LibWeb: Implement ReadableStream's async iterator

Libraries/LibWeb/CMakeLists.txt

@@ -743,6 +743,7 @@ set(SOURCES
     Streams/GenericTransformStream.cpp
     Streams/ReadableByteStreamController.cpp
     Streams/ReadableStream.cpp
+    Streams/ReadableStreamAsyncIterator.cpp
     Streams/ReadableStreamBYOBReader.cpp
     Streams/ReadableStreamBYOBRequest.cpp
     Streams/ReadableStreamDefaultController.cpp

Libraries/LibWeb/Forward.h

@@ -786,6 +786,7 @@ class ByteLengthQueuingStrategy;
 class CountQueuingStrategy;
 class ReadableByteStreamController;
 class ReadableStream;
+class ReadableStreamAsyncIterator;
 class ReadableStreamBYOBReader;
 class ReadableStreamBYOBRequest;
 class ReadableStreamDefaultController;

Libraries/LibWeb/Streams/ReadableStream.idl

@@ -24,8 +24,13 @@ dictionary ReadableStreamGetReaderOptions {
     ReadableStreamReaderMode mode;
 };
 
+// https://streams.spec.whatwg.org/#dictdef-readablestreamiteratoroptions
+dictionary ReadableStreamIteratorOptions {
+    boolean preventCancel = false;
+};
+
 // https://streams.spec.whatwg.org/#readablestream
-[Exposed=*, Transferable]
+[Exposed=*, Transferable, DefinesAsyncIteratorReturn]
 interface ReadableStream {
     constructor(optional object underlyingSource, optional QueuingStrategy strategy = {});
 
@@ -39,7 +44,7 @@ interface ReadableStream {
     Promise<undefined> pipeTo(WritableStream destination, optional StreamPipeOptions options = {});
     sequence<ReadableStream> tee();
 
-    // FIXME: async iterable<any>(optional ReadableStreamIteratorOptions options = {});
+    async iterable<any>(optional ReadableStreamIteratorOptions options = {});
 };
 
 typedef (ReadableStreamDefaultReader or ReadableStreamBYOBReader) ReadableStreamReader;

