Adding upstream version 124.0.1.upstream/124.0.1

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

40 files changed, 4599 insertions, 0 deletions

diff --git a/dom/file/ipc/FileCreatorChild.cpp b/dom/file/ipc/FileCreatorChild.cpp
new file mode 100644
index 0000000000..95ac19f17b
--- /dev/null
+++ b/dom/file/ipc/FileCreatorChild.cpp
@@ -0,0 +1,59 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "FileCreatorChild.h"
+#include "mozilla/dom/BlobImpl.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/IPCBlobUtils.h"
+
+namespace mozilla::dom {
+
+FileCreatorChild::FileCreatorChild() = default;
+
+FileCreatorChild::~FileCreatorChild() { MOZ_ASSERT(!mPromise); }
+
+void FileCreatorChild::SetPromise(Promise* aPromise) {
+  MOZ_ASSERT(aPromise);
+  MOZ_ASSERT(!mPromise);
+
+  mPromise = aPromise;
+}
+
+mozilla::ipc::IPCResult FileCreatorChild::Recv__delete__(
+    const FileCreationResult& aResult) {
+  MOZ_ASSERT(mPromise);
+
+  RefPtr<Promise> promise;
+  promise.swap(mPromise);
+
+  if (aResult.type() == FileCreationResult::TFileCreationErrorResult) {
+    promise->MaybeReject(aResult.get_FileCreationErrorResult().errorCode());
+    return IPC_OK();
+  }
+
+  MOZ_ASSERT(aResult.type() == FileCreationResult::TFileCreationSuccessResult);
+
+  RefPtr<dom::BlobImpl> impl = dom::IPCBlobUtils::Deserialize(
+      aResult.get_FileCreationSuccessResult().blob());
+
+  RefPtr<File> file = File::Create(promise->GetParentObject(), impl);
+  if (NS_WARN_IF(!file)) {
+    promise->MaybeReject(NS_ERROR_FAILURE);
+    return IPC_OK();
+  }
+
+  promise->MaybeResolve(file);
+  return IPC_OK();
+}
+
+void FileCreatorChild::ActorDestroy(ActorDestroyReason aWhy) {
+  if (mPromise) {
+    mPromise->MaybeReject(NS_ERROR_FAILURE);
+    mPromise = nullptr;
+  }
+};
+
+}  // namespace mozilla::dom
diff --git a/dom/file/ipc/FileCreatorChild.h b/dom/file/ipc/FileCreatorChild.h
new file mode 100644
index 0000000000..eb5dc09d92
--- /dev/null
+++ b/dom/file/ipc/FileCreatorChild.h
@@ -0,0 +1,33 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_FileCreatorChild_h
+#define mozilla_dom_FileCreatorChild_h
+
+#include "mozilla/dom/PFileCreatorChild.h"
+
+namespace mozilla::dom {
+
+class FileCreatorChild final : public mozilla::dom::PFileCreatorChild {
+  friend class mozilla::dom::PFileCreatorChild;
+
+ public:
+  FileCreatorChild();
+  ~FileCreatorChild() override;
+
+  void SetPromise(Promise* aPromise);
+
+ private:
+  mozilla::ipc::IPCResult Recv__delete__(const FileCreationResult& aResult);
+
+  void ActorDestroy(ActorDestroyReason aWhy) override;
+
+  RefPtr<Promise> mPromise;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_FileCreatorChild_h
diff --git a/dom/file/ipc/FileCreatorParent.cpp b/dom/file/ipc/FileCreatorParent.cpp
new file mode 100644
index 0000000000..77f8efd483
--- /dev/null
+++ b/dom/file/ipc/FileCreatorParent.cpp
@@ -0,0 +1,135 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "FileCreatorParent.h"
+#include "mozilla/dom/FileBlobImpl.h"
+#include "mozilla/dom/IPCBlobUtils.h"
+#include "mozilla/dom/MultipartBlobImpl.h"
+#include "nsIFile.h"
+
+namespace mozilla::dom {
+
+FileCreatorParent::FileCreatorParent()
+    : mBackgroundEventTarget(GetCurrentSerialEventTarget()), mIPCActive(true) {}
+
+FileCreatorParent::~FileCreatorParent() = default;
+
+mozilla::ipc::IPCResult FileCreatorParent::CreateAndShareFile(
+    const nsAString& aFullPath, const nsAString& aType, const nsAString& aName,
+    const Maybe<int64_t>& aLastModified, const bool& aExistenceCheck,
+    const bool& aIsFromNsIFile) {
+  RefPtr<dom::BlobImpl> blobImpl;
+  nsresult rv =
+      CreateBlobImpl(aFullPath, aType, aName, aLastModified.isSome(),
+                     aLastModified.isSome() ? aLastModified.value() : 0,
+                     aExistenceCheck, aIsFromNsIFile, getter_AddRefs(blobImpl));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    (void)Send__delete__(this, FileCreationErrorResult(rv));
+    return IPC_OK();
+  }
+
+  MOZ_ASSERT(blobImpl);
+
+  // FileBlobImpl is unable to return the correct type on this thread because
+  // nsIMIMEService is not thread-safe. We must exec the 'type' getter on
+  // main-thread before send the blob to the child actor.
+
+  RefPtr<FileCreatorParent> self = this;
+  NS_DispatchToMainThread(NS_NewRunnableFunction(
+      "FileCreatorParent::CreateAndShareFile", [self, blobImpl]() {
+        nsAutoString type;
+        blobImpl->GetType(type);
+
+        self->mBackgroundEventTarget->Dispatch(NS_NewRunnableFunction(
+            "FileCreatorParent::CreateAndShareFile return", [self, blobImpl]() {
+              if (self->mIPCActive) {
+                IPCBlob ipcBlob;
+                nsresult rv = dom::IPCBlobUtils::Serialize(blobImpl, ipcBlob);
+                if (NS_WARN_IF(NS_FAILED(rv))) {
+                  (void)Send__delete__(self, FileCreationErrorResult(rv));
+                  return;
+                }
+
+                (void)Send__delete__(self, FileCreationSuccessResult(ipcBlob));
+              }
+            }));
+      }));
+
+  return IPC_OK();
+}
+
+void FileCreatorParent::ActorDestroy(ActorDestroyReason aWhy) {
+  mIPCActive = false;
+}
+
+/* static */
+nsresult FileCreatorParent::CreateBlobImpl(
+    const nsAString& aPath, const nsAString& aType, const nsAString& aName,
+    bool aLastModifiedPassed, int64_t aLastModified, bool aExistenceCheck,
+    bool aIsFromNsIFile, BlobImpl** aBlobImpl) {
+  MOZ_ASSERT(!NS_IsMainThread());
+
+  nsCOMPtr<nsIFile> file;
+  nsresult rv = NS_NewLocalFile(aPath, true, getter_AddRefs(file));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  bool exists;
+  rv = file->Exists(&exists);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  if (aExistenceCheck) {
+    if (!exists) {
+      return NS_ERROR_FILE_NOT_FOUND;
+    }
+
+    bool isDir;
+    rv = file->IsDirectory(&isDir);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    if (isDir) {
+      return NS_ERROR_FILE_IS_DIRECTORY;
+    }
+  }
+
+  RefPtr<FileBlobImpl> impl = new FileBlobImpl(file);
+
+  // If the file doesn't exist, we cannot have its path, its size and so on.
+  // Let's set them now.
+  if (!exists) {
+    MOZ_ASSERT(!aExistenceCheck);
+
+    impl->SetMozFullPath(aPath);
+    impl->SetLastModified(0);
+    impl->SetEmptySize();
+  }
+
+  if (!aName.IsEmpty()) {
+    impl->SetName(aName);
+  }
+
+  if (!aType.IsEmpty()) {
+    impl->SetType(aType);
+  }
+
+  if (aLastModifiedPassed) {
+    impl->SetLastModified(aLastModified);
+  }
+
+  if (!aIsFromNsIFile) {
+    impl->SetMozFullPath(u""_ns);
+  }
+
+  impl.forget(aBlobImpl);
+  return NS_OK;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/file/ipc/FileCreatorParent.h b/dom/file/ipc/FileCreatorParent.h
new file mode 100644
index 0000000000..f43dbee886
--- /dev/null
+++ b/dom/file/ipc/FileCreatorParent.h
@@ -0,0 +1,45 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_FileCreatorParent_h
+#define mozilla_dom_FileCreatorParent_h
+
+#include "mozilla/dom/PFileCreatorParent.h"
+
+class nsIFile;
+
+namespace mozilla::dom {
+
+class BlobImpl;
+
+class FileCreatorParent final : public mozilla::dom::PFileCreatorParent {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(FileCreatorParent)
+
+  FileCreatorParent();
+
+  mozilla::ipc::IPCResult CreateAndShareFile(
+      const nsAString& aFullPath, const nsAString& aType,
+      const nsAString& aName, const Maybe<int64_t>& aLastModified,
+      const bool& aExistenceCheck, const bool& aIsFromNsIFile);
+
+ private:
+  ~FileCreatorParent() override;
+
+  void ActorDestroy(ActorDestroyReason aWhy) override;
+
+  nsresult CreateBlobImpl(const nsAString& aPath, const nsAString& aType,
+                          const nsAString& aName, bool aLastModifiedPassed,
+                          int64_t aLastModified, bool aExistenceCheck,
+                          bool aIsFromNsIFile, BlobImpl** aBlobImpl);
+
+  nsCOMPtr<nsIEventTarget> mBackgroundEventTarget;
+  bool mIPCActive;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_FileCreatorParent_h
diff --git a/dom/file/ipc/IPCBlob.ipdlh b/dom/file/ipc/IPCBlob.ipdlh
new file mode 100644
index 0000000000..4db1c662bd
--- /dev/null
+++ b/dom/file/ipc/IPCBlob.ipdlh
@@ -0,0 +1,56 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+include IPCStream;
+include ProtocolTypes;
+
+using struct mozilla::void_t from "mozilla/ipc/IPCCore.h";
+[RefCounted] using class mozilla::RemoteLazyInputStream from "mozilla/RemoteLazyInputStream.h";
+
+namespace mozilla {
+
+union RemoteLazyStream
+{
+  // Parent to Child: The child will receive a RemoteLazyInputStream. Nothing
+  // can be done with it except retrieving the size.
+  nullable RemoteLazyInputStream;
+
+  // Child to Parent: Normal serialization.
+  IPCStream;
+};
+
+namespace dom {
+
+// This contains any extra bit for making a File out of a Blob.
+// For more information about Blobs and IPC, please read the comments in
+// IPCBlobUtils.h
+
+struct IPCFile
+{
+  nsString name;
+  int64_t lastModified;
+  nsString DOMPath;
+  nsString fullPath;
+
+  // Useful for Entries API.
+  bool isDirectory;
+};
+
+struct IPCBlob
+{
+  nsString type;
+  uint64_t size;
+  nsString blobImplType;
+
+  RemoteLazyStream inputStream;
+
+  // Nothing is for Blob
+  IPCFile? file;
+
+  // This ID is used only by indexedDB tests.
+  int64_t fileId;
+};
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/file/ipc/IPCBlobUtils.cpp b/dom/file/ipc/IPCBlobUtils.cpp
new file mode 100644
index 0000000000..78409da529
--- /dev/null
+++ b/dom/file/ipc/IPCBlobUtils.cpp
@@ -0,0 +1,179 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "IPCBlobUtils.h"
+#include "RemoteLazyInputStream.h"
+#include "RemoteLazyInputStreamChild.h"
+#include "RemoteLazyInputStreamParent.h"
+#include "mozilla/dom/IPCBlob.h"
+#include "mozilla/ipc/BackgroundParent.h"
+#include "mozilla/ipc/PBackgroundParent.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "mozilla/dom/ContentParent.h"
+#include "mozilla/dom/ContentChild.h"
+#include "mozilla/ipc/IPCStreamUtils.h"
+#include "mozilla/ipc/ProtocolUtils.h"
+#include "RemoteLazyInputStreamStorage.h"
+#include "StreamBlobImpl.h"
+#include "prtime.h"
+
+namespace mozilla::dom::IPCBlobUtils {
+
+already_AddRefed<BlobImpl> Deserialize(const IPCBlob& aIPCBlob) {
+  nsCOMPtr<nsIInputStream> inputStream;
+
+  const RemoteLazyStream& stream = aIPCBlob.inputStream();
+  switch (stream.type()) {
+    // Parent to child: when an nsIInputStream is sent from parent to child, the
+    // child receives a RemoteLazyInputStream actor.
+    case RemoteLazyStream::TRemoteLazyInputStream: {
+      inputStream = stream.get_RemoteLazyInputStream();
+      break;
+    }
+
+    // Child to Parent: when a blob is created on the content process send it's
+    // sent to the parent, we have an IPCStream object.
+    case RemoteLazyStream::TIPCStream:
+      MOZ_ASSERT(XRE_IsParentProcess());
+      inputStream = DeserializeIPCStream(stream.get_IPCStream());
+      break;
+
+    default:
+      MOZ_CRASH("Unknown type.");
+      break;
+  }
+
+  MOZ_ASSERT(inputStream);
+
+  RefPtr<StreamBlobImpl> blobImpl;
+
+  if (aIPCBlob.file().isNothing()) {
+    blobImpl = StreamBlobImpl::Create(inputStream.forget(), aIPCBlob.type(),
+                                      aIPCBlob.size(), aIPCBlob.blobImplType());
+  } else {
+    const IPCFile& file = aIPCBlob.file().ref();
+    blobImpl = StreamBlobImpl::Create(inputStream.forget(), file.name(),
+                                      aIPCBlob.type(), file.lastModified(),
+                                      aIPCBlob.size(), aIPCBlob.blobImplType());
+    blobImpl->SetDOMPath(file.DOMPath());
+    blobImpl->SetFullPath(file.fullPath());
+    blobImpl->SetIsDirectory(file.isDirectory());
+  }
+
+  blobImpl->SetFileId(aIPCBlob.fileId());
+
+  return blobImpl.forget();
+}
+
+nsresult Serialize(BlobImpl* aBlobImpl, IPCBlob& aIPCBlob) {
+  MOZ_ASSERT(aBlobImpl);
+
+  nsAutoString value;
+  aBlobImpl->GetType(value);
+  aIPCBlob.type() = value;
+
+  aBlobImpl->GetBlobImplType(value);
+  aIPCBlob.blobImplType() = value;
+
+  ErrorResult rv;
+  aIPCBlob.size() = aBlobImpl->GetSize(rv);
+  if (NS_WARN_IF(rv.Failed())) {
+    return rv.StealNSResult();
+  }
+
+  if (!aBlobImpl->IsFile()) {
+    aIPCBlob.file() = Nothing();
+  } else {
+    IPCFile file;
+
+    aBlobImpl->GetName(value);
+    file.name() = value;
+
+    file.lastModified() = aBlobImpl->GetLastModified(rv) * PR_USEC_PER_MSEC;
+    if (NS_WARN_IF(rv.Failed())) {
+      return rv.StealNSResult();
+    }
+
+    aBlobImpl->GetDOMPath(value);
+    file.DOMPath() = value;
+
+    aBlobImpl->GetMozFullPathInternal(value, rv);
+    if (NS_WARN_IF(rv.Failed())) {
+      return rv.StealNSResult();
+    }
+    file.fullPath() = value;
+
+    file.isDirectory() = aBlobImpl->IsDirectory();
+
+    aIPCBlob.file() = Some(file);
+  }
+
+  aIPCBlob.fileId() = aBlobImpl->GetFileId();
+
+  nsCOMPtr<nsIInputStream> inputStream;
+  aBlobImpl->CreateInputStream(getter_AddRefs(inputStream), rv);
+  if (NS_WARN_IF(rv.Failed())) {
+    return rv.StealNSResult();
+  }
+
+  if (XRE_IsParentProcess()) {
+    RefPtr<RemoteLazyInputStream> stream =
+        RemoteLazyInputStream::WrapStream(inputStream);
+    if (NS_WARN_IF(!stream)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    aIPCBlob.inputStream() = stream;
+    return NS_OK;
+  }
+
+  mozilla::ipc::IPCStream stream;
+  if (!mozilla::ipc::SerializeIPCStream(inputStream.forget(), stream,
+                                        /* aAllowLazy */ true)) {
+    return NS_ERROR_FAILURE;
+  }
+  aIPCBlob.inputStream() = stream;
+  return NS_OK;
+}
+
+}  // namespace mozilla::dom::IPCBlobUtils
+
+namespace IPC {
+
+void ParamTraits<mozilla::dom::BlobImpl*>::Write(
+    IPC::MessageWriter* aWriter, mozilla::dom::BlobImpl* aParam) {
+  nsresult rv;
+  mozilla::dom::IPCBlob ipcblob;
+  if (aParam) {
+    rv = mozilla::dom::IPCBlobUtils::Serialize(aParam, ipcblob);
+  }
+  if (!aParam || NS_WARN_IF(NS_FAILED(rv))) {
+    WriteParam(aWriter, false);
+  } else {
+    WriteParam(aWriter, true);
+    WriteParam(aWriter, ipcblob);
+  }
+}
+
+bool ParamTraits<mozilla::dom::BlobImpl*>::Read(
+    IPC::MessageReader* aReader, RefPtr<mozilla::dom::BlobImpl>* aResult) {
+  *aResult = nullptr;
+
+  bool notnull = false;
+  if (!ReadParam(aReader, &notnull)) {
+    return false;
+  }
+  if (notnull) {
+    mozilla::dom::IPCBlob ipcblob;
+    if (!ReadParam(aReader, &ipcblob)) {
+      return false;
+    }
+    *aResult = mozilla::dom::IPCBlobUtils::Deserialize(ipcblob);
+  }
+  return true;
+}
+
+}  // namespace IPC
diff --git a/dom/file/ipc/IPCBlobUtils.h b/dom/file/ipc/IPCBlobUtils.h
new file mode 100644
index 0000000000..17fce3195a
--- /dev/null
+++ b/dom/file/ipc/IPCBlobUtils.h
@@ -0,0 +1,268 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_IPCBlobUtils_h
+#define mozilla_dom_IPCBlobUtils_h
+
+#include "mozilla/RefPtr.h"
+#include "mozilla/dom/File.h"
+#include "mozilla/ipc/IPDLParamTraits.h"
+
+/*
+ * Blobs and IPC
+ * ~~~~~~~~~~~~~
+ *
+ * Simplifying, DOM Blob objects are chunks of data with a content type and a
+ * size. DOM Files are Blobs with a name. They are are used in many APIs and
+ * they can be cloned and sent cross threads and cross processes.
+ *
+ * If we see Blobs from a platform point of view, the main (and often, the only)
+ * interesting part is how to retrieve data from it. This is done via
+ * nsIInputStream and, except for a couple of important details, this stream is
+ * used in the parent process.
+ *
+ * For this reason, when we consider the serialization of a blob via IPC
+ * messages, the biggest effort is put in how to manage the nsInputStream
+ * correctly. To serialize, we use the IPCBlob data struct: basically, the blob
+ * properties (size, type, name if it's a file) and the nsIInputStream.
+ *
+ * Before talking about the nsIInputStream it's important to say that we have
+ * different kinds of Blobs, based on the different kinds of sources. A non
+ * exaustive list is:
+ * - a memory buffer: MemoryBlobImpl
+ * - a string: StringBlobImpl
+ * - a real OS file: FileBlobImpl
+ * - a generic nsIInputStream: StreamBlobImpl
+ * - an empty blob: EmptyBlobImpl
+ * - more blobs combined together: MultipartBlobImpl
+ * Each one of these implementations has a custom ::CreateInputStream method.
+ * So, basically, each one has a different kind of nsIInputStream (nsFileStream,
+ * nsIStringInputStream, SlicedInputStream, and so on).
+ *
+ * Another important point to keep in mind is that a Blob can be created on the
+ * content process (for example: |new Blob([123])|) or it can be created on the
+ * parent process and sent to content (a FilePicker creates Blobs and it runs on
+ * the parent process).
+ *
+ * DocumentLoadListener uses blobs to serialize the POST data back to the
+ * content process (for insertion into session history). This lets it correctly
+ * handle OS files by reference, and avoid copying the underlying buffer data
+ * unless it is read. This can hopefully be removed once SessionHistory is
+ * handled in the parent process.
+ *
+ * Child to Parent Blob Serialization
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * When a document creates a blob, this can be sent, for different reasons to
+ * the parent process. For instance it can be sent as part of a FormData, or it
+ * can be converted to a BlobURL and broadcasted to any other existing
+ * processes.
+ *
+ * When this happens, we use the IPCStream data struct for the serialization
+ * of the nsIInputStream. This means that, if the stream is fully serializable
+ * and its size is lower than 1Mb, we are able to recreate the stream completely
+ * on the parent side. This happens, basically with any kind of child-to-parent
+ * stream except for huge memory streams. In this case we end up using
+ * DataPipe. See more information in IPCStreamUtils.h.
+ *
+ * In order to populate IPCStream correctly, we use SerializeIPCStream as
+ * documented in IPCStreamUtils.h.
