Adding upstream version 86.0.1.upstream/86.0.1upstream

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

11 files changed, 2735 insertions, 0 deletions

diff --git a/uriloader/preload/FetchPreloader.cpp b/uriloader/preload/FetchPreloader.cpp
new file mode 100644
index 0000000000..411ca266fc
--- /dev/null
+++ b/uriloader/preload/FetchPreloader.cpp
@@ -0,0 +1,339 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 "FetchPreloader.h"
+
+#include "mozilla/DebugOnly.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/LoadInfo.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/Unused.h"
+#include "nsContentPolicyUtils.h"
+#include "nsContentUtils.h"
+#include "nsIChannel.h"
+#include "nsIClassOfService.h"
+#include "nsIHttpChannel.h"
+#include "nsITimedChannel.h"
+#include "nsNetUtil.h"
+#include "nsStringStream.h"
+#include "nsIDocShell.h"
+
+namespace mozilla {
+
+NS_IMPL_ISUPPORTS(FetchPreloader, nsIStreamListener, nsIRequestObserver)
+
+FetchPreloader::FetchPreloader()
+    : FetchPreloader(nsIContentPolicy::TYPE_INTERNAL_FETCH_PRELOAD) {}
+
+FetchPreloader::FetchPreloader(nsContentPolicyType aContentPolicyType)
+    : mContentPolicyType(aContentPolicyType) {}
+
+nsresult FetchPreloader::OpenChannel(const PreloadHashKey& aKey, nsIURI* aURI,
+                                     const CORSMode aCORSMode,
+                                     const dom::ReferrerPolicy& aReferrerPolicy,
+                                     dom::Document* aDocument) {
+  nsresult rv;
+  nsCOMPtr<nsIChannel> channel;
+
+  auto notify = MakeScopeExit([&]() {
+    if (NS_FAILED(rv)) {
+      // Make sure we notify any <link preload> elements when opening fails
+      // because of various technical or security reasons.
+      NotifyStart(channel);
+      // Using the non-channel overload of this method to make it work even
+      // before NotifyOpen has been called on this preload.  We are not
+      // switching between channels, so it's safe to do so.
+      NotifyStop(rv);
+    }
+  });
+
+  nsCOMPtr<nsILoadGroup> loadGroup = aDocument->GetDocumentLoadGroup();
+  nsCOMPtr<nsPIDOMWindowOuter> window = aDocument->GetWindow();
+  nsCOMPtr<nsIInterfaceRequestor> prompter;
+  if (window) {
+    nsIDocShell* docshell = window->GetDocShell();
+    prompter = do_QueryInterface(docshell);
+  }
+
+  rv = CreateChannel(getter_AddRefs(channel), aURI, aCORSMode, aReferrerPolicy,
+                     aDocument, loadGroup, prompter);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Doing this now so that we have the channel and tainting set on it properly
+  // to notify the proper event (load or error) on the associated preload tags
+  // when the CSP check fails.
+  rv = CheckContentPolicy(aURI, aDocument);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  PrioritizeAsPreload(channel);
+  AddLoadBackgroundFlag(channel);
+
+  NotifyOpen(aKey, channel, aDocument, true);
+
+  return mAsyncConsumeResult = rv = channel->AsyncOpen(this);
+}
+
+nsresult FetchPreloader::CreateChannel(
+    nsIChannel** aChannel, nsIURI* aURI, const CORSMode aCORSMode,
+    const dom::ReferrerPolicy& aReferrerPolicy, dom::Document* aDocument,
+    nsILoadGroup* aLoadGroup, nsIInterfaceRequestor* aCallbacks) {
+  nsresult rv;
+
+  nsSecurityFlags securityFlags =
+      aCORSMode == CORS_NONE
+          ? nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_SEC_CONTEXT_IS_NULL
+          : nsILoadInfo::SEC_REQUIRE_CORS_INHERITS_SEC_CONTEXT;
+  if (aCORSMode == CORS_ANONYMOUS) {
+    securityFlags |= nsILoadInfo::SEC_COOKIES_SAME_ORIGIN;
+  } else if (aCORSMode == CORS_USE_CREDENTIALS) {
+    securityFlags |= nsILoadInfo::SEC_COOKIES_INCLUDE;
+  }
+
+  nsCOMPtr<nsIChannel> channel;
+  rv = NS_NewChannelWithTriggeringPrincipal(
+      getter_AddRefs(channel), aURI, aDocument, aDocument->NodePrincipal(),
+      securityFlags, nsIContentPolicy::TYPE_FETCH, nullptr, aLoadGroup,
+      aCallbacks);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (nsCOMPtr<nsIHttpChannel> httpChannel = do_QueryInterface(channel)) {
+    nsCOMPtr<nsIReferrerInfo> referrerInfo = new dom::ReferrerInfo(
+        aDocument->GetDocumentURIAsReferrer(), aReferrerPolicy);
+    rv = httpChannel->SetReferrerInfoWithoutClone(referrerInfo);
+    MOZ_ASSERT(NS_SUCCEEDED(rv));
+  }
+
+  if (nsCOMPtr<nsITimedChannel> timedChannel = do_QueryInterface(channel)) {
+    timedChannel->SetInitiatorType(u"link"_ns);
+  }
+
+  channel.forget(aChannel);
+  return NS_OK;
+}
+
+nsresult FetchPreloader::CheckContentPolicy(nsIURI* aURI,
+                                            dom::Document* aDocument) {
+  if (!aDocument) {
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsILoadInfo> secCheckLoadInfo = new net::LoadInfo(
+      aDocument->NodePrincipal(), aDocument->NodePrincipal(), aDocument,
+      nsILoadInfo::SEC_ONLY_FOR_EXPLICIT_CONTENTSEC_CHECK, mContentPolicyType);
+
+  int16_t shouldLoad = nsIContentPolicy::ACCEPT;
+  nsresult rv =
+      NS_CheckContentLoadPolicy(aURI, secCheckLoadInfo, ""_ns, &shouldLoad,
+                                nsContentUtils::GetContentPolicy());
+  if (NS_SUCCEEDED(rv) && NS_CP_ACCEPTED(shouldLoad)) {
+    return NS_OK;
+  }
+
+  return NS_ERROR_CONTENT_BLOCKED;
+}
+
+// PreloaderBase
+
+nsresult FetchPreloader::AsyncConsume(nsIStreamListener* aListener) {
+  if (NS_FAILED(mAsyncConsumeResult)) {
+    // Already being consumed or failed to open.
+    return mAsyncConsumeResult;
+  }
+
+  // Prevent duplicate calls.
+  mAsyncConsumeResult = NS_ERROR_NOT_AVAILABLE;
+
+  if (!mConsumeListener) {
+    // Called before we are getting response from the channel.
+    mConsumeListener = aListener;
+  } else {
+    // Channel already started, push cached calls to this listener.
+    // Can't be anything else than the `Cache`, hence a safe static_cast.
+    Cache* cache = static_cast<Cache*>(mConsumeListener.get());
+    cache->AsyncConsume(aListener);
+  }
+
+  return NS_OK;
+}
+
+// static
+void FetchPreloader::PrioritizeAsPreload(nsIChannel* aChannel) {
+  if (nsCOMPtr<nsIClassOfService> cos = do_QueryInterface(aChannel)) {
+    cos->AddClassFlags(nsIClassOfService::Unblocked);
+  }
+}
+
+void FetchPreloader::PrioritizeAsPreload() { PrioritizeAsPreload(Channel()); }
+
+// nsIRequestObserver + nsIStreamListener
+
+NS_IMETHODIMP FetchPreloader::OnStartRequest(nsIRequest* request) {
+  NotifyStart(request);
+
+  if (!mConsumeListener) {
+    // AsyncConsume not called yet.
+    mConsumeListener = new Cache();
+  }
+
+  return mConsumeListener->OnStartRequest(request);
+}
+
+NS_IMETHODIMP FetchPreloader::OnDataAvailable(nsIRequest* request,
+                                              nsIInputStream* input,
+                                              uint64_t offset, uint32_t count) {
+  return mConsumeListener->OnDataAvailable(request, input, offset, count);
+}
+
+NS_IMETHODIMP FetchPreloader::OnStopRequest(nsIRequest* request,
+                                            nsresult status) {
+  mConsumeListener->OnStopRequest(request, status);
+
+  // We want 404 or other types of server responses to be treated as 'error'.
+  if (nsCOMPtr<nsIHttpChannel> httpChannel = do_QueryInterface(request)) {
+    uint32_t responseStatus = 0;
+    Unused << httpChannel->GetResponseStatus(&responseStatus);
+    if (responseStatus / 100 != 2) {
+      status = NS_ERROR_FAILURE;
+    }
+  }
+
+  // Fetch preloader wants to keep the channel around so that consumers like XHR
+  // can access it even after the preload is done.
+  nsCOMPtr<nsIChannel> channel = mChannel;
+  NotifyStop(request, status);
+  mChannel.swap(channel);
+  return NS_OK;
+}
+
+// FetchPreloader::Cache
+
+NS_IMPL_ISUPPORTS(FetchPreloader::Cache, nsIStreamListener, nsIRequestObserver)
+
+NS_IMETHODIMP FetchPreloader::Cache::OnStartRequest(nsIRequest* request) {
+  mRequest = request;
+
+  if (mFinalListener) {
+    return mFinalListener->OnStartRequest(mRequest);
+  }
+
+  mCalls.AppendElement(Call{VariantIndex<0>{}, StartRequest{}});
+  return NS_OK;
+}
+
+NS_IMETHODIMP FetchPreloader::Cache::OnDataAvailable(nsIRequest* request,
+                                                     nsIInputStream* input,
+                                                     uint64_t offset,
+                                                     uint32_t count) {
+  if (mFinalListener) {
+    return mFinalListener->OnDataAvailable(mRequest, input, offset, count);
+  }
+
+  DataAvailable data;
+  if (!data.mData.SetLength(count, fallible)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  uint32_t read;
+  nsresult rv = input->Read(data.mData.BeginWriting(), count, &read);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  mCalls.AppendElement(Call{VariantIndex<1>{}, std::move(data)});
+  return NS_OK;
+}
+
+NS_IMETHODIMP FetchPreloader::Cache::OnStopRequest(nsIRequest* request,
+                                                   nsresult status) {
+  if (mFinalListener) {
+    return mFinalListener->OnStopRequest(mRequest, status);
+  }
+
+  mCalls.AppendElement(Call{VariantIndex<2>{}, StopRequest{status}});
+  return NS_OK;
+}
+
+void FetchPreloader::Cache::AsyncConsume(nsIStreamListener* aListener) {
+  // Must dispatch for two reasons:
+  // 1. This is called directly from FetchLoader::AsyncConsume, which must
+  // behave the same way as nsIChannel::AsyncOpen.
+  // 2. In case there are already stream listener events scheduled on the main
+  // thread we preserve the order - those will still end up in Cache.
+
+  // * The `Cache` object is fully main thread only for now, doesn't support
+  // retargeting, but it can be improved to allow it.
+
+  nsCOMPtr<nsIStreamListener> listener(aListener);
+  NS_DispatchToMainThread(NewRunnableMethod<nsCOMPtr<nsIStreamListener>>(
+      "FetchPreloader::Cache::Consume", this, &FetchPreloader::Cache::Consume,
+      listener));
+}
+
+void FetchPreloader::Cache::Consume(nsCOMPtr<nsIStreamListener> aListener) {
+  MOZ_ASSERT(!mFinalListener, "Duplicate call");
+
+  mFinalListener = std::move(aListener);
+
+  // Status of the channel read after each call.
+  nsresult status = NS_OK;
+  nsCOMPtr<nsIChannel> channel(do_QueryInterface(mRequest));
+
+  RefPtr<Cache> self(this);
+  for (auto& call : mCalls) {
+    nsresult rv = call.match(
+        [&](const StartRequest& startRequest) mutable {
+          return self->mFinalListener->OnStartRequest(self->mRequest);
+        },
+        [&](const DataAvailable& dataAvailable) mutable {
+          if (NS_FAILED(status)) {
+            // Channel has been cancelled during this mCalls loop.
+            return NS_OK;
+          }
+
+          nsCOMPtr<nsIInputStream> input;
+          rv = NS_NewCStringInputStream(getter_AddRefs(input),
+                                        dataAvailable.mData);
+          if (NS_FAILED(rv)) {
+            return rv;
+          }
+
+          return self->mFinalListener->OnDataAvailable(
+              self->mRequest, input, 0, dataAvailable.mData.Length());
+        },
+        [&](const StopRequest& stopRequest) {
+          // First cancellation overrides mStatus in nsHttpChannel.
+          nsresult stopStatus =
+              NS_FAILED(status) ? status : stopRequest.mStatus;
+          self->mFinalListener->OnStopRequest(self->mRequest, stopStatus);
+          self->mFinalListener = nullptr;
+          self->mRequest = nullptr;
+          return NS_OK;
+        });
+
+    if (!mRequest) {
+      // We are done!
