Bug 1813011 - Part 2: Return unsettled promise from BodyStream::PullCallbackImpl r=smaug

... and resolve it after successful enqueue. Note that this never rejects it since ErrorNative will do it for us.

eWaiting/eReading/eWriting is merged into eInitialized and the state assertions now use promise state.

Differential Revision: https://phabricator.services.mozilla.com/D169483

dom/base/BodyStream.cpp

@@ -191,26 +191,16 @@ already_AddRefed<Promise> BodyStream::PullCallback(
 
   MOZ_DIAGNOSTIC_ASSERT(mOwningEventTarget->IsOnCurrentThread());
 
-  MOZ_DIAGNOSTIC_ASSERT(mState == eInitializing || mState == eWaiting ||
-                        mState == eReading);
-
-  RefPtr<Promise> resolvedWithUndefinedPromise =
-      Promise::CreateResolvedWithUndefined(aController.GetParentObject(), aRv);
-  if (aRv.Failed()) {
-    return nullptr;
-  }
-
-  if (mState == eReading) {
-    // We are already reading data.
-    return resolvedWithUndefinedPromise.forget();
-  }
+  MOZ_DIAGNOSTIC_ASSERT(mState == eInitializing || mState == eInitialized);
+  MOZ_ASSERT(!mPullPromise);
+  mPullPromise = Promise::CreateInfallible(aController.GetParentObject());
 
   if (mState == eInitializing) {
     // The stream has been used for the first time.
     mStreamHolder->MarkAsRead();
   }
 
-  mState = eReading;
+  mState = eInitialized;
 
   if (!mInputStream) {
     // This is the first use of the stream. Let's convert the
@@ -240,7 +230,7 @@ already_AddRefed<Promise> BodyStream::PullCallback(
   mAsyncWaitWorkerRef = mWorkerRef;
 
   // All good.
-  return resolvedWithUndefinedPromise.forget();
+  return do_AddRef(mPullPromise);
 }
 
 void BodyStream::WriteIntoReadRequestBuffer(JSContext* aCx,
@@ -254,7 +244,9 @@ void BodyStream::WriteIntoReadRequestBuffer(JSContext* aCx,
   MOZ_DIAGNOSTIC_ASSERT(mOwningEventTarget->IsOnCurrentThread());
 
   MOZ_DIAGNOSTIC_ASSERT(mInputStream);
-  MOZ_DIAGNOSTIC_ASSERT(mState == eWriting);
+  MOZ_DIAGNOSTIC_ASSERT(mState == eInitialized);
+  MOZ_DIAGNOSTIC_ASSERT(mPullPromise->State() ==
+                        Promise::PromiseState::Pending);
 
   uint32_t written;
   nsresult rv;
@@ -437,7 +429,9 @@ BodyStream::OnInputStreamReady(nsIAsyncInputStream* aStream) {
   AutoEntryScript aes(mGlobal, "fetch body data available");
 
   MOZ_DIAGNOSTIC_ASSERT(mInputStream);
-  MOZ_DIAGNOSTIC_ASSERT(mState == eReading);
+  MOZ_DIAGNOSTIC_ASSERT(mState == eInitialized);
+  MOZ_DIAGNOSTIC_ASSERT(mPullPromise->State() ==
+                        Promise::PromiseState::Pending);
 
   JSContext* cx = aes.cx();
   ReadableStream* stream = mStreamHolder->GetReadableStreamBody();
@@ -455,8 +449,6 @@ BodyStream::OnInputStreamReady(nsIAsyncInputStream* aStream) {
     return NS_OK;
   }
 
-  mState = eWriting;
-
   ErrorResult errorResult;
   EnqueueChunkWithSizeIntoStream(cx, stream, size, errorResult);
   errorResult.WouldReportJSException();
@@ -465,7 +457,8 @@ BodyStream::OnInputStreamReady(nsIAsyncInputStream* aStream) {
     return NS_OK;
   }
 
-  mState = eWaiting;
+  mPullPromise->MaybeResolveWithUndefined();
+  mPullPromise = nullptr;
 
   // The previous call can execute JS (even up to running a nested event
   // loop), so |mState| can't be asserted to have any particular value, even
@@ -551,6 +544,10 @@ void BodyStream::ReleaseObjects() {
 
   mWorkerRef = nullptr;
   mGlobal = nullptr;
+  // It's okay to leave a potentially unsettled promise as-is as this is only
+  // used to prevent reentrant to PullCallback. CloseNative() or ErrorNative()
+  // will settle the read requests for us.
+  mPullPromise = nullptr;
 
   RefPtr<BodyStream> self = mStreamHolder->TakeBodyStream();
   mStreamHolder->NullifyStream();

dom/base/BodyStream.h

@@ -140,15 +140,8 @@ class BodyStream final : public nsIInputStreamCallback,
     // This is the beginning state before any reading operation.
     eInitializing,
 
-    // RequestDataCallback has not been called yet. We haven't started to read
-    // data from the stream yet.
-    eWaiting,
-
-    // We are reading data in a separate I/O thread.
-    eReading,
-
-    // We are ready to write something in the JS Buffer.
-    eWriting,
+    // Stream is initialized and being consumed.
+    eInitialized,
 
     // Operation completed.
     eClosed,
@@ -161,6 +154,9 @@ class BodyStream final : public nsIInputStreamCallback,
   nsCOMPtr<nsIGlobalObject> mGlobal;
   RefPtr<BodyStreamHolder> mStreamHolder;
   nsCOMPtr<nsIEventTarget> mOwningEventTarget;
+  // Same as mGlobal but set to nullptr on OnInputStreamReady (on the owning
+  // thread).
+  RefPtr<Promise> mPullPromise;
 
   // This is the original inputStream received during the CTOR. It will be
   // converted into an nsIAsyncInputStream and stored into mInputStream at the