Merge branch 'abortcontroller-work'

29 files changed, 1378 insertions, 43 deletions

diff --git a/dom/abort/AbortController.cpp b/dom/abort/AbortController.cpp
new file mode 100644
index 0000000000..bd8159e7b5
--- /dev/null
+++ b/dom/abort/AbortController.cpp
@@ -0,0 +1,98 @@
+/* -*- 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 "AbortController.h"
+#include "AbortSignal.h"
+#include "mozilla/dom/AbortControllerBinding.h"
+#include "WorkerPrivate.h"
+
+namespace mozilla {
+namespace dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(AbortController, mGlobal, mSignal)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(AbortController)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(AbortController)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(AbortController)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+/* static */ bool
+AbortController::IsEnabled(JSContext* aCx, JSObject* aGlobal)
+{
+  if (NS_IsMainThread()) {
+    return Preferences::GetBool("dom.abortController.enabled", false);
+  }
+
+  using namespace workers;
+
+  // Otherwise, check the pref via the WorkerPrivate
+  WorkerPrivate* workerPrivate = GetWorkerPrivateFromContext(aCx);
+  if (!workerPrivate) {
+    return false;
+  }
+
+  return workerPrivate->AbortControllerEnabled();
+}
+
+/* static */ already_AddRefed<AbortController>
+AbortController::Constructor(const GlobalObject& aGlobal, ErrorResult& aRv)
+{
+  nsCOMPtr<nsIGlobalObject> global = do_QueryInterface(aGlobal.GetAsSupports());
+  if (!global) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  RefPtr<AbortController> abortController = new AbortController(global);
+  return abortController.forget();
+}
+
+AbortController::AbortController(nsIGlobalObject* aGlobal)
+  : mGlobal(aGlobal)
+  , mAborted(false)
+{}
+
+JSObject*
+AbortController::WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto)
+{
+  return AbortControllerBinding::Wrap(aCx, this, aGivenProto);
+}
+
+nsIGlobalObject*
+AbortController::GetParentObject() const
+{
+  return mGlobal;
+}
+
+AbortSignal*
+AbortController::Signal()
+{
+  if (!mSignal) {
+    mSignal = new AbortSignal(this, mAborted);
+  }
+
+  return mSignal;
+}
+
+void
+AbortController::Abort()
+{
+  if (mAborted) {
+    return;
+  }
+
+  mAborted = true;
+
+  if (mSignal) {
+    mSignal->Abort();
+  }
+}
+
+} // dom namespace
+} // mozilla namespace
diff --git a/dom/abort/AbortController.h b/dom/abort/AbortController.h
new file mode 100644
index 0000000000..0b99dc49c2
--- /dev/null
+++ b/dom/abort/AbortController.h
@@ -0,0 +1,59 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_AbortController_h
+#define mozilla_dom_AbortController_h
+
+#include "mozilla/dom/BindingDeclarations.h"
+#include "mozilla/dom/AbortSignal.h" 
+#include "nsCycleCollectionParticipant.h"
+#include "nsWrapperCache.h"
+#include "mozilla/ErrorResult.h"
+#include "nsIGlobalObject.h"
+
+namespace mozilla {
+namespace dom {
+
+class AbortController final : public nsISupports
+                            , public nsWrapperCache
+{
+public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(AbortController)
+
+  static bool
+  IsEnabled(JSContext* aCx, JSObject* aGlobal);
+
+  static already_AddRefed<AbortController>
+  Constructor(const GlobalObject& aGlobal, ErrorResult& aRv);
+
+  explicit AbortController(nsIGlobalObject* aGlobal);
+
+  JSObject*
+  WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override;
+
+  nsIGlobalObject*
+  GetParentObject() const;
+
+  AbortSignal*
+  Signal();
+
+  void
+  Abort();
+
+private:
+  ~AbortController() = default;
+
+  nsCOMPtr<nsIGlobalObject> mGlobal;
+  RefPtr<AbortSignal> mSignal;
+
+  bool mAborted;
+};
+
+} // dom namespace
+} // mozilla namespace
+
+#endif // mozilla_dom_AbortController_h
diff --git a/dom/abort/AbortSignal.cpp b/dom/abort/AbortSignal.cpp
new file mode 100644
index 0000000000..20f36d2abb
--- /dev/null
+++ b/dom/abort/AbortSignal.cpp
@@ -0,0 +1,124 @@
+/* -*- 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 "AbortSignal.h"
+#include "AbortController.h"
+#include "mozilla/dom/Event.h"
+#include "mozilla/dom/AbortSignalBinding.h"
+
+namespace mozilla {
+namespace dom {
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(AbortSignal)
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(AbortSignal,
+                                                  DOMEventTargetHelper)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mController)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(AbortSignal,
+                                                DOMEventTargetHelper)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mController)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(AbortSignal)
+NS_INTERFACE_MAP_END_INHERITING(DOMEventTargetHelper)
+
+NS_IMPL_ADDREF_INHERITED(AbortSignal, DOMEventTargetHelper)
+NS_IMPL_RELEASE_INHERITED(AbortSignal, DOMEventTargetHelper)
+
+AbortSignal::AbortSignal(AbortController* aController,
+                         bool aAborted)
+  : DOMEventTargetHelper(aController->GetParentObject())
+  , mController(aController)
+  , mAborted(aAborted)
+{}
+
+AbortSignal::AbortSignal(bool aAborted)
+  : mAborted(aAborted)
+{}
+
+JSObject*
+AbortSignal::WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto)
+{
+  return AbortSignalBinding::Wrap(aCx, this, aGivenProto);
+}
+
+bool
+AbortSignal::Aborted() const
+{
+  return mAborted;
+}
+
+void
+AbortSignal::Abort()
+{
+  MOZ_ASSERT(!mAborted);
+  mAborted = true;
+
+  // Let's inform the followers.
+  for (uint32_t i = 0; i < mFollowers.Length(); ++i) {
+    mFollowers[i]->Aborted();
+  }
+
+  EventInit init;
+  init.mBubbles = false;
+  init.mCancelable = false;
+
+  RefPtr<Event> event =
+    Event::Constructor(this, NS_LITERAL_STRING("abort"), init);
+  event->SetTrusted(true);
+
+  bool dummy;
+  DispatchEvent(event, &dummy);
+}
+
+void
+AbortSignal::AddFollower(AbortSignal::Follower* aFollower)
+{
+  MOZ_DIAGNOSTIC_ASSERT(aFollower);
+  if (!mFollowers.Contains(aFollower)) {
+    mFollowers.AppendElement(aFollower);
+  }
+}
+
+void
+AbortSignal::RemoveFollower(AbortSignal::Follower* aFollower)
+{
+  MOZ_DIAGNOSTIC_ASSERT(aFollower);
+  mFollowers.RemoveElement(aFollower);
+}
+
+// AbortSignal::Follower
+// ----------------------------------------------------------------------------
+
+AbortSignal::Follower::~Follower()
+{
+  Unfollow();
+}
+
+void
+AbortSignal::Follower::Follow(AbortSignal* aSignal)
+{
+  MOZ_DIAGNOSTIC_ASSERT(aSignal);
+
+  Unfollow();
+
+  mFollowingSignal = aSignal;
+  aSignal->AddFollower(this);
+}
+
+void
+AbortSignal::Follower::Unfollow()
+{
+  if (mFollowingSignal) {
+    mFollowingSignal->RemoveFollower(this);
+    mFollowingSignal = nullptr;
+  }
+}
+
+} // dom namespace
+} // mozilla namespace
diff --git a/dom/abort/AbortSignal.h b/dom/abort/AbortSignal.h
new file mode 100644
index 0000000000..35e5829429
--- /dev/null
+++ b/dom/abort/AbortSignal.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_AbortSignal_h
+#define mozilla_dom_AbortSignal_h
+
+#include "mozilla/DOMEventTargetHelper.h"
+
+namespace mozilla {
+namespace dom {
+
+class AbortController;
+class AbortSignal;
+
+class AbortSignal final : public DOMEventTargetHelper
+{
+public:
+  // This class must be implemented by objects who want to follow a AbortSignal.
+  class Follower
+  {
+  public:
+    virtual void Aborted() = 0;
+
+  protected:
+    virtual ~Follower();
+
+    void
+    Follow(AbortSignal* aSignal);
+
