1 files changed, 706 insertions, 0 deletions
diff --git a/dom/fs/api/FileSystemWritableFileStream.cpp b/dom/fs/api/FileSystemWritableFileStream.cpp
new file mode 100644
index 0000000000..69d1181c16
--- /dev/null
+++ b/dom/fs/api/FileSystemWritableFileStream.cpp
@@ -0,0 +1,706 @@
+/* -*- 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 "FileSystemWritableFileStream.h"
+
+#include "mozilla/Buffer.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/dom/Blob.h"
+#include "mozilla/dom/FileSystemHandle.h"
+#include "mozilla/dom/FileSystemLog.h"
+#include "mozilla/dom/FileSystemManager.h"
+#include "mozilla/dom/FileSystemWritableFileStreamBinding.h"
+#include "mozilla/dom/FileSystemWritableFileStreamChild.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/WritableStreamDefaultController.h"
+#include "mozilla/dom/quota/QuotaCommon.h"
+#include "mozilla/dom/quota/ResultExtensions.h"
+#include "nsIInputStream.h"
+#include "nsNetUtil.h"
+#include "private/pprio.h"
+
+namespace mozilla::dom {
+
+namespace {
+
+class WritableFileStreamUnderlyingSinkAlgorithms final
+    : public UnderlyingSinkAlgorithmsBase {
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(
+      WritableFileStreamUnderlyingSinkAlgorithms, UnderlyingSinkAlgorithmsBase)
+
+  explicit WritableFileStreamUnderlyingSinkAlgorithms(
+      FileSystemWritableFileStream& aStream)
+      : mStream(&aStream) {}
+
+  // Streams algorithms
+  void StartCallback(JSContext* aCx,
+                     WritableStreamDefaultController& aController,
+                     JS::MutableHandle<JS::Value> aRetVal,
+                     ErrorResult& aRv) override;
+
+  MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> WriteCallback(
+      JSContext* aCx, JS::Handle<JS::Value> aChunk,
+      WritableStreamDefaultController& aController, ErrorResult& aRv) override;
+
+  MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> CloseCallback(
+      JSContext* aCx, ErrorResult& aRv) override;
+
+  MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> AbortCallback(
+      JSContext* aCx, const Optional<JS::Handle<JS::Value>>& aReason,
+      ErrorResult& aRv) override;
+
+  void ReleaseObjects() override;
+
+ private:
+  ~WritableFileStreamUnderlyingSinkAlgorithms() = default;
+
+  RefPtr<FileSystemWritableFileStream> mStream;
+};
+
+/**
+ * TODO: Duplicated from netwerk/cache2/CacheFileIOManager.cpp
+ * Please remove after bug 1286601 is fixed,
+ * https://bugzilla.mozilla.org/show_bug.cgi?id=1286601
+ */
+nsresult TruncFile(PRFileDesc* aFD, int64_t aEOF) {
+#if defined(XP_UNIX)
+  if (ftruncate(PR_FileDesc2NativeHandle(aFD), aEOF) != 0) {
+    NS_ERROR("ftruncate failed");
+    return NS_ERROR_FAILURE;
+  }
+#elif defined(XP_WIN)
+  const int64_t currentOffset = PR_Seek64(aFD, 0, PR_SEEK_CUR);
+  if (currentOffset == -1) {
+    return NS_ERROR_FAILURE;
+  }
+
+  int64_t cnt = PR_Seek64(aFD, aEOF, PR_SEEK_SET);
+  if (cnt == -1) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (!SetEndOfFile((HANDLE)PR_FileDesc2NativeHandle(aFD))) {
+    NS_ERROR("SetEndOfFile failed");
+    return NS_ERROR_FAILURE;
+  }
+
+  if (PR_Seek64(aFD, currentOffset, PR_SEEK_SET) == -1) {
+    NS_ERROR("Restoring seek offset failed");
+    return NS_ERROR_FAILURE;
+  }
+
+#else
+  MOZ_ASSERT(false, "Not implemented!");
+  return NS_ERROR_NOT_IMPLEMENTED;
+#endif
+
+  return NS_OK;
+}
