Issue #1442 - Part 13 - Implement FetchStreamReader.

https://bugzilla.mozilla.org/show_bug.cgi?id=1329298

9 files changed, 557 insertions, 62 deletions

diff --git a/dom/fetch/Fetch.cpp b/dom/fetch/Fetch.cpp
index 99e26e8511..ce21cd391a 100644
--- a/dom/fetch/Fetch.cpp
+++ b/dom/fetch/Fetch.cpp
@@ -881,6 +881,7 @@ FetchBody<Derived>::FetchBody(nsIGlobalObject* aOwner)
   : mWorkerPrivate(nullptr)
   , mOwner(aOwner)
   , mReadableStreamBody(nullptr)
+  , mReadableStreamReader(nullptr)
   , mBodyUsed(false)
 {
   MOZ_ASSERT(aOwner);
@@ -904,6 +905,12 @@ FetchBody<Derived>::~FetchBody()
 {
 }
 
+template
+FetchBody<Request>::~FetchBody();
+
+template
+FetchBody<Response>::~FetchBody();
+
 template <class Derived>
 bool
 FetchBody<Derived>::BodyUsed() const
@@ -958,13 +965,27 @@ FetchBody<Derived>::ConsumeBody(JSContext* aCx, FetchConsumeType aType, ErrorRes
 
   SetBodyUsed();
 
-  // If we already created a ReadableStreamBody we have to lock it now because
-  // it may have been shared with other objects..
+  // If we already have a ReadableStreamBody and it has been created by DOM, we
+  // have to lock it now because it can have been shared with other objects.
   if (mReadableStreamBody) {
-    JS::Rooted<JSObject*> body(aCx, mReadableStreamBody);
-    LockStream(aCx, body, aRv);
-    if (NS_WARN_IF(aRv.Failed())) {
-      return nullptr;
+    JS::Rooted<JSObject*> readableStreamObj(aCx, mReadableStreamBody);
+    if (JS::ReadableStreamGetMode(readableStreamObj) ==
+          JS::ReadableStreamMode::ExternalSource) {
+      LockStream(aCx, readableStreamObj, aRv);
+      if (NS_WARN_IF(aRv.Failed())) {
+        return nullptr;
+      }
+    } else {
+      // If this is not a native ReadableStream, let's activate the
+      // FetchStreamReader.
+      MOZ_ASSERT(mFetchStreamReader);
+      JS::Rooted<JSObject*> reader(aCx);
+      mFetchStreamReader->StartConsuming(aCx, readableStreamObj, &reader, aRv);
+      if (NS_WARN_IF(aRv.Failed())) {
+        return nullptr;
+      }
+
+      mReadableStreamReader = reader;
     }
   }
 
@@ -1038,6 +1059,11 @@ FetchBody<Derived>::GetBody(JSContext* aCx,
                             JS::MutableHandle<JSObject*> aBodyOut,
                             ErrorResult& aRv)
 {
+  if (mReadableStreamBody) {
+    aBodyOut.set(mReadableStreamBody);
+    return;
+  }
+
   nsCOMPtr<nsIInputStream> inputStream;
   DerivedClass()->GetBody(getter_AddRefs(inputStream));
 
@@ -1046,30 +1072,27 @@ FetchBody<Derived>::GetBody(JSContext* aCx,
     return;
   }
 
-  if (!mReadableStreamBody) {
-    JS::Rooted<JSObject*> body(aCx,
-                               FetchStream::Create(aCx,
-                                                   this,
-                                                   DerivedClass()->GetParentObject(),
-                                                   inputStream,
-                                                   aRv));
-    if (NS_WARN_IF(aRv.Failed())) {
-      return;
-    }
+  JS::Rooted<JSObject*> body(aCx,
+                             FetchStream::Create(aCx,
+                                                 this,
+                                                 DerivedClass()->GetParentObject(),
+                                                 inputStream,
+                                                 aRv));
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
 
-    MOZ_ASSERT(body);
+  MOZ_ASSERT(body);
 
