Add m-esr52 at 52.6.0

17 files changed, 5300 insertions, 0 deletions

diff --git a/dom/filehandle/ActorsChild.cpp b/dom/filehandle/ActorsChild.cpp
new file mode 100644
index 000000000..7a0b622f8
--- /dev/null
+++ b/dom/filehandle/ActorsChild.cpp
@@ -0,0 +1,743 @@
+/* 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 "ActorsChild.h"
+
+#include "BackgroundChildImpl.h"
+#include "FileHandleBase.h"
+#include "FileRequestBase.h"
+#include "js/Date.h"
+#include "mozilla/dom/EncodingUtils.h"
+#include "mozilla/dom/File.h"
+#include "mozilla/dom/ipc/BlobChild.h"
+#include "MutableFileBase.h"
+#include "nsCOMPtr.h"
+#include "nsContentUtils.h"
+#include "nsString.h"
+#include "xpcpublic.h"
+#include "mozilla/dom/BindingUtils.h"
+
+namespace mozilla {
+namespace dom {
+
+/*******************************************************************************
+ * Helpers
+ ******************************************************************************/
+
+namespace {
+
+class MOZ_STACK_CLASS AutoSetCurrentFileHandle final
+{
+  typedef mozilla::ipc::BackgroundChildImpl BackgroundChildImpl;
+
+  FileHandleBase* const mFileHandle;
+  FileHandleBase* mPreviousFileHandle;
+  FileHandleBase** mThreadLocalSlot;
+
+public:
+  explicit AutoSetCurrentFileHandle(FileHandleBase* aFileHandle)
+    : mFileHandle(aFileHandle)
+    , mPreviousFileHandle(nullptr)
+    , mThreadLocalSlot(nullptr)
+  {
+    if (aFileHandle) {
+      BackgroundChildImpl::ThreadLocal* threadLocal =
+        BackgroundChildImpl::GetThreadLocalForCurrentThread();
+      MOZ_ASSERT(threadLocal);
+
+      // Hang onto this location for resetting later.
+      mThreadLocalSlot = &threadLocal->mCurrentFileHandle;
+
+      // Save the current value.
+      mPreviousFileHandle = *mThreadLocalSlot;
+
+      // Set the new value.
+      *mThreadLocalSlot = aFileHandle;
+    }
+  }
+
+  ~AutoSetCurrentFileHandle()
+  {
+    MOZ_ASSERT_IF(mThreadLocalSlot, mFileHandle);
+    MOZ_ASSERT_IF(mThreadLocalSlot, *mThreadLocalSlot == mFileHandle);
+
+    if (mThreadLocalSlot) {
+      // Reset old value.
+      *mThreadLocalSlot = mPreviousFileHandle;
+    }
+  }
+
+  FileHandleBase*
+  FileHandle() const
+  {
+    return mFileHandle;
+  }
+};
+
+class MOZ_STACK_CLASS ResultHelper final
+  : public FileRequestBase::ResultCallback
+{
+  FileRequestBase* mFileRequest;
+  AutoSetCurrentFileHandle mAutoFileHandle;
+
+  union
+  {
+    File* mFile;
+    const nsCString* mString;
+    const FileRequestMetadata* mMetadata;
+    const JS::Handle<JS::Value>* mJSValHandle;
+  } mResult;
+
+  enum
+  {
+    ResultTypeFile,
+    ResultTypeString,
+    ResultTypeMetadata,
+    ResultTypeJSValHandle,
+  } mResultType;
+
+public:
+  ResultHelper(FileRequestBase* aFileRequest,
+               FileHandleBase* aFileHandle,
+               File* aResult)
+    : mFileRequest(aFileRequest)
+    , mAutoFileHandle(aFileHandle)
+    , mResultType(ResultTypeFile)
+  {
+    MOZ_ASSERT(aFileRequest);
+    MOZ_ASSERT(aFileHandle);
+    MOZ_ASSERT(aResult);
+
+    mResult.mFile = aResult;
+  }
+
+  ResultHelper(FileRequestBase* aFileRequest,
+               FileHandleBase* aFileHandle,
+               const nsCString* aResult)
+    : mFileRequest(aFileRequest)
+    , mAutoFileHandle(aFileHandle)
+    , mResultType(ResultTypeString)
+  {
+    MOZ_ASSERT(aFileRequest);
+    MOZ_ASSERT(aFileHandle);
+    MOZ_ASSERT(aResult);
+
+    mResult.mString = aResult;
+  }
+
+  ResultHelper(FileRequestBase* aFileRequest,
+               FileHandleBase* aFileHandle,
+               const FileRequestMetadata* aResult)
+    : mFileRequest(aFileRequest)
+    , mAutoFileHandle(aFileHandle)
+    , mResultType(ResultTypeMetadata)
+  {
+    MOZ_ASSERT(aFileRequest);
+    MOZ_ASSERT(aFileHandle);
+    MOZ_ASSERT(aResult);
+
+    mResult.mMetadata = aResult;
+  }
+
+
+  ResultHelper(FileRequestBase* aFileRequest,
+               FileHandleBase* aFileHandle,
+               const JS::Handle<JS::Value>* aResult)
+    : mFileRequest(aFileRequest)
+    , mAutoFileHandle(aFileHandle)
+    , mResultType(ResultTypeJSValHandle)
+  {
+    MOZ_ASSERT(aFileRequest);
+    MOZ_ASSERT(aFileHandle);
+    MOZ_ASSERT(aResult);
+
+    mResult.mJSValHandle = aResult;
+  }
+
+  FileRequestBase*
+  FileRequest() const
+  {
+    return mFileRequest;
+  }
+
+  FileHandleBase*
+  FileHandle() const
+  {
+    return mAutoFileHandle.FileHandle();
+  }
+
+  virtual nsresult
+  GetResult(JSContext* aCx, JS::MutableHandle<JS::Value> aResult) override
+  {
+    MOZ_ASSERT(aCx);
+    MOZ_ASSERT(mFileRequest);
+
+    switch (mResultType) {
+      case ResultTypeFile:
+        return GetResult(aCx, mResult.mFile, aResult);
+
+      case ResultTypeString:
+        return GetResult(aCx, mResult.mString, aResult);
+
+      case ResultTypeMetadata:
+        return GetResult(aCx, mResult.mMetadata, aResult);
+
+      case ResultTypeJSValHandle:
+        aResult.set(*mResult.mJSValHandle);
+        return NS_OK;
+
+      default:
+        MOZ_CRASH("Unknown result type!");
+    }
+
+    MOZ_CRASH("Should never get here!");
+  }
+
+private:
+  nsresult
+  GetResult(JSContext* aCx,
+            File* aFile,
+            JS::MutableHandle<JS::Value> aResult)
+  {
+    bool ok = GetOrCreateDOMReflector(aCx, aFile, aResult);
+    if (NS_WARN_IF(!ok)) {
+      return NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+    }
+
+    return NS_OK;
+  }
+
+  nsresult
+  GetResult(JSContext* aCx,
+            const nsCString* aString,
+            JS::MutableHandle<JS::Value> aResult)
+  {
+    const nsCString& data = *aString;
+
+    nsresult rv;
+
+    if (!mFileRequest->HasEncoding()) {
+      JS::Rooted<JSObject*> arrayBuffer(aCx);
+      rv = nsContentUtils::CreateArrayBuffer(aCx, data, arrayBuffer.address());
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+      }
+
+      aResult.setObject(*arrayBuffer);
+      return NS_OK;
+    }
+
+    nsAutoCString encoding;
+    // The BOM sniffing is baked into the "decode" part of the Encoding
+    // Standard, which the File API references.
+    if (!nsContentUtils::CheckForBOM(
+          reinterpret_cast<const unsigned char *>(data.get()),
+          data.Length(),
+          encoding)) {
+      // BOM sniffing failed. Try the API argument.
+      if (!EncodingUtils::FindEncodingForLabel(mFileRequest->GetEncoding(),
+                                               encoding)) {
+        // API argument failed. Since we are dealing with a file system file,
+        // we don't have a meaningful type attribute for the blob available,
+        // so proceeding to the next step, which is defaulting to UTF-8.
+        encoding.AssignLiteral("UTF-8");
+      }
+    }
+
+    nsString tmpString;
+    rv = nsContentUtils::ConvertStringFromEncoding(encoding, data, tmpString);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+    }
+
+    if (NS_WARN_IF(!xpc::StringToJsval(aCx, tmpString, aResult))) {
+      return NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+    }
+
+    return NS_OK;
+  }
+
+  nsresult
+  GetResult(JSContext* aCx,
+            const FileRequestMetadata* aMetadata,
+            JS::MutableHandle<JS::Value> aResult)
+  {
+    JS::Rooted<JSObject*> obj(aCx, JS_NewPlainObject(aCx));
+    if (NS_WARN_IF(!obj)) {
+      return NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+    }
+
+    const FileRequestSize& size = aMetadata->size();
+    if (size.type() != FileRequestSize::Tvoid_t) {
+      MOZ_ASSERT(size.type() == FileRequestSize::Tuint64_t);
+
+      JS::Rooted<JS::Value> number(aCx, JS_NumberValue(size.get_uint64_t()));
+
+      if (NS_WARN_IF(!JS_DefineProperty(aCx, obj, "size", number, 0))) {
+        return NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+      }
+    }
+
+    const FileRequestLastModified& lastModified = aMetadata->lastModified();
+    if (lastModified.type() != FileRequestLastModified::Tvoid_t) {
+      MOZ_ASSERT(lastModified.type() == FileRequestLastModified::Tint64_t);
+
+      JS::Rooted<JSObject*> date(aCx,
+        JS::NewDateObject(aCx, JS::TimeClip(lastModified.get_int64_t())));
+      if (NS_WARN_IF(!date)) {
+        return NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+      }
+
+      if (NS_WARN_IF(!JS_DefineProperty(aCx, obj, "lastModified", date, 0))) {
+        return NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+      }
+    }
+
+    aResult.setObject(*obj);
+    return NS_OK;
+  }
+};
+
+already_AddRefed<File>
+ConvertActorToFile(FileHandleBase* aFileHandle,
+                   const FileRequestGetFileResponse& aResponse)
+{
+  auto* actor = static_cast<BlobChild*>(aResponse.fileChild());
+
+  MutableFileBase* mutableFile = aFileHandle->MutableFile();
+  MOZ_ASSERT(mutableFile);
+
+  const FileRequestMetadata& metadata = aResponse.metadata();
+
+  const FileRequestSize& size = metadata.size();
+  MOZ_ASSERT(size.type() == FileRequestSize::Tuint64_t);
+
+  const FileRequestLastModified& lastModified = metadata.lastModified();
+  MOZ_ASSERT(lastModified.type() == FileRequestLastModified::Tint64_t);
+
+  actor->SetMysteryBlobInfo(mutableFile->Name(),
+                            mutableFile->Type(),
+                            size.get_uint64_t(),
+                            lastModified.get_int64_t());
+
+  RefPtr<BlobImpl> blobImpl = actor->GetBlobImpl();
+  MOZ_ASSERT(blobImpl);
+
+  RefPtr<File> file = mutableFile->CreateFileFor(blobImpl, aFileHandle);
+  return file.forget();
+}
+
+void
+HandleSuccess(ResultHelper* aResultHelper)
+{
+  MOZ_ASSERT(aResultHelper);
+
+  RefPtr<FileRequestBase> fileRequest = aResultHelper->FileRequest();
+  MOZ_ASSERT(fileRequest);
+  fileRequest->AssertIsOnOwningThread();
+
+  RefPtr<FileHandleBase> fileHandle = aResultHelper->FileHandle();
+  MOZ_ASSERT(fileHandle);
+
+  if (fileHandle->IsAborted()) {
+    fileRequest->SetError(NS_ERROR_DOM_FILEHANDLE_ABORT_ERR);
+    return;
+  }
+
+  MOZ_ASSERT(fileHandle->IsOpen());
+
+  fileRequest->SetResultCallback(aResultHelper);
+
+  MOZ_ASSERT(fileHandle->IsOpen() || fileHandle->IsAborted());
+}
+
+void
+HandleError(FileRequestBase* aFileRequest,
+            nsresult aErrorCode,
+            FileHandleBase* aFileHandle)
+{
+  MOZ_ASSERT(aFileRequest);
+  aFileRequest->AssertIsOnOwningThread();
+  MOZ_ASSERT(NS_FAILED(aErrorCode));
+  MOZ_ASSERT(NS_ERROR_GET_MODULE(aErrorCode) == NS_ERROR_MODULE_DOM_FILEHANDLE);
+  MOZ_ASSERT(aFileHandle);
+
+  RefPtr<FileRequestBase> fileRequest = aFileRequest;
+  RefPtr<FileHandleBase> fileHandle = aFileHandle;
+
+  AutoSetCurrentFileHandle ascfh(aFileHandle);
+
+  fileRequest->SetError(aErrorCode);
+
+  MOZ_ASSERT(fileHandle->IsOpen() || fileHandle->IsAborted());
+}
+
+} // anonymous namespace
+
+/*******************************************************************************
+ * BackgroundMutableFileChildBase
+ ******************************************************************************/
+
+BackgroundMutableFileChildBase::BackgroundMutableFileChildBase(
+                                             DEBUGONLY(PRThread* aOwningThread))
+  : ThreadObject(DEBUGONLY(aOwningThread))
+  , mMutableFile(nullptr)
+{
+  AssertIsOnOwningThread();
+
+  MOZ_COUNT_CTOR(BackgroundMutableFileChildBase);
+}
+
+BackgroundMutableFileChildBase::~BackgroundMutableFileChildBase()
+{
+  AssertIsOnOwningThread();
+
+  MOZ_COUNT_DTOR(BackgroundMutableFileChildBase);
+}
+
+void
+BackgroundMutableFileChildBase::EnsureDOMObject()
+{
+  AssertIsOnOwningThread();
+
+  if (mTemporaryStrongMutableFile) {
+    return;
+  }
+
+  mTemporaryStrongMutableFile = CreateMutableFile();
+
+  MOZ_ASSERT(mTemporaryStrongMutableFile);
+  mTemporaryStrongMutableFile->AssertIsOnOwningThread();
+
+  mMutableFile = mTemporaryStrongMutableFile;
+}
+
+void
+BackgroundMutableFileChildBase::ReleaseDOMObject()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mTemporaryStrongMutableFile);
+  mTemporaryStrongMutableFile->AssertIsOnOwningThread();
+  MOZ_ASSERT(mMutableFile == mTemporaryStrongMutableFile);
+
+  mTemporaryStrongMutableFile = nullptr;
+}
+
+void
+BackgroundMutableFileChildBase::SendDeleteMeInternal()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(!mTemporaryStrongMutableFile);
+
+  if (mMutableFile) {
+    mMutableFile->ClearBackgroundActor();
+    mMutableFile = nullptr;
+
+    MOZ_ALWAYS_TRUE(PBackgroundMutableFileChild::SendDeleteMe());
+  }
+}
+
+void
+BackgroundMutableFileChildBase::ActorDestroy(ActorDestroyReason aWhy)
+{
+  AssertIsOnOwningThread();
+
+  if (mMutableFile) {
+    mMutableFile->ClearBackgroundActor();
+    DEBUGONLY(mMutableFile = nullptr;)
+  }
+}
+
+PBackgroundFileHandleChild*
+BackgroundMutableFileChildBase::AllocPBackgroundFileHandleChild(
+                                                          const FileMode& aMode)
+{
+  MOZ_CRASH("PBackgroundFileHandleChild actors should be manually "
+            "constructed!");
+}
+
+bool
+BackgroundMutableFileChildBase::DeallocPBackgroundFileHandleChild(
+                                             PBackgroundFileHandleChild* aActor)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aActor);
+
+  delete static_cast<BackgroundFileHandleChild*>(aActor);
+  return true;
+}
+
+/*******************************************************************************
+ * BackgroundFileHandleChild
+ ******************************************************************************/
+
+BackgroundFileHandleChild::BackgroundFileHandleChild(
+                                             DEBUGONLY(PRThread* aOwningThread,)
+                                             FileHandleBase* aFileHandle)
+  : ThreadObject(DEBUGONLY(aOwningThread))
+  , mTemporaryStrongFileHandle(aFileHandle)
+  , mFileHandle(aFileHandle)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aFileHandle);
+  aFileHandle->AssertIsOnOwningThread();
+
+  MOZ_COUNT_CTOR(BackgroundFileHandleChild);
+}
+
+BackgroundFileHandleChild::~BackgroundFileHandleChild()
+{
+  AssertIsOnOwningThread();
+
+  MOZ_COUNT_DTOR(BackgroundFileHandleChild);
+}
+
+void
+BackgroundFileHandleChild::SendDeleteMeInternal()
+{
+  AssertIsOnOwningThread();
+
+  if (mFileHandle) {
+    NoteActorDestroyed();
+
+    MOZ_ALWAYS_TRUE(PBackgroundFileHandleChild::SendDeleteMe());
+  }
+}
+
+void
+BackgroundFileHandleChild::NoteActorDestroyed()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT_IF(mTemporaryStrongFileHandle, mFileHandle);
+
+  if (mFileHandle) {
+    mFileHandle->ClearBackgroundActor();
+
+    // Normally this would be DEBUG-only but NoteActorDestroyed is also called
+    // from SendDeleteMeInternal. In that case we're going to receive an actual
+    // ActorDestroy call later and we don't want to touch a dead object.
