4 files changed, 134 insertions, 8 deletions

diff --git a/dom/fetch/FetchController.cpp b/dom/fetch/FetchController.cpp
index b3d8a4d9c5..2eb40b9800 100644
--- a/dom/fetch/FetchController.cpp
+++ b/dom/fetch/FetchController.cpp
@@ -12,7 +12,8 @@
 namespace mozilla {
 namespace dom {
 
-NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(FetchController, mGlobal, mSignal)
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(FetchController, mGlobal, mSignal,
+                                      mFollowingSignal) 
 
 NS_IMPL_CYCLE_COLLECTING_ADDREF(FetchController)
 NS_IMPL_CYCLE_COLLECTING_RELEASE(FetchController)
@@ -97,13 +98,29 @@ FetchController::Abort()
 void
 FetchController::Follow(FetchSignal& aSignal)
 {
-  // TODO
+  FetchSignal::Follower::Follow(&aSignal);
 }
 
 void
 FetchController::Unfollow(FetchSignal& aSignal)
 {
-  // TODO
+  if (mFollowingSignal != &aSignal) {
+    return;
+  }
+
+  FetchSignal::Follower::Unfollow();
+}
+
+FetchSignal*
+FetchController::Following() const
+{
+  return mFollowingSignal;
+}
+
+void
+FetchController::Aborted()
+{
+  Abort();
 }
 
 } // dom namespace
diff --git a/dom/fetch/FetchController.h b/dom/fetch/FetchController.h
index 854c6f9743..7a0132dca2 100644
--- a/dom/fetch/FetchController.h
+++ b/dom/fetch/FetchController.h
@@ -8,6 +8,7 @@
 #define mozilla_dom_FetchController_h
 
 #include "mozilla/dom/BindingDeclarations.h"
+#include "mozilla/dom/FetchSignal.h" 
 #include "nsCycleCollectionParticipant.h"
 #include "nsWrapperCache.h"
 #include "mozilla/ErrorResult.h"
@@ -16,10 +17,9 @@
 namespace mozilla {
 namespace dom {
 
-class FetchSignal;
-
 class FetchController final : public nsISupports
                             , public nsWrapperCache
+                            , public FetchSignal::Follower
 {
 public:
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS
@@ -51,6 +51,13 @@ public:
   void
   Unfollow(FetchSignal& aSignal);
 
+  FetchSignal*
+  Following() const;
+
+  // FetchSignal::Follower
+
+  void Aborted() override;
+
 private:
   ~FetchController() = default;
 
diff --git a/dom/fetch/FetchSignal.cpp b/dom/fetch/FetchSignal.cpp
index 4395dbcf2f..1924263e80 100644
--- a/dom/fetch/FetchSignal.cpp
+++ b/dom/fetch/FetchSignal.cpp
@@ -16,12 +16,12 @@ NS_IMPL_CYCLE_COLLECTION_CLASS(FetchSignal)
 
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(FetchSignal,
                                                   DOMEventTargetHelper)
-    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mController)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mController)
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
 NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(FetchSignal,
                                                 DOMEventTargetHelper)
-    NS_IMPL_CYCLE_COLLECTION_UNLINK(mController)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mController)
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(FetchSignal)
@@ -55,6 +55,11 @@ FetchSignal::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;
@@ -65,7 +70,73 @@ FetchSignal::Abort()
     Event::Constructor(this, NS_LITERAL_STRING("abort"), init);
   event->SetTrusted(true);
 
-  DispatchDOMEvent(nullptr, event, nullptr, nullptr);
+  bool dummy;
+  DispatchEvent(event, &dummy);
+}
+
+void
+FetchSignal::AddFollower(FetchSignal::Follower* aFollower)
+{
+  MOZ_DIAGNOSTIC_ASSERT(aFollower);
+  if (!mFollowers.Contains(aFollower)) {
+    mFollowers.AppendElement(aFollower);
+  }
+}
+
+void
+FetchSignal::RemoveFollower(FetchSignal::Follower* aFollower)
+{
+  MOZ_DIAGNOSTIC_ASSERT(aFollower);
+  mFollowers.RemoveElement(aFollower);
+}
+
+bool
+FetchSignal::CanAcceptFollower(FetchSignal::Follower* aFollower) const
+{
+  MOZ_DIAGNOSTIC_ASSERT(aFollower);
+
+  if (aFollower == mController) {
+    return false;
+  }
+
+  FetchSignal* following = mController->Following();
+  if (!following) {
+    return true;
+  }
+
+  return following->CanAcceptFollower(aFollower);
+}
+
+// FetchSignal::Follower
+// ----------------------------------------------------------------------------
+
+FetchSignal::Follower::~Follower()
+{
+  Unfollow();
+}
+
+void
+FetchSignal::Follower::Follow(FetchSignal* aSignal)
+{
+  MOZ_DIAGNOSTIC_ASSERT(aSignal);
+
+  if (!aSignal->CanAcceptFollower(this)) {
+    return;
+  }
+
+  Unfollow();
+
+  mFollowingSignal = aSignal;
+  aSignal->AddFollower(this);
+}
+
+void
+FetchSignal::Follower::Unfollow()
+{
+  if (mFollowingSignal) {
+    mFollowingSignal->RemoveFollower(this);
+    mFollowingSignal = nullptr;
+  }
 }
 
 } // dom namespace
diff --git a/dom/fetch/FetchSignal.h b/dom/fetch/FetchSignal.h
index 5bb16b8348..5d2f13c689 100644
--- a/dom/fetch/FetchSignal.h
+++ b/dom/fetch/FetchSignal.h
@@ -13,10 +13,29 @@ namespace mozilla {
 namespace dom {
 
 class FetchController;
+class FetchSignal;
 
 class FetchSignal final : public DOMEventTargetHelper
 {
 public:
+  // This class must be implemented by objects who want to follow a FetchSignal.
+  class Follower
+  {
+  public:
+    virtual void Aborted() = 0;
+
+  protected:
+    virtual ~Follower();
+
+    void
+    Follow(FetchSignal* aSignal);
+
+    void
+    Unfollow();
+
+    RefPtr<FetchSignal> mFollowingSignal;
+  };
+
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(FetchSignal, DOMEventTargetHelper)
 
@@ -33,11 +52,23 @@ public:
 
   IMPL_EVENT_HANDLER(abort);
 
+  void
+  AddFollower(Follower* aFollower);
+
+  void
+  RemoveFollower(Follower* aFollower);
+
+  bool
+  CanAcceptFollower(Follower* aFollower) const;
+
 private:
   ~FetchSignal() = default;
 
   RefPtr<FetchController> mController;
 
+  // Raw pointers. Follower unregisters itself in the DTOR.
+  nsTArray<Follower*> mFollowers;
+
   bool mAborted;
 };