Libraries/LibWeb/Streams/ReadableStreamAsyncIterator.cpp

@@ -0,0 +1,169 @@
+/*
+ * Copyright (c) 2025, Tim Flynn <trflynn89@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/Bindings/Intrinsics.h>
+#include <LibWeb/Bindings/ReadableStreamAsyncIteratorPrototype.h>
+#include <LibWeb/Streams/AbstractOperations.h>
+#include <LibWeb/Streams/ReadableStream.h>
+#include <LibWeb/Streams/ReadableStreamAsyncIterator.h>
+#include <LibWeb/Streams/ReadableStreamDefaultReader.h>
+
+namespace Web::Bindings {
+
+template<>
+void Intrinsics::create_web_prototype_and_constructor<ReadableStreamAsyncIteratorPrototype>(JS::Realm& realm)
+{
+    auto prototype = realm.create<ReadableStreamAsyncIteratorPrototype>(realm);
+    m_prototypes.set("ReadableStreamAsyncIterator"_fly_string, prototype);
+}
+
+}
+
+namespace Web::Streams {
+
+GC_DEFINE_ALLOCATOR(ReadableStreamAsyncIterator);
+
+// https://streams.spec.whatwg.org/#ref-for-asynchronous-iterator-initialization-steps
+WebIDL::ExceptionOr<GC::Ref<ReadableStreamAsyncIterator>> ReadableStreamAsyncIterator::create(JS::Realm& realm, JS::Object::PropertyKind kind, ReadableStream& stream, ReadableStreamIteratorOptions options)
+{
+    // 1. Let reader be ? AcquireReadableStreamDefaultReader(stream).
+    // 2. Set iterator’s reader to reader.
+    auto reader = TRY(acquire_readable_stream_default_reader(stream));
+
+    // 3. Let preventCancel be args[0]["preventCancel"].
+    // 4. Set iterator’s prevent cancel to preventCancel.
+    auto prevent_cancel = options.prevent_cancel;
+
+    return realm.create<ReadableStreamAsyncIterator>(realm, kind, reader, prevent_cancel);
+}
+
+ReadableStreamAsyncIterator::ReadableStreamAsyncIterator(JS::Realm& realm, JS::Object::PropertyKind kind, GC::Ref<ReadableStreamDefaultReader> reader, bool prevent_cancel)
+    : AsyncIterator(realm, kind)
+    , m_reader(reader)
+    , m_prevent_cancel(prevent_cancel)
+{
+}
+
+ReadableStreamAsyncIterator::~ReadableStreamAsyncIterator() = default;
+
+void ReadableStreamAsyncIterator::initialize(JS::Realm& realm)
+{
+    Base::initialize(realm);
+    WEB_SET_PROTOTYPE_FOR_INTERFACE(ReadableStreamAsyncIterator);
+}
+
+void ReadableStreamAsyncIterator::visit_edges(JS::Cell::Visitor& visitor)
+{
+    Base::visit_edges(visitor);
+    visitor.visit(m_reader);
+}
+
+class ReadableStreamAsyncIteratorReadRequest final : public ReadRequest {
+    GC_CELL(ReadableStreamAsyncIteratorReadRequest, ReadRequest);
+    GC_DECLARE_ALLOCATOR(ReadableStreamAsyncIteratorReadRequest);
+
+public:
+    ReadableStreamAsyncIteratorReadRequest(JS::Realm& realm, ReadableStreamDefaultReader& reader, WebIDL::Promise& promise)
+        : m_realm(realm)
+        , m_reader(reader)
+        , m_promise(promise)
+    {
+    }
+
+    // chunk steps, given chunk
+    virtual void on_chunk(JS::Value chunk) override
+    {
+        // 1. Resolve promise with chunk.
+        WebIDL::resolve_promise(m_realm, m_promise, chunk);
+    }
+
+    // close steps
+    virtual void on_close() override
+    {
+        // 1. Perform ! ReadableStreamDefaultReaderRelease(reader).
+        readable_stream_default_reader_release(m_reader);
+
+        // 2. Resolve promise with end of iteration.
+        WebIDL::resolve_promise(m_realm, m_promise, JS::js_special_empty_value());
+    }
+
+    // error steps, given e
+    virtual void on_error(JS::Value error) override
+    {
+        // 1. Perform ! ReadableStreamDefaultReaderRelease(reader).
+        readable_stream_default_reader_release(m_reader);
+
+        // 2. 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_reader);
+        visitor.visit(m_promise);
+    }
+
+    GC::Ref<JS::Realm> m_realm;
+    GC::Ref<ReadableStreamDefaultReader> m_reader;
+    GC::Ref<WebIDL::Promise> m_promise;
+};
+
+GC_DEFINE_ALLOCATOR(ReadableStreamAsyncIteratorReadRequest);
+
+// https://streams.spec.whatwg.org/#ref-for-dfn-get-the-next-iteration-result
+GC::Ref<WebIDL::Promise> ReadableStreamAsyncIterator::next_iteration_result(JS::Realm& realm)
+{
+    // 1. Let reader be iterator’s reader.
+    // 2. Assert: reader.[[stream]] is not undefined.
+    VERIFY(m_reader->stream());
+
+    // 3. Let promise be a new promise.
+    auto promise = WebIDL::create_promise(realm);
+
+    // 4. Let readRequest be a new read request with the following items:
+    auto read_request = heap().allocate<ReadableStreamAsyncIteratorReadRequest>(realm, m_reader, promise);
+
+    // 5. Perform ! ReadableStreamDefaultReaderRead(this, readRequest).
+    readable_stream_default_reader_read(m_reader, read_request);
+
+    // 6. Return promise.
+    return promise;
+}
+
+// https://streams.spec.whatwg.org/#ref-for-asynchronous-iterator-return
+GC::Ref<WebIDL::Promise> ReadableStreamAsyncIterator::iterator_return(JS::Realm& realm, JS::Value arg)
+{
+    // 1. Let reader be iterator’s reader.
+    // 2. Assert: reader.[[stream]] is not undefined.
+    VERIFY(m_reader->stream());
+
+    // 3. Assert: reader.[[readRequests]] is empty, as the async iterator machinery guarantees that any previous calls
+    //    to next() have settled before this is called.
+    VERIFY(m_reader->read_requests().is_empty());
+
+    // 4. If iterator’s prevent cancel is false:
+    if (!m_prevent_cancel) {
+        // 1. Let result be ! ReadableStreamReaderGenericCancel(reader, arg).
+        auto result = readable_stream_reader_generic_cancel(m_reader, arg);
+
+        // 2. Perform ! ReadableStreamDefaultReaderRelease(reader).
+        readable_stream_default_reader_release(m_reader);
+
+        // 3. Return result.
+        return result;
+    }
+
+    // 5. Perform ! ReadableStreamDefaultReaderRelease(reader).
+    readable_stream_default_reader_release(m_reader);
+
+    // 6. Return a promise resolved with undefined.
+    return WebIDL::create_resolved_promise(realm, JS::js_undefined());
+}
+
+}