-    // If the body has been already consumed, we close the stream.
-    if (BodyUsed()) {
-      LockStream(aCx, body, aRv);
-      if (NS_WARN_IF(aRv.Failed())) {
-        return;
-      }
+  // If the body has been already consumed, we lock the stream.
+  if (BodyUsed()) {
+    LockStream(aCx, body, aRv);
+    if (NS_WARN_IF(aRv.Failed())) {
+      return;
     }
-
-    mReadableStreamBody = body;
   }
 
+  mReadableStreamBody = body;
   aBodyOut.set(mReadableStreamBody);
 }
 
@@ -1091,7 +1114,15 @@ FetchBody<Derived>::LockStream(JSContext* aCx,
                                JS::HandleObject aStream,
                                ErrorResult& aRv)
 {
-  // XXXMC: TODO
+  JS::Rooted<JSObject*> reader(aCx,
+                               JS::ReadableStreamGetReader(aCx, aStream,
+                                                           JS::ReadableStreamReaderMode::Default));
+  if (!reader) {
+    aRv.StealExceptionFromJSContext(aCx);
+    return;
+  }
+
+  mReadableStreamReader = reader;
 }
 
 template
@@ -1110,10 +1141,18 @@ template <class Derived>
 void
 FetchBody<Derived>::MaybeTeeReadableStreamBody(JSContext* aCx,
                                                JS::MutableHandle<JSObject*> aBodyOut,
+                                               FetchStreamReader** aStreamReader,
+                                               nsIInputStream** aInputStream,
                                                ErrorResult& aRv)
 {
+  MOZ_DIAGNOSTIC_ASSERT(aStreamReader);
+  MOZ_DIAGNOSTIC_ASSERT(aInputStream);
   MOZ_DIAGNOSTIC_ASSERT(!BodyUsed());
 
+  aBodyOut.set(nullptr);
+  *aStreamReader = nullptr;
+  *aInputStream = nullptr;
+
   if (!mReadableStreamBody) {
     return;
   }
@@ -1138,18 +1177,27 @@ FetchBody<Derived>::MaybeTeeReadableStreamBody(JSContext* aCx,
 
   mReadableStreamBody = branch1;
   aBodyOut.set(branch2);
+
+  aRv = FetchStreamReader::Create(aCx, mOwner, aStreamReader, aInputStream);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
 }
 
 template
 void
 FetchBody<Request>::MaybeTeeReadableStreamBody(JSContext* aCx,
                                                JS::MutableHandle<JSObject*> aMessage,
+                                               FetchStreamReader** aStreamReader,
+                                               nsIInputStream** aInputStream,
                                                ErrorResult& aRv);
 
 template
 void
 FetchBody<Response>::MaybeTeeReadableStreamBody(JSContext* aCx,
                                                 JS::MutableHandle<JSObject*> aMessage,
+                                                FetchStreamReader** aStreamReader,
+                                                nsIInputStream** aInputStream,
                                                 ErrorResult& aRv);
 
 } // namespace dom
diff --git a/dom/fetch/Fetch.h b/dom/fetch/Fetch.h
index 32c6671e08..f95a061bd9 100644
--- a/dom/fetch/Fetch.h
+++ b/dom/fetch/Fetch.h
@@ -17,6 +17,7 @@
 #include "mozilla/DebugOnly.h"

 #include "mozilla/ErrorResult.h"

 #include "mozilla/dom/Promise.h"

+#include "mozilla/dom/FetchStreamReader.h"

 #include "mozilla/dom/RequestBinding.h"

 

 class nsIGlobalObject;

@@ -183,6 +184,8 @@ public:
   void

   MaybeTeeReadableStreamBody(JSContext* aCx,

                              JS::MutableHandle<JSObject*> aBodyOut,

+                             FetchStreamReader** aStreamReader,

+                             nsIInputStream** aInputStream,

                              ErrorResult& aRv);

 

   // Utility public methods accessed by various runnables.

@@ -199,10 +202,13 @@ public:
     return mMimeType;

   }

 

+  // FetchStreamHolder

   void

   NullifyStream() override

   {

     mReadableStreamBody = nullptr;

+    mReadableStreamReader = nullptr;

+    mFetchStreamReader = nullptr;

   }

 

   virtual AbortSignal*

@@ -219,6 +225,10 @@ protected:
   // This is the ReadableStream exposed to content. Its underlying source is a FetchStream object.

