Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

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

1 files changed, 977 insertions, 0 deletions

diff --git a/dom/streams/ReadableStreamPipeTo.cpp b/dom/streams/ReadableStreamPipeTo.cpp
new file mode 100644
index 0000000000..45cc79b0b2
--- /dev/null
+++ b/dom/streams/ReadableStreamPipeTo.cpp
@@ -0,0 +1,977 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* 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 "ReadableStreamPipeTo.h"
+
+#include "mozilla/dom/AbortFollower.h"
+#include "mozilla/dom/AbortSignal.h"
+#include "mozilla/dom/ReadableStream.h"
+#include "mozilla/dom/ReadableStreamDefaultReader.h"
+#include "mozilla/dom/WritableStream.h"
+#include "mozilla/dom/WritableStreamDefaultWriter.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/Promise-inl.h"
+#include "mozilla/dom/PromiseNativeHandler.h"
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/ErrorResult.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsISupportsImpl.h"
+
+#include "js/Exception.h"
+
+namespace mozilla::dom {
+
+using namespace streams_abstract;
+
+struct PipeToReadRequest;
+class WriteFinishedPromiseHandler;
+class ShutdownActionFinishedPromiseHandler;
+
+// https://streams.spec.whatwg.org/#readable-stream-pipe-to (Steps 14-15.)
+//
+// This class implements everything that is required to read all chunks from
+// the reader (source) and write them to writer (destination), while
+// following the constraints given in the spec using our implementation-defined
+// behavior.
+//
+// The cycle-collected references look roughly like this:
+// clang-format off
+//
+// Closed promise <-- ReadableStreamDefaultReader <--> ReadableStream
+//         |                  ^              |
+//         |(PromiseHandler)  |(mReader)     |(ReadRequest)
+//         |                  |              |
+//         |-------------> PipeToPump <-------
+//                         ^  |   |
+//         |---------------|  |   |
+//         |                  |   |-------(mLastWrite) -------->
+//         |(PromiseHandler)  |   |< ---- (PromiseHandler) ---- Promise
+//         |                  |                                   ^
+//         |                  |(mWriter)                          |(mWriteRequests)
+//         |                  v                                   |
+// Closed promise <-- WritableStreamDefaultWriter <--------> WritableStream
+//
+// clang-format on
+class PipeToPump final : public AbortFollower {
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_CLASS(PipeToPump)
+
+  friend struct PipeToReadRequest;
+  friend class WriteFinishedPromiseHandler;
+  friend class ShutdownActionFinishedPromiseHandler;
+
+  PipeToPump(Promise* aPromise, ReadableStreamDefaultReader* aReader,
+             WritableStreamDefaultWriter* aWriter, bool aPreventClose,
+             bool aPreventAbort, bool aPreventCancel)
+      : mPromise(aPromise),
+        mReader(aReader),
+        mWriter(aWriter),
+        mPreventClose(aPreventClose),
+        mPreventAbort(aPreventAbort),
+        mPreventCancel(aPreventCancel) {}
+
+  MOZ_CAN_RUN_SCRIPT void Start(JSContext* aCx, AbortSignal* aSignal);
+
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY void RunAbortAlgorithm() override;
+
+ private:
+  ~PipeToPump() override = default;
+
+  MOZ_CAN_RUN_SCRIPT void PerformAbortAlgorithm(JSContext* aCx,
+                                                AbortSignalImpl* aSignal);
+
+  MOZ_CAN_RUN_SCRIPT bool SourceOrDestErroredOrClosed(JSContext* aCx);
+
+  using ShutdownAction = already_AddRefed<Promise> (*)(
+      JSContext*, PipeToPump*, JS::Handle<mozilla::Maybe<JS::Value>>,
+      ErrorResult&);
+
+  MOZ_CAN_RUN_SCRIPT void ShutdownWithAction(
+      JSContext* aCx, ShutdownAction aAction,
+      JS::Handle<mozilla::Maybe<JS::Value>> aError);
+  MOZ_CAN_RUN_SCRIPT void ShutdownWithActionAfterFinishedWrite(
+      JSContext* aCx, ShutdownAction aAction,
+      JS::Handle<mozilla::Maybe<JS::Value>> aError);
+
+  MOZ_CAN_RUN_SCRIPT void Shutdown(
+      JSContext* aCx, JS::Handle<mozilla::Maybe<JS::Value>> aError);
+
+  void Finalize(JSContext* aCx, JS::Handle<mozilla::Maybe<JS::Value>> aError);
+
+  MOZ_CAN_RUN_SCRIPT void OnReadFulfilled(JSContext* aCx,
+                                          JS::Handle<JS::Value> aChunk,
+                                          ErrorResult& aRv);
+  MOZ_CAN_RUN_SCRIPT void OnWriterReady(JSContext* aCx, JS::Handle<JS::Value>);
+  MOZ_CAN_RUN_SCRIPT void Read(JSContext* aCx);
+
+  MOZ_CAN_RUN_SCRIPT void OnSourceClosed(JSContext* aCx, JS::Handle<JS::Value>);
+  MOZ_CAN_RUN_SCRIPT void OnSourceErrored(
+      JSContext* aCx, JS::Handle<JS::Value> aSourceStoredError);
+
+  MOZ_CAN_RUN_SCRIPT void OnDestClosed(JSContext* aCx, JS::Handle<JS::Value>);
+  MOZ_CAN_RUN_SCRIPT void OnDestErrored(JSContext* aCx,
+                                        JS::Handle<JS::Value> aDestStoredError);
+
+  RefPtr<Promise> mPromise;
+  RefPtr<ReadableStreamDefaultReader> mReader;
+  RefPtr<WritableStreamDefaultWriter> mWriter;
+  RefPtr<Promise> mLastWritePromise;
+  const bool mPreventClose;
+  const bool mPreventAbort;
+  const bool mPreventCancel;
+  bool mShuttingDown = false;
+#ifdef DEBUG
+  bool mReadChunk = false;
+#endif
+};
+
+// This is a helper class for PipeToPump that allows it to attach
+// member functions as promise handlers.