+
+}  // namespace
+
+FileSystemWritableFileStream::FileSystemWritableFileStream(
+    nsIGlobalObject* aGlobal, RefPtr<FileSystemManager>& aManager,
+    RefPtr<FileSystemWritableFileStreamChild> aActor,
+    const ::mozilla::ipc::FileDescriptor& aFileDescriptor,
+    const fs::FileSystemEntryMetadata& aMetadata)
+    : WritableStream(aGlobal, HoldDropJSObjectsCaller::Explicit),
+      mManager(aManager),
+      mActor(std::move(aActor)),
+      mFileDesc(nullptr),
+      mMetadata(aMetadata),
+      mClosed(false) {
+  auto rawFD = aFileDescriptor.ClonePlatformHandle();
+  mFileDesc = PR_ImportFile(PROsfd(rawFD.release()));
+
+  LOG(("Created WritableFileStream %p for fd %p", this, mFileDesc));
+
+  // Connect with the actor directly in the constructor. This way the actor
+  // can call `FileSystemWritableFileStream::ClearActor` when we call
+  // `PFileSystemWritableFileStreamChild::Send__delete__` even when
+  // FileSystemWritableFileStream::Create fails, in which case the not yet
+  // fully constructed FileSystemWritableFileStream is being destroyed.
+  mActor->SetStream(this);
+
+  mozilla::HoldJSObjects(this);
+}
+
+FileSystemWritableFileStream::~FileSystemWritableFileStream() {
+  MOZ_ASSERT(!mActor);
+  MOZ_ASSERT(mClosed);
+
+  mozilla::DropJSObjects(this);
+}
+
+// https://streams.spec.whatwg.org/#writablestream-set-up
+// * This is fallible because of OOM handling of JSAPI. See bug 1762233.
+// * Consider extracting this as UnderlyingSinkAlgorithmsWrapper if more classes
+//   start subclassing WritableStream.
+//   For now this skips step 2 - 4 as they are not required here.
+// XXX(krosylight): _BOUNDARY because SetUpWritableStreamDefaultController here
+// can't run script because StartCallback here is no-op. Can we let the static
+// check automatically detect this situation?
+/* static */
+MOZ_CAN_RUN_SCRIPT_BOUNDARY already_AddRefed<FileSystemWritableFileStream>
+FileSystemWritableFileStream::Create(
+    nsIGlobalObject* aGlobal, RefPtr<FileSystemManager>& aManager,
+    RefPtr<FileSystemWritableFileStreamChild> aActor,
+    const ::mozilla::ipc::FileDescriptor& aFileDescriptor,
+    const fs::FileSystemEntryMetadata& aMetadata) {
+  AutoJSAPI jsapi;
+  if (!jsapi.Init(aGlobal)) {
+    return nullptr;
+  }
+  JSContext* cx = jsapi.cx();
+
+  // Step 5. Perform ! InitializeWritableStream(stream).
+  // (Done by the constructor)
+  RefPtr<FileSystemWritableFileStream> stream =
+      new FileSystemWritableFileStream(aGlobal, aManager, std::move(aActor),
+                                       aFileDescriptor, aMetadata);
+
+  // Step 1 - 3
+  auto algorithms =
+      MakeRefPtr<WritableFileStreamUnderlyingSinkAlgorithms>(*stream);
+
+  // Step 6. Let controller be a new WritableStreamDefaultController.
+  auto controller =
+      MakeRefPtr<WritableStreamDefaultController>(aGlobal, *stream);
+
+  // Step 7. Perform ! SetUpWritableStreamDefaultController(stream, controller,
+  // startAlgorithm, writeAlgorithm, closeAlgorithmWrapper,
+  // abortAlgorithmWrapper, highWaterMark, sizeAlgorithm).
+  IgnoredErrorResult rv;
+  SetUpWritableStreamDefaultController(
+      cx, stream, controller, algorithms,
+      // https://fs.spec.whatwg.org/#create-a-new-filesystemwritablefilestream
+      // Step 6. Let highWaterMark be 1.
+      1,
+      // Step 7. Let sizeAlgorithm be an algorithm that returns 1.
