LibWeb: Fix IDL getter for ReadableByteStreamController byobRequest

We were previously only returning the controllers current
[[byobRequest]] instead of taking into account pending pull intos.

Rename the getter function which would return the controllers
[[byobRequest]] slot to `raw_byob_request` to differentiate it from
the IDL getter.

This also leaves a FIXME for a spec step which we are also not currently
implementing correctly.

Userland/Libraries/LibWeb/Streams/AbstractOperations.cpp

@@ -505,7 +505,7 @@ void readable_byte_stream_controller_fill_head_pull_into_descriptor(ReadableByte
     VERIFY(controller.pending_pull_intos().is_empty() || &controller.pending_pull_intos().first() == &pull_into_descriptor);
 
     // 2. Assert: controller.[[byobRequest]] is null.
-    VERIFY(!controller.byob_request());
+    VERIFY(!controller.raw_byob_request());
 
     // 3. Set pullIntoDescriptor’s bytes filled to bytes filled + size.
     pull_into_descriptor.bytes_filled += size;
@@ -1057,6 +1057,38 @@ bool readable_stream_default_controller_should_call_pull(ReadableStreamDefaultCo
     return false;
 }
 
+// https://streams.spec.whatwg.org/#abstract-opdef-readablebytestreamcontrollergetbyobrequest
+JS::GCPtr<ReadableStreamBYOBRequest> readable_byte_stream_controller_get_byob_request(JS::NonnullGCPtr<ReadableByteStreamController> controller)
+{
+    auto& vm = controller->vm();
+    auto& realm = controller->realm();
+
+    // 1. If controller.[[byobRequest]] is null and controller.[[pendingPullIntos]] is not empty,
+    if (!controller->raw_byob_request() && !controller->pending_pull_intos().is_empty()) {
+        // 1. Let firstDescriptor be controller.[[pendingPullIntos]][0].
+        auto const& first_descriptor = controller->pending_pull_intos().first();
+
+        // 2. Let view be ! Construct(%Uint8Array%, « firstDescriptor’s buffer, firstDescriptor’s byte offset + firstDescriptor’s bytes filled, firstDescriptor’s byte length − firstDescriptor’s bytes filled »).
+        auto view = MUST(JS::construct(vm, *realm.intrinsics().uint8_array_constructor(), first_descriptor.buffer, JS::Value(first_descriptor.byte_offset + first_descriptor.bytes_filled), JS::Value(first_descriptor.byte_length - first_descriptor.bytes_filled)));
+
+        // 3. Let byobRequest be a new ReadableStreamBYOBRequest.
+        auto byob_request = realm.heap().allocate<ReadableStreamBYOBRequest>(realm, realm);
+
+        // 4. Set byobRequest.[[controller]] to controller.
+        byob_request->set_controller(controller);
+
+        // 5. Set byobRequest.[[view]] to view.
+        auto array_buffer_view = vm.heap().allocate<WebIDL::ArrayBufferView>(realm, view);
+        byob_request->set_view(array_buffer_view);
+
+        // 6. Set controller.[[byobRequest]] to byobRequest.
+        controller->set_byob_request(byob_request);
+    }
+
+    // 2. Return controller.[[byobRequest]].
+    return controller->raw_byob_request();
+}
+
 // https://streams.spec.whatwg.org/#readable-stream-default-controller-clear-algorithms
 void readable_stream_default_controller_clear_algorithms(ReadableStreamDefaultController& controller)
 {
@@ -1813,7 +1845,8 @@ WebIDL::ExceptionOr<void> readable_stream_enqueue(ReadableStreamController& cont
         // FIXME: 2. Assert: chunk is an ArrayBufferView.
 
         // 3. Let byobView be the current BYOB request view for stream.
-        auto byob_view = readable_byte_controller->byob_request();
+        // FIXME: This is not what the spec means by 'current BYOB request view'
+        auto byob_view = readable_byte_controller->raw_byob_request();
 
         // 4. If byobView is non-null, and chunk.[[ViewedArrayBuffer]] is byobView.[[ViewedArrayBuffer]], then:
         if (byob_view) {
@@ -2112,7 +2145,7 @@ WebIDL::ExceptionOr<void> readable_byte_stream_controller_enqueue_cloned_chunk_t
 PullIntoDescriptor readable_byte_stream_controller_shift_pending_pull_into(ReadableByteStreamController& controller)
 {
     // 1. Assert: controller.[[byobRequest]] is null.
-    VERIFY(!controller.byob_request());
+    VERIFY(!controller.raw_byob_request());
 
     // 2. Let descriptor be controller.[[pendingPullIntos]][0].
     // 3. Remove descriptor from controller.[[pendingPullIntos]].

