  if (mWrappedResponse) {
+    clone->mWrappedResponse = mWrappedResponse->Clone(aCloneType);
+    MOZ_ASSERT(!mBody);
+    return clone;
+  }
+
+  if (!mBody || aCloneType == eDontCloneInputStream) {
+    return clone;
+  }
+
+  nsCOMPtr<nsIInputStream> clonedBody;
+  nsCOMPtr<nsIInputStream> replacementBody;
+
+  nsresult rv = NS_CloneInputStream(mBody, getter_AddRefs(clonedBody),
+                                    getter_AddRefs(replacementBody));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return nullptr;
+  }
+
+  clone->mBody.swap(clonedBody);
+  if (replacementBody) {
+    mBody.swap(replacementBody);
+  }
+
+  return clone;
+}
+
+SafeRefPtr<InternalResponse> InternalResponse::BasicResponse() {
+  MOZ_ASSERT(!mWrappedResponse,
+             "Can't BasicResponse a already wrapped response");
+  SafeRefPtr<InternalResponse> basic = CreateIncompleteCopy();
+  basic->mType = ResponseType::Basic;
+  basic->mHeaders = InternalHeaders::BasicHeaders(Headers());
+  basic->mWrappedResponse = SafeRefPtrFromThis();
+  return basic;
+}
+
+SafeRefPtr<InternalResponse> InternalResponse::CORSResponse() {
+  MOZ_ASSERT(!mWrappedResponse,
+             "Can't CORSResponse a already wrapped response");
+  SafeRefPtr<InternalResponse> cors = CreateIncompleteCopy();
+  cors->mType = ResponseType::Cors;
+  cors->mHeaders = InternalHeaders::CORSHeaders(Headers(), mCredentialsMode);
+  cors->mWrappedResponse = SafeRefPtrFromThis();
+  return cors;
+}
+
+uint32_t InternalResponse::GetPaddingInfo() {
+  // If it's an opaque response, the paddingInfo should be generated only when
+  // paddingSize is unknown size.
+  // If it's not, the paddingInfo should be nothing and the paddingSize should
+  // be unknown size.
+  MOZ_DIAGNOSTIC_ASSERT(
+      (mType == ResponseType::Opaque && mPaddingSize == UNKNOWN_PADDING_SIZE &&
+       mPaddingInfo.isSome()) ||
+      (mType == ResponseType::Opaque && mPaddingSize != UNKNOWN_PADDING_SIZE &&
+       mPaddingInfo.isNothing()) ||
+      (mType != ResponseType::Opaque && mPaddingSize == UNKNOWN_PADDING_SIZE &&
+       mPaddingInfo.isNothing()));
+  return mPaddingInfo.isSome() ? mPaddingInfo.ref() : 0;
+}
+
+nsresult InternalResponse::GeneratePaddingInfo() {
+  MOZ_DIAGNOSTIC_ASSERT(mType == ResponseType::Opaque);
+  MOZ_DIAGNOSTIC_ASSERT(mPaddingSize == UNKNOWN_PADDING_SIZE);
+
+  // Utilize random generator to generator a random number
+  nsresult rv;
+  uint32_t randomNumber = 0;
+  nsCOMPtr<nsIRandomGenerator> randomGenerator =
+      do_GetService("@mozilla.org/security/random-generator;1", &rv);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    Maybe<uint64_t> maybeRandomNum = RandomUint64();
+    if (maybeRandomNum.isSome()) {
+      mPaddingInfo.emplace(uint32_t(maybeRandomNum.value() % kMaxRandomNumber));
+      return NS_OK;
+    }
+    return rv;
+  }
+
+  MOZ_DIAGNOSTIC_ASSERT(randomGenerator);
+
+  uint8_t* buffer;
+  rv = randomGenerator->GenerateRandomBytes(sizeof(randomNumber), &buffer);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    Maybe<uint64_t> maybeRandomNum = RandomUint64();
+    if (maybeRandomNum.isSome()) {
+      mPaddingInfo.emplace(uint32_t(maybeRandomNum.value() % kMaxRandomNumber));
+      return NS_OK;
+    }
+    return rv;
+  }
+
+  memcpy(&randomNumber, buffer, sizeof(randomNumber));
+  free(buffer);
+
+  mPaddingInfo.emplace(randomNumber % kMaxRandomNumber);
+
+  return rv;
+}
+
+int64_t InternalResponse::GetPaddingSize() {
+  // We initialize padding size to an unknown size (-1). After cached, we only
+  // pad opaque response. Opaque response's padding size might be unknown before
+  // cached.
+  MOZ_DIAGNOSTIC_ASSERT(mType == ResponseType::Opaque ||
+                        mPaddingSize == UNKNOWN_PADDING_SIZE);
+  MOZ_DIAGNOSTIC_ASSERT(mPaddingSize == UNKNOWN_PADDING_SIZE ||
+                        mPaddingSize >= 0);
+
+  return mPaddingSize;
+}
+
+void InternalResponse::SetPaddingSize(int64_t aPaddingSize) {
+  // We should only pad the opaque response.
+  MOZ_DIAGNOSTIC_ASSERT(
+      (mType == ResponseType::Opaque) !=
+      (aPaddingSize == InternalResponse::UNKNOWN_PADDING_SIZE));
+  MOZ_DIAGNOSTIC_ASSERT(aPaddingSize == UNKNOWN_PADDING_SIZE ||
+                        aPaddingSize >= 0);
+
+  mPaddingSize = aPaddingSize;
+}
+
+void InternalResponse::SetPrincipalInfo(
+    UniquePtr<mozilla::ipc::PrincipalInfo> aPrincipalInfo) {
+  mPrincipalInfo = std::move(aPrincipalInfo);
+}
+
+LoadTainting InternalResponse::GetTainting() const {
+  switch (mType) {
+    case ResponseType::Cors:
+      return LoadTainting::CORS;
+    case ResponseType::Opaque:
+      return LoadTainting::Opaque;
+    default:
+      return LoadTainting::Basic;
+  }
+}
+
+SafeRefPtr<InternalResponse> InternalResponse::Unfiltered() {
+  SafeRefPtr<InternalResponse> ref = mWrappedResponse.clonePtr();
+  if (!ref) {
+    ref = SafeRefPtrFromThis();
+  }
+  return ref;
+}
+
+SafeRefPtr<InternalResponse> InternalResponse::OpaqueResponse() {
+  MOZ_ASSERT(!mWrappedResponse,
+             "Can't OpaqueResponse a already wrapped response");
+  SafeRefPtr<InternalResponse> response =
+      MakeSafeRefPtr<InternalResponse>(0, ""_ns);
+  response->mType = ResponseType::Opaque;
+  response->mChannelInfo = mChannelInfo;
+  if (mPrincipalInfo) {
+    response->mPrincipalInfo =
+        MakeUnique<mozilla::ipc::PrincipalInfo>(*mPrincipalInfo);
+  }
+  response->mWrappedResponse = SafeRefPtrFromThis();
+  return response;
+}
+
+SafeRefPtr<InternalResponse> InternalResponse::OpaqueRedirectResponse() {
+  MOZ_ASSERT(!mWrappedResponse,
+             "Can't OpaqueRedirectResponse a already wrapped response");
+  MOZ_ASSERT(!mURLList.IsEmpty(),
+             "URLList should not be emtpy for internalResponse");
+  SafeRefPtr<InternalResponse> response = OpaqueResponse();
+  response->mType = ResponseType::Opaqueredirect;
+  response->mURLList = mURLList.Clone();
+  return response;
+}
+
+SafeRefPtr<InternalResponse> InternalResponse::CreateIncompleteCopy() {
+  SafeRefPtr<InternalResponse> copy =
+      MakeSafeRefPtr<InternalResponse>(mStatus, mStatusText);
+  copy->mType = mType;
+  copy->mURLList = mURLList.Clone();
+  copy->mChannelInfo = mChannelInfo;
+  if (mPrincipalInfo) {
+    copy->mPrincipalInfo =
+        MakeUnique<mozilla::ipc::PrincipalInfo>(*mPrincipalInfo);
+  }
+  return copy;
+}
+
+ParentToChildInternalResponse ToParentToChild(
+    const ParentToParentInternalResponse& aResponse,
+    NotNull<mozilla::ipc::PBackgroundParent*> aBackgroundParent) {
+  ParentToChildInternalResponse result(aResponse.metadata(), Nothing(),
+                                       aResponse.bodySize(), Nothing());
+
+  if (aResponse.body().isSome()) {
+    result.body() = Some(ToParentToChildStream(
+        aResponse.body().ref(), aResponse.bodySize(), aBackgroundParent));
+  }
+  if (aResponse.alternativeBody().isSome()) {
+    result.alternativeBody() = Some(ToParentToChildStream(
+        aResponse.alternativeBody().ref(), InternalResponse::UNKNOWN_BODY_SIZE,
+        aBackgroundParent));
+  }
+
+  return result;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/fetch/InternalResponse.h b/dom/fetch/InternalResponse.h
new file mode 100644
index 0000000000..e8a492a314
--- /dev/null
+++ b/dom/fetch/InternalResponse.h
@@ -0,0 +1,419 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_InternalResponse_h
+#define mozilla_dom_InternalResponse_h
+
+#include "mozilla/dom/FetchTypes.h"
+#include "nsIInputStream.h"
+#include "nsICacheInfoChannel.h"
+#include "nsISupportsImpl.h"
+#include "nsProxyRelease.h"
+
+#include "mozilla/dom/InternalHeaders.h"
+#include "mozilla/dom/RequestBinding.h"
+#include "mozilla/dom/ResponseBinding.h"
+#include "mozilla/dom/ChannelInfo.h"
+#include "mozilla/dom/SafeRefPtr.h"
+#include "mozilla/NotNull.h"
+#include "mozilla/UniquePtr.h"
+
+namespace mozilla {
+namespace ipc {
+class PBackgroundChild;
+class PBackgroundParent;
+class PrincipalInfo;
+}  // namespace ipc
+
+namespace dom {
+
+class ChildToParentInternalResponse;
+class InternalHeaders;
+class ParentToChildInternalResponse;
+class ParentToParentInternalResponse;
+
+class InternalResponse final : public AtomicSafeRefCounted<InternalResponse> {
+  friend class FetchDriver;
+
+ public:
+  MOZ_DECLARE_REFCOUNTED_TYPENAME(InternalResponse)
+
+  InternalResponse(
+      uint16_t aStatus, const nsACString& aStatusText,
+      RequestCredentials aCredentialsMode = RequestCredentials::Omit);
+
+  static SafeRefPtr<InternalResponse> FromIPC(
+      const ParentToChildInternalResponse& aIPCResponse);
+
+  static SafeRefPtr<InternalResponse> FromIPC(
+      const ParentToParentInternalResponse& aIPCResponse);
+
+  void ToChildToParentInternalResponse(
+      ChildToParentInternalResponse* aIPCResponse,
+      mozilla::ipc::PBackgroundChild* aManager);
+
+  ParentToParentInternalResponse ToParentToParentInternalResponse();
+
+  ParentToChildInternalResponse ToParentToChildInternalResponse(
+      NotNull<mozilla::ipc::PBackgroundParent*> aBackgroundParent);
+
+  enum CloneType {
+    eCloneInputStream,
+    eDontCloneInputStream,
+  };
+
+  SafeRefPtr<InternalResponse> Clone(CloneType aCloneType);
+
+  static SafeRefPtr<InternalResponse> NetworkError(nsresult aRv) {
+    MOZ_DIAGNOSTIC_ASSERT(NS_FAILED(aRv));
+    SafeRefPtr<InternalResponse> response =
+        MakeSafeRefPtr<InternalResponse>(0, ""_ns);
+    ErrorResult result;
+    response->Headers()->SetGuard(HeadersGuardEnum::Immutable, result);
+    MOZ_ASSERT(!result.Failed());
+    response->mType = ResponseType::Error;
+    response->mErrorCode = aRv;
+    return response;
+  }
+
+  SafeRefPtr<InternalResponse> OpaqueResponse();
+
+  SafeRefPtr<InternalResponse> OpaqueRedirectResponse();
+
+  SafeRefPtr<InternalResponse> BasicResponse();
+
+  SafeRefPtr<InternalResponse> CORSResponse();
+
+  ResponseType Type() const {
+    MOZ_ASSERT_IF(mType == ResponseType::Error, !mWrappedResponse);
+    MOZ_ASSERT_IF(mType == ResponseType::Default, !mWrappedResponse);
+    MOZ_ASSERT_IF(mType == ResponseType::Basic, mWrappedResponse);
+    MOZ_ASSERT_IF(mType == ResponseType::Cors, mWrappedResponse);
+    MOZ_ASSERT_IF(mType == ResponseType::Opaque, mWrappedResponse);
+    MOZ_ASSERT_IF(mType == ResponseType::Opaqueredirect, mWrappedResponse);
+    return mType;
+  }
+
+  bool IsError() const { return Type() == ResponseType::Error; }
+  // GetUrl should return last fetch URL in response's url list and null if
+  // response's url list is the empty list.
+  const nsCString& GetURL() const {
+    // Empty urlList when response is a synthetic response.