+      break;
+    }
+
+    bool isCancelled = false;
+    Unused << channel->GetCanceled(&isCancelled);
+    if (isCancelled) {
+      mRequest->GetStatus(&status);
+    } else if (NS_FAILED(rv)) {
+      status = rv;
+      mRequest->Cancel(status);
+    }
+  }
+
+  mCalls.Clear();
+}
+
+}  // namespace mozilla
diff --git a/uriloader/preload/FetchPreloader.h b/uriloader/preload/FetchPreloader.h
new file mode 100644
index 0000000000..f501a79c97
--- /dev/null
+++ b/uriloader/preload/FetchPreloader.h
@@ -0,0 +1,99 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 FetchPreloader_h_
+#define FetchPreloader_h_
+
+#include "mozilla/PreloaderBase.h"
+#include "mozilla/Variant.h"
+#include "nsCOMPtr.h"
+#include "nsIAsyncOutputStream.h"
+#include "nsIAsyncInputStream.h"
+#include "nsIContentPolicy.h"
+#include "nsIStreamListener.h"
+
+class nsIChannel;
+class nsILoadGroup;
+class nsIInterfaceRequestor;
+
+namespace mozilla {
+
+namespace dom {
+enum class ReferrerPolicy : uint8_t;
+}
+
+class FetchPreloader : public PreloaderBase, public nsIStreamListener {
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIREQUESTOBSERVER
+  NS_DECL_NSISTREAMLISTENER
+
+  FetchPreloader();
+  nsresult OpenChannel(const PreloadHashKey& aKey, nsIURI* aURI,
+                       const CORSMode aCORSMode,
+                       const dom::ReferrerPolicy& aReferrerPolicy,
+                       dom::Document* aDocument);
+
+  // PreloaderBase
+  nsresult AsyncConsume(nsIStreamListener* aListener) override;
+  static void PrioritizeAsPreload(nsIChannel* aChannel);
+  void PrioritizeAsPreload() override;
+
+ protected:
+  explicit FetchPreloader(nsContentPolicyType aContentPolicyType);
+  virtual ~FetchPreloader() = default;
+
+  // Create and setup the channel with necessary security properties.  This is
+  // overridable by subclasses to allow different initial conditions.
+  virtual nsresult CreateChannel(nsIChannel** aChannel, nsIURI* aURI,
+                                 const CORSMode aCORSMode,
+                                 const dom::ReferrerPolicy& aReferrerPolicy,
+                                 dom::Document* aDocument,
+                                 nsILoadGroup* aLoadGroup,
+                                 nsIInterfaceRequestor* aCallbacks);
+
+ private:
+  nsresult CheckContentPolicy(nsIURI* aURI, dom::Document* aDocument);
+
+  class Cache final : public nsIStreamListener {
+    NS_DECL_ISUPPORTS
+    NS_DECL_NSIREQUESTOBSERVER
+    NS_DECL_NSISTREAMLISTENER
+
+    void AsyncConsume(nsIStreamListener* aListener);
+    void Consume(nsCOMPtr<nsIStreamListener> aListener);
+
+   private:
+    virtual ~Cache() = default;
+
+    struct StartRequest {};
+    struct DataAvailable {
+      nsCString mData;
+    };
+    struct StopRequest {
+      nsresult mStatus;
+    };
+
+    typedef Variant<StartRequest, DataAvailable, StopRequest> Call;
+    nsCOMPtr<nsIRequest> mRequest;
+    nsCOMPtr<nsIStreamListener> mFinalListener;
+    nsTArray<Call> mCalls;
+  };
+
+  // The listener passed to AsyncConsume in case we haven't started getting the
+  // data from the channel yet.
+  nsCOMPtr<nsIStreamListener> mConsumeListener;
+
+  // Returned by AsyncConsume when a failure.  This remembers the result of
+  // opening the channel and prevents duplicate consumation.
+  nsresult mAsyncConsumeResult = NS_ERROR_NOT_AVAILABLE;
+
+  // The CP type to check against.  Derived classes have to override call to CSP
+  // constructor of this class.
+  nsContentPolicyType mContentPolicyType;
+};
+
+}  // namespace mozilla
+
+#endif
diff --git a/uriloader/preload/PreloadHashKey.cpp b/uriloader/preload/PreloadHashKey.cpp
new file mode 100644
index 0000000000..2096fedf0f
--- /dev/null
+++ b/uriloader/preload/PreloadHashKey.cpp
@@ -0,0 +1,213 @@
+/* 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 "PreloadHashKey.h"
+
+#include "mozilla/dom/Element.h"  // StringToCORSMode
+#include "mozilla/css/SheetLoadData.h"
+#include "mozilla/dom/ReferrerPolicyBinding.h"
+#include "nsIPrincipal.h"
+#include "nsIReferrerInfo.h"
+
+namespace mozilla {
+
+PreloadHashKey::PreloadHashKey(const nsIURI* aKey, ResourceType aAs)
+    : nsURIHashKey(aKey), mAs(aAs) {}
+
+PreloadHashKey::PreloadHashKey(const PreloadHashKey* aKey)
+    : nsURIHashKey(aKey->mKey) {
+  *this = *aKey;
+}
+
+PreloadHashKey::PreloadHashKey(PreloadHashKey&& aToMove)
+    : nsURIHashKey(std::move(aToMove)) {
+  mAs = std::move(aToMove.mAs);
+  mCORSMode = std::move(aToMove.mCORSMode);
+  mPrincipal = std::move(aToMove.mPrincipal);
+
+  switch (mAs) {
+    case ResourceType::SCRIPT:
+      mScript = std::move(aToMove.mScript);
+      break;
+    case ResourceType::STYLE:
+      mStyle = std::move(aToMove.mStyle);
+      break;
+    case ResourceType::IMAGE:
+      break;
+    case ResourceType::FONT:
+      break;
+    case ResourceType::FETCH:
+      break;
+    case ResourceType::NONE:
+      break;
+  }
+}
+
+PreloadHashKey& PreloadHashKey::operator=(const PreloadHashKey& aOther) {
+  MOZ_ASSERT(mAs == ResourceType::NONE || aOther.mAs == ResourceType::NONE,
+             "Assigning more than once, only reset is allowed");
+
+  nsURIHashKey::operator=(aOther);
+
+  mAs = aOther.mAs;
+  mCORSMode = aOther.mCORSMode;
+  mPrincipal = aOther.mPrincipal;
+
+  switch (mAs) {
+    case ResourceType::SCRIPT:
+      mScript = aOther.mScript;
+      break;
+    case ResourceType::STYLE:
+      mStyle = aOther.mStyle;
+      break;
+    case ResourceType::IMAGE:
+      break;
+    case ResourceType::FONT:
+      break;
+    case ResourceType::FETCH:
+      break;
+    case ResourceType::NONE:
+      break;
+  }
+
+  return *this;
+}
+
+// static
+PreloadHashKey PreloadHashKey::CreateAsScript(nsIURI* aURI, CORSMode aCORSMode,
+                                              dom::ScriptKind aScriptKind) {
+  PreloadHashKey key(aURI, ResourceType::SCRIPT);
+  key.mCORSMode = aCORSMode;
+
+  key.mScript.mScriptKind = aScriptKind;
+
+  return key;
+}
+
+// static
+PreloadHashKey PreloadHashKey::CreateAsScript(nsIURI* aURI,
+                                              const nsAString& aCrossOrigin,
+                                              const nsAString& aType) {
+  dom::ScriptKind scriptKind = dom::ScriptKind::eClassic;
+  if (aType.LowerCaseEqualsASCII("module")) {
+    scriptKind = dom::ScriptKind::eModule;
+  }
+  CORSMode crossOrigin = dom::Element::StringToCORSMode(aCrossOrigin);
+  return CreateAsScript(aURI, crossOrigin, scriptKind);
+}
+
+// static
+PreloadHashKey PreloadHashKey::CreateAsStyle(
+    nsIURI* aURI, nsIPrincipal* aPrincipal, CORSMode aCORSMode,
+    css::SheetParsingMode aParsingMode) {
+  PreloadHashKey key(aURI, ResourceType::STYLE);
+  key.mCORSMode = aCORSMode;
+  key.mPrincipal = aPrincipal;
+
+  key.mStyle.mParsingMode = aParsingMode;
+
+  return key;
+}
+
+// static
+PreloadHashKey PreloadHashKey::CreateAsStyle(
+    css::SheetLoadData& aSheetLoadData) {
+  return CreateAsStyle(aSheetLoadData.mURI, aSheetLoadData.mTriggeringPrincipal,
+                       aSheetLoadData.mSheet->GetCORSMode(),
+                       aSheetLoadData.mSheet->ParsingMode());
+}
+
+// static
+PreloadHashKey PreloadHashKey::CreateAsImage(nsIURI* aURI,
+                                             nsIPrincipal* aPrincipal,
+                                             CORSMode aCORSMode) {
+  PreloadHashKey key(aURI, ResourceType::IMAGE);
+  key.mCORSMode = aCORSMode;
+  key.mPrincipal = aPrincipal;
+
+  return key;
+}
+
+// static
+PreloadHashKey PreloadHashKey::CreateAsFetch(nsIURI* aURI, CORSMode aCORSMode) {
+  PreloadHashKey key(aURI, ResourceType::FETCH);
+  key.mCORSMode = aCORSMode;
+
+  return key;
+}
+
+// static
+PreloadHashKey PreloadHashKey::CreateAsFetch(nsIURI* aURI,
+                                             const nsAString& aCrossOrigin) {
+  return CreateAsFetch(aURI, dom::Element::StringToCORSMode(aCrossOrigin));
+}
+
+PreloadHashKey PreloadHashKey::CreateAsFont(nsIURI* aURI, CORSMode aCORSMode) {
+  PreloadHashKey key(aURI, ResourceType::FONT);
+  key.mCORSMode = aCORSMode;
+
+  return key;
+}
+
+bool PreloadHashKey::KeyEquals(KeyTypePointer aOther) const {
+  if (mAs != aOther->mAs || mCORSMode != aOther->mCORSMode) {
+    return false;
+  }
+
+  if (!mPrincipal != !aOther->mPrincipal) {
+    // One or the other has a principal, but not both... not equal
+    return false;
+  }
+
+  if (mPrincipal && !mPrincipal->Equals(aOther->mPrincipal)) {
+    return false;
+  }
+
+  if (!nsURIHashKey::KeyEquals(
+          static_cast<const nsURIHashKey*>(aOther)->GetKey())) {
+    return false;
+  }
+
+  switch (mAs) {
+    case ResourceType::SCRIPT:
+      if (mScript.mScriptKind != aOther->mScript.mScriptKind) {
+        return false;
+      }
+      break;
+    case ResourceType::STYLE: {
+      if (mStyle.mParsingMode != aOther->mStyle.mParsingMode) {
+        return false;
+      }
+      break;
+    }
+    case ResourceType::IMAGE:
+      // No more checks needed.  The image cache key consists of the document
+      // (which we are scoped into), origin attributes (which we compare as part
+      // of the principal check) and the URL.  imgLoader::ValidateEntry compares
+      // CORS, referrer info and principal, which we do by default.
+      break;
+    case ResourceType::FONT:
+      break;
+    case ResourceType::FETCH:
+      // No more checks needed.