   JS::Heap<JSObject*> mReadableStreamBody;

 

+  // This is the Reader used to retrieve data from the body.

+  JS::Heap<JSObject*> mReadableStreamReader;

+  RefPtr<FetchStreamReader> mFetchStreamReader;

+

   virtual ~FetchBody();

 

   void

diff --git a/dom/fetch/FetchStreamReader.cpp b/dom/fetch/FetchStreamReader.cpp
new file mode 100644
index 0000000000..98d2588a0e
--- /dev/null
+++ b/dom/fetch/FetchStreamReader.cpp
@@ -0,0 +1,307 @@
+/* -*- 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 "FetchStreamReader.h"
+#include "InternalResponse.h"
+#include "mozilla/dom/PromiseBinding.h"
+
+namespace mozilla {
+namespace dom {
+
+using namespace workers;
+
+namespace {
+
+class FetchStreamReaderWorkerHolder final : public WorkerHolder
+{
+public:
+  explicit FetchStreamReaderWorkerHolder(FetchStreamReader* aReader)
+    : WorkerHolder(WorkerHolder::Behavior::AllowIdleShutdownStart)
+    , mReader(aReader)
+    , mWasNotified(false)
+  {}
+
+  bool Notify(Status aStatus) override
+  {
+    if (!mWasNotified) {
+      mWasNotified = true;
+      mReader->CloseAndRelease(NS_ERROR_DOM_INVALID_STATE_ERR);
+    }
+
+    return true;
+  }
+
+private:
+  RefPtr<FetchStreamReader> mReader;
+  bool mWasNotified;
+};
+
+} // anonymous
+
+NS_IMPL_ISUPPORTS(FetchStreamReader, nsIOutputStreamCallback)
+
+/* static */ nsresult
+FetchStreamReader::Create(JSContext* aCx, nsIGlobalObject* aGlobal,
+                          FetchStreamReader** aStreamReader,
+                          nsIInputStream** aInputStream)
+{
+  MOZ_ASSERT(aCx);
+  MOZ_ASSERT(aGlobal);
+  MOZ_ASSERT(aStreamReader);
+  MOZ_ASSERT(aInputStream);
+
+  RefPtr<FetchStreamReader> streamReader = new FetchStreamReader(aGlobal);
+
+  nsCOMPtr<nsIAsyncInputStream> pipeIn;
+
+  nsresult rv = NS_NewPipe2(getter_AddRefs(pipeIn),
+                            getter_AddRefs(streamReader->mPipeOut),
+                            true, true, 0, 0);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  if (!NS_IsMainThread()) {
+    WorkerPrivate* workerPrivate = GetWorkerPrivateFromContext(aCx);
+    MOZ_ASSERT(workerPrivate);
+
+    // We need to know when the worker goes away.
+    UniquePtr<FetchStreamReaderWorkerHolder> holder(
+      new FetchStreamReaderWorkerHolder(streamReader));
+    if (NS_WARN_IF(!holder->HoldWorker(workerPrivate, Closing))) {
+      streamReader->mPipeOut->CloseWithStatus(NS_ERROR_DOM_INVALID_STATE_ERR);
+      return NS_ERROR_DOM_INVALID_STATE_ERR;
+    }
+
+    // These 2 objects create a ref-cycle here that is broken when the stream is
+    // closed or the worker shutsdown.
+    streamReader->mWorkerHolder = Move(holder);
+  }
+
+  pipeIn.forget(aInputStream);
+  streamReader.forget(aStreamReader);
+  return NS_OK;
+}
+
+FetchStreamReader::FetchStreamReader(nsIGlobalObject* aGlobal)
+  : mGlobal(aGlobal)
+  , mBufferRemaining(0)
+  , mBufferOffset(0)
+  , mStreamClosed(false)
+{
+  MOZ_ASSERT(aGlobal);
+}
+
+FetchStreamReader::~FetchStreamReader()
+{
+  CloseAndRelease(NS_BASE_STREAM_CLOSED);
+}
+
+void
+FetchStreamReader::CloseAndRelease(nsresult aStatus)
+{
+  NS_ASSERT_OWNINGTHREAD(FetchStreamReader);
+
+  if (mStreamClosed) {
+    // Already closed.
+    return;
+  }
+
+  RefPtr<FetchStreamReader> kungFuDeathGrip = this;
+
+  mStreamClosed = true;
+
+  mGlobal = nullptr;
+
+  mPipeOut->CloseWithStatus(aStatus);
+  mPipeOut = nullptr;
+
+  mWorkerHolder = nullptr;
+
+  mReader = nullptr;
+  mBuffer = nullptr;
+}
+
+void
+FetchStreamReader::StartConsuming(JSContext* aCx,
