LibWeb: Implement ReadableStreamBYOBRequest.respondWithNewView

The AO behind this prototype was added in commit ed1076d9ca,
so we can now trivially expose the prototype as well.

Tests/LibWeb/Text/expected/Streams/ReadableStreamBYOBReader-respondWithNewView.txt

@@ -0,0 +1,4 @@
+abcdefghijklmnopqrstuvwxyz
+ABCDEFGHIJKLMNOPQRSTUVWXYZ
+0123456789!@#$%^&*()-=_+,<
+Done!

Tests/LibWeb/Text/input/Streams/ReadableStreamBYOBReader-respondWithNewView.html

@@ -0,0 +1,80 @@
+<script src="../include.js"></script>
+<script>
+    const CHUNK1 = "abcdefghijklmnopqrstuvwxyz";
+    const CHUNK2 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+    const CHUNK3 = "0123456789!@#$%^&*()-=_+,<";
+
+    const readStream = stream => {
+        const reader = stream.getReader({ mode: "byob" });
+
+        let buffer = new ArrayBuffer(256);
+        let offset = 0;
+
+        return new Promise((resolve, reject) => {
+            const processText = ({ done, value }) => {
+                if (done) {
+                    println("Done!");
+                    resolve();
+                    return;
+                }
+
+                buffer = value.buffer;
+                offset += value.byteLength;
+
+                value = new TextDecoder().decode(value);
+                println(value);
+
+                return reader
+                    .read(new Uint8Array(buffer, offset, buffer.byteLength - offset))
+                    .then(processText);
+            };
+
+            reader
+                .read(new Uint8Array(buffer, offset, buffer.byteLength - offset))
+                .then(processText);
+        });
+    };
+
+    const writeStream = (controller, data) => {
+        const view = controller.byobRequest.view;
+
+        const target = new Uint8Array(view.buffer, view.byteOffset, view.byteLength);
+        const source = Uint8Array.from(Array.from(data).map(ch => ch.charCodeAt(0)));
+
+        for (let i = 0; i < source.length; ++i) {
+            target[i] = source[i];
+        }
+
+        controller.byobRequest.respondWithNewView(target.subarray(0, source.length));
+    };
+
+    asyncTest(done => {
+        const stream = new ReadableStream({
+            type: "bytes",
+
+            start(controller) {
+                pullCount = 0;
+            },
+
+            pull(controller) {
+                const view = controller.byobRequest.view;
+                ++pullCount;
+
+                if (pullCount == 1) {
+                    writeStream(controller, CHUNK1);
+                } else if (pullCount == 2) {
+                    writeStream(controller, CHUNK2);
+                } else if (pullCount == 3) {
+                    writeStream(controller, CHUNK3);
+                } else {
+                    controller.close();
+                    controller.byobRequest.respond(0);
+                }
+            },
+
+            cancel() {},
+        });
+
+        readStream(stream).then(done);
+    });
+</script>

Userland/Libraries/LibWeb/Streams/ReadableStreamBYOBRequest.cpp

@@ -60,4 +60,21 @@ WebIDL::ExceptionOr<void> ReadableStreamBYOBRequest::respond(WebIDL::UnsignedLon
     return readable_byte_stream_controller_respond(*m_controller, bytes_written);
 }
 
+// https://streams.spec.whatwg.org/#rs-byob-request-respond-with-new-view
+WebIDL::ExceptionOr<void> ReadableStreamBYOBRequest::respond_with_new_view(JS::Handle<WebIDL::ArrayBufferView> const& view)
+{
+    auto& realm = this->realm();
+
+    // 1. If this.[[controller]] is undefined, throw a TypeError exception.
+    if (!m_controller)
+        return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, "Controller is undefined"_string };
+
+    // 2. If ! IsDetachedBuffer(view.[[ViewedArrayBuffer]]) is true, throw a TypeError exception.
+    if (view->viewed_array_buffer()->is_detached())
+        return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, "Unable to respond with a detached ArrayBuffer"_string };
+
+    // 3. Return ? ReadableByteStreamControllerRespondWithNewView(this.[[controller]], view).
+    return TRY(readable_byte_stream_controller_respond_with_new_view(realm, *m_controller, *view));
+}
+
 }

Userland/Libraries/LibWeb/Streams/ReadableStreamBYOBRequest.h

@@ -30,6 +30,7 @@ public:
     void set_view(JS::GCPtr<WebIDL::ArrayBufferView> value) { m_view = value; }
 
     WebIDL::ExceptionOr<void> respond(WebIDL::UnsignedLongLong bytes_written);
+    WebIDL::ExceptionOr<void> respond_with_new_view(JS::Handle<WebIDL::ArrayBufferView> const& view);
 
 private:
     explicit ReadableStreamBYOBRequest(JS::Realm&);

Userland/Libraries/LibWeb/Streams/ReadableStreamBYOBRequest.idl

@@ -4,5 +4,5 @@ interface ReadableStreamBYOBRequest {
     readonly attribute ArrayBufferView? view;
 
     undefined respond([EnforceRange] unsigned long long bytesWritten);
-    // FIXME: undefined respondWithNewView(ArrayBufferView view);
+    undefined respondWithNewView(ArrayBufferView view);
 };