+ *
+ * Parent to Child Blob Serialization
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * This scenario is common when we talk about Blobs pointing to real files:
+ * HTMLInputElement (type=file), or Entries API, DataTransfer and so on. But we
+ * also have this scenario when a content process creates a Blob and it
+ * broadcasts it because of a BlobURL or because BroadcastChannel API is used.
+ *
+ * The approach here is this: normally, the content process doesn't really read
+ * data from the blob nsIInputStream. The content process needs to have the
+ * nsIInputStream and be able to send it back to the parent process when the
+ * "real" work needs to be done. This is true except for 2 usecases: FileReader
+ * API and BlobURL usage. So, if we ignore these 2, normally, the parent sends a
+ * blob nsIInputStream to a content process, and then, it will receive it back
+ * in order to do some networking, or whatever.
+ *
+ * For this reason, IPCBlobUtils uses a particular protocol for serializing
+ * nsIInputStream parent to child: PRemoteLazyInputStream. This protocol keeps
+ * the original nsIInputStream alive on the parent side, and gives its size and
+ * a UUID to the child side. The child side creates a RemoteLazyInputStream and
+ * that is incapsulated into a StreamBlobImpl.
+ *
+ * The UUID is useful when the content process sends the same nsIInputStream
+ * back to the parent process because, the only information it has to share is
+ * the UUID. Each nsIInputStream sent via PRemoteLazyInputStream, is registered
+ * into the RemoteLazyInputStreamStorage.
+ *
+ * On the content process side, RemoteLazyInputStream is a special inputStream:
+ * the only reliable methods are:
+ * - nsIInputStream.available() - the size is shared by PRemoteLazyInputStream
+ *   actor.
+ * - nsIIPCSerializableInputStream.serialize() - we can give back this stream to
+ *   the parent because we know its UUID.
+ * - nsICloneableInputStream.cloneable() and nsICloneableInputStream.clone() -
+ *   this stream can be cloned. We just need to have a reference of the
+ *   PRemoteLazyInputStream actor and its UUID.
+ * - nsIAsyncInputStream.asyncWait() - see next section.
+ *
+ * Any other method (read, readSegment and so on) will fail if asyncWait() is
+ * not previously called (see the next section). Basically, this inputStream
+ * cannot be used synchronously for any 'real' reading operation.
+ *
+ * When the parent receives the serialization of a RemoteLazyInputStream, it is
+ * able to retrieve the correct nsIInputStream using the UUID and
+ * RemoteLazyInputStreamStorage.
+ *
+ * Parent to Child Streams, FileReader and BlobURL
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * The FileReader and BlobURL scenarios are described here.
+ *
+ * When content process needs to read data from a Blob sent from the parent
+ * process, it must do it asynchronously using RemoteLazyInputStream as a
+ * nsIAsyncInputStream stream. This happens calling
+ * RemoteLazyInputStream.asyncWait(). At that point, the child actor will send a
+ * StreamNeeded() IPC message to the parent side. When this is received, the
+ * parent retrieves the 'real' stream from RemoteLazyInputStreamStorage using
+ * the UUID, it will serialize the 'real' stream, and it will send it to the
+ * child side.
+ *
+ * When the 'real' stream is received (RecvStreamReady()), the asyncWait
+ * callback will be executed and, from that moment, any RemoteLazyInputStream
+ * method will be forwarded to the 'real' stream ones. This means that the
+ * reading will be available.
+ *
+ * RemoteLazyInputStream Thread
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * RemoteLazyInputStreamChild actor can be created in any thread (sort of) and
+ * their top-level IPDL protocol is PBackground. These actors are wrapped by 1
+ * or more RemoteLazyInputStream objects in order to expose nsIInputStream
+ * interface and be thread-safe.
+ *
+ * But IPDL actors are not thread-safe and any SendFoo() method must be executed
+ * on the owning thread. This means that this thread must be kept alive for the
+ * life-time of the RemoteLazyInputStream.
+ *
+ * In doing this, there are 2 main issues:
+ * a. if a remote Blob is created on a worker (because of a
+ *    BroadcastChannel/MessagePort for instance) and it sent to the main-thread
+ *    via PostMessage(), we have to keep that worker alive.
+ * b. if the remote Blob is created on the main-thread, any SendFoo() has to be
+ *    executed on the main-thread. This is true also when the inputStream is
+ *    used on another thread (note that nsIInputStream could do I/O and usually
+ *    they are used on special I/O threads).
+ *
+ * In order to avoid this, RemoteLazyInputStreamChild are 'migrated' to a
+ * DOM-File thread. This is done in this way:
+ *
+ * 1. If RemoteLazyInputStreamChild actor is not already owned by DOM-File
+ *    thread, it calls Send__delete__ in order to inform the parent side that we
+ *    don't need this IPC channel on the current thread.
+ * 2. A new RemoteLazyInputStreamChild is created. RemoteLazyInputStreamThread
+ *    is used to assign this actor to the DOM-File thread.
+ *    RemoteLazyInputStreamThread::GetOrCreate() creates the DOM-File thread if
+ *    it doesn't exist yet. Pending operations and RemoteLazyInputStreams are
+ *    moved onto the new actor.
+ * 3. RemoteLazyInputStreamParent::Recv__delete__ is called on the parent side
+ *    and the parent actor is deleted. Doing this we don't remove the UUID from
+ *    RemoteLazyInputStreamStorage.
+ * 4. The RemoteLazyInputStream constructor is sent with the new
+ *    RemoteLazyInputStreamChild actor, with the DOM-File thread's PBackground
+ *    as its manager.
+ * 5. When the new RemoteLazyInputStreamParent actor is created, it will receive
+ *    the same UUID of the previous parent actor. The nsIInputStream will be
+ *    retrieved from RemoteLazyInputStreamStorage.
+ * 6. In order to avoid leaks, RemoteLazyInputStreamStorage will monitor child
+ *    processes and in case one of them dies, it will release the
+ *    nsIInputStream objects belonging to that process.
+ *
+ * If any API wants to retrieve a 'real inputStream when the migration is in
+ * progress, that operation is stored in a pending queue and processed at the
+ * end of the migration.
+ *
+ * IPCBlob and nsIAsyncInputStream
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * RemoteLazyInputStream is always async. If the remote inputStream is not
+ * async, RemoteLazyInputStream will create a pipe stream around it in order to
+ * be consistently async.
+ *
+ * Slicing IPCBlob
+ * ~~~~~~~~~~~~~~~
+ *
+ * Normally, slicing a blob consists of the creation of a new Blob, with a
+ * SlicedInputStream() wrapping a clone of the original inputStream. But this
+ * approach is extremely inefficient with IPCBlob, because it could be that we
+ * wrap the pipe stream and not the remote inputStream (See the previous section
+ * of this documentation). If we end up doing so, also if the remote
+ * inputStream is seekable, the pipe will not be, and in order to reach the
+ * starting point, SlicedInputStream will do consecutive read()s.
+ *
+ * This problem is fixed implmenting nsICloneableWithRange in
+ * RemoteLazyInputStream and using cloneWithRange() when a StreamBlobImpl is
+ * sliced. When the remote stream is received, it will be sliced directly.
+ *
+ * If we want to represent the hierarchy of the InputStream classes, instead
+ * of having: |SlicedInputStream(RemoteLazyInputStream(Async
+ * Pipe(RemoteStream)))|, we have: |RemoteLazyInputStream(Async
+ * Pipe(SlicedInputStream(RemoteStream)))|.
+ *
+ * When RemoteLazyInputStream is serialized and sent to the parent process,
+ * start and range are sent too and SlicedInputStream is used in the parent side
+ * as well.
+ *
+ * Socket Process
+ * ~~~~~~~~~~~~~~
+ *
+ * The socket process is a separate process used to do networking operations.
+ * When a website sends a blob as the body of a POST/PUT request, we need to
+ * send the corresponding RemoteLazyInputStream to the socket process.
+ *
+ * This is the only serialization of RemoteLazyInputStream from parent to child
+ * process and it works _only_ for the socket process. Do not expose this
+ * serialization to PContent or PBackground or any other top-level IPDL protocol
+ * without a DOM File peer review!
+ *
+ * The main difference between Socket Process is that DOM-File thread is not
+ * used. Here is a list of reasons:
+ * - DOM-File moves the ownership of the RemoteLazyInputStream actors to
+ *   PBackground, but in the Socket Process we don't have PBackground (yet?)
+ * - Socket Process is a stable process with a simple life-time configuration:
+ *   we can keep the actors on the main-thread because no Workers are involved.
+ */
+
+namespace mozilla::dom {
+
+class IPCBlob;
+
+namespace IPCBlobUtils {
+
+already_AddRefed<BlobImpl> Deserialize(const IPCBlob& aIPCBlob);
+
+nsresult Serialize(BlobImpl* aBlobImpl, IPCBlob& aIPCBlob);
+
+}  // namespace IPCBlobUtils
+}  // namespace mozilla::dom
+
+namespace IPC {
+
+// ParamTraits implementation for BlobImpl. N.B: If the original BlobImpl cannot
+// be successfully serialized, a warning will be produced and a nullptr will be
+// sent over the wire. When Read()-ing a BlobImpl,
+// __always make sure to handle null!__
+template <>
+struct ParamTraits<mozilla::dom::BlobImpl*> {
+  static void Write(IPC::MessageWriter* aWriter,
+                    mozilla::dom::BlobImpl* aParam);
+  static bool Read(IPC::MessageReader* aReader,
+                   RefPtr<mozilla::dom::BlobImpl>* aResult);
+};
+
+}  // namespace IPC
+
+#endif  // mozilla_dom_IPCBlobUtils_h
diff --git a/dom/file/ipc/PFileCreator.ipdl b/dom/file/ipc/PFileCreator.ipdl
new file mode 100644
index 0000000000..d690820906
--- /dev/null
+++ b/dom/file/ipc/PFileCreator.ipdl
@@ -0,0 +1,38 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+include protocol PBackground;
+
+include IPCBlob;
+
+namespace mozilla {
+namespace dom {
+
+struct FileCreationSuccessResult
+{
+  IPCBlob blob;
+};
+
+struct FileCreationErrorResult
+{
+  nsresult errorCode;
+};
+
+union FileCreationResult
+{
+  FileCreationSuccessResult;
+  FileCreationErrorResult;
+};
+
+[ManualDealloc]
+protocol PFileCreator
+{
+  manager PBackground;
+
+child:
+  async __delete__(FileCreationResult aResult);
+};
+
+} // namespace dom 
+} // namespace mozilla
diff --git a/dom/file/ipc/PRemoteLazyInputStream.ipdl b/dom/file/ipc/PRemoteLazyInputStream.ipdl
new file mode 100644
index 0000000000..8db41db491
--- /dev/null
+++ b/dom/file/ipc/PRemoteLazyInputStream.ipdl
@@ -0,0 +1,22 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+include IPCStream;
+
+namespace mozilla {
+
+[ChildProc=any]
+protocol PRemoteLazyInputStream
+{
+parent:
+  async Clone(Endpoint<PRemoteLazyInputStreamParent> aCloneEndpoint);
+
+  async StreamNeeded(uint64_t aStart, uint64_t aLength) returns (IPCStream? stream);
+
+  async LengthNeeded() returns (int64_t length);
+
+  async Goodbye();
+};
+
+} // namespace mozilla
diff --git a/dom/file/ipc/PTemporaryIPCBlob.ipdl b/dom/file/ipc/PTemporaryIPCBlob.ipdl
new file mode 100644
index 0000000000..2645d6fd50
--- /dev/null
+++ b/dom/file/ipc/PTemporaryIPCBlob.ipdl
@@ -0,0 +1,40 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+include protocol PBackground;
+
+include IPCBlob;
+
+namespace mozilla {
+namespace dom {
+
+union IPCBlobOrError
+{
+  IPCBlob;
+  nsresult;
+};
+
+[ManualDealloc]
+protocol PTemporaryIPCBlob
+{
+  manager PBackground;
+
+  // When this actor is created on the child side, the parent will send
+  // immediatelly back a FileDescriptor or a __delete__ in case of error.
+  // When the FileDescriptor is received, the child has to call
+  // OperationDone(). When OperationDone() is received on the parent side, the
+  // parent actor will send a __delete__.
+
+child:
+  async FileDesc(FileDescriptor aFD);
+  async __delete__(IPCBlobOrError aBlobOrError);
+
+parent:
+  async OperationFailed();
+
+  async OperationDone(nsCString aContentType, FileDescriptor aFD);
+};
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/file/ipc/RemoteLazyInputStream.cpp b/dom/file/ipc/RemoteLazyInputStream.cpp
new file mode 100644
index 0000000000..51b33d9da2
--- /dev/null
+++ b/dom/file/ipc/RemoteLazyInputStream.cpp
@@ -0,0 +1,1458 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "RemoteLazyInputStream.h"
+#include "RemoteLazyInputStreamChild.h"
+#include "RemoteLazyInputStreamParent.h"
+#include "chrome/common/ipc_message_utils.h"
+#include "mozilla/ErrorNames.h"
+#include "mozilla/Logging.h"
+#include "mozilla/PRemoteLazyInputStream.h"
+#include "mozilla/ipc/Endpoint.h"
+#include "mozilla/ipc/InputStreamParams.h"
+#include "mozilla/ipc/MessageChannel.h"
+#include "mozilla/ipc/ProtocolMessageUtils.h"
+#include "mozilla/net/SocketProcessParent.h"
+#include "mozilla/SlicedInputStream.h"
+#include "mozilla/NonBlockingAsyncInputStream.h"
+#include "nsIAsyncInputStream.h"
+#include "nsIAsyncOutputStream.h"
+#include "nsID.h"
+#include "nsIInputStream.h"
+#include "nsIPipe.h"
+#include "nsNetUtil.h"
+#include "nsStreamUtils.h"
+#include "nsStringStream.h"
+#include "RemoteLazyInputStreamStorage.h"
+#include "RemoteLazyInputStreamThread.h"
+
+namespace mozilla {
+
+mozilla::LazyLogModule gRemoteLazyStreamLog("RemoteLazyStream");
+
+namespace {
+
+class InputStreamCallbackRunnable final : public DiscardableRunnable {
+ public:
+  // Note that the execution can be synchronous in case the event target is
+  // null.
+  static void Execute(already_AddRefed<nsIInputStreamCallback> aCallback,
+                      already_AddRefed<nsIEventTarget> aEventTarget,
+                      RemoteLazyInputStream* aStream) {
+    RefPtr<InputStreamCallbackRunnable> runnable =
+        new InputStreamCallbackRunnable(std::move(aCallback), aStream);
+
+    nsCOMPtr<nsIEventTarget> target = std::move(aEventTarget);
+    if (target) {
+      target->Dispatch(runnable, NS_DISPATCH_NORMAL);
+    } else {
+      runnable->Run();
+    }
+  }
+
+  NS_IMETHOD
+  Run() override {
+    mCallback->OnInputStreamReady(mStream);
+    mCallback = nullptr;
+    mStream = nullptr;
+    return NS_OK;
+  }
+
+ private:
+  InputStreamCallbackRunnable(
+      already_AddRefed<nsIInputStreamCallback> aCallback,
+      RemoteLazyInputStream* aStream)
+      : DiscardableRunnable("dom::InputStreamCallbackRunnable"),
+        mCallback(std::move(aCallback)),
+        mStream(aStream) {
+    MOZ_ASSERT(mCallback);
+    MOZ_ASSERT(mStream);
+  }
+
+  RefPtr<nsIInputStreamCallback> mCallback;
+  RefPtr<RemoteLazyInputStream> mStream;
+};
+
+class FileMetadataCallbackRunnable final : public DiscardableRunnable {
+ public:
+  static void Execute(nsIFileMetadataCallback* aCallback,
+                      nsIEventTarget* aEventTarget,
+                      RemoteLazyInputStream* aStream) {
+    MOZ_ASSERT(aCallback);
+    MOZ_ASSERT(aEventTarget);
+
+    RefPtr<FileMetadataCallbackRunnable> runnable =
+        new FileMetadataCallbackRunnable(aCallback, aStream);
+
+    nsCOMPtr<nsIEventTarget> target = aEventTarget;
+    target->Dispatch(runnable, NS_DISPATCH_NORMAL);
+  }
+
+  NS_IMETHOD
+  Run() override {
+    mCallback->OnFileMetadataReady(mStream);
+    mCallback = nullptr;
+    mStream = nullptr;
+    return NS_OK;
+  }
+
+ private:
+  FileMetadataCallbackRunnable(nsIFileMetadataCallback* aCallback,
+                               RemoteLazyInputStream* aStream)
+      : DiscardableRunnable("dom::FileMetadataCallbackRunnable"),
+        mCallback(aCallback),
+        mStream(aStream) {
+    MOZ_ASSERT(mCallback);
+    MOZ_ASSERT(mStream);
+  }
+
+  nsCOMPtr<nsIFileMetadataCallback> mCallback;
+  RefPtr<RemoteLazyInputStream> mStream;
+};
+
+}  // namespace
+
+NS_IMPL_ADDREF(RemoteLazyInputStream);
+NS_IMPL_RELEASE(RemoteLazyInputStream);
+
+NS_INTERFACE_MAP_BEGIN(RemoteLazyInputStream)
+  NS_INTERFACE_MAP_ENTRY(nsIInputStream)
+  NS_INTERFACE_MAP_ENTRY(nsIAsyncInputStream)
+  NS_INTERFACE_MAP_ENTRY(nsIInputStreamCallback)
+  NS_INTERFACE_MAP_ENTRY(nsICloneableInputStream)
+  NS_INTERFACE_MAP_ENTRY(nsICloneableInputStreamWithRange)
+  NS_INTERFACE_MAP_ENTRY(nsIIPCSerializableInputStream)
+  NS_INTERFACE_MAP_ENTRY(nsIFileMetadata)
+  NS_INTERFACE_MAP_ENTRY(nsIAsyncFileMetadata)
+  NS_INTERFACE_MAP_ENTRY(nsIInputStreamLength)
+  NS_INTERFACE_MAP_ENTRY(nsIAsyncInputStreamLength)
+  NS_INTERFACE_MAP_ENTRY(mozIRemoteLazyInputStream)
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIInputStream)
+NS_INTERFACE_MAP_END
+
+RemoteLazyInputStream::RemoteLazyInputStream(RemoteLazyInputStreamChild* aActor,
+                                             uint64_t aStart, uint64_t aLength)
+    : mStart(aStart), mLength(aLength), mState(eInit), mActor(aActor) {
+  MOZ_ASSERT(aActor);
+
+  mActor->StreamCreated();
+
+  auto storage = RemoteLazyInputStreamStorage::Get().unwrapOr(nullptr);
+  if (storage) {
+    nsCOMPtr<nsIInputStream> stream;
+    storage->GetStream(mActor->StreamID(), mStart, mLength,
+                       getter_AddRefs(stream));
+    if (stream) {
+      mState = eRunning;
+      mInnerStream = stream;
+    }
+  }
+}
+
+RemoteLazyInputStream::RemoteLazyInputStream(nsIInputStream* aStream)
+    : mStart(0), mLength(UINT64_MAX), mState(eRunning), mInnerStream(aStream) {}
+
+static already_AddRefed<RemoteLazyInputStreamChild> BindChildActor(
+    nsID aId, mozilla::ipc::Endpoint<PRemoteLazyInputStreamChild> aEndpoint) {
+  auto* thread = RemoteLazyInputStreamThread::GetOrCreate();
+  if (NS_WARN_IF(!thread)) {
+    return nullptr;
+  }
+  auto actor = MakeRefPtr<RemoteLazyInputStreamChild>(aId);
+  thread->Dispatch(
+      NS_NewRunnableFunction("RemoteLazyInputStream::BindChildActor",
+                             [actor, childEp = std::move(aEndpoint)]() mutable {
+                               bool ok = childEp.Bind(actor);
+                               MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Debug,
+                                       ("Binding child actor for %s (%p): %s",
+                                        nsIDToCString(actor->StreamID()).get(),
+                                        actor.get(), ok ? "OK" : "ERROR"));
+                             }));
+
+  return actor.forget();
+}
+
+already_AddRefed<RemoteLazyInputStream> RemoteLazyInputStream::WrapStream(
+    nsIInputStream* aInputStream) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  if (nsCOMPtr<mozIRemoteLazyInputStream> lazyStream =
+          do_QueryInterface(aInputStream)) {
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Debug,
+            ("Returning already-wrapped stream"));
+    return lazyStream.forget().downcast<RemoteLazyInputStream>();
+  }
+
+  // If we have a stream and are in the parent process, create a new actor pair
+  // and transfer ownership of the stream into storage.
+  auto streamStorage = RemoteLazyInputStreamStorage::Get();
+  if (NS_WARN_IF(streamStorage.isErr())) {
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Warning,
+            ("Cannot wrap with no storage!"));
+    return nullptr;
+  }
+
+  nsID id = nsID::GenerateUUID();
+  MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+          ("Wrapping stream %p as %s", aInputStream, nsIDToCString(id).get()));
+  streamStorage.inspect()->AddStream(aInputStream, id);
+
+  mozilla::ipc::Endpoint<PRemoteLazyInputStreamParent> parentEp;
+  mozilla::ipc::Endpoint<PRemoteLazyInputStreamChild> childEp;
+  MOZ_ALWAYS_SUCCEEDS(
+      PRemoteLazyInputStream::CreateEndpoints(&parentEp, &childEp));
+
+  // Bind the actor on our background thread.