Libraries/LibWeb/Streams/ReadableStreamAsyncIterator.h

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2025, Tim Flynn <trflynn89@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/Bindings/PlatformObject.h>
+#include <LibWeb/Forward.h>
+#include <LibWeb/WebIDL/AsyncIterator.h>
+
+namespace Web::Streams {
+
+// https://streams.spec.whatwg.org/#dictdef-readablestreamiteratoroptions
+struct ReadableStreamIteratorOptions {
+    bool prevent_cancel { false };
+};
+
+class ReadableStreamAsyncIterator final : public WebIDL::AsyncIterator {
+    WEB_PLATFORM_OBJECT(ReadableStreamAsyncIterator, WebIDL::AsyncIterator);
+    GC_DECLARE_ALLOCATOR(ReadableStreamAsyncIterator);
+
+public:
+    static WebIDL::ExceptionOr<GC::Ref<ReadableStreamAsyncIterator>> create(JS::Realm&, JS::Object::PropertyKind, ReadableStream&, ReadableStreamIteratorOptions);
+
+    virtual ~ReadableStreamAsyncIterator() override;
+
+private:
+    ReadableStreamAsyncIterator(JS::Realm&, JS::Object::PropertyKind, GC::Ref<ReadableStreamDefaultReader>, bool prevent_cancel);
+
+    virtual void initialize(JS::Realm&) override;
+    virtual void visit_edges(Cell::Visitor&) override;
+
+    virtual GC::Ref<WebIDL::Promise> next_iteration_result(JS::Realm&) override;
+    virtual GC::Ref<WebIDL::Promise> iterator_return(JS::Realm&, JS::Value) override;
+
+    GC::Ref<ReadableStreamDefaultReader> m_reader;
+    bool m_prevent_cancel { false };
+};
+
+}

Libraries/LibWeb/idl_files.cmake

@@ -297,7 +297,7 @@ libweb_js_bindings(ServiceWorker/ServiceWorkerRegistration)
 libweb_js_bindings(Streams/ByteLengthQueuingStrategy)
 libweb_js_bindings(Streams/CountQueuingStrategy)
 libweb_js_bindings(Streams/ReadableByteStreamController)
-libweb_js_bindings(Streams/ReadableStream)
+libweb_js_bindings(Streams/ReadableStream ASYNC_ITERABLE)
 libweb_js_bindings(Streams/ReadableStreamBYOBReader)
 libweb_js_bindings(Streams/ReadableStreamBYOBRequest)
 libweb_js_bindings(Streams/ReadableStreamDefaultController)

Tests/LibWeb/Text/expected/wpt-import/streams/idlharness.any.txt

@@ -2,8 +2,7 @@ Harness status: OK
 
 Found 229 tests
 
-228 Pass
+229 Pass
-1 Fail
 Pass	idl_test setup
 Pass	idl_test validation
 Pass	ReadableStreamDefaultReader includes ReadableStreamGenericReader: member names are unique
@@ -21,7 +20,7 @@ Pass	ReadableStream interface: operation getReader(optional ReadableStreamGetRea
 Pass	ReadableStream interface: operation pipeThrough(ReadableWritablePair, optional StreamPipeOptions)
 Pass	ReadableStream interface: operation pipeTo(WritableStream, optional StreamPipeOptions)
 Pass	ReadableStream interface: operation tee()
-Fail	ReadableStream interface: async iterable<any>
+Pass	ReadableStream interface: async iterable<any>
 Pass	ReadableStream must be primary interface of new ReadableStream()
 Pass	Stringification of new ReadableStream()
 Pass	ReadableStream interface: new ReadableStream() must inherit property "from(any)" with the proper type

Tests/LibWeb/Text/expected/wpt-import/streams/readable-streams/async-iterator.any.txt