+      break;
+    case ResourceType::NONE:
+      break;
+  }
+
+  return true;
+}
+
+// static
+PLDHashNumber PreloadHashKey::HashKey(KeyTypePointer aKey) {
+  PLDHashNumber hash = nsURIHashKey::HashKey(aKey->mKey);
+
+  // Enough to use the common attributes
+  hash = AddToHash(hash, static_cast<uint32_t>(aKey->mAs));
+  hash = AddToHash(hash, static_cast<uint32_t>(aKey->mCORSMode));
+
+  return hash;
+}
+
+}  // namespace mozilla
diff --git a/uriloader/preload/PreloadHashKey.h b/uriloader/preload/PreloadHashKey.h
new file mode 100644
index 0000000000..2ab7af6013
--- /dev/null
+++ b/uriloader/preload/PreloadHashKey.h
@@ -0,0 +1,105 @@
+/* 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 PreloadHashKey_h__
+#define PreloadHashKey_h__
+
+#include "mozilla/CORSMode.h"
+#include "mozilla/css/SheetParsingMode.h"
+#include "mozilla/dom/ScriptKind.h"
+#include "nsURIHashKey.h"
+
+class nsIPrincipal;
+
+namespace mozilla {
+
+namespace css {
+class SheetLoadData;
+}
+
+/**
+ * This key is used for coalescing and lookup of preloading or regular
+ * speculative loads.  It consists of:
+ * - the resource type, which is the value of the 'as' attribute
+ * - the URI of the resource
+ * - set of attributes that is common to all resource types
+ * - resource-type-specific attributes that we use to distinguish loads that has
+ *   to be treated separately, some of these attributes may remain at their
+ *   default values
+ */
+class PreloadHashKey : public nsURIHashKey {
+ public:
+  enum class ResourceType : uint8_t { NONE, SCRIPT, STYLE, IMAGE, FONT, FETCH };
+
+  using KeyType = const PreloadHashKey&;
+  using KeyTypePointer = const PreloadHashKey*;
+
+  PreloadHashKey() = default;
+  PreloadHashKey(const nsIURI* aKey, ResourceType aAs);
+  explicit PreloadHashKey(const PreloadHashKey* aKey);
+  PreloadHashKey(PreloadHashKey&& aToMove);
+
+  PreloadHashKey& operator=(const PreloadHashKey& aOther);
+
+  // Construct key for "script"
+  static PreloadHashKey CreateAsScript(nsIURI* aURI, CORSMode aCORSMode,
+                                       dom::ScriptKind aScriptKind);
+  static PreloadHashKey CreateAsScript(nsIURI* aURI,
+                                       const nsAString& aCrossOrigin,
+                                       const nsAString& aType);
+
+  // Construct key for "style"
+  static PreloadHashKey CreateAsStyle(nsIURI* aURI, nsIPrincipal* aPrincipal,
+                                      CORSMode aCORSMode,
+                                      css::SheetParsingMode aParsingMode);
+  static PreloadHashKey CreateAsStyle(css::SheetLoadData&);
+
+  // Construct key for "image"
+  static PreloadHashKey CreateAsImage(nsIURI* aURI, nsIPrincipal* aPrincipal,
+                                      CORSMode aCORSMode);
+
+  // Construct key for "fetch"
+  static PreloadHashKey CreateAsFetch(nsIURI* aURI, CORSMode aCORSMode);
+  static PreloadHashKey CreateAsFetch(nsIURI* aURI,
+                                      const nsAString& aCrossOrigin);
+
+  // Construct key for "font"
+  static PreloadHashKey CreateAsFont(nsIURI* aURI, CORSMode aCORSMode);
+
+  KeyType GetKey() const { return *this; }
+  KeyTypePointer GetKeyPointer() const { return this; }
+  static KeyTypePointer KeyToPointer(KeyType aKey) { return &aKey; }
+
+  bool KeyEquals(KeyTypePointer aOther) const;
+  static PLDHashNumber HashKey(KeyTypePointer aKey);
+  ResourceType As() const { return mAs; }
+
+#ifdef MOZILLA_INTERNAL_API
+  size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const {
+    // Bug 1627752
+    return 0;
+  }
+#endif
+
+  enum { ALLOW_MEMMOVE = true };
+
+ private:
+  // Attributes common to all resource types
+  ResourceType mAs = ResourceType::NONE;
+
+  CORSMode mCORSMode = CORS_NONE;
+  nsCOMPtr<nsIPrincipal> mPrincipal;
+
+  struct {
+    dom::ScriptKind mScriptKind = dom::ScriptKind::eClassic;
+  } mScript;
+
+  struct {
+    css::SheetParsingMode mParsingMode = css::eAuthorSheetFeatures;
+  } mStyle;
+};
+
+}  // namespace mozilla
+
+#endif
diff --git a/uriloader/preload/PreloadService.cpp b/uriloader/preload/PreloadService.cpp
new file mode 100644
index 0000000000..5707c3d109
--- /dev/null
+++ b/uriloader/preload/PreloadService.cpp
@@ -0,0 +1,290 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 "PreloadService.h"
+
+#include "FetchPreloader.h"
+#include "PreloaderBase.h"
+#include "mozilla/AsyncEventDispatcher.h"
+#include "mozilla/dom/WindowGlobalChild.h"
+#include "mozilla/dom/HTMLLinkElement.h"
+#include "mozilla/dom/ScriptLoader.h"
+#include "mozilla/Encoding.h"
+#include "mozilla/FontPreloader.h"
+#include "mozilla/StaticPrefs_network.h"
+#include "nsNetUtil.h"
+
+namespace mozilla {
+
+PreloadService::PreloadService(dom::Document* aDoc) : mDocument(aDoc) {}
+PreloadService::~PreloadService() = default;
+
+bool PreloadService::RegisterPreload(const PreloadHashKey& aKey,
+                                     PreloaderBase* aPreload) {
+  if (PreloadExists(aKey)) {
+    return false;
+  }
+
+  mPreloads.Put(aKey, RefPtr{aPreload});
+  return true;
+}
+
+void PreloadService::DeregisterPreload(const PreloadHashKey& aKey) {
+  mPreloads.Remove(aKey);
+}
+
+void PreloadService::ClearAllPreloads() { mPreloads.Clear(); }
+
+bool PreloadService::PreloadExists(const PreloadHashKey& aKey) {
+  bool found;
+  mPreloads.GetWeak(aKey, &found);
+  return found;
+}
+
+already_AddRefed<PreloaderBase> PreloadService::LookupPreload(
+    const PreloadHashKey& aKey) const {
+  return mPreloads.Get(aKey);
+}
+
+already_AddRefed<nsIURI> PreloadService::GetPreloadURI(const nsAString& aURL) {
+  nsIURI* base = BaseURIForPreload();
+  auto encoding = mDocument->GetDocumentCharacterSet();
+
+  nsCOMPtr<nsIURI> uri;
+  nsresult rv = NS_NewURI(getter_AddRefs(uri), aURL, encoding, base);
+  if (NS_FAILED(rv)) {
+    return nullptr;
+  }
+
+  return uri.forget();
+}
+
+already_AddRefed<PreloaderBase> PreloadService::PreloadLinkElement(
+    dom::HTMLLinkElement* aLinkElement, nsContentPolicyType aPolicyType) {
+  // Even if the pref is disabled, we still want to collect telemetry about
+  // attempted preloads.
+  const bool preloadEnabled = StaticPrefs::network_preload();
+  if (aPolicyType == nsIContentPolicy::TYPE_INVALID) {
+    MOZ_ASSERT_UNREACHABLE("Caller should check");
+    return nullptr;
+  }
+
+  if (auto* wgc = mDocument->GetWindowGlobalChild()) {
+    wgc->MaybeSendUpdateDocumentWouldPreloadResources();
+  }
+
+  if (!preloadEnabled) {
+    return nullptr;
+  }
+
+  nsAutoString as, charset, crossOrigin, integrity, referrerPolicy, srcset,
+      sizes, type, url;
+
+  nsCOMPtr<nsIURI> uri = aLinkElement->GetURI();
+  aLinkElement->GetAs(as);
+  aLinkElement->GetCharset(charset);
+  aLinkElement->GetImageSrcset(srcset);
+  aLinkElement->GetImageSizes(sizes);
+  aLinkElement->GetHref(url);
+  aLinkElement->GetCrossOrigin(crossOrigin);
+  aLinkElement->GetIntegrity(integrity);
+  aLinkElement->GetReferrerPolicy(referrerPolicy);
+  aLinkElement->GetType(type);
+
+  auto result =
+      PreloadOrCoalesce(uri, url, aPolicyType, as, type, charset, srcset, sizes,
+                        integrity, crossOrigin, referrerPolicy);
+
+  if (!result.mPreloader) {
+    NotifyNodeEvent(aLinkElement, result.mAlreadyComplete);
+    return nullptr;
+  }
+
+  result.mPreloader->AddLinkPreloadNode(aLinkElement);
+  return result.mPreloader.forget();
+}
+
+void PreloadService::PreloadLinkHeader(
+    nsIURI* aURI, const nsAString& aURL, nsContentPolicyType aPolicyType,
+    const nsAString& aAs, const nsAString& aType, const nsAString& aIntegrity,
+    const nsAString& aSrcset, const nsAString& aSizes, const nsAString& aCORS,
+    const nsAString& aReferrerPolicy) {
+  // Even if the pref is disabled, we still want to collect telemetry about
+  // attempted preloads.
+  const bool preloadEnabled = StaticPrefs::network_preload();
+
+  if (aPolicyType == nsIContentPolicy::TYPE_INVALID) {
+    MOZ_ASSERT_UNREACHABLE("Caller should check");
+    return;
+  }
+
+  if (auto* wgc = mDocument->GetWindowGlobalChild()) {
+    wgc->MaybeSendUpdateDocumentWouldPreloadResources();
+  }
+
+  if (!preloadEnabled) {
+    return;
+  }
+
+  PreloadOrCoalesce(aURI, aURL, aPolicyType, aAs, aType, u""_ns, aSrcset,
+                    aSizes, aIntegrity, aCORS, aReferrerPolicy);
+}
+
+PreloadService::PreloadOrCoalesceResult PreloadService::PreloadOrCoalesce(
+    nsIURI* aURI, const nsAString& aURL, nsContentPolicyType aPolicyType,
+    const nsAString& aAs, const nsAString& aType, const nsAString& aCharset,
+    const nsAString& aSrcset, const nsAString& aSizes,
+    const nsAString& aIntegrity, const nsAString& aCORS,
+    const nsAString& aReferrerPolicy) {
+  if (!aURI) {
+    MOZ_ASSERT_UNREACHABLE("Should not pass null nsIURI");
+    return {nullptr, false};
+  }
+
+  bool isImgSet = false;
+  PreloadHashKey preloadKey;
+  nsCOMPtr<nsIURI> uri = aURI;
+
+  if (aAs.LowerCaseEqualsASCII("script")) {
+    preloadKey = PreloadHashKey::CreateAsScript(uri, aCORS, aType);
+  } else if (aAs.LowerCaseEqualsASCII("style")) {
+    preloadKey = PreloadHashKey::CreateAsStyle(
+        uri, mDocument->NodePrincipal(), dom::Element::StringToCORSMode(aCORS),
+        css::eAuthorSheetFeatures /* see Loader::LoadSheet */);
+  } else if (aAs.LowerCaseEqualsASCII("image")) {
+    uri = mDocument->ResolvePreloadImage(BaseURIForPreload(), aURL, aSrcset,
+                                         aSizes, &isImgSet);
+    if (!uri) {
+      return {nullptr, false};
+    }
+
+    preloadKey = PreloadHashKey::CreateAsImage(
+        uri, mDocument->NodePrincipal(), dom::Element::StringToCORSMode(aCORS));
+  } else if (aAs.LowerCaseEqualsASCII("font")) {
+    preloadKey = PreloadHashKey::CreateAsFont(
+        uri, dom::Element::StringToCORSMode(aCORS));
+  } else if (aAs.LowerCaseEqualsASCII("fetch")) {
+    preloadKey = PreloadHashKey::CreateAsFetch(
+        uri, dom::Element::StringToCORSMode(aCORS));
+  } else {
+    return {nullptr, false};
+  }
+
+  if (RefPtr<PreloaderBase> preload = LookupPreload(preloadKey)) {
+    return {std::move(preload), false};
+  }
+
+  if (aAs.LowerCaseEqualsASCII("script")) {
+    PreloadScript(uri, aType, aCharset, aCORS, aReferrerPolicy, aIntegrity,
+                  true /* isInHead - TODO */);
+  } else if (aAs.LowerCaseEqualsASCII("style")) {
+    switch (PreloadStyle(uri, aCharset, aCORS, aReferrerPolicy, aIntegrity)) {
+      case dom::SheetPreloadStatus::AlreadyComplete:
+        return {nullptr, /* already_complete = */ true};
+      case dom::SheetPreloadStatus::Errored:
+      case dom::SheetPreloadStatus::InProgress:
+        break;
+    }
+  } else if (aAs.LowerCaseEqualsASCII("image")) {
+    PreloadImage(uri, aCORS, aReferrerPolicy, isImgSet);
+  } else if (aAs.LowerCaseEqualsASCII("font")) {
+    PreloadFont(uri, aCORS, aReferrerPolicy);
+  } else if (aAs.LowerCaseEqualsASCII("fetch")) {
+    PreloadFetch(uri, aCORS, aReferrerPolicy);
+  }
+
+  return {LookupPreload(preloadKey), false};
+}
+
+void PreloadService::PreloadScript(nsIURI* aURI, const nsAString& aType,
+                                   const nsAString& aCharset,
+                                   const nsAString& aCrossOrigin,
+                                   const nsAString& aReferrerPolicy,
+                                   const nsAString& aIntegrity,
+                                   bool aScriptFromHead) {
+  mDocument->ScriptLoader()->PreloadURI(
+      aURI, aCharset, aType, aCrossOrigin, aIntegrity, aScriptFromHead, false,
+      false, false, true, PreloadReferrerPolicy(aReferrerPolicy));
+}
+
+dom::SheetPreloadStatus PreloadService::PreloadStyle(
+    nsIURI* aURI, const nsAString& aCharset, const nsAString& aCrossOrigin,
+    const nsAString& aReferrerPolicy, const nsAString& aIntegrity) {
+  return mDocument->PreloadStyle(
+      aURI, Encoding::ForLabel(aCharset), aCrossOrigin,
+      PreloadReferrerPolicy(aReferrerPolicy), aIntegrity, true);
+}
+
+void PreloadService::PreloadImage(nsIURI* aURI, const nsAString& aCrossOrigin,
+                                  const nsAString& aImageReferrerPolicy,
+                                  bool aIsImgSet) {
+  mDocument->PreLoadImage(aURI, aCrossOrigin,
+                          PreloadReferrerPolicy(aImageReferrerPolicy),
+                          aIsImgSet, true);
+}
+
+void PreloadService::PreloadFont(nsIURI* aURI, const nsAString& aCrossOrigin,
+                                 const nsAString& aReferrerPolicy) {
+  CORSMode cors = dom::Element::StringToCORSMode(aCrossOrigin);
+  auto key = PreloadHashKey::CreateAsFont(aURI, cors);
+
+  // * Bug 1618549: Depending on where we decide to do the deduplication, we may
+  // want to check if the font is already being preloaded here.
