fix(ext/web/streams): fix ReadableStream asyncIterator (#16276)

ext/web/06_streams.js

@@ -32,6 +32,7 @@
     ObjectDefineProperties,
     ObjectDefineProperty,
     ObjectGetPrototypeOf,
+    ObjectPrototype,
     ObjectPrototypeIsPrototypeOf,
     ObjectSetPrototypeOf,
     Promise,
@@ -4424,7 +4425,7 @@
    * @returns {IteratorResult<T>}
    */
   function createIteratorResult(value, done) {
-    const result = ObjectCreate(null);
+    const result = ObjectCreate(ObjectPrototype);
     ObjectDefineProperties(result, {
       value: { value, writable: true, enumerable: true, configurable: true },
       done: {
@@ -4442,57 +4443,99 @@
     ObjectGetPrototypeOf(async function* () {}).prototype,
   );
 
+  const _iteratorNext = Symbol("[[iteratorNext]]");
+  const _iteratorFinished = Symbol("[[iteratorFinished]]");
+
   /** @type {AsyncIterator<unknown>} */
   const readableStreamAsyncIteratorPrototype = ObjectSetPrototypeOf({
     /** @returns {Promise<IteratorResult<unknown>>} */
     next() {
       /** @type {ReadableStreamDefaultReader} */
       const reader = this[_reader];
-      if (reader[_stream] === undefined) {
-        return PromiseReject(
-          new TypeError(
-            "Cannot get the next iteration result once the reader has been released.",
-          ),
-        );
+      function nextSteps() {
+        if (reader[_iteratorFinished]) {
+          return PromiseResolve(createIteratorResult(undefined, true));
+        }
+
+        if (reader[_stream] === undefined) {
+          return PromiseReject(
+            new TypeError(
+              "Cannot get the next iteration result once the reader has been released.",
+            ),
+          );
+        }
+
+        /** @type {Deferred<IteratorResult<any>>} */
+        const promise = new Deferred();
+        /** @type {ReadRequest} */
+        const readRequest = {
+          chunkSteps(chunk) {
+            promise.resolve(createIteratorResult(chunk, false));
+          },
+          closeSteps() {
+            readableStreamDefaultReaderRelease(reader);
+            promise.resolve(createIteratorResult(undefined, true));
+          },
+          errorSteps(e) {
+            readableStreamDefaultReaderRelease(reader);
+            promise.reject(e);
+          },
+        };
+
+        readableStreamDefaultReaderRead(reader, readRequest);
+        return PromisePrototypeThen(promise.promise, (result) => {
+          reader[_iteratorNext] = null;
+          if (result.done === true) {
+            reader[_iteratorFinished] = true;
+            return createIteratorResult(undefined, true);
+          }
+          return result;
+        }, (reason) => {
+          reader[_iteratorNext] = null;
+          reader[_iteratorFinished] = true;
+          throw reason;
+        });
       }
-      /** @type {Deferred<IteratorResult<any>>} */
-      const promise = new Deferred();
-      /** @type {ReadRequest} */
-      const readRequest = {
-        chunkSteps(chunk) {
-          promise.resolve(createIteratorResult(chunk, false));
-        },
-        closeSteps() {
-          readableStreamDefaultReaderRelease(reader);
-          promise.resolve(createIteratorResult(undefined, true));
-        },
-        errorSteps(e) {
-          readableStreamDefaultReaderRelease(reader);
-          promise.reject(e);
-        },
-      };
-      readableStreamDefaultReaderRead(reader, readRequest);
-      return promise.promise;
+
+      reader[_iteratorNext] = reader[_iteratorNext]
+        ? PromisePrototypeThen(reader[_iteratorNext], nextSteps, nextSteps)
+        : nextSteps();
+
+      return reader[_iteratorNext];
     },
     /**
      * @param {unknown} arg
      * @returns {Promise<IteratorResult<unknown>>}
      */
-    async return(arg) {
+    return(arg) {
       /** @type {ReadableStreamDefaultReader} */
       const reader = this[_reader];
-      if (reader[_stream] === undefined) {
-        return createIteratorResult(undefined, true);
-      }
-      assert(reader[_readRequests].length === 0);
-      if (this[_preventCancel] === false) {
-        const result = readableStreamReaderGenericCancel(reader, arg);
+      const returnSteps = () => {
+        if (reader[_iteratorFinished]) {
+          return PromiseResolve(createIteratorResult(arg, true));
+        }
+        reader[_iteratorFinished] = true;
+
+        if (reader[_stream] === undefined) {
+          return PromiseResolve(createIteratorResult(undefined, true));
+        }
+        assert(reader[_readRequests].length === 0);
+        if (this[_preventCancel] === false) {
+          const result = readableStreamReaderGenericCancel(reader, arg);
+          readableStreamDefaultReaderRelease(reader);
+          return result;
+        }
         readableStreamDefaultReaderRelease(reader);
-        await result;
-        return createIteratorResult(arg, true);
-      }
-      readableStreamDefaultReaderRelease(reader);
-      return createIteratorResult(undefined, true);
+        return PromiseResolve(createIteratorResult(undefined, true));
+      };
+
+      const returnPromise = reader[_iteratorNext]
+        ? PromisePrototypeThen(reader[_iteratorNext], returnSteps, returnSteps)
+        : returnSteps();
+      return PromisePrototypeThen(
+        returnPromise,
+        () => createIteratorResult(arg, true),
+      );
     },
   }, asyncIteratorPrototype);
 

tools/wpt/expectation.json

@@ -1311,7 +1311,10 @@
       "respond-after-enqueue.any.worker.html": true
     },
     "readable-streams": {
-      "async-iterator.any.html": false,
+      "async-iterator.any.html": [
+        "next() that succeeds; return()",
+        "next() that succeeds; return() [no awaiting]"
+      ],
       "bad-strategies.any.html": true,
       "bad-strategies.any.worker.html": true,
       "bad-underlying-sources.any.html": true,