+    void
+    Unfollow();
+
+    RefPtr<AbortSignal> mFollowingSignal;
+  };
+
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(AbortSignal, DOMEventTargetHelper)
+
+  AbortSignal(AbortController* aController, bool aAborted);
+  explicit AbortSignal(bool aAborted);
+
+  JSObject*
+  WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override;
+
+  bool
+  Aborted() const;
+
+  void
+  Abort();
+
+  IMPL_EVENT_HANDLER(abort);
+
+  void
+  AddFollower(Follower* aFollower);
+
+  void
+  RemoveFollower(Follower* aFollower);
+
+private:
+  ~AbortSignal() = default;
+
+  RefPtr<AbortController> mController;
+
+  // Raw pointers. Follower unregisters itself in the DTOR.
+  nsTArray<Follower*> mFollowers;
+
+  bool mAborted;
+};
+
+} // dom namespace
+} // mozilla namespace
+
+#endif // mozilla_dom_AbortSignal_h
diff --git a/dom/abort/moz.build b/dom/abort/moz.build
new file mode 100644
index 0000000000..cb48ee15f4
--- /dev/null
+++ b/dom/abort/moz.build
@@ -0,0 +1,26 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+with Files("**"):
+    BUG_COMPONENT = ("Core", "DOM")
+
+TEST_DIRS += ['tests']
+
+EXPORTS.mozilla.dom += [
+    'AbortController.h',
+    'AbortSignal.h',
+]
+
+UNIFIED_SOURCES += [
+    'AbortController.cpp',
+    'AbortSignal.cpp',
+]
+
+LOCAL_INCLUDES += [
+    '../workers',
+]
+
+FINAL_LIBRARY = 'xul'
diff --git a/dom/abort/tests/file_abort_controller.html b/dom/abort/tests/file_abort_controller.html
new file mode 100644
index 0000000000..3a15fa3469
--- /dev/null
+++ b/dom/abort/tests/file_abort_controller.html
@@ -0,0 +1,113 @@
+<script>
+function ok(a, msg) {
+  parent.postMessage({ type: "check", status: !!a, message: msg }, "*");
+}
+
+function is(a, b, msg) {
+  ok(a === b, msg);
+}
+
+function testWebIDL() {
+  ok("FetchController" in self, "We have a FetchController prototype");
+  ok("FetchSignal" in self, "We have a FetchSignal prototype");
+
+  var fc = new FetchController();
+  ok(!!fc, "FetchController can be created");
+  ok(fc instanceof FetchController, "FetchController is a FetchController");
+
+  ok(!!fc.signal, "FetchController has a signal");
+  ok(fc.signal instanceof FetchSignal, "fetchSignal is a FetchSignal");
+  is(fc.signal.aborted, false, "By default FetchSignal.aborted is false");
+  next();
+}
+
+function testUpdateData() {
+  var fc = new FetchController();
+ 
+  is(fc.signal.aborted, false, "By default FetchSignal.aborted is false");
+ 
+  fc.abort();
+  is(fc.signal.aborted, true, "Signal is aborted");
+ 
+  next();
+}
+ 
+function testAbortEvent() {
+  var fc = new FetchController();
+  fc.signal.onabort = function(e) {
+    is(e.type, "abort", "Abort received");
+    next();
+  }
+  fc.abort();
+}
+ 
+function testAbortedFetch() {
+  var fc = new FetchController();
+  fc.abort();
+
+  fetch('slow.sjs', { signal: fc.signal }).then(() => {
+    ok(false, "Fetch should not return a resolved promise");
+  }, e => {
+    is(e.name, "AbortError", "We have an abort error");
+  }).then(next);
+}
+
+function testFetchAndAbort() {
+  var fc = new FetchController();
+
+  var p = fetch('slow.sjs', { signal: fc.signal });
+  fc.abort();
+
+  p.then(() => {
+    ok(false, "Fetch should not return a resolved promise");
+  }, e => {
+    is(e.name, "AbortError", "We have an abort error");
+  }).then(next);
+}
+
+function testWorkerAbortedFetch() {
+  var w = new Worker('worker_fetch_controller.js');
+  w.onmessage = function(e) {
+    ok(e.data, "Abort + Fetch works in workers");
+    next();
+  }
+  w.postMessage('testWorkerAbortedFetch');
+}
+
+function testWorkerFetchAndAbort() {
+  var w = new Worker('worker_fetch_controller.js');
+  w.onmessage = function(e) {
+    ok(e.data, "Abort + Fetch works in workers");
+    next();
+  }
+  w.postMessage('testWorkerFetchAndAbort');
+}
+
+var steps = [
+  // Simple stuff
+  testWebIDL,
+  testUpdateData,
+
+  // Event propagation
+  testAbortEvent,
+
+  // fetch + signaling
+  testAbortedFetch,
+  testFetchAndAbort,
+  testWorkerAbortedFetch,
+  testWorkerFetchAndAbort,
+];
+
+function next() {
+  if (!steps.length) {
+    parent.postMessage({ type: "finish" }, "*");
+    return;
+  }
+
+  var step = steps.shift();
+  step();
+}
+
+next();
+
+</script>
diff --git a/dom/abort/tests/mochitest.ini b/dom/abort/tests/mochitest.ini
new file mode 100644
index 0000000000..c8cc95fdab
--- /dev/null
+++ b/dom/abort/tests/mochitest.ini
@@ -0,0 +1,6 @@
+[DEFAULT]
+support-files =
+  file_abort_controller.html
+  worker_fetch_controller.js
+
+[test_abort_controller.html]
diff --git a/dom/abort/tests/moz.build b/dom/abort/tests/moz.build
new file mode 100644
index 0000000000..8e5cb5d717
--- /dev/null
+++ b/dom/abort/tests/moz.build
@@ -0,0 +1,8 @@
+# -*- 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/.
+
+MOCHITEST_MANIFESTS += ['mochitest.ini']
+
diff --git a/dom/abort/tests/test_abort_controller.html b/dom/abort/tests/test_abort_controller.html
new file mode 100644
index 0000000000..812fb91616
--- /dev/null
+++ b/dom/abort/tests/test_abort_controller.html
@@ -0,0 +1,40 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test FetchController</title>
+  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script class="testbody" type="text/javascript">
+
+SpecialPowers.pushPrefEnv({"set": [["dom.fetchController.enabled", true ]]}, () => {
+  let ifr = document.createElement('iframe');
+  ifr.src = "file_fetch_controller.html";
+  document.body.appendChild(ifr);
+
+  onmessage = function(e) {
+    if (e.data.type == "finish") {
+      SimpleTest.finish();
+      return;
+    }
+
+    if (e.data.type == "check") {
+      ok(e.data.status, e.data.message);
+      return;
+    }
+
+    ok(false, "Something when wrong.");
+  }
+});
+
+SimpleTest.waitForExplicitFinish();
+
+</script>
+</body>
+</html>
+
diff --git a/dom/abort/tests/worker_abort_controller.js b/dom/abort/tests/worker_abort_controller.js
new file mode 100644
index 0000000000..6fd1c78884
--- /dev/null
+++ b/dom/abort/tests/worker_abort_controller.js
@@ -0,0 +1,27 @@
+function testWorkerAbortedFetch() {
+  var fc = new AbortController();
+  fc.abort();
+
+  fetch('slow.sjs', { signal: fc.signal }).then(() => {
+    postMessage(false);
+  }, e => {
+    postMessage(e.name == "AbortError");
+  });
+}
+
+function testWorkerFetchAndAbort() {
+  var fc = new AbortController();
+
+  var p = fetch('slow.sjs', { signal: fc.signal });
+  fc.abort();
+
+  p.then(() => {
+    postMessage(false);
+  }, e => {
+    postMessage(e.name == "AbortError");
+  });
+}
+
+onmessage = function(e) {
+  self[e.data]();
+}
diff --git a/dom/base/nsGkAtomList.h b/dom/base/nsGkAtomList.h
index af3077604b..f4d2974cdd 100644
--- a/dom/base/nsGkAtomList.h
+++ b/dom/base/nsGkAtomList.h
@@ -909,7 +909,9 @@ GK_ATOM(onreadystatechange, "onreadystatechange")
 GK_ATOM(onreceived, "onreceived")
 GK_ATOM(onremoteheld, "onremoteheld")
 GK_ATOM(onremoteresumed, "onremoteresumed")
+GK_ATOM(onrequestprogress, "onrequestprogress")
 GK_ATOM(onresourcetimingbufferfull, "onresourcetimingbufferfull")
+GK_ATOM(onresponseprogress, "onresponseprogress")
 GK_ATOM(onretrieving, "onretrieving")
 GK_ATOM(onRequest, "onRequest")
 GK_ATOM(onrequestmediaplaystatus, "onrequestmediaplaystatus")
diff --git a/dom/fetch/Fetch.cpp b/dom/fetch/Fetch.cpp
index f944352e3b..191f4cfc3e 100644
--- a/dom/fetch/Fetch.cpp
+++ b/dom/fetch/Fetch.cpp
@@ -39,6 +39,7 @@
 #include "mozilla/dom/URLSearchParams.h"
 #include "mozilla/dom/workers/ServiceWorkerManager.h"
 