+      // (nullptr returns 1, See WritableStream::Constructor for details)
+      nullptr, rv);
+  if (rv.Failed()) {
+    return nullptr;
+  }
+  return stream.forget();
+}
+
+NS_IMPL_ISUPPORTS_CYCLE_COLLECTION_INHERITED_0(FileSystemWritableFileStream,
+                                               WritableStream)
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(FileSystemWritableFileStream)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(FileSystemWritableFileStream,
+                                                WritableStream)
+  // Per the comment for the FileSystemManager class, don't unlink mManager!
+  tmp->Close();
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(FileSystemWritableFileStream,
+                                                  WritableStream)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mManager)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+void FileSystemWritableFileStream::LastRelease() {
+  Close();
+
+  if (mActor) {
+    PFileSystemWritableFileStreamChild::Send__delete__(mActor);
+    MOZ_ASSERT(!mActor);
+  }
+}
+
+void FileSystemWritableFileStream::ClearActor() {
+  MOZ_ASSERT(mActor);
+
+  mActor = nullptr;
+}
+
+void FileSystemWritableFileStream::Close() {
+  // https://fs.spec.whatwg.org/#create-a-new-filesystemwritablefilestream
+  // Step 4. Let closeAlgorithm be these steps:
+
+  if (mClosed) {
+    return;
+  }
+
+  LOG(("%p: Closing", mFileDesc));
+
+  mClosed = true;
+
+  PR_Close(mFileDesc);
+  mFileDesc = nullptr;
+
+  if (mActor) {
+    mActor->SendClose();
+  }
+}
+
+already_AddRefed<Promise> FileSystemWritableFileStream::Write(
+    JSContext* aCx, JS::Handle<JS::Value> aChunk, ErrorResult& aError) {
+  MOZ_ASSERT(!mClosed);
+
+  // https://fs.spec.whatwg.org/#create-a-new-filesystemwritablefilestream
+  // Step 3. Let writeAlgorithm be an algorithm which takes a chunk argument
+  // and returns the result of running the write a chunk algorithm with stream
+  // and chunk.
+
+  // https://fs.spec.whatwg.org/#write-a-chunk
+  // Step 1. Let input be the result of converting chunk to a
+  // FileSystemWriteChunkType.
+
+  aError.MightThrowJSException();
+
+  ArrayBufferViewOrArrayBufferOrBlobOrUTF8StringOrWriteParams data;
+  if (!data.Init(aCx, aChunk)) {
+    aError.StealExceptionFromJSContext(aCx);
+    return nullptr;
+  }
+
+  // Step 2. Let p be a new promise.
+  RefPtr<Promise> promise = Promise::Create(GetParentObject(), aError);
+  if (aError.Failed()) {
+    return nullptr;
+  }
+
+  // Step 3.3. Let command be input.type if input is a WriteParams, ...
+  if (data.IsWriteParams()) {
+    const WriteParams& params = data.GetAsWriteParams();
+    switch (params.mType) {
+      // Step 3.4. If command is "write":
+      case WriteCommandType::Write: {
+        if (!params.mData.WasPassed()) {
+          promise->MaybeRejectWithSyntaxError("write() requires data");
+          return promise.forget();
+        }
+
+        // Step 3.4.2. If data is undefined, reject p with a TypeError and
+        // abort.
+        if (params.mData.Value().IsNull()) {
+          promise->MaybeRejectWithTypeError("write() of null data");
+          return promise.forget();
+        }
+
+        Maybe<uint64_t> position;
+
+        if (params.mPosition.WasPassed()) {
+          if (params.mPosition.Value().IsNull()) {
+            promise->MaybeRejectWithTypeError("write() with null position");
+            return promise.forget();
+          }
+
+          position = Some(params.mPosition.Value().Value());
+        }
+
+        Write(params.mData.Value().Value(), position, promise);
+        return promise.forget();
+      }
+
+      // Step 3.5. Otherwise, if command is "seek":
+      case WriteCommandType::Seek:
+        if (!params.mPosition.WasPassed()) {
+          promise->MaybeRejectWithSyntaxError("seek() requires a position");
+          return promise.forget();
+        }
+
+        // Step 3.5.1. If chunk.position is undefined, reject p with a TypeError
+        // and abort.