+  streamStorage.inspect()->TaskQueue()->Dispatch(NS_NewRunnableFunction(
+      "RemoteLazyInputStreamParent::Bind",
+      [parentEp = std::move(parentEp), id]() mutable {
+        auto actor = MakeRefPtr<RemoteLazyInputStreamParent>(id);
+        bool ok = parentEp.Bind(actor);
+        MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Debug,
+                ("Binding parent actor for %s (%p): %s",
+                 nsIDToCString(id).get(), actor.get(), ok ? "OK" : "ERROR"));
+      }));
+
+  RefPtr<RemoteLazyInputStreamChild> actor =
+      BindChildActor(id, std::move(childEp));
+
+  if (!actor) {
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Warning,
+            ("Wrapping stream failed as we are probably late in shutdown!"));
+    return do_AddRef(new RemoteLazyInputStream());
+  }
+
+  return do_AddRef(new RemoteLazyInputStream(actor));
+}
+
+NS_IMETHODIMP RemoteLazyInputStream::TakeInternalStream(
+    nsIInputStream** aStream) {
+  RefPtr<RemoteLazyInputStreamChild> actor;
+  {
+    MutexAutoLock lock(mMutex);
+    if (mState == eInit || mState == ePending) {
+      return NS_BASE_STREAM_WOULD_BLOCK;
+    }
+    if (mState == eClosed) {
+      return NS_BASE_STREAM_CLOSED;
+    }
+    if (mInputStreamCallback) {
+      MOZ_ASSERT_UNREACHABLE(
+          "Do not call TakeInternalStream after calling AsyncWait");
+      return NS_ERROR_UNEXPECTED;
+    }
+
+    // Take the inner stream and return it, then close ourselves.
+    if (mInnerStream) {
+      mInnerStream.forget(aStream);
+    } else if (mAsyncInnerStream) {
+      mAsyncInnerStream.forget(aStream);
+    }
+    mState = eClosed;
+    actor = mActor.forget();
+  }
+  if (actor) {
+    actor->StreamConsumed();
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP RemoteLazyInputStream::GetInternalStreamID(nsID& aID) {
+  MutexAutoLock lock(mMutex);
+  if (!mActor) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  aID = mActor->StreamID();
+  return NS_OK;
+}
+
+RemoteLazyInputStream::~RemoteLazyInputStream() { Close(); }
+
+nsCString RemoteLazyInputStream::Describe() {
+  const char* state = "?";
+  switch (mState) {
+    case eInit:
+      state = "i";
+      break;
+    case ePending:
+      state = "p";
+      break;
+    case eRunning:
+      state = "r";
+      break;
+    case eClosed:
+      state = "c";
+      break;
+  }
+  return nsPrintfCString(
+      "[%p, %s, %s, %p%s, %s%s|%s%s]", this, state,
+      mActor ? nsIDToCString(mActor->StreamID()).get() : "<no actor>",
+      mInnerStream ? mInnerStream.get() : mAsyncInnerStream.get(),
+      mAsyncInnerStream ? "(A)" : "", mInputStreamCallback ? "I" : "",
+      mInputStreamCallbackEventTarget ? "+" : "",
+      mFileMetadataCallback ? "F" : "",
+      mFileMetadataCallbackEventTarget ? "+" : "");
+}
+
+// nsIInputStream interface
+
+NS_IMETHODIMP
+RemoteLazyInputStream::Available(uint64_t* aLength) {
+  nsCOMPtr<nsIAsyncInputStream> stream;
+  {
+    MutexAutoLock lock(mMutex);
+
+    // We don't have a remoteStream yet: let's return 0.
+    if (mState == eInit || mState == ePending) {
+      *aLength = 0;
+      return NS_OK;
+    }
+
+    if (mState == eClosed) {
+      return NS_BASE_STREAM_CLOSED;
+    }
+
+    MOZ_ASSERT(mState == eRunning);
+    MOZ_ASSERT(mInnerStream || mAsyncInnerStream);
+
+    nsresult rv = EnsureAsyncRemoteStream();
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    stream = mAsyncInnerStream;
+  }
+
+  MOZ_ASSERT(stream);
+  return stream->Available(aLength);
+}
+
+NS_IMETHODIMP
+RemoteLazyInputStream::StreamStatus() {
+  nsCOMPtr<nsIAsyncInputStream> stream;
+  {
+    MutexAutoLock lock(mMutex);
+
+    // We don't have a remoteStream yet: let's return 0.
+    if (mState == eInit || mState == ePending) {
+      return NS_OK;
+    }
+
+    if (mState == eClosed) {
+      return NS_BASE_STREAM_CLOSED;
+    }
+
+    MOZ_ASSERT(mState == eRunning);
+    MOZ_ASSERT(mInnerStream || mAsyncInnerStream);
+
+    nsresult rv = EnsureAsyncRemoteStream();
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    stream = mAsyncInnerStream;
+  }
+
+  MOZ_ASSERT(stream);
+  return stream->StreamStatus();
+}
+
+NS_IMETHODIMP
+RemoteLazyInputStream::Read(char* aBuffer, uint32_t aCount,
+                            uint32_t* aReadCount) {
+  nsCOMPtr<nsIAsyncInputStream> stream;
+  {
+    MutexAutoLock lock(mMutex);
+
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+            ("Read(%u) %s", aCount, Describe().get()));
+
+    // Read is not available is we don't have a remoteStream.
+    if (mState == eInit || mState == ePending) {
+      return NS_BASE_STREAM_WOULD_BLOCK;
+    }
+
+    if (mState == eClosed) {
+      return NS_BASE_STREAM_CLOSED;
+    }
+
+    MOZ_ASSERT(mState == eRunning);
+    MOZ_ASSERT(mInnerStream || mAsyncInnerStream);
+
+    nsresult rv = EnsureAsyncRemoteStream();
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    stream = mAsyncInnerStream;
+  }
+
+  MOZ_ASSERT(stream);
+  nsresult rv = stream->Read(aBuffer, aCount, aReadCount);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // If some data has been read, we mark the stream as consumed.
+  if (*aReadCount > 0) {
+    MarkConsumed();
+  }
+
+  MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+          ("Read %u/%u bytes", *aReadCount, aCount));
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+RemoteLazyInputStream::ReadSegments(nsWriteSegmentFun aWriter, void* aClosure,
+                                    uint32_t aCount, uint32_t* aResult) {
+  nsCOMPtr<nsIAsyncInputStream> stream;
+  {
+    MutexAutoLock lock(mMutex);
+
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+            ("ReadSegments(%u) %s", aCount, Describe().get()));
+
+    // ReadSegments is not available is we don't have a remoteStream.
+    if (mState == eInit || mState == ePending) {
+      return NS_BASE_STREAM_WOULD_BLOCK;
+    }
+
+    if (mState == eClosed) {
+      return NS_BASE_STREAM_CLOSED;
+    }
+
+    MOZ_ASSERT(mState == eRunning);
+    MOZ_ASSERT(mInnerStream || mAsyncInnerStream);
+
+    nsresult rv = EnsureAsyncRemoteStream();
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Warning,
+              ("EnsureAsyncRemoteStream failed! %s %s",
+               mozilla::GetStaticErrorName(rv), Describe().get()));
+      return rv;
+    }
+
+    stream = mAsyncInnerStream;
+  }
+
+  MOZ_ASSERT(stream);
+  nsresult rv = stream->ReadSegments(aWriter, aClosure, aCount, aResult);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // If some data has been read, we mark the stream as consumed.
+  if (*aResult != 0) {
+    MarkConsumed();
+  }
+
+  MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+          ("ReadSegments %u/%u bytes", *aResult, aCount));
+
+  return NS_OK;
+}
+
+void RemoteLazyInputStream::MarkConsumed() {
+  RefPtr<RemoteLazyInputStreamChild> actor;
+  {
+    MutexAutoLock lock(mMutex);
+    if (mActor) {
+      MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Debug,
+              ("MarkConsumed %s", Describe().get()));
+    }
+
+    actor = mActor.forget();
+  }
+  if (actor) {
+    actor->StreamConsumed();
+  }
+}
+
+NS_IMETHODIMP
+RemoteLazyInputStream::IsNonBlocking(bool* aNonBlocking) {
+  *aNonBlocking = true;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+RemoteLazyInputStream::Close() {
+  RefPtr<RemoteLazyInputStreamChild> actor;
+
+  nsCOMPtr<nsIAsyncInputStream> asyncInnerStream;
+  nsCOMPtr<nsIInputStream> innerStream;
+
+  RefPtr<nsIInputStreamCallback> inputStreamCallback;
+  nsCOMPtr<nsIEventTarget> inputStreamCallbackEventTarget;
+
+  {
+    MutexAutoLock lock(mMutex);
+    if (mState == eClosed) {
+      return NS_OK;
+    }
+
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Debug,
+            ("Close %s", Describe().get()));
+
+    actor = mActor.forget();
+
+    asyncInnerStream = mAsyncInnerStream.forget();
+    innerStream = mInnerStream.forget();
+
+    // TODO(Bug 1737783): Notify to the mFileMetadataCallback that this
+    // lazy input stream has been closed.
+    mFileMetadataCallback = nullptr;
+    mFileMetadataCallbackEventTarget = nullptr;
+
+    inputStreamCallback = mInputStreamCallback.forget();
+    inputStreamCallbackEventTarget = mInputStreamCallbackEventTarget.forget();
+
+    mState = eClosed;
+  }
+
+  if (actor) {
+    actor->StreamConsumed();
+  }
+
+  if (inputStreamCallback) {
+    InputStreamCallbackRunnable::Execute(
+        inputStreamCallback.forget(), inputStreamCallbackEventTarget.forget(),
+        this);
+  }
+
+  if (asyncInnerStream) {
+    asyncInnerStream->CloseWithStatus(NS_BASE_STREAM_CLOSED);
+  }
+
+  if (innerStream) {
+    innerStream->Close();
+  }
+
+  return NS_OK;
+}
+
+// nsICloneableInputStream interface
+
+NS_IMETHODIMP
+RemoteLazyInputStream::GetCloneable(bool* aCloneable) {
+  *aCloneable = true;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+RemoteLazyInputStream::Clone(nsIInputStream** aResult) {
+  return CloneWithRange(0, UINT64_MAX, aResult);
+}
+
+// nsICloneableInputStreamWithRange interface
+
+NS_IMETHODIMP
+RemoteLazyInputStream::CloneWithRange(uint64_t aStart, uint64_t aLength,
+                                      nsIInputStream** aResult) {
+  MutexAutoLock lock(mMutex);
+  MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Debug,
+          ("CloneWithRange %" PRIu64 " %" PRIu64 " %s", aStart, aLength,
+           Describe().get()));
+
+  nsresult rv;
+
+  RefPtr<RemoteLazyInputStream> stream;
+  if (mState == eClosed) {
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose, ("Cloning closed stream"));
+    stream = new RemoteLazyInputStream();
+    stream.forget(aResult);
+    return NS_OK;
+  }
+
+  uint64_t start = 0;
+  uint64_t length = 0;
+  auto maxLength = CheckedUint64(mLength) - aStart;
+  if (maxLength.isValid()) {
+    start = mStart + aStart;
+    length = std::min(maxLength.value(), aLength);
+  }
+
+  // If the slice would be empty, wrap an empty input stream and return it.
+  if (length == 0) {
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose, ("Creating empty stream"));
+
+    nsCOMPtr<nsIInputStream> emptyStream;
+    rv = NS_NewCStringInputStream(getter_AddRefs(emptyStream), ""_ns);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    stream = new RemoteLazyInputStream(emptyStream);
+    stream.forget(aResult);
+    return NS_OK;
+  }
+
+  // If we still have a connection to our actor, that means we haven't read any
+  // data yet, and can clone + slice by building a new stream backed by the same
+  // actor.
+  if (mActor) {
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+            ("Cloning stream with actor"));
+
+    stream = new RemoteLazyInputStream(mActor, start, length);
+    stream.forget(aResult);
+    return NS_OK;
+  }
+
+  // We no longer have our actor, either because we were constructed without
+  // one, or we've already begun reading. Perform the clone locally on our inner
+  // input stream.
+
+  nsCOMPtr<nsIInputStream> innerStream = mInnerStream;
+  if (mAsyncInnerStream) {
+    innerStream = mAsyncInnerStream;
+  }
+
+  nsCOMPtr<nsICloneableInputStream> cloneable = do_QueryInterface(innerStream);
+  if (!cloneable || !cloneable->GetCloneable()) {
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+            ("Cloning non-cloneable stream - copying to pipe"));
+
+    // If our internal stream isn't cloneable, to perform a clone we'll need to
+    // copy into a pipe and replace our internal stream.
+    nsCOMPtr<nsIAsyncInputStream> pipeIn;
+    nsCOMPtr<nsIAsyncOutputStream> pipeOut;
+    NS_NewPipe2(getter_AddRefs(pipeIn), getter_AddRefs(pipeOut), true, true);
+
+    RefPtr<RemoteLazyInputStreamThread> thread =
+        RemoteLazyInputStreamThread::GetOrCreate();
+    if (NS_WARN_IF(!thread)) {
+      return NS_ERROR_ILLEGAL_DURING_SHUTDOWN;
+    }
+
+    mAsyncInnerStream = pipeIn;
+    mInnerStream = nullptr;
+
+    // If we have a callback pending, we need to re-call AsyncWait on the inner
+    // stream. This should not re-enter us immediately, as `pipeIn` hasn't been
+    // sent any data yet, but we may be called again as soon as `NS_AsyncCopy`
+    // has begun copying.
+    if (mInputStreamCallback) {
+      mAsyncInnerStream->AsyncWait(this, mInputStreamCallbackFlags,
+                                   mInputStreamCallbackRequestedCount,
+                                   mInputStreamCallbackEventTarget);
+    }
+
+    rv = NS_AsyncCopy(innerStream, pipeOut, thread,
+                      NS_ASYNCCOPY_VIA_WRITESEGMENTS);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      // The copy failed, revert the changes we did and restore our previous
+      // inner stream.
+      mAsyncInnerStream = nullptr;
+      mInnerStream = innerStream;
+      return rv;
+    }
+
+    cloneable = do_QueryInterface(mAsyncInnerStream);
+  }
+
+  MOZ_ASSERT(cloneable && cloneable->GetCloneable());
+
+  // Check if we can clone more efficiently with a range.
+  if (length < UINT64_MAX) {
+    if (nsCOMPtr<nsICloneableInputStreamWithRange> cloneableWithRange =
+            do_QueryInterface(cloneable)) {
+      MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose, ("Cloning with range"));
+      nsCOMPtr<nsIInputStream> cloned;
+      rv = cloneableWithRange->CloneWithRange(start, length,
+                                              getter_AddRefs(cloned));
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      stream = new RemoteLazyInputStream(cloned);
+      stream.forget(aResult);
+      return NS_OK;
+    }
+  }
+
+  // Directly clone our inner stream, and then slice it if needed.
+  nsCOMPtr<nsIInputStream> cloned;
+  rv = cloneable->Clone(getter_AddRefs(cloned));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (length < UINT64_MAX) {
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+            ("Slicing stream with %" PRIu64 " %" PRIu64, start, length));
+    cloned = new SlicedInputStream(cloned.forget(), start, length);
+  }
+
+  stream = new RemoteLazyInputStream(cloned);
+  stream.forget(aResult);
+  return NS_OK;
+}
+
+// nsIAsyncInputStream interface
+
+NS_IMETHODIMP
+RemoteLazyInputStream::CloseWithStatus(nsresult aStatus) { return Close(); }
+
+NS_IMETHODIMP
+RemoteLazyInputStream::AsyncWait(nsIInputStreamCallback* aCallback,
+                                 uint32_t aFlags, uint32_t aRequestedCount,
+                                 nsIEventTarget* aEventTarget) {
+  // Ensure we always have an event target for AsyncWait callbacks, so that
+  // calls to `AsyncWait` cannot reenter us with `OnInputStreamReady`.
+  nsCOMPtr<nsIEventTarget> eventTarget = aEventTarget;
+  if (aCallback && !eventTarget) {
+    eventTarget = RemoteLazyInputStreamThread::GetOrCreate();
+    if (NS_WARN_IF(!eventTarget)) {
+      return NS_ERROR_ILLEGAL_DURING_SHUTDOWN;
+    }
+  }
+
+  {
+    MutexAutoLock lock(mMutex);
+
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+            ("AsyncWait(%p, %u, %u, %p) %s", aCallback, aFlags, aRequestedCount,
+             aEventTarget, Describe().get()));
+
+    // See RemoteLazyInputStream.h for more information about this state
+    // machine.
+
+    nsCOMPtr<nsIAsyncInputStream> stream;
+    switch (mState) {
+      // First call, we need to retrieve the stream from the parent actor.
+      case eInit:
+        MOZ_ASSERT(mActor);
+
+        mInputStreamCallback = aCallback;
+        mInputStreamCallbackEventTarget = eventTarget;
+        mInputStreamCallbackFlags = aFlags;
+        mInputStreamCallbackRequestedCount = aRequestedCount;
+        mState = ePending;
+
+        StreamNeeded();
+        return NS_OK;
+
+      // We are still waiting for the remote inputStream
+      case ePending: {
+        if (NS_WARN_IF(mInputStreamCallback && aCallback &&
+                       mInputStreamCallback != aCallback)) {
+          return NS_ERROR_FAILURE;
+        }
+
+        mInputStreamCallback = aCallback;
+        mInputStreamCallbackEventTarget = eventTarget;
+        mInputStreamCallbackFlags = aFlags;
+        mInputStreamCallbackRequestedCount = aRequestedCount;
+        return NS_OK;
+      }
+
+      // We have the remote inputStream, let's check if we can execute the
+      // callback.
+      case eRunning: {
+        if (NS_WARN_IF(mInputStreamCallback && aCallback &&
+                       mInputStreamCallback != aCallback)) {
+          return NS_ERROR_FAILURE;
+        }
+
+        nsresult rv = EnsureAsyncRemoteStream();
+        if (NS_WARN_IF(NS_FAILED(rv))) {
+          return rv;
+        }
+
+        mInputStreamCallback = aCallback;
+        mInputStreamCallbackEventTarget = eventTarget;
+        mInputStreamCallbackFlags = aFlags;
+        mInputStreamCallbackRequestedCount = aRequestedCount;
+
+        stream = mAsyncInnerStream;
+        break;
+      }
+
+      case eClosed:
+        [[fallthrough]];
+      default:
+        MOZ_ASSERT(mState == eClosed);
+        if (NS_WARN_IF(mInputStreamCallback && aCallback &&
+                       mInputStreamCallback != aCallback)) {
+          return NS_ERROR_FAILURE;
+        }
+        break;
+    }
+
+    if (stream) {
+      return stream->AsyncWait(aCallback ? this : nullptr, aFlags,
+                               aRequestedCount, eventTarget);
+    }
+  }
+
+  if (aCallback) {
+    // if stream is nullptr here, that probably means the stream has
+    // been closed and the callback can be executed immediately
+    InputStreamCallbackRunnable::Execute(do_AddRef(aCallback),
+                                         do_AddRef(eventTarget), this);
+  }
+  return NS_OK;
+}
+
+void RemoteLazyInputStream::StreamNeeded() {
+  MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Debug,
+          ("StreamNeeded %s", Describe().get()));
+
+  auto* thread = RemoteLazyInputStreamThread::GetOrCreate();
+  if (NS_WARN_IF(!thread)) {
+    return;
+  }
+  thread->Dispatch(NS_NewRunnableFunction(
+      "RemoteLazyInputStream::StreamNeeded",
+      [self = RefPtr{this}, actor = mActor, start = mStart, length = mLength] {
+        MOZ_LOG(
+            gRemoteLazyStreamLog, LogLevel::Debug,
+            ("Sending StreamNeeded(%" PRIu64 " %" PRIu64 ") %s %d", start,
+             length, nsIDToCString(actor->StreamID()).get(), actor->CanSend()));
+
+        actor->SendStreamNeeded(
+            start, length,
+            [self](const Maybe<mozilla::ipc::IPCStream>& aStream) {
+              // Try to deserialize the stream from our remote, and close our
+              // stream if it fails.
+              nsCOMPtr<nsIInputStream> stream =
+                  mozilla::ipc::DeserializeIPCStream(aStream);
+              if (NS_WARN_IF(!stream)) {
+                NS_WARNING("Failed to deserialize IPC stream");
+                self->Close();
+              }
+
+              // Lock our mutex to update the inner stream, and collect any
+              // callbacks which we need to invoke.
+              MutexAutoLock lock(self->mMutex);
+
+              MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Debug,
+                      ("ResolveStreamNeeded(%p) %s", stream.get(),
+                       self->Describe().get()));
+
+              if (self->mState == ePending) {
+                self->mInnerStream = stream.forget();
+                self->mState = eRunning;
+
+                // Notify any listeners that we've now acquired the underlying
+                // stream, so file metadata information will be available.
