LibWeb: Implement ReadableStreamBYOBReader::read

Similiarly to the underlying AO's, currently only TypedArrays are
supported.

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

@@ -0,0 +1,3 @@
+About to read! [object ReadableStreamBYOBReader]
+Total bytes: 34
+'This is some data to be read! 🦬'

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

@@ -0,0 +1,31 @@
+<script src="../include.js"></script>
+<script>
+ asyncTest(async done => {
+    const array = ['This is some data to be read! 🦬'];
+    let blob = new Blob(array);
+
+    const stream = blob.stream();
+    const reader = stream.getReader({ mode: "byob" });
+
+    let buffer = new ArrayBuffer(200);
+    let bytesReceived = 0;
+    let offset = 0;
+
+    println(`About to read! ${reader}`);
+
+    while (true) {
+      let result = await reader.read(new Uint8Array(buffer, offset, buffer.byteLength - offset));
+
+      if (result.done) {
+        println(`Total bytes: ${bytesReceived}`);
+        println(`'${new TextDecoder().decode(result.value.buffer.slice(0, bytesReceived))}'`);
+        done();
+        return;
+      }
+
+      buffer = result.value.buffer;
+      offset += result.value.byteLength;
+      bytesReceived += result.value.byteLength;
+    }
+  });
+</script>

Userland/Libraries/LibWeb/Streams/ReadableStreamBYOBReader.cpp

@@ -6,6 +6,7 @@
  */
 
 #include <LibJS/Runtime/PromiseCapability.h>
+#include <LibJS/Runtime/TypedArray.h>
 #include <LibWeb/Bindings/Intrinsics.h>
 #include <LibWeb/Streams/AbstractOperations.h>
 #include <LibWeb/Streams/ReadableStream.h>
@@ -56,4 +57,101 @@ void ReadableStreamBYOBReader::visit_edges(Cell::Visitor& visitor)
         visitor.visit(request);
 }
 