+    mTemporaryStrongFileHandle = nullptr;
+    mFileHandle = nullptr;
+  }
+}
+
+void
+BackgroundFileHandleChild::NoteComplete()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT_IF(mFileHandle, mTemporaryStrongFileHandle);
+
+  mTemporaryStrongFileHandle = nullptr;
+}
+
+void
+BackgroundFileHandleChild::ActorDestroy(ActorDestroyReason aWhy)
+{
+  AssertIsOnOwningThread();
+
+  NoteActorDestroyed();
+}
+
+bool
+BackgroundFileHandleChild::RecvComplete(const bool& aAborted)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mFileHandle);
+
+  mFileHandle->HandleCompleteOrAbort(aAborted);
+
+  NoteComplete();
+  return true;
+}
+
+PBackgroundFileRequestChild*
+BackgroundFileHandleChild::AllocPBackgroundFileRequestChild(
+                                               const FileRequestParams& aParams)
+{
+  MOZ_CRASH("PBackgroundFileRequestChild actors should be manually "
+            "constructed!");
+}
+
+bool
+BackgroundFileHandleChild::DeallocPBackgroundFileRequestChild(
+                                            PBackgroundFileRequestChild* aActor)
+{
+  MOZ_ASSERT(aActor);
+
+  delete static_cast<BackgroundFileRequestChild*>(aActor);
+  return true;
+}
+
+/*******************************************************************************
+ * BackgroundFileRequestChild
+ ******************************************************************************/
+
+BackgroundFileRequestChild::BackgroundFileRequestChild(
+                                             DEBUGONLY(PRThread* aOwningThread,)
+                                             FileRequestBase* aFileRequest)
+  : ThreadObject(DEBUGONLY(aOwningThread))
+  , mFileRequest(aFileRequest)
+  , mFileHandle(aFileRequest->FileHandle())
+  , mActorDestroyed(false)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aFileRequest);
+  aFileRequest->AssertIsOnOwningThread();
+  MOZ_ASSERT(mFileHandle);
+  mFileHandle->AssertIsOnOwningThread();
+
+  MOZ_COUNT_CTOR(BackgroundFileRequestChild);
+}
+
+BackgroundFileRequestChild::~BackgroundFileRequestChild()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(!mFileHandle);
+
+  MOZ_COUNT_DTOR(BackgroundFileRequestChild);
+}
+
+void
+BackgroundFileRequestChild::HandleResponse(nsresult aResponse)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(NS_FAILED(aResponse));
+  MOZ_ASSERT(NS_ERROR_GET_MODULE(aResponse) == NS_ERROR_MODULE_DOM_FILEHANDLE);
+  MOZ_ASSERT(mFileHandle);
+
+  HandleError(mFileRequest, aResponse, mFileHandle);
+}
+
+void
+BackgroundFileRequestChild::HandleResponse(
+                                    const FileRequestGetFileResponse& aResponse)
+{
+  AssertIsOnOwningThread();
+
+  RefPtr<File> file = ConvertActorToFile(mFileHandle, aResponse);
+
+  ResultHelper helper(mFileRequest, mFileHandle, file);
+
+  HandleSuccess(&helper);
+}
+
+void
+BackgroundFileRequestChild::HandleResponse(const nsCString& aResponse)
+{
+  AssertIsOnOwningThread();
+
+  ResultHelper helper(mFileRequest, mFileHandle, &aResponse);
+
+  HandleSuccess(&helper);
+}
+
+void
+BackgroundFileRequestChild::HandleResponse(const FileRequestMetadata& aResponse)
+{
+  AssertIsOnOwningThread();
+
+  ResultHelper helper(mFileRequest, mFileHandle, &aResponse);
+
+  HandleSuccess(&helper);
+}
+
+void
+BackgroundFileRequestChild::HandleResponse(JS::Handle<JS::Value> aResponse)
+{
+  AssertIsOnOwningThread();
+
+  ResultHelper helper(mFileRequest, mFileHandle, &aResponse);
+
+  HandleSuccess(&helper);
+}
+
+void
+BackgroundFileRequestChild::ActorDestroy(ActorDestroyReason aWhy)
+{
+  AssertIsOnOwningThread();
+
+  MOZ_ASSERT(!mActorDestroyed);
+
+  mActorDestroyed = true;
+
+  if (mFileHandle) {
+    mFileHandle->AssertIsOnOwningThread();
+
+    mFileHandle->OnRequestFinished(/* aActorDestroyedNormally */
+                                   aWhy == Deletion);
+
+    DEBUGONLY(mFileHandle = nullptr;)
+  }
+}
+
+bool
+BackgroundFileRequestChild::Recv__delete__(const FileRequestResponse& aResponse)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mFileRequest);
+  MOZ_ASSERT(mFileHandle);
+
+  if (mFileHandle->IsAborted()) {
+    // Always handle an "error" with ABORT_ERR if the file handle was aborted,
+    // even if the request succeeded or failed with another error.
+    HandleResponse(NS_ERROR_DOM_FILEHANDLE_ABORT_ERR);
+  } else {
+    switch (aResponse.type()) {
+      case FileRequestResponse::Tnsresult:
+        HandleResponse(aResponse.get_nsresult());
+        break;
+
+      case FileRequestResponse::TFileRequestGetFileResponse:
+        HandleResponse(aResponse.get_FileRequestGetFileResponse());
+        break;
+
+      case FileRequestResponse::TFileRequestReadResponse:
+        HandleResponse(aResponse.get_FileRequestReadResponse().data());
+        break;
+
+      case FileRequestResponse::TFileRequestWriteResponse:
+        HandleResponse(JS::UndefinedHandleValue);
+        break;
+
+      case FileRequestResponse::TFileRequestTruncateResponse:
+        HandleResponse(JS::UndefinedHandleValue);
+        break;
+
+      case FileRequestResponse::TFileRequestFlushResponse:
+        HandleResponse(JS::UndefinedHandleValue);
+        break;
+
+      case FileRequestResponse::TFileRequestGetMetadataResponse:
+        HandleResponse(aResponse.get_FileRequestGetMetadataResponse()
+                                .metadata());
+        break;
+
+      default:
+        MOZ_CRASH("Unknown response type!");
+    }
+  }
+
+  mFileHandle->OnRequestFinished(/* aActorDestroyedNormally */ true);
+
+  // Null this out so that we don't try to call OnRequestFinished() again in
+  // ActorDestroy.
+  mFileHandle = nullptr;
+
+  return true;
+}
+
+bool
+BackgroundFileRequestChild::RecvProgress(const uint64_t& aProgress,
+                                         const uint64_t& aProgressMax)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mFileRequest);
+
+  mFileRequest->OnProgress(aProgress, aProgressMax);
+
+  return true;
+}
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/filehandle/ActorsChild.h b/dom/filehandle/ActorsChild.h
new file mode 100644
index 000000000..f2c35e2e1
--- /dev/null
+++ b/dom/filehandle/ActorsChild.h
@@ -0,0 +1,174 @@
+/* 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_filehandle_ActorsChild_h
+#define mozilla_dom_filehandle_ActorsChild_h
+
+#include "js/RootingAPI.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/dom/FileHandleCommon.h"
+#include "mozilla/dom/PBackgroundFileHandleChild.h"
+#include "mozilla/dom/PBackgroundFileRequestChild.h"
+#include "mozilla/dom/PBackgroundMutableFileChild.h"
+
+class nsCString;
+
+namespace mozilla {
+namespace dom {
+
+class FileHandleBase;
+class FileRequestBase;
+class MutableFileBase;
+
+class BackgroundMutableFileChildBase
+  : public ThreadObject
+  , public PBackgroundMutableFileChild
+{
+protected:
+  friend class MutableFileBase;
+
+  RefPtr<MutableFileBase> mTemporaryStrongMutableFile;
+  MutableFileBase* mMutableFile;
+
+public:
+  void
+  EnsureDOMObject();
+
+  MutableFileBase*
+  GetDOMObject() const
+  {
+    AssertIsOnOwningThread();
+    return mMutableFile;
+  }
+
+  void
+  ReleaseDOMObject();
+
+protected:
+  BackgroundMutableFileChildBase(DEBUGONLY(PRThread* aOwningThread));
+
+  ~BackgroundMutableFileChildBase();
+
+  void
+  SendDeleteMeInternal();
+
+  virtual already_AddRefed<MutableFileBase>
+  CreateMutableFile() = 0;
+
+  // IPDL methods are only called by IPDL.
+  virtual void
+  ActorDestroy(ActorDestroyReason aWhy) override;
+
+  virtual PBackgroundFileHandleChild*
+  AllocPBackgroundFileHandleChild(const FileMode& aMode) override;
+
+  virtual bool
+  DeallocPBackgroundFileHandleChild(PBackgroundFileHandleChild* aActor)
+                                    override;
+
+  bool
+  SendDeleteMe() = delete;
+};
+
+class BackgroundFileHandleChild
+  : public ThreadObject
+  , public PBackgroundFileHandleChild
+{
+  friend class BackgroundMutableFileChildBase;
+  friend class MutableFileBase;
+
+  // mTemporaryStrongFileHandle is strong and is only valid until the end of
+  // NoteComplete() member function or until the NoteActorDestroyed() member
+  // function is called.
+  RefPtr<FileHandleBase> mTemporaryStrongFileHandle;
+
+  // mFileHandle is weak and is valid until the NoteActorDestroyed() member
+  // function is called.
+  FileHandleBase* mFileHandle;
+
+public:
+  explicit BackgroundFileHandleChild(DEBUGONLY(PRThread* aOwningThread,)
+                                     FileHandleBase* aFileHandle);
+
+  void
+  SendDeleteMeInternal();
+
+private:
+  ~BackgroundFileHandleChild();
+
+  void
+  NoteActorDestroyed();
+
+  void
+  NoteComplete();
+
+  // IPDL methods are only called by IPDL.
+  virtual void
+  ActorDestroy(ActorDestroyReason aWhy) override;
+
+  bool
+  RecvComplete(const bool& aAborted) override;
+
+  virtual PBackgroundFileRequestChild*
+  AllocPBackgroundFileRequestChild(const FileRequestParams& aParams)
+                                   override;
+
+  virtual bool
+  DeallocPBackgroundFileRequestChild(PBackgroundFileRequestChild* aActor)
+                                     override;
+
+  bool
+  SendDeleteMe() = delete;
+};
+
+class BackgroundFileRequestChild final
+  : public ThreadObject
+  , public PBackgroundFileRequestChild
+{
+  friend class BackgroundFileHandleChild;
+  friend class FileHandleBase;
+
+  RefPtr<FileRequestBase> mFileRequest;
+  RefPtr<FileHandleBase> mFileHandle;
+  bool mActorDestroyed;
+
+private:
+  // Only created by FileHandleBase.
+  explicit BackgroundFileRequestChild(DEBUGONLY(PRThread* aOwningThread,)
+                                      FileRequestBase* aFileRequest);
+
+  // Only destroyed by BackgroundFileHandleChild.
+  ~BackgroundFileRequestChild();
+
+  void
+  HandleResponse(nsresult aResponse);
+
+  void
+  HandleResponse(const FileRequestGetFileResponse& aResponse);
+
+  void
+  HandleResponse(const nsCString& aResponse);
+
+  void
+  HandleResponse(const FileRequestMetadata& aResponse);
+
+  void
+  HandleResponse(JS::Handle<JS::Value> aResponse);
+
+  // IPDL methods are only called by IPDL.
+  virtual void
+  ActorDestroy(ActorDestroyReason aWhy) override;
+
+  virtual bool
+  Recv__delete__(const FileRequestResponse& aResponse) override;
+
+  virtual bool
+  RecvProgress(const uint64_t& aProgress,
+               const uint64_t& aProgressMax) override;
+};
+
+} // namespace dom
+} // namespace mozilla
+
+#endif // mozilla_dom_filehandle_ActorsChild_h
diff --git a/dom/filehandle/ActorsParent.cpp b/dom/filehandle/ActorsParent.cpp
new file mode 100644
index 000000000..6b81c782f
--- /dev/null
+++ b/dom/filehandle/ActorsParent.cpp
@@ -0,0 +1,2666 @@
+/* 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 "ActorsParent.h"
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/Unused.h"
+#include "mozilla/dom/File.h"
+#include "mozilla/dom/FileHandleCommon.h"
+#include "mozilla/dom/PBackgroundFileHandleParent.h"
+#include "mozilla/dom/PBackgroundFileRequestParent.h"
+#include "mozilla/dom/indexedDB/ActorsParent.h"
+#include "mozilla/dom/ipc/BlobParent.h"
+#include "nsAutoPtr.h"
+#include "nsComponentManagerUtils.h"
+#include "nsDebug.h"
+#include "nsError.h"
+#include "nsIEventTarget.h"
+#include "nsIFileStreams.h"
+#include "nsIInputStream.h"
+#include "nsIOutputStream.h"
+#include "nsIRunnable.h"
+#include "nsISeekableStream.h"
+#include "nsIThread.h"
+#include "nsIThreadPool.h"
+#include "nsNetUtil.h"
+#include "nsStreamUtils.h"
+#include "nsStringStream.h"
+#include "nsTArray.h"
+#include "nsThreadPool.h"
+#include "nsThreadUtils.h"
+#include "nsXPCOMCIDInternal.h"
+
+#define DISABLE_ASSERTS_FOR_FUZZING 0
+
+#if DISABLE_ASSERTS_FOR_FUZZING
+#define ASSERT_UNLESS_FUZZING(...) do { } while (0)
+#else
+#define ASSERT_UNLESS_FUZZING(...) MOZ_ASSERT(false, __VA_ARGS__)
+#endif
+
+namespace mozilla {
+namespace dom {
+
+using namespace mozilla::ipc;
+
+namespace {
+
+/******************************************************************************
+ * Constants
+ ******************************************************************************/
+
+const uint32_t kThreadLimit = 5;
+const uint32_t kIdleThreadLimit = 1;
+const uint32_t kIdleThreadTimeoutMs = 30000;
+
+const uint32_t kStreamCopyBlockSize = 32768;
+
+} // namespace
+
+class FileHandleThreadPool::FileHandleQueue final
+  : public Runnable
+{
+  friend class FileHandleThreadPool;
+
+  RefPtr<FileHandleThreadPool> mOwningFileHandleThreadPool;
+  RefPtr<FileHandle> mFileHandle;
+  nsTArray<RefPtr<FileHandleOp>> mQueue;
+  RefPtr<FileHandleOp> mCurrentOp;
+  bool mShouldFinish;
+
+public:
+  explicit
+  FileHandleQueue(FileHandleThreadPool* aFileHandleThreadPool,
+                  FileHandle* aFileHandle);
+
+  void
+  Enqueue(FileHandleOp* aFileHandleOp);
+
+  void
+  Finish();
+
+  void
+  ProcessQueue();
+
+private:
+  ~FileHandleQueue() {}
+
+  NS_DECL_NSIRUNNABLE
+};
+
+struct FileHandleThreadPool::DelayedEnqueueInfo
+{
+  RefPtr<FileHandle> mFileHandle;
+  RefPtr<FileHandleOp> mFileHandleOp;
+  bool mFinish;
+};
+
+class FileHandleThreadPool::DirectoryInfo
+{
+  friend class FileHandleThreadPool;
+
+  RefPtr<FileHandleThreadPool> mOwningFileHandleThreadPool;
+  nsTArray<RefPtr<FileHandleQueue>> mFileHandleQueues;
+  nsTArray<DelayedEnqueueInfo> mDelayedEnqueueInfos;
+  nsTHashtable<nsStringHashKey> mFilesReading;
+  nsTHashtable<nsStringHashKey> mFilesWriting;
+
+public:
+  FileHandleQueue*
+  CreateFileHandleQueue(FileHandle* aFileHandle);
+
+  FileHandleQueue*
+  GetFileHandleQueue(FileHandle* aFileHandle);
+
+  void
+  RemoveFileHandleQueue(FileHandle* aFileHandle);
+
+  bool
+  HasRunningFileHandles()
+  {
+    return !mFileHandleQueues.IsEmpty();
+  }
+
+  DelayedEnqueueInfo*
+  CreateDelayedEnqueueInfo(FileHandle* aFileHandle,
+                           FileHandleOp* aFileHandleOp,
+                           bool aFinish);
+
+  void
+  LockFileForReading(const nsAString& aFileName)
+  {
+    mFilesReading.PutEntry(aFileName);
+  }
+
+  void
+  LockFileForWriting(const nsAString& aFileName)
+  {
+    mFilesWriting.PutEntry(aFileName);
+  }
+
+  bool
+  IsFileLockedForReading(const nsAString& aFileName)
+  {
+    return mFilesReading.Contains(aFileName);
+  }
+
+  bool
+  IsFileLockedForWriting(const nsAString& aFileName)
+  {
+    return mFilesWriting.Contains(aFileName);
+  }
+
+private:
+  explicit DirectoryInfo(FileHandleThreadPool* aFileHandleThreadPool)
+    : mOwningFileHandleThreadPool(aFileHandleThreadPool)
+  { }
+};
+
+struct FileHandleThreadPool::StoragesCompleteCallback final
+{
+  friend class nsAutoPtr<StoragesCompleteCallback>;
+
+  nsTArray<nsCString> mDirectoryIds;
+  nsCOMPtr<nsIRunnable> mCallback;
+
+  StoragesCompleteCallback(nsTArray<nsCString>&& aDatabaseIds,
+                           nsIRunnable* aCallback);
+
+private:
+  ~StoragesCompleteCallback();
+};
+
+/******************************************************************************
+ * Actor class declarations
+ ******************************************************************************/
+
+class FileHandle
+  : public PBackgroundFileHandleParent
+{
+  friend class BackgroundMutableFileParentBase;
+
+  class FinishOp;
+
+  RefPtr<BackgroundMutableFileParentBase> mMutableFile;
+  nsCOMPtr<nsISupports> mStream;
+  uint64_t mActiveRequestCount;
+  FileHandleStorage mStorage;
+  Atomic<bool> mInvalidatedOnAnyThread;
+  FileMode mMode;
+  bool mHasBeenActive;
+  bool mActorDestroyed;
+  bool mInvalidated;
+  bool mAborted;
+  bool mFinishOrAbortReceived;
+  bool mFinishedOrAborted;
+  bool mForceAborted;
+
+  DEBUGONLY(nsCOMPtr<nsIEventTarget> mThreadPoolEventTarget;)
+
+public:
+  void
+  AssertIsOnThreadPool() const;
+
+  bool
+  IsActorDestroyed() const
+  {
+    AssertIsOnBackgroundThread();
+
+    return mActorDestroyed;
+  }
+
+  // Must be called on the background thread.
+  bool
+  IsInvalidated() const
+  {
+    MOZ_ASSERT(IsOnBackgroundThread(), "Use IsInvalidatedOnAnyThread()");
+    MOZ_ASSERT_IF(mInvalidated, mAborted);
+
+    return mInvalidated;
+  }
+
+  // May be called on any thread, but is more expensive than IsInvalidated().
+  bool
+  IsInvalidatedOnAnyThread() const
+  {
+    return mInvalidatedOnAnyThread;
+  }
+
+  void
+  SetActive()
+  {
+    AssertIsOnBackgroundThread();
+
+    mHasBeenActive = true;
+  }
+
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(mozilla::dom::FileHandle)
+
+  nsresult
+  GetOrCreateStream(nsISupports** aStream);
+
+  void
+  Abort(bool aForce);
+
+  FileHandleStorage
+  Storage() const
+  {
+    return mStorage;
+  }
+
+  FileMode
+  Mode() const
+  {
+    return mMode;
+  }
+
+  BackgroundMutableFileParentBase*
+  GetMutableFile() const
+  {
+    AssertIsOnBackgroundThread();
+    MOZ_ASSERT(mMutableFile);
+
+    return mMutableFile;
+  }
+
+  bool
+  IsAborted() const
+  {
+    AssertIsOnBackgroundThread();
+
+    return mAborted;
+  }
+
+  PBackgroundParent*
+  GetBackgroundParent() const
+  {
+    AssertIsOnBackgroundThread();
+    MOZ_ASSERT(!IsActorDestroyed());
+
+    return GetMutableFile()->GetBackgroundParent();
+  }
+
+  void
+  NoteActiveRequest();
+
+  void
+  NoteFinishedRequest();
+
+  void
+  Invalidate();
+
+private:
+  // This constructor is only called by BackgroundMutableFileParentBase.