+    if (mURLList.IsEmpty()) {
+      return EmptyCString();
+    }
+    return mURLList.LastElement();
+  }
+  void GetURLList(nsTArray<nsCString>& aURLList) const {
+    aURLList.Assign(mURLList);
+  }
+  const nsCString& GetUnfilteredURL() const {
+    if (mWrappedResponse) {
+      return mWrappedResponse->GetURL();
+    }
+    return GetURL();
+  }
+  void GetUnfilteredURLList(nsTArray<nsCString>& aURLList) const {
+    if (mWrappedResponse) {
+      return mWrappedResponse->GetURLList(aURLList);
+    }
+
+    return GetURLList(aURLList);
+  }
+
+  nsTArray<nsCString> GetUnfilteredURLList() const {
+    nsTArray<nsCString> list;
+    GetUnfilteredURLList(list);
+    return list;
+  }
+
+  void SetURLList(const nsTArray<nsCString>& aURLList) {
+    mURLList.Assign(aURLList);
+
+#ifdef DEBUG
+    for (uint32_t i = 0; i < mURLList.Length(); ++i) {
+      MOZ_ASSERT(mURLList[i].Find("#"_ns) == kNotFound);
+    }
+#endif
+  }
+
+  uint16_t GetStatus() const { return mStatus; }
+
+  uint16_t GetUnfilteredStatus() const {
+    if (mWrappedResponse) {
+      return mWrappedResponse->GetStatus();
+    }
+
+    return GetStatus();
+  }
+
+  const nsCString& GetStatusText() const { return mStatusText; }
+
+  const nsCString& GetUnfilteredStatusText() const {
+    if (mWrappedResponse) {
+      return mWrappedResponse->GetStatusText();
+    }
+
+    return GetStatusText();
+  }
+
+  InternalHeaders* Headers() { return mHeaders; }
+
+  InternalHeaders* UnfilteredHeaders() {
+    if (mWrappedResponse) {
+      return mWrappedResponse->Headers();
+    };
+
+    return Headers();
+  }
+
+  void GetUnfilteredBody(nsIInputStream** aStream,
+                         int64_t* aBodySize = nullptr) {
+    if (mWrappedResponse) {
+      MOZ_ASSERT(!mBody);
+      return mWrappedResponse->GetBody(aStream, aBodySize);
+    }
+    nsCOMPtr<nsIInputStream> stream = mBody;
+    stream.forget(aStream);
+    if (aBodySize) {
+      *aBodySize = mBodySize;
+    }
+  }
+
+  void GetBody(nsIInputStream** aStream, int64_t* aBodySize = nullptr) {
+    if (Type() == ResponseType::Opaque ||
+        Type() == ResponseType::Opaqueredirect) {
+      *aStream = nullptr;
+      if (aBodySize) {
+        *aBodySize = UNKNOWN_BODY_SIZE;
+      }
+      return;
+    }
+
+    GetUnfilteredBody(aStream, aBodySize);
+  }
+
+  void SetBodyBlobURISpec(nsACString& aBlobURISpec) {
+    mBodyBlobURISpec = aBlobURISpec;
+  }
+
+  const nsACString& BodyBlobURISpec() const {
+    if (mWrappedResponse) {
+      return mWrappedResponse->BodyBlobURISpec();
+    }
+    return mBodyBlobURISpec;
+  }
+
+  void SetBodyLocalPath(nsAString& aLocalPath) { mBodyLocalPath = aLocalPath; }
+
+  const nsAString& BodyLocalPath() const {
+    if (mWrappedResponse) {
+      return mWrappedResponse->BodyLocalPath();
+    }
+    return mBodyLocalPath;
+  }
+
+  void SetBody(nsIInputStream* aBody, int64_t aBodySize) {
+    if (mWrappedResponse) {
+      return mWrappedResponse->SetBody(aBody, aBodySize);
+    }
+    // A request's body may not be reset once set.
+    MOZ_ASSERT(!mBody);
+    MOZ_ASSERT(mBodySize == UNKNOWN_BODY_SIZE);
+    // Check arguments.
+    MOZ_ASSERT(aBodySize == UNKNOWN_BODY_SIZE || aBodySize >= 0);
+    // If body is not given, then size must be unknown.
+    MOZ_ASSERT_IF(!aBody, aBodySize == UNKNOWN_BODY_SIZE);
+
+    mBody = aBody;
+    mBodySize = aBodySize;
+  }
+
+  uint32_t GetPaddingInfo();
+
+  nsresult GeneratePaddingInfo();
+
+  int64_t GetPaddingSize();
+
+  void SetPaddingSize(int64_t aPaddingSize);
+
+  void SetAlternativeDataType(const nsACString& aAltDataType) {
+    if (mWrappedResponse) {
+      return mWrappedResponse->SetAlternativeDataType(aAltDataType);
+    }
+
+    MOZ_DIAGNOSTIC_ASSERT(mAlternativeDataType.IsEmpty());
+
+    mAlternativeDataType.Assign(aAltDataType);
+  }
+
+  const nsCString& GetAlternativeDataType() {
+    if (mWrappedResponse) {
+      return mWrappedResponse->GetAlternativeDataType();
+    }
+
+    return mAlternativeDataType;
+  }
+
+  void SetAlternativeBody(nsIInputStream* aAlternativeBody) {
+    if (mWrappedResponse) {
+      return mWrappedResponse->SetAlternativeBody(aAlternativeBody);
+    }
+    // A request's body may not be reset once set.
+    MOZ_DIAGNOSTIC_ASSERT(!mAlternativeBody);
+
+    mAlternativeBody = aAlternativeBody;
+  }
+
+  already_AddRefed<nsIInputStream> TakeAlternativeBody() {
+    if (mWrappedResponse) {
+      return mWrappedResponse->TakeAlternativeBody();
+    }
+
+    if (!mAlternativeBody) {
+      return nullptr;
+    }
+
+    // cleanup the non-alternative body here.
+    // Once alternative data is used, the real body is no need anymore.
+    mBody = nullptr;
+    mBodySize = UNKNOWN_BODY_SIZE;
+    return mAlternativeBody.forget();
+  }
+
+  void SetCacheInfoChannel(
+      const nsMainThreadPtrHandle<nsICacheInfoChannel>& aCacheInfoChannel) {
+    if (mWrappedResponse) {
+      return mWrappedResponse->SetCacheInfoChannel(aCacheInfoChannel);
+    }
+    MOZ_ASSERT(!mCacheInfoChannel);
+    mCacheInfoChannel = aCacheInfoChannel;
+  }
+
+  nsMainThreadPtrHandle<nsICacheInfoChannel> TakeCacheInfoChannel() {
+    if (mWrappedResponse) {
+      return mWrappedResponse->TakeCacheInfoChannel();
+    }
+    nsMainThreadPtrHandle<nsICacheInfoChannel> rtn = mCacheInfoChannel;
+    mCacheInfoChannel = nullptr;
+    return rtn;
+  }
+
+  bool HasCacheInfoChannel() const {
+    if (mWrappedResponse) {
+      return !!mWrappedResponse->HasCacheInfoChannel();
+    }
+    return !!mCacheInfoChannel;
+  }
+
+  bool HasBeenCloned() const { return mCloned; }
+
+  void SetSerializeAsLazy(bool aAllow) { mSerializeAsLazy = aAllow; }
+  bool CanSerializeAsLazy() const { return mSerializeAsLazy; }
+
+  void InitChannelInfo(nsIChannel* aChannel) {
+    mChannelInfo.InitFromChannel(aChannel);
+  }
+
+  void InitChannelInfo(nsITransportSecurityInfo* aSecurityInfo) {
+    mChannelInfo.InitFromTransportSecurityInfo(aSecurityInfo);
+  }
+
+  void InitChannelInfo(const ChannelInfo& aChannelInfo) {
+    mChannelInfo = aChannelInfo;
+  }
+
+  const ChannelInfo& GetChannelInfo() const { return mChannelInfo; }
+
+  const UniquePtr<mozilla::ipc::PrincipalInfo>& GetPrincipalInfo() const {
+    return mPrincipalInfo;
+  }
+
+  bool IsRedirected() const { return mURLList.Length() > 1; }
+
+  nsresult GetErrorCode() const { return mErrorCode; }
+
+  // Takes ownership of the principal info.
+  void SetPrincipalInfo(UniquePtr<mozilla::ipc::PrincipalInfo> aPrincipalInfo);
+
+  LoadTainting GetTainting() const;
+
+  SafeRefPtr<InternalResponse> Unfiltered();
+
+  InternalResponseMetadata GetMetadata();
+
+  RequestCredentials GetCredentialsMode() const {
+    if (mWrappedResponse) {
+      return mWrappedResponse->GetCredentialsMode();
+    }
+    return mCredentialsMode;
+  }
+
+  ~InternalResponse();
+
+ private:
+  explicit InternalResponse(const InternalResponse& aOther) = delete;
+  InternalResponse& operator=(const InternalResponse&) = delete;
+
+  // Returns an instance of InternalResponse which is a copy of this
+  // InternalResponse, except headers, body and wrapped response (if any) which
+  // are left uninitialized. Used for cloning and filtering.
+  SafeRefPtr<InternalResponse> CreateIncompleteCopy();
+
+  template <typename T>
+  static SafeRefPtr<InternalResponse> FromIPCTemplate(const T& aIPCResponse);
+
+  ResponseType mType;
+  // A response has an associated url list (a list of zero or more fetch URLs).
+  // Unless stated otherwise, it is the empty list. The current url is the last
+  // element in mURLlist
+  nsTArray<nsCString> mURLList;
+  const uint16_t mStatus;
+  const nsCString mStatusText;
+  RefPtr<InternalHeaders> mHeaders;
+  nsCOMPtr<nsIInputStream> mBody;
+  nsCString mBodyBlobURISpec;
+  nsString mBodyLocalPath;
+  int64_t mBodySize;
+  // It's used to passed to the CacheResponse to generate padding size. Once, we
+  // generate the padding size for resposne, we don't need it anymore.
+  Maybe<uint32_t> mPaddingInfo;
+  int64_t mPaddingSize;
+  nsresult mErrorCode;
+  RequestCredentials mCredentialsMode;
+
+  // For alternative data such as JS Bytecode cached in the HTTP cache.
+  nsCString mAlternativeDataType;
+  nsCOMPtr<nsIInputStream> mAlternativeBody;
+  nsMainThreadPtrHandle<nsICacheInfoChannel> mCacheInfoChannel;
+  bool mCloned;
+  // boolean to indicate the body/alternativeBody will be serialized as a
+  // RemoteLazyInputStream.
+  bool mSerializeAsLazy{true};
+
+ public:
+  static constexpr int64_t UNKNOWN_BODY_SIZE = -1;
+  static constexpr int64_t UNKNOWN_PADDING_SIZE = -1;
+
+ private:
+  ChannelInfo mChannelInfo;
+  UniquePtr<mozilla::ipc::PrincipalInfo> mPrincipalInfo;
+
+  // For filtered responses.
+  // Cache, and SW interception should always serialize/access the underlying
+  // unfiltered headers and when deserializing, create an InternalResponse
+  // with the unfiltered headers followed by wrapping it.
+  SafeRefPtr<InternalResponse> mWrappedResponse;
+};
+
+ParentToChildInternalResponse ToParentToChild(
+    const ParentToParentInternalResponse& aResponse,
+    NotNull<mozilla::ipc::PBackgroundParent*> aBackgroundParent);
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_InternalResponse_h
diff --git a/dom/fetch/PFetch.ipdl b/dom/fetch/PFetch.ipdl
new file mode 100644
index 0000000000..904ef0738d
--- /dev/null
+++ b/dom/fetch/PFetch.ipdl
@@ -0,0 +1,56 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+include protocol PBackground;
+
+include ClientIPCTypes;
+include FetchTypes;
+include IPCServiceWorkerDescriptor;
+include NeckoChannelParams;
+include PBackgroundSharedTypes;
+include PerformanceTimingTypes;
+
+namespace mozilla {
+namespace dom {
+
+struct FetchOpArgs{
+  IPCInternalRequest request;
+  PrincipalInfo principalInfo;
+  nsCString workerScript;
+  IPCClientInfo clientInfo;
+  IPCServiceWorkerDescriptor? controller;
+  CookieJarSettingsArgs? cookieJarSettings;
+  bool needOnDataAvailable;
+  bool hasCSPEventListener;
+  uint64_t associatedBrowsingContextID;
+};
+
+protocol PFetch {
+  manager PBackground;
+
+  parent:
+    async FetchOp(FetchOpArgs aArgs);
+
+    async AbortFetchOp();
+
+  child:
+    async OnResponseAvailableInternal(ParentToChildInternalResponse aResponse);
+
+    async OnResponseEnd(ResponseEndArgs aResponseEndArgs);
+
+    async OnDataAvailable();
+
+    async OnFlushConsoleReport(ConsoleReportCollected[] aReports);
+
+    async OnCSPViolationEvent(nsString aJSON);
+
+    async OnReportPerformanceTiming(ResponseTiming aTiming);
+
+    async OnNotifyNetworkMonitorAlternateStack(uint64_t aChannelID);
+
+    async __delete__(nsresult aResult);
+};
+
+}
+}
diff --git a/dom/fetch/Request.cpp b/dom/fetch/Request.cpp
new file mode 100644
index 0000000000..4fcb19b6f7
--- /dev/null
+++ b/dom/fetch/Request.cpp
@@ -0,0 +1,658 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "Request.h"
+
+#include "js/Value.h"
+#include "nsIURI.h"
+#include "nsNetUtil.h"
+#include "nsPIDOMWindow.h"
+
+#include "mozilla/ErrorResult.h"
+#include "mozilla/dom/Headers.h"
+#include "mozilla/dom/Fetch.h"
+#include "mozilla/dom/FetchUtil.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/URL.h"
+#include "mozilla/dom/WorkerPrivate.h"
+#include "mozilla/dom/WorkerRunnable.h"
+#include "mozilla/dom/WindowContext.h"
+#include "mozilla/ipc/PBackgroundSharedTypes.h"
+#include "mozilla/Unused.h"
+
+#include "mozilla/dom/ReadableStreamDefaultReader.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_ADDREF_INHERITED(Request, FetchBody<Request>)
+NS_IMPL_RELEASE_INHERITED(Request, FetchBody<Request>)
+
+// Can't use _INHERITED macro here because FetchBody<Request> is abstract.
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(Request)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(Request, FetchBody<Request>)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mOwner)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mHeaders)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mSignal)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mFetchStreamReader)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(Request, FetchBody<Request>)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mOwner)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mHeaders)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mSignal)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mFetchStreamReader)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(Request)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+NS_INTERFACE_MAP_END_INHERITING(FetchBody<Request>)
+
+Request::Request(nsIGlobalObject* aOwner, SafeRefPtr<InternalRequest> aRequest,
+                 AbortSignal* aSignal)
+    : FetchBody<Request>(aOwner), mRequest(std::move(aRequest)) {
+  MOZ_ASSERT(mRequest->Headers()->Guard() == HeadersGuardEnum::Immutable ||
+             mRequest->Headers()->Guard() == HeadersGuardEnum::Request ||
+             mRequest->Headers()->Guard() == HeadersGuardEnum::Request_no_cors);
+  if (aSignal) {
+    // If we don't have a signal as argument, we will create it when required by
+    // content, otherwise the Request's signal must follow what has been passed.
+    JS::Rooted<JS::Value> reason(RootingCx(), aSignal->RawReason());
+    mSignal = new AbortSignal(aOwner, aSignal->Aborted(), reason);
+    if (!mSignal->Aborted()) {
+      mSignal->Follow(aSignal);
+    }
+  }
+}
+
+Request::~Request() = default;
+
+SafeRefPtr<InternalRequest> Request::GetInternalRequest() {
+  return mRequest.clonePtr();
+}
+
+namespace {
+already_AddRefed<nsIURI> ParseURLFromDocument(Document* aDocument,
+                                              const nsAString& aInput,
+                                              ErrorResult& aRv) {
+  MOZ_ASSERT(aDocument);
+  MOZ_ASSERT(NS_IsMainThread());
+
+  // Don't use NS_ConvertUTF16toUTF8 because that doesn't let us handle OOM.