+#include "FetchObserver.h"
 #include "InternalRequest.h"
 #include "InternalResponse.h"
 
@@ -52,38 +53,141 @@ namespace dom {
 
 using namespace workers;
 
+// This class helps the proxying of AbortSignal changes cross threads.
+class AbortSignalProxy final : public AbortSignal::Follower
+{
+  // This is created and released on the main-thread.
+  RefPtr<AbortSignal> mSignalMainThread;
+
+  // This value is used only for the creation of AbortSignal on the
+  // main-thread. They are not updated.
+  const bool mAborted;
+
+  // This runnable propagates changes from the AbortSignal on workers to the
+  // AbortSignal on main-thread.
+  class AbortSignalProxyRunnable final : public Runnable
+  {
+    RefPtr<AbortSignalProxy> mProxy;
+
+  public:
+    explicit AbortSignalProxyRunnable(AbortSignalProxy* aProxy)
+      : mProxy(aProxy)
+    {}
+
+    NS_IMETHOD
+    Run() override
+    {
+      MOZ_ASSERT(NS_IsMainThread());
+      AbortSignal* signal = mProxy->GetOrCreateSignalForMainThread();
+      signal->Abort();
+      return NS_OK;
+    }
+  };
+
+public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(AbortSignalProxy)
+
+  explicit AbortSignalProxy(AbortSignal* aSignal)
+    : mAborted(aSignal->Aborted())
+  {
+    Follow(aSignal);
+  }
+
+  void
+  Aborted() override
+  {
+    RefPtr<AbortSignalProxyRunnable> runnable =
+      new AbortSignalProxyRunnable(this);
+    NS_DispatchToMainThread(runnable);
+  }
+
+  AbortSignal*
+  GetOrCreateSignalForMainThread()
+  {
+    MOZ_ASSERT(NS_IsMainThread());
+    if (!mSignalMainThread) {
+      mSignalMainThread = new AbortSignal(mAborted);
+    }
+    return mSignalMainThread;
+  }
+
+  void
+  Shutdown()
+  {
+    Unfollow();
+  }
+
+private:
+  ~AbortSignalProxy()
+  {
+    NS_ReleaseOnMainThread(mSignalMainThread.forget());
+  }
+};
+
 class WorkerFetchResolver final : public FetchDriverObserver
 {
   friend class MainThreadFetchRunnable;
+  friend class WorkerDataAvailableRunnable;
+  friend class WorkerFetchResponseEndBase;
   friend class WorkerFetchResponseEndRunnable;
   friend class WorkerFetchResponseRunnable;
 
   RefPtr<PromiseWorkerProxy> mPromiseProxy;
+  RefPtr<AbortSignalProxy> mSignalProxy;
+  RefPtr<FetchObserver> mFetchObserver;
+
 public:
   // Returns null if worker is shutting down.
   static already_AddRefed<WorkerFetchResolver>
-  Create(workers::WorkerPrivate* aWorkerPrivate, Promise* aPromise)
+  Create(workers::WorkerPrivate* aWorkerPrivate, Promise* aPromise,
+         AbortSignal* aSignal, FetchObserver* aObserver)
   {
     MOZ_ASSERT(aWorkerPrivate);
     aWorkerPrivate->AssertIsOnWorkerThread();
-    RefPtr<PromiseWorkerProxy> proxy = PromiseWorkerProxy::Create(aWorkerPrivate, aPromise);
+    RefPtr<PromiseWorkerProxy> proxy =
+      PromiseWorkerProxy::Create(aWorkerPrivate, aPromise);
     if (!proxy) {
       return nullptr;
     }
 
-    RefPtr<WorkerFetchResolver> r = new WorkerFetchResolver(proxy);
+    RefPtr<AbortSignalProxy> signalProxy;
+    if (aSignal) {
+      signalProxy = new AbortSignalProxy(aSignal);
+    }
+
+    RefPtr<WorkerFetchResolver> r =
+      new WorkerFetchResolver(proxy, signalProxy, aObserver);
     return r.forget();
   }
 
+  AbortSignal*
+  GetAbortSignal()
+  {
+    MOZ_ASSERT(NS_IsMainThread());
+
+    if (!mSignalProxy) {
+      return nullptr;
+    }
+
+    return mSignalProxy->GetOrCreateSignalForMainThread();
+  }
+
   void
   OnResponseAvailableInternal(InternalResponse* aResponse) override;
 
   void
-  OnResponseEnd() override;
+  OnResponseEnd(FetchDriverObserver::EndReason eReason) override;
+
+  void
+  OnDataAvailable() override;
 
 private:
-  explicit WorkerFetchResolver(PromiseWorkerProxy* aProxy)
+   WorkerFetchResolver(PromiseWorkerProxy* aProxy,
+                       AbortSignalProxy* aSignalProxy,
+                       FetchObserver* aObserver)
     : mPromiseProxy(aProxy)
+    , mSignalProxy(aSignalProxy)
+    , mFetchObserver(aObserver)
   {
     MOZ_ASSERT(!NS_IsMainThread());
     MOZ_ASSERT(mPromiseProxy);
@@ -100,12 +204,16 @@ class MainThreadFetchResolver final : public FetchDriverObserver
 {
   RefPtr<Promise> mPromise;
   RefPtr<Response> mResponse;
+  RefPtr<FetchObserver> mFetchObserver;
 
   nsCOMPtr<nsIDocument> mDocument;
 
   NS_DECL_OWNINGTHREAD
 public:
-  explicit MainThreadFetchResolver(Promise* aPromise);
+  MainThreadFetchResolver(Promise* aPromise, FetchObserver* aObserver)
+    : mPromise(aPromise)
+    , mFetchObserver(aObserver)
+  {}
 
   void
   OnResponseAvailableInternal(InternalResponse* aResponse) override;
@@ -115,11 +223,20 @@ public:
     mDocument = aDocument;
   }
 