+                nsCOMPtr<nsIFileMetadataCallback> fileMetadataCallback =
+                    self->mFileMetadataCallback.forget();
+                nsCOMPtr<nsIEventTarget> fileMetadataCallbackEventTarget =
+                    self->mFileMetadataCallbackEventTarget.forget();
+                if (fileMetadataCallback) {
+                  FileMetadataCallbackRunnable::Execute(
+                      fileMetadataCallback, fileMetadataCallbackEventTarget,
+                      self);
+                }
+
+                // **NOTE** we can re-enter this class here **NOTE**
+                // If we already have an input stream callback, attempt to
+                // register ourselves with AsyncWait on the underlying stream.
+                if (self->mInputStreamCallback) {
+                  if (NS_FAILED(self->EnsureAsyncRemoteStream()) ||
+                      NS_FAILED(self->mAsyncInnerStream->AsyncWait(
+                          self, self->mInputStreamCallbackFlags,
+                          self->mInputStreamCallbackRequestedCount,
+                          self->mInputStreamCallbackEventTarget))) {
+                    InputStreamCallbackRunnable::Execute(
+                        self->mInputStreamCallback.forget(),
+                        self->mInputStreamCallbackEventTarget.forget(), self);
+                  }
+                }
+              }
+
+              if (stream) {
+                NS_WARNING("Failed to save stream, closing it");
+                stream->Close();
+              }
+            },
+            [self](mozilla::ipc::ResponseRejectReason) {
+              NS_WARNING("SendStreamNeeded rejected");
+              self->Close();
+            });
+      }));
+}
+
+// nsIInputStreamCallback
+
+NS_IMETHODIMP
+RemoteLazyInputStream::OnInputStreamReady(nsIAsyncInputStream* aStream) {
+  RefPtr<nsIInputStreamCallback> callback;
+  nsCOMPtr<nsIEventTarget> callbackEventTarget;
+  {
+    MutexAutoLock lock(mMutex);
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Debug,
+            ("OnInputStreamReady %s", Describe().get()));
+
+    // We have been closed in the meantime.
+    if (mState == eClosed) {
+      return NS_OK;
+    }
+
+    // We got a callback from the wrong stream, likely due to a `CloneWithRange`
+    // call while we were waiting. Ignore this callback.
+    if (mAsyncInnerStream != aStream) {
+      return NS_OK;
+    }
+
+    MOZ_ASSERT(mState == eRunning);
+
+    // The callback has been canceled in the meantime.
+    if (!mInputStreamCallback) {
+      return NS_OK;
+    }
+
+    callback.swap(mInputStreamCallback);
+    callbackEventTarget.swap(mInputStreamCallbackEventTarget);
+  }
+
+  // This must be the last operation because the execution of the callback can
+  // be synchronous.
+  MOZ_ASSERT(callback);
+  InputStreamCallbackRunnable::Execute(callback.forget(),
+                                       callbackEventTarget.forget(), this);
+  return NS_OK;
+}
+
+// nsIIPCSerializableInputStream
+
+void RemoteLazyInputStream::SerializedComplexity(uint32_t aMaxSize,
+                                                 uint32_t* aSizeUsed,
+                                                 uint32_t* aNewPipes,
+                                                 uint32_t* aTransferables) {
+  *aTransferables = 1;
+}
+
+void RemoteLazyInputStream::Serialize(mozilla::ipc::InputStreamParams& aParams,
+                                      uint32_t aMaxSize, uint32_t* aSizeUsed) {
+  *aSizeUsed = 0;
+  aParams = mozilla::ipc::RemoteLazyInputStreamParams(WrapNotNull(this));
+}
+
+bool RemoteLazyInputStream::Deserialize(
+    const mozilla::ipc::InputStreamParams& aParams) {
+  MOZ_CRASH("This should never be called.");
+  return false;
+}
+
+// nsIAsyncFileMetadata
+
+NS_IMETHODIMP
+RemoteLazyInputStream::AsyncFileMetadataWait(nsIFileMetadataCallback* aCallback,
+                                             nsIEventTarget* aEventTarget) {
+  MOZ_ASSERT(!!aCallback == !!aEventTarget);
+
+  // If we have the callback, we must have the event target.
+  if (NS_WARN_IF(!!aCallback != !!aEventTarget)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // See RemoteLazyInputStream.h for more information about this state
+  // machine.
+
+  {
+    MutexAutoLock lock(mMutex);
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Debug,
+            ("AsyncFileMetadataWait(%p, %p) %s", aCallback, aEventTarget,
+             Describe().get()));
+
+    switch (mState) {
+      // First call, we need to retrieve the stream from the parent actor.
+      case eInit:
+        MOZ_ASSERT(mActor);
+
+        mFileMetadataCallback = aCallback;
+        mFileMetadataCallbackEventTarget = aEventTarget;
+        mState = ePending;
+
+        StreamNeeded();
+        return NS_OK;
+
+      // We are still waiting for the remote inputStream
+      case ePending:
+        if (mFileMetadataCallback && aCallback) {
+          return NS_ERROR_FAILURE;
+        }
+
+        mFileMetadataCallback = aCallback;
+        mFileMetadataCallbackEventTarget = aEventTarget;
+        return NS_OK;
+
+      // We have the remote inputStream, let's check if we can execute the
+      // callback.
+      case eRunning:
+        break;
+
+      // Stream is closed.
+      default:
+        MOZ_ASSERT(mState == eClosed);
+        return NS_BASE_STREAM_CLOSED;
+    }
+
+    MOZ_ASSERT(mState == eRunning);
+  }
+
+  FileMetadataCallbackRunnable::Execute(aCallback, aEventTarget, this);
+  return NS_OK;
+}
+
+// nsIFileMetadata
+
+NS_IMETHODIMP
+RemoteLazyInputStream::GetSize(int64_t* aRetval) {
+  nsCOMPtr<nsIFileMetadata> fileMetadata;
+  {
+    MutexAutoLock lock(mMutex);
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+            ("GetSize %s", Describe().get()));
+
+    fileMetadata = do_QueryInterface(mInnerStream);
+    if (!fileMetadata) {
+      return mState == eClosed ? NS_BASE_STREAM_CLOSED : NS_ERROR_FAILURE;
+    }
+  }
+
+  return fileMetadata->GetSize(aRetval);
+}
+
+NS_IMETHODIMP
+RemoteLazyInputStream::GetLastModified(int64_t* aRetval) {
+  nsCOMPtr<nsIFileMetadata> fileMetadata;
+  {
+    MutexAutoLock lock(mMutex);
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+            ("GetLastModified %s", Describe().get()));
+
+    fileMetadata = do_QueryInterface(mInnerStream);
+    if (!fileMetadata) {
+      return mState == eClosed ? NS_BASE_STREAM_CLOSED : NS_ERROR_FAILURE;
+    }
+  }
+
+  return fileMetadata->GetLastModified(aRetval);
+}
+
+NS_IMETHODIMP
+RemoteLazyInputStream::GetFileDescriptor(PRFileDesc** aRetval) {
+  nsCOMPtr<nsIFileMetadata> fileMetadata;
+  {
+    MutexAutoLock lock(mMutex);
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+            ("GetFileDescriptor %s", Describe().get()));
+
+    fileMetadata = do_QueryInterface(mInnerStream);
+    if (!fileMetadata) {
+      return mState == eClosed ? NS_BASE_STREAM_CLOSED : NS_ERROR_FAILURE;
+    }
+  }
+
+  return fileMetadata->GetFileDescriptor(aRetval);
+}
+
+nsresult RemoteLazyInputStream::EnsureAsyncRemoteStream() {
+  // We already have an async remote stream.
+  if (mAsyncInnerStream) {
+    return NS_OK;
+  }
+
+  MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Debug,
+          ("EnsureAsyncRemoteStream %s", Describe().get()));
+
+  if (NS_WARN_IF(!mInnerStream)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsCOMPtr<nsIInputStream> stream = mInnerStream;
+
+  // Check if the stream is blocking, if it is, we want to make it non-blocking
+  // using a pipe.
+  bool nonBlocking = false;
+  nsresult rv = stream->IsNonBlocking(&nonBlocking);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // We don't return NS_ERROR_NOT_IMPLEMENTED from ReadSegments,
+  // so it's possible that callers are expecting us to succeed in the future.
+  // We need to make sure the stream we return here supports ReadSegments,
+  // so wrap if in a buffered stream if necessary.
+  //
+  // We only need to do this if we won't be wrapping the stream in a pipe, which
+  // will add buffering anyway.
+  if (nonBlocking && !NS_InputStreamIsBuffered(stream)) {
+    nsCOMPtr<nsIInputStream> bufferedStream;
+    nsresult rv = NS_NewBufferedInputStream(getter_AddRefs(bufferedStream),
+                                            stream.forget(), 4096);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    stream = bufferedStream;
+  }
+
+  nsCOMPtr<nsIAsyncInputStream> asyncStream = do_QueryInterface(stream);
+
+  // If non-blocking and non-async, let's use NonBlockingAsyncInputStream.
+  if (nonBlocking && !asyncStream) {
+    rv = NonBlockingAsyncInputStream::Create(stream.forget(),
+                                             getter_AddRefs(asyncStream));
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    MOZ_ASSERT(asyncStream);
+  }
+
+  if (!asyncStream) {
+    // Let's make the stream async using the DOMFile thread.
+    nsCOMPtr<nsIAsyncInputStream> pipeIn;
+    nsCOMPtr<nsIAsyncOutputStream> pipeOut;
+    NS_NewPipe2(getter_AddRefs(pipeIn), getter_AddRefs(pipeOut), true, true);
+
+    RefPtr<RemoteLazyInputStreamThread> thread =
+        RemoteLazyInputStreamThread::GetOrCreate();
+    if (NS_WARN_IF(!thread)) {
+      return NS_ERROR_ILLEGAL_DURING_SHUTDOWN;
+    }
+
+    rv = NS_AsyncCopy(stream, pipeOut, thread, NS_ASYNCCOPY_VIA_WRITESEGMENTS);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    asyncStream = pipeIn;
+  }
+
+  MOZ_ASSERT(asyncStream);
+  mAsyncInnerStream = asyncStream;
+  mInnerStream = nullptr;
+
+  return NS_OK;
+}
+
+// nsIInputStreamLength
+
+NS_IMETHODIMP
+RemoteLazyInputStream::Length(int64_t* aLength) {
+  MutexAutoLock lock(mMutex);
+
+  if (mState == eClosed) {
+    return NS_BASE_STREAM_CLOSED;
+  }
+
+  if (!mActor) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  return NS_BASE_STREAM_WOULD_BLOCK;
+}
+
+namespace {
+
+class InputStreamLengthCallbackRunnable final : public DiscardableRunnable {
+ public:
+  static void Execute(nsIInputStreamLengthCallback* aCallback,
+                      nsIEventTarget* aEventTarget,
+                      RemoteLazyInputStream* aStream, int64_t aLength) {
+    MOZ_ASSERT(aCallback);
+    MOZ_ASSERT(aEventTarget);
+
+    RefPtr<InputStreamLengthCallbackRunnable> runnable =
+        new InputStreamLengthCallbackRunnable(aCallback, aStream, aLength);
+
+    nsCOMPtr<nsIEventTarget> target = aEventTarget;
+    target->Dispatch(runnable, NS_DISPATCH_NORMAL);
+  }
+
+  NS_IMETHOD
+  Run() override {
+    mCallback->OnInputStreamLengthReady(mStream, mLength);
+    mCallback = nullptr;
+    mStream = nullptr;
+    return NS_OK;
+  }
+
+ private:
+  InputStreamLengthCallbackRunnable(nsIInputStreamLengthCallback* aCallback,
+                                    RemoteLazyInputStream* aStream,
+                                    int64_t aLength)
+      : DiscardableRunnable("dom::InputStreamLengthCallbackRunnable"),
+        mCallback(aCallback),
+        mStream(aStream),
+        mLength(aLength) {
+    MOZ_ASSERT(mCallback);
+    MOZ_ASSERT(mStream);
+  }
+
+  nsCOMPtr<nsIInputStreamLengthCallback> mCallback;
+  RefPtr<RemoteLazyInputStream> mStream;
+  const int64_t mLength;
+};
+
+}  // namespace
+
+// nsIAsyncInputStreamLength
+
+NS_IMETHODIMP
+RemoteLazyInputStream::AsyncLengthWait(nsIInputStreamLengthCallback* aCallback,
+                                       nsIEventTarget* aEventTarget) {
+  // If we have the callback, we must have the event target.
+  if (NS_WARN_IF(!!aCallback != !!aEventTarget)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  {
+    MutexAutoLock lock(mMutex);
+
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+            ("AsyncLengthWait(%p, %p) %s", aCallback, aEventTarget,
+             Describe().get()));
+
+    if (mActor) {
+      if (aCallback) {
+        auto* thread = RemoteLazyInputStreamThread::GetOrCreate();
+        if (NS_WARN_IF(!thread)) {
+          return NS_ERROR_ILLEGAL_DURING_SHUTDOWN;
+        }
+        thread->Dispatch(NS_NewRunnableFunction(
+            "RemoteLazyInputStream::AsyncLengthWait",
+            [self = RefPtr{this}, actor = mActor,
+             callback = nsCOMPtr{aCallback},
+             eventTarget = nsCOMPtr{aEventTarget}] {
+              actor->SendLengthNeeded(
+                  [self, callback, eventTarget](int64_t aLength) {
+                    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+                            ("AsyncLengthWait resolve %" PRId64, aLength));
+                    int64_t length = -1;
+                    if (aLength > 0) {
+                      uint64_t sourceLength =
+                          aLength - std::min<uint64_t>(aLength, self->mStart);
+                      length = int64_t(
+                          std::min<uint64_t>(sourceLength, self->mLength));
+                    }
+                    InputStreamLengthCallbackRunnable::Execute(
+                        callback, eventTarget, self, length);
+                  },
+                  [self, callback,
+                   eventTarget](mozilla::ipc::ResponseRejectReason) {
+                    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Warning,
+                            ("AsyncLengthWait reject"));
+                    InputStreamLengthCallbackRunnable::Execute(
+                        callback, eventTarget, self, -1);
+                  });
+            }));
+      }
+
+      return NS_OK;
+    }
+  }
+
+  MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+          ("AsyncLengthWait immediate"));
+
+  // If execution has reached here, it means the stream is either closed or
+  // consumed, and therefore the callback can be executed immediately
+  InputStreamLengthCallbackRunnable::Execute(aCallback, aEventTarget, this, -1);
+  return NS_OK;
+}
+
+void RemoteLazyInputStream::IPCWrite(IPC::MessageWriter* aWriter) {
+  // If we have an actor still, serialize efficiently by cloning our actor to
+  // maintain a reference to the parent side.
+  RefPtr<RemoteLazyInputStreamChild> actor;
+
+  nsCOMPtr<nsIInputStream> innerStream;
+
+  RefPtr<nsIInputStreamCallback> inputStreamCallback;
+  nsCOMPtr<nsIEventTarget> inputStreamCallbackEventTarget;
+
+  {
+    MutexAutoLock lock(mMutex);
+
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+            ("Serialize %s", Describe().get()));
+
+    actor = mActor.forget();
+
+    if (mAsyncInnerStream) {
+      MOZ_ASSERT(!mInnerStream);
+      innerStream = mAsyncInnerStream.forget();
+    } else {
+      innerStream = mInnerStream.forget();
+    }
+
+    // TODO(Bug 1737783): Notify to the mFileMetadataCallback that this
+    // lazy input stream has been closed.
+    mFileMetadataCallback = nullptr;
+    mFileMetadataCallbackEventTarget = nullptr;
+
+    inputStreamCallback = mInputStreamCallback.forget();
+    inputStreamCallbackEventTarget = mInputStreamCallbackEventTarget.forget();
+
+    mState = eClosed;
+  }
+
+  if (inputStreamCallback) {
+    InputStreamCallbackRunnable::Execute(
+        inputStreamCallback.forget(), inputStreamCallbackEventTarget.forget(),
+        this);
+  }
+
+  bool closed = !actor && !innerStream;
+  IPC::WriteParam(aWriter, closed);
+  if (closed) {
+    return;
+  }
+
+  // If we still have a connection to our remote actor, create a clone endpoint
+  // for it and tell it that the stream has been consumed. The clone of the
+  // connection can be transferred to another process.
+  if (actor) {
+    MOZ_LOG(
+        gRemoteLazyStreamLog, LogLevel::Debug,
+        ("Serializing as actor: %s", nsIDToCString(actor->StreamID()).get()));
+    // Create a clone of the actor, and then tell it that this stream is no
+    // longer referencing it.
+    mozilla::ipc::Endpoint<PRemoteLazyInputStreamParent> parentEp;
+    mozilla::ipc::Endpoint<PRemoteLazyInputStreamChild> childEp;
+    MOZ_ALWAYS_SUCCEEDS(
+        PRemoteLazyInputStream::CreateEndpoints(&parentEp, &childEp));
+
+    auto* thread = RemoteLazyInputStreamThread::GetOrCreate();
+    if (thread) {
+      thread->Dispatch(NS_NewRunnableFunction(
+          "RemoteLazyInputStreamChild::SendClone",
+          [actor, parentEp = std::move(parentEp)]() mutable {
+            bool ok = actor->SendClone(std::move(parentEp));
+            MOZ_LOG(
+                gRemoteLazyStreamLog, LogLevel::Verbose,
+                ("SendClone for %s: %s", nsIDToCString(actor->StreamID()).get(),
+                 ok ? "OK" : "ERR"));
+          }));
+
+    }  // else we are shutting down xpcom threads.
+
+    // NOTE: Call `StreamConsumed` after dispatching the `SendClone` runnable,
+    // as this method may dispatch a runnable to `RemoteLazyInputStreamThread`
+    // to call `SendGoodbye`, which needs to happen after `SendClone`.
+    actor->StreamConsumed();
+
+    IPC::WriteParam(aWriter, actor->StreamID());
+    IPC::WriteParam(aWriter, mStart);
+    IPC::WriteParam(aWriter, mLength);
+    IPC::WriteParam(aWriter, std::move(childEp));
+
+    if (innerStream) {
+      innerStream->Close();
+    }
+    return;
+  }
+
+  // If we have a stream and are in the parent process, create a new actor pair
+  // and transfer ownership of the stream into storage.
+  auto streamStorage = RemoteLazyInputStreamStorage::Get();
+  if (streamStorage.isOk()) {
+    MOZ_ASSERT(XRE_IsParentProcess());
+    nsID id = nsID::GenerateUUID();
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Debug,
+            ("Serializing as new stream: %s", nsIDToCString(id).get()));
+
+    streamStorage.inspect()->AddStream(innerStream, id);
+
+    mozilla::ipc::Endpoint<PRemoteLazyInputStreamParent> parentEp;
+    mozilla::ipc::Endpoint<PRemoteLazyInputStreamChild> childEp;
+    MOZ_ALWAYS_SUCCEEDS(
+        PRemoteLazyInputStream::CreateEndpoints(&parentEp, &childEp));
+
+    // Bind the actor on our background thread.