+class PipeToPumpHandler final : public PromiseNativeHandler {
+  virtual ~PipeToPumpHandler() = default;
+
+  using FunPtr = void (PipeToPump::*)(JSContext*, JS::Handle<JS::Value>);
+
+  RefPtr<PipeToPump> mPipeToPump;
+  FunPtr mResolved;
+  FunPtr mRejected;
+
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_CLASS(PipeToPumpHandler)
+
+  explicit PipeToPumpHandler(PipeToPump* aPipeToPump, FunPtr aResolved,
+                             FunPtr aRejected)
+      : mPipeToPump(aPipeToPump), mResolved(aResolved), mRejected(aRejected) {}
+
+  void ResolvedCallback(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                        ErrorResult&) override {
+    if (mResolved) {
+      (mPipeToPump->*mResolved)(aCx, aValue);
+    }
+  }
+
+  void RejectedCallback(JSContext* aCx, JS::Handle<JS::Value> aReason,
+                        ErrorResult&) override {
+    if (mRejected) {
+      (mPipeToPump->*mRejected)(aCx, aReason);
+    }
+  }
+};
+
+NS_IMPL_CYCLE_COLLECTION(PipeToPumpHandler, mPipeToPump)
+NS_IMPL_CYCLE_COLLECTING_ADDREF(PipeToPumpHandler)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(PipeToPumpHandler)
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(PipeToPumpHandler)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+void PipeToPump::RunAbortAlgorithm() {
+  AutoJSAPI jsapi;
+  if (!jsapi.Init(mReader->GetStream()->GetParentObject())) {
+    NS_WARNING(
+        "Failed to initialize AutoJSAPI in PipeToPump::RunAbortAlgorithm");
+    return;
+  }
+  JSContext* cx = jsapi.cx();
+
+  RefPtr<AbortSignalImpl> signal = Signal();
+  PerformAbortAlgorithm(cx, signal);
+}
+
+void PipeToPump::PerformAbortAlgorithm(JSContext* aCx,
+                                       AbortSignalImpl* aSignal) {
+  MOZ_ASSERT(aSignal->Aborted());
+
+  // https://streams.spec.whatwg.org/#readable-stream-pipe-to
+  // Step 14.1. Let abortAlgorithm be the following steps:
+  // Note: All the following steps are 14.1.xx
+
+  // Step 1. Let error be signal’s abort reason.
+  JS::Rooted<JS::Value> error(aCx);
+  aSignal->GetReason(aCx, &error);
+
+  auto action = [](JSContext* aCx, PipeToPump* aPipeToPump,
+                   JS::Handle<mozilla::Maybe<JS::Value>> aError,
+                   ErrorResult& aRv) MOZ_CAN_RUN_SCRIPT {
+    JS::Rooted<JS::Value> error(aCx, *aError);
+
+    // Step 2. Let actions be an empty ordered set.
+    nsTArray<RefPtr<Promise>> actions;
+
+    // Step 3. If preventAbort is false, append the following action to actions:
+    if (!aPipeToPump->mPreventAbort) {
+      RefPtr<WritableStream> dest = aPipeToPump->mWriter->GetStream();
+
+      // Step 3.1. If dest.[[state]] is "writable", return !
+      // WritableStreamAbort(dest, error).
+      if (dest->State() == WritableStream::WriterState::Writable) {
+        RefPtr<Promise> p = WritableStreamAbort(aCx, dest, error, aRv);
+        if (aRv.Failed()) {
+          return already_AddRefed<Promise>();
+        }
+        actions.AppendElement(p);
+      }
+
+      // Step 3.2. Otherwise, return a promise resolved with undefined.
+      // Note: This is basically a no-op.
+    }
+
+    // Step 4. If preventCancel is false, append the following action action to
+    // actions:
+    if (!aPipeToPump->mPreventCancel) {
+      RefPtr<ReadableStream> source = aPipeToPump->mReader->GetStream();
+
+      // Step 4.1. If source.[[state]] is "readable", return !
+      // ReadableStreamCancel(source, error).
+      if (source->State() == ReadableStream::ReaderState::Readable) {
+        RefPtr<Promise> p = ReadableStreamCancel(aCx, source, error, aRv);
+        if (aRv.Failed()) {
+          return already_AddRefed<Promise>();
+        }
+        actions.AppendElement(p);
+      }
+
+      // Step 4.2. Otherwise, return a promise resolved with undefined.
+      // No-op again.
+    }
+
+    // Step 5. .. action consisting of getting a promise to wait for
+    // all of the actions in actions ...