+
+  RefPtr<FontPreloader> preloader = new FontPreloader();
+  dom::ReferrerPolicy referrerPolicy = PreloadReferrerPolicy(aReferrerPolicy);
+  preloader->OpenChannel(key, aURI, cors, referrerPolicy, mDocument);
+}
+
+void PreloadService::PreloadFetch(nsIURI* aURI, const nsAString& aCrossOrigin,
+                                  const nsAString& aReferrerPolicy) {
+  CORSMode cors = dom::Element::StringToCORSMode(aCrossOrigin);
+  auto key = PreloadHashKey::CreateAsFetch(aURI, cors);
+
+  // * Bug 1618549: Depending on where we decide to do the deduplication, we may
+  // want to check if a fetch is already being preloaded here.
+
+  RefPtr<FetchPreloader> preloader = new FetchPreloader();
+  dom::ReferrerPolicy referrerPolicy = PreloadReferrerPolicy(aReferrerPolicy);
+  preloader->OpenChannel(key, aURI, cors, referrerPolicy, mDocument);
+}
+
+// static
+void PreloadService::NotifyNodeEvent(nsINode* aNode, bool aSuccess) {
+  if (!aNode->IsInComposedDoc()) {
+    return;
+  }
+
+  // We don't dispatch synchronously since |node| might be in a DocGroup
+  // that we're not allowed to touch. (Our network request happens in the
+  // DocGroup of one of the mSources nodes--not necessarily this one).
+
+  RefPtr<AsyncEventDispatcher> dispatcher = new AsyncEventDispatcher(
+      aNode, aSuccess ? u"load"_ns : u"error"_ns, CanBubble::eNo);
+
+  dispatcher->RequireNodeInDocument();
+  dispatcher->PostDOMEvent();
+}
+
+dom::ReferrerPolicy PreloadService::PreloadReferrerPolicy(
+    const nsAString& aReferrerPolicy) {
+  dom::ReferrerPolicy referrerPolicy =
+      dom::ReferrerInfo::ReferrerPolicyAttributeFromString(aReferrerPolicy);
+  if (referrerPolicy == dom::ReferrerPolicy::_empty) {
+    referrerPolicy = mDocument->GetPreloadReferrerInfo()->ReferrerPolicy();
+  }
+
+  return referrerPolicy;
+}
+
+nsIURI* PreloadService::BaseURIForPreload() {
+  nsIURI* documentURI = mDocument->GetDocumentURI();
+  nsIURI* documentBaseURI = mDocument->GetDocBaseURI();
+  return (documentURI == documentBaseURI)
+             ? (mSpeculationBaseURI ? mSpeculationBaseURI.get() : documentURI)
+             : documentBaseURI;
+}
+
+}  // namespace mozilla
diff --git a/uriloader/preload/PreloadService.h b/uriloader/preload/PreloadService.h
new file mode 100644
index 0000000000..44077e819a
--- /dev/null
+++ b/uriloader/preload/PreloadService.h
@@ -0,0 +1,126 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 PreloadService_h__
+#define PreloadService_h__
+
+#include "nsIContentPolicy.h"
+#include "nsIURI.h"
+#include "nsRefPtrHashtable.h"
+#include "mozilla/PreloadHashKey.h"
+
+class nsINode;
+
+namespace mozilla {
+
+class PreloaderBase;
+
+namespace dom {
+
+class HTMLLinkElement;
+class Document;
+enum class ReferrerPolicy : uint8_t;
+enum class SheetPreloadStatus : uint8_t;
+
+}  // namespace dom
+
+/**
+ * Intended to scope preloads and speculative loads under one roof.  This class
+ * is intended to be a member of dom::Document. Provides registration of
+ * speculative loads via a `key` which is defined to consist of the URL,
+ * resource type, and resource-specific attributes that are further
+ * distinguishing loads with otherwise same type and url.
+ */
+class PreloadService {
+ public:
+  explicit PreloadService(dom::Document*);
+  ~PreloadService();
+
+  // Called by resource loaders to register a running resource load.  This is
+  // called for a speculative load when it's started the first time, being it
+  // either regular speculative load or a preload.
+  //
+  // Returns false and does nothing if a preload is already registered under
+  // this key, true otherwise.
+  bool RegisterPreload(const PreloadHashKey& aKey, PreloaderBase* aPreload);
+
+  // Called when the load is about to be cancelled.  Exact behavior is to be
+  // determined yet.
+  void DeregisterPreload(const PreloadHashKey& aKey);
+
+  // Called when the scope is to go away.
+  void ClearAllPreloads();
+
+  // True when there is a preload registered under the key.
+  bool PreloadExists(const PreloadHashKey& aKey);
+
+  // Returns an existing preload under the key or null, when there is none
+  // registered under the key.
+  already_AddRefed<PreloaderBase> LookupPreload(
+      const PreloadHashKey& aKey) const;
+
+  void SetSpeculationBase(nsIURI* aURI) { mSpeculationBaseURI = aURI; }
+  already_AddRefed<nsIURI> GetPreloadURI(const nsAString& aURL);
+
+  already_AddRefed<PreloaderBase> PreloadLinkElement(
+      dom::HTMLLinkElement* aLink, nsContentPolicyType aPolicyType);
+
+  void PreloadLinkHeader(nsIURI* aURI, const nsAString& aURL,
+                         nsContentPolicyType aPolicyType, const nsAString& aAs,
+                         const nsAString& aType, const nsAString& aIntegrity,
+                         const nsAString& aSrcset, const nsAString& aSizes,
+                         const nsAString& aCORS,
+                         const nsAString& aReferrerPolicy);
+
+  void PreloadScript(nsIURI* aURI, const nsAString& aType,
+                     const nsAString& aCharset, const nsAString& aCrossOrigin,
+                     const nsAString& aReferrerPolicy,
+                     const nsAString& aIntegrity, bool aScriptFromHead);
+
+  dom::SheetPreloadStatus PreloadStyle(nsIURI* aURI, const nsAString& aCharset,
+                                       const nsAString& aCrossOrigin,
+                                       const nsAString& aReferrerPolicy,
+                                       const nsAString& aIntegrity);
+
+  void PreloadImage(nsIURI* aURI, const nsAString& aCrossOrigin,
+                    const nsAString& aImageReferrerPolicy, bool aIsImgSet);
+
+  void PreloadFont(nsIURI* aURI, const nsAString& aCrossOrigin,
+                   const nsAString& aReferrerPolicy);
+
+  void PreloadFetch(nsIURI* aURI, const nsAString& aCrossOrigin,
+                    const nsAString& aReferrerPolicy);
+
+  static void NotifyNodeEvent(nsINode* aNode, bool aSuccess);
+
+ private:
+  dom::ReferrerPolicy PreloadReferrerPolicy(const nsAString& aReferrerPolicy);
+  nsIURI* BaseURIForPreload();
+
+  struct PreloadOrCoalesceResult {
+    RefPtr<PreloaderBase> mPreloader;
+    bool mAlreadyComplete;
+  };
+
+  PreloadOrCoalesceResult PreloadOrCoalesce(
+      nsIURI* aURI, const nsAString& aURL, nsContentPolicyType aPolicyType,
+      const nsAString& aAs, const nsAString& aType, const nsAString& aCharset,
+      const nsAString& aSrcset, const nsAString& aSizes,
+      const nsAString& aIntegrity, const nsAString& aCORS,
+      const nsAString& aReferrerPolicy);
+
+ private:
+  nsRefPtrHashtable<PreloadHashKey, PreloaderBase> mPreloads;
+
+  // Raw pointer only, we are intended to be a direct member of dom::Document
+  dom::Document* mDocument;
+
+  // Set by `nsHtml5TreeOpExecutor::SetSpeculationBase`.
+  nsCOMPtr<nsIURI> mSpeculationBaseURI;
+};
+
+}  // namespace mozilla
+
+#endif
diff --git a/uriloader/preload/PreloaderBase.cpp b/uriloader/preload/PreloaderBase.cpp
new file mode 100644
index 0000000000..56f8c7e7bf
--- /dev/null
+++ b/uriloader/preload/PreloaderBase.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 "PreloaderBase.h"
+
+#include "mozilla/dom/Document.h"
+#include "mozilla/Telemetry.h"
+#include "nsContentUtils.h"
+#include "nsIAsyncVerifyRedirectCallback.h"
+#include "nsIChannel.h"
+#include "nsILoadGroup.h"
+#include "nsIInterfaceRequestorUtils.h"
+#include "nsIRedirectResultListener.h"
+
+// Change this if we want to cancel and remove the associated preload on removal
+// of all <link rel=preload> tags from the tree.
+constexpr static bool kCancelAndRemovePreloadOnZeroReferences = false;
+
+namespace mozilla {
+
+PreloaderBase::UsageTimer::UsageTimer(PreloaderBase* aPreload,
+                                      dom::Document* aDocument)
+    : mDocument(aDocument), mPreload(aPreload) {}
+
+class PreloaderBase::RedirectSink final : public nsIInterfaceRequestor,
+                                          public nsIChannelEventSink,
+                                          public nsIRedirectResultListener {
+  RedirectSink() = delete;
+  virtual ~RedirectSink();
+
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIINTERFACEREQUESTOR
+  NS_DECL_NSICHANNELEVENTSINK
+  NS_DECL_NSIREDIRECTRESULTLISTENER
+
+  RedirectSink(PreloaderBase* aPreloader, nsIInterfaceRequestor* aCallbacks);
+
+ private:
+  MainThreadWeakPtr<PreloaderBase> mPreloader;
+  nsCOMPtr<nsIInterfaceRequestor> mCallbacks;
+  nsCOMPtr<nsIChannel> mRedirectChannel;
+};
+
+PreloaderBase::RedirectSink::RedirectSink(PreloaderBase* aPreloader,
+                                          nsIInterfaceRequestor* aCallbacks)
+    : mPreloader(aPreloader), mCallbacks(aCallbacks) {}
+
+PreloaderBase::RedirectSink::~RedirectSink() = default;
+
+NS_IMPL_ISUPPORTS(PreloaderBase::RedirectSink, nsIInterfaceRequestor,
+                  nsIChannelEventSink, nsIRedirectResultListener)
+
+NS_IMETHODIMP PreloaderBase::RedirectSink::AsyncOnChannelRedirect(
+    nsIChannel* aOldChannel, nsIChannel* aNewChannel, uint32_t aFlags,
+    nsIAsyncVerifyRedirectCallback* aCallback) {
+  MOZ_DIAGNOSTIC_ASSERT(NS_IsMainThread());
+
+  mRedirectChannel = aNewChannel;
+
+  // Deliberately adding this before confirmation.
+  nsCOMPtr<nsIURI> uri;
+  aNewChannel->GetOriginalURI(getter_AddRefs(uri));
+  if (mPreloader) {
+    mPreloader->mRedirectRecords.AppendElement(
+        RedirectRecord(aFlags, uri.forget()));
+  }
+
+  if (mCallbacks) {
+    nsCOMPtr<nsIChannelEventSink> sink(do_GetInterface(mCallbacks));
+    if (sink) {
+      return sink->AsyncOnChannelRedirect(aOldChannel, aNewChannel, aFlags,
+                                          aCallback);
+    }
+  }
+
+  aCallback->OnRedirectVerifyCallback(NS_OK);
+  return NS_OK;
+}
+
+NS_IMETHODIMP PreloaderBase::RedirectSink::OnRedirectResult(bool proceeding) {
+  if (proceeding && mRedirectChannel) {
+    mPreloader->mChannel = std::move(mRedirectChannel);
+  } else {
+    mRedirectChannel = nullptr;
+  }
+
+  if (mCallbacks) {
+    nsCOMPtr<nsIRedirectResultListener> sink(do_GetInterface(mCallbacks));
+    if (sink) {
+      return sink->OnRedirectResult(proceeding);
+    }
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP PreloaderBase::RedirectSink::GetInterface(const nsIID& aIID,
+                                                        void** aResult) {
+  NS_ENSURE_ARG_POINTER(aResult);
+
+  if (aIID.Equals(NS_GET_IID(nsIChannelEventSink)) ||
+      aIID.Equals(NS_GET_IID(nsIRedirectResultListener))) {
+    return QueryInterface(aIID, aResult);
+  }
+
+  if (mCallbacks) {
+    return mCallbacks->GetInterface(aIID, aResult);
+  }
+
+  *aResult = nullptr;
+  return NS_ERROR_NO_INTERFACE;
+}
+
+PreloaderBase::~PreloaderBase() { MOZ_ASSERT(NS_IsMainThread()); }
+
+// static
+void PreloaderBase::AddLoadBackgroundFlag(nsIChannel* aChannel) {
+  nsLoadFlags loadFlags;
+  aChannel->GetLoadFlags(&loadFlags);
+  aChannel->SetLoadFlags(loadFlags | nsIRequest::LOAD_BACKGROUND);
+}
+
+void PreloaderBase::NotifyOpen(const PreloadHashKey& aKey,
+                               dom::Document* aDocument, bool aIsPreload) {
+  if (aDocument && !aDocument->Preloads().RegisterPreload(aKey, this)) {
+    // This means there is already a preload registered under this key in this
+    // document.  We only allow replacement when this is a regular load.
+    // Otherwise, this should never happen and is a suspected misuse of the API.