@@ -2,45 +2,46 @@ Harness status: OK
 
 Found 41 tests
 
-41 Fail
+36 Pass
-Fail	Async iterator instances should have the correct list of properties
+5 Fail
-Fail	Async-iterating a push source
+Pass	Async iterator instances should have the correct list of properties
-Fail	Async-iterating a pull source
+Pass	Async-iterating a push source
-Fail	Async-iterating a push source with undefined values
+Pass	Async-iterating a pull source
-Fail	Async-iterating a pull source with undefined values
+Pass	Async-iterating a push source with undefined values
-Fail	Async-iterating a pull source manually
+Pass	Async-iterating a pull source with undefined values
-Fail	Async-iterating an errored stream throws
+Pass	Async-iterating a pull source manually
-Fail	Async-iterating a closed stream never executes the loop body, but works fine
+Pass	Async-iterating an errored stream throws
-Fail	Async-iterating an empty but not closed/errored stream never executes the loop body and stalls the async function
+Pass	Async-iterating a closed stream never executes the loop body, but works fine
-Fail	Async-iterating a partially consumed stream
+Pass	Async-iterating an empty but not closed/errored stream never executes the loop body and stalls the async function
+Pass	Async-iterating a partially consumed stream
 Fail	Cancellation behavior when throwing inside loop body; preventCancel = false
-Fail	Cancellation behavior when throwing inside loop body; preventCancel = true
+Pass	Cancellation behavior when throwing inside loop body; preventCancel = true
 Fail	Cancellation behavior when breaking inside loop body; preventCancel = false
-Fail	Cancellation behavior when breaking inside loop body; preventCancel = true
+Pass	Cancellation behavior when breaking inside loop body; preventCancel = true
 Fail	Cancellation behavior when returning inside loop body; preventCancel = false
-Fail	Cancellation behavior when returning inside loop body; preventCancel = true
+Pass	Cancellation behavior when returning inside loop body; preventCancel = true
-Fail	Cancellation behavior when manually calling return(); preventCancel = false
+Pass	Cancellation behavior when manually calling return(); preventCancel = false
-Fail	Cancellation behavior when manually calling return(); preventCancel = true
+Pass	Cancellation behavior when manually calling return(); preventCancel = true
-Fail	next() rejects if the stream errors
+Pass	next() rejects if the stream errors
-Fail	return() does not rejects if the stream has not errored yet
+Pass	return() does not rejects if the stream has not errored yet
-Fail	return() rejects if the stream has errored
+Pass	return() rejects if the stream has errored
-Fail	next() that succeeds; next() that reports an error; next()
+Pass	next() that succeeds; next() that reports an error; next()
-Fail	next() that succeeds; next() that reports an error(); next() [no awaiting]
+Pass	next() that succeeds; next() that reports an error(); next() [no awaiting]
-Fail	next() that succeeds; next() that reports an error(); return()
+Pass	next() that succeeds; next() that reports an error(); return()
-Fail	next() that succeeds; next() that reports an error(); return() [no awaiting]
+Pass	next() that succeeds; next() that reports an error(); return() [no awaiting]
-Fail	next() that succeeds; return()
+Pass	next() that succeeds; return()
-Fail	next() that succeeds; return() [no awaiting]
+Pass	next() that succeeds; return() [no awaiting]
-Fail	return(); next()
+Pass	return(); next()
-Fail	return(); next() [no awaiting]
+Pass	return(); next() [no awaiting]
-Fail	return(); next() with delayed cancel()
+Pass	return(); next() with delayed cancel()
-Fail	return(); next() with delayed cancel() [no awaiting]
+Pass	return(); next() with delayed cancel() [no awaiting]
-Fail	return(); return()
+Pass	return(); return()
-Fail	return(); return() [no awaiting]
+Pass	return(); return() [no awaiting]
-Fail	values() throws if there's already a lock
+Pass	values() throws if there's already a lock
-Fail	Acquiring a reader after exhaustively async-iterating a stream
+Pass	Acquiring a reader after exhaustively async-iterating a stream
-Fail	Acquiring a reader after return()ing from a stream that errors
+Pass	Acquiring a reader after return()ing from a stream that errors
 Fail	Acquiring a reader after partially async-iterating a stream
 Fail	Acquiring a reader and reading the remaining chunks after partially async-iterating a stream with preventCancel = true
-Fail	return() should unlock the stream synchronously when preventCancel = false
+Pass	return() should unlock the stream synchronously when preventCancel = false
-Fail	return() should unlock the stream synchronously when preventCancel = true
+Pass	return() should unlock the stream synchronously when preventCancel = true
-Fail	close() while next() is pending
+Pass	close() while next() is pending