-  virtual void OnResponseEnd() override
+  void OnResponseEnd(FetchDriverObserver::EndReason aReason) override
   {
+    if (aReason == eAborted) {
+      mPromise->MaybeReject(NS_ERROR_DOM_ABORT_ERR);
+    }
+
+    mFetchObserver = nullptr;
+
     FlushConsoleReport();
   }
 
+  void
+  OnDataAvailable() override;
+
 private:
   ~MainThreadFetchResolver();
 
@@ -170,9 +287,11 @@ public:
       fetch->SetWorkerScript(spec);
     }
 
+    RefPtr<AbortSignal> signal = mResolver->GetAbortSignal();
+
     // ...but release it before calling Fetch, because mResolver's callback can
     // be called synchronously and they want the mutex, too.
-    return fetch->Fetch(mResolver);
+    return fetch->Fetch(signal, mResolver);
   }
 };
 
@@ -210,6 +329,23 @@ FetchRequest(nsIGlobalObject* aGlobal, const RequestOrUSVString& aInput,
 
   RefPtr<InternalRequest> r = request->GetInternalRequest();
 
+  RefPtr<AbortSignal> signal;
+  if (aInit.mSignal.WasPassed()) {
+    signal = &aInit.mSignal.Value();
+  }
+  
+  if (signal && signal->Aborted()) {
+    // An already aborted signal should reject immediately.
+    aRv.Throw(NS_ERROR_DOM_ABORT_ERR);
+    return nullptr;
+  }
+
+  RefPtr<FetchObserver> observer;
+  if (aInit.mObserve.WasPassed()) {
+    observer = new FetchObserver(aGlobal, signal);
+    aInit.mObserve.Value().HandleEvent(*observer);
+  }
+
   if (NS_IsMainThread()) {
     nsCOMPtr<nsPIDOMWindowInner> window = do_QueryInterface(aGlobal);
     nsCOMPtr<nsIDocument> doc;
@@ -236,11 +372,12 @@ FetchRequest(nsIGlobalObject* aGlobal, const RequestOrUSVString& aInput,
       }
     }
 
-    RefPtr<MainThreadFetchResolver> resolver = new MainThreadFetchResolver(p);
+    RefPtr<MainThreadFetchResolver> resolver =
+      new MainThreadFetchResolver(p, observer);
     RefPtr<FetchDriver> fetch = new FetchDriver(r, principal, loadGroup);
     fetch->SetDocument(doc);
     resolver->SetDocument(doc);
-    aRv = fetch->Fetch(resolver);
+    aRv = fetch->Fetch(signal, resolver);
     if (NS_WARN_IF(aRv.Failed())) {
       return nullptr;
     }
@@ -252,7 +389,8 @@ FetchRequest(nsIGlobalObject* aGlobal, const RequestOrUSVString& aInput,
       r->SetSkipServiceWorker();
     }
 
-    RefPtr<WorkerFetchResolver> resolver = WorkerFetchResolver::Create(worker, p);
+    RefPtr<WorkerFetchResolver> resolver =
+      WorkerFetchResolver::Create(worker, p, signal, observer);
     if (!resolver) {
       NS_WARNING("Could not add WorkerFetchResolver workerHolder to worker");
       aRv.Throw(NS_ERROR_DOM_ABORT_ERR);
@@ -266,11 +404,6 @@ FetchRequest(nsIGlobalObject* aGlobal, const RequestOrUSVString& aInput,
   return p.forget();
 }
 
-MainThreadFetchResolver::MainThreadFetchResolver(Promise* aPromise)
-  : mPromise(aPromise)
-{
-}
-
 void
 MainThreadFetchResolver::OnResponseAvailableInternal(InternalResponse* aResponse)
 {
@@ -278,16 +411,39 @@ MainThreadFetchResolver::OnResponseAvailableInternal(InternalResponse* aResponse
   AssertIsOnMainThread();
 
   if (aResponse->Type() != ResponseType::Error) {
+    if (mFetchObserver) {
+      mFetchObserver->SetState(FetchState::Complete);
+    }
+
     nsCOMPtr<nsIGlobalObject> go = mPromise->GetParentObject();
     mResponse = new Response(go, aResponse);
     mPromise->MaybeResolve(mResponse);
   } else {
+    if (mFetchObserver) {
+      mFetchObserver->SetState(FetchState::Errored);
+    }
+
     ErrorResult result;
     result.ThrowTypeError<MSG_FETCH_FAILED>();
     mPromise->MaybeReject(result);
   }
 }
 
+void
+MainThreadFetchResolver::OnDataAvailable()
+{
+  NS_ASSERT_OWNINGTHREAD(MainThreadFetchResolver);
+  AssertIsOnMainThread();
+
+  if (!mFetchObserver) {
+    return;
+  }
+
+  if (mFetchObserver->State() == FetchState::Requesting) {
+    mFetchObserver->SetState(FetchState::Responding);
+  }
+}
+
 MainThreadFetchResolver::~MainThreadFetchResolver()
 {
   NS_ASSERT_OWNINGTHREAD(MainThreadFetchResolver);
@@ -306,6 +462,7 @@ public:
     , mResolver(aResolver)
     , mInternalResponse(aResponse)
   {
+     MOZ_ASSERT(mResolver);
   }
 
   bool
@@ -317,10 +474,18 @@ public:
     RefPtr<Promise> promise = mResolver->mPromiseProxy->WorkerPromise();
 
     if (mInternalResponse->Type() != ResponseType::Error) {
+      if (mResolver->mFetchObserver) {
+        mResolver->mFetchObserver->SetState(FetchState::Complete);
+      }
+
       RefPtr<nsIGlobalObject> global = aWorkerPrivate->GlobalScope();
       RefPtr<Response> response = new Response(global, mInternalResponse);
       promise->MaybeResolve(response);
     } else {
+      if (mResolver->mFetchObserver) {
+        mResolver->mFetchObserver->SetState(FetchState::Errored);
+      }
+
       ErrorResult result;
       result.ThrowTypeError<MSG_FETCH_FAILED>();
       promise->MaybeReject(result);
@@ -329,14 +494,42 @@ public:
   }
 };
 
+class WorkerDataAvailableRunnable final : public MainThreadWorkerRunnable
+{
+  RefPtr<WorkerFetchResolver> mResolver;
+public:
+  WorkerDataAvailableRunnable(WorkerPrivate* aWorkerPrivate,
+                              WorkerFetchResolver* aResolver)
+    : MainThreadWorkerRunnable(aWorkerPrivate)
+    , mResolver(aResolver)
+  {
+  }
+
+  bool
+  WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override
+  {
+    MOZ_ASSERT(aWorkerPrivate);
+    aWorkerPrivate->AssertIsOnWorkerThread();
+
+    if (mResolver->mFetchObserver &&
+        mResolver->mFetchObserver->State() == FetchState::Requesting) {
+      mResolver->mFetchObserver->SetState(FetchState::Responding);
+    }
+
+    return true;
+  }
+};
+
 class WorkerFetchResponseEndBase
 {
-  RefPtr<PromiseWorkerProxy> mPromiseProxy;
+protected:
+  RefPtr<WorkerFetchResolver> mResolver;
+
 public:
-  explicit WorkerFetchResponseEndBase(PromiseWorkerProxy* aPromiseProxy)
-    : mPromiseProxy(aPromiseProxy)
+  explicit WorkerFetchResponseEndBase(WorkerFetchResolver* aResolver)
+    : mResolver(aResolver)
   {
-    MOZ_ASSERT(mPromiseProxy);
+    MOZ_ASSERT(aResolver);
   }
 