+        if (params.mPosition.Value().IsNull()) {
+          promise->MaybeRejectWithTypeError("seek() with null position");
+          return promise.forget();
+        }
+
+        Seek(params.mPosition.Value().Value(), promise);
+        return promise.forget();
+
+      // Step 3.6. Otherwise, if command is "truncate":
+      case WriteCommandType::Truncate:
+        if (!params.mSize.WasPassed()) {
+          promise->MaybeRejectWithSyntaxError("truncate() requires a size");
+          return promise.forget();
+        }
+
+        // Step 3.6.1. If chunk.size is undefined, reject p with a TypeError
+        // and abort.
+        if (params.mSize.Value().IsNull()) {
+          promise->MaybeRejectWithTypeError("truncate() with null size");
+          return promise.forget();
+        }
+
+        Truncate(params.mSize.Value().Value(), promise);
+        return promise.forget();
+
+      default:
+        MOZ_CRASH("Bad WriteParams value!");
+    }
+  }
+
+  // Step 3.3. ... and "write" otherwise.
+  // Step 3.4. If command is "write":
+  Write(data, Nothing(), promise);
+  return promise.forget();
+}
+
+// WebIDL Boilerplate
+
+JSObject* FileSystemWritableFileStream::WrapObject(
+    JSContext* aCx, JS::Handle<JSObject*> aGivenProto) {
+  return FileSystemWritableFileStream_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+// WebIDL Interface
+
+already_AddRefed<Promise> FileSystemWritableFileStream::Write(
+    const ArrayBufferViewOrArrayBufferOrBlobOrUTF8StringOrWriteParams& aData,
+    ErrorResult& aError) {
+  // https://fs.spec.whatwg.org/#dom-filesystemwritablefilestream-write
+  // Step 1. Let writer be the result of getting a writer for this.
+  RefPtr<WritableStreamDefaultWriter> writer = GetWriter(aError);
+  if (aError.Failed()) {
+    return nullptr;
+  }
+
+  // Step 2. Let result be the result of writing a chunk to writer given data.
+  AutoJSAPI jsapi;
+  if (!jsapi.Init(GetParentObject())) {
+    aError.ThrowUnknownError("Internal error");
+    return nullptr;
+  }
+
+  JSContext* cx = jsapi.cx();
+
+  JS::Rooted<JSObject*> global(cx, JS::CurrentGlobalOrNull(cx));
+
+  JS::Rooted<JS::Value> val(cx);
+  if (!aData.ToJSVal(cx, global, &val)) {
+    aError.ThrowUnknownError("Internal error");
+    return nullptr;
+  }
+
+  RefPtr<Promise> promise = writer->Write(cx, val, aError);
+
+  // Step 3. Release writer.
+  {
+    IgnoredErrorResult error;
+    writer->ReleaseLock(cx, error);
+  }
+
+  // Step 4. Return result.
+  return promise.forget();
+}
+
+already_AddRefed<Promise> FileSystemWritableFileStream::Seek(
+    uint64_t aPosition, ErrorResult& aError) {
+  // https://fs.spec.whatwg.org/#dom-filesystemwritablefilestream-seek
+  // Step 1. Let writer be the result of getting a writer for this.
+  RefPtr<WritableStreamDefaultWriter> writer = GetWriter(aError);
+  if (aError.Failed()) {
+    return nullptr;
+  }
+
+  // Step 2. Let result be the result of writing a chunk to writer given
+  // «[ "type" → "seek", "position" → position ]».
+  AutoJSAPI jsapi;
+  if (!jsapi.Init(GetParentObject())) {
+    aError.ThrowUnknownError("Internal error");
+    return nullptr;
+  }
+
+  JSContext* cx = jsapi.cx();
+
+  RootedDictionary<WriteParams> writeParams(cx);
+  writeParams.mType = WriteCommandType::Seek;
+  writeParams.mPosition.Construct(aPosition);
+
+  JS::Rooted<JS::Value> val(cx);
+  if (!ToJSValue(cx, writeParams, &val)) {
+    aError.ThrowUnknownError("Internal error");
+    return nullptr;
+  }
+
+  RefPtr<Promise> promise = writer->Write(cx, val, aError);
+
+  // Step 3. Release writer.