+  nsAutoCString input;
+  if (!AppendUTF16toUTF8(aInput, input, fallible)) {
+    aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+    return nullptr;
+  }
+
+  nsCOMPtr<nsIURI> resolvedURI;
+  nsresult rv = NS_NewURI(getter_AddRefs(resolvedURI), input, nullptr,
+                          aDocument->GetBaseURI());
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    aRv.ThrowTypeError<MSG_INVALID_URL>(input);
+  }
+  return resolvedURI.forget();
+}
+void GetRequestURLFromDocument(Document* aDocument, const nsAString& aInput,
+                               nsAString& aRequestURL, nsACString& aURLfragment,
+                               ErrorResult& aRv) {
+  nsCOMPtr<nsIURI> resolvedURI = ParseURLFromDocument(aDocument, aInput, aRv);
+  if (aRv.Failed()) {
+    return;
+  }
+  // This fails with URIs with weird protocols, even when they are valid,
+  // so we ignore the failure
+  nsAutoCString credentials;
+  Unused << resolvedURI->GetUserPass(credentials);
+  if (!credentials.IsEmpty()) {
+    aRv.ThrowTypeError<MSG_URL_HAS_CREDENTIALS>(NS_ConvertUTF16toUTF8(aInput));
+    return;
+  }
+
+  nsCOMPtr<nsIURI> resolvedURIClone;
+  aRv = NS_GetURIWithoutRef(resolvedURI, getter_AddRefs(resolvedURIClone));
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+  nsAutoCString spec;
+  aRv = resolvedURIClone->GetSpec(spec);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+  CopyUTF8toUTF16(spec, aRequestURL);
+
+  // Get the fragment from nsIURI.
+  aRv = resolvedURI->GetRef(aURLfragment);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+}
+already_AddRefed<nsIURI> ParseURLFromChrome(const nsAString& aInput,
+                                            ErrorResult& aRv) {
+  MOZ_ASSERT(NS_IsMainThread());
+  // Don't use NS_ConvertUTF16toUTF8 because that doesn't let us handle OOM.
+  nsAutoCString input;
+  if (!AppendUTF16toUTF8(aInput, input, fallible)) {
+    aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+    return nullptr;
+  }
+
+  nsCOMPtr<nsIURI> uri;
+  nsresult rv = NS_NewURI(getter_AddRefs(uri), input);
+  if (NS_FAILED(rv)) {
+    aRv.ThrowTypeError<MSG_INVALID_URL>(input);
+  }
+  return uri.forget();
+}
+void GetRequestURLFromChrome(const nsAString& aInput, nsAString& aRequestURL,
+                             nsACString& aURLfragment, ErrorResult& aRv) {
+  nsCOMPtr<nsIURI> uri = ParseURLFromChrome(aInput, aRv);
+  if (aRv.Failed()) {
+    return;
+  }
+  // This fails with URIs with weird protocols, even when they are valid,
+  // so we ignore the failure
+  nsAutoCString credentials;
+  Unused << uri->GetUserPass(credentials);
+  if (!credentials.IsEmpty()) {
+    aRv.ThrowTypeError<MSG_URL_HAS_CREDENTIALS>(NS_ConvertUTF16toUTF8(aInput));
+    return;
+  }
+
+  nsCOMPtr<nsIURI> uriClone;
+  aRv = NS_GetURIWithoutRef(uri, getter_AddRefs(uriClone));
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+  nsAutoCString spec;
+  aRv = uriClone->GetSpec(spec);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+  CopyUTF8toUTF16(spec, aRequestURL);
+
+  // Get the fragment from nsIURI.
+  aRv = uri->GetRef(aURLfragment);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+}
+already_AddRefed<URL> ParseURLFromWorker(nsIGlobalObject* aGlobal,
+                                         const nsAString& aInput,
+                                         ErrorResult& aRv) {
+  WorkerPrivate* worker = GetCurrentThreadWorkerPrivate();
+  MOZ_ASSERT(worker);
+  worker->AssertIsOnWorkerThread();
+
+  NS_ConvertUTF8toUTF16 baseURL(worker->GetLocationInfo().mHref);
+  RefPtr<URL> url = URL::Constructor(aGlobal, aInput, baseURL, aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    aRv.ThrowTypeError<MSG_INVALID_URL>(NS_ConvertUTF16toUTF8(aInput));
+  }
+  return url.forget();
+}
+void GetRequestURLFromWorker(nsIGlobalObject* aGlobal, const nsAString& aInput,
+                             nsAString& aRequestURL, nsACString& aURLfragment,
+                             ErrorResult& aRv) {
+  RefPtr<URL> url = ParseURLFromWorker(aGlobal, aInput, aRv);
+  if (aRv.Failed()) {
+    return;
+  }
+  nsString username;
+  url->GetUsername(username);
+
+  nsString password;
+  url->GetPassword(password);
+
+  if (!username.IsEmpty() || !password.IsEmpty()) {
+    aRv.ThrowTypeError<MSG_URL_HAS_CREDENTIALS>(NS_ConvertUTF16toUTF8(aInput));
+    return;
+  }
+
+  // Get the fragment from URL.
+  nsAutoString fragment;
+  url->GetHash(fragment);
+
+  // Note: URL::GetHash() includes the "#" and we want the fragment with out
+  // the hash symbol.
+  if (!fragment.IsEmpty()) {
+    CopyUTF16toUTF8(Substring(fragment, 1), aURLfragment);
+  }
+
+  url->SetHash(u""_ns);
+  url->GetHref(aRequestURL);
+}
+
+class ReferrerSameOriginChecker final : public WorkerMainThreadRunnable {
+ public:
+  ReferrerSameOriginChecker(WorkerPrivate* aWorkerPrivate,
+                            const nsAString& aReferrerURL, nsresult& aResult)
+      : WorkerMainThreadRunnable(aWorkerPrivate,
+                                 "Fetch :: Referrer same origin check"_ns),
+        mReferrerURL(aReferrerURL),
+        mResult(aResult) {
+    mWorkerPrivate->AssertIsOnWorkerThread();
+  }
+
+  bool MainThreadRun() override {
+    nsCOMPtr<nsIURI> uri;
+    if (NS_SUCCEEDED(NS_NewURI(getter_AddRefs(uri), mReferrerURL))) {
+      nsCOMPtr<nsIPrincipal> principal = mWorkerPrivate->GetPrincipal();
+      if (principal) {
+        mResult = principal->CheckMayLoad(uri,
+                                          /* allowIfInheritsPrincipal */ false);
+      }
+    }
+    return true;
+  }
+
+ private:
+  const nsString mReferrerURL;
+  nsresult& mResult;
+};
+
+}  // namespace
+
+/*static*/
+SafeRefPtr<Request> Request::Constructor(const GlobalObject& aGlobal,
+                                         const RequestOrUSVString& aInput,
+                                         const RequestInit& aInit,
+                                         ErrorResult& aRv) {
+  nsCOMPtr<nsIGlobalObject> global = do_QueryInterface(aGlobal.GetAsSupports());
+  return Constructor(global, aGlobal.Context(), aInput, aInit, aRv);
+}
+
+/*static*/
+SafeRefPtr<Request> Request::Constructor(nsIGlobalObject* aGlobal,
+                                         JSContext* aCx,
+                                         const RequestOrUSVString& aInput,
+                                         const RequestInit& aInit,
+                                         ErrorResult& aRv) {
+  bool hasCopiedBody = false;
+  SafeRefPtr<InternalRequest> request;
+
+  RefPtr<AbortSignal> signal;
+
+  if (aInput.IsRequest()) {
+    RefPtr<Request> inputReq = &aInput.GetAsRequest();
+    nsCOMPtr<nsIInputStream> body;
+    inputReq->GetBody(getter_AddRefs(body));
+    if (inputReq->BodyUsed()) {
+      aRv.ThrowTypeError<MSG_FETCH_BODY_CONSUMED_ERROR>();
+      return nullptr;
+    }
+
+    // The body will be copied when GetRequestConstructorCopy() is executed.
+    if (body) {
+      hasCopiedBody = true;
+    }
+
+    request = inputReq->GetInternalRequest();
+    signal = inputReq->GetOrCreateSignal();
+  } else {
+    // aInput is USVString.
+    // We need to get url before we create a InternalRequest.
+    nsAutoString input;
+    input.Assign(aInput.GetAsUSVString());
+    nsAutoString requestURL;
+    nsCString fragment;
+    if (NS_IsMainThread()) {
+      nsCOMPtr<nsPIDOMWindowInner> inner(do_QueryInterface(aGlobal));
+      Document* doc = inner ? inner->GetExtantDoc() : nullptr;
+      if (doc) {
+        GetRequestURLFromDocument(doc, input, requestURL, fragment, aRv);
+      } else {
+        // If we don't have a document, we must assume that this is a full URL.
+        GetRequestURLFromChrome(input, requestURL, fragment, aRv);
+      }
+    } else {
+      GetRequestURLFromWorker(aGlobal, input, requestURL, fragment, aRv);
+    }
+    if (aRv.Failed()) {
+      return nullptr;
+    }
+    request = MakeSafeRefPtr<InternalRequest>(NS_ConvertUTF16toUTF8(requestURL),
+                                              fragment);
+  }
+  request = request->GetRequestConstructorCopy(aGlobal, aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+  RequestMode fallbackMode = RequestMode::EndGuard_;
+  RequestCredentials fallbackCredentials = RequestCredentials::EndGuard_;
+  RequestCache fallbackCache = RequestCache::EndGuard_;
+  if (aInput.IsUSVString()) {
+    fallbackMode = RequestMode::Cors;
+    fallbackCredentials = RequestCredentials::Same_origin;
+    fallbackCache = RequestCache::Default;
+  }
+
+  RequestMode mode =
+      aInit.mMode.WasPassed() ? aInit.mMode.Value() : fallbackMode;
+  RequestCredentials credentials = aInit.mCredentials.WasPassed()
+                                       ? aInit.mCredentials.Value()
+                                       : fallbackCredentials;
+
+  if (mode == RequestMode::Navigate) {
+    aRv.ThrowTypeError<MSG_INVALID_REQUEST_MODE>("navigate");
+    return nullptr;
+  }
+  if (aInit.IsAnyMemberPresent() && request->Mode() == RequestMode::Navigate) {
+    mode = RequestMode::Same_origin;
+  }
+
+  if (aInit.IsAnyMemberPresent()) {
+    request->SetReferrer(
+        NS_LITERAL_STRING_FROM_CSTRING(kFETCH_CLIENT_REFERRER_STR));
+    request->SetReferrerPolicy(ReferrerPolicy::_empty);
+  }
+  if (aInit.mReferrer.WasPassed()) {
+    const nsString& referrer = aInit.mReferrer.Value();
+    if (referrer.IsEmpty()) {
+      request->SetReferrer(u""_ns);
+    } else {
+      nsAutoString referrerURL;
+      if (NS_IsMainThread()) {
+        nsCOMPtr<nsPIDOMWindowInner> inner(do_QueryInterface(aGlobal));
+        Document* doc = inner ? inner->GetExtantDoc() : nullptr;
+        nsCOMPtr<nsIURI> uri;
+        if (doc) {
+          uri = ParseURLFromDocument(doc, referrer, aRv);
+        } else {
+          // If we don't have a document, we must assume that this is a full
+          // URL.
+          uri = ParseURLFromChrome(referrer, aRv);
+        }
+        if (NS_WARN_IF(aRv.Failed())) {
+          aRv.ThrowTypeError<MSG_INVALID_REFERRER_URL>(
+              NS_ConvertUTF16toUTF8(referrer));
+          return nullptr;
+        }
+        nsAutoCString spec;
+        uri->GetSpec(spec);
+        CopyUTF8toUTF16(spec, referrerURL);
+        if (!referrerURL.EqualsLiteral(kFETCH_CLIENT_REFERRER_STR)) {
+          nsCOMPtr<nsIPrincipal> principal = aGlobal->PrincipalOrNull();
+          if (principal) {
+            nsresult rv =
+                principal->CheckMayLoad(uri,
+                                        /* allowIfInheritsPrincipal */ false);
+            if (NS_FAILED(rv)) {
+              referrerURL.AssignLiteral(kFETCH_CLIENT_REFERRER_STR);
+            }
+          }
+        }
+      } else {
+        RefPtr<URL> url = ParseURLFromWorker(aGlobal, referrer, aRv);
+        if (NS_WARN_IF(aRv.Failed())) {
+          aRv.ThrowTypeError<MSG_INVALID_REFERRER_URL>(
+              NS_ConvertUTF16toUTF8(referrer));
+          return nullptr;
+        }
+        url->GetHref(referrerURL);
+        if (!referrerURL.EqualsLiteral(kFETCH_CLIENT_REFERRER_STR)) {
+          WorkerPrivate* worker = GetCurrentThreadWorkerPrivate();
+          nsresult rv = NS_OK;
+          // ReferrerSameOriginChecker uses a sync loop to get the main thread
+          // to perform the same-origin check.  Overall, on Workers this method
+          // can create 3 sync loops (two for constructing URLs and one here) so
+          // in the future we may want to optimize it all by off-loading all of
+          // this work in a single sync loop.
+          RefPtr<ReferrerSameOriginChecker> checker =
+              new ReferrerSameOriginChecker(worker, referrerURL, rv);
+          IgnoredErrorResult error;
+          checker->Dispatch(Canceling, error);
+          if (error.Failed() || NS_FAILED(rv)) {
+            referrerURL.AssignLiteral(kFETCH_CLIENT_REFERRER_STR);
+          }
+        }
+      }
+      request->SetReferrer(referrerURL);
+    }
+  }
+
+  if (aInit.mReferrerPolicy.WasPassed()) {
+    request->SetReferrerPolicy(aInit.mReferrerPolicy.Value());
+  }
+
+  if (aInit.mSignal.WasPassed()) {
+    signal = aInit.mSignal.Value();
+  }
+
+  UniquePtr<mozilla::ipc::PrincipalInfo> principalInfo;
+  nsILoadInfo::CrossOriginEmbedderPolicy coep =
+      nsILoadInfo::EMBEDDER_POLICY_NULL;
+
+  if (NS_IsMainThread()) {
+    nsCOMPtr<nsPIDOMWindowInner> window = do_QueryInterface(aGlobal);
+    if (window) {
+      nsCOMPtr<Document> doc;
+      doc = window->GetExtantDoc();
+      if (doc) {
+        request->SetEnvironmentReferrerPolicy(doc->GetReferrerPolicy());
+
+        principalInfo.reset(new mozilla::ipc::PrincipalInfo());
+        nsresult rv =
+            PrincipalToPrincipalInfo(doc->NodePrincipal(), principalInfo.get());
+        if (NS_WARN_IF(NS_FAILED(rv))) {
+          aRv.ThrowTypeError<MSG_FETCH_BODY_CONSUMED_ERROR>();
+          return nullptr;
+        }
+      }
+      if (window->GetWindowContext()) {
+        coep = window->GetWindowContext()->GetEmbedderPolicy();
+      }
+    }
+  } else {
+    WorkerPrivate* worker = GetCurrentThreadWorkerPrivate();
+    if (worker) {
+      worker->AssertIsOnWorkerThread();
+      request->SetEnvironmentReferrerPolicy(worker->GetReferrerPolicy());
+      principalInfo =
+          MakeUnique<mozilla::ipc::PrincipalInfo>(worker->GetPrincipalInfo());
+      coep = worker->GetEmbedderPolicy();
+      // For dedicated worker, the response must respect the owner's COEP.