+    streamStorage.inspect()->TaskQueue()->Dispatch(NS_NewRunnableFunction(
+        "RemoteLazyInputStreamParent::Bind",
+        [parentEp = std::move(parentEp), id]() mutable {
+          auto stream = MakeRefPtr<RemoteLazyInputStreamParent>(id);
+          parentEp.Bind(stream);
+        }));
+
+    IPC::WriteParam(aWriter, id);
+    IPC::WriteParam(aWriter, 0);
+    IPC::WriteParam(aWriter, UINT64_MAX);
+    IPC::WriteParam(aWriter, std::move(childEp));
+    return;
+  }
+
+  MOZ_CRASH("Cannot serialize new RemoteLazyInputStream from this process");
+}
+
+already_AddRefed<RemoteLazyInputStream> RemoteLazyInputStream::IPCRead(
+    IPC::MessageReader* aReader) {
+  MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose, ("Deserialize"));
+
+  bool closed;
+  if (NS_WARN_IF(!IPC::ReadParam(aReader, &closed))) {
+    return nullptr;
+  }
+  if (closed) {
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+            ("Deserialize closed stream"));
+    return do_AddRef(new RemoteLazyInputStream());
+  }
+
+  nsID id{};
+  uint64_t start;
+  uint64_t length;
+  mozilla::ipc::Endpoint<PRemoteLazyInputStreamChild> endpoint;
+  if (NS_WARN_IF(!IPC::ReadParam(aReader, &id)) ||
+      NS_WARN_IF(!IPC::ReadParam(aReader, &start)) ||
+      NS_WARN_IF(!IPC::ReadParam(aReader, &length)) ||
+      NS_WARN_IF(!IPC::ReadParam(aReader, &endpoint))) {
+    return nullptr;
+  }
+
+  if (!endpoint.IsValid()) {
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Warning,
+            ("Deserialize failed due to invalid endpoint!"));
+    return do_AddRef(new RemoteLazyInputStream());
+  }
+
+  RefPtr<RemoteLazyInputStreamChild> actor =
+      BindChildActor(id, std::move(endpoint));
+
+  if (!actor) {
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Warning,
+            ("Deserialize failed as we are probably late in shutdown!"));
+    return do_AddRef(new RemoteLazyInputStream());
+  }
+
+  return do_AddRef(new RemoteLazyInputStream(actor, start, length));
+}
+
+}  // namespace mozilla
+
+void IPC::ParamTraits<mozilla::RemoteLazyInputStream*>::Write(
+    IPC::MessageWriter* aWriter, mozilla::RemoteLazyInputStream* aParam) {
+  bool nonNull = !!aParam;
+  IPC::WriteParam(aWriter, nonNull);
+  if (aParam) {
+    aParam->IPCWrite(aWriter);
+  }
+}
+
+bool IPC::ParamTraits<mozilla::RemoteLazyInputStream*>::Read(
+    IPC::MessageReader* aReader,
+    RefPtr<mozilla::RemoteLazyInputStream>* aResult) {
+  bool nonNull = false;
+  if (!IPC::ReadParam(aReader, &nonNull)) {
+    return false;
+  }
+  if (!nonNull) {
+    *aResult = nullptr;
+    return true;
+  }
+  *aResult = mozilla::RemoteLazyInputStream::IPCRead(aReader);
+  return *aResult;
+}
diff --git a/dom/file/ipc/RemoteLazyInputStream.h b/dom/file/ipc/RemoteLazyInputStream.h
new file mode 100644
index 0000000000..08bb168e27
--- /dev/null
+++ b/dom/file/ipc/RemoteLazyInputStream.h
@@ -0,0 +1,155 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_RemoteLazyInputStream_h
+#define mozilla_RemoteLazyInputStream_h
+
+#include "chrome/common/ipc_message_utils.h"
+#include "mozilla/Mutex.h"
+#include "mozIRemoteLazyInputStream.h"
+#include "nsIAsyncInputStream.h"
+#include "nsICloneableInputStream.h"
+#include "nsIFileStreams.h"
+#include "nsIIPCSerializableInputStream.h"
+#include "nsIInputStreamLength.h"
+#include "nsCOMPtr.h"
+
+namespace mozilla {
+
+class RemoteLazyInputStreamChild;
+
+class RemoteLazyInputStream final : public nsIAsyncInputStream,
+                                    public nsIInputStreamCallback,
+                                    public nsICloneableInputStreamWithRange,
+                                    public nsIIPCSerializableInputStream,
+                                    public nsIAsyncFileMetadata,
+                                    public nsIInputStreamLength,
+                                    public nsIAsyncInputStreamLength,
+                                    public mozIRemoteLazyInputStream {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIINPUTSTREAM
+  NS_DECL_NSIASYNCINPUTSTREAM
+  NS_DECL_NSIINPUTSTREAMCALLBACK
+  NS_DECL_NSICLONEABLEINPUTSTREAM
+  NS_DECL_NSICLONEABLEINPUTSTREAMWITHRANGE
+  NS_DECL_NSIIPCSERIALIZABLEINPUTSTREAM
+  NS_DECL_NSIFILEMETADATA
+  NS_DECL_NSIASYNCFILEMETADATA
+  NS_DECL_NSIINPUTSTREAMLENGTH
+  NS_DECL_NSIASYNCINPUTSTREAMLENGTH
+
+  // Create a new lazy RemoteLazyInputStream, and move the provided aInputStream
+  // into storage as referenced by it. May only be called in processes with
+  // RemoteLazyInputStreamStorage.
+  static already_AddRefed<RemoteLazyInputStream> WrapStream(
+      nsIInputStream* aInputStream);
+
+  // mozIRemoteLazyInputStream
+  NS_IMETHOD TakeInternalStream(nsIInputStream** aStream) override;
+  NS_IMETHOD GetInternalStreamID(nsID& aID) override;
+
+ private:
+  friend struct IPC::ParamTraits<mozilla::RemoteLazyInputStream*>;
+
+  // Constructor for an already-closed RemoteLazyInputStream.
+  RemoteLazyInputStream() = default;
+
+  explicit RemoteLazyInputStream(RemoteLazyInputStreamChild* aActor,
+                                 uint64_t aStart = 0,
+                                 uint64_t aLength = UINT64_MAX);
+
+  explicit RemoteLazyInputStream(nsIInputStream* aStream);
+
+  ~RemoteLazyInputStream();
+
+  void StreamNeeded() MOZ_REQUIRES(mMutex);
+
+  // Upon receiving the stream from our actor, we will not wrap it into an async
+  // stream until needed. This allows callers to get access to the underlying
+  // potentially-sync stream using `TakeInternalStream` before reading.
+  nsresult EnsureAsyncRemoteStream() MOZ_REQUIRES(mMutex);
+
+  // Note that data has been read from our input stream, and disconnect from our
+  // remote actor.
+  void MarkConsumed();
+
+  void IPCWrite(IPC::MessageWriter* aWriter);
+  static already_AddRefed<RemoteLazyInputStream> IPCRead(
+      IPC::MessageReader* aReader);
+
+  // Helper method to generate a description of a stream for use in loggging.
+  nsCString Describe() MOZ_REQUIRES(mMutex);
+
+  // Start and length of the slice to apply on this RemoteLazyInputStream when
+  // fetching the underlying stream with `SendStreamNeeded`.
+  const uint64_t mStart = 0;
+  const uint64_t mLength = UINT64_MAX;
+
+  // Any non-const member of this class is protected by mutex because it is
+  // touched on multiple threads.
+  Mutex mMutex{"RemoteLazyInputStream::mMutex"};
+
+  // This is the list of possible states.
+  enum {
+    // The initial state. Only ::Available() can be used without receiving an
+    // error. The available size is known by the actor.
+    eInit,
+
+    // AsyncWait() has been called for the first time. SendStreamNeeded() has
+    // been called and we are waiting for the 'real' inputStream.
+    ePending,
+
+    // When the child receives the stream from the parent, we move to this
+    // state. The received stream is stored in mInnerStream. From now on, any
+    // method call will be forwared to mInnerStream or mAsyncInnerStream.
+    eRunning,
+
+    // If Close() or CloseWithStatus() is called, we move to this state.
+    // mInnerStream is released and any method will return
+    // NS_BASE_STREAM_CLOSED.
+    eClosed,
+  } mState MOZ_GUARDED_BY(mMutex) = eClosed;
+
+  // The actor which will be used to provide the underlying stream or length
+  // information when needed, as well as to efficiently allow transferring the
+  // stream over IPC.
+  //
+  // The connection to our actor will be cleared once the stream has been closed
+  // or has started reading, at which point this stream will be serialized and
+  // cloned as-if it was the underlying stream.
+  RefPtr<RemoteLazyInputStreamChild> mActor MOZ_GUARDED_BY(mMutex);
+
+  nsCOMPtr<nsIInputStream> mInnerStream MOZ_GUARDED_BY(mMutex);
+  nsCOMPtr<nsIAsyncInputStream> mAsyncInnerStream MOZ_GUARDED_BY(mMutex);
+
+  // These 2 values are set only if mState is ePending or eRunning.
+  // RefPtr is used instead of nsCOMPtr to avoid invoking QueryInterface when
+  // assigning in debug builds, as `mInputStreamCallback` may not be threadsafe.
+  RefPtr<nsIInputStreamCallback> mInputStreamCallback MOZ_GUARDED_BY(mMutex);
+  nsCOMPtr<nsIEventTarget> mInputStreamCallbackEventTarget
+      MOZ_GUARDED_BY(mMutex);
+  uint32_t mInputStreamCallbackFlags MOZ_GUARDED_BY(mMutex) = 0;
+  uint32_t mInputStreamCallbackRequestedCount MOZ_GUARDED_BY(mMutex) = 0;
+
+  // These 2 values are set only if mState is ePending.
+  nsCOMPtr<nsIFileMetadataCallback> mFileMetadataCallback
+      MOZ_GUARDED_BY(mMutex);
+  nsCOMPtr<nsIEventTarget> mFileMetadataCallbackEventTarget
+      MOZ_GUARDED_BY(mMutex);
+};
+
+}  // namespace mozilla
+
+template <>
+struct IPC::ParamTraits<mozilla::RemoteLazyInputStream*> {
+  static void Write(IPC::MessageWriter* aWriter,
+                    mozilla::RemoteLazyInputStream* aParam);
+  static bool Read(IPC::MessageReader* aReader,
+                   RefPtr<mozilla::RemoteLazyInputStream>* aResult);
+};
+
+#endif  // mozilla_RemoteLazyInputStream_h
diff --git a/dom/file/ipc/RemoteLazyInputStreamChild.cpp b/dom/file/ipc/RemoteLazyInputStreamChild.cpp
new file mode 100644
index 0000000000..f03aa47aad
--- /dev/null
+++ b/dom/file/ipc/RemoteLazyInputStreamChild.cpp
@@ -0,0 +1,55 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "RemoteLazyInputStreamChild.h"
+#include "RemoteLazyInputStreamThread.h"
+
+namespace mozilla {
+
+extern mozilla::LazyLogModule gRemoteLazyStreamLog;
+
+RemoteLazyInputStreamChild::RemoteLazyInputStreamChild(const nsID& aID)
+    : mID(aID) {}
+
+RemoteLazyInputStreamChild::~RemoteLazyInputStreamChild() = default;
+
+void RemoteLazyInputStreamChild::StreamCreated() {
+  size_t count = ++mStreamCount;
+  MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+          ("Child::StreamCreated %s = %zu", nsIDToCString(mID).get(), count));
+}
+
+void RemoteLazyInputStreamChild::StreamConsumed() {
+  size_t count = --mStreamCount;
+  MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+          ("Child::StreamConsumed %s = %zu", nsIDToCString(mID).get(), count));
+
+  // When the count reaches zero, close the underlying actor.
+  if (count == 0) {
+    auto* t = RemoteLazyInputStreamThread::Get();
+    if (t) {
+      t->Dispatch(
+          NS_NewRunnableFunction("RemoteLazyInputStreamChild::StreamConsumed",
+                                 [self = RefPtr{this}]() {
+                                   if (self->CanSend()) {
+                                     self->SendGoodbye();
+                                   }
+                                 }));
+    }  // else the xpcom thread shutdown has already started.
+  }
+}
+
+void RemoteLazyInputStreamChild::ActorDestroy(ActorDestroyReason aReason) {
+  if (mStreamCount != 0) {
+    NS_WARNING(
+        nsPrintfCString("RemoteLazyInputStreamChild disconnected unexpectedly "
+                        "(%zu streams remaining)! %p %s",
+                        size_t(mStreamCount), this, nsIDToCString(mID).get())
+            .get());
+  }
+}
+
+}  // namespace mozilla
diff --git a/dom/file/ipc/RemoteLazyInputStreamChild.h b/dom/file/ipc/RemoteLazyInputStreamChild.h
new file mode 100644
index 0000000000..c95ed9f058
--- /dev/null
+++ b/dom/file/ipc/RemoteLazyInputStreamChild.h
@@ -0,0 +1,41 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_RemoteLazyInputStreamChild_h
+#define mozilla_RemoteLazyInputStreamChild_h
+
+#include "mozilla/PRemoteLazyInputStreamChild.h"
+
+namespace mozilla {
+
+class RemoteLazyInputStream;
+
+class RemoteLazyInputStreamChild final : public PRemoteLazyInputStreamChild {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(RemoteLazyInputStreamChild, final)
+
+  explicit RemoteLazyInputStreamChild(const nsID& aID);
+
+  const nsID& StreamID() const { return mID; }
+
+  // Manage the count of streams registered on this actor. When the count
+  // reaches 0 the connection to our remote process will be closed.
+  void StreamCreated();
+  void StreamConsumed();
+
+  void ActorDestroy(ActorDestroyReason aReason) override;
+
+ private:
+  ~RemoteLazyInputStreamChild() override;
+
+  const nsID mID;
+
+  std::atomic<size_t> mStreamCount{0};
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_RemoteLazyInputStreamChild_h
diff --git a/dom/file/ipc/RemoteLazyInputStreamParent.cpp b/dom/file/ipc/RemoteLazyInputStreamParent.cpp
new file mode 100644
index 0000000000..d92c529546
--- /dev/null
+++ b/dom/file/ipc/RemoteLazyInputStreamParent.cpp
@@ -0,0 +1,123 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "RemoteLazyInputStreamParent.h"
+#include "RemoteLazyInputStreamStorage.h"
+#include "mozilla/InputStreamLengthHelper.h"
+#include "mozilla/ipc/Endpoint.h"
+#include "mozilla/ipc/IPCStreamUtils.h"
+#include "mozilla/ipc/InputStreamParams.h"
+#include "mozilla/ipc/ProtocolUtils.h"
+#include "nsStreamUtils.h"
+#include "nsServiceManagerUtils.h"
+#include "nsNetCID.h"
+
+namespace mozilla {
+
+extern mozilla::LazyLogModule gRemoteLazyStreamLog;
+
+RemoteLazyInputStreamParent::RemoteLazyInputStreamParent(const nsID& aID)
+    : mID(aID) {
+  auto storage = RemoteLazyInputStreamStorage::Get().unwrapOr(nullptr);
+  if (storage) {
+    storage->ActorCreated(mID);
+  }
+}
+
+void RemoteLazyInputStreamParent::ActorDestroy(
+    IProtocol::ActorDestroyReason aReason) {
+  auto storage = RemoteLazyInputStreamStorage::Get().unwrapOr(nullptr);
+  if (storage) {
+    storage->ActorDestroyed(mID);
+  }
+}
+
+mozilla::ipc::IPCResult RemoteLazyInputStreamParent::RecvClone(
+    mozilla::ipc::Endpoint<PRemoteLazyInputStreamParent>&& aCloneEndpoint) {
+  if (!aCloneEndpoint.IsValid()) {
+    return IPC_FAIL(this, "Unexpected invalid endpoint in RecvClone");
+  }
+
+  MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Debug,
+          ("Parent::RecvClone %s", nsIDToCString(mID).get()));
+
+  auto* newActor = new RemoteLazyInputStreamParent(mID);
+  aCloneEndpoint.Bind(newActor);
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult RemoteLazyInputStreamParent::RecvStreamNeeded(
+    uint64_t aStart, uint64_t aLength, StreamNeededResolver&& aResolver) {
+  nsCOMPtr<nsIInputStream> stream;
+  auto storage = RemoteLazyInputStreamStorage::Get().unwrapOr(nullptr);
+  if (storage) {
+    storage->GetStream(mID, aStart, aLength, getter_AddRefs(stream));
+  }
+
+  if (!stream) {
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Warning,
+            ("Parent::RecvStreamNeeded not available! %s",
+             nsIDToCString(mID).get()));
+    aResolver(Nothing());
+    return IPC_OK();
+  }
+
+  Maybe<IPCStream> ipcStream;
+  if (NS_WARN_IF(!SerializeIPCStream(stream.forget(), ipcStream,
+                                     /* aAllowLazy */ false))) {
+    return IPC_FAIL(this, "IPCStream serialization failed!");
+  }
+
+  MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+          ("Parent::RecvStreamNeeded resolve %s", nsIDToCString(mID).get()));
+  aResolver(ipcStream);
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult RemoteLazyInputStreamParent::RecvLengthNeeded(
+    LengthNeededResolver&& aResolver) {
+  nsCOMPtr<nsIInputStream> stream;
+  auto storage = RemoteLazyInputStreamStorage::Get().unwrapOr(nullptr);
+  if (storage) {
+    storage->GetStream(mID, 0, UINT64_MAX, getter_AddRefs(stream));
+  }
+
+  if (!stream) {
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Warning,
+            ("Parent::RecvLengthNeeded not available! %s",
+             nsIDToCString(mID).get()));
+    aResolver(-1);
+    return IPC_OK();
+  }
+
+  int64_t length = -1;
+  if (InputStreamLengthHelper::GetSyncLength(stream, &length)) {
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+            ("Parent::RecvLengthNeeded sync resolve %" PRId64 "! %s", length,
+             nsIDToCString(mID).get()));
+    aResolver(length);
+    return IPC_OK();
+  }
+
+  InputStreamLengthHelper::GetAsyncLength(
+      stream, [aResolver, id = mID](int64_t aLength) {
+        MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+                ("Parent::RecvLengthNeeded async resolve %" PRId64 "! %s",
+                 aLength, nsIDToCString(id).get()));
+        aResolver(aLength);
+      });
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult RemoteLazyInputStreamParent::RecvGoodbye() {
+  MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+          ("Parent::RecvGoodbye! %s", nsIDToCString(mID).get()));
+  Close();
+  return IPC_OK();
+}
+
+}  // namespace mozilla
diff --git a/dom/file/ipc/RemoteLazyInputStreamParent.h b/dom/file/ipc/RemoteLazyInputStreamParent.h
new file mode 100644
index 0000000000..cb5b1d4285
--- /dev/null
+++ b/dom/file/ipc/RemoteLazyInputStreamParent.h
@@ -0,0 +1,44 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_RemoteLazyInputStreamParent_h
+#define mozilla_RemoteLazyInputStreamParent_h
+
+#include "mozilla/PRemoteLazyInputStreamParent.h"
+
+class nsIInputStream;
+
+namespace mozilla {
+
+class RemoteLazyInputStreamParent final : public PRemoteLazyInputStreamParent {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(RemoteLazyInputStreamParent, final)
+
+  explicit RemoteLazyInputStreamParent(const nsID& aID);
+
+  const nsID& ID() const { return mID; }
+
+  mozilla::ipc::IPCResult RecvClone(
+      mozilla::ipc::Endpoint<PRemoteLazyInputStreamParent>&& aCloneEndpoint);
+
+  mozilla::ipc::IPCResult RecvStreamNeeded(uint64_t aStart, uint64_t aLength,
+                                           StreamNeededResolver&& aResolver);
+
+  mozilla::ipc::IPCResult RecvLengthNeeded(LengthNeededResolver&& aResolver);
+
+  mozilla::ipc::IPCResult RecvGoodbye();
+
+  void ActorDestroy(IProtocol::ActorDestroyReason aReason) override;
+
+ private:
+  ~RemoteLazyInputStreamParent() override = default;
+
+  const nsID mID;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_RemoteLazyInputStreamParent_h
diff --git a/dom/file/ipc/RemoteLazyInputStreamStorage.cpp b/dom/file/ipc/RemoteLazyInputStreamStorage.cpp
new file mode 100644
index 0000000000..8ce2c22657
--- /dev/null
+++ b/dom/file/ipc/RemoteLazyInputStreamStorage.cpp
@@ -0,0 +1,243 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/SlicedInputStream.h"
+#include "mozilla/dom/ContentParent.h"
+#include "mozilla/StaticMutex.h"
+#include "mozilla/StaticPtr.h"
+#include "nsIPropertyBag2.h"
+#include "nsStreamUtils.h"
+#include "RemoteLazyInputStreamParent.h"
+#include "RemoteLazyInputStreamStorage.h"
+
+namespace mozilla {
+
+using namespace hal;
+
+extern mozilla::LazyLogModule gRemoteLazyStreamLog;
+
+namespace {
+StaticMutex gMutex;
+StaticRefPtr<RemoteLazyInputStreamStorage> gStorage;
+}  // namespace
+
+NS_INTERFACE_MAP_BEGIN(RemoteLazyInputStreamStorage)
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIObserver)
+  NS_INTERFACE_MAP_ENTRY(nsIObserver)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_ADDREF(RemoteLazyInputStreamStorage)
+NS_IMPL_RELEASE(RemoteLazyInputStreamStorage)
+
+/* static */
+Result<RefPtr<RemoteLazyInputStreamStorage>, nsresult>
+RemoteLazyInputStreamStorage::Get() {
+  mozilla::StaticMutexAutoLock lock(gMutex);
+  if (gStorage) {
+    RefPtr<RemoteLazyInputStreamStorage> storage = gStorage;
+    return storage;
+  }
+
+  return Err(NS_ERROR_NOT_INITIALIZED);
+}
+
+/* static */
+void RemoteLazyInputStreamStorage::Initialize() {
+  mozilla::StaticMutexAutoLock lock(gMutex);
+  MOZ_ASSERT(!gStorage);
+
+  gStorage = new RemoteLazyInputStreamStorage();
+
+  MOZ_ALWAYS_SUCCEEDS(NS_CreateBackgroundTaskQueue(
+      "RemoteLazyInputStreamStorage", getter_AddRefs(gStorage->mTaskQueue)));
+
+  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+  if (obs) {
+    obs->AddObserver(gStorage, "xpcom-shutdown", false);
+  }
+}
+
+NS_IMETHODIMP
+RemoteLazyInputStreamStorage::Observe(nsISupports* aSubject, const char* aTopic,
+                                      const char16_t* aData) {
+  MOZ_ASSERT(!strcmp(aTopic, "xpcom-shutdown"));
+
+  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+  if (obs) {
+    obs->RemoveObserver(this, "xpcom-shutdown");
+  }
+
+  mozilla::StaticMutexAutoLock lock(gMutex);
+  gStorage = nullptr;
+  return NS_OK;
+}
+
+void RemoteLazyInputStreamStorage::AddStream(nsIInputStream* aInputStream,
+                                             const nsID& aID) {
+  MOZ_ASSERT(aInputStream);
+
+  MOZ_LOG(
+      gRemoteLazyStreamLog, LogLevel::Verbose,
+      ("Storage::AddStream(%s) = %p", nsIDToCString(aID).get(), aInputStream));
+
+  UniquePtr<StreamData> data = MakeUnique<StreamData>();
+  data->mInputStream = aInputStream;
+
+  mozilla::StaticMutexAutoLock lock(gMutex);
+  mStorage.InsertOrUpdate(aID, std::move(data));
+}
+
+nsCOMPtr<nsIInputStream> RemoteLazyInputStreamStorage::ForgetStream(
+    const nsID& aID) {
+  MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+          ("Storage::ForgetStream(%s)", nsIDToCString(aID).get()));
+
+  UniquePtr<StreamData> entry;
+
+  mozilla::StaticMutexAutoLock lock(gMutex);
+  mStorage.Remove(aID, &entry);
+
+  if (!entry) {
+    return nullptr;
+  }
+
+  return std::move(entry->mInputStream);
+}
+
+bool RemoteLazyInputStreamStorage::HasStream(const nsID& aID) {
+  mozilla::StaticMutexAutoLock lock(gMutex);
+  StreamData* data = mStorage.Get(aID);
+  return !!data;
+}
+
+void RemoteLazyInputStreamStorage::GetStream(const nsID& aID, uint64_t aStart,
+                                             uint64_t aLength,
+                                             nsIInputStream** aInputStream) {
+  *aInputStream = nullptr;
+
+  MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+          ("Storage::GetStream(%s, %" PRIu64 " %" PRIu64 ")",
+           nsIDToCString(aID).get(), aStart, aLength));
+
+  nsCOMPtr<nsIInputStream> inputStream;
+
+  // NS_CloneInputStream cannot be called when the mutex is locked because it
+  // can, recursively call GetStream() in case the child actor lives on the
+  // parent process.