+  {
+    IgnoredErrorResult error;
+    writer->ReleaseLock(cx, error);
+  }
+
+  // Step 4. Return result.
+  return promise.forget();
+}
+
+already_AddRefed<Promise> FileSystemWritableFileStream::Truncate(
+    uint64_t aSize, ErrorResult& aError) {
+  // https://fs.spec.whatwg.org/#dom-filesystemwritablefilestream-truncate
+  // Step 1. Let writer be the result of getting a writer for this.
+  RefPtr<WritableStreamDefaultWriter> writer = GetWriter(aError);
+  if (aError.Failed()) {
+    return nullptr;
+  }
+
+  // Step 2. Let result be the result of writing a chunk to writer given
+  // «[ "type" → "truncate", "size" → size ]».
+  AutoJSAPI jsapi;
+  if (!jsapi.Init(GetParentObject())) {
+    aError.ThrowUnknownError("Internal error");
+    return nullptr;
+  }
+
+  JSContext* cx = jsapi.cx();
+
+  RootedDictionary<WriteParams> writeParams(cx);
+  writeParams.mType = WriteCommandType::Truncate;
+  writeParams.mSize.Construct(aSize);
+
+  JS::Rooted<JS::Value> val(cx);
+  if (!ToJSValue(cx, writeParams, &val)) {
+    aError.ThrowUnknownError("Internal error");
+    return nullptr;
+  }
+
+  RefPtr<Promise> promise = writer->Write(cx, val, aError);
+
+  // Step 3. Release writer.
+  {
+    IgnoredErrorResult error;
+    writer->ReleaseLock(cx, error);
+  }
+
+  // Step 4. Return result.
+  return promise.forget();
+}
+
+template <typename T>
+void FileSystemWritableFileStream::Write(const T& aData,
+                                         const Maybe<uint64_t> aPosition,
+                                         RefPtr<Promise> aPromise) {
+  MOZ_ASSERT(!mClosed);
+
+  auto rejectAndReturn = [&aPromise](const nsresult rv) {
+    if (rv == NS_ERROR_FILE_NOT_FOUND) {
+      aPromise->MaybeRejectWithNotFoundError("File not found");
+    } else {
+      aPromise->MaybeReject(rv);
+    }
+  };
+
+  // https://fs.spec.whatwg.org/#write-a-chunk
+  // Step 3.4.6 If data is a BufferSource, let dataBytes be a copy of data.
+  if (aData.IsArrayBuffer() || aData.IsArrayBufferView()) {
+    const auto dataSpan = [&aData]() {
+      if (aData.IsArrayBuffer()) {
+        const ArrayBuffer& buffer = aData.GetAsArrayBuffer();
+        buffer.ComputeState();
+        return Span{buffer.Data(), buffer.Length()};
+      }
+      MOZ_ASSERT(aData.IsArrayBufferView());
+      const ArrayBufferView& buffer = aData.GetAsArrayBufferView();
+      buffer.ComputeState();
+      return Span{buffer.Data(), buffer.Length()};
+    }();
+
+    nsCString dataBuffer;
+    QM_TRY(MOZ_TO_RESULT(dataBuffer.Assign(
+               AsChars(dataSpan).data(), dataSpan.Length(), mozilla::fallible)),
+           rejectAndReturn);
+    QM_TRY_INSPECT(const auto& written, WriteBuffer(dataBuffer, aPosition),
+                   rejectAndReturn);
+
+    LOG_VERBOSE(("WritableFileStream: Wrote %" PRId64, written));
+    aPromise->MaybeResolve(written);
+    return;
+  }
+
+  // Step 3.4.7 Otherwise, if data is a Blob ...