+      if (coep == nsILoadInfo::EMBEDDER_POLICY_NULL &&
+          worker->IsDedicatedWorker()) {
+        coep = worker->GetOwnerEmbedderPolicy();
+      }
+    }
+  }
+
+  request->SetPrincipalInfo(std::move(principalInfo));
+  request->SetEmbedderPolicy(coep);
+
+  if (mode != RequestMode::EndGuard_) {
+    request->SetMode(mode);
+  }
+
+  if (credentials != RequestCredentials::EndGuard_) {
+    request->SetCredentialsMode(credentials);
+  }
+
+  RequestCache cache =
+      aInit.mCache.WasPassed() ? aInit.mCache.Value() : fallbackCache;
+  if (cache != RequestCache::EndGuard_) {
+    if (cache == RequestCache::Only_if_cached &&
+        request->Mode() != RequestMode::Same_origin) {
+      nsCString modeString(RequestModeValues::GetString(request->Mode()));
+      aRv.ThrowTypeError<MSG_ONLY_IF_CACHED_WITHOUT_SAME_ORIGIN>(modeString);
+      return nullptr;
+    }
+    request->SetCacheMode(cache);
+  }
+
+  if (aInit.mRedirect.WasPassed()) {
+    request->SetRedirectMode(aInit.mRedirect.Value());
+  }
+
+  if (aInit.mIntegrity.WasPassed()) {
+    request->SetIntegrity(aInit.mIntegrity.Value());
+  }
+
+  if (aInit.mMozErrors.WasPassed() && aInit.mMozErrors.Value()) {
+    request->SetMozErrors();
+  }
+
+  // Request constructor step 14.
+  if (aInit.mMethod.WasPassed()) {
+    nsAutoCString method(aInit.mMethod.Value());
+
+    // Step 14.1. Disallow forbidden methods, and anything that is not a HTTP
+    // token, since HTTP states that Method may be any of the defined values or
+    // a token (extension method).
+    nsAutoCString outMethod;
+    nsresult rv = FetchUtil::GetValidRequestMethod(method, outMethod);
+    if (NS_FAILED(rv)) {
+      aRv.ThrowTypeError<MSG_INVALID_REQUEST_METHOD>(method);
+      return nullptr;
+    }
+
+    // Step 14.2
+    request->SetMethod(outMethod);
+  }
+
+  RefPtr<InternalHeaders> requestHeaders = request->Headers();
+
+  RefPtr<InternalHeaders> headers;
+  if (aInit.mHeaders.WasPassed()) {
+    RefPtr<Headers> h = Headers::Create(aGlobal, aInit.mHeaders.Value(), aRv);
+    if (aRv.Failed()) {
+      return nullptr;
+    }
+    headers = h->GetInternalHeaders();
+  } else {
+    headers = new InternalHeaders(*requestHeaders);
+  }
+
+  requestHeaders->Clear();
+  // From "Let r be a new Request object associated with request and a new
+  // Headers object whose guard is "request"."
+  requestHeaders->SetGuard(HeadersGuardEnum::Request, aRv);
+  MOZ_ASSERT(!aRv.Failed());
+
+  if (request->Mode() == RequestMode::No_cors) {
+    if (!request->HasSimpleMethod()) {
+      nsAutoCString method;
+      request->GetMethod(method);
+      aRv.ThrowTypeError<MSG_INVALID_REQUEST_METHOD>(method);
+      return nullptr;
+    }
+
+    requestHeaders->SetGuard(HeadersGuardEnum::Request_no_cors, aRv);
+    if (aRv.Failed()) {
+      return nullptr;
+    }
+  }
+
+  requestHeaders->Fill(*headers, aRv);
+  if (aRv.Failed()) {
+    return nullptr;
+  }
+
+  if ((aInit.mBody.WasPassed() && !aInit.mBody.Value().IsNull()) ||
+      hasCopiedBody) {
+    // HEAD and GET are not allowed to have a body.
+    nsAutoCString method;
+    request->GetMethod(method);
+    // method is guaranteed to be uppercase due to step 14.2 above.
+    if (method.EqualsLiteral("HEAD") || method.EqualsLiteral("GET")) {
+      aRv.ThrowTypeError("HEAD or GET Request cannot have a body.");
+      return nullptr;
+    }
+  }
+
+  if (aInit.mBody.WasPassed()) {
+    const Nullable<fetch::OwningBodyInit>& bodyInitNullable =
+        aInit.mBody.Value();
+    if (!bodyInitNullable.IsNull()) {
+      const fetch::OwningBodyInit& bodyInit = bodyInitNullable.Value();
+      nsCOMPtr<nsIInputStream> stream;
+      nsAutoCString contentTypeWithCharset;
+      uint64_t contentLength = 0;
+      aRv = ExtractByteStreamFromBody(bodyInit, getter_AddRefs(stream),
+                                      contentTypeWithCharset, contentLength);
+      if (NS_WARN_IF(aRv.Failed())) {
+        return nullptr;
+      }
+
+      nsCOMPtr<nsIInputStream> temporaryBody = stream;
+
+      if (!contentTypeWithCharset.IsVoid() &&
+          !requestHeaders->Has("Content-Type"_ns, aRv)) {
+        requestHeaders->Append("Content-Type"_ns, contentTypeWithCharset, aRv);
+      }
+
+      if (NS_WARN_IF(aRv.Failed())) {
+        return nullptr;
+      }
+
+      if (hasCopiedBody) {
+        request->SetBody(nullptr, 0);
+      }
+
+      request->SetBody(temporaryBody, contentLength);
+    }
+  }
+
+  auto domRequest =
+      MakeSafeRefPtr<Request>(aGlobal, std::move(request), signal);
+
+  if (aInput.IsRequest()) {
+    RefPtr<Request> inputReq = &aInput.GetAsRequest();
+    nsCOMPtr<nsIInputStream> body;
+    inputReq->GetBody(getter_AddRefs(body));
+    if (body) {
+      inputReq->SetBody(nullptr, 0);
+      inputReq->SetBodyUsed(aCx, aRv);
+      if (NS_WARN_IF(aRv.Failed())) {
+        return nullptr;
+      }
+    }
+  }
+  return domRequest;
+}
+
+SafeRefPtr<Request> Request::Clone(ErrorResult& aRv) {
+  if (BodyUsed()) {
+    aRv.ThrowTypeError<MSG_FETCH_BODY_CONSUMED_ERROR>();
+    return nullptr;
+  }
+
+  SafeRefPtr<InternalRequest> ir = mRequest->Clone();
+  if (!ir) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  return MakeSafeRefPtr<Request>(mOwner, std::move(ir), GetOrCreateSignal());
+}
+
+Headers* Request::Headers_() {
+  if (!mHeaders) {
+    mHeaders = new Headers(mOwner, mRequest->Headers());
+  }
+
+  return mHeaders;
+}
+
+AbortSignal* Request::GetOrCreateSignal() {
+  if (!mSignal) {
+    mSignal = new AbortSignal(mOwner, false, JS::UndefinedHandleValue);
+  }
+
+  return mSignal;
+}
+
+AbortSignalImpl* Request::GetSignalImpl() const { return mSignal; }
+
+AbortSignalImpl* Request::GetSignalImplToConsumeBody() const {
+  // This is a hack, see Response::GetSignalImplToConsumeBody.
+  return nullptr;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/fetch/Request.h b/dom/fetch/Request.h
new file mode 100644
index 0000000000..0086e076de
--- /dev/null
+++ b/dom/fetch/Request.h
@@ -0,0 +1,142 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_Request_h
+#define mozilla_dom_Request_h
+
+#include "nsISupportsImpl.h"
+#include "nsWrapperCache.h"
+
+#include "mozilla/dom/Fetch.h"
+#include "mozilla/dom/InternalRequest.h"
+// Required here due to certain WebIDL enums/classes being declared in both
+// files.
+#include "mozilla/dom/RequestBinding.h"
+#include "mozilla/dom/SafeRefPtr.h"
+
+namespace mozilla::dom {
+
+class Headers;
+class InternalHeaders;
+class RequestOrUSVString;
+
+class Request final : public FetchBody<Request>, public nsWrapperCache {
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS_INHERITED(Request,
+                                                        FetchBody<Request>)
+
+ public:
+  Request(nsIGlobalObject* aOwner, SafeRefPtr<InternalRequest> aRequest,
+          AbortSignal* aSignal);
+
+  JSObject* WrapObject(JSContext* aCx,
+                       JS::Handle<JSObject*> aGivenProto) override {
+    return Request_Binding::Wrap(aCx, this, aGivenProto);
+  }
+
+  void GetUrl(nsAString& aUrl) const {
+    nsAutoCString url;
+    mRequest->GetURL(url);
+    CopyUTF8toUTF16(url, aUrl);
+  }
+
+  void GetMethod(nsCString& aMethod) const { aMethod = mRequest->mMethod; }
+
+  RequestMode Mode() const { return mRequest->mMode; }
+
+  RequestCredentials Credentials() const { return mRequest->mCredentialsMode; }
+
+  RequestCache Cache() const { return mRequest->GetCacheMode(); }
+
+  RequestRedirect Redirect() const { return mRequest->GetRedirectMode(); }
+
+  void GetIntegrity(nsAString& aIntegrity) const {
+    aIntegrity = mRequest->GetIntegrity();
+  }
+
+  bool MozErrors() const { return mRequest->MozErrors(); }
+
+  RequestDestination Destination() const { return mRequest->Destination(); }
+
+  void OverrideContentPolicyType(uint32_t aContentPolicyType) {
+    mRequest->OverrideContentPolicyType(
+        static_cast<nsContentPolicyType>(aContentPolicyType));
+  }
+
+  bool IsContentPolicyTypeOverridden() const {
+    return mRequest->IsContentPolicyTypeOverridden();
+  }
+
+  void GetReferrer(nsAString& aReferrer) const {
+    mRequest->GetReferrer(aReferrer);
+  }
+
+  ReferrerPolicy ReferrerPolicy_() const { return mRequest->ReferrerPolicy_(); }
+
+  InternalHeaders* GetInternalHeaders() const { return mRequest->Headers(); }
+
+  Headers* Headers_();
+
+  using FetchBody::GetBody;
+
+  void GetBody(nsIInputStream** aStream, int64_t* aBodyLength = nullptr) {
+    mRequest->GetBody(aStream, aBodyLength);
+  }
+
+  void SetBody(nsIInputStream* aStream, int64_t aBodyLength) {
+    mRequest->SetBody(aStream, aBodyLength);
+  }
+
+  using FetchBody::BodyBlobURISpec;
+
+  const nsACString& BodyBlobURISpec() const {
+    return mRequest->BodyBlobURISpec();
+  }
+
+  using FetchBody::BodyLocalPath;
+
+  const nsAString& BodyLocalPath() const { return mRequest->BodyLocalPath(); }
+
+  static SafeRefPtr<Request> Constructor(const GlobalObject& aGlobal,
+                                         const RequestOrUSVString& aInput,
+                                         const RequestInit& aInit,
+                                         ErrorResult& rv);
+
+  static SafeRefPtr<Request> Constructor(nsIGlobalObject* aGlobal,
+                                         JSContext* aCx,
+                                         const RequestOrUSVString& aInput,
+                                         const RequestInit& aInit,
+                                         ErrorResult& rv);
+
+  nsIGlobalObject* GetParentObject() const { return mOwner; }
+
+  SafeRefPtr<Request> Clone(ErrorResult& aRv);
+
+  SafeRefPtr<InternalRequest> GetInternalRequest();
+
+  const UniquePtr<mozilla::ipc::PrincipalInfo>& GetPrincipalInfo() const {
+    return mRequest->GetPrincipalInfo();
+  }
+
+  AbortSignal* GetOrCreateSignal();
+
+  // This can return a null AbortSignalImpl.
+  AbortSignalImpl* GetSignalImpl() const override;
+  AbortSignalImpl* GetSignalImplToConsumeBody() const final;
+
+ private:
+  ~Request();
+
+  SafeRefPtr<InternalRequest> mRequest;
+
+  // Lazily created.
+  RefPtr<Headers> mHeaders;
+  RefPtr<AbortSignal> mSignal;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_Request_h
diff --git a/dom/fetch/Response.cpp b/dom/fetch/Response.cpp
new file mode 100644
index 0000000000..fbdc5b0d20
--- /dev/null
+++ b/dom/fetch/Response.cpp
@@ -0,0 +1,477 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "Response.h"
+
+#include "nsISupportsImpl.h"
+#include "nsIURI.h"
+#include "nsNetUtil.h"
+#include "nsPIDOMWindow.h"
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/HoldDropJSObjects.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/FetchBinding.h"
+#include "mozilla/dom/ResponseBinding.h"
+#include "mozilla/dom/Headers.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/URL.h"
+#include "mozilla/dom/WorkerPrivate.h"
+
+#include "nsDOMString.h"
+
+#include "BodyExtractor.h"
+#include "FetchStreamReader.h"
+#include "InternalResponse.h"
+
+#include "mozilla/dom/ReadableStreamDefaultReader.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_ADDREF_INHERITED(Response, FetchBody<Response>)
+NS_IMPL_RELEASE_INHERITED(Response, FetchBody<Response>)
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(Response)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(Response, FetchBody<Response>)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mOwner)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mHeaders)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mSignalImpl)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mFetchStreamReader)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(Response, FetchBody<Response>)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mOwner)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mHeaders)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mSignalImpl)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mFetchStreamReader)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(Response, FetchBody<Response>)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(Response)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+NS_INTERFACE_MAP_END_INHERITING(FetchBody<Response>)
+
+Response::Response(nsIGlobalObject* aGlobal,
+                   SafeRefPtr<InternalResponse> aInternalResponse,
+                   AbortSignalImpl* aSignalImpl)
+    : FetchBody<Response>(aGlobal),
+      mInternalResponse(std::move(aInternalResponse)),
+      mSignalImpl(aSignalImpl) {
+  MOZ_ASSERT(
+      mInternalResponse->Headers()->Guard() == HeadersGuardEnum::Immutable ||
+      mInternalResponse->Headers()->Guard() == HeadersGuardEnum::Response);
+
+  mozilla::HoldJSObjects(this);
+}
+
+Response::~Response() { mozilla::DropJSObjects(this); }
+
+/* static */
+already_AddRefed<Response> Response::Error(const GlobalObject& aGlobal) {
+  nsCOMPtr<nsIGlobalObject> global = do_QueryInterface(aGlobal.GetAsSupports());
+  RefPtr<Response> r = new Response(
+      global, InternalResponse::NetworkError(NS_ERROR_FAILURE), nullptr);
+  return r.forget();
+}
+
+/* static */
+already_AddRefed<Response> Response::Redirect(const GlobalObject& aGlobal,
+                                              const nsAString& aUrl,
+                                              uint16_t aStatus,
+                                              ErrorResult& aRv) {
+  nsAutoString parsedURL;
+
+  if (NS_IsMainThread()) {
+    nsIURI* baseURI = nullptr;
+    nsCOMPtr<nsPIDOMWindowInner> inner(
+        do_QueryInterface(aGlobal.GetAsSupports()));
+    Document* doc = inner ? inner->GetExtantDoc() : nullptr;
+    if (doc) {
+      baseURI = doc->GetBaseURI();
+    }
+    // Don't use NS_ConvertUTF16toUTF8 because that doesn't let us handle OOM.
