LibWeb: Implement WritableStream.getWriter()

Userland/Libraries/LibWeb/Streams/AbstractOperations.cpp

@@ -738,6 +738,21 @@ WebIDL::ExceptionOr<void> set_up_readable_stream_default_controller_from_underly
     return set_up_readable_stream_default_controller(stream, controller, move(start_algorithm), move(pull_algorithm), move(cancel_algorithm), high_water_mark, move(size_algorithm));
 }
 
+// https://streams.spec.whatwg.org/#acquire-writable-stream-default-writer
+WebIDL::ExceptionOr<JS::NonnullGCPtr<WritableStreamDefaultWriter>> acquire_writable_stream_default_writer(WritableStream& stream)
+{
+    auto& realm = stream.realm();
+
+    // 1. Let writer be a new WritableStreamDefaultWriter.
+    auto writer = MUST_OR_THROW_OOM(stream.heap().allocate<WritableStreamDefaultWriter>(realm, realm));
+
+    // 2. Perform ? SetUpWritableStreamDefaultWriter(writer, stream).
+    TRY(set_up_writable_stream_default_writer(*writer, stream));
+
+    // 3. Return writer.
+    return writer;
+}
+
 // https://streams.spec.whatwg.org/#is-writable-stream-locked
 bool is_writable_stream_locked(WritableStream const& stream)
 {

Userland/Libraries/LibWeb/Streams/AbstractOperations.h

@@ -53,6 +53,7 @@ bool readable_stream_default_controller_can_close_or_enqueue(ReadableStreamDefau
 WebIDL::ExceptionOr<void> set_up_readable_stream_default_controller(ReadableStream&, ReadableStreamDefaultController&, StartAlgorithm&&, PullAlgorithm&&, CancelAlgorithm&&, double high_water_mark, SizeAlgorithm&&);
 WebIDL::ExceptionOr<void> set_up_readable_stream_default_controller_from_underlying_source(ReadableStream&, JS::Value underlying_source_value, UnderlyingSource, double high_water_mark, SizeAlgorithm&&);
 
+WebIDL::ExceptionOr<JS::NonnullGCPtr<WritableStreamDefaultWriter>> acquire_writable_stream_default_writer(WritableStream&);
 bool is_writable_stream_locked(WritableStream const&);
 WebIDL::ExceptionOr<void> set_up_writable_stream_default_writer(WritableStreamDefaultWriter&, WritableStream&);
 WebIDL::ExceptionOr<JS::NonnullGCPtr<WebIDL::Promise>> writable_stream_close(WritableStream&);

Userland/Libraries/LibWeb/Streams/WritableStream.cpp

@@ -76,6 +76,13 @@ WebIDL::ExceptionOr<JS::GCPtr<JS::Object>> WritableStream::close()
     return TRY(writable_stream_close(*this))->promise();
 }
 
+// https://streams.spec.whatwg.org/#ws-get-writer
+WebIDL::ExceptionOr<JS::NonnullGCPtr<WritableStreamDefaultWriter>> WritableStream::get_writer()
+{
+    // 1. Return ? AcquireWritableStreamDefaultWriter(this).
+    return acquire_writable_stream_default_writer(*this);
+}
+
 WritableStream::WritableStream(JS::Realm& realm)
     : Bindings::PlatformObject(realm)
 {

Userland/Libraries/LibWeb/Streams/WritableStream.h

@@ -48,6 +48,7 @@ public:
 
     bool locked() const;
     WebIDL::ExceptionOr<JS::GCPtr<JS::Object>> close();
+    WebIDL::ExceptionOr<JS::NonnullGCPtr<WritableStreamDefaultWriter>> get_writer();
 
     bool backpressure() const { return m_backpressure; }
     void set_backpressure(bool value) { m_backpressure = value; }

Userland/Libraries/LibWeb/Streams/WritableStream.idl

@@ -1,3 +1,5 @@
+#import <Streams/WritableStreamDefaultWriter.idl>
+
 [Exposed=*, Transferable]
 interface WritableStream {
     // FIXME: optional QueuingStrategy strategy = {}
@@ -7,7 +9,7 @@ interface WritableStream {
 
     // FIXME:
     // Promise<undefined> abort(optional any reason);
-    // WritableStreamDefaultWriter getWriter();
 
     Promise<undefined> close();
+    WritableStreamDefaultWriter getWriter();
 };