+                                  JS::HandleObject aStream,
+                                  JS::MutableHandle<JSObject*> aReader,
+                                  ErrorResult& aRv)
+{
+  MOZ_DIAGNOSTIC_ASSERT(!mReader);
+  MOZ_DIAGNOSTIC_ASSERT(aStream);
+
+  JS::Rooted<JSObject*> reader(aCx,
+                               JS::ReadableStreamGetReader(aCx, aStream,
+                                                           JS::ReadableStreamReaderMode::Default));
+  if (!reader) {
+    aRv.StealExceptionFromJSContext(aCx);
+    CloseAndRelease(NS_ERROR_DOM_INVALID_STATE_ERR);
+    return;
+  }
+
+  mReader = reader;
+  aReader.set(reader);
+
+  aRv = mPipeOut->AsyncWait(this, 0, 0, mOwningEventTarget);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+}
+
+// nsIOutputStreamCallback interface
+
+NS_IMETHODIMP
+FetchStreamReader::OnOutputStreamReady(nsIAsyncOutputStream* aStream)
+{
+  NS_ASSERT_OWNINGTHREAD(FetchStreamReader);
+  MOZ_ASSERT(aStream == mPipeOut);
+  MOZ_ASSERT(mReader);
+
+  if (mStreamClosed) {
+    return NS_OK;
+  }
+
+  if (mBuffer) {
+    return WriteBuffer();
+  }
+
+  AutoJSAPI jsapi;
+  if (NS_WARN_IF(!jsapi.Init(mGlobal))) {
+    CloseAndRelease(NS_ERROR_DOM_INVALID_STATE_ERR);
+    return NS_ERROR_FAILURE;
+  }
+
+  JSContext* cx = jsapi.cx();
+
+  JS::Rooted<JSObject*> reader(cx, mReader);
+  JS::Rooted<JSObject*> promise(cx,
+                                JS::ReadableStreamDefaultReaderRead(cx,
+                                                                    reader));
+  if (NS_WARN_IF(!promise)) {
+    // Let's close the stream.
+    CloseAndRelease(NS_ERROR_DOM_INVALID_STATE_ERR);
+    return NS_ERROR_FAILURE;
+  }
+
+  RefPtr<Promise> domPromise = Promise::CreateFromExisting(mGlobal, promise);
+  if (NS_WARN_IF(!domPromise)) {
+    // Let's close the stream.
+    CloseAndRelease(NS_ERROR_DOM_INVALID_STATE_ERR);
+    return NS_ERROR_FAILURE;
+  }
+
+  // Let's wait.
+  domPromise->AppendNativeHandler(this);
+  return NS_OK;
+}
+
+void
+FetchStreamReader::ResolvedCallback(JSContext* aCx,
+                                    JS::Handle<JS::Value> aValue)
+{
+  if (mStreamClosed) {
+    return;
+  }
+
+  // This promise should be resolved with { done: boolean, value: something },
+  // "value" is interesting only if done is false.
+
+  // We don't want to play with JS api, let's WebIDL bindings doing it for us.
+  // FetchReadableStreamReadDataDone is a dictionary with just a boolean, if the
+  // parsing succeeded, we can proceed with the parsing of the "value", which it
+  // must be a Uint8Array.
+  FetchReadableStreamReadDataDone valueDone;
+  if (!valueDone.Init(aCx, aValue)) {
+    JS_ClearPendingException(aCx);
+    CloseAndRelease(NS_ERROR_DOM_INVALID_STATE_ERR);
+    return;
+  }
+
+  if (valueDone.mDone) {
+    // Stream is completed.
+    CloseAndRelease(NS_BASE_STREAM_CLOSED);
+    return;
+  }
+
+  UniquePtr<FetchReadableStreamReadDataArray> value(
+    new FetchReadableStreamReadDataArray);
+  if (!value->Init(aCx, aValue) || !value->mValue.WasPassed()) {
+    JS_ClearPendingException(aCx);
+    CloseAndRelease(NS_ERROR_DOM_INVALID_STATE_ERR);
+    return;
+  }
+
+  Uint8Array& array = value->mValue.Value();
+  array.ComputeLengthAndData();
+  uint32_t len = array.Length();
+
+  if (len == 0) {
+    // If there is nothing to read, let's do another reading.
+    OnOutputStreamReady(mPipeOut);
+    return;
+  }
+
+  MOZ_DIAGNOSTIC_ASSERT(!mBuffer);
+  mBuffer = Move(value);
+
+  mBufferOffset = 0;