   void
@@ -344,23 +537,41 @@ public:
   {
     MOZ_ASSERT(aWorkerPrivate);
     aWorkerPrivate->AssertIsOnWorkerThread();
-    mPromiseProxy->CleanUp();
+
+    mResolver->mPromiseProxy->CleanUp();
+
+    mResolver->mFetchObserver = nullptr;
+
+    if (mResolver->mSignalProxy) {
+      mResolver->mSignalProxy->Shutdown();
+      mResolver->mSignalProxy = nullptr;
+    }
   }
 };
 
 class WorkerFetchResponseEndRunnable final : public MainThreadWorkerRunnable
                                            , public WorkerFetchResponseEndBase
 {
+  FetchDriverObserver::EndReason mReason;
+
 public:
-  explicit WorkerFetchResponseEndRunnable(PromiseWorkerProxy* aPromiseProxy)
-    : MainThreadWorkerRunnable(aPromiseProxy->GetWorkerPrivate())
-    , WorkerFetchResponseEndBase(aPromiseProxy)
+  WorkerFetchResponseEndRunnable(WorkerPrivate* aWorkerPrivate,
+                                 WorkerFetchResolver* aResolver,
+                                 FetchDriverObserver::EndReason aReason)
+    : MainThreadWorkerRunnable(aWorkerPrivate)
+    , WorkerFetchResponseEndBase(aResolver)
+    , mReason(aReason)
   {
   }
 
   bool
   WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override
   {
+    if (mReason == FetchDriverObserver::eAborted) {
+      RefPtr<Promise> promise = mResolver->mPromiseProxy->WorkerPromise();
+      promise->MaybeReject(NS_ERROR_DOM_ABORT_ERR);
+    }
+
     WorkerRunInternal(aWorkerPrivate);
     return true;
   }
@@ -379,9 +590,10 @@ class WorkerFetchResponseEndControlRunnable final : public MainThreadWorkerContr
                                                   , public WorkerFetchResponseEndBase
 {
 public:
-  explicit WorkerFetchResponseEndControlRunnable(PromiseWorkerProxy* aPromiseProxy)
-    : MainThreadWorkerControlRunnable(aPromiseProxy->GetWorkerPrivate())
-    , WorkerFetchResponseEndBase(aPromiseProxy)
+  WorkerFetchResponseEndControlRunnable(WorkerPrivate* aWorkerPrivate,
+                                        WorkerFetchResolver* aResolver)
+    : MainThreadWorkerControlRunnable(aWorkerPrivate)
+    , WorkerFetchResponseEndBase(aResolver)
   {
   }
 
@@ -415,7 +627,22 @@ WorkerFetchResolver::OnResponseAvailableInternal(InternalResponse* aResponse)
 }
 
 void
-WorkerFetchResolver::OnResponseEnd()
+WorkerFetchResolver::OnDataAvailable()
+{
+  AssertIsOnMainThread();
+
+  MutexAutoLock lock(mPromiseProxy->Lock());
+  if (mPromiseProxy->CleanedUp()) {
+    return;
+  }
+
+  RefPtr<WorkerDataAvailableRunnable> r =
+    new WorkerDataAvailableRunnable(mPromiseProxy->GetWorkerPrivate(), this);
+  Unused << r->Dispatch();
+}
+
+void
+WorkerFetchResolver::OnResponseEnd(FetchDriverObserver::EndReason aReason)
 {
   AssertIsOnMainThread();
   MutexAutoLock lock(mPromiseProxy->Lock());
@@ -426,11 +653,13 @@ WorkerFetchResolver::OnResponseEnd()
   FlushConsoleReport();
 
   RefPtr<WorkerFetchResponseEndRunnable> r =
-    new WorkerFetchResponseEndRunnable(mPromiseProxy);
+    new WorkerFetchResponseEndRunnable(mPromiseProxy->GetWorkerPrivate(),
+                                       this, aReason);
 
   if (!r->Dispatch()) {
     RefPtr<WorkerFetchResponseEndControlRunnable> cr =
-      new WorkerFetchResponseEndControlRunnable(mPromiseProxy);
+      new WorkerFetchResponseEndControlRunnable(mPromiseProxy->GetWorkerPrivate(),
+                                                this);
     // This can fail if the worker thread is canceled or killed causing
     // the PromiseWorkerProxy to give up its WorkerHolder immediately,
     // allowing the worker thread to become Dead.
diff --git a/dom/fetch/FetchDriver.cpp b/dom/fetch/FetchDriver.cpp
index 6294b0dc5c..067e32db48 100644
--- a/dom/fetch/FetchDriver.cpp
+++ b/dom/fetch/FetchDriver.cpp
@@ -67,7 +67,7 @@ FetchDriver::~FetchDriver()
 }
 
 nsresult
-FetchDriver::Fetch(FetchDriverObserver* aObserver)
+FetchDriver::Fetch(AbortSignal* aSignal, FetchDriverObserver* aObserver)
 {
   workers::AssertIsOnMainThread();
 #ifdef DEBUG
@@ -90,6 +90,18 @@ FetchDriver::Fetch(FetchDriverObserver* aObserver)
   }
 
   mRequest->SetPrincipalInfo(Move(principalInfo));
+
+  // If the signal is aborted, it's time to inform the observer and terminate
+  // the operation.
+  if (aSignal) {
+    if (aSignal->Aborted()) {
+      Aborted();
+      return NS_OK;
+    }
+
+    Follow(aSignal);
+  }
+
   if (NS_FAILED(HttpFetch())) {
     FailWithNetworkError();
   }
@@ -114,11 +126,7 @@ FetchDriver::HttpFetch()
   nsAutoCString url;
   mRequest->GetURL(url);
   nsCOMPtr<nsIURI> uri;
-  rv = NS_NewURI(getter_AddRefs(uri),
-                          url,
-                          nullptr,
-                          nullptr,
-                          ios);
+  rv = NS_NewURI(getter_AddRefs(uri), url, nullptr, nullptr, ios);
   NS_ENSURE_SUCCESS(rv, rv);
 
   // Unsafe requests aren't allowed with when using no-core mode.
@@ -380,6 +388,8 @@ FetchDriver::HttpFetch()
   NS_ENSURE_SUCCESS(rv, rv);
 
   // Step 4 onwards of "HTTP Fetch" is handled internally by Necko.
+
+  mChannel = chan;
   return NS_OK;
 }
 already_AddRefed<InternalResponse>
@@ -433,9 +443,11 @@ FetchDriver::FailWithNetworkError()
 #ifdef DEBUG
     mResponseAvailableCalled = true;
 #endif
-    mObserver->OnResponseEnd();
+    mObserver->OnResponseEnd(FetchDriverObserver::eByNetworking);
     mObserver = nullptr;
   }
+  
+  mChannel = nullptr;
 }
 
 namespace {
@@ -655,6 +667,31 @@ FetchDriver::OnStartRequest(nsIRequest* aRequest,
   return NS_OK;
 }
 
+namespace {
+
+// Runnable to call the observer OnDataAvailable on the main-thread.
+class DataAvailableRunnable final : public Runnable
+{
+  RefPtr<FetchDriverObserver> mObserver;
+
+public:
+  explicit DataAvailableRunnable(FetchDriverObserver* aObserver)
+    : mObserver(aObserver)
+  {
+     MOZ_ASSERT(aObserver);
+  }
+
+  NS_IMETHOD
+  Run() override
+  {
+    mObserver->OnDataAvailable();
+    mObserver = nullptr;
+    return NS_OK;
+  }
+};
+
+} // anonymous namespace
+
 NS_IMETHODIMP
 FetchDriver::OnDataAvailable(nsIRequest* aRequest,
                              nsISupports* aContext,
@@ -666,6 +703,18 @@ FetchDriver::OnDataAvailable(nsIRequest* aRequest,
   // called between OnStartRequest and OnStopRequest, so we don't need to worry
   // about races.
 