+    nsAutoCString url;
+    if (!AppendUTF16toUTF8(aUrl, url, fallible)) {
+      aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+      return nullptr;
+    }
+
+    nsCOMPtr<nsIURI> resolvedURI;
+    nsresult rv = NS_NewURI(getter_AddRefs(resolvedURI), url, nullptr, baseURI);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      aRv.ThrowTypeError<MSG_INVALID_URL>(url);
+      return nullptr;
+    }
+
+    nsAutoCString spec;
+    rv = resolvedURI->GetSpec(spec);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      aRv.ThrowTypeError<MSG_INVALID_URL>(url);
+      return nullptr;
+    }
+
+    CopyUTF8toUTF16(spec, parsedURL);
+  } else {
+    WorkerPrivate* worker = GetCurrentThreadWorkerPrivate();
+    MOZ_ASSERT(worker);
+    worker->AssertIsOnWorkerThread();
+
+    NS_ConvertUTF8toUTF16 baseURL(worker->GetLocationInfo().mHref);
+    RefPtr<URL> url =
+        URL::Constructor(aGlobal.GetAsSupports(), aUrl, baseURL, aRv);
+    if (aRv.Failed()) {
+      return nullptr;
+    }
+
+    url->GetHref(parsedURL);
+  }
+
+  if (aStatus != 301 && aStatus != 302 && aStatus != 303 && aStatus != 307 &&
+      aStatus != 308) {
+    aRv.ThrowRangeError("Invalid redirect status code.");
+    return nullptr;
+  }
+
+  // We can't just pass nullptr for our null-valued Nullable, because the
+  // fetch::ResponseBodyInit is a non-temporary type due to the MOZ_RAII
+  // annotations on some of its members.
+  Nullable<fetch::ResponseBodyInit> body;
+  ResponseInit init;
+  init.mStatus = aStatus;
+  init.mStatusText.AssignASCII("");
+  RefPtr<Response> r = Response::Constructor(aGlobal, body, init, aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  r->GetInternalHeaders()->Set("Location"_ns, NS_ConvertUTF16toUTF8(parsedURL),
+                               aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+  r->GetInternalHeaders()->SetGuard(HeadersGuardEnum::Immutable, aRv);
+  MOZ_ASSERT(!aRv.Failed());
+
+  return r.forget();
+}
+
+/* static */ already_AddRefed<Response> Response::CreateAndInitializeAResponse(
+    const GlobalObject& aGlobal, const Nullable<fetch::ResponseBodyInit>& aBody,
+    const nsACString& aDefaultContentType, const ResponseInit& aInit,
+    ErrorResult& aRv) {
+  nsCOMPtr<nsIGlobalObject> global = do_QueryInterface(aGlobal.GetAsSupports());
+
+  if (NS_WARN_IF(!global)) {
+    aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
+    return nullptr;
+  }
+
+  // Initialize a response, Step 1.
+  if (aInit.mStatus < 200 || aInit.mStatus > 599) {
+    aRv.ThrowRangeError("Invalid response status code.");
+    return nullptr;
+  }
+
+  // Initialize a response, Step 2: Check if the status text contains illegal
+  // characters
+  nsACString::const_iterator start, end;
+  aInit.mStatusText.BeginReading(start);
+  aInit.mStatusText.EndReading(end);
+  if (FindCharInReadable('\r', start, end)) {
+    aRv.ThrowTypeError<MSG_RESPONSE_INVALID_STATUSTEXT_ERROR>();
+    return nullptr;
+  }
+  // Reset iterator since FindCharInReadable advances it.
+  aInit.mStatusText.BeginReading(start);
+  if (FindCharInReadable('\n', start, end)) {
+    aRv.ThrowTypeError<MSG_RESPONSE_INVALID_STATUSTEXT_ERROR>();
+    return nullptr;
+  }
+
+  // Initialize a response, Step 3-4.
+  SafeRefPtr<InternalResponse> internalResponse =
+      MakeSafeRefPtr<InternalResponse>(aInit.mStatus, aInit.mStatusText);
+
+  UniquePtr<mozilla::ipc::PrincipalInfo> principalInfo;
+
+  // Grab a valid channel info from the global so this response is 'valid' for
+  // interception.
+  if (NS_IsMainThread()) {
+    ChannelInfo info;
+    nsCOMPtr<nsPIDOMWindowInner> window = do_QueryInterface(global);
+    if (window) {
+      Document* doc = window->GetExtantDoc();
+      MOZ_ASSERT(doc);
+      info.InitFromDocument(doc);
+
+      principalInfo.reset(new mozilla::ipc::PrincipalInfo());
+      nsresult rv =
+          PrincipalToPrincipalInfo(doc->NodePrincipal(), principalInfo.get());
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        aRv.ThrowTypeError<MSG_FETCH_BODY_CONSUMED_ERROR>();
+        return nullptr;
+      }
+
+      internalResponse->InitChannelInfo(info);
+    } else if (global->PrincipalOrNull()->IsSystemPrincipal()) {
+      info.InitFromChromeGlobal(global);
+
+      internalResponse->InitChannelInfo(info);
+    }
+
+    /**
+     * The channel info is left uninitialized if neither the above `if` nor
+     * `else if` statements are executed; this could be because we're in a
+     * WebExtensions content script, where the global (i.e. `global`) is a
+     * wrapper, and the principal is an expanded principal. In this case,
+     * as far as I can tell, there's no way to get the security info, but we'd
+     * like the `Response` to be successfully constructed.
+     */
+  } else {
+    WorkerPrivate* worker = GetCurrentThreadWorkerPrivate();
+    MOZ_ASSERT(worker);
+    internalResponse->InitChannelInfo(worker->GetChannelInfo());
+    principalInfo =
+        MakeUnique<mozilla::ipc::PrincipalInfo>(worker->GetPrincipalInfo());
+  }
+
+  internalResponse->SetPrincipalInfo(std::move(principalInfo));
+
+  RefPtr<Response> r =
+      new Response(global, internalResponse.clonePtr(), nullptr);
+
+  if (aInit.mHeaders.WasPassed()) {
+    internalResponse->Headers()->Clear();
+
+    // Instead of using Fill, create an object to allow the constructor to
+    // unwrap the HeadersInit.
+    RefPtr<Headers> headers =
+        Headers::Create(global, aInit.mHeaders.Value(), aRv);
+    if (aRv.Failed()) {
+      return nullptr;
+    }
+
+    internalResponse->Headers()->Fill(*headers->GetInternalHeaders(), aRv);
+    if (NS_WARN_IF(aRv.Failed())) {
+      return nullptr;
+    }
+  }
+
+  if (!aBody.IsNull()) {
+    if (aInit.mStatus == 204 || aInit.mStatus == 205 || aInit.mStatus == 304) {
+      aRv.ThrowTypeError("Response body is given with a null body status.");
+      return nullptr;
+    }
+
+    nsCString contentTypeWithCharset;
+    nsCOMPtr<nsIInputStream> bodyStream;
+    int64_t bodySize = InternalResponse::UNKNOWN_BODY_SIZE;
+
+    const fetch::ResponseBodyInit& body = aBody.Value();
+    if (body.IsReadableStream()) {
+      JSContext* cx = aGlobal.Context();
+      aRv.MightThrowJSException();
+
+      ReadableStream& readableStream = body.GetAsReadableStream();
+
+      if (readableStream.Locked() || readableStream.Disturbed()) {
+        aRv.ThrowTypeError<MSG_FETCH_BODY_CONSUMED_ERROR>();
+        return nullptr;
+      }
+
+      r->SetReadableStreamBody(cx, &readableStream);
+
+      // If this is a DOM generated ReadableStream, we can extract the
+      // inputStream directly.
+      if (nsIInputStream* underlyingSource =
+              readableStream.MaybeGetInputStreamIfUnread()) {
+        bodyStream = underlyingSource;
+      } else {
+        // If this is a JS-created ReadableStream, let's create a
+        // FetchStreamReader.
+        aRv = FetchStreamReader::Create(aGlobal.Context(), global,
+                                        getter_AddRefs(r->mFetchStreamReader),
+                                        getter_AddRefs(bodyStream));
+        if (NS_WARN_IF(aRv.Failed())) {
+          return nullptr;
+        }
+      }
+    } else {
+      uint64_t size = 0;
+      aRv = ExtractByteStreamFromBody(body, getter_AddRefs(bodyStream),
+                                      contentTypeWithCharset, size);
+      if (NS_WARN_IF(aRv.Failed())) {
+        return nullptr;
+      }
+
+      if (!aDefaultContentType.IsVoid()) {
+        contentTypeWithCharset = aDefaultContentType;
+      }
+
+      bodySize = size;
+    }
+
+    internalResponse->SetBody(bodyStream, bodySize);
+
+    if (!contentTypeWithCharset.IsVoid() &&
+        !internalResponse->Headers()->Has("Content-Type"_ns, aRv)) {
+      // Ignore Append() failing here.
+      ErrorResult error;
+      internalResponse->Headers()->Append("Content-Type"_ns,
+                                          contentTypeWithCharset, error);
+      error.SuppressException();
+    }
+
+    if (aRv.Failed()) {
+      return nullptr;
+    }
+  }
+
+  return r.forget();
+}
+
+/* static */
+already_AddRefed<Response> Response::CreateFromJson(const GlobalObject& aGlobal,
+                                                    JSContext* aCx,
+                                                    JS::Handle<JS::Value> aData,
+                                                    const ResponseInit& aInit,
+                                                    ErrorResult& aRv) {
+  aRv.MightThrowJSException();
+  nsAutoString serializedValue;
+  if (!nsContentUtils::StringifyJSON(aCx, aData, serializedValue,
+                                     UndefinedIsVoidString)) {
+    aRv.StealExceptionFromJSContext(aCx);
+    return nullptr;
+  }
+  if (serializedValue.IsVoid()) {
+    aRv.ThrowTypeError<MSG_JSON_INVALID_VALUE>();
+    return nullptr;
+  }
+  Nullable<fetch::ResponseBodyInit> body;
+  body.SetValue().SetAsUSVString().ShareOrDependUpon(serializedValue);
+  return CreateAndInitializeAResponse(aGlobal, body, "application/json"_ns,
+                                      aInit, aRv);
+}
+
+/*static*/
+already_AddRefed<Response> Response::Constructor(
+    const GlobalObject& aGlobal, const Nullable<fetch::ResponseBodyInit>& aBody,
+    const ResponseInit& aInit, ErrorResult& aRv) {
+  return CreateAndInitializeAResponse(aGlobal, aBody, VoidCString(), aInit,
+                                      aRv);
+}
+
+already_AddRefed<Response> Response::Clone(JSContext* aCx, ErrorResult& aRv) {
+  bool bodyUsed = BodyUsed();
+
+  if (!bodyUsed && mReadableStreamBody) {
+    bool locked = mReadableStreamBody->Locked();
+    bodyUsed = locked;
+  }
+
+  if (bodyUsed) {
+    aRv.ThrowTypeError<MSG_FETCH_BODY_CONSUMED_ERROR>();
+    return nullptr;
+  }
+
+  RefPtr<FetchStreamReader> streamReader;
+  nsCOMPtr<nsIInputStream> inputStream;
+
+  RefPtr<ReadableStream> body;
+  MaybeTeeReadableStreamBody(aCx, getter_AddRefs(body),
+                             getter_AddRefs(streamReader),
+                             getter_AddRefs(inputStream), aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  MOZ_ASSERT_IF(body, streamReader);
+  MOZ_ASSERT_IF(body, inputStream);
+
+  SafeRefPtr<InternalResponse> ir =
+      mInternalResponse->Clone(body ? InternalResponse::eDontCloneInputStream
+                                    : InternalResponse::eCloneInputStream);
+
+  RefPtr<Response> response =
+      new Response(mOwner, ir.clonePtr(), GetSignalImpl());
+
+  if (body) {
+    // Maybe we have a body, but we receive null from MaybeTeeReadableStreamBody
+    // if this body is a native stream.   In this case the InternalResponse will
+    // have a clone of the native body and the ReadableStream will be created
+    // lazily if needed.
+    response->SetReadableStreamBody(aCx, body);
+    response->mFetchStreamReader = streamReader;
+    ir->SetBody(inputStream, InternalResponse::UNKNOWN_BODY_SIZE);
+  }
+
+  return response.forget();
+}
+
+already_AddRefed<Response> Response::CloneUnfiltered(JSContext* aCx,
+                                                     ErrorResult& aRv) {
+  if (BodyUsed()) {
+    aRv.ThrowTypeError<MSG_FETCH_BODY_CONSUMED_ERROR>();
+    return nullptr;
+  }
+
+  RefPtr<FetchStreamReader> streamReader;
+  nsCOMPtr<nsIInputStream> inputStream;
+
+  RefPtr<ReadableStream> body;
+  MaybeTeeReadableStreamBody(aCx, getter_AddRefs(body),
+                             getter_AddRefs(streamReader),
+                             getter_AddRefs(inputStream), aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  MOZ_ASSERT_IF(body, streamReader);
+  MOZ_ASSERT_IF(body, inputStream);
+
+  SafeRefPtr<InternalResponse> clone =
+      mInternalResponse->Clone(body ? InternalResponse::eDontCloneInputStream
+                                    : InternalResponse::eCloneInputStream);
+
+  SafeRefPtr<InternalResponse> ir = clone->Unfiltered();
+  RefPtr<Response> ref = new Response(mOwner, ir.clonePtr(), GetSignalImpl());
+
+  if (body) {
+    // Maybe we have a body, but we receive null from MaybeTeeReadableStreamBody
+    // if this body is a native stream.   In this case the InternalResponse will
+    // have a clone of the native body and the ReadableStream will be created
+    // lazily if needed.