+  FileHandle(BackgroundMutableFileParentBase* aMutableFile,
+             FileMode aMode);
+
+  // Reference counted.
+  ~FileHandle();
+
+  void
+  MaybeFinishOrAbort()
+  {
+    AssertIsOnBackgroundThread();
+
+    // If we've already finished or aborted then there's nothing else to do.
+    if (mFinishedOrAborted) {
+      return;
+    }
+
+    // If there are active requests then we have to wait for those requests to
+    // complete (see NoteFinishedRequest).
+    if (mActiveRequestCount) {
+      return;
+    }
+
+    // If we haven't yet received a finish or abort message then there could be
+    // additional requests coming so we should wait unless we're being forced to
+    // abort.
+    if (!mFinishOrAbortReceived && !mForceAborted) {
+      return;
+    }
+
+    FinishOrAbort();
+  }
+
+  void
+  SendCompleteNotification(bool aAborted);
+
+  bool
+  VerifyRequestParams(const FileRequestParams& aParams) const;
+
+  bool
+  VerifyRequestData(const FileRequestData& aData) const;
+
+  void
+  FinishOrAbort();
+
+  // IPDL methods are only called by IPDL.
+  virtual void
+  ActorDestroy(ActorDestroyReason aWhy) override;
+
+  virtual bool
+  RecvDeleteMe() override;
+
+  virtual bool
+  RecvFinish() override;
+
+  virtual bool
+  RecvAbort() override;
+
+  virtual PBackgroundFileRequestParent*
+  AllocPBackgroundFileRequestParent(const FileRequestParams& aParams) override;
+
+  virtual bool
+  RecvPBackgroundFileRequestConstructor(PBackgroundFileRequestParent* aActor,
+                                        const FileRequestParams& aParams)
+                                        override;
+
+  virtual bool
+  DeallocPBackgroundFileRequestParent(PBackgroundFileRequestParent* aActor)
+                                      override;
+};
+
+class FileHandleOp
+{
+protected:
+  nsCOMPtr<nsIEventTarget> mOwningThread;
+  RefPtr<FileHandle> mFileHandle;
+
+public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(FileHandleOp)
+
+  void
+  AssertIsOnOwningThread() const
+  {
+    AssertIsOnBackgroundThread();
+    MOZ_ASSERT(mOwningThread);
+    DebugOnly<bool> current;
+    MOZ_ASSERT(NS_SUCCEEDED(mOwningThread->IsOnCurrentThread(&current)));
+    MOZ_ASSERT(current);
+  }
+
+  nsIEventTarget*
+  OwningThread() const
+  {
+    return mOwningThread;
+  }
+
+  void
+  AssertIsOnThreadPool() const
+  {
+    MOZ_ASSERT(mFileHandle);
+    mFileHandle->AssertIsOnThreadPool();
+  }
+
+  void
+  Enqueue();
+
+  virtual void
+  RunOnThreadPool() = 0;
+
+  virtual void
+  RunOnOwningThread() = 0;
+
+protected:
+  FileHandleOp(FileHandle* aFileHandle)
+    : mOwningThread(NS_GetCurrentThread())
+    , mFileHandle(aFileHandle)
+  {
+    AssertIsOnOwningThread();
+    MOZ_ASSERT(aFileHandle);
+  }
+
+  virtual
+  ~FileHandleOp()
+  { }
+};
+
+class FileHandle::FinishOp
+  : public FileHandleOp
+{
+  friend class FileHandle;
+
+  bool mAborted;
+
+private:
+  FinishOp(FileHandle* aFileHandle,
+           bool aAborted)
+    : FileHandleOp(aFileHandle)
+    , mAborted(aAborted)
+  {
+    MOZ_ASSERT(aFileHandle);
+  }
+
+  ~FinishOp()
+  { }
+
+  virtual void
+  RunOnThreadPool() override;
+
+  virtual void
+  RunOnOwningThread() override;
+};
+
+class NormalFileHandleOp
+  : public FileHandleOp
+  , public PBackgroundFileRequestParent
+{
+  nsresult mResultCode;
+  Atomic<bool> mOperationMayProceed;
+  bool mActorDestroyed;
+  const bool mFileHandleIsAborted;
+
+  DEBUGONLY(bool mResponseSent;)
+
+protected:
+  nsCOMPtr<nsISupports> mFileStream;
+
+public:
+  void
+  NoteActorDestroyed()
+  {
+    AssertIsOnOwningThread();
+
+    mActorDestroyed = true;
+    mOperationMayProceed = false;
+  }
+
+  bool
+  IsActorDestroyed() const
+  {
+    AssertIsOnOwningThread();
+
+    return mActorDestroyed;
+  }
+
+  // May be called on any thread, but you should call IsActorDestroyed() if
+  // you know you're on the background thread because it is slightly faster.
+  bool
+  OperationMayProceed() const
+  {
+    return mOperationMayProceed;
+  }
+
+  // May be overridden by subclasses if they need to perform work on the
+  // background thread before being enqueued. Returning false will kill the
+  // child actors and prevent enqueue.
+  virtual bool
+  Init(FileHandle* aFileHandle);
+
+  // This callback will be called on the background thread before releasing the
+  // final reference to this request object. Subclasses may perform any
+  // additional cleanup here but must always call the base class implementation.
+  virtual void
+  Cleanup();
+
+protected:
+  NormalFileHandleOp(FileHandle* aFileHandle)
+    : FileHandleOp(aFileHandle)
+    , mResultCode(NS_OK)
+    , mOperationMayProceed(true)
+    , mActorDestroyed(false)
+    , mFileHandleIsAborted(aFileHandle->IsAborted())
+    DEBUGONLY(, mResponseSent(false))
+  {
+    MOZ_ASSERT(aFileHandle);
+  }
+
+  virtual
+  ~NormalFileHandleOp();
+
+  // Must be overridden in subclasses. Called on the target thread to allow the
+  // subclass to perform necessary file operations. A successful return value
+  // will trigger a SendSuccessResult callback on the background thread while
+  // a failure value will trigger a SendFailureResult callback.
+  virtual nsresult
+  DoFileWork(FileHandle* aFileHandle) = 0;
+
+  // Subclasses use this override to set the IPDL response value.
+  virtual void
+  GetResponse(FileRequestResponse& aResponse) = 0;
+
+private:
+  nsresult
+  SendSuccessResult();
+
+  bool
+  SendFailureResult(nsresult aResultCode);
+
+  virtual void
+  RunOnThreadPool() override;
+
+  virtual void
+  RunOnOwningThread() override;
+
+  // IPDL methods.
+  virtual void
+  ActorDestroy(ActorDestroyReason aWhy) override;
+};
+
+class CopyFileHandleOp
+  : public NormalFileHandleOp
+{
+  class ProgressRunnable;
+
+protected:
+  nsCOMPtr<nsISupports> mBufferStream;
+
+  uint64_t mOffset;
+  uint64_t mSize;
+
+  bool mRead;
+
+protected:
+  CopyFileHandleOp(FileHandle* aFileHandle)
+    : NormalFileHandleOp(aFileHandle)
+    , mOffset(0)
+    , mSize(0)
+    , mRead(true)
+  { }
+
+  virtual nsresult
+  DoFileWork(FileHandle* aFileHandle) override;
+
+  virtual void
+  Cleanup() override;
+};
+
+class CopyFileHandleOp::ProgressRunnable final
+  : public Runnable
+{
+  RefPtr<CopyFileHandleOp> mCopyFileHandleOp;
+  uint64_t mProgress;
+  uint64_t mProgressMax;
+
+public:
+  ProgressRunnable(CopyFileHandleOp* aCopyFileHandleOp,
+                   uint64_t aProgress,
+                   uint64_t aProgressMax)
+    : mCopyFileHandleOp(aCopyFileHandleOp)
+    , mProgress(aProgress)
+    , mProgressMax(aProgressMax)
+  { }
+
+private:
+  ~ProgressRunnable() {}
+
+  NS_DECL_NSIRUNNABLE
+};
+
+class GetMetadataOp
+  : public NormalFileHandleOp
+{
+  friend class FileHandle;
+
+  const FileRequestGetMetadataParams mParams;
+
+protected:
+  FileRequestMetadata mMetadata;
+
+protected:
+  // Only created by FileHandle.
+  GetMetadataOp(FileHandle* aFileHandle,
+                const FileRequestParams& aParams);
+
+  ~GetMetadataOp()
+  { }
+
+  virtual nsresult
+  DoFileWork(FileHandle* aFileHandle) override;
+
+  virtual void
+  GetResponse(FileRequestResponse& aResponse) override;
+};
+
+class ReadOp final
+  : public CopyFileHandleOp
+{
+  friend class FileHandle;
+
+  class MemoryOutputStream;
+
+  const FileRequestReadParams mParams;
+
+private:
+  // Only created by FileHandle.
+  ReadOp(FileHandle* aFileHandle,
+         const FileRequestParams& aParams);
+
+  ~ReadOp()
+  { }
+
+  virtual bool
+  Init(FileHandle* aFileHandle) override;
+
+  virtual void
+  GetResponse(FileRequestResponse& aResponse) override;
+};
+
+class ReadOp::MemoryOutputStream final
+  : public nsIOutputStream
+{
+  nsCString mData;
+  uint64_t mOffset;
+
+public:
+  static already_AddRefed<MemoryOutputStream>
+  Create(uint64_t aSize);
+
+  const nsCString&
+  Data() const
+  {
+    return mData;
+  }
+
+private:
+  MemoryOutputStream()
+  : mOffset(0)
+  { }
+
+  virtual ~MemoryOutputStream()
+  { }
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIOUTPUTSTREAM
+};
+
+class WriteOp final
+  : public CopyFileHandleOp
+{
+  friend class FileHandle;
+
+  const FileRequestWriteParams mParams;
+
+private:
+  // Only created by FileHandle.
+  WriteOp(FileHandle* aFileHandle,
+          const FileRequestParams& aParams);
+
+  ~WriteOp()
+  { }
+
+  virtual bool
+  Init(FileHandle* aFileHandle) override;
+
+  virtual void
+  GetResponse(FileRequestResponse& aResponse) override;
+};
+
+class TruncateOp final
+  : public NormalFileHandleOp
+{
+  friend class FileHandle;
+
+  const FileRequestTruncateParams mParams;
+
+private:
+  // Only created by FileHandle.
+  TruncateOp(FileHandle* aFileHandle,
+                        const FileRequestParams& aParams);
+
+  ~TruncateOp()
+  { }
+
+  virtual nsresult
+  DoFileWork(FileHandle* aFileHandle) override;
+
+  virtual void
+  GetResponse(FileRequestResponse& aResponse) override;
+};
+
+class FlushOp final
+  : public NormalFileHandleOp
+{
+  friend class FileHandle;
+
+  const FileRequestFlushParams mParams;
+
+private:
+  // Only created by FileHandle.
+  FlushOp(FileHandle* aFileHandle,
+          const FileRequestParams& aParams);
+
+  ~FlushOp()
+  { }
+
+  virtual nsresult
+  DoFileWork(FileHandle* aFileHandle) override;
+
+  virtual void
+  GetResponse(FileRequestResponse& aResponse) override;
+};
+
+class GetFileOp final
+  : public GetMetadataOp
+{
+  friend class FileHandle;
+
+  PBackgroundParent* mBackgroundParent;
+
+private:
+  // Only created by FileHandle.
+  GetFileOp(FileHandle* aFileHandle,
+            const FileRequestParams& aParams);
+
+  ~GetFileOp()
+  { }
+
+  virtual void
+  GetResponse(FileRequestResponse& aResponse) override;
+};
+
+namespace {
+
+/*******************************************************************************
+ * Helper Functions
+ ******************************************************************************/
+
+FileHandleThreadPool*
+GetFileHandleThreadPoolFor(FileHandleStorage aStorage)
+{
+  switch (aStorage) {
+    case FILE_HANDLE_STORAGE_IDB:
+      return mozilla::dom::indexedDB::GetFileHandleThreadPool();
+
+    default:
+      MOZ_CRASH("Bad file handle storage value!");
+  }
+}
+
+} // namespace
+
+/*******************************************************************************
+ * FileHandleThreadPool implementation
+ ******************************************************************************/
+
+FileHandleThreadPool::FileHandleThreadPool()
+  : mOwningThread(NS_GetCurrentThread())
+  , mShutdownRequested(false)
+  , mShutdownComplete(false)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mOwningThread);
+  AssertIsOnOwningThread();
+}
+
+FileHandleThreadPool::~FileHandleThreadPool()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(!mDirectoryInfos.Count());
+  MOZ_ASSERT(mCompleteCallbacks.IsEmpty());
+  MOZ_ASSERT(mShutdownRequested);
+  MOZ_ASSERT(mShutdownComplete);
+}
+
+// static
+already_AddRefed<FileHandleThreadPool>
+FileHandleThreadPool::Create()
+{
+  AssertIsOnBackgroundThread();
+
+  RefPtr<FileHandleThreadPool> fileHandleThreadPool =
+    new FileHandleThreadPool();
+  fileHandleThreadPool->AssertIsOnOwningThread();
+
+  if (NS_WARN_IF(NS_FAILED(fileHandleThreadPool->Init()))) {
+    return nullptr;
+  }
+
+  return fileHandleThreadPool.forget();
+}
+
+#ifdef DEBUG
+
+void
+FileHandleThreadPool::AssertIsOnOwningThread() const
+{
+  MOZ_ASSERT(mOwningThread);
+
+  bool current;
+  MOZ_ALWAYS_SUCCEEDS(mOwningThread->IsOnCurrentThread(&current));
+  MOZ_ASSERT(current);
+}
+
+nsIEventTarget*
+FileHandleThreadPool::GetThreadPoolEventTarget() const
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mThreadPool);
+
+  return mThreadPool;
+}
+
+#endif // DEBUG
+
+void
+FileHandleThreadPool::Enqueue(FileHandle* aFileHandle,
+                              FileHandleOp* aFileHandleOp,
+                              bool aFinish)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aFileHandle);
+  MOZ_ASSERT(!mShutdownRequested);
+
+  BackgroundMutableFileParentBase* mutableFile = aFileHandle->GetMutableFile();
+
+  const nsACString& directoryId = mutableFile->DirectoryId();
+  const nsAString& fileName = mutableFile->FileName();
+  bool modeIsWrite = aFileHandle->Mode() == FileMode::Readwrite;
+
+  DirectoryInfo* directoryInfo;
+  if (!mDirectoryInfos.Get(directoryId, &directoryInfo)) {
+    nsAutoPtr<DirectoryInfo> newDirectoryInfo(new DirectoryInfo(this));
+
+    mDirectoryInfos.Put(directoryId, newDirectoryInfo);
+
+    directoryInfo = newDirectoryInfo.forget();
+  }
+
+  FileHandleQueue* existingFileHandleQueue =
+    directoryInfo->GetFileHandleQueue(aFileHandle);
+
+  if (existingFileHandleQueue) {
+    existingFileHandleQueue->Enqueue(aFileHandleOp);
+    if (aFinish) {
+      existingFileHandleQueue->Finish();
+    }
+    return;
+  }
+
+  bool lockedForReading = directoryInfo->IsFileLockedForReading(fileName);
+  bool lockedForWriting = directoryInfo->IsFileLockedForWriting(fileName);
+
+  if (modeIsWrite) {
+    if (!lockedForWriting) {
+      directoryInfo->LockFileForWriting(fileName);
+    }
+  }
+  else {
+    if (!lockedForReading) {
+      directoryInfo->LockFileForReading(fileName);
+    }
+  }
+
+  if (lockedForWriting || (lockedForReading && modeIsWrite)) {
+    directoryInfo->CreateDelayedEnqueueInfo(aFileHandle,
+                                            aFileHandleOp,
+                                            aFinish);
+  }
+  else {
+    FileHandleQueue* fileHandleQueue =
+      directoryInfo->CreateFileHandleQueue(aFileHandle);
+
+    if (aFileHandleOp) {
+      fileHandleQueue->Enqueue(aFileHandleOp);
+      if (aFinish) {
+        fileHandleQueue->Finish();
+      }
+    }
+  }
+}
+
+void
+FileHandleThreadPool::WaitForDirectoriesToComplete(
+                                             nsTArray<nsCString>&& aDirectoryIds,
+                                             nsIRunnable* aCallback)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(!aDirectoryIds.IsEmpty());
+  MOZ_ASSERT(aCallback);
+
+  nsAutoPtr<StoragesCompleteCallback> callback(
+    new StoragesCompleteCallback(Move(aDirectoryIds), aCallback));
+
+  if (!MaybeFireCallback(callback)) {
+    mCompleteCallbacks.AppendElement(callback.forget());
+  }
+}
+
+void
+FileHandleThreadPool::Shutdown()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(!mShutdownRequested);
+  MOZ_ASSERT(!mShutdownComplete);
+
+  mShutdownRequested = true;
+
+  if (!mThreadPool) {
+    MOZ_ASSERT(!mDirectoryInfos.Count());
+    MOZ_ASSERT(mCompleteCallbacks.IsEmpty());
+
+    mShutdownComplete = true;
+    return;
+  }
+
+  if (!mDirectoryInfos.Count()) {
+    Cleanup();
+
+    MOZ_ASSERT(mShutdownComplete);
+    return;
+  }
+
+  nsIThread* currentThread = NS_GetCurrentThread();
+  MOZ_ASSERT(currentThread);
+
+  while (!mShutdownComplete) {
+    MOZ_ALWAYS_TRUE(NS_ProcessNextEvent(currentThread));
+  }
+}
+
+nsresult
+FileHandleThreadPool::Init()
+{
+  AssertIsOnOwningThread();
+
+  mThreadPool = new nsThreadPool();
+
+  nsresult rv = mThreadPool->SetName(NS_LITERAL_CSTRING("FileHandles"));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = mThreadPool->SetThreadLimit(kThreadLimit);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = mThreadPool->SetIdleThreadLimit(kIdleThreadLimit);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = mThreadPool->SetIdleThreadTimeout(kIdleThreadTimeoutMs);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+void
+FileHandleThreadPool::Cleanup()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mThreadPool);
+  MOZ_ASSERT(mShutdownRequested);
+  MOZ_ASSERT(!mShutdownComplete);
+  MOZ_ASSERT(!mDirectoryInfos.Count());
+
+  MOZ_ALWAYS_SUCCEEDS(mThreadPool->Shutdown());
+
+  if (!mCompleteCallbacks.IsEmpty()) {
+    // Run all callbacks manually now.