+  if (aData.IsBlob()) {
+    Blob& blob = aData.GetAsBlob();
+
+    nsCOMPtr<nsIInputStream> stream;
+    ErrorResult error;
+    blob.CreateInputStream(getter_AddRefs(stream), error);
+    QM_TRY((MOZ_TO_RESULT(!error.Failed()).mapErr([&error](const nsresult rv) {
+             return error.StealNSResult();
+           })),
+           rejectAndReturn);
+
+    QM_TRY_INSPECT(const auto& written,
+                   WriteStream(std::move(stream), aPosition), rejectAndReturn);
+
+    LOG_VERBOSE(("WritableFileStream: Wrote %" PRId64, written));
+    aPromise->MaybeResolve(written);
+    return;
+  }
+
+  // Step 3.4.8 Otherwise ...
+  MOZ_ASSERT(aData.IsUTF8String());
+
+  QM_TRY_INSPECT(const auto& written,
+                 WriteBuffer(aData.GetAsUTF8String(), aPosition),
+                 rejectAndReturn);
+
+  LOG_VERBOSE(("WritableFileStream: Wrote %" PRId64, written));
+  aPromise->MaybeResolve(written);
+}
+
+void FileSystemWritableFileStream::Seek(uint64_t aPosition,
+                                        RefPtr<Promise> aPromise) {
+  MOZ_ASSERT(!mClosed);
+
+  LOG_VERBOSE(("%p: Seeking to %" PRIu64, mFileDesc, aPosition));
+
+  QM_TRY(SeekPosition(aPosition), [&aPromise](const nsresult rv) {
+    aPromise->MaybeReject(rv);
+    return;
+  });
+
+  aPromise->MaybeResolveWithUndefined();
+}
+
+void FileSystemWritableFileStream::Truncate(uint64_t aSize,
+                                            RefPtr<Promise> aPromise) {
+  MOZ_ASSERT(!mClosed);
+
+  // truncate filehandle (can extend with 0's)
+  LOG_VERBOSE(("%p: Truncate to %" PRIu64, mFileDesc, aSize));
+  if (NS_WARN_IF(NS_FAILED(TruncFile(mFileDesc, aSize)))) {
+    aPromise->MaybeReject(NS_ErrorAccordingToNSPR());
+    return;
+  }
+
+  // We truncated; per non-normative text in the spec (2.5.3) we should
+  // adjust the cursor position to be within the new file size
+  int64_t where = PR_Seek(mFileDesc, 0, PR_SEEK_CUR);
+  if (where == -1) {
+    aPromise->MaybeReject(NS_ErrorAccordingToNSPR());
+    return;
+  }
+
+  if (where > (int64_t)aSize) {
+    where = PR_Seek(mFileDesc, 0, PR_SEEK_END);
+    if (where == -1) {
+      aPromise->MaybeReject(NS_ErrorAccordingToNSPR());
+      return;
+    }
+  }
+
+  aPromise->MaybeResolveWithUndefined();
+}
+
+Result<uint64_t, nsresult> FileSystemWritableFileStream::WriteBuffer(
+    const nsACString& aBuffer, const Maybe<uint64_t> aPosition) {
+  MOZ_ASSERT(!mClosed);
+
+  const auto checkedLength = CheckedInt<PRInt32>(aBuffer.Length());
+  QM_TRY(MOZ_TO_RESULT(checkedLength.isValid()));
+
+  if (aPosition) {
+    QM_TRY(SeekPosition(*aPosition));
+  }
+
+  return PR_Write(mFileDesc, aBuffer.BeginReading(), checkedLength.value());
+}
+
+Result<uint64_t, nsresult> FileSystemWritableFileStream::WriteStream(
+    nsCOMPtr<nsIInputStream> aStream, const Maybe<uint64_t> aPosition) {
+  MOZ_ASSERT(aStream);
+  MOZ_ASSERT(!mClosed);
+
+  nsCString rawBuffer;
+  QM_TRY(MOZ_TO_RESULT(NS_ReadInputStreamToString(aStream, rawBuffer, -1)));
+  QM_TRY_RETURN(WriteBuffer(rawBuffer, aPosition));
+}
+
+Result<Ok, nsresult> FileSystemWritableFileStream::SeekPosition(
+    uint64_t aPosition) {
+  MOZ_ASSERT(!mClosed);
+
+  const auto checkedPosition = CheckedInt<int64_t>(aPosition);
