LibWeb: Implement ReadableStreamBYOBReader::read

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

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()) };
+}
 }