+    return Promise::All(aCx, actions, aRv);
+  };
+
+  // Step 5. Shutdown with an action consisting of getting a promise to wait for
+  // all of the actions in actions, and with error.
+  JS::Rooted<Maybe<JS::Value>> someError(aCx, Some(error.get()));
+  ShutdownWithAction(aCx, action, someError);
+}
+
+bool PipeToPump::SourceOrDestErroredOrClosed(JSContext* aCx) {
+  // (Constraint) Error and close states must be propagated:
+  // the following conditions must be applied in order.
+  RefPtr<ReadableStream> source = mReader->GetStream();
+  RefPtr<WritableStream> dest = mWriter->GetStream();
+
+  // Step 1. Errors must be propagated forward: if source.[[state]] is or
+  // becomes "errored", then
+  if (source->State() == ReadableStream::ReaderState::Errored) {
+    JS::Rooted<JS::Value> storedError(aCx, source->StoredError());
+    OnSourceErrored(aCx, storedError);
+    return true;
+  }
+
+  // Step 2. Errors must be propagated backward: if dest.[[state]] is or becomes
+  // "errored", then
+  if (dest->State() == WritableStream::WriterState::Errored) {
+    JS::Rooted<JS::Value> storedError(aCx, dest->StoredError());
+    OnDestErrored(aCx, storedError);
+    return true;
+  }
+
+  // Step 3. Closing must be propagated forward: if source.[[state]] is or
+  // becomes "closed", then
+  if (source->State() == ReadableStream::ReaderState::Closed) {
+    OnSourceClosed(aCx, JS::UndefinedHandleValue);
+    return true;
+  }
+
+  // Step 4. Closing must be propagated backward:
+  // if ! WritableStreamCloseQueuedOrInFlight(dest) is true
+  // or dest.[[state]] is "closed", then
+  if (dest->CloseQueuedOrInFlight() ||
+      dest->State() == WritableStream::WriterState::Closed) {
+    OnDestClosed(aCx, JS::UndefinedHandleValue);
+    return true;
+  }
+
+  return false;
+}
+
+// https://streams.spec.whatwg.org/#readable-stream-pipe-to
+// Steps 14-15.
+void PipeToPump::Start(JSContext* aCx, AbortSignal* aSignal) {
+  // Step 14. If signal is not undefined,
+  if (aSignal) {
+    // Step 14.1. Let abortAlgorithm be the following steps:
+    // ... This is implemented by RunAbortAlgorithm.
+
+    // Step 14.2. If signal is aborted, perform abortAlgorithm and
+    // return promise.
+    if (aSignal->Aborted()) {
+      PerformAbortAlgorithm(aCx, aSignal);
+      return;
+    }
+
+    // Step 14.3. Add abortAlgorithm to signal.
+    Follow(aSignal);
+  }
+
+  // Step 15. In parallel but not really; see #905, using reader and writer,
+  // read all chunks from source and write them to dest.
+  // Due to the locking provided by the reader and writer,
+  // the exact manner in which this happens is not observable to author code,
+  // and so there is flexibility in how this is done.
+
+  // (Constraint) Error and close states must be propagated
+
+  // Before piping has started, we have to check for source/destination being
+  // errored/closed manually.
+  if (SourceOrDestErroredOrClosed(aCx)) {
+    return;
+  }
+
+  // We use the following two promises to propagate error and close states
+  // during piping.
+  RefPtr<Promise> readerClosed = mReader->ClosedPromise();
+  readerClosed->AppendNativeHandler(new PipeToPumpHandler(
+      this, &PipeToPump::OnSourceClosed, &PipeToPump::OnSourceErrored));
+
+  // Note: Because we control the destination/writer it should never be closed
+  // after we did the initial check above with SourceOrDestErroredOrClosed.
+  RefPtr<Promise> writerClosed = mWriter->ClosedPromise();
+  writerClosed->AppendNativeHandler(new PipeToPumpHandler(
+      this, &PipeToPump::OnDestClosed, &PipeToPump::OnDestErrored));
+
+  Read(aCx);
+}
+
+class WriteFinishedPromiseHandler final : public PromiseNativeHandler {
+  RefPtr<PipeToPump> mPipeToPump;
+  PipeToPump::ShutdownAction mAction;
+  bool mHasError;
+  JS::Heap<JS::Value> mError;
+
+  virtual ~WriteFinishedPromiseHandler() { mozilla::DropJSObjects(this); };
+
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(WriteFinishedPromiseHandler)
+
+  explicit WriteFinishedPromiseHandler(
+      JSContext* aCx, PipeToPump* aPipeToPump,
+      PipeToPump::ShutdownAction aAction,
+      JS::Handle<mozilla::Maybe<JS::Value>> aError)
+      : mPipeToPump(aPipeToPump), mAction(aAction) {
+    mHasError = aError.isSome();
+    if (mHasError) {
+      mError = *aError;
+    }
+    mozilla::HoldJSObjects(this);
+  }
+
+  MOZ_CAN_RUN_SCRIPT void WriteFinished(JSContext* aCx) {
+    RefPtr<PipeToPump> pipeToPump = mPipeToPump;  // XXX known-live?