+  {
+    mozilla::StaticMutexAutoLock lock(gMutex);
+    StreamData* data = mStorage.Get(aID);
+    if (!data) {
+      return;
+    }
+
+    inputStream = data->mInputStream;
+  }
+
+  MOZ_ASSERT(inputStream);
+
+  // We cannot return always the same inputStream because not all of them are
+  // able to be reused. Better to clone them.
+
+  nsCOMPtr<nsIInputStream> clonedStream;
+  nsCOMPtr<nsIInputStream> replacementStream;
+
+  nsresult rv = NS_CloneInputStream(inputStream, getter_AddRefs(clonedStream),
+                                    getter_AddRefs(replacementStream));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return;
+  }
+
+  if (replacementStream) {
+    mozilla::StaticMutexAutoLock lock(gMutex);
+    StreamData* data = mStorage.Get(aID);
+    // data can be gone in the meantime.
+    if (!data) {
+      return;
+    }
+
+    data->mInputStream = replacementStream;
+  }
+
+  // Now it's the right time to apply a slice if needed.
+  if (aStart > 0 || aLength < UINT64_MAX) {
+    clonedStream =
+        new SlicedInputStream(clonedStream.forget(), aStart, aLength);
+  }
+
+  clonedStream.forget(aInputStream);
+}
+
+void RemoteLazyInputStreamStorage::StoreCallback(
+    const nsID& aID, RemoteLazyInputStreamParentCallback* aCallback) {
+  MOZ_ASSERT(aCallback);
+
+  MOZ_LOG(
+      gRemoteLazyStreamLog, LogLevel::Verbose,
+      ("Storage::StoreCallback(%s, %p)", nsIDToCString(aID).get(), aCallback));
+
+  mozilla::StaticMutexAutoLock lock(gMutex);
+  StreamData* data = mStorage.Get(aID);
+  if (data) {
+    MOZ_ASSERT(!data->mCallback);
+    data->mCallback = aCallback;
+  }
+}
+
+already_AddRefed<RemoteLazyInputStreamParentCallback>
+RemoteLazyInputStreamStorage::TakeCallback(const nsID& aID) {
+  MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+          ("Storage::TakeCallback(%s)", nsIDToCString(aID).get()));
+
+  mozilla::StaticMutexAutoLock lock(gMutex);
+  StreamData* data = mStorage.Get(aID);
+  if (!data) {
+    return nullptr;
+  }
+
+  RefPtr<RemoteLazyInputStreamParentCallback> callback;
+  data->mCallback.swap(callback);
+  return callback.forget();
+}
+
+void RemoteLazyInputStreamStorage::ActorCreated(const nsID& aID) {
+  mozilla::StaticMutexAutoLock lock(gMutex);
+  StreamData* data = mStorage.Get(aID);
+  if (!data) {
+    return;
+  }
+
+  size_t count = ++data->mActorCount;
+
+  MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+          ("Storage::ActorCreated(%s) = %zu", nsIDToCString(aID).get(), count));
+}
+
+void RemoteLazyInputStreamStorage::ActorDestroyed(const nsID& aID) {
+  UniquePtr<StreamData> entry;
+  {
+    mozilla::StaticMutexAutoLock lock(gMutex);
+    StreamData* data = mStorage.Get(aID);
+    if (!data) {
+      return;
+    }
+
+    auto newCount = --data->mActorCount;
+    MOZ_LOG(gRemoteLazyStreamLog, LogLevel::Verbose,
+            ("Storage::ActorDestroyed(%s) = %zu (cb=%p)",
+             nsIDToCString(aID).get(), newCount, data->mCallback.get()));
+
+    if (newCount == 0) {
+      mStorage.Remove(aID, &entry);
+    }
+  }
+
+  if (entry && entry->mCallback) {
+    entry->mCallback->ActorDestroyed(aID);
+  }
+}
+
+}  // namespace mozilla
diff --git a/dom/file/ipc/RemoteLazyInputStreamStorage.h b/dom/file/ipc/RemoteLazyInputStreamStorage.h
new file mode 100644
index 0000000000..296a8d9313
--- /dev/null
+++ b/dom/file/ipc/RemoteLazyInputStreamStorage.h
@@ -0,0 +1,78 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_RemoteLazyInputStreamStorage_h
+#define mozilla_RemoteLazyInputStreamStorage_h
+
+#include "mozilla/RefPtr.h"
+#include "nsClassHashtable.h"
+#include "nsIObserver.h"
+
+class nsIInputStream;
+struct nsID;
+
+namespace mozilla {
+
+class NS_NO_VTABLE RemoteLazyInputStreamParentCallback {
+ public:
+  virtual void ActorDestroyed(const nsID& aID) = 0;
+
+  NS_INLINE_DECL_PURE_VIRTUAL_REFCOUNTING
+
+ protected:
+  virtual ~RemoteLazyInputStreamParentCallback() = default;
+};
+
+class RemoteLazyInputStreamStorage final : public nsIObserver {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  // This initializes the singleton and it must be called on the main-thread.
+  static void Initialize();
+
+  static Result<RefPtr<RemoteLazyInputStreamStorage>, nsresult> Get();
+
+  nsISerialEventTarget* TaskQueue() { return mTaskQueue; }
+
+  void AddStream(nsIInputStream* aInputStream, const nsID& aID);
+
+  // Removes and returns the stream corresponding to the nsID. May return a
+  // nullptr if there's no stream stored for the nsID.
+  nsCOMPtr<nsIInputStream> ForgetStream(const nsID& aID);
+
+  bool HasStream(const nsID& aID);
+
+  void GetStream(const nsID& aID, uint64_t aStart, uint64_t aLength,
+                 nsIInputStream** aInputStream);
+
+  void StoreCallback(const nsID& aID,
+                     RemoteLazyInputStreamParentCallback* aCallback);
+
+  already_AddRefed<RemoteLazyInputStreamParentCallback> TakeCallback(
+      const nsID& aID);
+
+  void ActorCreated(const nsID& aID);
+  void ActorDestroyed(const nsID& aID);
+
+ private:
+  RemoteLazyInputStreamStorage() = default;
+  ~RemoteLazyInputStreamStorage() = default;
+
+  nsCOMPtr<nsISerialEventTarget> mTaskQueue;
+
+  struct StreamData {
+    nsCOMPtr<nsIInputStream> mInputStream;
+    RefPtr<RemoteLazyInputStreamParentCallback> mCallback;
+    size_t mActorCount = 0;
+  };
+
+  nsClassHashtable<nsIDHashKey, StreamData> mStorage;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_RemoteLazyInputStreamStorage_h
diff --git a/dom/file/ipc/RemoteLazyInputStreamThread.cpp b/dom/file/ipc/RemoteLazyInputStreamThread.cpp
new file mode 100644
index 0000000000..5883c44d4c
--- /dev/null
+++ b/dom/file/ipc/RemoteLazyInputStreamThread.cpp
@@ -0,0 +1,238 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "RemoteLazyInputStreamThread.h"
+
+#include "ErrorList.h"
+#include "mozilla/AppShutdown.h"
+#include "mozilla/SchedulerGroup.h"
+#include "mozilla/StaticMutex.h"
+#include "mozilla/StaticPtr.h"
+#include "mozilla/ipc/BackgroundChild.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "nsXPCOMPrivate.h"
+
+using namespace mozilla::ipc;
+
+namespace mozilla {
+
+namespace {
+
+StaticMutex gRemoteLazyThreadMutex;
+StaticRefPtr<RemoteLazyInputStreamThread> gRemoteLazyThread;
+
+class ThreadInitializeRunnable final : public Runnable {
+ public:
+  ThreadInitializeRunnable() : Runnable("dom::ThreadInitializeRunnable") {}
+
+  NS_IMETHOD
+  Run() override {
+    StaticMutexAutoLock lock(gRemoteLazyThreadMutex);
+    MOZ_ASSERT(gRemoteLazyThread);
+    if (NS_WARN_IF(!gRemoteLazyThread->InitializeOnMainThread())) {
+      // RemoteLazyInputStreamThread::GetOrCreate might have handed out a
+      // pointer to our thread already at this point such that we cannot
+      // just do gRemoteLazyThread = nullptr; here.
+      MOZ_DIAGNOSTIC_ASSERT(
+          false, "Async gRemoteLazyThread->InitializeOnMainThread() failed.");
+      return NS_ERROR_FAILURE;
+    }
+    return NS_OK;
+  }
+};
+
+}  // namespace
+
+NS_IMPL_ISUPPORTS(RemoteLazyInputStreamThread, nsIObserver, nsIEventTarget,
+                  nsISerialEventTarget, nsIDirectTaskDispatcher)
+
+bool RLISThreadIsInOrBeyondShutdown() {
+  // ShutdownPhase::XPCOMShutdownThreads matches
+  // obs->AddObserver(this, NS_XPCOM_SHUTDOWN_THREADS_OBSERVER_ID, false);
+  return AppShutdown::IsInOrBeyond(ShutdownPhase::XPCOMShutdownThreads);
+}
+
+/* static */
+RemoteLazyInputStreamThread* RemoteLazyInputStreamThread::Get() {
+  if (RLISThreadIsInOrBeyondShutdown()) {
+    return nullptr;
+  }
+
+  StaticMutexAutoLock lock(gRemoteLazyThreadMutex);
+
+  return gRemoteLazyThread;
+}
+
+/* static */
+RemoteLazyInputStreamThread* RemoteLazyInputStreamThread::GetOrCreate() {
+  if (RLISThreadIsInOrBeyondShutdown()) {
+    return nullptr;
+  }
+
+  StaticMutexAutoLock lock(gRemoteLazyThreadMutex);
+
+  if (!gRemoteLazyThread) {
+    gRemoteLazyThread = new RemoteLazyInputStreamThread();
+    if (!gRemoteLazyThread->Initialize()) {
+      gRemoteLazyThread = nullptr;
+    }
+  }
+
+  return gRemoteLazyThread;
+}
+
+bool RemoteLazyInputStreamThread::Initialize() {
+  nsCOMPtr<nsIThread> thread;
+  nsresult rv = NS_NewNamedThread("RemoteLzyStream", getter_AddRefs(thread));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return false;
+  }
+
+  mThread = thread;
+
+  if (!NS_IsMainThread()) {
+    RefPtr<Runnable> runnable = new ThreadInitializeRunnable();
+    nsresult rv = SchedulerGroup::Dispatch(runnable.forget());
+    return !NS_WARN_IF(NS_FAILED(rv));
+  }
+
+  return InitializeOnMainThread();
+}
+
+bool RemoteLazyInputStreamThread::InitializeOnMainThread() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  nsCOMPtr<nsIObserverService> obs = services::GetObserverService();
+  if (NS_WARN_IF(!obs)) {
+    return false;
+  }
+
+  nsresult rv =
+      obs->AddObserver(this, NS_XPCOM_SHUTDOWN_THREADS_OBSERVER_ID, false);
+  return !NS_WARN_IF(NS_FAILED(rv));
+}
+
+NS_IMETHODIMP
+RemoteLazyInputStreamThread::Observe(nsISupports* aSubject, const char* aTopic,
+                                     const char16_t* aData) {
+  MOZ_ASSERT(!strcmp(aTopic, NS_XPCOM_SHUTDOWN_THREADS_OBSERVER_ID));
+
+  StaticMutexAutoLock lock(gRemoteLazyThreadMutex);
+
+  if (mThread) {
+    mThread->Shutdown();
+    mThread = nullptr;
+  }
+
+  gRemoteLazyThread = nullptr;
+
+  return NS_OK;
+}
+
+// nsIEventTarget
+
+NS_IMETHODIMP_(bool)
+RemoteLazyInputStreamThread::IsOnCurrentThreadInfallible() {
+  return mThread->IsOnCurrentThread();
+}
+
+NS_IMETHODIMP
+RemoteLazyInputStreamThread::IsOnCurrentThread(bool* aRetval) {
+  return mThread->IsOnCurrentThread(aRetval);
+}
+
+NS_IMETHODIMP
+RemoteLazyInputStreamThread::Dispatch(already_AddRefed<nsIRunnable> aRunnable,
+                                      uint32_t aFlags) {
+  nsCOMPtr<nsIRunnable> runnable(aRunnable);
+
+  if (RLISThreadIsInOrBeyondShutdown()) {
+    // nsIEventTarget::Dispatch must leak the runnable if the dispatch fails.
+    (void)runnable.forget();
+
+    return NS_ERROR_ILLEGAL_DURING_SHUTDOWN;
+  }
+
+  StaticMutexAutoLock lock(gRemoteLazyThreadMutex);
+
+  return mThread->Dispatch(runnable.forget(), aFlags);
+}
+
+NS_IMETHODIMP
+RemoteLazyInputStreamThread::DispatchFromScript(nsIRunnable* aRunnable,
+                                                uint32_t aFlags) {
+  nsCOMPtr<nsIRunnable> runnable(aRunnable);
+  return Dispatch(runnable.forget(), aFlags);
+}
+
+NS_IMETHODIMP
+RemoteLazyInputStreamThread::DelayedDispatch(already_AddRefed<nsIRunnable>,
+                                             uint32_t) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+RemoteLazyInputStreamThread::RegisterShutdownTask(nsITargetShutdownTask*) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+RemoteLazyInputStreamThread::UnregisterShutdownTask(nsITargetShutdownTask*) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+RemoteLazyInputStreamThread::DispatchDirectTask(
+    already_AddRefed<nsIRunnable> aRunnable) {
+  nsCOMPtr<nsIRunnable> runnable(aRunnable);
+
+  StaticMutexAutoLock lock(gRemoteLazyThreadMutex);
+
+  nsCOMPtr<nsIDirectTaskDispatcher> dispatcher = do_QueryInterface(mThread);
+
+  if (dispatcher) {
+    return dispatcher->DispatchDirectTask(runnable.forget());
+  }
+
+  return NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP RemoteLazyInputStreamThread::DrainDirectTasks() {
+  StaticMutexAutoLock lock(gRemoteLazyThreadMutex);
+
+  nsCOMPtr<nsIDirectTaskDispatcher> dispatcher = do_QueryInterface(mThread);
+
+  if (dispatcher) {
+    return dispatcher->DrainDirectTasks();
+  }
+
+  return NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP RemoteLazyInputStreamThread::HaveDirectTasks(bool* aValue) {
+  StaticMutexAutoLock lock(gRemoteLazyThreadMutex);
+
+  nsCOMPtr<nsIDirectTaskDispatcher> dispatcher = do_QueryInterface(mThread);
+
+  if (dispatcher) {
+    return dispatcher->HaveDirectTasks(aValue);
+  }
+
+  return NS_ERROR_FAILURE;
+}
+
+bool IsOnDOMFileThread() {
+  MOZ_ASSERT(!RLISThreadIsInOrBeyondShutdown());
+
+  StaticMutexAutoLock lock(gRemoteLazyThreadMutex);
+  MOZ_ASSERT(gRemoteLazyThread);
+
+  return gRemoteLazyThread->IsOnCurrentThreadInfallible();
+}
+
+void AssertIsOnDOMFileThread() { MOZ_ASSERT(IsOnDOMFileThread()); }
+
+}  // namespace mozilla
diff --git a/dom/file/ipc/RemoteLazyInputStreamThread.h b/dom/file/ipc/RemoteLazyInputStreamThread.h
new file mode 100644
index 0000000000..378cb09009
--- /dev/null
+++ b/dom/file/ipc/RemoteLazyInputStreamThread.h
@@ -0,0 +1,52 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_RemoteLazyInputStreamThread_h
+#define mozilla_RemoteLazyInputStreamThread_h
+
+#include "mozilla/RemoteLazyInputStreamChild.h"
+#include "nsIEventTarget.h"
+#include "nsIObserver.h"
+#include "nsTArray.h"
+
+class nsIThread;
+
+namespace mozilla {
+
+class RemoteLazyInputStreamChild;
+
+// XXX Rename this class since it's used by LSNG too.
+class RemoteLazyInputStreamThread final : public nsIObserver,
+                                          public nsISerialEventTarget,
+                                          public nsIDirectTaskDispatcher {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+  NS_DECL_NSIEVENTTARGET
+  NS_DECL_NSISERIALEVENTTARGET
+  NS_DECL_NSIDIRECTTASKDISPATCHER
+
+  static RemoteLazyInputStreamThread* Get();
+
+  static RemoteLazyInputStreamThread* GetOrCreate();
+
+  bool Initialize();
+
+  bool InitializeOnMainThread();
+
+ private:
+  ~RemoteLazyInputStreamThread() = default;
+
+  nsCOMPtr<nsIThread> mThread;
+};
+
+bool IsOnDOMFileThread();
+
+void AssertIsOnDOMFileThread();
+
+}  // namespace mozilla
+
+#endif  // mozilla_RemoteLazyInputStreamThread_h
diff --git a/dom/file/ipc/TemporaryIPCBlobChild.cpp b/dom/file/ipc/TemporaryIPCBlobChild.cpp
new file mode 100644
index 0000000000..7c7df55d81
--- /dev/null
+++ b/dom/file/ipc/TemporaryIPCBlobChild.cpp
@@ -0,0 +1,86 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "TemporaryIPCBlobChild.h"
+#include "mozilla/dom/BlobImpl.h"
+#include "mozilla/dom/MutableBlobStorage.h"
+#include "mozilla/dom/IPCBlobUtils.h"
+#include <private/pprio.h>
+
+namespace mozilla::dom {
+
+TemporaryIPCBlobChild::TemporaryIPCBlobChild(MutableBlobStorage* aStorage)
+    : mMutableBlobStorage(aStorage), mActive(true) {
+  MOZ_ASSERT(aStorage);
+}
+
+TemporaryIPCBlobChild::~TemporaryIPCBlobChild() = default;
+
+mozilla::ipc::IPCResult TemporaryIPCBlobChild::RecvFileDesc(
+    const FileDescriptor& aFD) {
+  MOZ_ASSERT(mActive);
+
+  auto rawFD = aFD.ClonePlatformHandle();
+  PRFileDesc* prfile = PR_ImportFile(PROsfd(rawFD.release()));
+
+  mMutableBlobStorage->TemporaryFileCreated(prfile);
+  mMutableBlobStorage = nullptr;
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult TemporaryIPCBlobChild::Recv__delete__(
+    const IPCBlobOrError& aBlobOrError) {
+  mActive = false;
+  mMutableBlobStorage = nullptr;
+
+  if (aBlobOrError.type() == IPCBlobOrError::TIPCBlob) {
+    // This must be always deserialized.
