stream: allow transfer of readable byte streams

Updates the `ReadableStream` constructor to mark byte streams as
transferable. When transferred, byte streams become regular streams.

Refs: #39062
Refs: https://streams.spec.whatwg.org/#rs-transfer
PR-URL: #45955
Reviewed-By: Daeyeon Jeong <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: James M Snell <[email protected]>

Author: mrbbot

lib/internal/webstreams/readablestream.js

@@ -281,17 +281,16 @@ class ReadableStream {
         this,
         source,
         extractHighWaterMark(highWaterMark, 0));
-      return;
+    } else {
+      if (type !== undefined)
+        throw new ERR_INVALID_ARG_VALUE('source.type', type);
+      setupReadableStreamDefaultControllerFromSource(
+        this,
+        source,
+        extractHighWaterMark(highWaterMark, 1),
+        extractSizeAlgorithm(size));
     }
 
-    if (type !== undefined)
-      throw new ERR_INVALID_ARG_VALUE('source.type', type);
-    setupReadableStreamDefaultControllerFromSource(
-      this,
-      source,
-      extractHighWaterMark(highWaterMark, 1),
-      extractSizeAlgorithm(size));
-
     // eslint-disable-next-line no-constructor-return
     return makeTransferable(this);
   }

test/parallel/test-whatwg-webstreams-transfer.js

@@ -15,6 +15,7 @@ const {
 
 const {
   isReadableStream,
+  isReadableByteStreamController,
 } = require('internal/webstreams/readablestream');
 
 const {
@@ -25,6 +26,10 @@ const {
   isTransformStream,
 } = require('internal/webstreams/transformstream');
 
+const {
+  kState,
+} = require('internal/webstreams/util');
+
 const {
   makeTransferable,
   kClone,
@@ -107,6 +112,56 @@ const theData = 'hello';
   assert(readable.locked);
 }
 
+{
+  const { port1, port2 } = new MessageChannel();
+  port1.onmessageerror = common.mustNotCall();
+  port2.onmessageerror = common.mustNotCall();
+
+  // This test repeats the test above, but with a readable byte stream.
+  // Note transferring a readable byte stream results in a regular
+  // value-oriented stream on the other side:
+  // https://streams.spec.whatwg.org/#abstract-opdef-setupcrossrealmtransformwritable
+
+  const theByteData = new Uint8Array([1, 2, 3]);
+
+  const readable = new ReadableStream({
+    type: 'bytes',
+    start: common.mustCall((controller) => {
+      // `enqueue` will detach its argument's buffer, so clone first
+      controller.enqueue(theByteData.slice());
+      controller.close();
+    }),
+  });
+  assert(isReadableByteStreamController(readable[kState].controller));
+
+  port2.onmessage = common.mustCall(({ data }) => {
+    assert(isReadableStream(data));
+    assert(!isReadableByteStreamController(data[kState].controller));
+
+    const reader = data.getReader();
+    reader.read().then(common.mustCall((chunk) => {
+      assert.deepStrictEqual(chunk, { done: false, value: theByteData });
+    }));
+
+    port2.close();
+  });
+
+  port1.onmessage = common.mustCall(({ data }) => {
+    assert(isReadableStream(data));
+    assert(!isReadableByteStreamController(data[kState].controller));
+    assert(!data.locked);
+    port1.postMessage(data, [data]);
+    assert(data.locked);
+  });
+
+  assert.throws(() => port2.postMessage(readable), {
+    code: 'ERR_MISSING_TRANSFERABLE_IN_TRANSFER_LIST',
+  });
+
+  port2.postMessage(readable, [readable]);
+  assert(readable.locked);
+}
+
 {
   const { port1, port2 } = new MessageChannel();
   port1.onmessageerror = common.mustNotCall();