+  mBufferRemaining = len;
+
+  WriteBuffer();
+}
+
+nsresult
+FetchStreamReader::WriteBuffer()
+{
+  MOZ_ASSERT(mBuffer);
+  MOZ_ASSERT(mBuffer->mValue.WasPassed());
+
+  Uint8Array& array = mBuffer->mValue.Value();
+  char* data = reinterpret_cast<char*>(array.Data());
+
+  while (1) {
+    uint32_t written = 0;
+    nsresult rv =
+      mPipeOut->Write(data + mBufferOffset, mBufferRemaining, &written);
+
+    if (rv == NS_BASE_STREAM_WOULD_BLOCK) {
+      break;
+    }
+
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      CloseAndRelease(rv);
+      return rv;
+    }
+
+    MOZ_ASSERT(written <= mBufferRemaining);
+    mBufferRemaining -= written;
+    mBufferOffset += written;
+
+    if (mBufferRemaining == 0) {
+      mBuffer = nullptr;
+      break;
+    }
+  }
+
+  nsresult rv = mPipeOut->AsyncWait(this, 0, 0, mOwningEventTarget);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    CloseAndRelease(rv);
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+void
+FetchStreamReader::RejectedCallback(JSContext* aCx,
+                                    JS::Handle<JS::Value> aValue)
+{
+  CloseAndRelease(NS_ERROR_FAILURE);
+}
+
+} // dom namespace
+} // mozilla namespace
diff --git a/dom/fetch/FetchStreamReader.h b/dom/fetch/FetchStreamReader.h
new file mode 100644
index 0000000000..8984a2ea73
--- /dev/null
+++ b/dom/fetch/FetchStreamReader.h
@@ -0,0 +1,77 @@
+/* -*- 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_FetchStreamReader_h
+#define mozilla_dom_FetchStreamReader_h
+
+#include "jsapi.h"
+#include "mozilla/dom/FetchBinding.h"
+#include "mozilla/dom/PromiseNativeHandler.h"
+#include "nsIAsyncOutputStream.h"
+
+namespace mozilla {
+namespace dom {
+
+namespace workers {
+class WorkerHolder;
+}
+
+class FetchStreamReader final : public nsIOutputStreamCallback
+                              , public PromiseNativeHandler
+{
+public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOUTPUTSTREAMCALLBACK
+
+  // This creates a nsIInputStream able to retrieve data from the ReadableStream
+  // object. The reading starts when StartConsuming() is called.
+  static nsresult
+  Create(JSContext* aCx, nsIGlobalObject* aGlobal,
+         FetchStreamReader** aStreamReader,
+         nsIInputStream** aInputStream);
+
+  void
+  ResolvedCallback(JSContext* aCx, JS::Handle<JS::Value> aValue) override;
+
+  void
+  RejectedCallback(JSContext* aCx, JS::Handle<JS::Value> aValue) override;
+
+  void
+  CloseAndRelease(nsresult aStatus);
+
+  void
+  StartConsuming(JSContext* aCx,
+                 JS::HandleObject aStream,
+                 JS::MutableHandle<JSObject*> aReader,
+                 ErrorResult& aRv);
+
+private:
+  explicit FetchStreamReader(nsIGlobalObject* aGlobal);
+  ~FetchStreamReader();
+
+  nsresult
+  WriteBuffer();
+
+  nsCOMPtr<nsIGlobalObject> mGlobal;
+  nsCOMPtr<nsIEventTarget> mOwningEventTarget;
+
+  nsCOMPtr<nsIAsyncOutputStream> mPipeOut;
+
+  UniquePtr<workers::WorkerHolder> mWorkerHolder;
+
+  JS::Heap<JSObject*> mReader;
+
+  UniquePtr<FetchReadableStreamReadDataArray> mBuffer;
+  uint32_t mBufferRemaining;
+  uint32_t mBufferOffset;
+
+  bool mStreamClosed;
+};
+
+} // dom namespace
+} // mozilla namespace
+
+#endif // mozilla_dom_FetchStreamReader_h
diff --git a/dom/fetch/InternalResponse.cpp b/dom/fetch/InternalResponse.cpp
index ec32c4e216..f4fd1912f9 100644
--- a/dom/fetch/InternalResponse.cpp
+++ b/dom/fetch/InternalResponse.cpp
@@ -139,18 +139,18 @@ InternalResponse::ToIPC(IPCInternalResponse* aIPCResponse,
 }
 