+    MOZ_ASSERT(!aIsPreload);
+    aDocument->Preloads().DeregisterPreload(aKey);
+    aDocument->Preloads().RegisterPreload(aKey, this);
+  }
+
+  mKey = aKey;
+  mIsUsed = !aIsPreload;
+
+  if (!mIsUsed && !mUsageTimer) {
+    auto callback = MakeRefPtr<UsageTimer>(this, aDocument);
+    NS_NewTimerWithCallback(getter_AddRefs(mUsageTimer), callback, 10000,
+                            nsITimer::TYPE_ONE_SHOT);
+  }
+
+  ReportUsageTelemetry();
+}
+
+void PreloaderBase::NotifyOpen(const PreloadHashKey& aKey, nsIChannel* aChannel,
+                               dom::Document* aDocument, bool aIsPreload) {
+  NotifyOpen(aKey, aDocument, aIsPreload);
+  mChannel = aChannel;
+
+  nsCOMPtr<nsIInterfaceRequestor> callbacks;
+  mChannel->GetNotificationCallbacks(getter_AddRefs(callbacks));
+  RefPtr<RedirectSink> sink(new RedirectSink(this, callbacks));
+  mChannel->SetNotificationCallbacks(sink);
+}
+
+void PreloaderBase::NotifyUsage(LoadBackground aLoadBackground) {
+  if (!mIsUsed && mChannel && aLoadBackground == LoadBackground::Drop) {
+    nsLoadFlags loadFlags;
+    mChannel->GetLoadFlags(&loadFlags);
+
+    // Preloads are initially set the LOAD_BACKGROUND flag.  When becoming
+    // regular loads by hitting its consuming tag, we need to drop that flag,
+    // which also means to re-add the request from/to it's loadgroup to reflect
+    // that flag change.
+    if (loadFlags & nsIRequest::LOAD_BACKGROUND) {
+      nsCOMPtr<nsILoadGroup> loadGroup;
+      mChannel->GetLoadGroup(getter_AddRefs(loadGroup));
+
+      if (loadGroup) {
+        nsresult status;
+        mChannel->GetStatus(&status);
+
+        nsresult rv = loadGroup->RemoveRequest(mChannel, nullptr, status);
+        mChannel->SetLoadFlags(loadFlags & ~nsIRequest::LOAD_BACKGROUND);
+        if (NS_SUCCEEDED(rv)) {
+          loadGroup->AddRequest(mChannel, nullptr);
+        }
+      }
+    }
+  }
+
+  mIsUsed = true;
+  ReportUsageTelemetry();
+  CancelUsageTimer();
+}
+
+void PreloaderBase::RemoveSelf(dom::Document* aDocument) {
+  if (aDocument) {
+    aDocument->Preloads().DeregisterPreload(mKey);
+  }
+}
+
+void PreloaderBase::NotifyRestart(dom::Document* aDocument,
+                                  PreloaderBase* aNewPreloader) {
+  RemoveSelf(aDocument);
+  mKey = PreloadHashKey();
+
+  CancelUsageTimer();
+
+  if (aNewPreloader) {
+    aNewPreloader->mNodes = std::move(mNodes);
+  }
+}
+
+void PreloaderBase::NotifyStart(nsIRequest* aRequest) {
+  // If there is no channel assigned on this preloader, we are not between
+  // channel switching, so we can freely update the mShouldFireLoadEvent using
+  // the given channel.
+  if (mChannel && !SameCOMIdentity(aRequest, mChannel)) {
+    return;
+  }
+
+  nsCOMPtr<nsIHttpChannel> httpChannel = do_QueryInterface(aRequest);
+  if (!httpChannel) {
+    return;
+  }
+
+  // if the load is cross origin without CORS, or the CORS access is rejected,
+  // always fire load event to avoid leaking site information.
+  nsresult rv;
+  nsCOMPtr<nsILoadInfo> loadInfo = httpChannel->LoadInfo();
+  mShouldFireLoadEvent =
+      loadInfo->GetTainting() == LoadTainting::Opaque ||
+      (loadInfo->GetTainting() == LoadTainting::CORS &&
+       (NS_FAILED(httpChannel->GetStatus(&rv)) || NS_FAILED(rv)));
+}
+
+void PreloaderBase::NotifyStop(nsIRequest* aRequest, nsresult aStatus) {
+  // Filter out notifications that may be arriving from the old channel before
+  // restarting this request.
+  if (!SameCOMIdentity(aRequest, mChannel)) {
+    return;
+  }
+
+  NotifyStop(aStatus);
+}
+
+void PreloaderBase::NotifyStop(nsresult aStatus) {
+  mOnStopStatus.emplace(aStatus);
+
+  nsTArray<nsWeakPtr> nodes = std::move(mNodes);
+
+  for (nsWeakPtr& weak : nodes) {
+    nsCOMPtr<nsINode> node = do_QueryReferent(weak);
+    if (node) {
+      NotifyNodeEvent(node);
+    }
+  }
+
+  mChannel = nullptr;
+}
+
+void PreloaderBase::NotifyValidating() { mOnStopStatus.reset(); }
+
+void PreloaderBase::NotifyValidated(nsresult aStatus) {
+  NotifyStop(nullptr, aStatus);
+}
+
+void PreloaderBase::AddLinkPreloadNode(nsINode* aNode) {
+  if (mOnStopStatus) {
+    return NotifyNodeEvent(aNode);
+  }
+
+  mNodes.AppendElement(do_GetWeakReference(aNode));
+}
+
+void PreloaderBase::RemoveLinkPreloadNode(nsINode* aNode) {
+  // Note that do_GetWeakReference returns the internal weak proxy, which is
+  // always the same, so we can use it to search the array using default
+  // comparator.
+  nsWeakPtr node = do_GetWeakReference(aNode);
+  mNodes.RemoveElement(node);
+
+  if (kCancelAndRemovePreloadOnZeroReferences && mNodes.Length() == 0 &&
+      !mIsUsed) {
+    // Keep a reference, because the following call may release us.  The caller
+    // may use a WeakPtr to access this.
+    RefPtr<PreloaderBase> self(this);
+    RemoveSelf(aNode->OwnerDoc());
+
+    if (mChannel) {
+      mChannel->Cancel(NS_BINDING_ABORTED);
+    }
+  }
+}
+
+void PreloaderBase::NotifyNodeEvent(nsINode* aNode) {
+  PreloadService::NotifyNodeEvent(
+      aNode, mShouldFireLoadEvent || NS_SUCCEEDED(*mOnStopStatus));
+}
+
+void PreloaderBase::CancelUsageTimer() {
+  if (mUsageTimer) {
+    mUsageTimer->Cancel();
+    mUsageTimer = nullptr;
+  }
+}
+
+void PreloaderBase::ReportUsageTelemetry() {
+  if (mUsageTelementryReported) {
+    return;
+  }
+  mUsageTelementryReported = true;
+
+  if (mKey.As() == PreloadHashKey::ResourceType::NONE) {
+    return;
+  }
+
+  // The labels are structured as type1-used, type1-unused, type2-used, ...
+  // The first "as" resource type is NONE with value 0.
+  auto index = (static_cast<uint32_t>(mKey.As()) - 1) * 2;
+  if (!mIsUsed) {
+    ++index;
+  }
+
+  auto label = static_cast<Telemetry::LABELS_REL_PRELOAD_MISS_RATIO>(index);
+  Telemetry::AccumulateCategorical(label);
+}
+
+nsresult PreloaderBase::AsyncConsume(nsIStreamListener* aListener) {
+  // We want to return an error so that consumers can't ever use a preload to
+  // consume data unless it's properly implemented.
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+// PreloaderBase::RedirectRecord
+
+nsCString PreloaderBase::RedirectRecord::Spec() const {
+  nsCOMPtr<nsIURI> noFragment;
+  NS_GetURIWithoutRef(mURI, getter_AddRefs(noFragment));
+  MOZ_ASSERT(noFragment);
+  return noFragment->GetSpecOrDefault();
+}
+
+nsCString PreloaderBase::RedirectRecord::Fragment() const {
+  nsCString fragment;
+  mURI->GetRef(fragment);
+  return fragment;
+}
+
+// PreloaderBase::UsageTimer
+
+NS_IMPL_ISUPPORTS(PreloaderBase::UsageTimer, nsITimerCallback)
+
+NS_IMETHODIMP PreloaderBase::UsageTimer::Notify(nsITimer* aTimer) {
+  if (!mPreload || !mDocument) {
+    return NS_OK;
+  }
+
+  MOZ_ASSERT(aTimer == mPreload->mUsageTimer);
+  mPreload->mUsageTimer = nullptr;
+
+  if (mPreload->IsUsed()) {
+    // Left in the hashtable, but marked as used.  This is a valid case, and we
+    // don't want to emit a warning for this preload then.
+    return NS_OK;
+  }
+
+  mPreload->ReportUsageTelemetry();
+
+  // PreloadHashKey overrides GetKey, we need to use the nsURIHashKey one to get
+  // the URI.
+  nsIURI* uri = static_cast<nsURIHashKey*>(&mPreload->mKey)->GetKey();
+  if (!uri) {
+    return NS_OK;
+  }
+
+  nsString spec;
+  NS_GetSanitizedURIStringFromURI(uri, spec);
+  nsContentUtils::ReportToConsole(nsIScriptError::warningFlag, "DOM"_ns,
+                                  mDocument, nsContentUtils::eDOM_PROPERTIES,
+                                  "UnusedLinkPreloadPending",
+                                  nsTArray<nsString>({std::move(spec)}));
+  return NS_OK;
+}
+
+}  // namespace mozilla
diff --git a/uriloader/preload/PreloaderBase.h b/uriloader/preload/PreloaderBase.h
new file mode 100644
index 0000000000..dcd3738217
--- /dev/null
+++ b/uriloader/preload/PreloaderBase.h
@@ -0,0 +1,200 @@
+/* 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 PreloaderBase_h__
+#define PreloaderBase_h__
+
+#include "mozilla/Maybe.h"
+#include "mozilla/PreloadHashKey.h"
+#include "mozilla/WeakPtr.h"
+#include "nsCOMPtr.h"
+#include "nsISupports.h"
+#include "nsITimer.h"
+#include "nsIURI.h"
+#include "nsIWeakReferenceUtils.h"
+#include "nsTArray.h"
+
+class nsIChannel;
+class nsINode;
+class nsIRequest;
+class nsIStreamListener;
+
+namespace mozilla {
+
+namespace dom {
+
+class Document;
+
+}  // namespace dom
+
+/**
+ * A half-abstract base class that resource loaders' respective
+ * channel-listening classes should derive from.  Provides a unified API to
+ * register the load or preload in a document scoped service, links <link
+ * rel="preload"> DOM nodes with the load progress and provides API to possibly
+ * consume the data by later, dynamically discovered consumers.
+ *
+ * This class is designed to be used only on the main thread.
+ */
+class PreloaderBase : public SupportsWeakPtr, public nsISupports {
+ public:
+  PreloaderBase() = default;
+
+  // Called by resource loaders to register this preload in the document's
+  // preload service to provide coalescing, and access to the preload when it
+  // should be used for an actual load.
+  void NotifyOpen(const PreloadHashKey& aKey, dom::Document* aDocument,
+                  bool aIsPreload);
+  void NotifyOpen(const PreloadHashKey& aKey, nsIChannel* aChannel,
+                  dom::Document* aDocument, bool aIsPreload);
+
+  // Called when the load is about to be started all over again and thus this
+  // PreloaderBase will be registered again with the same key.  This method
+  // taks care to deregister this preload prior to that.
+  // @param aNewPreloader: If there is a new request and loader created for the
+  // restarted load, we will pass any necessary information into it.
+  void NotifyRestart(dom::Document* aDocument,
+                     PreloaderBase* aNewPreloader = nullptr);
+
+  // Called by the loading object when the channel started to load
+  // (OnStartRequest or equal) and when it finished (OnStopRequest or equal)
+  void NotifyStart(nsIRequest* aRequest);
+  void NotifyStop(nsIRequest* aRequest, nsresult aStatus);
+  // Use this variant only in complement to NotifyOpen without providing a
+  // channel.
+  void NotifyStop(nsresult aStatus);
+
+  // Called when this currently existing load has to be asynchronously
+  // revalidated before it can be used.  This prevents link preload DOM nodes
+  // being notified until the validation is resolved.
+  void NotifyValidating();
+  // Called when the validation process has been done.  This will notify
+  // associated link DOM nodes.
+  void NotifyValidated(nsresult aStatus);
+
+  // Called by resource loaders or any suitable component to notify the preload
+  // has been used for an actual load.  This is intended to stop any usage
+  // timers.
+  // @param aDropLoadBackground: If `Keep` then the loading channel, if still in
+  // progress, will not be removed the LOAD_BACKGROUND flag, for instance XHR is
+  // the user here.
+  enum class LoadBackground { Keep, Drop };
+  void NotifyUsage(LoadBackground aLoadBackground = LoadBackground::Drop);
+  // Whether this preloader has been used for a regular/actual load or not.
+  bool IsUsed() const { return mIsUsed; }
+
+  // Removes itself from the document's preloads hashtable
+  void RemoveSelf(dom::Document* aDocument);
+
+  // When a loader starting an actual load finds a preload, the data can be
+  // delivered using this method.  It will deliver stream listener notifications
+  // as if it were coming from the resource loading channel.  The |request|
+  // argument will be the channel that loaded/loads the resource.