+    ref->SetReadableStreamBody(aCx, body);
+    ref->mFetchStreamReader = streamReader;
+    ir->SetBody(inputStream, InternalResponse::UNKNOWN_BODY_SIZE);
+  }
+
+  return ref.forget();
+}
+
+void Response::SetBody(nsIInputStream* aBody, int64_t aBodySize) {
+  MOZ_ASSERT(!BodyUsed());
+  mInternalResponse->SetBody(aBody, aBodySize);
+}
+
+SafeRefPtr<InternalResponse> Response::GetInternalResponse() const {
+  return mInternalResponse.clonePtr();
+}
+
+Headers* Response::Headers_() {
+  if (!mHeaders) {
+    mHeaders = new Headers(mOwner, mInternalResponse->Headers());
+  }
+
+  return mHeaders;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/fetch/Response.h b/dom/fetch/Response.h
new file mode 100644
index 0000000000..1aa0e56c31
--- /dev/null
+++ b/dom/fetch/Response.h
@@ -0,0 +1,161 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_Response_h
+#define mozilla_dom_Response_h
+
+#include "nsWrapperCache.h"
+#include "nsISupportsImpl.h"
+
+#include "mozilla/dom/Fetch.h"
+#include "mozilla/dom/ResponseBinding.h"
+
+#include "InternalHeaders.h"
+#include "InternalResponse.h"
+
+namespace mozilla {
+namespace ipc {
+class PrincipalInfo;
+}  // namespace ipc
+
+namespace dom {
+
+class Headers;
+
+class Response final : public FetchBody<Response>, public nsWrapperCache {
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(Response,
+                                                         FetchBody<Response>)
+
+ public:
+  Response(nsIGlobalObject* aGlobal,
+           SafeRefPtr<InternalResponse> aInternalResponse,
+           AbortSignalImpl* aSignalImpl);
+
+  Response(const Response& aOther) = delete;
+
+  JSObject* WrapObject(JSContext* aCx,
+                       JS::Handle<JSObject*> aGivenProto) override {
+    return Response_Binding::Wrap(aCx, this, aGivenProto);
+  }
+
+  ResponseType Type() const { return mInternalResponse->Type(); }
+  void GetUrl(nsAString& aUrl) const {
+    CopyUTF8toUTF16(mInternalResponse->GetURL(), aUrl);
+  }
+  bool Redirected() const { return mInternalResponse->IsRedirected(); }
+  uint16_t Status() const { return mInternalResponse->GetStatus(); }
+
+  bool Ok() const {
+    return mInternalResponse->GetStatus() >= 200 &&
+           mInternalResponse->GetStatus() <= 299;
+  }
+
+  void GetStatusText(nsCString& aStatusText) const {
+    aStatusText = mInternalResponse->GetStatusText();
+  }
+
+  InternalHeaders* GetInternalHeaders() const {
+    return mInternalResponse->Headers();
+  }
+
+  void InitChannelInfo(nsIChannel* aChannel) {
+    mInternalResponse->InitChannelInfo(aChannel);
+  }
+
+  const ChannelInfo& GetChannelInfo() const {
+    return mInternalResponse->GetChannelInfo();
+  }
+
+  const UniquePtr<mozilla::ipc::PrincipalInfo>& GetPrincipalInfo() const {
+    return mInternalResponse->GetPrincipalInfo();
+  }
+
+  bool HasCacheInfoChannel() const {
+    return mInternalResponse->HasCacheInfoChannel();
+  }
+
+  Headers* Headers_();
+
+  void GetBody(nsIInputStream** aStream, int64_t* aBodyLength = nullptr) {
+    mInternalResponse->GetBody(aStream, aBodyLength);
+  }
+
+  using FetchBody::GetBody;
+
+  using FetchBody::BodyBlobURISpec;
+
+  const nsACString& BodyBlobURISpec() const {
+    return mInternalResponse->BodyBlobURISpec();
+  }
+
+  using FetchBody::BodyLocalPath;
+
+  const nsAString& BodyLocalPath() const {
+    return mInternalResponse->BodyLocalPath();
+  }
+
+  static already_AddRefed<Response> Error(const GlobalObject& aGlobal);
+
+  static already_AddRefed<Response> Redirect(const GlobalObject& aGlobal,
+                                             const nsAString& aUrl,
+                                             uint16_t aStatus,
+                                             ErrorResult& aRv);
+
+  static already_AddRefed<Response> CreateFromJson(const GlobalObject&,
+                                                   JSContext*,
+                                                   JS::Handle<JS::Value>,
+                                                   const ResponseInit&,
+                                                   ErrorResult&);
+
+  static already_AddRefed<Response> Constructor(
+      const GlobalObject& aGlobal,
+      const Nullable<fetch::ResponseBodyInit>& aBody, const ResponseInit& aInit,
+      ErrorResult& rv);
+
+  nsIGlobalObject* GetParentObject() const { return mOwner; }
+
+  already_AddRefed<Response> Clone(JSContext* aCx, ErrorResult& aRv);
+
+  already_AddRefed<Response> CloneUnfiltered(JSContext* aCx, ErrorResult& aRv);
+
+  void SetBody(nsIInputStream* aBody, int64_t aBodySize);
+
+  SafeRefPtr<InternalResponse> GetInternalResponse() const;
+
+  AbortSignalImpl* GetSignalImpl() const override { return mSignalImpl; }
+  AbortSignalImpl* GetSignalImplToConsumeBody() const final {
+    // XXX: BodyConsumer is supposed to work in terms of ReadableStream and
+    // should be affected by: https://fetch.spec.whatwg.org/#abort-fetch
+    //
+    // Step 6: If response’s body is not null and is readable, then error
+    // response’s body with error.
+    //
+    // But since it's written before streams work, it's currently depending on
+    // abort signal to be aborted.
+    // Please fix this when DOM ReadableStream is ready. (Bug 1730584)
+    return mSignalImpl;
+  }
+
+ private:
+  static already_AddRefed<Response> CreateAndInitializeAResponse(
+      const GlobalObject& aGlobal,
+      const Nullable<fetch::ResponseBodyInit>& aBody,
+      const nsACString& aDefaultContentType, const ResponseInit& aInit,
+      ErrorResult& aRv);
+
+  ~Response();
+
+  SafeRefPtr<InternalResponse> mInternalResponse;
+  // Lazily created
+  RefPtr<Headers> mHeaders;
+  RefPtr<AbortSignalImpl> mSignalImpl;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_Response_h
diff --git a/dom/fetch/moz.build b/dom/fetch/moz.build
new file mode 100644
index 0000000000..6d7aa31027
--- /dev/null
+++ b/dom/fetch/moz.build
@@ -0,0 +1,72 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+with Files("**"):
+    BUG_COMPONENT = ("Core", "DOM: Networking")
+
+EXPORTS.mozilla.dom += [
+    "BodyExtractor.h",
+    "ChannelInfo.h",
+    "Fetch.h",
+    "FetchChild.h",
+    "FetchDriver.h",
+    "FetchIPCTypes.h",
+    "FetchObserver.h",
+    "FetchParent.h",
+    "FetchService.h",
+    "FetchStreamReader.h",
+    "FetchStreamUtils.h",
+    "FetchUtil.h",
+    "Headers.h",
+    "InternalHeaders.h",
+    "InternalRequest.h",
+    "InternalResponse.h",
+    "Request.h",
+    "Response.h",
+]
+
+UNIFIED_SOURCES += [
+    "BodyExtractor.cpp",
+    "ChannelInfo.cpp",
+    "Fetch.cpp",
+    "FetchChild.cpp",
+    "FetchDriver.cpp",
+    "FetchObserver.cpp",
+    "FetchParent.cpp",
+    "FetchService.cpp",
+    "FetchStreamReader.cpp",
+    "FetchStreamUtils.cpp",
+    "FetchUtil.cpp",
+    "Headers.cpp",
+    "InternalHeaders.cpp",
+    "InternalRequest.cpp",
+    "InternalResponse.cpp",
+    "Request.cpp",
+    "Response.cpp",
+]
+
+IPDL_SOURCES += [
+    "FetchTypes.ipdlh",
+    "PFetch.ipdl",
+]
+
+LOCAL_INCLUDES += [
+    # For nsDOMSerializer
+    "/dom/base",
+    # For HttpBaseChannel.h dependencies
+    "/netwerk/base",
+    # For nsDataHandler.h
+    "/netwerk/protocol/data",
+    # For HttpBaseChannel.h
+    "/netwerk/protocol/http",
+]
+
+BROWSER_CHROME_MANIFESTS += ["tests/browser.ini"]
+MOCHITEST_MANIFESTS += ["tests/mochitest.ini"]
+
+FINAL_LIBRARY = "xul"
+
+include("/ipc/chromium/chromium-config.mozbuild")
diff --git a/dom/fetch/tests/browser.ini b/dom/fetch/tests/browser.ini
new file mode 100644
index 0000000000..6fd8244288
--- /dev/null
+++ b/dom/fetch/tests/browser.ini
@@ -0,0 +1,23 @@
+[DEFAULT]
+[browser_blobFromFile.js]
+[browser_origin_trial_coep_credentialless_fetch_1.js]
+support-files =
+  open_credentialless_document.sjs
+  store_header.sjs
+[browser_origin_trial_coep_credentialless_fetch_2.js]
+support-files =
+  open_credentialless_document.sjs
+  store_header.sjs
+[browser_origin_trial_coep_credentialless_fetch_3.js]
+support-files =
+  open_credentialless_document.sjs
+  store_header.sjs
+[browser_origin_trial_coep_credentialless_worker.js]
+support-files =
+  open_credentialless_document.sjs
+  store_header.sjs
+  credentialless_worker.sjs
+[browser_origin_trial_coep_credentialless_cache.js]
+support-files =
+  open_credentialless_document.sjs
+  credentialless_resource.sjs
diff --git a/dom/fetch/tests/browser_blobFromFile.js b/dom/fetch/tests/browser_blobFromFile.js
new file mode 100644
index 0000000000..07a8c6669e
--- /dev/null
+++ b/dom/fetch/tests/browser_blobFromFile.js
@@ -0,0 +1,64 @@
+add_task(async function test() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.tabs.remote.separateFileUriProcess", true]],
+  });
+
+  let fileData = "";
+  for (var i = 0; i < 100; ++i) {
+    fileData += "hello world!";
+  }
+
+  let file = Cc["@mozilla.org/file/directory_service;1"]
+    .getService(Ci.nsIDirectoryService)
+    .QueryInterface(Ci.nsIProperties)
+    .get("ProfD", Ci.nsIFile);
+  file.append("file.txt");
+  file.createUnique(Ci.nsIFile.NORMAL_FILE_TYPE, 0o600);
+
+  let outStream = Cc[
+    "@mozilla.org/network/file-output-stream;1"
+  ].createInstance(Ci.nsIFileOutputStream);
+  outStream.init(
+    file,
+    0x02 | 0x08 | 0x20, // write, create, truncate
+    0o666,
+    0
+  );
+  outStream.write(fileData, fileData.length);
+  outStream.close();
+
+  let fileHandler = Cc["@mozilla.org/network/io-service;1"]
+    .getService(Ci.nsIIOService)
+    .getProtocolHandler("file")
+    .QueryInterface(Ci.nsIFileProtocolHandler);
+
+  let fileURL = fileHandler.getURLSpecFromActualFile(file);
+
+  info("Opening url: " + fileURL);
+  let tab = BrowserTestUtils.addTab(gBrowser, fileURL);
+
+  let browser = gBrowser.getBrowserForTab(tab);
+  await BrowserTestUtils.browserLoaded(browser);
+
+  let blob = await SpecialPowers.spawn(
+    browser,
+    [file.leafName],
+    function (fileName) {
+      return new content.window.Promise(resolve => {
+        content.window
+          .fetch(fileName)
+          .then(r => r.blob())
+          .then(blob => resolve(blob));
+      });
+    }
+  );
+
+  ok(File.isInstance(blob), "We have a file");
+
+  is(blob.size, file.fileSize, "The size matches");
+  is(blob.name, file.leafName, "The name is correct");
+
+  file.remove(false);
+
+  gBrowser.removeTab(tab);
+});
diff --git a/dom/fetch/tests/browser_origin_trial_coep_credentialless_cache.js b/dom/fetch/tests/browser_origin_trial_coep_credentialless_cache.js
new file mode 100644
index 0000000000..c9b72a3393
--- /dev/null
+++ b/dom/fetch/tests/browser_origin_trial_coep_credentialless_cache.js
@@ -0,0 +1,139 @@
+const TOP_LEVEL_URL =
+  getRootDirectory(gTestPath).replace(
+    "chrome://mochitests/content",
+    "https://example.com"
+  ) + "open_credentialless_document.sjs";
+
+const SAME_ORIGIN = "https://example.com";
+const CROSS_ORIGIN = "https://test1.example.com";
+
+const RESOURCE_URL =
+  getRootDirectory(gTestPath).replace(
+    "chrome://mochitests/content",
+    "https://test1.example.com"
+  ) + "credentialless_resource.sjs";
+
+async function store(storer, url, requestCredentialMode) {
+  await SpecialPowers.spawn(
+    storer.linkedBrowser,
+    [url, requestCredentialMode],
+    async function (url, requestCredentialMode) {
+      const cache = await content.caches.open("v1");
+      const fetchRequest = new content.Request(url, {
+        mode: "no-cors",
+        credentials: requestCredentialMode,
+      });
+
+      const fetchResponse = await content.fetch(fetchRequest);
+      content.wrappedJSObject.console.log(fetchResponse.headers);
+      await cache.put(fetchRequest, fetchResponse);
+    }
+  );
+}
+
+async function retrieve(retriever, resourceURL) {
+  return await SpecialPowers.spawn(
+    retriever.linkedBrowser,
+    [resourceURL],
+    async function (url) {
+      const cache = await content.caches.open("v1");
+      try {
+        await cache.match(url);
+        return "retrieved";
+      } catch (error) {
+        return "error";
+      }
+    }
+  );
+}
+
+async function testCache(
+  storer,
+  storeRequestCredentialMode,
+  resourceCOEP,
+  retriever,
+  expectation
+) {
+  const resourceURL = RESOURCE_URL + "?" + resourceCOEP;
+
+  await store(storer, resourceURL, storeRequestCredentialMode);
+  const result = await retrieve(retriever, resourceURL);
+
+  is(result, expectation);
+}
+
+add_task(async function () {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.tabs.remote.coep.credentialless", false],
+      ["dom.origin-trials.enabled", true],
+      ["dom.origin-trials.test-key.enabled", true],
+    ],
+  });
+
+  const noneTab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    TOP_LEVEL_URL
+  );
+  const requireCorpTab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    TOP_LEVEL_URL + "?requirecorp"
+  );
+  const credentiallessTab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    TOP_LEVEL_URL + "?credentialless"
+  );
+
+  await testCache(noneTab, "include", "", noneTab, "retrieved");
+  await testCache(noneTab, "include", "", credentiallessTab, "error");
+  await testCache(noneTab, "omit", "", credentiallessTab, "retrieved");
+  await testCache(
+    noneTab,
+    "include",
+    "corp_cross_origin",
+    credentiallessTab,
+    "retrieved"
+  );
+  await testCache(noneTab, "include", "", requireCorpTab, "error");
+  await testCache(
+    noneTab,
+    "include",
+    "corp_cross_origin",
+    requireCorpTab,
+    "retrieved"
+  );
+  await testCache(credentiallessTab, "include", "", noneTab, "retrieved");
+  await testCache(
+    credentiallessTab,
+    "include",
+    "",
+    credentiallessTab,
+    "retrieved"
+  );
+  await testCache(credentiallessTab, "include", "", requireCorpTab, "error");
+  await testCache(
+    requireCorpTab,
+    "include",
+    "corp_cross_origin",
+    noneTab,
+    "retrieved"
+  );
+  await testCache(
+    requireCorpTab,
+    "include",
+    "corp_cross_origin",
+    credentiallessTab,
+    "retrieved"
+  );
+  await testCache(
+    requireCorpTab,
+    "include",
+    "corp_cross_origin",
+    requireCorpTab,
+    "retrieved"
+  );
+
+  await BrowserTestUtils.removeTab(noneTab);
+  await BrowserTestUtils.removeTab(requireCorpTab);
+  await BrowserTestUtils.removeTab(credentiallessTab);
+});
diff --git a/dom/fetch/tests/browser_origin_trial_coep_credentialless_fetch_1.js b/dom/fetch/tests/browser_origin_trial_coep_credentialless_fetch_1.js
new file mode 100644
index 0000000000..773c15e72a
--- /dev/null
+++ b/dom/fetch/tests/browser_origin_trial_coep_credentialless_fetch_1.js
@@ -0,0 +1,145 @@
+const TOP_LEVEL_URL =
+  getRootDirectory(gTestPath).replace(
+    "chrome://mochitests/content",
+    "https://example.com"
+  ) + "open_credentialless_document.sjs";
+
+const SAME_ORIGIN = "https://example.com";
+const CROSS_ORIGIN = "https://test1.example.com";
+
+const GET_STATE_URL =
+  getRootDirectory(gTestPath).replace(
+    "chrome://mochitests/content",
+    "https://example.com"
+  ) + "store_header.sjs?getstate";
+
+async function addCookieToOrigin(origin) {
+  const fetchRequestURL =
+    getRootDirectory(gTestPath).replace("chrome://mochitests/content", origin) +
+    "store_header.sjs?addcookie";
+
+  const addcookieTab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    fetchRequestURL
+  );
+
+  await SpecialPowers.spawn(addcookieTab.linkedBrowser, [], async function () {
+    content.document.cookie = "coep=credentialless; SameSite=None; Secure";
+  });
+  await BrowserTestUtils.removeTab(addcookieTab);
+}
+
+async function testOrigin(
+  fetchOrigin,
+  isCredentialless,
+  useMetaTag,
+  fetchRequestMode,
+  fetchRequestCrendentials,
+  expectedCookieResult
+) {
+  let params = [];
+  if (isCredentialless) {
+    params.push("credentialless");
+  }
+  if (useMetaTag) {
+    params.push("meta");
+  }
+
+  let topLevelUrl = TOP_LEVEL_URL;
+  if (params.length) {
+    topLevelUrl += "?" + params.join("&");
+  }
+
+  const noCredentiallessTab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    topLevelUrl
+  );
+
+  const fetchRequestURL =
+    getRootDirectory(gTestPath).replace(
+      "chrome://mochitests/content",
+      fetchOrigin
+    ) + "store_header.sjs?checkheader";
+
+  await SpecialPowers.spawn(
+    noCredentiallessTab.linkedBrowser,
+    [
+      !useMetaTag && isCredentialless,
+      fetchRequestURL,
+      fetchRequestMode,
+      fetchRequestCrendentials,
+      GET_STATE_URL,
+      expectedCookieResult,
+    ],
+    async function (
+      sharedArrayBufferEnabled,
+      fetchRequestURL,
+      fetchRequestMode,
+      fetchRequestCrendentials,
+      getStateURL,
+      expectedCookieResult
+    ) {
+      if (sharedArrayBufferEnabled) {
+        ok(content.crossOriginIsolated);
+      }
+      // When store_header.sjs receives this request, it will store
+      // whether it has received the cookie as a shared state.