+    RefPtr<BlobImpl> blobImpl =
+        IPCBlobUtils::Deserialize(aBlobOrError.get_IPCBlob());
+    MOZ_ASSERT(blobImpl);
+
+    if (mCallback) {
+      mCallback->OperationSucceeded(blobImpl);
+    }
+  } else if (mCallback) {
+    MOZ_ASSERT(aBlobOrError.type() == IPCBlobOrError::Tnsresult);
+    mCallback->OperationFailed(aBlobOrError.get_nsresult());
+  }
+
+  mCallback = nullptr;
+
+  return IPC_OK();
+}
+
+void TemporaryIPCBlobChild::ActorDestroy(ActorDestroyReason aWhy) {
+  mActive = false;
+  mMutableBlobStorage = nullptr;
+
+  if (mCallback) {
+    mCallback->OperationFailed(NS_ERROR_FAILURE);
+    mCallback = nullptr;
+  }
+}
+
+void TemporaryIPCBlobChild::AskForBlob(TemporaryIPCBlobChildCallback* aCallback,
+                                       const nsACString& aContentType,
+                                       PRFileDesc* aFD) {
+  MOZ_ASSERT(aCallback);
+  MOZ_ASSERT(!mCallback);
+
+  if (!mActive) {
+    aCallback->OperationFailed(NS_ERROR_FAILURE);
+    return;
+  }
+
+  FileDescriptor fdd = FileDescriptor(
+      FileDescriptor::PlatformHandleType(PR_FileDesc2NativeHandle(aFD)));
+
+  mCallback = aCallback;
+  SendOperationDone(aContentType, fdd);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/file/ipc/TemporaryIPCBlobChild.h b/dom/file/ipc/TemporaryIPCBlobChild.h
new file mode 100644
index 0000000000..a909ee0d53
--- /dev/null
+++ b/dom/file/ipc/TemporaryIPCBlobChild.h
@@ -0,0 +1,53 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TemporaryIPCBlobChild_h
+#define mozilla_dom_TemporaryIPCBlobChild_h
+
+#include "mozilla/dom/PTemporaryIPCBlob.h"
+#include "mozilla/dom/PTemporaryIPCBlobChild.h"
+
+namespace mozilla::dom {
+
+class BlobImpl;
+class MutableBlobStorage;
+
+class TemporaryIPCBlobChildCallback {
+ public:
+  NS_INLINE_DECL_PURE_VIRTUAL_REFCOUNTING
+
+  virtual void OperationSucceeded(BlobImpl* aBlobImpl) = 0;
+  virtual void OperationFailed(nsresult aRv) = 0;
+};
+
+class TemporaryIPCBlobChild final : public PTemporaryIPCBlobChild {
+  friend class PTemporaryIPCBlobChild;
+
+ public:
+  NS_INLINE_DECL_REFCOUNTING(TemporaryIPCBlobChild)
+
+  explicit TemporaryIPCBlobChild(MutableBlobStorage* aStorage);
+
+  void AskForBlob(TemporaryIPCBlobChildCallback* aCallback,
+                  const nsACString& aContentType, PRFileDesc* aFD);
+
+ private:
+  ~TemporaryIPCBlobChild() override;
+
+  mozilla::ipc::IPCResult RecvFileDesc(const FileDescriptor& aFD);
+
+  mozilla::ipc::IPCResult Recv__delete__(const IPCBlobOrError& aBlobOrError);
+
+  void ActorDestroy(ActorDestroyReason aWhy) override;
+
+  RefPtr<MutableBlobStorage> mMutableBlobStorage;
+  RefPtr<TemporaryIPCBlobChildCallback> mCallback;
+  bool mActive;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_TemporaryIPCBlobChild_h
diff --git a/dom/file/ipc/TemporaryIPCBlobParent.cpp b/dom/file/ipc/TemporaryIPCBlobParent.cpp
new file mode 100644
index 0000000000..bd2c6beefc
--- /dev/null
+++ b/dom/file/ipc/TemporaryIPCBlobParent.cpp
@@ -0,0 +1,102 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "private/pprio.h"
+#include "TemporaryIPCBlobParent.h"
+#include "mozilla/dom/FileBlobImpl.h"
+#include "nsAnonymousTemporaryFile.h"
+#include "TemporaryFileBlobImpl.h"
+#include "mozilla/dom/IPCBlobUtils.h"
+
+namespace mozilla::dom {
+
+TemporaryIPCBlobParent::TemporaryIPCBlobParent() : mActive(true) {}
+
+TemporaryIPCBlobParent::~TemporaryIPCBlobParent() {
+  // If we still have mFile, let's remove it.
+  if (mFile) {
+    mFile->Remove(false);
+  }
+}
+
+mozilla::ipc::IPCResult TemporaryIPCBlobParent::CreateAndShareFile() {
+  MOZ_ASSERT(mActive);
+  MOZ_ASSERT(!mFile);
+
+  nsresult rv = NS_OpenAnonymousTemporaryNsIFile(getter_AddRefs(mFile));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return SendDeleteError(rv);
+  }
+
+  PRFileDesc* fd;
+  rv = mFile->OpenNSPRFileDesc(PR_RDWR, PR_IRWXU, &fd);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return SendDeleteError(rv);
+  }
+
+  FileDescriptor fdd = FileDescriptor(
+      FileDescriptor::PlatformHandleType(PR_FileDesc2NativeHandle(fd)));
+
+  // The FileDescriptor object owns a duplicate of the file handle; we
+  // must close the original (and clean up the NSPR descriptor).
+  PR_Close(fd);
+
+  (void)SendFileDesc(fdd);
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult TemporaryIPCBlobParent::RecvOperationFailed() {
+  MOZ_ASSERT(mActive);
+  mActive = false;
+
+  // Nothing to do.
+  (void)Send__delete__(this, NS_ERROR_FAILURE);
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult TemporaryIPCBlobParent::RecvOperationDone(
+    const nsCString& aContentType, const FileDescriptor& aFD) {
+  MOZ_ASSERT(mActive);
+  mActive = false;
+
+  // We have received a file descriptor because in this way we have kept the
+  // file locked on windows during the IPC communication. After the creation of
+  // the TemporaryFileBlobImpl, this prfile can be closed.
+  auto rawFD = aFD.ClonePlatformHandle();
+  PRFileDesc* prfile = PR_ImportFile(PROsfd(rawFD.release()));
+
+  // Let's create the BlobImpl.
+  nsCOMPtr<nsIFile> file = std::move(mFile);
+
+  RefPtr<TemporaryFileBlobImpl> blobImpl =
+      new TemporaryFileBlobImpl(file, NS_ConvertUTF8toUTF16(aContentType));
+
+  PR_Close(prfile);
+
+  IPCBlob ipcBlob;
+  nsresult rv = IPCBlobUtils::Serialize(blobImpl, ipcBlob);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    (void)Send__delete__(this, NS_ERROR_FAILURE);
+    return IPC_OK();
+  }
+
+  (void)Send__delete__(this, ipcBlob);
+  return IPC_OK();
+}
+
+void TemporaryIPCBlobParent::ActorDestroy(ActorDestroyReason aWhy) {
+  mActive = false;
+}
+
+mozilla::ipc::IPCResult TemporaryIPCBlobParent::SendDeleteError(nsresult aRv) {
+  MOZ_ASSERT(mActive);
+  mActive = false;
+
+  (void)Send__delete__(this, aRv);
+  return IPC_OK();
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/file/ipc/TemporaryIPCBlobParent.h b/dom/file/ipc/TemporaryIPCBlobParent.h
new file mode 100644
index 0000000000..2609e8d820
--- /dev/null
+++ b/dom/file/ipc/TemporaryIPCBlobParent.h
@@ -0,0 +1,43 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TemporaryIPCBlobParent_h
+#define mozilla_dom_TemporaryIPCBlobParent_h
+
+#include "mozilla/dom/PTemporaryIPCBlob.h"
+#include "mozilla/dom/PTemporaryIPCBlobParent.h"
+
+class nsIFile;
+
+namespace mozilla::dom {
+
+class TemporaryIPCBlobParent final : public PTemporaryIPCBlobParent {
+  friend class PTemporaryIPCBlobParent;
+
+ public:
+  explicit TemporaryIPCBlobParent();
+
+  mozilla::ipc::IPCResult CreateAndShareFile();
+
+ private:
+  ~TemporaryIPCBlobParent() override;
+
+  mozilla::ipc::IPCResult RecvOperationFailed();
+
+  mozilla::ipc::IPCResult RecvOperationDone(const nsCString& aContentType,
+                                            const FileDescriptor& aFD);
+
+  void ActorDestroy(ActorDestroyReason aWhy) override;
+
+  mozilla::ipc::IPCResult SendDeleteError(nsresult aRv);
+
+  nsCOMPtr<nsIFile> mFile;
+  bool mActive;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_TemporaryIPCBlobParent_h
diff --git a/dom/file/ipc/moz.build b/dom/file/ipc/moz.build
new file mode 100644
index 0000000000..c34abb0b01
--- /dev/null
+++ b/dom/file/ipc/moz.build
@@ -0,0 +1,69 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+with Files("**"):
+    BUG_COMPONENT = ("Core", "DOM: File")
+
+XPIDL_SOURCES += [
+    "mozIRemoteLazyInputStream.idl",
+]
+
+XPIDL_MODULE = "dom"
+
+EXPORTS.mozilla.dom += [
+    "FileCreatorChild.h",
+    "FileCreatorParent.h",
+    "IPCBlobUtils.h",
+    "TemporaryIPCBlobChild.h",
+    "TemporaryIPCBlobParent.h",
+]
+
+EXPORTS.mozilla += [
+    "RemoteLazyInputStream.h",
+    "RemoteLazyInputStreamChild.h",
+    "RemoteLazyInputStreamParent.h",
+    "RemoteLazyInputStreamStorage.h",
+    "RemoteLazyInputStreamThread.h",
+]
+
+UNIFIED_SOURCES += [
+    "FileCreatorChild.cpp",
+    "FileCreatorParent.cpp",
+    "IPCBlobUtils.cpp",
+    "RemoteLazyInputStream.cpp",
+    "RemoteLazyInputStreamChild.cpp",
+    "RemoteLazyInputStreamParent.cpp",
+    "RemoteLazyInputStreamStorage.cpp",
+    "RemoteLazyInputStreamThread.cpp",
+    "TemporaryIPCBlobChild.cpp",
+    "TemporaryIPCBlobParent.cpp",
+]
+
+IPDL_SOURCES += [
+    "IPCBlob.ipdlh",
+    "PFileCreator.ipdl",
+    "PRemoteLazyInputStream.ipdl",
+    "PTemporaryIPCBlob.ipdl",
+]
+
+LOCAL_INCLUDES += [
+    "/dom/file",
+    "/dom/ipc",
+    "/xpcom/build",
+]
+
+include("/ipc/chromium/chromium-config.mozbuild")
+
+# Add libFuzzer configuration directives
+include("/tools/fuzzing/libfuzzer-config.mozbuild")
+
+FINAL_LIBRARY = "xul"
+
+if CONFIG["MOZ_WIDGET_TOOLKIT"] == "gtk":
+    CXXFLAGS += CONFIG["MOZ_GTK3_CFLAGS"]
+
+BROWSER_CHROME_MANIFESTS += ["tests/browser.toml"]
+MOCHITEST_MANIFESTS += ["tests/mochitest.toml"]
diff --git a/dom/file/ipc/mozIRemoteLazyInputStream.idl b/dom/file/ipc/mozIRemoteLazyInputStream.idl
new file mode 100644
index 0000000000..8303b2e0fc
--- /dev/null
+++ b/dom/file/ipc/mozIRemoteLazyInputStream.idl
@@ -0,0 +1,29 @@
+/* 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 "nsISupports.idl"
+
+interface nsIInputStream;
+
+/*
+ * A simple interface to get the underlying stream from an
+ * RemoteLazyInputStream.
+ */
+[scriptable, builtinclass, uuid(4125585f-b0c2-4964-a83c-4b0d99f26d49)]
+interface mozIRemoteLazyInputStream : nsISupports
+{
+  /**
+   * Attempts to take the internal stream out of this mozIRemoteLazyInputStream.
+   * Throws NS_BASE_STREAM_WOULD_BLOCK if the stream isn't available yet, and
+   * NS_BASE_STREAM_CLOSED if it was already closed.
+   */
+  [noscript] nsIInputStream TakeInternalStream();
+
+  /**
+   * If this RemoteLazyInputStream is actively backed by an actor, get the
+   * underlying actor's ID. Will throw if the underlying actor is no longer
+   * available.
+   */
+  [noscript] readonly attribute nsIDRef internalStreamID;
+};
diff --git a/dom/file/ipc/tests/browser.toml b/dom/file/ipc/tests/browser.toml
new file mode 100644
index 0000000000..a27ae63e87
--- /dev/null
+++ b/dom/file/ipc/tests/browser.toml
@@ -0,0 +1,7 @@
+[DEFAULT]
+support-files = ["empty.html"]
+
+["browser_ipcBlob.js"]
+
+["browser_ipcBlob_temporary.js"]
+support-files = ["temporary.sjs"]
diff --git a/dom/file/ipc/tests/browser_ipcBlob.js b/dom/file/ipc/tests/browser_ipcBlob.js
new file mode 100644
index 0000000000..5b46db7221
--- /dev/null
+++ b/dom/file/ipc/tests/browser_ipcBlob.js
@@ -0,0 +1,250 @@
+/* -*- Mode: javascript; tab-width: 2; indent-tabs-mode: nil; js-indent-level: 2 -*- */
+
+requestLongerTimeout(3);
+
+const BASE_URI = "http://mochi.test:8888/browser/dom/file/ipc/tests/empty.html";
+
+// More than 1mb memory blob childA-parent-childB.
+add_task(async function test_CtoPtoC_big() {
+  let tab1 = await BrowserTestUtils.openNewForegroundTab(gBrowser, BASE_URI);
+  let browser1 = gBrowser.getBrowserForTab(tab1);
+
+  let blob = await SpecialPowers.spawn(browser1, [], function () {
+    let innerBlob = new Blob([new Array(1024 * 1024).join("123456789ABCDEF")]);
+    return innerBlob;
+  });
+
+  ok(blob, "CtoPtoC-big: We have a blob!");
+  is(
+    blob.size,
+    new Array(1024 * 1024).join("123456789ABCDEF").length,
+    "CtoPtoC-big: The size matches"
+  );
+
+  let tab2 = await BrowserTestUtils.openNewForegroundTab(gBrowser, BASE_URI);
+  let browser2 = gBrowser.getBrowserForTab(tab2);
+
+  let status = await SpecialPowers.spawn(
+    browser2,
+    [blob],
+    function (innerBlob) {
+      return new Promise(resolve => {
+        let fr = new content.FileReader();
+        fr.readAsText(innerBlob);
+        fr.onloadend = function () {
+          resolve(fr.result == new Array(1024 * 1024).join("123456789ABCDEF"));
+        };
+      });
+    }
+  );
+
+  ok(status, "CtoPtoC-big: Data match!");
+
+  BrowserTestUtils.removeTab(tab1);
+  BrowserTestUtils.removeTab(tab2);
+});
+
+// Less than 1mb memory blob childA-parent-childB.
+add_task(async function test_CtoPtoC_small() {
+  let tab1 = await BrowserTestUtils.openNewForegroundTab(gBrowser, BASE_URI);
+  let browser1 = gBrowser.getBrowserForTab(tab1);
+
+  let blob = await SpecialPowers.spawn(browser1, [], function () {
+    let innerBlob = new Blob(["hello world!"]);
+    return innerBlob;
+  });
+
+  ok(blob, "CtoPtoC-small: We have a blob!");
+  is(blob.size, "hello world!".length, "CtoPtoC-small: The size matches");
+
+  let tab2 = await BrowserTestUtils.openNewForegroundTab(gBrowser, BASE_URI);
+  let browser2 = gBrowser.getBrowserForTab(tab2);
+
+  let status = await SpecialPowers.spawn(
+    browser2,
+    [blob],
+    function (innerBlob) {
+      return new Promise(resolve => {
+        let fr = new content.FileReader();
+        fr.readAsText(innerBlob);
+        fr.onloadend = function () {
+          resolve(fr.result == "hello world!");
+        };
+      });
+    }
+  );
+
+  ok(status, "CtoPtoC-small: Data match!");
+
+  BrowserTestUtils.removeTab(tab1);
+  BrowserTestUtils.removeTab(tab2);
+});
+
+// More than 1mb memory blob childA-parent-childB: BroadcastChannel
+add_task(async function test_CtoPtoC_bc_big() {
+  let tab1 = await BrowserTestUtils.openNewForegroundTab(gBrowser, BASE_URI);
+  let browser1 = gBrowser.getBrowserForTab(tab1);
+
+  await SpecialPowers.spawn(browser1, [], function () {
+    var bc = new content.BroadcastChannel("test");
+    bc.onmessage = function () {
+      bc.postMessage(
+        new Blob([new Array(1024 * 1024).join("123456789ABCDEF")])
+      );
+    };
+  });
+
+  let tab2 = await BrowserTestUtils.openNewForegroundTab(gBrowser, BASE_URI);
+  let browser2 = gBrowser.getBrowserForTab(tab2);
+
+  let status = await SpecialPowers.spawn(browser2, [], function () {
+    return new Promise(resolve => {
+      var bc = new content.BroadcastChannel("test");
+      bc.onmessage = function (e) {
+        let fr = new content.FileReader();
+        fr.readAsText(e.data);
+        fr.onloadend = function () {
+          resolve(fr.result == new Array(1024 * 1024).join("123456789ABCDEF"));
+        };
+      };
+
+      bc.postMessage("GO!");
+    });
+  });
+
+  ok(status, "CtoPtoC-broadcastChannel-big: Data match!");
+
+  BrowserTestUtils.removeTab(tab1);
+  BrowserTestUtils.removeTab(tab2);
+});
+
+// Less than 1mb memory blob childA-parent-childB: BroadcastChannel
+add_task(async function test_CtoPtoC_bc_small() {
+  let tab1 = await BrowserTestUtils.openNewForegroundTab(gBrowser, BASE_URI);
+  let browser1 = gBrowser.getBrowserForTab(tab1);
+
+  await SpecialPowers.spawn(browser1, [], function () {
+    var bc = new content.BroadcastChannel("test");
+    bc.onmessage = function () {
+      bc.postMessage(new Blob(["hello world!"]));
+    };
+  });
+
+  let tab2 = await BrowserTestUtils.openNewForegroundTab(gBrowser, BASE_URI);
+  let browser2 = gBrowser.getBrowserForTab(tab2);
+
+  let status = await SpecialPowers.spawn(browser2, [], function () {
+    return new Promise(resolve => {
+      var bc = new content.BroadcastChannel("test");
+      bc.onmessage = function (e) {
+        let fr = new content.FileReader();
+        fr.readAsText(e.data);
+        fr.onloadend = function () {
+          resolve(fr.result == "hello world!");
+        };
+      };
+
+      bc.postMessage("GO!");
+    });
+  });
+
+  ok(status, "CtoPtoC-broadcastChannel-small: Data match!");
+
+  BrowserTestUtils.removeTab(tab1);
+  BrowserTestUtils.removeTab(tab2);
+});
+
+// blob URL childA-parent-childB
+add_task(async function test_CtoPtoC_bc_small() {
+  let tab1 = await BrowserTestUtils.openNewForegroundTab(gBrowser, BASE_URI);
+  let browser1 = gBrowser.getBrowserForTab(tab1);
+
+  let blobURL = await SpecialPowers.spawn(browser1, [], function () {
+    return content.URL.createObjectURL(new content.Blob(["hello world!"]));
+  });
+
+  let tab2 = await BrowserTestUtils.openNewForegroundTab(gBrowser, BASE_URI);
+  let browser2 = gBrowser.getBrowserForTab(tab2);
+
+  let status = await SpecialPowers.spawn(
+    browser2,
+    [blobURL],
+    function (innerBlobURL) {
+      return new Promise(resolve => {
+        var xhr = new content.XMLHttpRequest();
+        xhr.open("GET", innerBlobURL);
+        xhr.onloadend = function () {
+          resolve(xhr.response == "hello world!");
+        };
+
+        xhr.send();
+      });
+    }
+  );
+
+  ok(status, "CtoPtoC-blobURL: Data match!");
+
+  BrowserTestUtils.removeTab(tab1);
+  BrowserTestUtils.removeTab(tab2);
+});
+
+// Multipart Blob childA-parent-childB.