+  // This method must keep to the nsIChannel.AsyncOpen contract.  A loader is
+  // not obligated to re-implement this method when not necessarily needed.
+  virtual nsresult AsyncConsume(nsIStreamListener* aListener);
+
+  // Accessor to the resource loading channel.
+  nsIChannel* Channel() const { return mChannel; }
+
+  // May change priority of the resource loading channel so that it's treated as
+  // preload when this was initially representing a normal speculative load but
+  // later <link rel="preload"> was found for this resource.
+  virtual void PrioritizeAsPreload() = 0;
+
+  // Helper function to set the LOAD_BACKGROUND flag on channel initiated by
+  // <link rel=preload>.  This MUST be used before the channel is AsyncOpen'ed.
+  static void AddLoadBackgroundFlag(nsIChannel* aChannel);
+
+  // These are linking this preload to <link rel="preload"> DOM nodes.  If we
+  // are already loaded, immediately notify events on the node, otherwise wait
+  // for NotifyStop() call.
+  void AddLinkPreloadNode(nsINode* aNode);
+  void RemoveLinkPreloadNode(nsINode* aNode);
+
+  // A collection of redirects, the main consumer is fetch.
+  class RedirectRecord {
+   public:
+    RedirectRecord(uint32_t aFlags, already_AddRefed<nsIURI> aURI)
+        : mFlags(aFlags), mURI(aURI) {}
+
+    uint32_t Flags() const { return mFlags; }
+    nsCString Spec() const;
+    nsCString Fragment() const;
+
+   private:
+    uint32_t mFlags;
+    nsCOMPtr<nsIURI> mURI;
+  };
+
+  const nsTArray<RedirectRecord>& Redirects() { return mRedirectRecords; }
+
+ protected:
+  virtual ~PreloaderBase();
+
+  // The loading channel.  This will update when a redirect occurs.
+  nsCOMPtr<nsIChannel> mChannel;
+
+ private:
+  void NotifyNodeEvent(nsINode* aNode);
+  void CancelUsageTimer();
+
+  void ReportUsageTelemetry();
+
+  // A helper class that will update the PreloaderBase.mChannel member when a
+  // redirect happens, so that we can reprioritize or cancel when needed.
+  // Having a separate class instead of implementing this on PreloaderBase
+  // directly is to keep PreloaderBase as simple as possible so that derived
+  // classes don't have to deal with calling super when implementing these
+  // interfaces from some reason as well.
+  class RedirectSink;
+
+  // A timer callback to trigger the unuse warning for this preload
+  class UsageTimer final : public nsITimerCallback {
+    NS_DECL_ISUPPORTS
+    NS_DECL_NSITIMERCALLBACK
+
+    UsageTimer(PreloaderBase* aPreload, dom::Document* aDocument);
+
+   private:
+    ~UsageTimer() = default;
+
+    WeakPtr<dom::Document> mDocument;
+    WeakPtr<PreloaderBase> mPreload;
+  };
+
+ private:
+  // Reference to HTMLLinkElement DOM nodes to deliver onload and onerror
+  // notifications to.
+  nsTArray<nsWeakPtr> mNodes;
+
+  // History of redirects.
+  nsTArray<RedirectRecord> mRedirectRecords;
+
+  // Usage timer, emits warning when the preload is not used in time.  Started
+  // in NotifyOpen and stopped in NotifyUsage.
+  nsCOMPtr<nsITimer> mUsageTimer;
+
+  // The key this preload has been registered under.  We want to remember it to
+  // be able to deregister itself from the document's preloads.
+  PreloadHashKey mKey;
+
+  // This overrides the final event we send to DOM nodes to be always 'load'.
+  // Modified in NotifyStart based on LoadInfo data of the loading channel.
+  bool mShouldFireLoadEvent = false;
+
+  // True after call to NotifyUsage.
+  bool mIsUsed = false;
+
+  // True after we have reported the usage telemetry.  Prevent duplicates.
+  bool mUsageTelementryReported = false;
+
+  // Emplaced when the data delivery has finished, in NotifyStop, holds the
+  // result of the load.
+  Maybe<nsresult> mOnStopStatus;
+};
+
+}  // namespace mozilla
+
+#endif  // !PreloaderBase_h__
diff --git a/uriloader/preload/gtest/TestFetchPreloader.cpp b/uriloader/preload/gtest/TestFetchPreloader.cpp
new file mode 100644
index 0000000000..4d4d2b5103
--- /dev/null
+++ b/uriloader/preload/gtest/TestFetchPreloader.cpp
@@ -0,0 +1,937 @@
+#include "gtest/gtest.h"
+
+#include "mozilla/CORSMode.h"
+#include "mozilla/dom/XMLDocument.h"
+#include "mozilla/dom/ReferrerPolicyBinding.h"
+#include "mozilla/FetchPreloader.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/PreloadHashKey.h"
+#include "mozilla/SpinEventLoopUntil.h"
+#include "nsNetUtil.h"
+#include "nsIChannel.h"
+#include "nsIStreamListener.h"
+#include "nsThreadUtils.h"
+#include "nsStringStream.h"
+
+namespace {
+
+auto const ERROR_CANCEL = NS_ERROR_ABORT;
+auto const ERROR_ONSTOP = NS_ERROR_NET_INTERRUPT;
+auto const ERROR_THROW = NS_ERROR_FAILURE;
+
+class FakeChannel : public nsIChannel {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSICHANNEL
+  NS_DECL_NSIREQUEST
+
+  nsresult Start() { return mListener->OnStartRequest(this); }
+  nsresult Data(const nsACString& aData) {
+    if (NS_FAILED(mStatus)) {
+      return mStatus;
+    }
+    nsCOMPtr<nsIInputStream> is;
+    NS_NewCStringInputStream(getter_AddRefs(is), aData);
+    return mListener->OnDataAvailable(this, is, 0, aData.Length());
+  }
+  nsresult Stop(nsresult status) {
+    if (NS_SUCCEEDED(mStatus)) {
+      mStatus = status;
+    }
+    mListener->OnStopRequest(this, mStatus);
+    mListener = nullptr;
+    return mStatus;
+  }
+
+ private:
+  virtual ~FakeChannel() = default;
+  bool mIsPending = false;
+  bool mCanceled = false;
+  nsresult mStatus = NS_OK;
+  nsCOMPtr<nsIStreamListener> mListener;
+};
+
+NS_IMPL_ISUPPORTS(FakeChannel, nsIChannel, nsIRequest)
+
+NS_IMETHODIMP FakeChannel::GetName(nsACString& result) { return NS_OK; }
+NS_IMETHODIMP FakeChannel::IsPending(bool* result) {
+  *result = mIsPending;
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::GetStatus(nsresult* status) {
+  *status = mStatus;
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::Cancel(nsresult status) {
+  if (!mCanceled) {
+    mCanceled = true;
+    mStatus = status;
+  }
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::Suspend() { return NS_OK; }
+NS_IMETHODIMP FakeChannel::Resume() { return NS_OK; }
+NS_IMETHODIMP FakeChannel::GetLoadFlags(nsLoadFlags* aLoadFlags) {
+  *aLoadFlags = 0;
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::SetLoadFlags(nsLoadFlags aLoadFlags) {
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::GetTRRMode(nsIRequest::TRRMode* aTRRMode) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+NS_IMETHODIMP FakeChannel::SetTRRMode(nsIRequest::TRRMode aTRRMode) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+NS_IMETHODIMP FakeChannel::GetLoadGroup(nsILoadGroup** aLoadGroup) {
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::SetLoadGroup(nsILoadGroup* aLoadGroup) {
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::GetOriginalURI(nsIURI** aURI) { return NS_OK; }
+NS_IMETHODIMP FakeChannel::SetOriginalURI(nsIURI* aURI) { return NS_OK; }
+NS_IMETHODIMP FakeChannel::GetURI(nsIURI** aURI) { return NS_OK; }
+NS_IMETHODIMP FakeChannel::GetOwner(nsISupports** aOwner) { return NS_OK; }
+NS_IMETHODIMP FakeChannel::SetOwner(nsISupports* aOwner) { return NS_OK; }
+NS_IMETHODIMP FakeChannel::SetLoadInfo(nsILoadInfo* aLoadInfo) { return NS_OK; }
+NS_IMETHODIMP FakeChannel::GetLoadInfo(nsILoadInfo** aLoadInfo) {
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::GetIsDocument(bool* aIsDocument) {
+  *aIsDocument = false;
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::GetNotificationCallbacks(
+    nsIInterfaceRequestor** aCallbacks) {
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::SetNotificationCallbacks(
+    nsIInterfaceRequestor* aCallbacks) {
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::GetSecurityInfo(nsISupports** aSecurityInfo) {
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::GetContentType(nsACString& aContentType) {
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::SetContentType(const nsACString& aContentType) {
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::GetContentCharset(nsACString& aContentCharset) {
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::SetContentCharset(
+    const nsACString& aContentCharset) {
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::GetContentDisposition(
+    uint32_t* aContentDisposition) {
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::SetContentDisposition(uint32_t aContentDisposition) {
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::GetContentDispositionFilename(
+    nsAString& aContentDispositionFilename) {
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::SetContentDispositionFilename(
+    const nsAString& aContentDispositionFilename) {
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::GetContentDispositionHeader(
+    nsACString& aContentDispositionHeader) {
+  return NS_ERROR_NOT_AVAILABLE;
+}
+NS_IMETHODIMP FakeChannel::GetContentLength(int64_t* aContentLength) {
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::SetContentLength(int64_t aContentLength) {
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::GetCanceled(bool* aCanceled) {
+  *aCanceled = mCanceled;
+  return NS_OK;
+}
+NS_IMETHODIMP FakeChannel::Open(nsIInputStream** aStream) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+NS_IMETHODIMP
+FakeChannel::AsyncOpen(nsIStreamListener* aListener) {
+  mIsPending = true;
+  mListener = aListener;
+  return NS_OK;
+}
+
+class FakePreloader : public mozilla::FetchPreloader {
+ public:
+  explicit FakePreloader(FakeChannel* aChannel) : mDrivingChannel(aChannel) {}
+
+ private:
+  RefPtr<FakeChannel> mDrivingChannel;
+
+  virtual nsresult CreateChannel(
+      nsIChannel** aChannel, nsIURI* aURI, const mozilla::CORSMode aCORSMode,
+      const mozilla::dom::ReferrerPolicy& aReferrerPolicy,
+      mozilla::dom::Document* aDocument, nsILoadGroup* aLoadGroup,
+      nsIInterfaceRequestor* aCallbacks) override {
+    mDrivingChannel.forget(aChannel);
+    return NS_OK;
+  }
+};
+
+class FakeListener : public nsIStreamListener {
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIREQUESTOBSERVER
+  NS_DECL_NSISTREAMLISTENER
+
+  enum { Never, OnStart, OnData, OnStop } mCancelIn = Never;
+
+  nsresult mOnStartResult = NS_OK;
+  nsresult mOnDataResult = NS_OK;
+  nsresult mOnStopResult = NS_OK;
+
+  bool mOnStart = false;
+  nsCString mOnData;
+  Maybe<nsresult> mOnStop;
+
+ private:
+  virtual ~FakeListener() = default;
+};
+
+NS_IMPL_ISUPPORTS(FakeListener, nsIStreamListener, nsIRequestObserver)
+
+NS_IMETHODIMP FakeListener::OnStartRequest(nsIRequest* request) {
+  EXPECT_FALSE(mOnStart);
+  mOnStart = true;
+
+  if (mCancelIn == OnStart) {
+    request->Cancel(ERROR_CANCEL);
+  }
+
+  return mOnStartResult;
+}
+NS_IMETHODIMP FakeListener::OnDataAvailable(nsIRequest* request,
+                                            nsIInputStream* input,
+                                            uint64_t offset, uint32_t count) {
+  nsAutoCString data;
+  data.SetLength(count);
+
+  uint32_t read;
+  input->Read(data.BeginWriting(), count, &read);
+  mOnData += data;
+
+  if (mCancelIn == OnData) {
+    request->Cancel(ERROR_CANCEL);
+  }
+
+  return mOnDataResult;
+}
+NS_IMETHODIMP FakeListener::OnStopRequest(nsIRequest* request,
+                                          nsresult status) {
+  EXPECT_FALSE(mOnStop);
+  mOnStop.emplace(status);
+
+  if (mCancelIn == OnStop) {
+    request->Cancel(ERROR_CANCEL);
+  }
+
+  return mOnStopResult;
+}
+
+bool eventInProgress = true;
+
+void Await() {
+  MOZ_ALWAYS_TRUE(mozilla::SpinEventLoopUntil([&]() {
+    bool yield = !eventInProgress;
+    eventInProgress = true;  // Just for convenience
+    return yield;
+  }));
+}
+
+void Yield() { eventInProgress = false; }
+
+}  // namespace
+
+// ****************************************************************************
+// Test body
+// ****************************************************************************
+
+// Caching with all good results (data + NS_OK)
+TEST(TestFetchPreloader, CacheNoneBeforeConsume)
+{
+  nsCOMPtr<nsIURI> uri;
+  NS_NewURI(getter_AddRefs(uri), "https://example.com"_ns);
+  auto key = mozilla::PreloadHashKey::CreateAsFetch(uri, mozilla::CORS_NONE);
+
+  RefPtr<FakeChannel> channel = new FakeChannel();
+  RefPtr<FakePreloader> preloader = new FakePreloader(channel);
+  RefPtr<mozilla::dom::Document> doc;
+  NS_NewXMLDocument(getter_AddRefs(doc));
+
+  EXPECT_TRUE(NS_SUCCEEDED(
+      preloader->OpenChannel(key, uri, mozilla::CORS_NONE,
+                             mozilla::dom::ReferrerPolicy::_empty, doc)));
+
+  RefPtr<FakeListener> listener = new FakeListener();