+  QM_TRY(MOZ_TO_RESULT(checkedPosition.isValid()));
+
+  int64_t cnt = PR_Seek64(mFileDesc, checkedPosition.value(), PR_SEEK_SET);
+  if (cnt == int64_t(-1)) {
+    LOG(("Failed to seek to %" PRIu64 " (errno %d)", aPosition, errno));
+    return Err(NS_ErrorAccordingToNSPR());
+  }
+
+  if (cnt != checkedPosition.value()) {
+    LOG(("Failed to seek to %" PRIu64 " (errno %d), ended up at %" PRId64,
+         aPosition, errno, cnt));
+    return Err(NS_ERROR_FAILURE);
+  }
+
+  return Ok{};
+}
+
+NS_IMPL_ISUPPORTS_CYCLE_COLLECTION_INHERITED_0(
+    WritableFileStreamUnderlyingSinkAlgorithms, UnderlyingSinkAlgorithmsBase)
+NS_IMPL_CYCLE_COLLECTION_INHERITED(WritableFileStreamUnderlyingSinkAlgorithms,
+                                   UnderlyingSinkAlgorithmsBase, mStream)
+
+void WritableFileStreamUnderlyingSinkAlgorithms::StartCallback(
+    JSContext* aCx, WritableStreamDefaultController& aController,
+    JS::MutableHandle<JS::Value> aRetVal, ErrorResult& aRv) {
+  // https://streams.spec.whatwg.org/#writablestream-set-up
+  // Step 1. Let startAlgorithm be an algorithm that returns undefined.
+  aRetVal.setUndefined();
+}
+
+already_AddRefed<Promise>
+WritableFileStreamUnderlyingSinkAlgorithms::WriteCallback(
+    JSContext* aCx, JS::Handle<JS::Value> aChunk,
+    WritableStreamDefaultController& aController, ErrorResult& aRv) {
+  return mStream->Write(aCx, aChunk, aRv);
+}
+
+already_AddRefed<Promise>
+WritableFileStreamUnderlyingSinkAlgorithms::CloseCallback(JSContext* aCx,
+                                                          ErrorResult& aRv) {
+  // https://streams.spec.whatwg.org/#writablestream-set-up
+  // Step 2. Let closeAlgorithmWrapper be an algorithm that runs these steps:
+
+  RefPtr<Promise> promise = Promise::Create(mStream->GetParentObject(), aRv);
+  if (aRv.Failed()) {
+    return nullptr;
+  }
+
+  if (mStream->IsClosed()) {
+    promise->MaybeRejectWithTypeError("WritableFileStream closed");
+    return promise.forget();
+  }
+
+  // XXX The close should be async. For now we have to always fallback to the
+  // Step 2.3 below.
+  mStream->Close();
+
+  // Step 2.3. Return a promise resolved with undefined.
+  promise->MaybeResolveWithUndefined();
+  return promise.forget();
+}
+
+already_AddRefed<Promise>
+WritableFileStreamUnderlyingSinkAlgorithms::AbortCallback(
+    JSContext* aCx, const Optional<JS::Handle<JS::Value>>& aReason,
+    ErrorResult& aRv) {
+  // https://streams.spec.whatwg.org/#writablestream-set-up
+  // Step 3. Let abortAlgorithmWrapper be an algorithm that runs these steps:
+
+  // XXX The close or rather a dedicated abort should be async. For now we have
+  // to always fall back to the Step 3.3 below.
+  mStream->Close();
+
+  // Step 3.3. Return a promise resolved with undefined.
+  return Promise::CreateResolvedWithUndefined(mStream->GetParentObject(), aRv);
+}
+
+void WritableFileStreamUnderlyingSinkAlgorithms::ReleaseObjects() {
+  // XXX We shouldn't be calling close here. We should just release the lock.
+  // However, calling close here is not a big issue for now because we don't
+  // write to a temporary file which would atomically replace the real file
+  // during close.
+  mStream->Close();
+}
+
+}  // namespace mozilla::dom