+    JS::Rooted<Maybe<JS::Value>> error(aCx);
+    if (mHasError) {
+      error = Some(mError);
+    }
+    pipeToPump->ShutdownWithActionAfterFinishedWrite(aCx, mAction, error);
+  }
+
+  MOZ_CAN_RUN_SCRIPT void ResolvedCallback(JSContext* aCx,
+                                           JS::Handle<JS::Value> aValue,
+                                           ErrorResult&) override {
+    WriteFinished(aCx);
+  }
+
+  MOZ_CAN_RUN_SCRIPT void RejectedCallback(JSContext* aCx,
+                                           JS::Handle<JS::Value> aReason,
+                                           ErrorResult&) override {
+    WriteFinished(aCx);
+  }
+};
+
+NS_IMPL_CYCLE_COLLECTION_WITH_JS_MEMBERS(WriteFinishedPromiseHandler,
+                                         (mPipeToPump), (mError))
+NS_IMPL_CYCLE_COLLECTING_ADDREF(WriteFinishedPromiseHandler)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(WriteFinishedPromiseHandler)
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(WriteFinishedPromiseHandler)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+// https://streams.spec.whatwg.org/#rs-pipeTo-shutdown-with-action
+// Shutdown with an action: if any of the above requirements ask to shutdown
+// with an action action, optionally with an error originalError, then:
+void PipeToPump::ShutdownWithAction(
+    JSContext* aCx, ShutdownAction aAction,
+    JS::Handle<mozilla::Maybe<JS::Value>> aError) {
+  // Step 1. If shuttingDown is true, abort these substeps.
+  if (mShuttingDown) {
+    return;
+  }
+
+  // Step 2. Set shuttingDown to true.
+  mShuttingDown = true;
+
+  // Step 3. If dest.[[state]] is "writable" and !
+  // WritableStreamCloseQueuedOrInFlight(dest) is false,
+  RefPtr<WritableStream> dest = mWriter->GetStream();
+  if (dest->State() == WritableStream::WriterState::Writable &&
+      !dest->CloseQueuedOrInFlight()) {
+    // Step 3.1. If any chunks have been read but not yet written, write them to
+    // dest.
+    // Step 3.2. Wait until every chunk that has been read has been
+    // written (i.e. the corresponding promises have settled).
+    //
+    // Note: Write requests are processed in order, so when the promise
+    // for the last written chunk is settled all previous chunks have been
+    // written as well.
+    if (mLastWritePromise) {
+      mLastWritePromise->AppendNativeHandler(
+          new WriteFinishedPromiseHandler(aCx, this, aAction, aError));
+      return;
+    }
+  }
+
+  // Don't have to wait for last write, immediately continue.
+  ShutdownWithActionAfterFinishedWrite(aCx, aAction, aError);
+}
+
+class ShutdownActionFinishedPromiseHandler final : public PromiseNativeHandler {
+  RefPtr<PipeToPump> mPipeToPump;
+  bool mHasError;
+  JS::Heap<JS::Value> mError;
+
+  virtual ~ShutdownActionFinishedPromiseHandler() {
+    mozilla::DropJSObjects(this);
+  }
+
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(
+      ShutdownActionFinishedPromiseHandler)
+
+  explicit ShutdownActionFinishedPromiseHandler(
+      JSContext* aCx, PipeToPump* aPipeToPump,
+      JS::Handle<mozilla::Maybe<JS::Value>> aError)
+      : mPipeToPump(aPipeToPump) {
+    mHasError = aError.isSome();
+    if (mHasError) {
+      mError = *aError;
+    }
+    mozilla::HoldJSObjects(this);
+  }
+
+  void ResolvedCallback(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                        ErrorResult&) override {
+    // https://streams.spec.whatwg.org/#rs-pipeTo-shutdown-with-action
+    // Step 5. Upon fulfillment of p, finalize, passing along originalError if
+    // it was given.
+    JS::Rooted<Maybe<JS::Value>> error(aCx);
+    if (mHasError) {
+      error = Some(mError);
+    }
+    mPipeToPump->Finalize(aCx, error);
+  }
+
+  void RejectedCallback(JSContext* aCx, JS::Handle<JS::Value> aReason,
+                        ErrorResult&) override {
+    // https://streams.spec.whatwg.org/#rs-pipeTo-shutdown-with-action
+    // Step 6. Upon rejection of p with reason newError, finalize with
+    // newError.
+    JS::Rooted<Maybe<JS::Value>> error(aCx, Some(aReason));
+    mPipeToPump->Finalize(aCx, error);
+  }
+};
+
+NS_IMPL_CYCLE_COLLECTION_WITH_JS_MEMBERS(ShutdownActionFinishedPromiseHandler,
+                                         (mPipeToPump), (mError))
+NS_IMPL_CYCLE_COLLECTING_ADDREF(ShutdownActionFinishedPromiseHandler)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(ShutdownActionFinishedPromiseHandler)
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(ShutdownActionFinishedPromiseHandler)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+// https://streams.spec.whatwg.org/#rs-pipeTo-shutdown-with-action
+// Continuation after Step 3. triggered a promise resolution.
+void PipeToPump::ShutdownWithActionAfterFinishedWrite(
+    JSContext* aCx, ShutdownAction aAction,
+    JS::Handle<mozilla::Maybe<JS::Value>> aError) {
+  if (!aAction) {
+    // Used to implement shutdown without action. Finalize immediately.
+    Finalize(aCx, aError);
+    return;
+  }
+
+  // Step 4. Let p be the result of performing action.