+  if (mObserver) {
+    if (NS_IsMainThread()) {
+      mObserver->OnDataAvailable();
+    } else {
+      RefPtr<Runnable> runnable = new DataAvailableRunnable(mObserver);
+      nsresult rv = NS_DispatchToMainThread(runnable);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+    }
+  }
+
   uint32_t aRead;
   MOZ_ASSERT(mResponse);
   MOZ_ASSERT(mPipeOutputStream);
@@ -777,10 +826,11 @@ FetchDriver::OnStopRequest(nsIRequest* aRequest,
       #endif
     }
 
-    mObserver->OnResponseEnd();
+    mObserver->OnResponseEnd(FetchDriverObserver::eByNetworking);
     mObserver = nullptr;
   }
 
+  mChannel = nullptr;
   return NS_OK;
 }
 
@@ -921,5 +971,21 @@ FetchDriver::SetRequestHeaders(nsIHttpChannel* aChannel) const
   }
 }
 
+void FetchDriver::Aborted()
+{
+  if (mObserver) {
+#ifdef DEBUG
+    mResponseAvailableCalled = true;
+#endif
+    mObserver->OnResponseEnd(FetchDriverObserver::eAborted);
+    mObserver = nullptr;
+  }
+
+  if (mChannel) {
+    mChannel->Cancel(NS_BINDING_ABORTED);
+    mChannel = nullptr;
+  }
+}
+
 } // namespace dom
 } // namespace mozilla
diff --git a/dom/fetch/FetchDriver.h b/dom/fetch/FetchDriver.h
index f74298a48c..57dffa5a70 100644
--- a/dom/fetch/FetchDriver.h
+++ b/dom/fetch/FetchDriver.h
@@ -12,6 +12,7 @@
 #include "nsIStreamListener.h"
 #include "nsIThreadRetargetableStreamListener.h"
 #include "mozilla/ConsoleReportCollector.h"
+#include "mozilla/dom/AbortSignal.h"
 #include "mozilla/dom/SRIMetadata.h"
 #include "mozilla/RefPtr.h"
 
@@ -49,7 +50,14 @@ public:
     mGotResponseAvailable = true;
     OnResponseAvailableInternal(aResponse);
   }
-  virtual void OnResponseEnd()
+
+  enum EndReason
+  {
+    eAborted,
+    eByNetworking,
+  };
+
+  virtual void OnResponseEnd(EndReason aReason)
   { };
 
   nsIConsoleReportCollector* GetReporter() const
@@ -58,6 +66,9 @@ public:
   }
 
   virtual void FlushConsoleReport() = 0;
+
+  virtual void OnDataAvailable() = 0;
+
 protected:
   virtual ~FetchDriverObserver()
   { };
@@ -72,7 +83,8 @@ private:
 class FetchDriver final : public nsIStreamListener,
                           public nsIChannelEventSink,
                           public nsIInterfaceRequestor,
-                          public nsIThreadRetargetableStreamListener
+                          public nsIThreadRetargetableStreamListener,
+                          public AbortSignal::Follower
 {
 public:
   NS_DECL_ISUPPORTS
@@ -82,9 +94,12 @@ public:
   NS_DECL_NSIINTERFACEREQUESTOR
   NS_DECL_NSITHREADRETARGETABLESTREAMLISTENER
 
-  explicit FetchDriver(InternalRequest* aRequest, nsIPrincipal* aPrincipal,
-                       nsILoadGroup* aLoadGroup);
-  NS_IMETHOD Fetch(FetchDriverObserver* aObserver);
+  FetchDriver(InternalRequest* aRequest,
+              nsIPrincipal* aPrincipal,
+              nsILoadGroup* aLoadGroup);
+
+  nsresult Fetch(AbortSignal* aSignal,
+                 FetchDriverObserver* aObserver);
 
   void
   SetDocument(nsIDocument* aDocument);
@@ -96,6 +111,11 @@ public:
     mWorkerScript = aWorkerScirpt;
   }
 
+  // AbortSignal::Follower
+
+  void
+  Aborted() override;
+
 private:
   nsCOMPtr<nsIPrincipal> mPrincipal;
   nsCOMPtr<nsILoadGroup> mLoadGroup;
@@ -104,6 +124,7 @@ private:
   nsCOMPtr<nsIOutputStream> mPipeOutputStream;
   RefPtr<FetchDriverObserver> mObserver;
   nsCOMPtr<nsIDocument> mDocument;
+  nsCOMPtr<nsIChannel> mChannel;
   nsAutoPtr<SRICheckDataVerifier> mSRIDataVerifier;
   SRIMetadata mSRIMetadata;
   nsCString mWorkerScript;
diff --git a/dom/fetch/FetchObserver.cpp b/dom/fetch/FetchObserver.cpp
new file mode 100644
index 0000000000..93d93773f7
--- /dev/null
+++ b/dom/fetch/FetchObserver.cpp
@@ -0,0 +1,117 @@
+/* -*- 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 "FetchObserver.h"
+#include "WorkerPrivate.h"
+#include "mozilla/dom/Event.h"
+
+namespace mozilla {
+namespace dom {
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(FetchObserver)
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(FetchObserver,
+                                                  DOMEventTargetHelper)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(FetchObserver,
+                                                DOMEventTargetHelper)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(FetchObserver)
+NS_INTERFACE_MAP_END_INHERITING(DOMEventTargetHelper)
+
+NS_IMPL_ADDREF_INHERITED(FetchObserver, DOMEventTargetHelper)
+NS_IMPL_RELEASE_INHERITED(FetchObserver, DOMEventTargetHelper)
+
+/* static */ bool
+FetchObserver::IsEnabled(JSContext* aCx, JSObject* aGlobal)
+{
+  if (NS_IsMainThread()) {
+    return Preferences::GetBool("dom.fetchObserver.enabled", false);
+  }
+
+  using namespace workers;
+
+  // Otherwise, check the pref via the WorkerPrivate
+  WorkerPrivate* workerPrivate = GetWorkerPrivateFromContext(aCx);
+  if (!workerPrivate) {
+    return false;
+  }
+
+  return workerPrivate->FetchObserverEnabled();
+}
+
+FetchObserver::FetchObserver(nsIGlobalObject* aGlobal,
+                             AbortSignal* aSignal)
+  : DOMEventTargetHelper(aGlobal)
+  , mState(FetchState::Requesting)
+{
+  if (aSignal) {
+    Follow(aSignal);
+  }
+}
+
+JSObject*
+FetchObserver::WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto)
+{
+  return FetchObserverBinding::Wrap(aCx, this, aGivenProto);
+}
+
+FetchState
+FetchObserver::State() const
+{
+  return mState;
+}
+
+void
+FetchObserver::Aborted()
+{
+  SetState(FetchState::Aborted);
+}
+
+void
+FetchObserver::SetState(FetchState aState)
+{
+  MOZ_ASSERT(mState < aState);
+
+  if (mState == FetchState::Aborted ||
+      mState == FetchState::Errored ||
+      mState == FetchState::Complete) {
+    // We are already in a final state.
+    return;
+  }
+
+  // We cannot pass from Requesting to Complete directly.
+  if (mState == FetchState::Requesting &&
+      aState == FetchState::Complete) {
+    SetState(FetchState::Responding);
+  }
+
+  mState = aState;
+
+  if (mState == FetchState::Aborted ||
+      mState == FetchState::Errored ||
+      mState == FetchState::Complete) {
+    Unfollow();
+  }
+
+  EventInit init;
+  init.mBubbles = false;
+  init.mCancelable = false;
+
+  // TODO which kind of event should we dispatch here?
+
+  RefPtr<Event> event =
+    Event::Constructor(this, NS_LITERAL_STRING("statechange"), init);
+  event->SetTrusted(true);
+
+  bool dummy;
+  DispatchEvent(event, &dummy);
+}
+
+} // dom namespace
+} // mozilla namespace
diff --git a/dom/fetch/FetchObserver.h b/dom/fetch/FetchObserver.h
new file mode 100644
index 0000000000..5cd835b3df
--- /dev/null
+++ b/dom/fetch/FetchObserver.h
@@ -0,0 +1,54 @@
+/* -*- 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_FetchObserver_h
+#define mozilla_dom_FetchObserver_h
+
+#include "mozilla/DOMEventTargetHelper.h"
+#include "mozilla/dom/FetchObserverBinding.h"
+#include "mozilla/dom/AbortSignal.h"
+
+namespace mozilla {
+namespace dom {
+
+class FetchObserver final : public DOMEventTargetHelper
+                          , public AbortSignal::Follower
+{
+public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(FetchObserver, DOMEventTargetHelper)
+
+  static bool
+  IsEnabled(JSContext* aCx, JSObject* aGlobal);
+
+  FetchObserver(nsIGlobalObject* aGlobal, AbortSignal* aSignal);
+
+  JSObject*
+  WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override;
+
+  FetchState
+  State() const;
+
+  IMPL_EVENT_HANDLER(statechange);
+  IMPL_EVENT_HANDLER(requestprogress);
+  IMPL_EVENT_HANDLER(responseprogress);
+
+  void
+  Aborted() override;
+
+  void
+  SetState(FetchState aState);
+
+private:
+  ~FetchObserver() = default;
+
+  FetchState mState;
+};
+
+} // dom namespace
+} // mozilla namespace
+
+#endif // mozilla_dom_FetchObserver_h
diff --git a/dom/fetch/Request.h b/dom/fetch/Request.h
index d33c748122..f6fe9be7bd 100644
--- a/dom/fetch/Request.h
+++ b/dom/fetch/Request.h
@@ -12,6 +12,7 @@
 #include "nsWrapperCache.h"
 