+  EXPECT_TRUE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Start()));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("one"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("two"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("three"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Stop(NS_OK)));
+
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(listener->mOnStart);
+    EXPECT_TRUE(listener->mOnData.EqualsLiteral("onetwothree"));
+    EXPECT_TRUE(listener->mOnStop && *listener->mOnStop == NS_OK);
+
+    Yield();
+  }));
+
+  Await();
+
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+}
+
+TEST(TestFetchPreloader, CacheStartBeforeConsume)
+{
+  nsCOMPtr<nsIURI> uri;
+  NS_NewURI(getter_AddRefs(uri), "https://example.com"_ns);
+  auto key = mozilla::PreloadHashKey::CreateAsFetch(uri, mozilla::CORS_NONE);
+
+  RefPtr<FakeChannel> channel = new FakeChannel();
+  RefPtr<FakePreloader> preloader = new FakePreloader(channel);
+  RefPtr<mozilla::dom::Document> doc;
+  NS_NewXMLDocument(getter_AddRefs(doc));
+
+  EXPECT_TRUE(NS_SUCCEEDED(
+      preloader->OpenChannel(key, uri, mozilla::CORS_NONE,
+                             mozilla::dom::ReferrerPolicy::_empty, doc)));
+
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Start()));
+
+  RefPtr<FakeListener> listener = new FakeListener();
+  EXPECT_TRUE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(listener->mOnStart);
+
+    EXPECT_TRUE(NS_SUCCEEDED(channel->Data("one"_ns)));
+    EXPECT_TRUE(NS_SUCCEEDED(channel->Data("two"_ns)));
+    EXPECT_TRUE(NS_SUCCEEDED(channel->Data("three"_ns)));
+    EXPECT_TRUE(listener->mOnData.EqualsLiteral("onetwothree"));
+
+    EXPECT_TRUE(NS_SUCCEEDED(channel->Stop(NS_OK)));
+    EXPECT_TRUE(listener->mOnStop && *listener->mOnStop == NS_OK);
+
+    Yield();
+  }));
+
+  Await();
+
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+}
+
+TEST(TestFetchPreloader, CachePartOfDataBeforeConsume)
+{
+  nsCOMPtr<nsIURI> uri;
+  NS_NewURI(getter_AddRefs(uri), "https://example.com"_ns);
+  auto key = mozilla::PreloadHashKey::CreateAsFetch(uri, mozilla::CORS_NONE);
+
+  RefPtr<FakeChannel> channel = new FakeChannel();
+  RefPtr<FakePreloader> preloader = new FakePreloader(channel);
+  RefPtr<mozilla::dom::Document> doc;
+  NS_NewXMLDocument(getter_AddRefs(doc));
+
+  EXPECT_TRUE(NS_SUCCEEDED(
+      preloader->OpenChannel(key, uri, mozilla::CORS_NONE,
+                             mozilla::dom::ReferrerPolicy::_empty, doc)));
+
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Start()));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("one"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("two"_ns)));
+
+  RefPtr<FakeListener> listener = new FakeListener();
+  EXPECT_TRUE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(listener->mOnStart);
+
+    EXPECT_TRUE(NS_SUCCEEDED(channel->Data("three"_ns)));
+    EXPECT_TRUE(listener->mOnData.EqualsLiteral("onetwothree"));
+
+    EXPECT_TRUE(NS_SUCCEEDED(channel->Stop(NS_OK)));
+    EXPECT_TRUE(listener->mOnStop && *listener->mOnStop == NS_OK);
+
+    Yield();
+  }));
+
+  Await();
+
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+}
+
+TEST(TestFetchPreloader, CacheAllDataBeforeConsume)
+{
+  nsCOMPtr<nsIURI> uri;
+  NS_NewURI(getter_AddRefs(uri), "https://example.com"_ns);
+  auto key = mozilla::PreloadHashKey::CreateAsFetch(uri, mozilla::CORS_NONE);
+
+  RefPtr<FakeChannel> channel = new FakeChannel();
+  RefPtr<FakePreloader> preloader = new FakePreloader(channel);
+  RefPtr<mozilla::dom::Document> doc;
+  NS_NewXMLDocument(getter_AddRefs(doc));
+
+  EXPECT_TRUE(NS_SUCCEEDED(
+      preloader->OpenChannel(key, uri, mozilla::CORS_NONE,
+                             mozilla::dom::ReferrerPolicy::_empty, doc)));
+
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Start()));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("one"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("two"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("three"_ns)));
+
+  // Request consumation of the preload...
+  RefPtr<FakeListener> listener = new FakeListener();
+  EXPECT_TRUE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(listener->mOnStart);
+    EXPECT_TRUE(listener->mOnData.EqualsLiteral("onetwothree"));
+
+    EXPECT_TRUE(NS_SUCCEEDED(channel->Stop(NS_OK)));
+    EXPECT_TRUE(listener->mOnStop && *listener->mOnStop == NS_OK);
+
+    Yield();
+  }));
+
+  Await();
+
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+}
+
+TEST(TestFetchPreloader, CacheAllBeforeConsume)
+{
+  nsCOMPtr<nsIURI> uri;
+  NS_NewURI(getter_AddRefs(uri), "https://example.com"_ns);
+  auto key = mozilla::PreloadHashKey::CreateAsFetch(uri, mozilla::CORS_NONE);
+
+  RefPtr<FakeChannel> channel = new FakeChannel();
+  RefPtr<FakePreloader> preloader = new FakePreloader(channel);
+  RefPtr<mozilla::dom::Document> doc;
+  NS_NewXMLDocument(getter_AddRefs(doc));
+
+  EXPECT_TRUE(NS_SUCCEEDED(
+      preloader->OpenChannel(key, uri, mozilla::CORS_NONE,
+                             mozilla::dom::ReferrerPolicy::_empty, doc)));
+
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Start()));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("one"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("two"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("three"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Stop(NS_OK)));
+
+  RefPtr<FakeListener> listener = new FakeListener();
+  EXPECT_TRUE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(listener->mOnStart);
+    EXPECT_TRUE(listener->mOnData.EqualsLiteral("onetwothree"));
+    EXPECT_TRUE(listener->mOnStop && *listener->mOnStop == NS_OK);
+
+    Yield();
+  }));
+
+  Await();
+
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+}
+
+// Get data before the channel fails
+TEST(TestFetchPreloader, CacheAllBeforeConsumeWithChannelError)
+{
+  nsCOMPtr<nsIURI> uri;
+  NS_NewURI(getter_AddRefs(uri), "https://example.com"_ns);
+  auto key = mozilla::PreloadHashKey::CreateAsFetch(uri, mozilla::CORS_NONE);
+
+  RefPtr<FakeChannel> channel = new FakeChannel();
+  RefPtr<FakePreloader> preloader = new FakePreloader(channel);
+  RefPtr<mozilla::dom::Document> doc;
+  NS_NewXMLDocument(getter_AddRefs(doc));
+
+  EXPECT_TRUE(NS_SUCCEEDED(
+      preloader->OpenChannel(key, uri, mozilla::CORS_NONE,
+                             mozilla::dom::ReferrerPolicy::_empty, doc)));
+
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Start()));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("one"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("two"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("three"_ns)));
+  EXPECT_TRUE(NS_FAILED(channel->Stop(ERROR_ONSTOP)));
+
+  RefPtr<FakeListener> listener = new FakeListener();
+  EXPECT_TRUE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(listener->mOnStart);
+    EXPECT_TRUE(listener->mOnData.EqualsLiteral("onetwothree"));
+    EXPECT_TRUE(listener->mOnStop && *listener->mOnStop == ERROR_ONSTOP);
+
+    Yield();
+  }));
+
+  Await();
+
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+}
+
+// Cancel the channel between caching and consuming
+TEST(TestFetchPreloader, CacheAllBeforeConsumeWithChannelCancel)
+{
+  nsCOMPtr<nsIURI> uri;
+  NS_NewURI(getter_AddRefs(uri), "https://example.com"_ns);
+  auto key = mozilla::PreloadHashKey::CreateAsFetch(uri, mozilla::CORS_NONE);
+
+  RefPtr<FakeChannel> channel = new FakeChannel();
+  RefPtr<FakePreloader> preloader = new FakePreloader(channel);
+  RefPtr<mozilla::dom::Document> doc;
+  NS_NewXMLDocument(getter_AddRefs(doc));
+
+  EXPECT_TRUE(NS_SUCCEEDED(
+      preloader->OpenChannel(key, uri, mozilla::CORS_NONE,
+                             mozilla::dom::ReferrerPolicy::_empty, doc)));
+
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Start()));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("one"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("two"_ns)));
+  channel->Cancel(ERROR_CANCEL);
+  EXPECT_TRUE(NS_FAILED(channel->Stop(ERROR_CANCEL)));
+
+  RefPtr<FakeListener> listener = new FakeListener();
+  EXPECT_TRUE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(listener->mOnStart);
+    // XXX - This is hard to solve; the data is there but we won't deliver it.
+    // This is a bit different case than e.g. a network error.  We want to
+    // deliver some data in that case.  Cancellation probably happens because of
+    // navigation or a demand to not consume the channel anyway.
+    EXPECT_TRUE(listener->mOnData.IsEmpty());
+    EXPECT_TRUE(listener->mOnStop && *listener->mOnStop == ERROR_CANCEL);
+
+    Yield();
+  }));
+
+  Await();
+
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+}
+
+// Let the listener throw while data is already cached
+TEST(TestFetchPreloader, CacheAllBeforeConsumeThrowFromOnStartRequest)
+{
+  nsCOMPtr<nsIURI> uri;
+  NS_NewURI(getter_AddRefs(uri), "https://example.com"_ns);
+  auto key = mozilla::PreloadHashKey::CreateAsFetch(uri, mozilla::CORS_NONE);
+
+  RefPtr<FakeChannel> channel = new FakeChannel();
+  RefPtr<FakePreloader> preloader = new FakePreloader(channel);
+  RefPtr<mozilla::dom::Document> doc;
+  NS_NewXMLDocument(getter_AddRefs(doc));
+
+  EXPECT_TRUE(NS_SUCCEEDED(
+      preloader->OpenChannel(key, uri, mozilla::CORS_NONE,
+                             mozilla::dom::ReferrerPolicy::_empty, doc)));
+
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Start()));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("one"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("two"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("three"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Stop(NS_OK)));
+
+  RefPtr<FakeListener> listener = new FakeListener();
+  listener->mOnStartResult = ERROR_THROW;
+
+  EXPECT_TRUE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(listener->mOnStart);
+    EXPECT_TRUE(listener->mOnData.IsEmpty());
+    EXPECT_TRUE(listener->mOnStop && *listener->mOnStop == ERROR_THROW);
+
+    Yield();
+  }));
+
+  Await();
+
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+}
+
+TEST(TestFetchPreloader, CacheAllBeforeConsumeThrowFromOnDataAvailable)
+{
+  nsCOMPtr<nsIURI> uri;
+  NS_NewURI(getter_AddRefs(uri), "https://example.com"_ns);
+  auto key = mozilla::PreloadHashKey::CreateAsFetch(uri, mozilla::CORS_NONE);
+
+  RefPtr<FakeChannel> channel = new FakeChannel();
+  RefPtr<FakePreloader> preloader = new FakePreloader(channel);
+  RefPtr<mozilla::dom::Document> doc;
+  NS_NewXMLDocument(getter_AddRefs(doc));
+
+  EXPECT_TRUE(NS_SUCCEEDED(
+      preloader->OpenChannel(key, uri, mozilla::CORS_NONE,
+                             mozilla::dom::ReferrerPolicy::_empty, doc)));
+
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Start()));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("one"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("two"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("three"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Stop(NS_OK)));
+
+  RefPtr<FakeListener> listener = new FakeListener();
+  listener->mOnDataResult = ERROR_THROW;
+
+  EXPECT_TRUE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(listener->mOnStart);
+    EXPECT_TRUE(listener->mOnData.EqualsLiteral("one"));
+    EXPECT_TRUE(listener->mOnStop && *listener->mOnStop == ERROR_THROW);
+
+    Yield();
+  }));
+
+  Await();
+
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+}
+
+TEST(TestFetchPreloader, CacheAllBeforeConsumeThrowFromOnStopRequest)
+{
+  nsCOMPtr<nsIURI> uri;
+  NS_NewURI(getter_AddRefs(uri), "https://example.com"_ns);
+  auto key = mozilla::PreloadHashKey::CreateAsFetch(uri, mozilla::CORS_NONE);
+
+  RefPtr<FakeChannel> channel = new FakeChannel();
+  RefPtr<FakePreloader> preloader = new FakePreloader(channel);
+  RefPtr<mozilla::dom::Document> doc;
+  NS_NewXMLDocument(getter_AddRefs(doc));
+
+  EXPECT_TRUE(NS_SUCCEEDED(
+      preloader->OpenChannel(key, uri, mozilla::CORS_NONE,
+                             mozilla::dom::ReferrerPolicy::_empty, doc)));
+
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Start()));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("one"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("two"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("three"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Stop(NS_OK)));
+
+  RefPtr<FakeListener> listener = new FakeListener();
+  listener->mOnStopResult = ERROR_THROW;
+
+  EXPECT_TRUE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(listener->mOnStart);
+    EXPECT_TRUE(listener->mOnData.EqualsLiteral("onetwothree"));
+    // Throwing from OnStopRequest is generally ignored.