 already_AddRefed<InternalResponse>
-InternalResponse::Clone()
+InternalResponse::Clone(CloneType aCloneType)
 {
   RefPtr<InternalResponse> clone = CreateIncompleteCopy();
 
   clone->mHeaders = new InternalHeaders(*mHeaders);
   if (mWrappedResponse) {
-    clone->mWrappedResponse = mWrappedResponse->Clone();
+    clone->mWrappedResponse = mWrappedResponse->Clone(aCloneType);
     MOZ_ASSERT(!mBody);
     return clone.forget();
   }
 
-  if (!mBody) {
+  if (!mBody || aCloneType == eDontCloneInputStream) {
     return clone.forget();
   }
 
diff --git a/dom/fetch/InternalResponse.h b/dom/fetch/InternalResponse.h
index e4b4a0ab62..d5c759d577 100644
--- a/dom/fetch/InternalResponse.h
+++ b/dom/fetch/InternalResponse.h
@@ -46,7 +46,13 @@ public:
         M* aManager,
         UniquePtr<mozilla::ipc::AutoIPCStream>& aAutoStream);
 
-  already_AddRefed<InternalResponse> Clone();
+  enum CloneType
+  {
+    eCloneInputStream,
+    eDontCloneInputStream,
+  };
+
+  already_AddRefed<InternalResponse> Clone(CloneType eCloneType);
 
   static already_AddRefed<InternalResponse>
   NetworkError()
diff --git a/dom/fetch/Request.cpp b/dom/fetch/Request.cpp
index eec4828131..ec140a22d4 100644
--- a/dom/fetch/Request.cpp
+++ b/dom/fetch/Request.cpp
@@ -44,7 +44,8 @@ NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(Request)
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
 NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(Request)
-  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mReadableStreamBody)
+  MOZ_DIAGNOSTIC_ASSERT(!tmp->mReadableStreamReader);
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mReadableStreamReader)
   NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER
 NS_IMPL_CYCLE_COLLECTION_TRACE_END
 
diff --git a/dom/fetch/Response.cpp b/dom/fetch/Response.cpp
index b92e918e7c..5055db4e24 100644
--- a/dom/fetch/Response.cpp
+++ b/dom/fetch/Response.cpp
@@ -21,6 +21,7 @@
 
 #include "BodyExtractor.h"
 #include "FetchStream.h"
+#include "FetchStreamReader.h"
 #include "InternalResponse.h"
 #include "WorkerPrivate.h"
 
@@ -37,6 +38,7 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(Response)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mHeaders)
 
   tmp->mReadableStreamBody = nullptr;
+  tmp->mReadableStreamReader = nullptr;
 
   NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
@@ -48,6 +50,7 @@ NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
 NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(Response)
   NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mReadableStreamBody)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mReadableStreamReader)
   NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER
 NS_IMPL_CYCLE_COLLECTION_TRACE_END
 
@@ -227,7 +230,7 @@ Response::Constructor(const GlobalObject& aGlobal,
 
     nsCString contentTypeWithCharset;
     nsCOMPtr<nsIInputStream> bodyStream;
-    uint64_t bodySize = 0;
+    int64_t bodySize = InternalResponse::UNKNOWN_BODY_SIZE;
     
     if (aBody.Value().IsReadableStream()) {
       const ReadableStream& readableStream =
@@ -245,37 +248,50 @@ Response::Constructor(const GlobalObject& aGlobal,
 
       r->SetReadableStreamBody(readableStreamObj);
 
-      // XXXMC: TODO
-      MOZ_ASSERT(JS::ReadableStreamGetMode(readableStreamObj) !=
-                   JS::ReadableStreamMode::ExternalSource);
-
-      void* underlyingSource = nullptr;
-      if (!JS::ReadableStreamGetExternalUnderlyingSource(aGlobal.Context(),
-                                                         readableStreamObj,
-                                                         &underlyingSource)) {
-        aRv.StealExceptionFromJSContext(aGlobal.Context());
-        return nullptr;
+      if (JS::ReadableStreamGetMode(readableStreamObj) ==
+            JS::ReadableStreamMode::ExternalSource) {
+        // If this is a DOM generated ReadableStream, we can extract the
+        // inputStream directly.
+        void* underlyingSource = nullptr;
+        if (!JS::ReadableStreamGetExternalUnderlyingSource(aGlobal.Context(),
+                                                           readableStreamObj,
+                                                           &underlyingSource)) {
+          aRv.StealExceptionFromJSContext(aGlobal.Context());
+          return nullptr;
+        }
+
+        MOZ_ASSERT(underlyingSource);
+
+        aRv = FetchStream::RetrieveInputStream(underlyingSource,
+                                               getter_AddRefs(bodyStream));
+
+        // The releasing of the external source is needed in order to avoid an
+        // extra stream lock.
+        JS::ReadableStreamReleaseExternalUnderlyingSource(readableStreamObj);
+        if (NS_WARN_IF(aRv.Failed())) {
+          return nullptr;
+        }
+      } else {
+        // If this is a JS-created ReadableStream, let's create a
+        // FetchStreamReader.
+        aRv = FetchStreamReader::Create(aGlobal.Context(), global,
+                                        getter_AddRefs(r->mFetchStreamReader),
+                                        getter_AddRefs(bodyStream));
+        if (NS_WARN_IF(aRv.Failed())) {
+          return nullptr;
+        }
       }
-
-      bodySize = InternalResponse::UNKNOWN_BODY_SIZE;
-
-      MOZ_ASSERT(underlyingSource);
-      aRv = FetchStream::RetrieveInputStream(underlyingSource,
-                                             getter_AddRefs(bodyStream));
-
-      // Releasing of the external source is needed in order to avoid an extra stream lock.
-      JS::ReadableStreamReleaseExternalUnderlyingSource(readableStreamObj);
-      if (NS_WARN_IF(aRv.Failed())) {
-        return nullptr;
-      }    
     } else {
+      uint64_t size = 0;
       aRv = ExtractByteStreamFromBody(aBody.Value(),
                                       getter_AddRefs(bodyStream),
                                       contentTypeWithCharset,
-                                      bodySize);
+                                      size);
       if (NS_WARN_IF(aRv.Failed())) {
         return nullptr;
       }
+
+      bodySize = size;
     }
     
     internalResponse->SetBody(bodyStream, bodySize);
@@ -306,21 +322,35 @@ Response::Clone(JSContext* aCx, ErrorResult& aRv)
     return nullptr;
   }
 
-  RefPtr<InternalResponse> ir = mInternalResponse->Clone();
-  RefPtr<Response> response = new Response(mOwner, ir, mSignal);
+  RefPtr<FetchStreamReader> streamReader;
+  nsCOMPtr<nsIInputStream> inputStream;
 