 #include "mozilla/dom/Fetch.h"
+#include "mozilla/dom/AbortSignal.h"
 #include "mozilla/dom/InternalRequest.h"
 // Required here due to certain WebIDL enums/classes being declared in both
 // files.
diff --git a/dom/fetch/moz.build b/dom/fetch/moz.build
index be820ab570..e2b4664282 100644
--- a/dom/fetch/moz.build
+++ b/dom/fetch/moz.build
@@ -9,6 +9,7 @@ EXPORTS.mozilla.dom += [
     'Fetch.h',
     'FetchDriver.h',
     'FetchIPCTypes.h',
+    'FetchObserver.h',
     'FetchUtil.h',
     'Headers.h',
     'InternalHeaders.h',
@@ -28,6 +29,7 @@ UNIFIED_SOURCES += [
 SOURCES += [
     'ChannelInfo.cpp',
     'FetchDriver.cpp',
+    'FetchObserver.cpp',
     'FetchUtil.cpp',
     'Headers.cpp',
     'InternalHeaders.cpp',
diff --git a/dom/moz.build b/dom/moz.build
index 89c539b4b1..8a958982f3 100644
--- a/dom/moz.build
+++ b/dom/moz.build
@@ -37,6 +37,7 @@ interfaces = [
 DIRS += ['interfaces/' + i for i in interfaces]
 