+    EXPECT_TRUE(listener->mOnStop && *listener->mOnStop == NS_OK);
+
+    Yield();
+  }));
+
+  Await();
+
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+}
+
+// Cancel the channel in various callbacks
+TEST(TestFetchPreloader, CacheAllBeforeConsumeCancelInOnStartRequest)
+{
+  nsCOMPtr<nsIURI> uri;
+  NS_NewURI(getter_AddRefs(uri), "https://example.com"_ns);
+  auto key = mozilla::PreloadHashKey::CreateAsFetch(uri, mozilla::CORS_NONE);
+
+  RefPtr<FakeChannel> channel = new FakeChannel();
+  RefPtr<FakePreloader> preloader = new FakePreloader(channel);
+  RefPtr<mozilla::dom::Document> doc;
+  NS_NewXMLDocument(getter_AddRefs(doc));
+
+  EXPECT_TRUE(NS_SUCCEEDED(
+      preloader->OpenChannel(key, uri, mozilla::CORS_NONE,
+                             mozilla::dom::ReferrerPolicy::_empty, doc)));
+
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Start()));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("one"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("two"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("three"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Stop(NS_OK)));
+
+  RefPtr<FakeListener> listener = new FakeListener();
+  listener->mCancelIn = FakeListener::OnStart;
+  // check that throwing from OnStartRequest doesn't affect the cancellation
+  // status.
+  listener->mOnStartResult = ERROR_THROW;
+
+  EXPECT_TRUE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(listener->mOnStart);
+    EXPECT_TRUE(listener->mOnData.IsEmpty());
+    EXPECT_TRUE(listener->mOnStop && *listener->mOnStop == ERROR_CANCEL);
+
+    Yield();
+  }));
+
+  Await();
+
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+}
+
+TEST(TestFetchPreloader, CacheAllBeforeConsumeCancelInOnDataAvailable)
+{
+  nsCOMPtr<nsIURI> uri;
+  NS_NewURI(getter_AddRefs(uri), "https://example.com"_ns);
+  auto key = mozilla::PreloadHashKey::CreateAsFetch(uri, mozilla::CORS_NONE);
+
+  RefPtr<FakeChannel> channel = new FakeChannel();
+  RefPtr<FakePreloader> preloader = new FakePreloader(channel);
+  RefPtr<mozilla::dom::Document> doc;
+  NS_NewXMLDocument(getter_AddRefs(doc));
+
+  EXPECT_TRUE(NS_SUCCEEDED(
+      preloader->OpenChannel(key, uri, mozilla::CORS_NONE,
+                             mozilla::dom::ReferrerPolicy::_empty, doc)));
+
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Start()));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("one"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("two"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("three"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Stop(NS_OK)));
+
+  RefPtr<FakeListener> listener = new FakeListener();
+  listener->mCancelIn = FakeListener::OnData;
+  // check that throwing from OnStartRequest doesn't affect the cancellation
+  // status.
+  listener->mOnDataResult = ERROR_THROW;
+
+  EXPECT_TRUE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(listener->mOnStart);
+    EXPECT_TRUE(listener->mOnData.EqualsLiteral("one"));
+    EXPECT_TRUE(listener->mOnStop && *listener->mOnStop == ERROR_CANCEL);
+
+    Yield();
+  }));
+
+  Await();
+
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+}
+
+// Corner cases
+TEST(TestFetchPreloader, CachePartlyBeforeConsumeCancelInOnDataAvailable)
+{
+  nsCOMPtr<nsIURI> uri;
+  NS_NewURI(getter_AddRefs(uri), "https://example.com"_ns);
+  auto key = mozilla::PreloadHashKey::CreateAsFetch(uri, mozilla::CORS_NONE);
+
+  RefPtr<FakeChannel> channel = new FakeChannel();
+  RefPtr<FakePreloader> preloader = new FakePreloader(channel);
+  RefPtr<mozilla::dom::Document> doc;
+  NS_NewXMLDocument(getter_AddRefs(doc));
+
+  EXPECT_TRUE(NS_SUCCEEDED(
+      preloader->OpenChannel(key, uri, mozilla::CORS_NONE,
+                             mozilla::dom::ReferrerPolicy::_empty, doc)));
+
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Start()));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("one"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("two"_ns)));
+
+  RefPtr<FakeListener> listener = new FakeListener();
+  listener->mCancelIn = FakeListener::OnData;
+
+  EXPECT_TRUE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(NS_FAILED(channel->Data("three"_ns)));
+    EXPECT_TRUE(NS_FAILED(channel->Stop(NS_OK)));
+
+    EXPECT_TRUE(listener->mOnStart);
+    EXPECT_TRUE(listener->mOnData.EqualsLiteral("one"));
+    EXPECT_TRUE(listener->mOnStop && *listener->mOnStop == ERROR_CANCEL);
+
+    Yield();
+  }));
+
+  Await();
+
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+}
+
+TEST(TestFetchPreloader, CachePartlyBeforeConsumeCancelInOnStartRequestAndRace)
+{
+  nsCOMPtr<nsIURI> uri;
+  NS_NewURI(getter_AddRefs(uri), "https://example.com"_ns);
+  auto key = mozilla::PreloadHashKey::CreateAsFetch(uri, mozilla::CORS_NONE);
+
+  RefPtr<FakeChannel> channel = new FakeChannel();
+  RefPtr<FakePreloader> preloader = new FakePreloader(channel);
+  RefPtr<mozilla::dom::Document> doc;
+  NS_NewXMLDocument(getter_AddRefs(doc));
+
+  EXPECT_TRUE(NS_SUCCEEDED(
+      preloader->OpenChannel(key, uri, mozilla::CORS_NONE,
+                             mozilla::dom::ReferrerPolicy::_empty, doc)));
+
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Start()));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("one"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("two"_ns)));
+
+  // This has to simulate a possibiilty when stream listener notifications from
+  // the channel are already pending in the queue while AsyncConsume is called.
+  // At this moment the listener has not been notified yet.
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(NS_SUCCEEDED(channel->Data("three"_ns)));
+    EXPECT_TRUE(NS_SUCCEEDED(channel->Stop(NS_OK)));
+  }));
+
+  RefPtr<FakeListener> listener = new FakeListener();
+  listener->mCancelIn = FakeListener::OnStart;
+
+  EXPECT_TRUE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+
+  // Check listener's been fed properly.  Expected is to NOT get any data and
+  // propagate the cancellation code and not being called duplicated
+  // OnStopRequest.
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(listener->mOnStart);
+    EXPECT_TRUE(listener->mOnData.IsEmpty());
+    EXPECT_TRUE(listener->mOnStop && *listener->mOnStop == ERROR_CANCEL);
+
+    Yield();
+  }));
+
+  Await();
+
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+}
+
+TEST(TestFetchPreloader, CachePartlyBeforeConsumeCancelInOnDataAvailableAndRace)
+{
+  nsCOMPtr<nsIURI> uri;
+  NS_NewURI(getter_AddRefs(uri), "https://example.com"_ns);
+  auto key = mozilla::PreloadHashKey::CreateAsFetch(uri, mozilla::CORS_NONE);
+
+  RefPtr<FakeChannel> channel = new FakeChannel();
+  RefPtr<FakePreloader> preloader = new FakePreloader(channel);
+  RefPtr<mozilla::dom::Document> doc;
+  NS_NewXMLDocument(getter_AddRefs(doc));
+
+  EXPECT_TRUE(NS_SUCCEEDED(
+      preloader->OpenChannel(key, uri, mozilla::CORS_NONE,
+                             mozilla::dom::ReferrerPolicy::_empty, doc)));
+
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Start()));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("one"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("two"_ns)));
+
+  // This has to simulate a possibiilty when stream listener notifications from
+  // the channel are already pending in the queue while AsyncConsume is called.
+  // At this moment the listener has not been notified yet.
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(NS_SUCCEEDED(channel->Data("three"_ns)));
+    EXPECT_TRUE(NS_SUCCEEDED(channel->Stop(NS_OK)));
+  }));
+
+  RefPtr<FakeListener> listener = new FakeListener();
+  listener->mCancelIn = FakeListener::OnData;
+
+  EXPECT_TRUE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+
+  // Check listener's been fed properly.  Expected is to NOT get anything after
+  // the first OnData and propagate the cancellation code and not being called
+  // duplicated OnStopRequest.
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(listener->mOnStart);
+    EXPECT_TRUE(listener->mOnData.EqualsLiteral("one"));
+    EXPECT_TRUE(listener->mOnStop && *listener->mOnStop == ERROR_CANCEL);
+
+    Yield();
+  }));
+
+  Await();
+
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+}
+
+TEST(TestFetchPreloader, CachePartlyBeforeConsumeThrowFromOnStartRequestAndRace)
+{
+  nsCOMPtr<nsIURI> uri;
+  NS_NewURI(getter_AddRefs(uri), "https://example.com"_ns);
+  auto key = mozilla::PreloadHashKey::CreateAsFetch(uri, mozilla::CORS_NONE);
+
+  RefPtr<FakeChannel> channel = new FakeChannel();
+  RefPtr<FakePreloader> preloader = new FakePreloader(channel);
+  RefPtr<mozilla::dom::Document> doc;
+  NS_NewXMLDocument(getter_AddRefs(doc));
+
+  EXPECT_TRUE(NS_SUCCEEDED(
+      preloader->OpenChannel(key, uri, mozilla::CORS_NONE,
+                             mozilla::dom::ReferrerPolicy::_empty, doc)));
+
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Start()));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("one"_ns)));
+  EXPECT_TRUE(NS_SUCCEEDED(channel->Data("two"_ns)));
+
+  // This has to simulate a possibiilty when stream listener notifications from
+  // the channel are already pending in the queue while AsyncConsume is called.
+  // At this moment the listener has not been notified yet.
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(NS_SUCCEEDED(channel->Data("three"_ns)));
+    EXPECT_TRUE(NS_SUCCEEDED(channel->Stop(NS_OK)));
+  }));
+
+  RefPtr<FakeListener> listener = new FakeListener();
+  listener->mOnStartResult = ERROR_THROW;
+
+  EXPECT_TRUE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+
+  // Check listener's been fed properly.  Expected is to NOT get any data and
+  // propagate the throwing code and not being called duplicated OnStopRequest.
+  NS_DispatchToMainThread(NS_NewRunnableFunction("test", [&]() {
+    EXPECT_TRUE(listener->mOnStart);
+    EXPECT_TRUE(listener->mOnData.IsEmpty());
+    EXPECT_TRUE(listener->mOnStop && *listener->mOnStop == ERROR_THROW);
+
+    Yield();
+  }));
+
+  Await();
+
+  EXPECT_FALSE(NS_SUCCEEDED(preloader->AsyncConsume(listener)));
+}
diff --git a/uriloader/preload/gtest/moz.build b/uriloader/preload/gtest/moz.build
new file mode 100644
index 0000000000..72c2afa539
--- /dev/null
+++ b/uriloader/preload/gtest/moz.build
@@ -0,0 +1,18 @@
+# -*- Mode: python; c-basic-offset: 4; 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/.
+
+UNIFIED_SOURCES += [
+    "TestFetchPreloader.cpp",
+]
+
+LOCAL_INCLUDES += [
+    "/netwerk/base",
+    "/xpcom/tests/gtest",
+]
+
+FINAL_LIBRARY = "xul-gtest"
+
+LOCAL_INCLUDES += ["!/xpcom", "/xpcom/components"]
diff --git a/uriloader/preload/moz.build b/uriloader/preload/moz.build
new file mode 100644
index 0000000000..5ce2f28d89
--- /dev/null
+++ b/uriloader/preload/moz.build
@@ -0,0 +1,28 @@
+# -*- 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", "Networking")
+
+TEST_DIRS += ["gtest"]
+
+EXPORTS.mozilla += [
+    "FetchPreloader.h",
+    "PreloaderBase.h",
+    "PreloadHashKey.h",
+    "PreloadService.h",
+]
+
+UNIFIED_SOURCES += [
+    "FetchPreloader.cpp",
+    "PreloaderBase.cpp",
+    "PreloadHashKey.cpp",
+    "PreloadService.cpp",
+]
+
+FINAL_LIBRARY = "xul"
+
+include("/ipc/chromium/chromium-config.mozbuild")