+      await content.fetch(fetchRequestURL, {
+        mode: fetchRequestMode,
+        credentials: fetchRequestCrendentials,
+      });
+
+      // This request is used to get the saved state from the
+      // previous fetch request.
+      const response = await content.fetch(getStateURL, {
+        mode: "cors",
+      });
+      const text = await response.text();
+      is(text, expectedCookieResult);
+    }
+  );
+
+  await BrowserTestUtils.removeTab(noCredentiallessTab);
+}
+
+async function doTest(
+  origin,
+  fetchRequestMode,
+  fetchRequestCrendentials,
+  expectedCookieResultForNoCredentialless,
+  expectedCookieResultForCredentialless
+) {
+  for (let credentialless of [true, false]) {
+    for (let meta of [true, false]) {
+      await testOrigin(
+        origin,
+        credentialless,
+        meta,
+        fetchRequestMode,
+        fetchRequestCrendentials,
+        credentialless
+          ? expectedCookieResultForCredentialless
+          : expectedCookieResultForNoCredentialless
+      );
+    }
+  }
+}
+
+add_task(async function () {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.tabs.remote.coep.credentialless", false],
+      ["dom.origin-trials.enabled", true],
+      ["dom.origin-trials.test-key.enabled", true],
+    ],
+  });
+
+  await addCookieToOrigin(SAME_ORIGIN);
+  await addCookieToOrigin(CROSS_ORIGIN);
+
+  // Cookies never sent with omit
+  await doTest(SAME_ORIGIN, "no-cors", "omit", "noCookie", "noCookie");
+  await doTest(SAME_ORIGIN, "cors", "omit", "noCookie", "noCookie");
+  await doTest(CROSS_ORIGIN, "no-cors", "omit", "noCookie", "noCookie");
+  await doTest(CROSS_ORIGIN, "cors", "omit", "noCookie", "noCookie");
+});
diff --git a/dom/fetch/tests/browser_origin_trial_coep_credentialless_fetch_2.js b/dom/fetch/tests/browser_origin_trial_coep_credentialless_fetch_2.js
new file mode 100644
index 0000000000..7a1e6879ac
--- /dev/null
+++ b/dom/fetch/tests/browser_origin_trial_coep_credentialless_fetch_2.js
@@ -0,0 +1,145 @@
+const TOP_LEVEL_URL =
+  getRootDirectory(gTestPath).replace(
+    "chrome://mochitests/content",
+    "https://example.com"
+  ) + "open_credentialless_document.sjs";
+
+const SAME_ORIGIN = "https://example.com";
+const CROSS_ORIGIN = "https://test1.example.com";
+
+const GET_STATE_URL =
+  getRootDirectory(gTestPath).replace(
+    "chrome://mochitests/content",
+    "https://example.com"
+  ) + "store_header.sjs?getstate";
+
+async function addCookieToOrigin(origin) {
+  const fetchRequestURL =
+    getRootDirectory(gTestPath).replace("chrome://mochitests/content", origin) +
+    "store_header.sjs?addcookie";
+
+  const addcookieTab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    fetchRequestURL
+  );
+
+  await SpecialPowers.spawn(addcookieTab.linkedBrowser, [], async function () {
+    content.document.cookie = "coep=credentialless; SameSite=None; Secure";
+  });
+  await BrowserTestUtils.removeTab(addcookieTab);
+}
+
+async function testOrigin(
+  fetchOrigin,
+  isCredentialless,
+  useMetaTag,
+  fetchRequestMode,
+  fetchRequestCrendentials,
+  expectedCookieResult
+) {
+  let params = [];
+  if (isCredentialless) {
+    params.push("credentialless");
+  }
+  if (useMetaTag) {
+    params.push("meta");
+  }
+
+  let topLevelUrl = TOP_LEVEL_URL;
+  if (params.length) {
+    topLevelUrl += "?" + params.join("&");
+  }
+
+  const noCredentiallessTab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    topLevelUrl
+  );
+
+  const fetchRequestURL =
+    getRootDirectory(gTestPath).replace(
+      "chrome://mochitests/content",
+      fetchOrigin
+    ) + "store_header.sjs?checkheader";
+
+  await SpecialPowers.spawn(
+    noCredentiallessTab.linkedBrowser,
+    [
+      !useMetaTag && isCredentialless,
+      fetchRequestURL,
+      fetchRequestMode,
+      fetchRequestCrendentials,
+      GET_STATE_URL,
+      expectedCookieResult,
+    ],
+    async function (
+      sharedArrayBufferEnabled,
+      fetchRequestURL,
+      fetchRequestMode,
+      fetchRequestCrendentials,
+      getStateURL,
+      expectedCookieResult
+    ) {
+      if (sharedArrayBufferEnabled) {
+        ok(content.crossOriginIsolated);
+      }
+      // When store_header.sjs receives this request, it will store
+      // whether it has received the cookie as a shared state.
+      await content.fetch(fetchRequestURL, {
+        mode: fetchRequestMode,
+        credentials: fetchRequestCrendentials,
+      });
+
+      // This request is used to get the saved state from the
+      // previous fetch request.
+      const response = await content.fetch(getStateURL, {
+        mode: "cors",
+      });
+      const text = await response.text();
+      is(text, expectedCookieResult);
+    }
+  );
+
+  await BrowserTestUtils.removeTab(noCredentiallessTab);
+}
+
+async function doTest(
+  origin,
+  fetchRequestMode,
+  fetchRequestCrendentials,
+  expectedCookieResultForNoCredentialless,
+  expectedCookieResultForCredentialless
+) {
+  for (let credentialless of [true, false]) {
+    for (let meta of [true, false]) {
+      await testOrigin(
+        origin,
+        credentialless,
+        meta,
+        fetchRequestMode,
+        fetchRequestCrendentials,
+        credentialless
+          ? expectedCookieResultForCredentialless
+          : expectedCookieResultForNoCredentialless
+      );
+    }
+  }
+}
+
+add_task(async function () {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.tabs.remote.coep.credentialless", false],
+      ["dom.origin-trials.enabled", true],
+      ["dom.origin-trials.test-key.enabled", true],
+    ],
+  });
+
+  await addCookieToOrigin(SAME_ORIGIN);
+  await addCookieToOrigin(CROSS_ORIGIN);
+
+  // Same-origin request contains Cookies.
+  await doTest(SAME_ORIGIN, "no-cors", "include", "hasCookie", "hasCookie");
+  await doTest(SAME_ORIGIN, "cors", "include", "hasCookie", "hasCookie");
+  await doTest(SAME_ORIGIN, "no-cors", "same-origin", "hasCookie", "hasCookie");
+  await doTest(SAME_ORIGIN, "cors", "same-origin", "hasCookie", "hasCookie");
+});
diff --git a/dom/fetch/tests/browser_origin_trial_coep_credentialless_fetch_3.js b/dom/fetch/tests/browser_origin_trial_coep_credentialless_fetch_3.js
new file mode 100644
index 0000000000..a1a1edb2ff
--- /dev/null
+++ b/dom/fetch/tests/browser_origin_trial_coep_credentialless_fetch_3.js
@@ -0,0 +1,150 @@
+const TOP_LEVEL_URL =
+  getRootDirectory(gTestPath).replace(
+    "chrome://mochitests/content",
+    "https://example.com"
+  ) + "open_credentialless_document.sjs";
+
+const SAME_ORIGIN = "https://example.com";
+const CROSS_ORIGIN = "https://test1.example.com";
+
+const GET_STATE_URL =
+  getRootDirectory(gTestPath).replace(
+    "chrome://mochitests/content",
+    "https://example.com"
+  ) + "store_header.sjs?getstate";
+
+async function addCookieToOrigin(origin) {
+  const fetchRequestURL =
+    getRootDirectory(gTestPath).replace("chrome://mochitests/content", origin) +
+    "store_header.sjs?addcookie";
+
+  const addcookieTab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    fetchRequestURL
+  );
+
+  await SpecialPowers.spawn(addcookieTab.linkedBrowser, [], async function () {
+    content.document.cookie = "coep=credentialless; SameSite=None; Secure";
+  });
+  await BrowserTestUtils.removeTab(addcookieTab);
+}
+
+async function testOrigin(
+  fetchOrigin,
+  isCredentialless,
+  useMetaTag,
+  fetchRequestMode,
+  fetchRequestCrendentials,
+  expectedCookieResult
+) {
+  let params = [];
+  if (isCredentialless) {
+    params.push("credentialless");
+  }
+  if (useMetaTag) {
+    params.push("meta");
+  }
+
+  let topLevelUrl = TOP_LEVEL_URL;
+  if (params.length) {
+    topLevelUrl += "?" + params.join("&");
+  }
+
+  const noCredentiallessTab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    topLevelUrl
+  );
+
+  const fetchRequestURL =
+    getRootDirectory(gTestPath).replace(
+      "chrome://mochitests/content",
+      fetchOrigin
+    ) + "store_header.sjs?checkheader";
+
+  await SpecialPowers.spawn(
+    noCredentiallessTab.linkedBrowser,
+    [
+      !useMetaTag && isCredentialless,
+      fetchRequestURL,
+      fetchRequestMode,
+      fetchRequestCrendentials,
+      GET_STATE_URL,
+      expectedCookieResult,
+    ],
+    async function (
+      sharedArrayBufferEnabled,
+      fetchRequestURL,
+      fetchRequestMode,
+      fetchRequestCrendentials,
+      getStateURL,
+      expectedCookieResult
+    ) {
+      if (sharedArrayBufferEnabled) {
+        ok(content.crossOriginIsolated);
+      }
+      // When store_header.sjs receives this request, it will store
+      // whether it has received the cookie as a shared state.
+      await content.fetch(fetchRequestURL, {
+        mode: fetchRequestMode,
+        credentials: fetchRequestCrendentials,
+      });
+
+      // This request is used to get the saved state from the
+      // previous fetch request.
+      const response = await content.fetch(getStateURL, {
+        mode: "cors",
+      });
+      const text = await response.text();
+      is(text, expectedCookieResult);
+    }
+  );
+
+  await BrowserTestUtils.removeTab(noCredentiallessTab);
+}
+
+async function doTest(
+  origin,
+  fetchRequestMode,
+  fetchRequestCrendentials,
+  expectedCookieResultForNoCredentialless,
+  expectedCookieResultForCredentialless
+) {
+  for (let credentialless of [true, false]) {
+    for (let meta of [true, false]) {
+      await testOrigin(
+        origin,
+        credentialless,
+        meta,
+        fetchRequestMode,
+        fetchRequestCrendentials,
+        credentialless
+          ? expectedCookieResultForCredentialless
+          : expectedCookieResultForNoCredentialless
+      );
+    }
+  }
+}
+
+add_task(async function () {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.tabs.remote.coep.credentialless", false],
+      ["dom.origin-trials.enabled", true],
+      ["dom.origin-trials.test-key.enabled", true],
+    ],
+  });
+
+  await addCookieToOrigin(SAME_ORIGIN);
+  await addCookieToOrigin(CROSS_ORIGIN);
+
+  // Cross-origin CORS requests contains Cookies, if credentials mode is set to
+  // 'include'. This does not depends on COEP.
+  await doTest(CROSS_ORIGIN, "cors", "include", "hasCookie", "hasCookie");
+  await doTest(CROSS_ORIGIN, "cors", "same-origin", "noCookie", "noCookie");
+
+  // Cross-origin no-CORS requests includes Cookies when:
+  // 1. credentials mode is 'include'
+  // 2. COEP: is not credentialless.