+    for (uint32_t count = mCompleteCallbacks.Length(), index = 0;
+         index < count;
+         index++) {
+      nsAutoPtr<StoragesCompleteCallback> completeCallback(
+        mCompleteCallbacks[index].forget());
+      MOZ_ASSERT(completeCallback);
+      MOZ_ASSERT(completeCallback->mCallback);
+
+      Unused << completeCallback->mCallback->Run();
+    }
+
+    mCompleteCallbacks.Clear();
+
+    // And make sure they get processed.
+    nsIThread* currentThread = NS_GetCurrentThread();
+    MOZ_ASSERT(currentThread);
+
+    MOZ_ALWAYS_SUCCEEDS(NS_ProcessPendingEvents(currentThread));
+  }
+
+  mShutdownComplete = true;
+}
+
+void
+FileHandleThreadPool::FinishFileHandle(FileHandle* aFileHandle)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aFileHandle);
+
+  BackgroundMutableFileParentBase* mutableFile = aFileHandle->GetMutableFile();
+  const nsACString& directoryId = mutableFile->DirectoryId();
+
+  DirectoryInfo* directoryInfo;
+  if (!mDirectoryInfos.Get(directoryId, &directoryInfo)) {
+    NS_ERROR("We don't know anyting about this directory?!");
+    return;
+  }
+
+  directoryInfo->RemoveFileHandleQueue(aFileHandle);
+
+  if (!directoryInfo->HasRunningFileHandles()) {
+    mDirectoryInfos.Remove(directoryId);
+
+    // See if we need to fire any complete callbacks.
+    uint32_t index = 0;
+    while (index < mCompleteCallbacks.Length()) {
+      if (MaybeFireCallback(mCompleteCallbacks[index])) {
+        mCompleteCallbacks.RemoveElementAt(index);
+      }
+      else {
+        index++;
+      }
+    }
+
+    if (mShutdownRequested && !mDirectoryInfos.Count()) {
+      Cleanup();
+    }
+  }
+}
+
+bool
+FileHandleThreadPool::MaybeFireCallback(StoragesCompleteCallback* aCallback)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aCallback);
+  MOZ_ASSERT(!aCallback->mDirectoryIds.IsEmpty());
+  MOZ_ASSERT(aCallback->mCallback);
+
+  for (uint32_t count = aCallback->mDirectoryIds.Length(), index = 0;
+       index < count;
+       index++) {
+    const nsCString& directoryId = aCallback->mDirectoryIds[index];
+    MOZ_ASSERT(!directoryId.IsEmpty());
+
+    if (mDirectoryInfos.Get(directoryId, nullptr)) {
+      return false;
+    }
+  }
+
+  aCallback->mCallback->Run();
+  return true;
+}
+
+FileHandleThreadPool::
+FileHandleQueue::FileHandleQueue(FileHandleThreadPool* aFileHandleThreadPool,
+                                 FileHandle* aFileHandle)
+  : mOwningFileHandleThreadPool(aFileHandleThreadPool)
+  , mFileHandle(aFileHandle)
+  , mShouldFinish(false)
+{
+  MOZ_ASSERT(aFileHandleThreadPool);
+  aFileHandleThreadPool->AssertIsOnOwningThread();
+  MOZ_ASSERT(aFileHandle);
+}
+
+void
+FileHandleThreadPool::
+FileHandleQueue::Enqueue(FileHandleOp* aFileHandleOp)
+{
+  MOZ_ASSERT(!mShouldFinish, "Enqueue called after Finish!");
+
+  mQueue.AppendElement(aFileHandleOp);
+
+  ProcessQueue();
+}
+
+void
+FileHandleThreadPool::
+FileHandleQueue::Finish()
+{
+  MOZ_ASSERT(!mShouldFinish, "Finish called more than once!");
+
+  mShouldFinish = true;
+}
+
+void
+FileHandleThreadPool::
+FileHandleQueue::ProcessQueue()
+{
+  if (mCurrentOp) {
+    return;
+  }
+
+  if (mQueue.IsEmpty()) {
+    if (mShouldFinish) {
+      mOwningFileHandleThreadPool->FinishFileHandle(mFileHandle);
+
+      // Make sure this is released on this thread.
+      mOwningFileHandleThreadPool = nullptr;
+    }
+
+    return;
+  }
+
+  mCurrentOp = mQueue[0];
+  mQueue.RemoveElementAt(0);
+
+  nsCOMPtr<nsIThreadPool> threadPool = mOwningFileHandleThreadPool->mThreadPool;
+  MOZ_ASSERT(threadPool);
+
+  MOZ_ALWAYS_SUCCEEDS(threadPool->Dispatch(this, NS_DISPATCH_NORMAL));
+}
+
+NS_IMETHODIMP
+FileHandleThreadPool::
+FileHandleQueue::Run()
+{
+  MOZ_ASSERT(mCurrentOp);
+
+  if (IsOnBackgroundThread()) {
+    RefPtr<FileHandleOp> currentOp;
+
+    mCurrentOp.swap(currentOp);
+    ProcessQueue();
+
+    currentOp->RunOnOwningThread();
+  } else {
+    mCurrentOp->RunOnThreadPool();
+
+    nsCOMPtr<nsIEventTarget> backgroundThread = mCurrentOp->OwningThread();
+
+    MOZ_ALWAYS_SUCCEEDS(
+      backgroundThread->Dispatch(this, NS_DISPATCH_NORMAL));
+  }
+
+  return NS_OK;
+}
+
+auto
+FileHandleThreadPool::
+DirectoryInfo::CreateFileHandleQueue(FileHandle* aFileHandle)
+  -> FileHandleQueue*
+{
+  RefPtr<FileHandleQueue>* fileHandleQueue =
+    mFileHandleQueues.AppendElement();
+  *fileHandleQueue = new FileHandleQueue(mOwningFileHandleThreadPool,
+                                         aFileHandle);
+  return fileHandleQueue->get();
+}
+
+auto
+FileHandleThreadPool::
+DirectoryInfo::GetFileHandleQueue(FileHandle* aFileHandle) -> FileHandleQueue*
+{
+  uint32_t count = mFileHandleQueues.Length();
+  for (uint32_t index = 0; index < count; index++) {
+    RefPtr<FileHandleQueue>& fileHandleQueue = mFileHandleQueues[index];
+    if (fileHandleQueue->mFileHandle == aFileHandle) {
+      return fileHandleQueue;
+    }
+  }
+  return nullptr;
+}
+
+void
+FileHandleThreadPool::
+DirectoryInfo::RemoveFileHandleQueue(FileHandle* aFileHandle)
+{
+  for (uint32_t index = 0; index < mDelayedEnqueueInfos.Length(); index++) {
+    if (mDelayedEnqueueInfos[index].mFileHandle == aFileHandle) {
+      MOZ_ASSERT(!mDelayedEnqueueInfos[index].mFileHandleOp, "Should be null!");
+      mDelayedEnqueueInfos.RemoveElementAt(index);
+      return;
+    }
+  }
+
+  uint32_t fileHandleCount = mFileHandleQueues.Length();
+
+  // We can't just remove entries from lock hash tables, we have to rebuild
+  // them instead. Multiple FileHandle objects may lock the same file
+  // (one entry can represent multiple locks).
+
+  mFilesReading.Clear();
+  mFilesWriting.Clear();
+
+  for (uint32_t index = 0, count = fileHandleCount; index < count; index++) {
+    FileHandle* fileHandle = mFileHandleQueues[index]->mFileHandle;
+    if (fileHandle == aFileHandle) {
+      MOZ_ASSERT(count == fileHandleCount, "More than one match?!");
+
+      mFileHandleQueues.RemoveElementAt(index);
+      index--;
+      count--;
+
+      continue;
+    }
+
+    const nsAString& fileName = fileHandle->GetMutableFile()->FileName();
+
+    if (fileHandle->Mode() == FileMode::Readwrite) {
+      if (!IsFileLockedForWriting(fileName)) {
+        LockFileForWriting(fileName);
+      }
+    }
+    else {
+      if (!IsFileLockedForReading(fileName)) {
+        LockFileForReading(fileName);
+      }
+    }
+  }
+
+  MOZ_ASSERT(mFileHandleQueues.Length() == fileHandleCount - 1,
+             "Didn't find the file handle we were looking for!");
+
+  nsTArray<DelayedEnqueueInfo> delayedEnqueueInfos;
+  delayedEnqueueInfos.SwapElements(mDelayedEnqueueInfos);
+
+  for (uint32_t index = 0; index < delayedEnqueueInfos.Length(); index++) {
+    DelayedEnqueueInfo& delayedEnqueueInfo = delayedEnqueueInfos[index];
+    mOwningFileHandleThreadPool->Enqueue(delayedEnqueueInfo.mFileHandle,
+                                         delayedEnqueueInfo.mFileHandleOp,
+                                         delayedEnqueueInfo.mFinish);
+  }
+}
+
+auto
+FileHandleThreadPool::
+DirectoryInfo::CreateDelayedEnqueueInfo(FileHandle* aFileHandle,
+                                        FileHandleOp* aFileHandleOp,
+                                        bool aFinish) -> DelayedEnqueueInfo*
+{
+  DelayedEnqueueInfo* info = mDelayedEnqueueInfos.AppendElement();
+  info->mFileHandle = aFileHandle;
+  info->mFileHandleOp = aFileHandleOp;
+  info->mFinish = aFinish;
+  return info;
+}
+
+FileHandleThreadPool::
+StoragesCompleteCallback::StoragesCompleteCallback(
+                                             nsTArray<nsCString>&& aDirectoryIds,
+                                             nsIRunnable* aCallback)
+  : mDirectoryIds(Move(aDirectoryIds))
+  , mCallback(aCallback)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mDirectoryIds.IsEmpty());
+  MOZ_ASSERT(aCallback);
+
+  MOZ_COUNT_CTOR(FileHandleThreadPool::StoragesCompleteCallback);
+}
+
+FileHandleThreadPool::
+StoragesCompleteCallback::~StoragesCompleteCallback()
+{
+  AssertIsOnBackgroundThread();
+
+  MOZ_COUNT_DTOR(FileHandleThreadPool::StoragesCompleteCallback);
+}
+
+/*******************************************************************************
+ * BackgroundMutableFileParentBase
+ ******************************************************************************/
+
+BackgroundMutableFileParentBase::BackgroundMutableFileParentBase(
+                                                 FileHandleStorage aStorage,
+                                                 const nsACString& aDirectoryId,
+                                                 const nsAString& aFileName,
+                                                 nsIFile* aFile)
+  : mDirectoryId(aDirectoryId)
+  , mFileName(aFileName)
+  , mStorage(aStorage)
+  , mInvalidated(false)
+  , mActorWasAlive(false)
+  , mActorDestroyed(false)
+  , mFile(aFile)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aStorage != FILE_HANDLE_STORAGE_MAX);
+  MOZ_ASSERT(!aDirectoryId.IsEmpty());
+  MOZ_ASSERT(!aFileName.IsEmpty());
+  MOZ_ASSERT(aFile);
+}
+
+BackgroundMutableFileParentBase::~BackgroundMutableFileParentBase()
+{
+  MOZ_ASSERT_IF(mActorWasAlive, mActorDestroyed);
+}
+
+void
+BackgroundMutableFileParentBase::Invalidate()
+{
+  AssertIsOnBackgroundThread();
+
+  class MOZ_STACK_CLASS Helper final
+  {
+  public:
+    static bool
+    InvalidateFileHandles(nsTHashtable<nsPtrHashKey<FileHandle>>& aTable)
+    {
+      AssertIsOnBackgroundThread();
+
+      const uint32_t count = aTable.Count();
+      if (!count) {
+        return true;
+      }
+
+      FallibleTArray<RefPtr<FileHandle>> fileHandles;
+      if (NS_WARN_IF(!fileHandles.SetCapacity(count, fallible))) {
+        return false;
+      }
+
+      for (auto iter = aTable.Iter(); !iter.Done(); iter.Next()) {
+        if (NS_WARN_IF(!fileHandles.AppendElement(iter.Get()->GetKey(),
+                                                  fallible))) {
+          return false;
+        }
+      }
+
+      if (count) {
+        for (uint32_t index = 0; index < count; index++) {
+          RefPtr<FileHandle> fileHandle = fileHandles[index].forget();
+          MOZ_ASSERT(fileHandle);
+
+          fileHandle->Invalidate();
+        }
+      }
+
+      return true;
+    }
+  };
+
+  if (mInvalidated) {
+    return;
+  }
+
+  mInvalidated = true;
+
+  if (!Helper::InvalidateFileHandles(mFileHandles)) {
+    NS_WARNING("Failed to abort all file handles!");
+  }
+}
+
+bool
+BackgroundMutableFileParentBase::RegisterFileHandle(FileHandle* aFileHandle)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aFileHandle);
+  MOZ_ASSERT(!mFileHandles.GetEntry(aFileHandle));
+  MOZ_ASSERT(!mInvalidated);
+
+  if (NS_WARN_IF(!mFileHandles.PutEntry(aFileHandle, fallible))) {
+    return false;
+  }
+
+  if (mFileHandles.Count() == 1) {
+    NoteActiveState();
+  }
+
+  return true;
+}
+
+void
+BackgroundMutableFileParentBase::UnregisterFileHandle(FileHandle* aFileHandle)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aFileHandle);
+  MOZ_ASSERT(mFileHandles.GetEntry(aFileHandle));
+
+  mFileHandles.RemoveEntry(aFileHandle);
+
+  if (!mFileHandles.Count()) {
+    NoteInactiveState();
+  }
+}
+
+void
+BackgroundMutableFileParentBase::SetActorAlive()
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mActorWasAlive);
+  MOZ_ASSERT(!mActorDestroyed);
+
+  mActorWasAlive = true;
+
+  // This reference will be absorbed by IPDL and released when the actor is
+  // destroyed.
+  AddRef();
+}
+
+already_AddRefed<nsISupports>
+BackgroundMutableFileParentBase::CreateStream(bool aReadOnly)
+{
+  AssertIsOnBackgroundThread();
+
+  nsresult rv;
+
+  if (aReadOnly) {
+    nsCOMPtr<nsIInputStream> stream;
+    rv = NS_NewLocalFileInputStream(getter_AddRefs(stream), mFile, -1, -1,
+                                    nsIFileInputStream::DEFER_OPEN);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return nullptr;
+    }
+    return stream.forget();
+  }
+
+  nsCOMPtr<nsIFileStream> stream;
+  rv = NS_NewLocalFileStream(getter_AddRefs(stream), mFile, -1, -1,
+                             nsIFileStream::DEFER_OPEN);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return nullptr;
+  }
+  return stream.forget();
+}
+
+void
+BackgroundMutableFileParentBase::ActorDestroy(ActorDestroyReason aWhy)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mActorDestroyed);
+
+  mActorDestroyed = true;
+
+  if (!IsInvalidated()) {
+    Invalidate();
+  }
+}
+
+PBackgroundFileHandleParent*
+BackgroundMutableFileParentBase::AllocPBackgroundFileHandleParent(
+                                                          const FileMode& aMode)
+{
+  AssertIsOnBackgroundThread();
+
+  if (NS_WARN_IF(aMode != FileMode::Readonly &&
+                 aMode != FileMode::Readwrite)) {
+    ASSERT_UNLESS_FUZZING();
+    return nullptr;
+  }
+
+  RefPtr<FileHandle> fileHandle = new FileHandle(this, aMode);
+
+  return fileHandle.forget().take();
+}
+
+bool
+BackgroundMutableFileParentBase::RecvPBackgroundFileHandleConstructor(
+                                            PBackgroundFileHandleParent* aActor,
+                                            const FileMode& aMode)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aActor);
+  MOZ_ASSERT(aMode == FileMode::Readonly || aMode == FileMode::Readwrite);
+
+  FileHandleThreadPool* fileHandleThreadPool =
+    GetFileHandleThreadPoolFor(mStorage);
+  MOZ_ASSERT(fileHandleThreadPool);
+
+  auto* fileHandle = static_cast<FileHandle*>(aActor);
+
+  // Add a placeholder for this file handle immediately.