+  RefPtr<PipeToPump> thisRefPtr = this;
+  ErrorResult rv;
+  RefPtr<Promise> p = aAction(aCx, thisRefPtr, aError, rv);
+
+  // Error while calling actions above, continue immediately with finalization.
+  if (rv.MaybeSetPendingException(aCx)) {
+    JS::Rooted<Maybe<JS::Value>> someError(aCx);
+
+    JS::Rooted<JS::Value> error(aCx);
+    if (JS_GetPendingException(aCx, &error)) {
+      someError = Some(error.get());
+    }
+
+    JS_ClearPendingException(aCx);
+
+    Finalize(aCx, someError);
+    return;
+  }
+
+  // Steps 5-6.
+  p->AppendNativeHandler(
+      new ShutdownActionFinishedPromiseHandler(aCx, this, aError));
+}
+
+// https://streams.spec.whatwg.org/#rs-pipeTo-shutdown
+// Shutdown: if any of the above requirements or steps ask to shutdown,
+// optionally with an error error, then:
+void PipeToPump::Shutdown(JSContext* aCx,
+                          JS::Handle<mozilla::Maybe<JS::Value>> aError) {
+  // Note: We implement "shutdown" in terms of "shutdown with action".
+  // We can observe that when passing along an action that always succeeds
+  // shutdown with action and shutdown have the same behavior, when
+  // Ignoring the potential micro task for the promise that we skip anyway.
+  ShutdownWithAction(aCx, nullptr, aError);
+}
+
+// https://streams.spec.whatwg.org/#rs-pipeTo-finalize
+// Finalize: both forms of shutdown will eventually ask to finalize,
+// optionally with an error error, which means to perform the following steps:
+void PipeToPump::Finalize(JSContext* aCx,
+                          JS::Handle<mozilla::Maybe<JS::Value>> aError) {
+  IgnoredErrorResult rv;
+  // Step 1. Perform ! WritableStreamDefaultWriterRelease(writer).
+  WritableStreamDefaultWriterRelease(aCx, mWriter);
+
+  // Step 2. If reader implements ReadableStreamBYOBReader,
+  // perform ! ReadableStreamBYOBReaderRelease(reader).
+  // Note: We always use a default reader.
+  MOZ_ASSERT(!mReader->IsBYOB());
+
+  // Step 3. Otherwise, perform ! ReadableStreamDefaultReaderRelease(reader).
+  ReadableStreamDefaultReaderRelease(aCx, mReader, rv);
+  NS_WARNING_ASSERTION(!rv.Failed(),
+                       "ReadableStreamReaderGenericRelease should not fail.");
+
+  // Step 3. If signal is not undefined, remove abortAlgorithm from signal.
+  if (IsFollowing()) {
+    Unfollow();
+  }
+
+  // Step 4. If error was given, reject promise with error.
+  if (aError.isSome()) {
+    JS::Rooted<JS::Value> error(aCx, *aError);
+    mPromise->MaybeReject(error);
+  } else {
+    // Step 5. Otherwise, resolve promise with undefined.
+    mPromise->MaybeResolveWithUndefined();
+  }
+
+  // Remove all references.
+  mPromise = nullptr;
+  mReader = nullptr;
+  mWriter = nullptr;
+  mLastWritePromise = nullptr;
+  Unfollow();
+}
+
+void PipeToPump::OnReadFulfilled(JSContext* aCx, JS::Handle<JS::Value> aChunk,
+                                 ErrorResult& aRv) {
+  // (Constraint) Shutdown must stop activity:
+  // if shuttingDown becomes true, the user agent must not initiate further
+  // reads from reader, and must only perform writes of already-read chunks ...
+  //
+  // We may reach this point after |On{Source,Dest}{Clos,Error}ed| has responded
+  // to an out-of-band change.  Per the comment in |OnSourceErrored|, we want to
+  // allow the implicated shutdown to proceed, and we don't want to interfere
+  // with or additionally alter its operation.  Particularly, we don't want to
+  // queue up the successfully-read chunk (if there was one, and this isn't just
+  // reporting "done") to be written: it wasn't "already-read" when that
+  // error/closure happened.
+  //
+  // All specified reactions to a closure/error invoke either the shutdown, or
+  // shutdown with an action, algorithms.  Those algorithms each abort if either
+  // shutdown algorithm has already been invoked.  So we check for shutdown here
+  // in case of asynchronous closure/error and abort if shutdown has already
+  // started (and possibly finished).
+  //
+  // TODO: Implement the eventual resolution from
+  // https://github.com/whatwg/streams/issues/1207
+  if (mShuttingDown) {
+    return;
+  }
+
+  // Write asynchronously. Roughly this is like:
+  // `Promise.resolve().then(() => stream.write(chunk));`
+  // XXX: The spec currently does not require asynchronicity, but this still
+  // matches other engines' behavior. See
+  // https://github.com/whatwg/streams/issues/1243.