+  await doTest(CROSS_ORIGIN, "no-cors", "include", "hasCookie", "noCookie");
+  await doTest(CROSS_ORIGIN, "no-cors", "same-origin", "noCookie", "noCookie");
+});
diff --git a/dom/fetch/tests/browser_origin_trial_coep_credentialless_worker.js b/dom/fetch/tests/browser_origin_trial_coep_credentialless_worker.js
new file mode 100644
index 0000000000..be77add88e
--- /dev/null
+++ b/dom/fetch/tests/browser_origin_trial_coep_credentialless_worker.js
@@ -0,0 +1,164 @@
+const TOP_LEVEL_URL =
+  getRootDirectory(gTestPath).replace(
+    "chrome://mochitests/content",
+    "https://example.com"
+  ) + "open_credentialless_document.sjs";
+
+const WORKER_URL =
+  getRootDirectory(gTestPath).replace(
+    "chrome://mochitests/content",
+    "https://example.com"
+  ) + "credentialless_worker.sjs";
+
+const GET_STATE_URL =
+  getRootDirectory(gTestPath).replace(
+    "chrome://mochitests/content",
+    "https://example.com"
+  ) + "store_header.sjs?getstate";
+
+const SAME_ORIGIN = "https://example.com";
+const CROSS_ORIGIN = "https://test1.example.com";
+
+const WORKER_USES_CREDENTIALLESS = "credentialless";
+const WORKER_NOT_USE_CREDENTIALLESS = "";
+
+async function addCookieToOrigin(origin) {
+  const fetchRequestURL =
+    getRootDirectory(gTestPath).replace("chrome://mochitests/content", origin) +
+    "store_header.sjs?addcookie";
+
+  const addcookieTab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    fetchRequestURL
+  );
+
+  await SpecialPowers.spawn(addcookieTab.linkedBrowser, [], async function () {
+    content.document.cookie = "coep=credentialless; SameSite=None; Secure";
+  });
+  await BrowserTestUtils.removeTab(addcookieTab);
+}
+
+async function testOrigin(
+  fetchOrigin,
+  isCredentialless,
+  workerUsesCredentialless,
+  expectedCookieResult
+) {
+  let topLevelUrl = TOP_LEVEL_URL;
+  if (isCredentialless) {
+    topLevelUrl += "?credentialless";
+  }
+  const noCredentiallessTab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    topLevelUrl
+  );
+
+  const fetchRequestURL =
+    getRootDirectory(gTestPath).replace(
+      "chrome://mochitests/content",
+      fetchOrigin
+    ) + "store_header.sjs?checkheader";
+
+  let workerScriptURL = WORKER_URL + "?" + workerUsesCredentialless;
+
+  await SpecialPowers.spawn(
+    noCredentiallessTab.linkedBrowser,
+    [fetchRequestURL, GET_STATE_URL, workerScriptURL, expectedCookieResult],
+    async function (
+      fetchRequestURL,
+      getStateURL,
+      workerScriptURL,
+      expectedCookieResult
+    ) {
+      const worker = new content.Worker(workerScriptURL, {});
+
+      // When the worker receives this message, it'll send
+      // a fetch request to fetchRequestURL, and fetchRequestURL
+      // will store whether it has received the cookie as a
+      // shared state.
+      worker.postMessage(fetchRequestURL);
+
+      if (expectedCookieResult == "error") {
+        await new Promise(r => {
+          worker.onerror = function () {
+            ok(true, "worker has error");
+            r();
+          };
+        });
+      } else {
+        await new Promise(r => {
+          worker.addEventListener("message", async function () {
+            // This request is used to get the saved state from the
+            // previous fetch request.
+            const response = await content.fetch(getStateURL, {
+              mode: "cors",
+            });
+            const text = await response.text();
+            is(text, expectedCookieResult);
+            r();
+          });
+        });
+      }
+    }
+  );
+  await BrowserTestUtils.removeTab(noCredentiallessTab);
+}
+
+async function dedicatedWorkerTest(
+  origin,
+  workerCOEP,
+  expectedCookieResultForNoCredentialless,
+  expectedCookieResultForCredentialless
+) {
+  await testOrigin(
+    origin,
+    false,
+    workerCOEP,
+    expectedCookieResultForNoCredentialless
+  );
+  await testOrigin(
+    origin,
+    true,
+    workerCOEP,
+    expectedCookieResultForCredentialless
+  );
+}
+
+add_task(async function () {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.tabs.remote.coep.credentialless", false], // Explicitly set credentialless to false because we want to test origin trial
+      ["dom.origin-trials.enabled", true],
+      ["dom.origin-trials.test-key.enabled", true],
+    ],
+  });
+
+  await addCookieToOrigin(SAME_ORIGIN);
+  await addCookieToOrigin(CROSS_ORIGIN);
+
+  await dedicatedWorkerTest(
+    SAME_ORIGIN,
+    WORKER_NOT_USE_CREDENTIALLESS,
+    "hasCookie",
+    "error"
+  );
+  await dedicatedWorkerTest(
+    SAME_ORIGIN,
+    WORKER_USES_CREDENTIALLESS,
+    "hasCookie",
+    "hasCookie"
+  );
+
+  await dedicatedWorkerTest(
+    CROSS_ORIGIN,
+    WORKER_NOT_USE_CREDENTIALLESS,
+    "hasCookie",
+    "error"
+  );
+  await dedicatedWorkerTest(
+    CROSS_ORIGIN,
+    WORKER_USES_CREDENTIALLESS,
+    "noCookie",
+    "noCookie"
+  );
+});
diff --git a/dom/fetch/tests/crashtests/1577196.html b/dom/fetch/tests/crashtests/1577196.html
new file mode 100644
index 0000000000..a2cdae06d0
--- /dev/null
+++ b/dom/fetch/tests/crashtests/1577196.html
@@ -0,0 +1,26 @@
+<!DOCTYPE html>
+<html>
+<body>
+<script>
+
+function test() {
+  const xhr = new XMLHttpRequest();
+  const frame = document.createElement("frame");
+  document.documentElement.appendChild(frame);
+  const win = frame.contentWindow;
+  const div = document.createElement("div");
+  div.insertBefore(frame, div.childNodes[0]);
+  SpecialPowers.forceCC();
+  SpecialPowers.gc();
+  xhr.open("P", "", false);
+  xhr.send();
+  win.fetch(null, {}).then(function(arg14) {});
+}
+
+for (let i = 0; i < 10; i++) {
+  test();
+}
+
+</script>
+</body>
+</html>
diff --git a/dom/fetch/tests/crashtests/1664514.html b/dom/fetch/tests/crashtests/1664514.html
new file mode 100644
index 0000000000..b033d842fa
--- /dev/null
+++ b/dom/fetch/tests/crashtests/1664514.html
@@ -0,0 +1,5 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<script>
+  fetch("./url.url")
+</script>
diff --git a/dom/fetch/tests/crashtests/crashtests.list b/dom/fetch/tests/crashtests/crashtests.list
new file mode 100644
index 0000000000..f79a122734
--- /dev/null
+++ b/dom/fetch/tests/crashtests/crashtests.list
@@ -0,0 +1,2 @@
+load 1577196.html
+load 1664514.html
diff --git a/dom/fetch/tests/crashtests/url.url b/dom/fetch/tests/crashtests/url.url
new file mode 100644
index 0000000000..95e9cf8db0
--- /dev/null
+++ b/dom/fetch/tests/crashtests/url.url
@@ -0,0 +1,5 @@
+[{000214A0-0000-0000-C000-000000000046}]

+Prop3=19,11

+[InternetShortcut]

+IDList=

+URL=http://localhost:8000/

diff --git a/dom/fetch/tests/credentialless_resource.sjs b/dom/fetch/tests/credentialless_resource.sjs
new file mode 100644
index 0000000000..72d0d738ec
--- /dev/null
+++ b/dom/fetch/tests/credentialless_resource.sjs
@@ -0,0 +1,21 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+// small red image
+const IMG_BYTES = atob(
+  "iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12" +
+    "P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg=="
+);
+
+function handleRequest(request, response) {
+  response.seizePower();
+  response.write("HTTP/1.1 200 OK\r\n");
+  response.write("Content-Type: image/png\r\n");
+  if (request.queryString === "corp_cross_origin") {
+    response.write("Cross-Origin-Resource-Policy: cross-origin\r\n");
+  }
+  response.write("\r\n");
+  response.write(IMG_BYTES);
+  response.finish();
+}
diff --git a/dom/fetch/tests/credentialless_worker.sjs b/dom/fetch/tests/credentialless_worker.sjs
new file mode 100644
index 0000000000..a9e2197d18
--- /dev/null
+++ b/dom/fetch/tests/credentialless_worker.sjs
@@ -0,0 +1,25 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const WORKER = `
+  onmessage = function(event) {
+    fetch(event.data, {
+      mode: "no-cors",
+      credentials: "include"
+    }).then(function() {
+      postMessage("fetch done");
+    });
+  }
+`;
+
+function handleRequest(request, response) {
+  if (request.queryString === "credentialless") {
+    response.setHeader("Cross-Origin-Embedder-Policy", "credentialless", true);
+  }
+
+  response.setHeader("Content-Type", "application/javascript", false);
+  response.setStatusLine(request.httpVersion, "200", "Found");
+  response.write(WORKER);
+}
diff --git a/dom/fetch/tests/mochitest.ini b/dom/fetch/tests/mochitest.ini
new file mode 100644
index 0000000000..32eb841faf
--- /dev/null
+++ b/dom/fetch/tests/mochitest.ini
@@ -0,0 +1,2 @@
+[test_ext_response_constructor.html]
+[test_invalid_header_exception.html]
diff --git a/dom/fetch/tests/open_credentialless_document.sjs b/dom/fetch/tests/open_credentialless_document.sjs
new file mode 100644
index 0000000000..6269e73d78
--- /dev/null
+++ b/dom/fetch/tests/open_credentialless_document.sjs
@@ -0,0 +1,28 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+"use strict";
+
+// Created with: mktoken --origin 'https://example.com' --feature CoepCredentialless --expiry 'Wed, 01 Jan 3000 01:00:00 +0100' --sign test-keys/test-ecdsa.pkcs8
+const TOKEN =
+  "Az+DK2Kczk8Xz1cAlD+TkvPZmuM2uJZ2CFefbp2hLuCU9FbUqxWTyQ2tEYr50r0syKELcOZLAPaABw8aYTLHn5YAAABUeyJvcmlnaW4iOiJodHRwczovL2V4YW1wbGUuY29tIiwiZmVhdHVyZSI6IkNvZXBDcmVkZW50aWFsbGVzcyIsImV4cGlyeSI6MzI1MDM2ODAwMDB9";
+
+function handleRequest(request, response) {
+  let params = (request.queryString || "").split("&");
+  if (params.includes("credentialless")) {
+    response.setHeader("Cross-Origin-Embedder-Policy", "credentialless");
+    // Enables the SharedArrayBuffer feature
+    response.setHeader("Cross-Origin-Opener-Policy", "same-origin");
+  } else if (params.includes("requirecorp")) {
+    response.setHeader("Cross-Origin-Embedder-Policy", "require-corp");
+  }
+  let html = "<!doctype html>";
+  if (!params.includes("meta")) {
+    response.setHeader("Origin-Trial", TOKEN);
+  } else {
+    html += `<meta http-equiv="origin-trial" content="${TOKEN}">`;
+  }
+  html += "<body>Hello, world!</body>";
+  response.setHeader("Content-Type", "text/html;charset=utf-8", false);
+  response.setStatusLine(request.httpVersion, "200", "Found");
+  response.write(html);
+}
diff --git a/dom/fetch/tests/store_header.sjs b/dom/fetch/tests/store_header.sjs
new file mode 100644
index 0000000000..3290a09995
--- /dev/null
+++ b/dom/fetch/tests/store_header.sjs
@@ -0,0 +1,23 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const key = "store_header";
+function handleRequest(request, response) {
+  response.setHeader("Content-Type", "text/plain");
+  response.setHeader("Access-Control-Allow-Origin", "https://example.com");
+  response.setHeader("Access-Control-Allow-Credentials", "true");
+
+  if (request.queryString === "getstate") {
+    response.write(getSharedState(key));
+  } else if (request.queryString === "checkheader") {
+    if (request.hasHeader("Cookie")) {
+      setSharedState(key, "hasCookie");
+    } else {
+      setSharedState(key, "noCookie");
+    }
+  } else {
+    // This is the first request which sets the cookie
+  }
+}
diff --git a/dom/fetch/tests/test_ext_response_constructor.html b/dom/fetch/tests/test_ext_response_constructor.html
new file mode 100644
index 0000000000..e4b6cf4eb2
--- /dev/null
+++ b/dom/fetch/tests/test_ext_response_constructor.html
@@ -0,0 +1,47 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Test `Response` constructor in a WebExtension</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script src="/tests/SimpleTest/ExtensionTestUtils.js"></script>
+  <link rel="stylesheet" href="/tests/SimpleTest/test.css"/>
+  <script>
+    add_task(async function testResponseConstructor() {
+      /* eslint-env webextensions */
+      function contentScript() {
+        new Response();
+        browser.test.notifyPass("done");
+      }
+
+      const extension = ExtensionTestUtils.loadExtension({
+        manifest: {
+          content_scripts: [
+            {
+              matches: ["<all_urls>"],
+              js: ["content_script.js"],
+            },
+          ],
+        },
+
+        files: {
+          "content_script.js": contentScript,
+        },
+      });
+
+      await extension.startup();
+
+      const win = window.open("https://example.com");
+      await extension.awaitFinish("done");
+      win.close();
+
+      await extension.unload();
+    });
+  </script>
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none"></div>
+<pre id="test"></pre>
+</body>
+</html>
diff --git a/dom/fetch/tests/test_invalid_header_exception.html b/dom/fetch/tests/test_invalid_header_exception.html
new file mode 100644
index 0000000000..710afffcc6
--- /dev/null
+++ b/dom/fetch/tests/test_invalid_header_exception.html
@@ -0,0 +1,39 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1629390
+-->
+<head>
+  <title>Test for Bug 1629390</title>
+  <meta charset="UTF-8">
+  <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1629390">Mozilla Bug 1629390</a>
+<p id="display"></p>
+<div id="content" style="display: none"></div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+/** Test for Bug 1629390 **/
+let headerNames = [
+  ['a˻b', 'a\uFFFD\uFFFDb'],
+  ['Àaª', '\uFFFDa\uFFFD'],
+  ['˻b', '\uFFFD\uFFFDb'],
+  ['\xEAa', '\uFFFDa'],
+  ['\xC2\x7F', '\uFFFD\x7F'],
+];
+for (let [invalid, corrected] of headerNames) {
+  try {
+    new Headers([[invalid, '']]);
+  } catch(e) {
+    is(e.message, `Headers constructor: ${corrected} is an invalid header name.`);
+  }
+}
+
+</script>
+</pre>
+</body>
+</html>