+  fileHandleThreadPool->Enqueue(fileHandle, nullptr, false);
+
+  fileHandle->SetActive();
+
+  if (NS_WARN_IF(!RegisterFileHandle(fileHandle))) {
+    fileHandle->Abort(/* aForce */ false);
+    return true;
+  }
+
+  return true;
+}
+
+bool
+BackgroundMutableFileParentBase::DeallocPBackgroundFileHandleParent(
+                                            PBackgroundFileHandleParent* aActor)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aActor);
+
+  RefPtr<FileHandle> fileHandle =
+    dont_AddRef(static_cast<FileHandle*>(aActor));
+  return true;
+}
+
+bool
+BackgroundMutableFileParentBase::RecvDeleteMe()
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mActorDestroyed);
+
+  return PBackgroundMutableFileParent::Send__delete__(this);
+}
+
+bool
+BackgroundMutableFileParentBase::RecvGetFileId(int64_t* aFileId)
+{
+  AssertIsOnBackgroundThread();
+
+  *aFileId = -1;
+  return true;
+}
+
+/*******************************************************************************
+ * FileHandle
+ ******************************************************************************/
+
+FileHandle::FileHandle(BackgroundMutableFileParentBase* aMutableFile,
+                       FileMode aMode)
+  : mMutableFile(aMutableFile)
+  , mActiveRequestCount(0)
+  , mStorage(aMutableFile->Storage())
+  , mInvalidatedOnAnyThread(false)
+  , mMode(aMode)
+  , mHasBeenActive(false)
+  , mActorDestroyed(false)
+  , mInvalidated(false)
+  , mAborted(false)
+  , mFinishOrAbortReceived(false)
+  , mFinishedOrAborted(false)
+  , mForceAborted(false)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aMutableFile);
+
+#ifdef DEBUG
+  FileHandleThreadPool* fileHandleThreadPool =
+    GetFileHandleThreadPoolFor(mStorage);
+  MOZ_ASSERT(fileHandleThreadPool);
+
+  mThreadPoolEventTarget = fileHandleThreadPool->GetThreadPoolEventTarget();
+#endif
+}
+
+FileHandle::~FileHandle()
+{
+  MOZ_ASSERT(!mActiveRequestCount);
+  MOZ_ASSERT(mActorDestroyed);
+  MOZ_ASSERT_IF(mHasBeenActive, mFinishedOrAborted);
+}
+
+void
+FileHandle::AssertIsOnThreadPool() const
+{
+  MOZ_ASSERT(mThreadPoolEventTarget);
+  DebugOnly<bool> current;
+  MOZ_ASSERT(NS_SUCCEEDED(mThreadPoolEventTarget->IsOnCurrentThread(&current)));
+  MOZ_ASSERT(current);
+}
+
+nsresult
+FileHandle::GetOrCreateStream(nsISupports** aStream)
+{
+  AssertIsOnBackgroundThread();
+
+  if (!mStream) {
+    nsCOMPtr<nsISupports> stream =
+      mMutableFile->CreateStream(mMode == FileMode::Readonly);
+    if (NS_WARN_IF(!stream)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    stream.swap(mStream);
+  }
+
+  nsCOMPtr<nsISupports> stream(mStream);
+  stream.forget(aStream);
+
+  return NS_OK;
+}
+
+void
+FileHandle::Abort(bool aForce)
+{
+  AssertIsOnBackgroundThread();
+
+  mAborted = true;
+
+  if (aForce) {
+    mForceAborted = true;
+  }
+
+  MaybeFinishOrAbort();
+}
+
+void
+FileHandle::NoteActiveRequest()
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mActiveRequestCount < UINT64_MAX);
+
+  mActiveRequestCount++;
+}
+
+void
+FileHandle::NoteFinishedRequest()
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mActiveRequestCount);
+
+  mActiveRequestCount--;
+
+  MaybeFinishOrAbort();
+}
+
+void
+FileHandle::Invalidate()
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mInvalidated == mInvalidatedOnAnyThread);
+
+  if (!mInvalidated) {
+    mInvalidated = true;
+    mInvalidatedOnAnyThread = true;
+
+    Abort(/* aForce */ true);
+  }
+}
+
+void
+FileHandle::SendCompleteNotification(bool aAborted)
+{
+  AssertIsOnBackgroundThread();
+
+  if (!IsActorDestroyed()) {
+    Unused << SendComplete(aAborted);
+  }
+}
+
+bool
+FileHandle::VerifyRequestParams(const FileRequestParams& aParams) const
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aParams.type() != FileRequestParams::T__None);
+
+  switch (aParams.type()) {
+    case FileRequestParams::TFileRequestGetMetadataParams: {
+      const FileRequestGetMetadataParams& params =
+        aParams.get_FileRequestGetMetadataParams();
+
+      if (NS_WARN_IF(!params.size() && !params.lastModified())) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      break;
+    }
+
+    case FileRequestParams::TFileRequestReadParams: {
+      const FileRequestReadParams& params =
+        aParams.get_FileRequestReadParams();
+
+      if (NS_WARN_IF(params.offset() == UINT64_MAX)) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      if (NS_WARN_IF(!params.size())) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      break;
+    }
+
+    case FileRequestParams::TFileRequestWriteParams: {
+      if (NS_WARN_IF(mMode != FileMode::Readwrite)) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      const FileRequestWriteParams& params =
+        aParams.get_FileRequestWriteParams();
+
+
+      if (NS_WARN_IF(!params.dataLength())) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      if (NS_WARN_IF(!VerifyRequestData(params.data()))) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      break;
+    }
+
+    case FileRequestParams::TFileRequestTruncateParams: {
+      if (NS_WARN_IF(mMode != FileMode::Readwrite)) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      const FileRequestTruncateParams& params =
+        aParams.get_FileRequestTruncateParams();
+
+      if (NS_WARN_IF(params.offset() == UINT64_MAX)) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      break;
+    }
+
+    case FileRequestParams::TFileRequestFlushParams: {
+      if (NS_WARN_IF(mMode != FileMode::Readwrite)) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      break;
+    }
+
+    case FileRequestParams::TFileRequestGetFileParams: {
+      break;
+    }
+
+    default:
+      MOZ_CRASH("Should never get here!");
+  }
+
+  return true;
+}
+
+bool
+FileHandle::VerifyRequestData(const FileRequestData& aData) const
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aData.type() != FileRequestData::T__None);
+
+  switch (aData.type()) {
+    case FileRequestData::TFileRequestStringData: {
+      const FileRequestStringData& data =
+        aData.get_FileRequestStringData();
+
+      if (NS_WARN_IF(data.string().IsEmpty())) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      break;
+    }
+
+    case FileRequestData::TFileRequestBlobData: {
+      const FileRequestBlobData& data =
+        aData.get_FileRequestBlobData();
+
+      if (NS_WARN_IF(data.blobChild())) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      if (NS_WARN_IF(!data.blobParent())) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      break;
+    }
+
+    default:
+      MOZ_CRASH("Should never get here!");
+  }
+
+  return true;
+}
+
+void
+FileHandle::FinishOrAbort()
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mFinishedOrAborted);
+
+  mFinishedOrAborted = true;
+
+  if (!mHasBeenActive) {
+    return;
+  }
+
+  RefPtr<FinishOp> finishOp = new FinishOp(this, mAborted);
+
+  FileHandleThreadPool* fileHandleThreadPool =
+    GetFileHandleThreadPoolFor(mStorage);
+  MOZ_ASSERT(fileHandleThreadPool);
+
+  fileHandleThreadPool->Enqueue(this, finishOp, true);
+}
+
+void
+FileHandle::ActorDestroy(ActorDestroyReason aWhy)
+{
+  AssertIsOnBackgroundThread();
+
+  MOZ_ASSERT(!mActorDestroyed);
+
+  mActorDestroyed = true;
+
+  if (!mFinishedOrAborted) {
+    mAborted = true;
+
+    mForceAborted = true;
+
+    MaybeFinishOrAbort();
+  }
+}
+
+bool
+FileHandle::RecvDeleteMe()
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!IsActorDestroyed());
+
+  return PBackgroundFileHandleParent::Send__delete__(this);
+}
+
+bool
+FileHandle::RecvFinish()
+{
+  AssertIsOnBackgroundThread();
+
+  if (NS_WARN_IF(mFinishOrAbortReceived)) {
+    ASSERT_UNLESS_FUZZING();
+    return false;
+  }
+
+  mFinishOrAbortReceived = true;
+
+  MaybeFinishOrAbort();
+  return true;
+}
+
+bool
+FileHandle::RecvAbort()
+{
+  AssertIsOnBackgroundThread();
+
+  if (NS_WARN_IF(mFinishOrAbortReceived)) {
+    ASSERT_UNLESS_FUZZING();
+    return false;
+  }
+
+  mFinishOrAbortReceived = true;
+
+  Abort(/* aForce */ false);
+  return true;
+}
+
+PBackgroundFileRequestParent*
+FileHandle::AllocPBackgroundFileRequestParent(const FileRequestParams& aParams)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aParams.type() != FileRequestParams::T__None);
+
+#ifdef DEBUG
+  // Always verify parameters in DEBUG builds!
+  bool trustParams = false;
+#else
+  PBackgroundParent* backgroundActor = GetBackgroundParent();
+  MOZ_ASSERT(backgroundActor);
+
+  bool trustParams = !BackgroundParent::IsOtherProcessActor(backgroundActor);
+#endif
+
+  if (NS_WARN_IF(!trustParams && !VerifyRequestParams(aParams))) {
+    ASSERT_UNLESS_FUZZING();
+    return nullptr;
+  }
+
+  if (NS_WARN_IF(mFinishOrAbortReceived)) {
+    ASSERT_UNLESS_FUZZING();
+    return nullptr;
+  }
+
+  RefPtr<NormalFileHandleOp> actor;
+
+  switch (aParams.type()) {
+    case FileRequestParams::TFileRequestGetMetadataParams:
+      actor = new GetMetadataOp(this, aParams);
+      break;
+
+    case FileRequestParams::TFileRequestReadParams:
+      actor = new ReadOp(this, aParams);
+      break;
+
+    case FileRequestParams::TFileRequestWriteParams:
+      actor = new WriteOp(this, aParams);
+      break;
+
+    case FileRequestParams::TFileRequestTruncateParams:
+      actor = new TruncateOp(this, aParams);
+      break;
+
+    case FileRequestParams::TFileRequestFlushParams:
+      actor = new FlushOp(this, aParams);
+      break;
+
+    case FileRequestParams::TFileRequestGetFileParams:
+      actor = new GetFileOp(this, aParams);
+      break;
+
+    default:
+      MOZ_CRASH("Should never get here!");
+  }
+
+  MOZ_ASSERT(actor);
+
+  // Transfer ownership to IPDL.
+  return actor.forget().take();
+}
+
+bool
+FileHandle::RecvPBackgroundFileRequestConstructor(
+                                           PBackgroundFileRequestParent* aActor,
+                                           const FileRequestParams& aParams)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aActor);
+  MOZ_ASSERT(aParams.type() != FileRequestParams::T__None);
+
+  auto* op = static_cast<NormalFileHandleOp*>(aActor);
+
+  if (NS_WARN_IF(!op->Init(this))) {
+    op->Cleanup();
+    return false;
+  }
+
+  op->Enqueue();
+  return true;
+}
+
+bool
+FileHandle::DeallocPBackgroundFileRequestParent(
+                                           PBackgroundFileRequestParent* aActor)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aActor);
+
+  // Transfer ownership back from IPDL.
+  RefPtr<NormalFileHandleOp> actor =
+    dont_AddRef(static_cast<NormalFileHandleOp*>(aActor));
+  return true;
+}
+
+/*******************************************************************************
+ * Local class implementations
+ ******************************************************************************/
+
+void
+FileHandleOp::Enqueue()
+{
+  AssertIsOnOwningThread();
+
+  FileHandleThreadPool* fileHandleThreadPool =
+    GetFileHandleThreadPoolFor(mFileHandle->Storage());
+  MOZ_ASSERT(fileHandleThreadPool);
+
+  fileHandleThreadPool->Enqueue(mFileHandle, this, false);
+
+  mFileHandle->NoteActiveRequest();
+}
+
+void
+FileHandle::
+FinishOp::RunOnThreadPool()
+{
+  AssertIsOnThreadPool();
+  MOZ_ASSERT(mFileHandle);
+
+  nsCOMPtr<nsISupports>& stream = mFileHandle->mStream;
+
+  if (!stream) {
+    return;
+  }
+
+  nsCOMPtr<nsIInputStream> inputStream = do_QueryInterface(stream);
+  MOZ_ASSERT(inputStream);
+
+  MOZ_ALWAYS_SUCCEEDS(inputStream->Close());
+
+  stream = nullptr;
+}
+
+void
+FileHandle::
+FinishOp::RunOnOwningThread()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mFileHandle);
+
+  mFileHandle->SendCompleteNotification(mAborted);
+
+  mFileHandle->GetMutableFile()->UnregisterFileHandle(mFileHandle);
+
+  mFileHandle = nullptr;
+}
+
+NormalFileHandleOp::~NormalFileHandleOp()
+{
+  MOZ_ASSERT(!mFileHandle,
+             "NormalFileHandleOp::Cleanup() was not called by a subclass!");
+}
+
+bool
+NormalFileHandleOp::Init(FileHandle* aFileHandle)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aFileHandle);
+
+  nsresult rv = aFileHandle->GetOrCreateStream(getter_AddRefs(mFileStream));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return false;
+  }
+
+  return true;
+}
+
+void
+NormalFileHandleOp::Cleanup()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mFileHandle);
+  MOZ_ASSERT_IF(!IsActorDestroyed(), mResponseSent);
+
+  mFileHandle = nullptr;
+}
+
+nsresult
+NormalFileHandleOp::SendSuccessResult()
+{
+  AssertIsOnOwningThread();
+
+  if (!IsActorDestroyed()) {
+    FileRequestResponse response;
+    GetResponse(response);
+
+    MOZ_ASSERT(response.type() != FileRequestResponse::T__None);
+
+    if (response.type() == FileRequestResponse::Tnsresult) {
+      MOZ_ASSERT(NS_FAILED(response.get_nsresult()));
+
+      return response.get_nsresult();
+    }
+
+    if (NS_WARN_IF(!PBackgroundFileRequestParent::Send__delete__(this,
+                                                                 response))) {
+      return NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+    }
+  }
+
+  DEBUGONLY(mResponseSent = true;)
+
+  return NS_OK;
+}
+
+bool
+NormalFileHandleOp::SendFailureResult(nsresult aResultCode)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(NS_FAILED(aResultCode));
+
+  bool result = false;
+
+  if (!IsActorDestroyed()) {
+    result =
+      PBackgroundFileRequestParent::Send__delete__(this, aResultCode);
+  }
+
+  DEBUGONLY(mResponseSent = true;)
+
+  return result;
+}
+
+void
+NormalFileHandleOp::RunOnThreadPool()
+{
+  AssertIsOnThreadPool();
+  MOZ_ASSERT(mFileHandle);
+  MOZ_ASSERT(NS_SUCCEEDED(mResultCode));
+
+  // There are several cases where we don't actually have to to any work here.
+
+  if (mFileHandleIsAborted) {
+    // This transaction is already set to be aborted.
+    mResultCode = NS_ERROR_DOM_FILEHANDLE_ABORT_ERR;
+  } else if (mFileHandle->IsInvalidatedOnAnyThread()) {
+    // This file handle is being invalidated.
+    mResultCode = NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+  } else if (!OperationMayProceed()) {
+    // The operation was canceled in some way, likely because the child process
+    // has crashed.
+    mResultCode = NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+  } else {
+    nsresult rv = DoFileWork(mFileHandle);
+    if (NS_FAILED(rv)) {
+      mResultCode = rv;
+    }
+  }
+}
+
+void
+NormalFileHandleOp::RunOnOwningThread()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mFileHandle);
+
+  if (NS_WARN_IF(IsActorDestroyed())) {
+    // Don't send any notifications if the actor was destroyed already.
+    if (NS_SUCCEEDED(mResultCode)) {
+      mResultCode = NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+    }
+  } else {
+    if (mFileHandle->IsInvalidated()) {
+      mResultCode = NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+    } else if (mFileHandle->IsAborted()) {
+      // Aborted file handles always see their requests fail with ABORT_ERR,
+      // even if the request succeeded or failed with another error.
+      mResultCode = NS_ERROR_DOM_FILEHANDLE_ABORT_ERR;
+    } else if (NS_SUCCEEDED(mResultCode)) {
+      // This may release the IPDL reference.
+      mResultCode = SendSuccessResult();
+    }
+
+    if (NS_FAILED(mResultCode)) {
+      // This should definitely release the IPDL reference.
+      if (!SendFailureResult(mResultCode)) {
+        // Abort the file handle.
+        mFileHandle->Abort(/* aForce */ false);
+      }
+    }
+  }
+
+  mFileHandle->NoteFinishedRequest();
+
+  Cleanup();
+}
+
+void
+NormalFileHandleOp::ActorDestroy(ActorDestroyReason aWhy)
+{
+  AssertIsOnOwningThread();
+
+  NoteActorDestroyed();
+}
+
+nsresult
+CopyFileHandleOp::DoFileWork(FileHandle* aFileHandle)
+{
+  AssertIsOnThreadPool();
+
+  nsCOMPtr<nsIInputStream> inputStream;
+  nsCOMPtr<nsIOutputStream> outputStream;
+
+  if (mRead) {
+    inputStream = do_QueryInterface(mFileStream);
+    outputStream = do_QueryInterface(mBufferStream);
+  } else {
+    inputStream = do_QueryInterface(mBufferStream);
+    outputStream = do_QueryInterface(mFileStream);
+  }
+
+  MOZ_ASSERT(inputStream);
+  MOZ_ASSERT(outputStream);
+
+  nsCOMPtr<nsISeekableStream> seekableStream =
+    do_QueryInterface(mFileStream);
+
+  nsresult rv;
+
+  if (seekableStream) {
+    if (mOffset == UINT64_MAX) {
+      rv = seekableStream->Seek(nsISeekableStream::NS_SEEK_END, 0);
+    }
+    else {
+      rv = seekableStream->Seek(nsISeekableStream::NS_SEEK_SET, mOffset);
+    }
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+
+  mOffset = 0;
+
+  do {
+    char copyBuffer[kStreamCopyBlockSize];
+
+    uint64_t max = mSize - mOffset;
+    if (max == 0) {
+      break;
+    }
+
+    uint32_t count = sizeof(copyBuffer);
+    if (count > max) {
+      count = max;
+    }
+
+    uint32_t numRead;
+    rv = inputStream->Read(copyBuffer, count, &numRead);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    if (!numRead) {
+      break;
+    }
+
+    uint32_t numWrite;
+    rv = outputStream->Write(copyBuffer, numRead, &numWrite);
+    if (rv == NS_ERROR_FILE_NO_DEVICE_SPACE) {
+      rv = NS_ERROR_DOM_FILEHANDLE_QUOTA_ERR;
+    }
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    if (NS_WARN_IF(numWrite != numRead)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    mOffset += numWrite;
+
+    nsCOMPtr<nsIRunnable> runnable =
+      new ProgressRunnable(this, mOffset, mSize);
+
+    mOwningThread->Dispatch(runnable, NS_DISPATCH_NORMAL);
+  } while (true);
+
+  MOZ_ASSERT(mOffset == mSize);
+
+  if (mRead) {
+    MOZ_ALWAYS_SUCCEEDS(outputStream->Close());
+  } else {
+    MOZ_ALWAYS_SUCCEEDS(inputStream->Close());
+  }
+
+  return NS_OK;
+}
+
+void
+CopyFileHandleOp::Cleanup()
+{
+  AssertIsOnOwningThread();
+
+  mBufferStream = nullptr;
+
+  NormalFileHandleOp::Cleanup();
+}
+
+NS_IMETHODIMP
+CopyFileHandleOp::
+ProgressRunnable::Run()
+{
+  AssertIsOnBackgroundThread();
+
+  Unused << mCopyFileHandleOp->SendProgress(mProgress, mProgressMax);
+
+  mCopyFileHandleOp = nullptr;
+
+  return NS_OK;
+}
+
+GetMetadataOp::GetMetadataOp(FileHandle* aFileHandle,
+                             const FileRequestParams& aParams)
+  : NormalFileHandleOp(aFileHandle)
+  , mParams(aParams.get_FileRequestGetMetadataParams())
+{
+  MOZ_ASSERT(aParams.type() ==
+             FileRequestParams::TFileRequestGetMetadataParams);
+}
+
+nsresult
+GetMetadataOp::DoFileWork(FileHandle* aFileHandle)
+{
+  AssertIsOnThreadPool();
+
+  nsresult rv;
+
+  if (mFileHandle->Mode() == FileMode::Readwrite) {
+    // Force a flush (so all pending writes are flushed to the disk and file
+    // metadata is updated too).