+class BYOBReaderReadIntoRequest : public ReadIntoRequest {
+    JS_CELL(BYOBReaderReadIntoRequest, ReadIntoRequest);
+
+public:
+    BYOBReaderReadIntoRequest(JS::Realm& realm, WebIDL::Promise& promise)
+        : m_realm(realm)
+        , m_promise(promise)
+    {
+    }
+
+    // chunk steps, given chunk
+    virtual void on_chunk(JS::Value chunk) override
+    {
+        // 1. Resolve promise with «[ "value" → chunk, "done" → false ]».
+        WebIDL::resolve_promise(m_realm, m_promise, JS::create_iterator_result_object(m_realm.vm(), chunk, false));
+    }
+
+    // close steps, given chunk
+    virtual void on_close(JS::Value chunk) override
+    {
+        // 1. Resolve promise with «[ "value" → chunk, "done" → true ]».
+        WebIDL::resolve_promise(m_realm, m_promise, JS::create_iterator_result_object(m_realm.vm(), chunk, true));
+    }
+
+    // error steps, given e
+    virtual void on_error(JS::Value error) override
+    {
+        // 1. Reject promise with e.
+        WebIDL::reject_promise(m_realm, m_promise, error);
+    }
+
+private:
+    virtual void visit_edges(Visitor& visitor) override
+    {
+        Base::visit_edges(visitor);
+        visitor.visit(m_realm);
+        visitor.visit(m_promise);
+    }
+
+    JS::Realm& m_realm;
+    WebIDL::Promise& m_promise;
+};
+
+// https://streams.spec.whatwg.org/#byob-reader-read
+WebIDL::ExceptionOr<JS::NonnullGCPtr<JS::Promise>> ReadableStreamBYOBReader::read(JS::Value view_value)
+{
+    auto& realm = this->realm();
+
+    // FIXME: Support DataViews
+    auto& view = verify_cast<JS::TypedArrayBase>(view_value.as_object());
+
+    // 1. If view.[[ByteLength]] is 0, return a promise rejected with a TypeError exception.
+    if (view.byte_length() == 0) {
+        auto exception = JS::TypeError::create(realm, "Cannot read in an empty buffer"sv);
+        auto promise_capability = WebIDL::create_rejected_promise(realm, exception);
+        return JS::NonnullGCPtr { verify_cast<JS::Promise>(*promise_capability->promise()) };
+    }
+
+    // 2. If view.[[ViewedArrayBuffer]].[[ArrayBufferByteLength]] is 0, return a promise rejected with a TypeError exception.
+    if (view.viewed_array_buffer()->byte_length() == 0) {
+        auto exception = JS::TypeError::create(realm, "Cannot read in an empty buffer"sv);
+        auto promise_capability = WebIDL::create_rejected_promise(realm, exception);
+        return JS::NonnullGCPtr { verify_cast<JS::Promise>(*promise_capability->promise()) };
+    }
+
+    // 3. If ! IsDetachedBuffer(view.[[ViewedArrayBuffer]]) is true, return a promise rejected with a TypeError exception.
+    if (view.viewed_array_buffer()->is_detached()) {
+        auto exception = JS::TypeError::create(realm, "Cannot read in a detached buffer"sv);
+        auto promise_capability = WebIDL::create_rejected_promise(realm, exception);
+        return JS::NonnullGCPtr { verify_cast<JS::Promise>(*promise_capability->promise()) };
+    }
+
+    // 4. If this.[[stream]] is undefined, return a promise rejected with a TypeError exception.
+    if (!m_stream) {
+        auto exception = JS::TypeError::create(realm, "Cannot read from an empty stream"sv);
+        auto promise_capability = WebIDL::create_rejected_promise(realm, exception);
+        return JS::NonnullGCPtr { verify_cast<JS::Promise>(*promise_capability->promise()) };
+    }
+
+    // 5. Let promise be a new promise.
+    auto promise_capability = WebIDL::create_promise(realm);
+
+    // 6. Let readIntoRequest be a new read-into request with the following items:
+    //    chunk steps, given chunk
+    //        Resolve promise with «[ "value" → chunk, "done" → false ]».
+    //    close steps, given chunk
+    //        Resolve promise with «[ "value" → chunk, "done" → true ]».
+    //    error steps, given e
+    //        Reject promise with e.
+    auto read_into_request = heap().allocate_without_realm<BYOBReaderReadIntoRequest>(realm, promise_capability);
+
+    // 7. Perform ! ReadableStreamBYOBReaderRead(this, view, readIntoRequest).
+    readable_stream_byob_reader_read(*this, view_value, *read_into_request);
+
+    // 8. Return promise.
+    return JS::NonnullGCPtr { verify_cast<JS::Promise>(*promise_capability->promise()) };
+}
 }

Userland/Libraries/LibWeb/Streams/ReadableStreamBYOBReader.h

@@ -44,6 +44,8 @@ public:
 
     virtual ~ReadableStreamBYOBReader() override = default;
 
+    WebIDL::ExceptionOr<JS::NonnullGCPtr<JS::Promise>> read(JS::Value);
+
     void release_lock();
 
     Vector<JS::NonnullGCPtr<ReadIntoRequest>>& read_into_requests() { return m_read_into_requests; }

Userland/Libraries/LibWeb/Streams/ReadableStreamBYOBReader.idl

@@ -1,4 +1,5 @@
 #import <Streams/ReadableStream.idl>
+#import <Streams/ReadableStreamDefaultReader.idl>
 #import <Streams/ReadableStreamGenericReader.idl>
 
 // https://streams.spec.whatwg.org/#readablestreambyobreader
@@ -6,7 +7,9 @@
 interface ReadableStreamBYOBReader {
     constructor(ReadableStream stream);
 
-    // FIXME: Promise<ReadableStreamReadResult> read(ArrayBufferView view);
+    // FIXME: This should accept an ArrayBufferView
+    Promise<ReadableStreamReadResult> read(any view);
+
     undefined releaseLock();
 };
 ReadableStreamBYOBReader includes ReadableStreamGenericReader;