   JS::Rooted<JSObject*> body(aCx);
-  MaybeTeeReadableStreamBody(aCx, &body, aRv);
+  MaybeTeeReadableStreamBody(aCx, &body,
+                             getter_AddRefs(streamReader),
+                             getter_AddRefs(inputStream), aRv);
   if (NS_WARN_IF(aRv.Failed())) {
     return nullptr;
   }
 
+  MOZ_ASSERT_IF(body, streamReader);
+  MOZ_ASSERT_IF(body, inputStream);
+
+  RefPtr<InternalResponse> ir =
+    mInternalResponse->Clone(body
+      ? InternalResponse::eDontCloneInputStream
+      : InternalResponse::eCloneInputStream);
+
+  RefPtr<Response> response = new Response(mOwner, ir, nullptr);
+
   if (body) {
     // Maybe we have a body, but we receive null from MaybeTeeReadableStreamBody
     // if this body is a native stream. In this case, the InternalResponse will
     // have a clone of the native body and the ReadableStream will be created
     // lazily if needed.
     response->SetReadableStreamBody(body);
+    response->mFetchStreamReader = streamReader;
+    ir->SetBody(inputStream, InternalResponse::UNKNOWN_BODY_SIZE);
   }
 
   return response.forget();
@@ -334,22 +364,36 @@ Response::CloneUnfiltered(JSContext* aCx, ErrorResult& aRv)
     return nullptr;
   }
 
-  RefPtr<InternalResponse> clone = mInternalResponse->Clone();
-  RefPtr<InternalResponse> ir = clone->Unfiltered();
-  RefPtr<Response> ref = new Response(mOwner, ir, mSignal);
+  RefPtr<FetchStreamReader> streamReader;
+  nsCOMPtr<nsIInputStream> inputStream;
 
   JS::Rooted<JSObject*> body(aCx);
-  MaybeTeeReadableStreamBody(aCx, &body, aRv);
+  MaybeTeeReadableStreamBody(aCx, &body,
+                             getter_AddRefs(streamReader),
+                             getter_AddRefs(inputStream), aRv);
   if (NS_WARN_IF(aRv.Failed())) {
     return nullptr;
   }
 
+  MOZ_ASSERT_IF(body, streamReader);
+  MOZ_ASSERT_IF(body, inputStream);
+
+  RefPtr<InternalResponse> clone =
+    mInternalResponse->Clone(body
+      ? InternalResponse::eDontCloneInputStream
+      : InternalResponse::eCloneInputStream);
+
+  RefPtr<InternalResponse> ir = clone->Unfiltered();
+  RefPtr<Response> ref = new Response(mOwner, ir, nullptr);
+
   if (body) {
     // Maybe we have a body, but we receive null from MaybeTeeReadableStreamBody
     // if this body is a native stream. In this case, the InternalResponse will
     // have a clone of the native body and the ReadableStream will be created
     // lazily if needed.
     ref->SetReadableStreamBody(body);
+    ref->mFetchStreamReader = streamReader;
+    ir->SetBody(inputStream, InternalResponse::UNKNOWN_BODY_SIZE);
   }
 
   return ref.forget();
diff --git a/dom/fetch/moz.build b/dom/fetch/moz.build
index d08bdf0cf2..f01254e042 100644
--- a/dom/fetch/moz.build
+++ b/dom/fetch/moz.build
@@ -10,6 +10,7 @@ EXPORTS.mozilla.dom += [
     'FetchDriver.h',
     'FetchIPCTypes.h',
     'FetchObserver.h',
+    'FetchStreamReader.h',
     'FetchUtil.h',
     'Headers.h',
     'InternalHeaders.h',
@@ -27,6 +28,7 @@ UNIFIED_SOURCES += [
     'FetchDriver.cpp',
     'FetchObserver.cpp',
     'FetchStream.cpp',
+    'FetchStreamReader.cpp',
     'FetchUtil.cpp',
     'Headers.cpp',
     'InternalHeaders.cpp',