+
+    nsCOMPtr<nsIOutputStream> ostream = do_QueryInterface(mFileStream);
+    MOZ_ASSERT(ostream);
+
+    rv = ostream->Flush();
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+
+  nsCOMPtr<nsIFileMetadata> metadata = do_QueryInterface(mFileStream);
+  MOZ_ASSERT(metadata);
+
+  if (mParams.size()) {
+    int64_t size;
+    rv = metadata->GetSize(&size);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    if (NS_WARN_IF(size < 0)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    mMetadata.size() = uint64_t(size);
+  } else {
+    mMetadata.size() = void_t();
+  }
+
+  if (mParams.lastModified()) {
+    int64_t lastModified;
+    rv = metadata->GetLastModified(&lastModified);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    mMetadata.lastModified() = lastModified;
+  } else {
+    mMetadata.lastModified() = void_t();
+  }
+
+  return NS_OK;
+}
+
+void
+GetMetadataOp::GetResponse(FileRequestResponse& aResponse)
+{
+  AssertIsOnOwningThread();
+
+  aResponse = FileRequestGetMetadataResponse(mMetadata);
+}
+
+ReadOp::ReadOp(FileHandle* aFileHandle,
+               const FileRequestParams& aParams)
+  : CopyFileHandleOp(aFileHandle)
+  , mParams(aParams.get_FileRequestReadParams())
+{
+  MOZ_ASSERT(aParams.type() == FileRequestParams::TFileRequestReadParams);
+}
+
+bool
+ReadOp::Init(FileHandle* aFileHandle)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aFileHandle);
+
+  if (NS_WARN_IF(!NormalFileHandleOp::Init(aFileHandle))) {
+    return false;
+  }
+
+  mBufferStream = MemoryOutputStream::Create(mParams.size());
+  if (NS_WARN_IF(!mBufferStream)) {
+    return false;
+  }
+
+  mOffset = mParams.offset();
+  mSize = mParams.size();
+  mRead = true;
+
+  return true;
+}
+
+void
+ReadOp::GetResponse(FileRequestResponse& aResponse)
+{
+  AssertIsOnOwningThread();
+
+  auto* stream = static_cast<MemoryOutputStream*>(mBufferStream.get());
+
+  aResponse = FileRequestReadResponse(stream->Data());
+}
+
+// static
+already_AddRefed<ReadOp::MemoryOutputStream>
+ReadOp::
+MemoryOutputStream::Create(uint64_t aSize)
+{
+  MOZ_ASSERT(aSize, "Passed zero size!");
+
+  if (NS_WARN_IF(aSize > UINT32_MAX)) {
+    return nullptr;
+  }
+
+  RefPtr<MemoryOutputStream> stream = new MemoryOutputStream();
+
+  char* dummy;
+  uint32_t length = stream->mData.GetMutableData(&dummy, aSize, fallible);
+  if (NS_WARN_IF(length != aSize)) {
+    return nullptr;
+  }
+
+  return stream.forget();
+}
+
+NS_IMPL_ISUPPORTS(ReadOp::MemoryOutputStream, nsIOutputStream)
+
+NS_IMETHODIMP
+ReadOp::
+MemoryOutputStream::Close()
+{
+  mData.Truncate(mOffset);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+ReadOp::
+MemoryOutputStream::Write(const char* aBuf, uint32_t aCount, uint32_t* _retval)
+{
+  return WriteSegments(NS_CopySegmentToBuffer, (char*)aBuf, aCount, _retval);
+}
+
+NS_IMETHODIMP
+ReadOp::
+MemoryOutputStream::Flush()
+{
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+ReadOp::
+MemoryOutputStream::WriteFrom(nsIInputStream* aFromStream, uint32_t aCount,
+                              uint32_t* _retval)
+{
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+ReadOp::
+MemoryOutputStream::WriteSegments(nsReadSegmentFun aReader, void* aClosure,
+                                  uint32_t aCount, uint32_t* _retval)
+{
+  NS_ASSERTION(mData.Length() >= mOffset, "Bad stream state!");
+
+  uint32_t maxCount = mData.Length() - mOffset;
+  if (maxCount == 0) {
+    *_retval = 0;
+    return NS_OK;
+  }
+
+  if (aCount > maxCount) {
+    aCount = maxCount;
+  }
+
+  nsresult rv = aReader(this, aClosure, mData.BeginWriting() + mOffset, 0,
+                        aCount, _retval);
+  if (NS_SUCCEEDED(rv)) {
+    NS_ASSERTION(*_retval <= aCount,
+                 "Reader should not read more than we asked it to read!");
+    mOffset += *_retval;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+ReadOp::
+MemoryOutputStream::IsNonBlocking(bool* _retval)
+{
+  *_retval = false;
+  return NS_OK;
+}
+
+WriteOp::WriteOp(FileHandle* aFileHandle,
+                 const FileRequestParams& aParams)
+  : CopyFileHandleOp(aFileHandle)
+  , mParams(aParams.get_FileRequestWriteParams())
+{
+  MOZ_ASSERT(aParams.type() == FileRequestParams::TFileRequestWriteParams);
+}
+
+bool
+WriteOp::Init(FileHandle* aFileHandle)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aFileHandle);
+
+  if (NS_WARN_IF(!NormalFileHandleOp::Init(aFileHandle))) {
+    return false;
+  }
+
+  nsCOMPtr<nsIInputStream> inputStream;
+
+  const FileRequestData& data = mParams.data();
+  switch (data.type()) {
+    case FileRequestData::TFileRequestStringData: {
+      const FileRequestStringData& stringData =
+        data.get_FileRequestStringData();
+
+      const nsCString& string = stringData.string();
+
+      nsresult rv =
+        NS_NewCStringInputStream(getter_AddRefs(inputStream), string);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return false;
+      }
+
+      break;
+    }
+    case FileRequestData::TFileRequestBlobData: {
+      const FileRequestBlobData& blobData =
+        data.get_FileRequestBlobData();
+
+      auto blobActor = static_cast<BlobParent*>(blobData.blobParent());
+
+      RefPtr<BlobImpl> blobImpl = blobActor->GetBlobImpl();
+
+      ErrorResult rv;
+      blobImpl->GetInternalStream(getter_AddRefs(inputStream), rv);
+      if (NS_WARN_IF(rv.Failed())) {
+        rv.SuppressException();
+        return false;
+      }
+
+      break;
+    }
+
+    default:
+      MOZ_CRASH("Should never get here!");
+  }
+
+  mBufferStream = inputStream;
+  mOffset = mParams.offset();
+  mSize = mParams.dataLength();
+  mRead = false;
+
+  return true;
+}
+
+void
+WriteOp::GetResponse(FileRequestResponse& aResponse)
+{
+  AssertIsOnOwningThread();
+  aResponse = FileRequestWriteResponse();
+}
+
+TruncateOp::TruncateOp(FileHandle* aFileHandle,
+                       const FileRequestParams& aParams)
+  : NormalFileHandleOp(aFileHandle)
+  , mParams(aParams.get_FileRequestTruncateParams())
+{
+  MOZ_ASSERT(aParams.type() == FileRequestParams::TFileRequestTruncateParams);
+}
+
+nsresult
+TruncateOp::DoFileWork(FileHandle* aFileHandle)
+{
+  AssertIsOnThreadPool();
+
+  nsCOMPtr<nsISeekableStream> sstream = do_QueryInterface(mFileStream);
+  MOZ_ASSERT(sstream);
+
+  nsresult rv = sstream->Seek(nsISeekableStream::NS_SEEK_SET, mParams.offset());
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = sstream->SetEOF();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+void
+TruncateOp::GetResponse(FileRequestResponse& aResponse)
+{
+  AssertIsOnOwningThread();
+  aResponse = FileRequestTruncateResponse();
+}
+
+FlushOp::FlushOp(FileHandle* aFileHandle,
+                 const FileRequestParams& aParams)
+  : NormalFileHandleOp(aFileHandle)
+  , mParams(aParams.get_FileRequestFlushParams())
+{
+  MOZ_ASSERT(aParams.type() == FileRequestParams::TFileRequestFlushParams);
+}
+
+nsresult
+FlushOp::DoFileWork(FileHandle* aFileHandle)
+{
+  AssertIsOnThreadPool();
+
+  nsCOMPtr<nsIOutputStream> ostream = do_QueryInterface(mFileStream);
+  MOZ_ASSERT(ostream);
+
+  nsresult rv = ostream->Flush();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+void
+FlushOp::GetResponse(FileRequestResponse& aResponse)
+{
+  AssertIsOnOwningThread();
+  aResponse = FileRequestFlushResponse();
+}
+
+GetFileOp::GetFileOp(FileHandle* aFileHandle,
+                     const FileRequestParams& aParams)
+  : GetMetadataOp(aFileHandle,
+                  FileRequestGetMetadataParams(true, true))
+  , mBackgroundParent(aFileHandle->GetBackgroundParent())
+{
+  MOZ_ASSERT(aParams.type() == FileRequestParams::TFileRequestGetFileParams);
+  MOZ_ASSERT(mBackgroundParent);
+}
+
+void
+GetFileOp::GetResponse(FileRequestResponse& aResponse)
+{
+  AssertIsOnOwningThread();
+
+  RefPtr<BlobImpl> blobImpl = mFileHandle->GetMutableFile()->CreateBlobImpl();
+  MOZ_ASSERT(blobImpl);
+
+  PBlobParent* actor =
+    BackgroundParent::GetOrCreateActorForBlobImpl(mBackgroundParent, blobImpl);
+  if (NS_WARN_IF(!actor)) {
+    // This can only fail if the child has crashed.
+    aResponse = NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+    return;
+  }
+
+  FileRequestGetFileResponse response;
+  response.fileParent() = actor;
+  response.metadata() = mMetadata;
+
+  aResponse = response;
+}
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/filehandle/ActorsParent.h b/dom/filehandle/ActorsParent.h
new file mode 100644
index 000000000..5d251715e
--- /dev/null
+++ b/dom/filehandle/ActorsParent.h
@@ -0,0 +1,221 @@
+/* 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_filehandle_ActorsParent_h
+#define mozilla_dom_filehandle_ActorsParent_h
+
+#include "mozilla/dom/FileHandleStorage.h"
+#include "mozilla/dom/PBackgroundMutableFileParent.h"
+#include "mozilla/ipc/BackgroundParent.h"
+#include "nsAutoPtr.h"
+#include "nsClassHashtable.h"
+#include "nsCOMPtr.h"
+#include "nsHashKeys.h"
+#include "nsString.h"
+#include "nsTArrayForwardDeclare.h"
+#include "nsTHashtable.h"
+
+template <class> struct already_AddRefed;
+class nsIFile;
+class nsIRunnable;
+class nsIThreadPool;
+
+namespace mozilla {
+
+namespace ipc {
+
+class PBackgroundParent;
+
+} // namespace ipc
+
+namespace dom {
+
+class BlobImpl;
+class FileHandle;
+class FileHandleOp;
+
+class FileHandleThreadPool final
+{
+  class FileHandleQueue;
+  struct DelayedEnqueueInfo;
+  class DirectoryInfo;
+  struct StoragesCompleteCallback;
+
+  nsCOMPtr<nsIThreadPool> mThreadPool;
+  nsCOMPtr<nsIEventTarget> mOwningThread;
+
+  nsClassHashtable<nsCStringHashKey, DirectoryInfo> mDirectoryInfos;
+
+  nsTArray<nsAutoPtr<StoragesCompleteCallback>> mCompleteCallbacks;
+
+  bool mShutdownRequested;
+  bool mShutdownComplete;
+
+public:
+  static already_AddRefed<FileHandleThreadPool>
+  Create();
+
+#ifdef DEBUG
+  void
+  AssertIsOnOwningThread() const;
+
+  nsIEventTarget*
+  GetThreadPoolEventTarget() const;
+#else
+  void
+  AssertIsOnOwningThread() const
+  { }
+#endif
+
+  void
+  Enqueue(FileHandle* aFileHandle,
+          FileHandleOp* aFileHandleOp,
+          bool aFinish);
+
+  NS_INLINE_DECL_REFCOUNTING(FileHandleThreadPool)
+
+  void
+  WaitForDirectoriesToComplete(nsTArray<nsCString>&& aDirectoryIds,
+                               nsIRunnable* aCallback);
+
+  void
+  Shutdown();
+
+private:
+  FileHandleThreadPool();
+
+  // Reference counted.
+  ~FileHandleThreadPool();
+
+  nsresult
+  Init();
+
+  void
+  Cleanup();
+
+  void
+  FinishFileHandle(FileHandle* aFileHandle);
+
+  bool
+  MaybeFireCallback(StoragesCompleteCallback* aCallback);
+};
+
+class BackgroundMutableFileParentBase
+  : public PBackgroundMutableFileParent
+{
+  nsTHashtable<nsPtrHashKey<FileHandle>> mFileHandles;
+  nsCString mDirectoryId;
+  nsString mFileName;
+  FileHandleStorage mStorage;
+  bool mInvalidated;
+  bool mActorWasAlive;
+  bool mActorDestroyed;
+
+protected:
+  nsCOMPtr<nsIFile> mFile;
+
+public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(BackgroundMutableFileParentBase)
+
+  void
+  Invalidate();
+
+  FileHandleStorage
+  Storage() const
+  {
+    return mStorage;
+  }
+
+  const nsCString&
+  DirectoryId() const
+  {
+    return mDirectoryId;
+  }
+
+  const nsString&
+  FileName() const
+  {
+    return mFileName;
+  }
+
+  bool
+  RegisterFileHandle(FileHandle* aFileHandle);
+
+  void
+  UnregisterFileHandle(FileHandle* aFileHandle);
+
+  void
+  SetActorAlive();
+
+  bool
+  IsActorDestroyed() const
+  {
+    mozilla::ipc::AssertIsOnBackgroundThread();
+
+    return mActorWasAlive && mActorDestroyed;
+  }
+
+  bool
+  IsInvalidated() const
+  {
+    mozilla::ipc::AssertIsOnBackgroundThread();
+
+    return mInvalidated;
+  }
+
+  virtual void
+  NoteActiveState()
+  { }
+
+  virtual void
+  NoteInactiveState()
+  { }
+
+  virtual mozilla::ipc::PBackgroundParent*
+  GetBackgroundParent() const = 0;
+
+  virtual already_AddRefed<nsISupports>
+  CreateStream(bool aReadOnly);
+
+  virtual already_AddRefed<BlobImpl>
+  CreateBlobImpl()
+  {
+    return nullptr;
+  }
+
+protected:
+  BackgroundMutableFileParentBase(FileHandleStorage aStorage,
+                                  const nsACString& aDirectoryId,
+                                  const nsAString& aFileName,
+                                  nsIFile* aFile);
+
+  // Reference counted.
+  ~BackgroundMutableFileParentBase();
+
+  // IPDL methods are only called by IPDL.
+  virtual void
+  ActorDestroy(ActorDestroyReason aWhy) override;
+
+  virtual PBackgroundFileHandleParent*
+  AllocPBackgroundFileHandleParent(const FileMode& aMode) override;
+
+  virtual bool
+  RecvPBackgroundFileHandleConstructor(PBackgroundFileHandleParent* aActor,
+                                       const FileMode& aMode) override;
+
+  virtual bool
+  DeallocPBackgroundFileHandleParent(PBackgroundFileHandleParent* aActor)
+                                     override;
+
+  virtual bool
+  RecvDeleteMe() override;
+
+  virtual bool
+  RecvGetFileId(int64_t* aFileId) override;
+};
+
+} // namespace dom
+} // namespace mozilla
+
+#endif // mozilla_dom_filehandle_ActorsParent_h
diff --git a/dom/filehandle/FileHandleBase.cpp b/dom/filehandle/FileHandleBase.cpp
new file mode 100644
index 000000000..ebfd6f077
--- /dev/null
+++ b/dom/filehandle/FileHandleBase.cpp
@@ -0,0 +1,636 @@
+/* -*- 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 "FileHandleBase.h"
+
+#include "ActorsChild.h"
+#include "BackgroundChildImpl.h"
+#include "FileRequestBase.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/dom/File.h"
+#include "mozilla/dom/PBackgroundFileHandle.h"
+#include "mozilla/dom/UnionConversions.h"
+#include "mozilla/ipc/BackgroundChild.h"
+#include "MutableFileBase.h"
+#include "nsCOMPtr.h"
+#include "nsDebug.h"
+#include "nsError.h"
+#include "nsString.h"
+
+namespace mozilla {
+namespace dom {
+
+using namespace mozilla::ipc;
+
+FileHandleBase::FileHandleBase(DEBUGONLY(PRThread* aOwningThread,)
+                               FileMode aMode)
+  : RefCountedThreadObject(DEBUGONLY(aOwningThread))
+  , mBackgroundActor(nullptr)
+  , mLocation(0)
+  , mPendingRequestCount(0)
+  , mReadyState(INITIAL)
+  , mMode(aMode)
+  , mAborted(false)
+  , mCreating(false)
+  DEBUGONLY(, mSentFinishOrAbort(false))
+  DEBUGONLY(, mFiredCompleteOrAbort(false))
+{
+  AssertIsOnOwningThread();
+}
+
+FileHandleBase::~FileHandleBase()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(!mPendingRequestCount);
+  MOZ_ASSERT(!mCreating);
+  MOZ_ASSERT(mSentFinishOrAbort);
+  MOZ_ASSERT_IF(mBackgroundActor, mFiredCompleteOrAbort);
+
+  if (mBackgroundActor) {
+    mBackgroundActor->SendDeleteMeInternal();
+
+    MOZ_ASSERT(!mBackgroundActor, "SendDeleteMeInternal should have cleared!");
+  }
+}
+
+// static
+FileHandleBase*
+FileHandleBase::GetCurrent()
+{
+  MOZ_ASSERT(BackgroundChild::GetForCurrentThread());
+
+  BackgroundChildImpl::ThreadLocal* threadLocal =
+    BackgroundChildImpl::GetThreadLocalForCurrentThread();
+  MOZ_ASSERT(threadLocal);
+
+  return threadLocal->mCurrentFileHandle;
+}
+
+void
+FileHandleBase::SetBackgroundActor(BackgroundFileHandleChild* aActor)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aActor);
+  MOZ_ASSERT(!mBackgroundActor);
+
+  mBackgroundActor = aActor;
+}
+
+void
+FileHandleBase::StartRequest(FileRequestBase* aFileRequest,
+                             const FileRequestParams& aParams)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aFileRequest);
+  MOZ_ASSERT(aParams.type() != FileRequestParams::T__None);
+
+  BackgroundFileRequestChild* actor =
+    new BackgroundFileRequestChild(DEBUGONLY(mBackgroundActor->OwningThread(),)
+                                   aFileRequest);
+
+  mBackgroundActor->SendPBackgroundFileRequestConstructor(actor, aParams);
+
+  // Balanced in BackgroundFileRequestChild::Recv__delete__().