+add_task(async function test_CtoPtoC_multipart() {
+  let tab1 = await BrowserTestUtils.openNewForegroundTab(gBrowser, BASE_URI);
+  let browser1 = gBrowser.getBrowserForTab(tab1);
+
+  let blob = await SpecialPowers.spawn(browser1, [], function () {
+    return new Blob(["!"]);
+  });
+
+  ok(blob, "CtoPtoC-multipart: We have a blob!");
+  is(blob.size, "!".length, "CtoPtoC-multipart: The size matches");
+
+  let newBlob = new Blob(["world", blob]);
+
+  let tab2 = await BrowserTestUtils.openNewForegroundTab(gBrowser, BASE_URI);
+  let browser2 = gBrowser.getBrowserForTab(tab2);
+
+  let status = await SpecialPowers.spawn(
+    browser2,
+    [newBlob],
+    function (innerBlob) {
+      return new Promise(resolve => {
+        let fr = new content.FileReader();
+        fr.readAsText(new Blob(["hello ", innerBlob]));
+        fr.onloadend = function () {
+          resolve(fr.result == "hello world!");
+        };
+      });
+    }
+  );
+
+  ok(status, "CtoPtoC-multipart: Data match!");
+
+  BrowserTestUtils.removeTab(tab1);
+  BrowserTestUtils.removeTab(tab2);
+});
+
+// Multipart Blob childA-parent with a max size
+add_task(async function test_CtoPsize_multipart() {
+  let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, BASE_URI);
+  let browser = gBrowser.getBrowserForTab(tab);
+
+  let blob = await SpecialPowers.spawn(browser, [], function () {
+    let data = new Array(1024 * 512).join("A");
+    let blob1 = new Blob([data]);
+    let blob2 = new Blob([data]);
+    let blob3 = new Blob([data]);
+
+    return new Blob([blob1, blob2, blob3]);
+  });
+
+  ok(blob, "CtoPsize-multipart: We have a blob!");
+  is(
+    blob.size,
+    new Array(1024 * 512).join("A").length * 3,
+    "CtoPsize-multipart: The size matches"
+  );
+
+  BrowserTestUtils.removeTab(tab);
+});
diff --git a/dom/file/ipc/tests/browser_ipcBlob_temporary.js b/dom/file/ipc/tests/browser_ipcBlob_temporary.js
new file mode 100644
index 0000000000..56952e849f
--- /dev/null
+++ b/dom/file/ipc/tests/browser_ipcBlob_temporary.js
@@ -0,0 +1,115 @@
+/* -*- Mode: javascript; tab-width: 2; indent-tabs-mode: nil; js-indent-level: 2 -*- */
+
+requestLongerTimeout(3);
+
+const BASE_URI = "http://mochi.test:8888/browser/dom/file/ipc/tests/empty.html";
+
+add_task(async function test() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["dom.blob.memoryToTemporaryFile", 1],
+      ["dom.ipc.processCount", 4],
+    ],
+  });
+
+  let tab1 = await BrowserTestUtils.openNewForegroundTab(gBrowser, BASE_URI);
+  let browser1 = gBrowser.getBrowserForTab(tab1);
+
+  let tab2 = await BrowserTestUtils.openNewForegroundTab(gBrowser, BASE_URI);
+  let browser2 = gBrowser.getBrowserForTab(tab2);
+
+  await SpecialPowers.spawn(browser2, [], function () {
+    content.window.testPromise = new content.window.Promise(resolve => {
+      let bc = new content.window.BroadcastChannel("foobar");
+      bc.onmessage = e => {
+        function realTest() {
+          return new content.window.Promise(innerResolve => {
+            let count = 10;
+            for (let i = 0; i < count; ++i) {
+              info("FileReader at the same time: " + i);
+              let fr = new content.window.FileReader();
+              fr.readAsText(e.data);
+              fr.onerror = () => {
+                ok(false, "Something wrong happened.");
+              };
+
+              fr.onloadend = () => {
+                is(fr.result.length, e.data.size, "FileReader worked fine.");
+                if (!--count) {
+                  innerResolve(true);
+                }
+              };
+            }
+          });
+        }
+
+        let promises = [];
+        for (let i = 0; i < 5; ++i) {
+          promises.push(realTest());
+        }
+
+        Promise.all(promises).then(() => {
+          resolve(true);
+        });
+      };
+    });
+  });
+
+  let status = await SpecialPowers.spawn(browser1, [], function () {
+    let p = new content.window.Promise(resolve => {
+      let xhr = new content.window.XMLHttpRequest();
+      xhr.open("GET", "temporary.sjs", true);
+      xhr.responseType = "blob";
+      xhr.onload = () => {
+        resolve(xhr.response);
+      };
+      xhr.send();
+    });
+
+    return p.then(blob => {
+      function realTest() {
+        return new content.window.Promise(resolve => {
+          info("Let's broadcast the blob...");
+          let bc = new content.window.BroadcastChannel("foobar");
+          bc.postMessage(blob);
+
+          info("Here the test...");
+          let count = 10;
+          for (let i = 0; i < count; ++i) {
+            info("FileReader at the same time: " + i);
+            let fr = new content.window.FileReader();
+            fr.readAsText(blob);
+            fr.onerror = () => {
+              ok(false, "Something wrong happened.");
+            };
+
+            fr.onloadend = () => {
+              is(fr.result.length, blob.size, "FileReader worked fine.");
+              if (!--count) {
+                resolve(true);
+              }
+            };
+          }
+        });
+      }
+
+      let promises = [];
+      for (let i = 0; i < 5; ++i) {
+        promises.push(realTest());
+      }
+
+      return Promise.all(promises);
+    });
+  });
+
+  ok(status, "All good for tab1!");
+
+  status = await SpecialPowers.spawn(browser2, [], function () {
+    return content.window.testPromise;
+  });
+
+  ok(status, "All good for tab2!");
+
+  BrowserTestUtils.removeTab(tab1);
+  BrowserTestUtils.removeTab(tab2);
+});
diff --git a/dom/file/ipc/tests/empty.html b/dom/file/ipc/tests/empty.html
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/dom/file/ipc/tests/empty.html
diff --git a/dom/file/ipc/tests/green.jpg b/dom/file/ipc/tests/green.jpg
new file mode 100644
index 0000000000..48c454d27c
--- /dev/null
+++ b/dom/file/ipc/tests/green.jpg
diff --git a/dom/file/ipc/tests/mochitest.toml b/dom/file/ipc/tests/mochitest.toml
new file mode 100644
index 0000000000..73e25bba06
--- /dev/null
+++ b/dom/file/ipc/tests/mochitest.toml
@@ -0,0 +1,18 @@
+[DEFAULT]
+support-files = ["script_file.js"]
+
+["test_ipcBlob_createImageBitmap.html"]
+support-files = ["green.jpg"]
+skip-if = [
+  "http3",
+  "http2",
+]
+
+["test_ipcBlob_emptyMultiplex.html"]
+
+["test_ipcBlob_fileReaderSync.html"]
+
+["test_ipcBlob_mixedMultiplex.html"]
+support-files = ["ok.sjs"]
+
+["test_ipcBlob_workers.html"]
diff --git a/dom/file/ipc/tests/ok.sjs b/dom/file/ipc/tests/ok.sjs
new file mode 100644
index 0000000000..42f65733d9
--- /dev/null
+++ b/dom/file/ipc/tests/ok.sjs
@@ -0,0 +1,11 @@
+const CC = Components.Constructor;
+const BinaryInputStream = CC(
+  "@mozilla.org/binaryinputstream;1",
+  "nsIBinaryInputStream",
+  "setInputStream"
+);
+
+function handleRequest(request, response) {
+  response.setHeader("Content-Type", "text/html", false);
+  response.write(request.getHeader("Content-Length"));
+}
diff --git a/dom/file/ipc/tests/script_file.js b/dom/file/ipc/tests/script_file.js
new file mode 100644
index 0000000000..03cefeb3f1
--- /dev/null
+++ b/dom/file/ipc/tests/script_file.js
@@ -0,0 +1,52 @@
+/* eslint-env mozilla/chrome-script */
+
+// eslint-disable-next-line mozilla/reject-importGlobalProperties
+Cu.importGlobalProperties(["File"]);
+
+addMessageListener("file.open", function (e) {
+  var testFile = Services.dirsvc
+    .QueryInterface(Ci.nsIProperties)
+    .get("ProfD", Ci.nsIFile);
+  testFile.append("ipc_fileReader_testing");
+  testFile.createUnique(Ci.nsIFile.NORMAL_FILE_TYPE, 0o600);
+
+  var outStream = Cc[
+    "@mozilla.org/network/file-output-stream;1"
+  ].createInstance(Ci.nsIFileOutputStream);
+  outStream.init(
+    testFile,
+    0x02 | 0x08 | 0x20, // write, create, truncate
+    0o666,
+    0
+  );
+
+  var fileData = "Hello World!";
+  outStream.write(fileData, fileData.length);
+  outStream.close();
+
+  File.createFromNsIFile(testFile).then(function (file) {
+    sendAsyncMessage("file.opened", { file });
+  });
+});
+
+addMessageListener("emptyfile.open", function (e) {
+  var testFile = Services.dirsvc
+    .QueryInterface(Ci.nsIProperties)
+    .get("ProfD", Ci.nsIFile);
+  testFile.append("ipc_fileReader_testing");
+  testFile.createUnique(Ci.nsIFile.NORMAL_FILE_TYPE, 0o600);
+
+  var outStream = Cc[
+    "@mozilla.org/network/file-output-stream;1"
+  ].createInstance(Ci.nsIFileOutputStream);
+  outStream.init(
+    testFile,
+    0x02 | 0x08 | 0x20, // write, create, truncate
+    0o666,
+    0
+  );
+
+  File.createFromNsIFile(testFile).then(function (file) {
+    sendAsyncMessage("emptyfile.opened", { file });
+  });
+});
diff --git a/dom/file/ipc/tests/temporary.sjs b/dom/file/ipc/tests/temporary.sjs
new file mode 100644
index 0000000000..76db4e2f2e
--- /dev/null
+++ b/dom/file/ipc/tests/temporary.sjs
@@ -0,0 +1,6 @@
+function handleRequest(request, response) {
+  response.setHeader("Content-Type", "text/plain", false);
+
+  var data = new Array(1024 * 64).join("1234567890ABCDEF");
+  response.bodyOutputStream.write(data, data.length);
+}
diff --git a/dom/file/ipc/tests/test_ipcBlob_createImageBitmap.html b/dom/file/ipc/tests/test_ipcBlob_createImageBitmap.html
new file mode 100644
index 0000000000..27e8079229
--- /dev/null
+++ b/dom/file/ipc/tests/test_ipcBlob_createImageBitmap.html
@@ -0,0 +1,84 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test IPCBlob and CreateImageBitmap</title>
+  <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script type="text/javascript">
+
+SimpleTest.waitForExplicitFinish();
+
+function test_mainThread() {
+  let bc = new BroadcastChannel('testMainThread');
+  bc.onmessage = e => {
+    createImageBitmap(e.data).then(image => {
+      ok(image.height, "this image has a valid size.");
+    }, () => {
+      ok(false, "error creating the image!");
+    }).then(next);
+  }
+
+  fetch('green.jpg').then(r => r.blob()).then(blob => {
+    let innerBc = new BroadcastChannel('testMainThread');
+    innerBc.postMessage(blob);
+  });
+}
+
+function test_worker() {
+  function workerScript() {
+    function ok(a, msg) { postMessage({ type: 'test', status: !!a, msg }); };
+    function finish() { postMessage({ type: 'finish' }); };
+
+    let bc = new BroadcastChannel('testWorker');
+    bc.onmessage = e => {
+      createImageBitmap(e.data).then(image => {
+        ok(image.height, "this image has a valid size.");
+      }, () => {
+        ok(false, "error creating the image!");
+      }).then(finish);
+    }
+
+    fetch('http://mochi.test:8888/tests/dom/file/ipc/tests/green.jpg').then(r => r.blob()).then(blob => {
+      let innerBc = new BroadcastChannel('testWorker');
+      innerBc.postMessage(blob);
+    });
+  }
+  let workerUrl = URL.createObjectURL(new Blob(["(", workerScript.toString(), ")()"]));
+  let worker = new Worker(workerUrl);
+
+  worker.onmessage = event => {
+    if (event.data.type == 'test') {
+      ok(event.data.status, event.data.msg);
+      return;
+    }
+
+    if (event.data.type == 'finish') {
+      next();
+    }
+  }
+}
+
+let tests = [
+  test_mainThread,
+  test_worker,
+];
+
+function next() {
+  if (!tests.length) {
+    SimpleTest.finish();
+    return;
+  }
+
+  let test = tests.shift();
+  test();
+}
+
+next();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/file/ipc/tests/test_ipcBlob_emptyMultiplex.html b/dom/file/ipc/tests/test_ipcBlob_emptyMultiplex.html
new file mode 100644
index 0000000000..0487069467
--- /dev/null
+++ b/dom/file/ipc/tests/test_ipcBlob_emptyMultiplex.html
@@ -0,0 +1,45 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test an empty IPCBlob together with other parts</title>
+  <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script type="text/javascript">
+
+function checkContent(msg, content) {
+  return new Promise(resolve => {
+    let fr = new FileReader();
+    fr.readAsText(new Blob(content));
+    fr.onloadend = () => {
+      is(fr.result, "Hello world!", "The content matches: " + msg);
+      resolve();
+    };
+  });
+}
+
+SimpleTest.waitForExplicitFinish();
+
+let url = SimpleTest.getTestFileURL("script_file.js");
+
+let script = SpecialPowers.loadChromeScript(url);
+script.addMessageListener("emptyfile.opened", message => {
+  checkContent("middle", ["Hello ", message.file, "world!"]).
+  then(() => checkContent("begin", [message.file, "Hello world!"])).
+  then(() => checkContent("end", ["Hello world!", message.file])).
+  then(() => checkContent("random", [message.file, message.file, "Hello world!", message.file])).
+  then(() => checkContent("random 2", [message.file, message.file, "Hello ",
+                                       message.file, "world", message.file,
+                                       message.file, "!", message.file, "",
+                                       message.file, message.file])).
+  then(SimpleTest.finish);
+});
+
+script.sendAsyncMessage("emptyfile.open");
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/file/ipc/tests/test_ipcBlob_fileReaderSync.html b/dom/file/ipc/tests/test_ipcBlob_fileReaderSync.html
new file mode 100644
index 0000000000..cbf8156e6e
--- /dev/null
+++ b/dom/file/ipc/tests/test_ipcBlob_fileReaderSync.html
@@ -0,0 +1,102 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test IPCBlob and FileReaderSync</title>
+  <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script type="text/javascript">
+
+function workerScript() {
+  // Available to workers.
+  /* global FileReaderSync */
+  onmessage = function(event) {
+    let readerMemoryBlob = new FileReaderSync();
+    let status = readerMemoryBlob.readAsText(new Blob(['hello world'])) == 'hello world';
+    postMessage({ status, message: "FileReaderSync with memory blob still works" });
+
+    let readerIPCBlob1 = new FileReaderSync();
+    postMessage({ blob: event.data, method: 'readAsText',
+                  data: readerIPCBlob1.readAsText(event.data)});
+
+    let readerIPCBlob2 = new FileReaderSync();
+    postMessage({ blob: event.data, method: 'readAsArrayBuffer',
+                  data: readerIPCBlob2.readAsArrayBuffer(event.data)});
+
+    let readerIPCBlob3 = new FileReaderSync();
+    postMessage({ blob: event.data, method: 'readAsDataURL',
+                  data: readerIPCBlob3.readAsDataURL(event.data)});
+
+    let multipartBlob = new Blob(['wow', event.data]);
+
+    let readerIPCBlobMultipart1 = new FileReaderSync();
+    postMessage({ blob: multipartBlob, method: 'readAsText',
+                  data: readerIPCBlobMultipart1.readAsText(multipartBlob)});
+
+    let readerIPCBlobMultipart2 = new FileReaderSync();
+    postMessage({ blob: multipartBlob, method: 'readAsArrayBuffer',
+                  data: readerIPCBlobMultipart2.readAsArrayBuffer(multipartBlob)});
+
+    let readerIPCBlobMultipart3 = new FileReaderSync();
+    postMessage({ blob: multipartBlob, method: 'readAsDataURL',
+                  data: readerIPCBlobMultipart3.readAsDataURL(multipartBlob)});
+
+    postMessage({ finish: true });
+  }
+}
+
+let completed = false;
+let pendingTasks = 0;
+function maybeFinish() {
+  if (completed && !pendingTasks) {
+    SimpleTest.finish();
+  }
+}
+
+let workerUrl = URL.createObjectURL(new Blob(["(", workerScript.toString(), ")()"]));
+let worker = new Worker(workerUrl);
+worker.onmessage = event => {
+  if ("status" in event.data) {
+    ok(event.data.status, event.data.message);
+    return;
+  }
+
+  if ("blob" in event.data) {
+    let fr = new FileReader();
+    fr[event.data.method](event.data.blob);
+    ++pendingTasks;
+    fr.onload = () => {
+      if (event.data.method != 'readAsArrayBuffer') {
+        is(event.data.data, fr.result, "The file has been read");
+      } else {
+        is(event.data.data.byteLength, fr.result.byteLength, "The file has been read");
+      }
+      --pendingTasks;
+      maybeFinish();
+    }
+
+    return;
+  }
+
+  if ("finish" in event.data) {
+    completed = true;
+    maybeFinish();
+  }
+};
+
+let url = SimpleTest.getTestFileURL("script_file.js");
+let script = SpecialPowers.loadChromeScript(url);
+script.addMessageListener("file.opened", message => {
+  worker.postMessage(message.file);
+});
+
+script.sendAsyncMessage("file.open");
+
+SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/file/ipc/tests/test_ipcBlob_mixedMultiplex.html b/dom/file/ipc/tests/test_ipcBlob_mixedMultiplex.html
new file mode 100644
index 0000000000..c8e046fa88
--- /dev/null
+++ b/dom/file/ipc/tests/test_ipcBlob_mixedMultiplex.html
@@ -0,0 +1,41 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test an empty IPCBlob together with other parts</title>
+  <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script type="text/javascript">
+
+let url = SimpleTest.getTestFileURL("script_file.js");
+let data = new Array(1024*1024).join('A');
+
+let script = SpecialPowers.loadChromeScript(url);
+script.addMessageListener("file.opened", message => {
+  let blob = new Blob([data]);
+
+  let form = new FormData();
+  form.append("blob1", blob);
+  form.append("blob2", message.file);
+  form.append("blob3", blob);
+
+  fetch("ok.sjs", {
+    method: "POST",
+    body: form,
+  })
+  .then(r => r.text())
+  .then(r => {
+    ok(parseInt(r, 10) > (data.length * 2), "We have data");
+  })
+  . then(SimpleTest.finish);
+});
+
+script.sendAsyncMessage("file.open");
+SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/file/ipc/tests/test_ipcBlob_workers.html b/dom/file/ipc/tests/test_ipcBlob_workers.html
new file mode 100644
index 0000000000..23e8963bb2
--- /dev/null
+++ b/dom/file/ipc/tests/test_ipcBlob_workers.html
@@ -0,0 +1,124 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test IPCBlob and Workers</title>
+  <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script type="text/javascript">
+
+// Available to workers.
+/* global FileReaderSync */
+
+function test_workerOwner() {
+  info("test_workerOwner");
+
+  function workerScript() {
+    onmessage = e => {
+      e.ports[0].onmessage = event => {
+        let reader = new FileReader();
+        reader.readAsText(event.data);
+        reader.onloadend = () => {
+          let status = reader.result == 'hello world';
+          postMessage(status);
+        }
+      }
+    }
+  }
+
+  let mc = new MessageChannel();
+  mc.port1.postMessage(new Blob(['hello world']));
+
+  let workerUrl = URL.createObjectURL(new Blob(["(", workerScript.toString(), ")()"]));
+  let worker = new Worker(workerUrl);
+
+  worker.postMessage("", [mc.port2]);
+  worker.onmessage = event => {
+    ok(event.data, "All is done!");
+    next();
+  }
+}
+
+function test_workerToMainThread() {
+  info("test_workerToMainThread");
+  function workerScript() {
+    onmessage = e => {
+      e.ports[0].onmessage = event => {
+        postMessage(event.data);
+      }
+    }
+  }
+
+  let mc = new MessageChannel();
+  mc.port1.postMessage(new Blob(['hello world']));
+
+  let workerUrl = URL.createObjectURL(new Blob(["(", workerScript.toString(), ")()"]));
+  let worker = new Worker(workerUrl);
+
+  worker.postMessage("", [mc.port2]);
+  worker.onmessage = event => {
+    info("Blob received back, terminate the worker and force GC");
+    worker.terminate();
+    worker = null;
+    SpecialPowers.forceGC();
+
+    var fr = new FileReader();
+    fr.readAsText(event.data);
+    fr.onloadend = () => {
+      is(fr.result, "hello world", "Data matches");
+      next();
+    }
+  }
+}
+
+function test_workerOwnerPlusFileReaderSync() {
+  info("test_workerOwnerPlusFileReaderSync");
+
+  function workerScript() {
+    onmessage = e => {
+      e.ports[0].onmessage = event => {
+        let reader = new FileReaderSync();
+        let status = reader.readAsText(event.data) == 'hello world';
+         postMessage(status);
+      }
+    }
+  }
+
+  let mc = new MessageChannel();
+  mc.port1.postMessage(new Blob(['hello world']));
+
+  let workerUrl = URL.createObjectURL(new Blob(["(", workerScript.toString(), ")()"]));
+  let worker = new Worker(workerUrl);
+
+  worker.postMessage("", [mc.port2]);
+  worker.onmessage = event => {
+    ok(event.data, "All is done!");
+    next();
+  }
+}
+
+var tests = [
+  test_workerOwner,
+  test_workerToMainThread,
+  test_workerOwnerPlusFileReaderSync,
+];
+
+function next() {
+  if (!tests.length) {
+    SimpleTest.finish();
+    return;
+  }
+
+  var test = tests.shift();
+  test();
+}
+
+SimpleTest.waitForExplicitFinish();
+next();
+
+</script>
+</pre>
+</body>
+</html>