+  RefPtr<Promise> promise =
+      Promise::CreateInfallible(mWriter->GetParentObject());
+  promise->MaybeResolveWithUndefined();
+  auto result = promise->ThenWithCycleCollectedArgsJS(
+      [](JSContext* aCx, JS::Handle<JS::Value>, ErrorResult& aRv,
+         const RefPtr<PipeToPump>& aSelf,
+         const RefPtr<WritableStreamDefaultWriter>& aWriter,
+         JS::Handle<JS::Value> aChunk)
+          MOZ_CAN_RUN_SCRIPT_FOR_DEFINITION -> already_AddRefed<Promise> {
+            RefPtr<Promise> promise =
+                WritableStreamDefaultWriterWrite(aCx, aWriter, aChunk, aRv);
+
+            // Last read has finished, so it's time to start reading again.
+            aSelf->Read(aCx);
+
+            return promise.forget();
+          },
+      std::make_tuple(RefPtr{this}, mWriter), std::make_tuple(aChunk));
+  if (result.isErr()) {
+    mLastWritePromise = nullptr;
+    return;
+  }
+  mLastWritePromise = result.unwrap();
+
+  mLastWritePromise->AppendNativeHandler(
+      new PipeToPumpHandler(this, nullptr, &PipeToPump::OnDestErrored));
+}
+
+void PipeToPump::OnWriterReady(JSContext* aCx, JS::Handle<JS::Value>) {
+  // Writer is ready again (i.e. backpressure was resolved), so read.
+  Read(aCx);
+}
+
+struct PipeToReadRequest : public ReadRequest {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(PipeToReadRequest, ReadRequest)
+
+  RefPtr<PipeToPump> mPipeToPump;
+
+  explicit PipeToReadRequest(PipeToPump* aPipeToPump)
+      : mPipeToPump(aPipeToPump) {}
+
+  MOZ_CAN_RUN_SCRIPT void ChunkSteps(JSContext* aCx,
+                                     JS::Handle<JS::Value> aChunk,
+                                     ErrorResult& aRv) override {
+    RefPtr<PipeToPump> pipeToPump = mPipeToPump;  // XXX known live?
+    pipeToPump->OnReadFulfilled(aCx, aChunk, aRv);
+  }
+
+  // The reader's closed promise handlers will already call OnSourceClosed/
+  // OnSourceErrored, so these steps can just be ignored.
+  void CloseSteps(JSContext* aCx, ErrorResult& aRv) override {}
+  void ErrorSteps(JSContext* aCx, JS::Handle<JS::Value> aError,
+                  ErrorResult& aRv) override {}
+
+ protected:
+  virtual ~PipeToReadRequest() = default;
+};
+
+NS_IMPL_CYCLE_COLLECTION_INHERITED(PipeToReadRequest, ReadRequest, mPipeToPump)
+
+NS_IMPL_ADDREF_INHERITED(PipeToReadRequest, ReadRequest)
+NS_IMPL_RELEASE_INHERITED(PipeToReadRequest, ReadRequest)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(PipeToReadRequest)
+NS_INTERFACE_MAP_END_INHERITING(ReadRequest)
+
+void PipeToPump::Read(JSContext* aCx) {
+#ifdef DEBUG
+  mReadChunk = true;
+#endif
+
+  // (Constraint) Shutdown must stop activity:
+  // If shuttingDown becomes true, the user agent must not initiate
+  // further reads from reader
+  if (mShuttingDown) {
+    return;
+  }
+
+  // (Constraint) Backpressure must be enforced:
+  // While WritableStreamDefaultWriterGetDesiredSize(writer) is ≤ 0 or is null,
+  // the user agent must not read from reader.
+  Nullable<double> desiredSize =
+      WritableStreamDefaultWriterGetDesiredSize(mWriter);
+  if (desiredSize.IsNull()) {
+    // This means the writer has errored. This is going to be handled
+    // by the writer closed promise.
+    return;
+  }
+
+  if (desiredSize.Value() <= 0) {
+    // Wait for the writer to become ready before reading more data from
+    // the reader. We don't care about rejections here, because those are
+    // already handled by the writer closed promise.
+    RefPtr<Promise> readyPromise = mWriter->Ready();
+    readyPromise->AppendNativeHandler(
+        new PipeToPumpHandler(this, &PipeToPump::OnWriterReady, nullptr));
+    return;
+  }
+
+  RefPtr<ReadableStreamDefaultReader> reader = mReader;
+  RefPtr<ReadRequest> request = new PipeToReadRequest(this);
+  ErrorResult rv;
+  ReadableStreamDefaultReaderRead(aCx, reader, request, rv);
+  if (rv.MaybeSetPendingException(aCx)) {
+    // XXX It's actually not quite obvious what we should do here.
+    // We've got an error during reading, so on the surface it seems logical
+    // to invoke `OnSourceErrored`. However in certain cases the required
+    // condition > source.[[state]] is or becomes "errored" < won't actually
+    // happen i.e. when `WritableStreamDefaultWriterWrite` called from
+    // `OnReadFulfilled` (via PipeToReadRequest::ChunkSteps) fails in
+    // a synchronous fashion.
+    JS::Rooted<JS::Value> error(aCx);
+    JS::Rooted<Maybe<JS::Value>> someError(aCx);
+
+    // The error was moved to the JSContext by MaybeSetPendingException.
+    if (JS_GetPendingException(aCx, &error)) {
+      someError = Some(error.get());
+    }
+
+    JS_ClearPendingException(aCx);
+
+    Shutdown(aCx, someError);
+  }
+}
+
+// Step 3. Closing must be propagated forward: if source.[[state]] is or
+// becomes "closed", then
+void PipeToPump::OnSourceClosed(JSContext* aCx, JS::Handle<JS::Value>) {
+  // Step 3.1. If preventClose is false, shutdown with an action of
+  // ! WritableStreamDefaultWriterCloseWithErrorPropagation(writer).