+  OnNewRequest();
+}
+
+void
+FileHandleBase::OnNewRequest()
+{
+  AssertIsOnOwningThread();
+
+  if (!mPendingRequestCount) {
+    MOZ_ASSERT(mReadyState == INITIAL);
+    mReadyState = LOADING;
+  }
+
+  ++mPendingRequestCount;
+}
+
+void
+FileHandleBase::OnRequestFinished(bool aActorDestroyedNormally)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mPendingRequestCount);
+
+  --mPendingRequestCount;
+
+  if (!mPendingRequestCount && !MutableFile()->IsInvalidated()) {
+    mReadyState = FINISHING;
+
+    if (aActorDestroyedNormally) {
+      if (!mAborted) {
+        SendFinish();
+      } else {
+        SendAbort();
+      }
+    } else {
+      // Don't try to send any more messages to the parent if the request actor
+      // was killed.
+#ifdef DEBUG
+      MOZ_ASSERT(!mSentFinishOrAbort);
+      mSentFinishOrAbort = true;
+#endif
+    }
+  }
+}
+
+bool
+FileHandleBase::IsOpen() const
+{
+  AssertIsOnOwningThread();
+
+  // If we haven't started anything then we're open.
+  if (mReadyState == INITIAL) {
+    return true;
+  }
+
+  // If we've already started then we need to check to see if we still have the
+  // mCreating flag set. If we do (i.e. we haven't returned to the event loop
+  // from the time we were created) then we are open. Otherwise check the
+  // currently running file handles to see if it's the same. We only allow other
+  // requests to be made if this file handle is currently running.
+  if (mReadyState == LOADING && (mCreating || GetCurrent() == this)) {
+    return true;
+  }
+
+  return false;
+}
+
+void
+FileHandleBase::Abort()
+{
+  AssertIsOnOwningThread();
+
+  if (IsFinishingOrDone()) {
+    // Already started (and maybe finished) the finish or abort so there is
+    // nothing to do here.
+    return;
+  }
+
+  const bool isInvalidated = MutableFile()->IsInvalidated();
+  bool needToSendAbort = mReadyState == INITIAL && !isInvalidated;
+
+#ifdef DEBUG
+  if (isInvalidated) {
+    mSentFinishOrAbort = true;
+  }
+#endif
+
+  mAborted = true;
+  mReadyState = DONE;
+
+  // Fire the abort event if there are no outstanding requests. Otherwise the
+  // abort event will be fired when all outstanding requests finish.
+  if (needToSendAbort) {
+    SendAbort();
+  }
+}
+
+already_AddRefed<FileRequestBase>
+FileHandleBase::Read(uint64_t aSize, bool aHasEncoding,
+                     const nsAString& aEncoding, ErrorResult& aRv)
+{
+  AssertIsOnOwningThread();
+
+  // State and argument checking for read
+  if (!CheckStateAndArgumentsForRead(aSize, aRv)) {
+    return nullptr;
+  }
+
+  // Do nothing if the window is closed
+  if (!CheckWindow()) {
+    return nullptr;
+  }
+
+  FileRequestReadParams params;
+  params.offset() = mLocation;
+  params.size() = aSize;
+
+  RefPtr<FileRequestBase> fileRequest = GenerateFileRequest();
+  if (aHasEncoding) {
+    fileRequest->SetEncoding(aEncoding);
+  }
+
+  StartRequest(fileRequest, params);
+
+  mLocation += aSize;
+
+  return fileRequest.forget();
+}
+
+already_AddRefed<FileRequestBase>
+FileHandleBase::Truncate(const Optional<uint64_t>& aSize, ErrorResult& aRv)
+{
+  AssertIsOnOwningThread();
+
+  // State checking for write
+  if (!CheckStateForWrite(aRv)) {
+    return nullptr;
+  }
+
+  // Getting location and additional state checking for truncate
+  uint64_t location;
+  if (aSize.WasPassed()) {
+    // Just in case someone calls us from C++
+    MOZ_ASSERT(aSize.Value() != UINT64_MAX, "Passed wrong size!");
+    location = aSize.Value();
+  } else {
+    if (mLocation == UINT64_MAX) {
+      aRv.Throw(NS_ERROR_DOM_FILEHANDLE_NOT_ALLOWED_ERR);
+      return nullptr;
+    }
+    location = mLocation;
+  }
+
+  // Do nothing if the window is closed
+  if (!CheckWindow()) {
+    return nullptr;
+  }
+
+  FileRequestTruncateParams params;
+  params.offset() = location;
+
+  RefPtr<FileRequestBase> fileRequest = GenerateFileRequest();
+
+  StartRequest(fileRequest, params);
+
+  if (aSize.WasPassed()) {
+    mLocation = aSize.Value();
+  }
+
+  return fileRequest.forget();
+}
+
+already_AddRefed<FileRequestBase>
+FileHandleBase::Flush(ErrorResult& aRv)
+{
+  AssertIsOnOwningThread();
+
+  // State checking for write
+  if (!CheckStateForWrite(aRv)) {
+    return nullptr;
+  }
+
+  // Do nothing if the window is closed
+  if (!CheckWindow()) {
+    return nullptr;
+  }
+
+  FileRequestFlushParams params;
+
+  RefPtr<FileRequestBase> fileRequest = GenerateFileRequest();
+
+  StartRequest(fileRequest, params);
+
+  return fileRequest.forget();
+}
+
+void
+FileHandleBase::Abort(ErrorResult& aRv)
+{
+  AssertIsOnOwningThread();
+
+  // This method is special enough for not using generic state checking methods.
+
+  if (IsFinishingOrDone()) {
+    aRv.Throw(NS_ERROR_DOM_FILEHANDLE_NOT_ALLOWED_ERR);
+    return;
+  }
+
+  Abort();
+}
+
+void
+FileHandleBase::HandleCompleteOrAbort(bool aAborted)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(!mFiredCompleteOrAbort);
+
+  mReadyState = DONE;
+
+  DEBUGONLY(mFiredCompleteOrAbort = true;)
+}
+
+void
+FileHandleBase::OnReturnToEventLoop()
+{
+  AssertIsOnOwningThread();
+
+  // We're back at the event loop, no longer newborn.
+  mCreating = false;
+
+  // Maybe finish if there were no requests generated.
+  if (mReadyState == INITIAL) {
+    mReadyState = DONE;
+
+    SendFinish();
+  }
+}
+
+bool
+FileHandleBase::CheckState(ErrorResult& aRv)
+{
+  if (!IsOpen()) {
+    aRv.Throw(NS_ERROR_DOM_FILEHANDLE_INACTIVE_ERR);
+    return false;
+  }
+
+  return true;
+}
+
+bool
+FileHandleBase::CheckStateAndArgumentsForRead(uint64_t aSize, ErrorResult& aRv)
+{
+  // Common state checking
+  if (!CheckState(aRv)) {
+    return false;
+  }
+
+  // Additional state checking for read
+  if (mLocation == UINT64_MAX) {
+    aRv.Throw(NS_ERROR_DOM_FILEHANDLE_NOT_ALLOWED_ERR);
+    return false;
+  }
+
+  // Argument checking for read
+  if (!aSize) {
+    aRv.ThrowTypeError<MSG_INVALID_READ_SIZE>();
+    return false;
+  }
+
+  return true;
+}
+
+bool
+FileHandleBase::CheckStateForWrite(ErrorResult& aRv)
+{
+  // Common state checking
+  if (!CheckState(aRv)) {
+    return false;
+  }
+
+  // Additional state checking for write
+  if (mMode != FileMode::Readwrite) {
+    aRv.Throw(NS_ERROR_DOM_FILEHANDLE_READ_ONLY_ERR);
+    return false;
+  }
+
+  return true;
+}
+
+bool
+FileHandleBase::CheckStateForWriteOrAppend(bool aAppend, ErrorResult& aRv)
+{
+  // State checking for write
+  if (!CheckStateForWrite(aRv)) {
+    return false;
+  }
+
+  // Additional state checking for write
+  if (!aAppend && mLocation == UINT64_MAX) {
+    aRv.Throw(NS_ERROR_DOM_FILEHANDLE_NOT_ALLOWED_ERR);
+    return false;
+  }
+
+  return true;
+}
+
+already_AddRefed<FileRequestBase>
+FileHandleBase::WriteOrAppend(
+                       const StringOrArrayBufferOrArrayBufferViewOrBlob& aValue,
+                       bool aAppend,
+                       ErrorResult& aRv)
+{
+  AssertIsOnOwningThread();
+
+  if (aValue.IsString()) {
+    return WriteOrAppend(aValue.GetAsString(), aAppend, aRv);
+  }
+
+  if (aValue.IsArrayBuffer()) {
+    return WriteOrAppend(aValue.GetAsArrayBuffer(), aAppend, aRv);
+  }
+
+  if (aValue.IsArrayBufferView()) {
+    return WriteOrAppend(aValue.GetAsArrayBufferView(), aAppend, aRv);
+  }
+
+  MOZ_ASSERT(aValue.IsBlob());
+  return WriteOrAppend(aValue.GetAsBlob(), aAppend, aRv);
+}
+
+already_AddRefed<FileRequestBase>
+FileHandleBase::WriteOrAppend(const nsAString& aValue,
+                              bool aAppend,
+                              ErrorResult& aRv)
+{
+  AssertIsOnOwningThread();
+
+  // State checking for write or append
+  if (!CheckStateForWriteOrAppend(aAppend, aRv)) {
+    return nullptr;
+  }
+
+  NS_ConvertUTF16toUTF8 cstr(aValue);
+
+  uint64_t dataLength = cstr.Length();;
+  if (!dataLength) {
+    return nullptr;
+  }
+
+  FileRequestStringData stringData(cstr);
+
+  // Do nothing if the window is closed
+  if (!CheckWindow()) {
+    return nullptr;
+  }
+
+  return WriteInternal(stringData, dataLength, aAppend, aRv);
+}
+
+already_AddRefed<FileRequestBase>
+FileHandleBase::WriteOrAppend(const ArrayBuffer& aValue,
+                              bool aAppend,
+                              ErrorResult& aRv)
+{
+  AssertIsOnOwningThread();
+
+  // State checking for write or append
+  if (!CheckStateForWriteOrAppend(aAppend, aRv)) {
+    return nullptr;
+  }
+
+  aValue.ComputeLengthAndData();
+
+  uint64_t dataLength = aValue.Length();;
+  if (!dataLength) {
+    return nullptr;
+  }
+
+  const char* data = reinterpret_cast<const char*>(aValue.Data());
+
+  FileRequestStringData stringData;
+  if (NS_WARN_IF(!stringData.string().Assign(data, aValue.Length(),
+                                             fallible_t()))) {
+    aRv.Throw(NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR);
+    return nullptr;
+  }
+
+  // Do nothing if the window is closed
+  if (!CheckWindow()) {
+    return nullptr;
+  }
+
+  return WriteInternal(stringData, dataLength, aAppend, aRv);
+}
+
+already_AddRefed<FileRequestBase>
+FileHandleBase::WriteOrAppend(const ArrayBufferView& aValue,
+                              bool aAppend,
+                              ErrorResult& aRv)
+{
+  AssertIsOnOwningThread();
+
+  // State checking for write or append
+  if (!CheckStateForWriteOrAppend(aAppend, aRv)) {
+    return nullptr;
+  }
+
+  aValue.ComputeLengthAndData();
+
+  uint64_t dataLength = aValue.Length();;
+  if (!dataLength) {
+    return nullptr;
+  }
+
+  const char* data = reinterpret_cast<const char*>(aValue.Data());
+
+  FileRequestStringData stringData;
+  if (NS_WARN_IF(!stringData.string().Assign(data, aValue.Length(),
+                                             fallible_t()))) {
+    aRv.Throw(NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR);
+    return nullptr;
+  }
+
+  // Do nothing if the window is closed
+  if (!CheckWindow()) {
+    return nullptr;
+  }
+
+  return WriteInternal(stringData, dataLength, aAppend, aRv);
+}
+
+already_AddRefed<FileRequestBase>
+FileHandleBase::WriteOrAppend(Blob& aValue,
+                              bool aAppend,
+                              ErrorResult& aRv)
+{
+  AssertIsOnOwningThread();
+
+  // State checking for write or append
+  if (!CheckStateForWriteOrAppend(aAppend, aRv)) {
+    return nullptr;
+  }
+
+  ErrorResult rv;
+  uint64_t dataLength = aValue.GetSize(rv);
+  if (NS_WARN_IF(rv.Failed())) {
+    aRv.Throw(NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR);
+    return nullptr;
+  }
+
+  if (!dataLength) {
+    return nullptr;
+  }
+
+  PBackgroundChild* backgroundActor = BackgroundChild::GetForCurrentThread();
+  MOZ_ASSERT(backgroundActor);
+
+  PBlobChild* blobActor =
+    BackgroundChild::GetOrCreateActorForBlob(backgroundActor, &aValue);
+  if (NS_WARN_IF(!blobActor)) {
+    aRv.Throw(NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR);
+    return nullptr;
+  }
+
+  FileRequestBlobData blobData;
+  blobData.blobChild() = blobActor;
+
+  // Do nothing if the window is closed
+  if (!CheckWindow()) {
+    return nullptr;
+  }
+
+  return WriteInternal(blobData, dataLength, aAppend, aRv);
+}
+
+already_AddRefed<FileRequestBase>
+FileHandleBase::WriteInternal(const FileRequestData& aData,
+                              uint64_t aDataLength,
+                              bool aAppend,
+                              ErrorResult& aRv)
+{
+  AssertIsOnOwningThread();
+
+  DebugOnly<ErrorResult> error;
+  MOZ_ASSERT(CheckStateForWrite(error));
+  MOZ_ASSERT_IF(!aAppend, mLocation != UINT64_MAX);
+  MOZ_ASSERT(aDataLength);
+  MOZ_ASSERT(CheckWindow());
+
+  FileRequestWriteParams params;
+  params.offset() = aAppend ? UINT64_MAX : mLocation;
+  params.data() = aData;
+  params.dataLength() = aDataLength;
+
+  RefPtr<FileRequestBase> fileRequest = GenerateFileRequest();
+  MOZ_ASSERT(fileRequest);
+
+  StartRequest(fileRequest, params);
+
+  if (aAppend) {
+    mLocation = UINT64_MAX;
+  }
+  else {
+    mLocation += aDataLength;
+  }
+
+  return fileRequest.forget();
+}
+
+void
+FileHandleBase::SendFinish()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(!mAborted);
+  MOZ_ASSERT(IsFinishingOrDone());
+  MOZ_ASSERT(!mSentFinishOrAbort);
+  MOZ_ASSERT(!mPendingRequestCount);
+
+  MOZ_ASSERT(mBackgroundActor);
+  mBackgroundActor->SendFinish();
+
+  DEBUGONLY(mSentFinishOrAbort = true;)
+}
+
+void
+FileHandleBase::SendAbort()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mAborted);
+  MOZ_ASSERT(IsFinishingOrDone());
+  MOZ_ASSERT(!mSentFinishOrAbort);
+
+  MOZ_ASSERT(mBackgroundActor);
+  mBackgroundActor->SendAbort();
+
+  DEBUGONLY(mSentFinishOrAbort = true;)
+}
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/filehandle/FileHandleBase.h b/dom/filehandle/FileHandleBase.h
new file mode 100644
index 000000000..859a6e9ae
--- /dev/null
+++ b/dom/filehandle/FileHandleBase.h
@@ -0,0 +1,246 @@
+/* -*- 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_FileHandle_h
+#define mozilla_dom_FileHandle_h
+
+#include "FileHandleCommon.h"
+#include "mozilla/dom/BindingDeclarations.h"
+#include "mozilla/dom/FileModeBinding.h"
+#include "mozilla/dom/Nullable.h"
+#include "mozilla/dom/TypedArray.h"
+
+template <class> struct already_AddRefed;
+class nsAString;
+struct PRThread;
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+class BackgroundFileHandleChild;
+class Blob;
+class FileRequestBase;
+class FileRequestData;
+class FileRequestParams;
+class MutableFileBase;
+class StringOrArrayBufferOrArrayBufferViewOrBlob;
+
+/**
+ * This class provides a base for FileHandle implementations.
+ */
+class FileHandleBase
+  : public RefCountedThreadObject
+{
+public:
+  enum ReadyState
+  {
+    INITIAL = 0,
+    LOADING,
+    FINISHING,
+    DONE
+  };
+
+private:
+  BackgroundFileHandleChild* mBackgroundActor;
+
+  uint64_t mLocation;
+
+  uint32_t mPendingRequestCount;
+
+  ReadyState mReadyState;
+  FileMode mMode;
+
+  bool mAborted;
+  bool mCreating;
+
+  DEBUGONLY(bool mSentFinishOrAbort;)
+  DEBUGONLY(bool mFiredCompleteOrAbort;)
+
+public:
+  static FileHandleBase*
+  GetCurrent();
+
+  void
+  SetBackgroundActor(BackgroundFileHandleChild* aActor);
+
+  void
+  ClearBackgroundActor()
+  {
+    AssertIsOnOwningThread();
+
+    mBackgroundActor = nullptr;
+  }
+
+  void
+  StartRequest(FileRequestBase* aFileRequest, const FileRequestParams& aParams);
+
+  void
+  OnNewRequest();
+
+  void
+  OnRequestFinished(bool aActorDestroyedNormally);
+
+  bool
+  IsOpen() const;
+
+  bool
+  IsFinishingOrDone() const
+  {
+    AssertIsOnOwningThread();
+
+    return mReadyState == FINISHING || mReadyState == DONE;
+  }
+
+  bool
+  IsDone() const
+  {
+    AssertIsOnOwningThread();
+
+    return mReadyState == DONE;
+  }
+
+  bool
+  IsAborted() const
+  {
+    AssertIsOnOwningThread();
+    return mAborted;
+  }
+
+  void
+  SetCreating()
+  {
+    mCreating = true;
+  }
+
+  void
+  Abort();
+
+  // Shared WebIDL (IndexedDB FileHandle and FileSystem FileHandle)
+  FileMode
+  Mode() const
+  {
+    AssertIsOnOwningThread();
+    return mMode;
+  }
+
+  bool
+  Active() const
+  {
+    AssertIsOnOwningThread();
+    return IsOpen();
+  }
+
+  Nullable<uint64_t>
+  GetLocation() const
+  {
+    AssertIsOnOwningThread();
+
+    if (mLocation == UINT64_MAX) {
+      return Nullable<uint64_t>();
+    }
+
+    return Nullable<uint64_t>(mLocation);
+  }
+
+  void
+  SetLocation(const Nullable<uint64_t>& aLocation)
+  {
+    AssertIsOnOwningThread();
+
+    // Null means the end-of-file.
