add ReadableByteStreamControllerGetBYOBRequest abstract op

index.bs

@@ -1885,13 +1885,7 @@ ReadableByteStreamController(<var>stream</var>, <var>underlyingByteSource</var>,
 
 <emu-alg>
   1. If IsReadableByteStreamController(*this*) is *false*, throw a *TypeError* exception.
-  1. If *this*.[[byobRequest]] is *undefined* and *this*.[[pendingPullIntos]] is not empty,
-    1. Let _firstDescriptor_ be the first element of *this*.[[pendingPullIntos]].
-    1. Let _view_ be ! Construct(<a idl>%Uint8Array%</a>, « _firstDescriptor_.[[buffer]],
-       _firstDescriptor_.[[byteOffset]] + _firstDescriptor_.[[bytesFilled]], _firstDescriptor_.[[byteLength]] −
-       _firstDescriptor_.[[bytesFilled]] »).
-    1. Set *this*.[[byobRequest]] to ! Construct(`<a idl>ReadableStreamBYOBRequest</a>`, « *this*, _view_ »).
-  1. Return *this*.[[byobRequest]].
+  1. Return ! ReadableByteStreamControllerGetBYOBRequest(*this*).
 </emu-alg>
 
 <h5 id="rbs-controller-desired-size" attribute for="ReadableByteStreamController" lt="desiredSize">get desiredSize</h5>
@@ -2285,6 +2279,20 @@ nothrow>ReadableByteStreamControllerFillPullIntoDescriptorFromQueue ( <var>contr
   1. Return _ready_.
 </emu-alg>
 
+<h4 id="readable-byte-stream-controller-get-byob-request" aoid="ReadableByteStreamControllerGetBYOBRequest"
+nothrow>ReadableByteStreamControllerGetBYOBRequest ( <var>controller</var> )</h4>
+
+<emu-alg>
+  1. If _controller_.[[byobRequest]] is *undefined* and _controller_.[[pendingPullIntos]] is not empty,
+    1. Let _firstDescriptor_ be the first element of _controller_.[[pendingPullIntos]].
+    1. Let _view_ be ! Construct(<a idl>%Uint8Array%</a>, « _firstDescriptor_.[[buffer]],
+       _firstDescriptor_.[[byteOffset]] + _firstDescriptor_.[[bytesFilled]], _firstDescriptor_.[[byteLength]] −
+       _firstDescriptor_.[[bytesFilled]] »).
+    1. Set _controller_.[[byobRequest]] to ! Construct(`<a idl>ReadableStreamBYOBRequest</a>`,
+       « _controller_, _view_ »).
+  1. Return _controller_.[[byobRequest]].
+</emu-alg>
+
 <h4 id="readable-byte-stream-controller-get-desired-size" aoid="ReadableByteStreamControllerGetDesiredSize"
 nothrow>ReadableByteStreamControllerGetDesiredSize ( <var>controller</var> )</h4>
 

reference-implementation/lib/readable-stream.js

@@ -1212,16 +1212,7 @@ class ReadableByteStreamController {
       throw byteStreamControllerBrandCheckException('byobRequest');
     }
 
-    if (this._byobRequest === undefined && this._pendingPullIntos.length > 0) {
-      const firstDescriptor = this._pendingPullIntos[0];
-      const view = new Uint8Array(firstDescriptor.buffer,
-                                  firstDescriptor.byteOffset + firstDescriptor.bytesFilled,
-                                  firstDescriptor.byteLength - firstDescriptor.bytesFilled);
-
-      this._byobRequest = new ReadableStreamBYOBRequest(this, view);
-    }
-
-    return this._byobRequest;
+    return ReadableByteStreamControllerGetBYOBRequest(this);
   }
 
   get desiredSize() {
@@ -1772,6 +1763,19 @@ function ReadableByteStreamControllerError(controller, e) {
   ReadableStreamError(stream, e);
 }
 
+function ReadableByteStreamControllerGetBYOBRequest(controller) {
+  if (controller._byobRequest === undefined && controller._pendingPullIntos.length > 0) {
+    const firstDescriptor = controller._pendingPullIntos[0];
+    const view = new Uint8Array(firstDescriptor.buffer,
+                                firstDescriptor.byteOffset + firstDescriptor.bytesFilled,
+                                firstDescriptor.byteLength - firstDescriptor.bytesFilled);
+
+    controller._byobRequest = new ReadableStreamBYOBRequest(controller, view);
+  }
+
+  return controller._byobRequest;
+}
+
 function ReadableByteStreamControllerGetDesiredSize(controller) {
   return controller._strategyHWM - controller._totalQueuedBytes;
 }