Userland/Libraries/LibWeb/Streams/AbstractOperations.h

@@ -78,6 +78,7 @@ WebIDL::ExceptionOr<void> set_up_readable_stream_default_controller_from_underly
 WebIDL::ExceptionOr<void> set_up_readable_stream_controller_with_byte_reading_support(ReadableStream&, Optional<PullAlgorithm>&& = {}, Optional<CancelAlgorithm>&& = {}, double high_water_mark = 0);
 WebIDL::ExceptionOr<void> set_up_readable_byte_stream_controller(ReadableStream&, ReadableByteStreamController&, StartAlgorithm&&, PullAlgorithm&&, CancelAlgorithm&&, double high_water_mark, JS::Value auto_allocate_chunk_size);
 WebIDL::ExceptionOr<void> set_up_readable_byte_stream_controller_from_underlying_source(ReadableStream&, JS::Value underlying_source, UnderlyingSource const& underlying_source_dict, double high_water_mark);
+JS::GCPtr<ReadableStreamBYOBRequest> readable_byte_stream_controller_get_byob_request(JS::NonnullGCPtr<ReadableByteStreamController>);
 
 WebIDL::ExceptionOr<void> readable_stream_enqueue(ReadableStreamController& controller, JS::Value chunk);
 WebIDL::ExceptionOr<void> readable_byte_stream_controller_enqueue(ReadableByteStreamController& controller, JS::Value chunk);

Userland/Libraries/LibWeb/Streams/ReadableByteStreamController.cpp

@@ -6,6 +6,7 @@
  */
 
 #include <LibWeb/Bindings/Intrinsics.h>
+#include <LibWeb/Streams/AbstractOperations.h>
 #include <LibWeb/Streams/ReadableByteStreamController.h>
 #include <LibWeb/Streams/ReadableStream.h>
 #include <LibWeb/Streams/ReadableStreamBYOBRequest.h>
@@ -22,6 +23,13 @@ Optional<double> ReadableByteStreamController::desired_size() const
     return readable_byte_stream_controller_get_desired_size(*this);
 }
 
+// https://streams.spec.whatwg.org/#rbs-controller-byob-request
+JS::GCPtr<ReadableStreamBYOBRequest> ReadableByteStreamController::byob_request()
+{
+    // 1. Return ! ReadableByteStreamControllerGetBYOBRequest(this).
+    return readable_byte_stream_controller_get_byob_request(*this);
+}
+
 // https://streams.spec.whatwg.org/#rbs-controller-close
 WebIDL::ExceptionOr<void> ReadableByteStreamController::close()
 {

Userland/Libraries/LibWeb/Streams/ReadableByteStreamController.h

@@ -77,10 +77,15 @@ class ReadableByteStreamController : public Bindings::PlatformObject {
 public:
     virtual ~ReadableByteStreamController() override = default;
 
-    JS::GCPtr<ReadableStreamBYOBRequest const> byob_request() const { return m_byob_request; }
-    JS::GCPtr<ReadableStreamBYOBRequest> byob_request() { return m_byob_request; }
+    // IDL getter, returns current [[byobRequest]] (if any), and otherwise the [[byobRequest]] for the next pending pull into request
+    JS::GCPtr<ReadableStreamBYOBRequest> byob_request();
+
     void set_byob_request(JS::GCPtr<ReadableStreamBYOBRequest> request) { m_byob_request = request; }
 
+    // Raw [[byobRequest]] slot
+    JS::GCPtr<ReadableStreamBYOBRequest const> raw_byob_request() const { return m_byob_request; }
+    JS::GCPtr<ReadableStreamBYOBRequest> raw_byob_request() { return m_byob_request; }
+
     Optional<double> desired_size() const;
     WebIDL::ExceptionOr<void> close();
     void error(JS::Value error);