 DIRS += [
+    'abort',
     'animation',
     'apps',
     'base',
diff --git a/dom/tests/mochitest/fetch/file_fetch_observer.html b/dom/tests/mochitest/fetch/file_fetch_observer.html
new file mode 100644
index 0000000000..668e609ec4
--- /dev/null
+++ b/dom/tests/mochitest/fetch/file_fetch_observer.html
@@ -0,0 +1,146 @@
+<script>
+function ok(a, msg) {
+  parent.postMessage({ type: "check", status: !!a, message: msg }, "*");
+}
+
+function is(a, b, msg) {
+  ok(a === b, msg);
+}
+
+function testObserver() {
+  ok("FetchObserver" in self, "We have a FetchObserver prototype");
+
+  fetch('http://mochi.test:8888/tests/dom/tests/mochitest/fetch/slow.sjs', { observe: o => {
+    ok(!!o, "We have an observer");
+    ok(o instanceof FetchObserver, "The correct object has been passed");
+    is(o.state, "requesting", "By default the state is requesting");
+    next();
+  }});
+}
+
+function testObserveAbort() {
+  var fc = new AbortController();
+
+  fetch('http://mochi.test:8888/tests/dom/tests/mochitest/fetch/slow.sjs', {
+    signal: fc.signal,
+    observe: o => {
+      o.onstatechange = () => {
+        ok(true, "StateChange event dispatched");
+        if (o.state == "aborted") {
+          ok(true, "Aborted!");
+          next();
+        }
+      }
+      fc.abort();
+    }
+  });
+}
+
+function testObserveComplete() {
+  var fc = new AbortController();
+
+  fetch('http://mochi.test:8888/tests/dom/tests/mochitest/fetch/slow.sjs', {
+    signal: fc.signal,
+    observe: o => {
+      o.onstatechange = () => {
+        ok(true, "StateChange event dispatched");
+        if (o.state == "complete") {
+          ok(true, "Operation completed");
+          next();
+        }
+      }
+    }
+  });
+}
+
+function testObserveErrored() {
+  var fc = new AbortController();
+
+  fetch('foo: bar', {
+    signal: fc.signal,
+    observe: o => {
+      o.onstatechange = () => {
+        ok(true, "StateChange event dispatched");
+        if (o.state == "errored") {
+          ok(true, "Operation completed");
+          next();
+        }
+      }
+    }
+  });
+}
+
+function testObserveResponding() {
+  var fc = new AbortController();
+
+  fetch('http://mochi.test:8888/tests/dom/tests/mochitest/fetch/slow.sjs', {
+    signal: fc.signal,
+    observe: o => {
+      o.onstatechange = () => {
+        if (o.state == "responding") {
+          ok(true, "We have responding events");
+          next();
+        }
+      }
+    }
+  });
+}
+
+function workify(worker) {
+  function methods() {
+    function ok(a, msg) {
+      postMessage( { type: 'check', state: !!a, message: msg });
+    };
+    function is(a, b, msg) {
+      postMessage( { type: 'check', state: a === b, message: msg });
+    };
+    function next() {
+      postMessage( { type: 'finish' });
+    };
+  }
+
+  var str = methods.toString();
+  var methodsContent = str.substring(0, str.length - 1).split('\n').splice(1).join('\n');
+
+  str = worker.toString();
+  var workerContent = str.substring(0, str.length - 1).split('\n').splice(1).join('\n');
+
+  var content = methodsContent + workerContent;
+  var url = URL.createObjectURL(new Blob([content], { type: "application/javascript" }));
+  var w = new Worker(url);
+  w.onmessage = e => {
+    if (e.data.type == 'check') {
+      ok(e.data.state, "WORKER: " + e.data.message);
+    } else if (e.data.type == 'finish') {
+      next();
+    } else {
+      ok(false, "Something went wrong");
+    }
+  }
+}
+
+var steps = [
+  testObserver,
+  testObserveAbort,
+  function() { workify(testObserveAbort); },
+  testObserveComplete,
+  function() { workify(testObserveComplete); },
+  testObserveErrored,
+  function() { workify(testObserveErrored); },
+  testObserveResponding,
+  function() { workify(testObserveResponding); },
+];
+
+function next() {
+  if (!steps.length) {
+    parent.postMessage({ type: "finish" }, "*");
+    return;
+  }
+
+  var step = steps.shift();
+  step();
+}
+
+next();
+
+</script>
diff --git a/dom/tests/mochitest/fetch/mochitest.ini b/dom/tests/mochitest/fetch/mochitest.ini
index cf4477463c..a9447d0d91 100644
--- a/dom/tests/mochitest/fetch/mochitest.ini
+++ b/dom/tests/mochitest/fetch/mochitest.ini
@@ -4,6 +4,7 @@ support-files =
   test_fetch_basic.js
   test_fetch_basic_http.js
   test_fetch_cors.js
+  file_fetch_observer.html
   test_formdataparsing.js
   test_headers_common.js
   test_request.js
@@ -15,6 +16,7 @@ support-files =
   reroute.html
   reroute.js
   reroute.js^headers^
+  slow.sjs
   sw_reroute.js
   empty.js
   empty.js^headers^
@@ -47,6 +49,7 @@ skip-if = toolkit == 'android' # Bug 1210282
 skip-if = toolkit == 'android' # Bug 1210282
 [test_fetch_cors_sw_empty_reroute.html]
 skip-if = toolkit == 'android' # Bug 1210282
+[test_fetch_observer.html] 
 [test_formdataparsing.html]
 [test_formdataparsing_sw_reroute.html]
 [test_request.html]
diff --git a/dom/tests/mochitest/fetch/slow.sjs b/dom/tests/mochitest/fetch/slow.sjs
new file mode 100644
index 0000000000..feab0f1fce
--- /dev/null
+++ b/dom/tests/mochitest/fetch/slow.sjs
@@ -0,0 +1,11 @@
+function handleRequest(request, response)
+{
+  response.processAsync();
+
+  timer = Components.classes["@mozilla.org/timer;1"].
+          createInstance(Components.interfaces.nsITimer);
+  timer.init(function() {
+    response.write("Here the content. But slowly.");
+    response.finish();
+  }, 1000, Components.interfaces.nsITimer.TYPE_ONE_SHOT);
+}
diff --git a/dom/tests/mochitest/fetch/test_fetch_observer.html b/dom/tests/mochitest/fetch/test_fetch_observer.html
new file mode 100644
index 0000000000..2af86977c0
--- /dev/null
+++ b/dom/tests/mochitest/fetch/test_fetch_observer.html
@@ -0,0 +1,41 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test FetchObserver</title>
+  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script class="testbody" type="text/javascript">
+
+SpecialPowers.pushPrefEnv({"set": [["dom.fetchObserver.enabled", true ],
+                                   ["dom.fetchController.enabled", true ]]}, () => {
+  let ifr = document.createElement('iframe');
+  ifr.src = "file_fetch_observer.html";
+  document.body.appendChild(ifr);
+
+  onmessage = function(e) {
+    if (e.data.type == "finish") {
+      SimpleTest.finish();
+      return;
+    }
+
+    if (e.data.type == "check") {
+      ok(e.data.status, e.data.message);
+      return;
+    }
+
+    ok(false, "Something when wrong.");
+  }
+});
+
+SimpleTest.waitForExplicitFinish();
+
+</script>
+</body>
+</html>
+
diff --git a/dom/webidl/AbortController.webidl b/dom/webidl/AbortController.webidl
new file mode 100644
index 0000000000..4e91240751
--- /dev/null
+++ b/dom/webidl/AbortController.webidl
@@ -0,0 +1,13 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/.
+ */
+
+[Constructor(), Exposed=(Window,Worker),
+ Func="AbortController::IsEnabled"]
+interface AbortController {
+  readonly attribute AbortSignal signal;
+
+  void abort();
+};
diff --git a/dom/webidl/AbortSignal.webidl b/dom/webidl/AbortSignal.webidl
new file mode 100644
index 0000000000..b4b03bb7e1
--- /dev/null
+++ b/dom/webidl/AbortSignal.webidl
@@ -0,0 +1,13 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/.
+ */
+
+[Exposed=(Window,Worker),
+ Func="AbortController::IsEnabled"]
+interface AbortSignal : EventTarget {
+  readonly attribute boolean aborted;
+
+  attribute EventHandler onabort;
+};
diff --git a/dom/webidl/FetchObserver.webidl b/dom/webidl/FetchObserver.webidl
new file mode 100644
index 0000000000..eecd67e668
--- /dev/null
+++ b/dom/webidl/FetchObserver.webidl
@@ -0,0 +1,27 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/.
+ */
+
+callback interface ObserverCallback {
+  void handleEvent(FetchObserver observer);
+};
+
+enum FetchState {
+  // Pending states
+  "requesting", "responding",
+  // Final states
+  "aborted", "errored", "complete"
+};
+
+[Exposed=(Window,Worker),
+ Func="FetchObserver::IsEnabled"]
+interface FetchObserver : EventTarget {
+  readonly attribute FetchState state;
+
+  // Events
+  attribute EventHandler onstatechange;
+  attribute EventHandler onrequestprogress;
+  attribute EventHandler onresponseprogress;
+};
diff --git a/dom/webidl/Request.webidl b/dom/webidl/Request.webidl
index e29c084d00..fe6a63ec0d 100644
--- a/dom/webidl/Request.webidl
+++ b/dom/webidl/Request.webidl
@@ -47,6 +47,12 @@ dictionary RequestInit {
   RequestCache cache;
   RequestRedirect redirect;
   DOMString integrity;
+
+  [Func="AbortController::IsEnabled"]
+  AbortSignal signal;
+
+  [Func="FetchObserver::IsEnabled"]
+  ObserverCallback observe;
 };
 
 // Gecko currently does not ship RequestContext, so please don't use it in IDL
diff --git a/dom/webidl/moz.build b/dom/webidl/moz.build
index 78faeac12e..8a86da783f 100644
--- a/dom/webidl/moz.build
+++ b/dom/webidl/moz.build
@@ -17,6 +17,8 @@ PREPROCESSED_WEBIDL_FILES = [
 ]
 
 WEBIDL_FILES = [
+    'AbortController.webidl',
+    'AbortSignal.webidl',
     'AbstractWorker.webidl',
     'AnalyserNode.webidl',
     'Animatable.webidl',
@@ -142,6 +144,7 @@ WEBIDL_FILES = [
     'FakePluginTagInit.webidl',
     'Fetch.webidl',
     'FetchEvent.webidl',
+    'FetchObserver.webidl',
     'File.webidl',
     'FileList.webidl',
     'FileMode.webidl',
diff --git a/dom/workers/WorkerPrefs.h b/dom/workers/WorkerPrefs.h
index 9a1be4801f..b552d89561 100644
--- a/dom/workers/WorkerPrefs.h
+++ b/dom/workers/WorkerPrefs.h
@@ -39,6 +39,8 @@ WORKER_SIMPLE_PREF("dom.push.enabled", PushEnabled, PUSH_ENABLED)
 WORKER_SIMPLE_PREF("dom.requestcontext.enabled", RequestContextEnabled, REQUESTCONTEXT_ENABLED)
 WORKER_SIMPLE_PREF("gfx.offscreencanvas.enabled", OffscreenCanvasEnabled, OFFSCREENCANVAS_ENABLED)
 WORKER_SIMPLE_PREF("dom.webkitBlink.dirPicker.enabled", WebkitBlinkDirectoryPickerEnabled, DOM_WEBKITBLINK_DIRPICKER_WEBKITBLINK)
+WORKER_SIMPLE_PREF("dom.abortController.enabled", AbortControllerEnabled, ABORTCONTROLLER_ENABLED)
+WORKER_SIMPLE_PREF("dom.fetchObserver.enabled", FetchObserverEnabled, FETCHOBSERVER_ENABLED)
 WORKER_PREF("dom.workers.latestJSVersion", JSVersionChanged)
 WORKER_PREF("intl.accept_languages", PrefLanguagesChanged)
 WORKER_PREF("general.appname.override", AppNameOverrideChanged)