+    if (aLocation.IsNull()) {
+      mLocation = UINT64_MAX;
+    } else {
+      mLocation = aLocation.Value();
+    }
+  }
+
+  already_AddRefed<FileRequestBase>
+  Read(uint64_t aSize, bool aHasEncoding, const nsAString& aEncoding,
+       ErrorResult& aRv);
+
+  already_AddRefed<FileRequestBase>
+  Truncate(const Optional<uint64_t>& aSize, ErrorResult& aRv);
+
+  already_AddRefed<FileRequestBase>
+  Flush(ErrorResult& aRv);
+
+  void
+  Abort(ErrorResult& aRv);
+
+  //  Must be overridden in subclasses.
+  virtual MutableFileBase*
+  MutableFile() const = 0;
+
+  //  May be overridden in subclasses.
+  virtual void
+  HandleCompleteOrAbort(bool aAborted);
+
+protected:
+  FileHandleBase(DEBUGONLY(PRThread* aOwningThread,)
+                 FileMode aMode);
+
+  ~FileHandleBase();
+
+  void
+  OnReturnToEventLoop();
+
+  bool
+  CheckState(ErrorResult& aRv);
+
+  bool
+  CheckStateAndArgumentsForRead(uint64_t aSize, ErrorResult& aRv);
+
+  bool
+  CheckStateForWrite(ErrorResult& aRv);
+
+  bool
+  CheckStateForWriteOrAppend(bool aAppend, ErrorResult& aRv);
+
+  already_AddRefed<FileRequestBase>
+  WriteOrAppend(const StringOrArrayBufferOrArrayBufferViewOrBlob& aValue,
+                bool aAppend,
+                ErrorResult& aRv);
+
+  //  Must be overridden in subclasses.
+  virtual bool
+  CheckWindow() = 0;
+
+  //  Must be overridden in subclasses.
+  virtual already_AddRefed<FileRequestBase>
+  GenerateFileRequest() = 0;
+
+private:
+  already_AddRefed<FileRequestBase>
+  WriteOrAppend(const nsAString& aValue, bool aAppend, ErrorResult& aRv);
+
+  already_AddRefed<FileRequestBase>
+  WriteOrAppend(const ArrayBuffer& aValue, bool aAppend, ErrorResult& aRv);
+
+  already_AddRefed<FileRequestBase>
+  WriteOrAppend(const ArrayBufferView& aValue, bool aAppend, ErrorResult& aRv);
+
+  already_AddRefed<FileRequestBase>
+  WriteOrAppend(Blob& aValue, bool aAppend, ErrorResult& aRv);
+
+  already_AddRefed<FileRequestBase>
+  WriteInternal(const FileRequestData& aData, uint64_t aDataLength,
+                bool aAppend, ErrorResult& aRv);
+
+  void
+  SendFinish();
+
+  void
+  SendAbort();
+};
+
+} // namespace dom
+} // namespace mozilla
+
+#endif // mozilla_dom_FileHandle_h
diff --git a/dom/filehandle/FileHandleCommon.cpp b/dom/filehandle/FileHandleCommon.cpp
new file mode 100644
index 000000000..0c465ec17
--- /dev/null
+++ b/dom/filehandle/FileHandleCommon.cpp
@@ -0,0 +1,34 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=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 "FileHandleCommon.h"
+
+#include "mozilla/Assertions.h"
+#include "prthread.h"
+
+namespace mozilla {
+namespace dom {
+
+#ifdef DEBUG
+
+void
+ThreadObject::AssertIsOnOwningThread() const
+{
+  MOZ_ASSERT(mOwningThread);
+  MOZ_ASSERT(PR_GetCurrentThread() == mOwningThread);
+}
+
+PRThread*
+ThreadObject::OwningThread() const
+{
+  MOZ_ASSERT(mOwningThread);
+  return mOwningThread;
+}
+
+#endif // DEBUG
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/filehandle/FileHandleCommon.h b/dom/filehandle/FileHandleCommon.h
new file mode 100644
index 000000000..47cffa017
--- /dev/null
+++ b/dom/filehandle/FileHandleCommon.h
@@ -0,0 +1,73 @@
+/* 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_FileHandleCommon_h
+#define mozilla_dom_FileHandleCommon_h
+
+#include "nscore.h"
+
+#ifdef DEBUG
+#define DEBUGONLY(...)  __VA_ARGS__
+#else
+#define DEBUGONLY(...)  /* nothing */
+#endif
+
+struct PRThread;
+
+namespace mozilla {
+namespace dom {
+
+class RefCountedObject
+{
+public:
+  NS_IMETHOD_(MozExternalRefCountType)
+  AddRef() = 0;
+
+  NS_IMETHOD_(MozExternalRefCountType)
+  Release() = 0;
+
+protected:
+  virtual ~RefCountedObject()
+  { }
+};
+
+class ThreadObject
+{
+  DEBUGONLY(PRThread* mOwningThread;)
+
+public:
+  explicit ThreadObject(DEBUGONLY(PRThread* aOwningThread))
+    DEBUGONLY(: mOwningThread(aOwningThread))
+  { }
+
+  virtual ~ThreadObject()
+  { }
+
+#ifdef DEBUG
+  void
+  AssertIsOnOwningThread() const;
+
+  PRThread*
+  OwningThread() const;
+#else
+  void
+  AssertIsOnOwningThread() const
+  { }
+#endif
+};
+
+class RefCountedThreadObject
+  : public RefCountedObject
+  , public ThreadObject
+{
+public:
+  explicit RefCountedThreadObject(DEBUGONLY(PRThread* aOwningThread))
+    : ThreadObject(DEBUGONLY(aOwningThread))
+  { }
+};
+
+} // namespace dom
+} // namespace mozilla
+
+#endif // mozilla_dom_FileHandleCommon_h
diff --git a/dom/filehandle/FileHandleStorage.h b/dom/filehandle/FileHandleStorage.h
new file mode 100644
index 000000000..957f4005a
--- /dev/null
+++ b/dom/filehandle/FileHandleStorage.h
@@ -0,0 +1,24 @@
+/* -*- 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_FileHandleStorage_h
+#define mozilla_dom_FileHandleStorage_h
+
+namespace mozilla {
+namespace dom {
+
+enum FileHandleStorage
+{
+  FILE_HANDLE_STORAGE_IDB = 0,
+  // A placeholder for bug 997471
+  //FILE_HANDLE_STORAGE_FS
+  FILE_HANDLE_STORAGE_MAX
+};
+
+} // namespace dom
+} // namespace mozilla
+
+#endif // mozilla_dom_FileHandleStorage_h
diff --git a/dom/filehandle/FileRequestBase.h b/dom/filehandle/FileRequestBase.h
new file mode 100644
index 000000000..bff3997d7
--- /dev/null
+++ b/dom/filehandle/FileRequestBase.h
@@ -0,0 +1,93 @@
+/* -*- 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_FileRequest_h
+#define mozilla_dom_FileRequest_h
+
+#include "FileHandleCommon.h"
+#include "js/TypeDecls.h"
+#include "nsString.h"
+
+struct PRThread;
+
+namespace mozilla {
+namespace dom {
+
+class FileHandleBase;
+
+/**
+ * This class provides a base for FileRequest implementations.
+ */
+class FileRequestBase
+  : public RefCountedThreadObject
+{
+  nsString mEncoding;
+
+  bool mHasEncoding;
+
+public:
+  class ResultCallback;
+
+  void
+  SetEncoding(const nsAString& aEncoding)
+  {
+    mEncoding = aEncoding;
+    mHasEncoding = true;
+  }
+
+  const nsAString&
+  GetEncoding() const
+  {
+    return mEncoding;
+  }
+
+  bool
+  HasEncoding() const
+  {
+    return mHasEncoding;
+  }
+
+  virtual FileHandleBase*
+  FileHandle() const = 0;
+
+  virtual void
+  OnProgress(uint64_t aProgress, uint64_t aProgressMax) = 0;
+
+  virtual void
+  SetResultCallback(ResultCallback* aCallback) = 0;
+
+  virtual void
+  SetError(nsresult aError) = 0;
+
+protected:
+  FileRequestBase(DEBUGONLY(PRThread* aOwningThread))
+    : RefCountedThreadObject(DEBUGONLY(aOwningThread))
+    , mHasEncoding(false)
+  {
+    AssertIsOnOwningThread();
+  }
+
+  virtual ~FileRequestBase()
+  {
+    AssertIsOnOwningThread();
+  }
+};
+
+class NS_NO_VTABLE FileRequestBase::ResultCallback
+{
+public:
+  virtual nsresult
+  GetResult(JSContext* aCx, JS::MutableHandle<JS::Value> aResult) = 0;
+
+protected:
+  ResultCallback()
+  { }
+};
+
+} // namespace dom
+} // namespace mozilla
+
+#endif // mozilla_dom_FileRequest_h
diff --git a/dom/filehandle/MutableFileBase.cpp b/dom/filehandle/MutableFileBase.cpp
new file mode 100644
index 000000000..dc577e8f5
--- /dev/null
+++ b/dom/filehandle/MutableFileBase.cpp
@@ -0,0 +1,36 @@
+/* -*- 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 "MutableFileBase.h"
+
+#include "ActorsChild.h"
+#include "mozilla/Assertions.h"
+#include "prthread.h"
+
+namespace mozilla {
+namespace dom {
+
+MutableFileBase::MutableFileBase(DEBUGONLY(PRThread* aOwningThread,)
+                                 BackgroundMutableFileChildBase* aActor)
+  : RefCountedThreadObject(DEBUGONLY(aOwningThread))
+  , mBackgroundActor(aActor)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aActor);
+}
+
+MutableFileBase::~MutableFileBase()
+{
+  AssertIsOnOwningThread();
+
+  if (mBackgroundActor) {
+    mBackgroundActor->SendDeleteMeInternal();
+    MOZ_ASSERT(!mBackgroundActor, "SendDeleteMeInternal should have cleared!");
+  }
+}
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/filehandle/MutableFileBase.h b/dom/filehandle/MutableFileBase.h
new file mode 100644
index 000000000..88d53ff78
--- /dev/null
+++ b/dom/filehandle/MutableFileBase.h
@@ -0,0 +1,76 @@
+/* -*- 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_MutableFile_h
+#define mozilla_dom_MutableFile_h
+
+#include "mozilla/dom/FileHandleCommon.h"
+#include "nscore.h"
+
+template <class> struct already_AddRefed;
+class nsISupports;
+class nsString;
+struct PRThread;
+
+namespace mozilla {
+namespace dom {
+
+class BackgroundMutableFileChildBase;
+class BlobImpl;
+class File;
+class FileHandleBase;
+
+/**
+ * This class provides a base for MutableFile implementations.
+ * (for example IDBMutableFile provides IndexedDB specific implementation).
+ */
+class MutableFileBase
+  : public RefCountedThreadObject
+{
+protected:
+  BackgroundMutableFileChildBase* mBackgroundActor;
+
+public:
+  BackgroundMutableFileChildBase*
+  GetBackgroundActor() const
+  {
+    AssertIsOnOwningThread();
+
+    return mBackgroundActor;
+  }
+
+  void
+  ClearBackgroundActor()
+  {
+    AssertIsOnOwningThread();
+
+    mBackgroundActor = nullptr;
+  }
+
+  virtual const nsString&
+  Name() const = 0;
+
+  virtual const nsString&
+  Type() const = 0;
+
+  virtual bool
+  IsInvalidated() = 0;
+
+  virtual already_AddRefed<File>
+  CreateFileFor(BlobImpl* aBlobImpl,
+                FileHandleBase* aFileHandle) = 0;
+
+protected:
+  MutableFileBase(DEBUGONLY(PRThread* aOwningThread,)
+                  BackgroundMutableFileChildBase* aActor);
+
+  virtual ~MutableFileBase();
+};
+
+} // namespace dom
+} // namespace mozilla
+
+#endif // mozilla_dom_MutableFile_h
diff --git a/dom/filehandle/PBackgroundFileHandle.ipdl b/dom/filehandle/PBackgroundFileHandle.ipdl
new file mode 100644
index 000000000..60fdfafbf
--- /dev/null
+++ b/dom/filehandle/PBackgroundFileHandle.ipdl
@@ -0,0 +1,91 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+include protocol PBackgroundFileRequest;
+include protocol PBackgroundMutableFile;
+include protocol PBlob;
+
+namespace mozilla {
+namespace dom {
+
+struct FileRequestGetMetadataParams
+{
+  bool size;
+  bool lastModified;
+};
+
+struct FileRequestReadParams
+{
+  uint64_t offset;
+  uint64_t size;
+};
+
+struct FileRequestStringData
+{
+  nsCString string;
+};
+
+struct FileRequestBlobData
+{
+  PBlob blob;
+};
+
+union FileRequestData
+{
+  FileRequestStringData;
+  FileRequestBlobData;
+};
+
+struct FileRequestWriteParams
+{
+  uint64_t offset;
+  FileRequestData data;
+  uint64_t dataLength;
+};
+
+struct FileRequestTruncateParams
+{
+  uint64_t offset;
+};
+
+struct FileRequestFlushParams
+{
+};
+
+struct FileRequestGetFileParams
+{
+};
+
+union FileRequestParams
+{
+  FileRequestGetMetadataParams;
+  FileRequestReadParams;
+  FileRequestWriteParams;
+  FileRequestTruncateParams;
+  FileRequestFlushParams;
+  FileRequestGetFileParams;
+};
+
+protocol PBackgroundFileHandle
+{
+  manager PBackgroundMutableFile;
+
+  manages PBackgroundFileRequest;
+
+parent:
+  async DeleteMe();
+
+  async Finish();
+  async Abort();
+
+  async PBackgroundFileRequest(FileRequestParams params);
+
+child:
+  async __delete__();
+
+  async Complete(bool aborted);
+};
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/filehandle/PBackgroundFileRequest.ipdl b/dom/filehandle/PBackgroundFileRequest.ipdl
new file mode 100644
index 000000000..9fb678b75
--- /dev/null
+++ b/dom/filehandle/PBackgroundFileRequest.ipdl
@@ -0,0 +1,83 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+include protocol PBackgroundFileHandle;
+include protocol PBlob;
+
+using struct mozilla::void_t
+  from "ipc/IPCMessageUtils.h";
+
+namespace mozilla {
+namespace dom {
+
+union FileRequestSize
+{
+  void_t;
+  uint64_t;
+};
+
+union FileRequestLastModified
+{
+  void_t;
+  int64_t;
+};
+
+struct FileRequestMetadata
+{
+  FileRequestSize size;
+  FileRequestLastModified lastModified;
+};
+
+struct FileRequestGetMetadataResponse
+{
+  FileRequestMetadata metadata;
+};
+
+struct FileRequestReadResponse
+{
+  nsCString data;
+};
+
+struct FileRequestWriteResponse
+{
+};
+
+struct FileRequestTruncateResponse
+{
+};
+
+struct FileRequestFlushResponse
+{
+};
+
+struct FileRequestGetFileResponse
+{
+  PBlob file;
+  FileRequestMetadata metadata;
+};
+
+union FileRequestResponse
+{
+  nsresult;
+  FileRequestGetMetadataResponse;
+  FileRequestReadResponse;
+  FileRequestWriteResponse;
+  FileRequestTruncateResponse;
+  FileRequestFlushResponse;
+  FileRequestGetFileResponse;
+};
+
+protocol PBackgroundFileRequest
+{
+  manager PBackgroundFileHandle;
+
+child:
+  async __delete__(FileRequestResponse response);
+
+  async Progress(uint64_t progress,
+                 uint64_t progressMax);
+};
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/filehandle/PBackgroundMutableFile.ipdl b/dom/filehandle/PBackgroundMutableFile.ipdl
new file mode 100644
index 000000000..0f87f3b6d
--- /dev/null
+++ b/dom/filehandle/PBackgroundMutableFile.ipdl
@@ -0,0 +1,36 @@
+/* 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 PBackgroundFileHandle;
+include protocol PBackgroundIDBDatabase;
+
+include "mozilla/dom/filehandle/SerializationHelpers.h";
+
+using mozilla::dom::FileMode
+  from "mozilla/dom/FileModeBinding.h";
+
+namespace mozilla {
+namespace dom {
+
+sync protocol PBackgroundMutableFile
+{
+  manager PBackgroundIDBDatabase;
+
+  manages PBackgroundFileHandle;
+
+parent:
+  async DeleteMe();
+
+  async PBackgroundFileHandle(FileMode mode);
+
+  // Use only for testing!
+  sync GetFileId()
+    returns (int64_t fileId);
+
+child:
+  async __delete__();
+};
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/filehandle/SerializationHelpers.h b/dom/filehandle/SerializationHelpers.h
new file mode 100644
index 000000000..12a30442c
--- /dev/null
+++ b/dom/filehandle/SerializationHelpers.h
@@ -0,0 +1,23 @@
+/* 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_filehandle_SerializationHelpers_h
+#define mozilla_dom_filehandle_SerializationHelpers_h
+
+#include "ipc/IPCMessageUtils.h"
+
+#include "mozilla/dom/FileModeBinding.h"
+
+namespace IPC {
+
+template <>
+struct ParamTraits<mozilla::dom::FileMode> :
+  public ContiguousEnumSerializer<mozilla::dom::FileMode,
+                                  mozilla::dom::FileMode::Readonly,
+                                  mozilla::dom::FileMode::EndGuard_>
+{ };
+
+} // namespace IPC
+
+#endif // mozilla_dom_filehandle_SerializationHelpers_h
diff --git a/dom/filehandle/moz.build b/dom/filehandle/moz.build
new file mode 100644
index 000000000..b4e3b64c0
--- /dev/null
+++ b/dom/filehandle/moz.build
@@ -0,0 +1,45 @@
+# -*- 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/.
+
+EXPORTS.mozilla.dom.filehandle += [
+    'ActorsChild.h',
+    'ActorsParent.h',
+    'SerializationHelpers.h',
+]
+
+EXPORTS.mozilla.dom += [
+    'FileHandleBase.h',
+    'FileHandleCommon.h',
+    'FileHandleStorage.h',
+    'FileRequestBase.h',
+    'MutableFileBase.h',
+]
+
+UNIFIED_SOURCES += [
+    'ActorsChild.cpp',
+    'ActorsParent.cpp',
+    'FileHandleBase.cpp',
+    'FileHandleCommon.cpp',
+    'MutableFileBase.cpp',
+]
+
+IPDL_SOURCES += [
+    'PBackgroundFileHandle.ipdl',
+    'PBackgroundFileRequest.ipdl',
+    'PBackgroundMutableFile.ipdl',
+]
+
+include('/ipc/chromium/chromium-config.mozbuild')
+
+LOCAL_INCLUDES += [
+    '../base',
+]
+
+FINAL_LIBRARY = 'xul'
+
+LOCAL_INCLUDES += [
+    '/xpcom/threads',
+]