+  if (!mPreventClose) {
+    ShutdownWithAction(
+        aCx,
+        [](JSContext* aCx, PipeToPump* aPipeToPump,
+           JS::Handle<mozilla::Maybe<JS::Value>> aError, ErrorResult& aRv)
+            MOZ_CAN_RUN_SCRIPT {
+              RefPtr<WritableStreamDefaultWriter> writer = aPipeToPump->mWriter;
+              return WritableStreamDefaultWriterCloseWithErrorPropagation(
+                  aCx, writer, aRv);
+            },
+        JS::NothingHandleValue);
+  } else {
+    // Step 3.2 Otherwise, shutdown.
+    Shutdown(aCx, JS::NothingHandleValue);
+  }
+}
+
+// Step 1. Errors must be propagated forward: if source.[[state]] is or
+// becomes "errored", then
+void PipeToPump::OnSourceErrored(JSContext* aCx,
+                                 JS::Handle<JS::Value> aSourceStoredError) {
+  // If |source| becomes errored not during a pending read, it's clear we must
+  // react immediately.
+  //
+  // But what if |source| becomes errored *during* a pending read?  Should this
+  // first error, or the pending-read second error, predominate?  Two semantics
+  // are possible when |source|/|dest| become closed or errored while there's a
+  // pending read:
+  //
+  //   1. Wait until the read fulfills or rejects, then respond to the
+  //      closure/error without regard to the read having fulfilled or rejected.
+  //      (This will simply not react to the read being rejected, or it will
+  //      queue up the read chunk to be written during shutdown.)
+  //   2. React to the closure/error immediately per "Error and close states
+  //      must be propagated".  Then when the read fulfills or rejects later, do
+  //      nothing.
+  //
+  // The spec doesn't clearly require either semantics.  It requires that
+  // *already-read* chunks be written (at least if |dest| didn't become errored
+  // or closed such that no further writes can occur).  But it's silent as to
+  // not-fully-read chunks.  (These semantic differences may only be observable
+  // with very carefully constructed readable/writable streams.)
+  //
+  // It seems best, generally, to react to the temporally-earliest problem that
+  // arises, so we implement option #2.  (Blink, in contrast, currently
+  // implements option #1.)
+  //
+  // All specified reactions to a closure/error invoke either the shutdown, or
+  // shutdown with an action, algorithms.  Those algorithms each abort if either
+  // shutdown algorithm has already been invoked.  So we don't need to do
+  // anything special here to deal with a pending read.
+  //
+  // TODO: Implement the eventual resolution from
+  // https://github.com/whatwg/streams/issues/1207
+
+  // Step 1.1 If preventAbort is false, shutdown with an action of
+  // ! WritableStreamAbort(dest, source.[[storedError]])
+  // and with source.[[storedError]].
+  JS::Rooted<Maybe<JS::Value>> error(aCx, Some(aSourceStoredError));
+  if (!mPreventAbort) {
+    ShutdownWithAction(
+        aCx,
+        [](JSContext* aCx, PipeToPump* aPipeToPump,
+           JS::Handle<mozilla::Maybe<JS::Value>> aError, ErrorResult& aRv)
+            MOZ_CAN_RUN_SCRIPT {
+              JS::Rooted<JS::Value> error(aCx, *aError);
+              RefPtr<WritableStream> dest = aPipeToPump->mWriter->GetStream();
+              return WritableStreamAbort(aCx, dest, error, aRv);
+            },
+        error);
+  } else {
+    // Step 1.1. Otherwise, shutdown with source.[[storedError]].
+    Shutdown(aCx, error);
+  }
+}
+
+// Step 4. Closing must be propagated backward:
+// if ! WritableStreamCloseQueuedOrInFlight(dest) is true
+// or dest.[[state]] is "closed", then
+void PipeToPump::OnDestClosed(JSContext* aCx, JS::Handle<JS::Value>) {
+  // Step 4.1. Assert: no chunks have been read or written.
+  // Note: No reading automatically implies no writing.
+  // In a perfect world OnDestClosed would only be called before we start
+  // piping, because afterwards the writer has an exclusive lock on the stream.
+  // In reality the closed promise can still be resolved after we release
+  // the lock on the writer in Finalize.
+  if (mShuttingDown) {
+    return;
+  }
+  MOZ_ASSERT(!mReadChunk);
+
+  // Step 4.2. Let destClosed be a new TypeError.
+  JS::Rooted<Maybe<JS::Value>> destClosed(aCx, Nothing());
+  {
+    ErrorResult rv;
+    rv.ThrowTypeError("Cannot pipe to closed stream");
+    JS::Rooted<JS::Value> error(aCx);
+    bool ok = ToJSValue(aCx, std::move(rv), &error);
+    MOZ_RELEASE_ASSERT(ok, "must be ok");
+    destClosed = Some(error.get());
+  }
+
+  // Step 4.3. If preventCancel is false, shutdown with an action of
+  // ! ReadableStreamCancel(source, destClosed) and with destClosed.
