Bug 1398556 - IPCBlobInputStream should call OnInputStreamReady() on the current thread if ::AsyncWait() is called without passing nsIEventTarget, r=smaug

dom/file/ipc/IPCBlobInputStream.cpp

@@ -25,20 +25,24 @@ static NS_DEFINE_CID(kStreamTransportServiceCID, NS_STREAMTRANSPORTSERVICE_CID);
 class InputStreamCallbackRunnable final : public CancelableRunnable
 {
 public:
+  // Note that the execution can be synchronous in case the event target is
+  // null.
   static void
   Execute(nsIInputStreamCallback* aCallback,
           nsIEventTarget* aEventTarget,
           IPCBlobInputStream* aStream)
   {
+    MOZ_ASSERT(aCallback);
+
     RefPtr<InputStreamCallbackRunnable> runnable =
       new InputStreamCallbackRunnable(aCallback, aStream);
 
     nsCOMPtr<nsIEventTarget> target = aEventTarget;
-    if (!target) {
-      target = NS_GetCurrentThread();
+    if (aEventTarget) {
+      target->Dispatch(runnable, NS_DISPATCH_NORMAL);
+    } else {
+      runnable->Run();
     }
-
-    target->Dispatch(runnable, NS_DISPATCH_NORMAL);
   }
 
   NS_IMETHOD
@@ -73,14 +77,13 @@ public:
           nsIEventTarget* aEventTarget,
           IPCBlobInputStream* aStream)
   {
+    MOZ_ASSERT(aCallback);
+    MOZ_ASSERT(aEventTarget);
+
     RefPtr<FileMetadataCallbackRunnable> runnable =
       new FileMetadataCallbackRunnable(aCallback, aStream);
 
     nsCOMPtr<nsIEventTarget> target = aEventTarget;
-    if (!target) {
-      target = NS_GetCurrentThread();
-    }
-
     target->Dispatch(runnable, NS_DISPATCH_NORMAL);
   }
 
@@ -509,6 +512,8 @@ IPCBlobInputStream::OnInputStreamReady(nsIAsyncInputStream* aStream)
   nsCOMPtr<nsIEventTarget> callbackEventTarget;
   callbackEventTarget.swap(mInputStreamCallbackEventTarget);
  
+  // This must be the last operation because the execution of the callback can
+  // be synchronous.
   InputStreamCallbackRunnable::Execute(callback, callbackEventTarget, this);
   return NS_OK;
 }
@@ -547,6 +552,13 @@ NS_IMETHODIMP
 IPCBlobInputStream::AsyncWait(nsIFileMetadataCallback* aCallback,
                               nsIEventTarget* aEventTarget)
 {
+  MOZ_ASSERT(!!aCallback != !!aEventTarget);
+
+  // If we have the callback, we must have the event target.
+  if (NS_WARN_IF(!!aCallback != !!aEventTarget)) {
+    return NS_ERROR_FAILURE;
+  }
+
   // See IPCBlobInputStream.h for more information about this state machine.
 
   switch (mState) {

dom/file/ipc/IPCBlobInputStreamChild.cpp

@@ -277,7 +277,7 @@ IPCBlobInputStreamChild::StreamNeeded(IPCBlobInputStream* aStream,
 
   PendingOperation* opt = mPendingOperations.AppendElement();
   opt->mStream = aStream;
-  opt->mEventTarget = aEventTarget ? aEventTarget : NS_GetCurrentThread();
+  opt->mEventTarget = aEventTarget;
 
   if (mState == eActiveMigrating || mState == eInactiveMigrating) {
     // This operation will be continued when the migration is completed.
@@ -316,7 +316,16 @@ IPCBlobInputStreamChild::RecvStreamReady(const OptionalIPCStream& aStream)
 
   RefPtr<StreamReadyRunnable> runnable =
     new StreamReadyRunnable(pendingStream, stream);
-  eventTarget->Dispatch(runnable, NS_DISPATCH_NORMAL);
+
+  // If IPCBlobInputStream::AsyncWait() has been executed without passing an
+  // event target, we run the callback synchronous because any thread could be
+  // result to be the wrong one. See more in nsIAsyncInputStream::asyncWait
+  // documentation.
+  if (eventTarget) {
+    eventTarget->Dispatch(runnable, NS_DISPATCH_NORMAL);
+  } else {
+    runnable->Run();
+  }
 
   return IPC_OK();
 }

netwerk/base/nsIFileStreams.idl

@@ -222,6 +222,13 @@ interface nsIAsyncFileMetadata : nsIFileMetadata
 {
     /**
      * Asynchronously wait for the object to be ready.
+     *
+     * @param aCallback The callback will be used when the stream is ready to
+     *                  return File metadata. Use a nullptr to cancel a
+     *                  previous operation.
+     *
+     * @param aEventTarget The event target where aCallback will be executed.
+     *                     If aCallback is passed, aEventTarget cannot be null.
      */
     void asyncWait(in nsIFileMetadataCallback aCallback,
                    in nsIEventTarget aEventTarget);