+  if (!mPreventCancel) {
+    ShutdownWithAction(
+        aCx,
+        [](JSContext* aCx, PipeToPump* aPipeToPump,
+           JS::Handle<mozilla::Maybe<JS::Value>> aError, ErrorResult& aRv)
+            MOZ_CAN_RUN_SCRIPT {
+              JS::Rooted<JS::Value> error(aCx, *aError);
+              RefPtr<ReadableStream> dest = aPipeToPump->mReader->GetStream();
+              return ReadableStreamCancel(aCx, dest, error, aRv);
+            },
+        destClosed);
+  } else {
+    // Step 4.4. Otherwise, shutdown with destClosed.
+    Shutdown(aCx, destClosed);
+  }
+}
+
+// Step 2. Errors must be propagated backward: if dest.[[state]] is or becomes
+// "errored", then
+void PipeToPump::OnDestErrored(JSContext* aCx,
+                               JS::Handle<JS::Value> aDestStoredError) {
+  // Step 2.1. If preventCancel is false, shutdown with an action of
+  // ! ReadableStreamCancel(source, dest.[[storedError]])
+  // and with dest.[[storedError]].
+  JS::Rooted<Maybe<JS::Value>> error(aCx, Some(aDestStoredError));
+  if (!mPreventCancel) {
+    ShutdownWithAction(
+        aCx,
+        [](JSContext* aCx, PipeToPump* aPipeToPump,
+           JS::Handle<mozilla::Maybe<JS::Value>> aError, ErrorResult& aRv)
+            MOZ_CAN_RUN_SCRIPT {
+              JS::Rooted<JS::Value> error(aCx, *aError);
+              RefPtr<ReadableStream> dest = aPipeToPump->mReader->GetStream();
+              return ReadableStreamCancel(aCx, dest, error, aRv);
+            },
+        error);
+  } else {
+    // Step 2.1. Otherwise, shutdown with dest.[[storedError]].
+    Shutdown(aCx, error);
+  }
+}
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(PipeToPump)
+NS_IMPL_CYCLE_COLLECTING_ADDREF(PipeToPump)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(PipeToPump)
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(PipeToPump)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(PipeToPump)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mPromise)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mReader)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mWriter)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mLastWritePromise)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(PipeToPump)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mPromise)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mReader)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mWriter)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mLastWritePromise)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+namespace streams_abstract {
+// https://streams.spec.whatwg.org/#readable-stream-pipe-to
+already_AddRefed<Promise> ReadableStreamPipeTo(
+    ReadableStream* aSource, WritableStream* aDest, bool aPreventClose,
+    bool aPreventAbort, bool aPreventCancel, AbortSignal* aSignal,
+    mozilla::ErrorResult& aRv) {
+  // Step 1. Assert: source implements ReadableStream. (Implicit)
+  // Step 2. Assert: dest implements WritableStream. (Implicit)
+  // Step 3. Assert: preventClose, preventAbort, and preventCancel are all
+  //         booleans (Implicit)
+  // Step 4. If signal was not given, let signal be
+  //         undefined. (Implicit)
+  // Step 5. Assert: either signal is undefined, or signal
+  //         implements AbortSignal. (Implicit)
+  // Step 6. Assert: !IsReadableStreamLocked(source) is false.
+  MOZ_ASSERT(!IsReadableStreamLocked(aSource));
+
+  // Step 7. Assert: !IsWritableStreamLocked(dest) is false.
+  MOZ_ASSERT(!IsWritableStreamLocked(aDest));
+
+  AutoJSAPI jsapi;
+  if (!jsapi.Init(aSource->GetParentObject())) {
+    aRv.ThrowUnknownError("Internal error");
+    return nullptr;
+  }
+  JSContext* cx = jsapi.cx();
+
+  // Step 8. If source.[[controller]] implements ReadableByteStreamController,
+  //         let reader be either !AcquireReadableStreamBYOBReader(source) or
+  //         !AcquireReadableStreamDefaultReader(source), at the user agent’s
+  //         discretion.
+  // Step 9. Otherwise, let reader be
+  //         !AcquireReadableStreamDefaultReader(source).
+
+  // Note: In the interests of simplicity, we choose here to always acquire
+  // a default reader.
+  RefPtr<ReadableStreamDefaultReader> reader =
+      AcquireReadableStreamDefaultReader(aSource, aRv);
+  if (aRv.Failed()) {
+    return nullptr;
+  }
+
+  // Step 10. Let writer be ! AcquireWritableStreamDefaultWriter(dest).
+  RefPtr<WritableStreamDefaultWriter> writer =
+      AcquireWritableStreamDefaultWriter(aDest, aRv);
+  if (aRv.Failed()) {
+    return nullptr;
+  }
+
+  // Step 11. Set source.[[disturbed]] to true.
+  aSource->SetDisturbed(true);
+
+  // Step 12. Let shuttingDown be false.
+  // Note: PipeToPump ensures this by construction.
+
+  // Step 13. Let promise be a new promise.
+  RefPtr<Promise> promise =
+      Promise::CreateInfallible(aSource->GetParentObject());
+
+  // Steps 14-15.
+  RefPtr<PipeToPump> pump = new PipeToPump(
+      promise, reader, writer, aPreventClose, aPreventAbort, aPreventCancel);
+  pump->Start(cx, aSignal);
+
+  // Step 16. Return promise.
+  return promise.forget();
+}
+}  // namespace streams_abstract
+
+}  // namespace mozilla::dom