LibWeb: Start filling out BaseAudioContext/AudioContext interfaces

- Fills out both IDLs and implements some basic attributes/methods.
- No actual audio processing yet though :^)

Userland/Libraries/LibWeb/Forward.h

@@ -27,6 +27,7 @@ namespace Web::Bindings {
 class Intrinsics;
 class OptionConstructor;
 
+enum class AudioContextLatencyCategory;
 enum class CanPlayTypeResult;
 enum class CanvasFillRule;
 enum class DOMParserSupportedType;
@@ -603,6 +604,10 @@ class Table;
 namespace Web::WebAudio {
 class AudioContext;
 class BaseAudioContext;
+
+enum class AudioContextState;
+
+struct AudioContextOptions;
 }
 
 namespace Web::WebGL {

Userland/Libraries/LibWeb/HTML/EventNames.h

@@ -84,6 +84,7 @@ namespace Web::HTML::EventNames {
     __ENUMERATE_HTML_EVENT(select)                   \
     __ENUMERATE_HTML_EVENT(slotchange)               \
     __ENUMERATE_HTML_EVENT(stalled)                  \
+    __ENUMERATE_HTML_EVENT(statechange)              \
     __ENUMERATE_HTML_EVENT(storage)                  \
     __ENUMERATE_HTML_EVENT(submit)                   \
     __ENUMERATE_HTML_EVENT(suspend)                  \

Userland/Libraries/LibWeb/WebAudio/AudioContext.cpp

@@ -5,20 +5,76 @@
  */
 
 #include <LibWeb/Bindings/Intrinsics.h>
+#include <LibWeb/DOM/Event.h>
+#include <LibWeb/HTML/HTMLMediaElement.h>
 #include <LibWeb/WebAudio/AudioContext.h>
+#include <LibWeb/WebIDL/Promise.h>
 
 namespace Web::WebAudio {
 
 // https://webaudio.github.io/web-audio-api/#dom-audiocontext-audiocontext
-WebIDL::ExceptionOr<JS::NonnullGCPtr<AudioContext>> AudioContext::construct_impl(JS::Realm& realm)
+WebIDL::ExceptionOr<JS::NonnullGCPtr<AudioContext>> AudioContext::construct_impl(JS::Realm& realm, AudioContextOptions const& context_options)
 {
-    dbgln("(STUBBED) new AudioContext()");
+    return MUST_OR_THROW_OOM(realm.heap().allocate<AudioContext>(realm, realm, context_options));
-    return MUST_OR_THROW_OOM(realm.heap().allocate<AudioContext>(realm, realm));
 }
 
-AudioContext::AudioContext(JS::Realm& realm)
+AudioContext::AudioContext(JS::Realm& realm, AudioContextOptions const& context_options)
     : BaseAudioContext(realm)
 {
+    // FIXME: If the current settings object’s responsible document is NOT fully active, throw an InvalidStateError and abort these steps.
+
+    // 1: Set a [[control thread state]] to suspended on the AudioContext.
+    BaseAudioContext::set_control_state(Bindings::AudioContextState::Suspended);
+
+    // 2: Set a [[rendering thread state]] to suspended on the AudioContext.
+    BaseAudioContext::set_rendering_state(Bindings::AudioContextState::Suspended);
+
+    // 3: Let [[pending resume promises]] be a slot on this AudioContext, that is an initially empty ordered list of promises.
+
+    // 4: If contextOptions is given, apply the options:
+    // 4.1: Set the internal latency of this AudioContext according to contextOptions.latencyHint, as described in latencyHint.
+    switch (context_options.latency_hint) {
+    case Bindings::AudioContextLatencyCategory::Balanced:
+        // FIXME: Determine optimal settings for balanced.
+        break;
+    case Bindings::AudioContextLatencyCategory::Interactive:
+        // FIXME: Determine optimal settings for interactive.
+        break;
+    case Bindings::AudioContextLatencyCategory::Playback:
+        // FIXME: Determine optimal settings for playback.
+        break;
+    default:
+        VERIFY_NOT_REACHED();
+    }
+
+    // 4.2: If contextOptions.sampleRate is specified, set the sampleRate of this AudioContext to this value. Otherwise,
+    //      use the sample rate of the default output device. If the selected sample rate differs from the sample rate of the output device,
+    //      this AudioContext MUST resample the audio output to match the sample rate of the output device.
+    if (context_options.sample_rate.has_value()) {
+        BaseAudioContext::set_sample_rate(context_options.sample_rate.value());
+    } else {
+        // FIXME: This would ideally be coming from the default output device, but we can only get this on Serenity
+        // For now we'll just have to resample
+        BaseAudioContext::set_sample_rate(44100);
+    }
+
+    // FIXME: 5: If the context is allowed to start, send a control message to start processing.
+    // FIXME: Implement control message queue to run following steps on the rendering thread
+    if (m_allowed_to_start) {
+        // FIXME: 5.1: Attempt to acquire system resources. In case of failure, abort the following steps.
+
+        // 5.2: Set the [[rendering thread state]] to "running" on the AudioContext.
+        BaseAudioContext::set_rendering_state(Bindings::AudioContextState::Running);
+
+        // 5.3: queue a media element task to execute the following steps:
+        queue_a_media_element_task([&realm, this]() {
+            // 5.3.1: Set the state attribute of the AudioContext to "running".
+            BaseAudioContext::set_control_state(Bindings::AudioContextState::Running);
+
+            // 5.3.2: queue a media element task to fire an event named statechange at the AudioContext.
+            this->dispatch_event(DOM::Event::create(realm, HTML::EventNames::statechange).release_value_but_fixme_should_propagate_errors());
+        });
+    }
 }
 
 AudioContext::~AudioContext() = default;
@@ -31,4 +87,219 @@ JS::ThrowCompletionOr<void> AudioContext::initialize(JS::Realm& realm)
     return {};
 }
 
+void AudioContext::visit_edges(Cell::Visitor& visitor)
+{
+    Base::visit_edges(visitor);
+    for (auto& promise : m_pending_promises)
+        visitor.visit(promise);
+    for (auto& promise : m_pending_resume_promises)
+        visitor.visit(promise);
+}
+
+// https://www.w3.org/TR/webaudio/#dom-audiocontext-getoutputtimestamp
+AudioTimestamp AudioContext::get_output_timestamp()
+{
+    dbgln("(STUBBED) getOutputTimestamp()");
+    return {};
+}
+
+// https://www.w3.org/TR/webaudio/#dom-audiocontext-resume
+WebIDL::ExceptionOr<JS::NonnullGCPtr<JS::Promise>> AudioContext::resume()
+{
+    auto& realm = this->realm();
+    auto& vm = realm.vm();
+
+    // FIXME: 1. If this's relevant global object's associated Document is not fully active then return a promise rejected with "InvalidStateError" DOMException.
+
+    // 2. Let promise be a new Promise.
+    auto promise = WebIDL::create_promise(realm);
+
+    // 3. If the [[control thread state]] on the AudioContext is closed reject the promise with InvalidStateError, abort these steps, returning promise.
+    if (state() == Bindings::AudioContextState::Closed) {
+        WebIDL::reject_promise(realm, promise, WebIDL::InvalidStateError::create(realm, "Audio context is already closed."));
+        return JS::NonnullGCPtr { verify_cast<JS::Promise>(*promise->promise()) };
+    }
+
+    // 4. Set [[suspended by user]] to true.
+    m_suspended_by_user = true;
+
+    // 5. If the context is not allowed to start, append promise to [[pending promises]] and [[pending resume promises]] and abort these steps, returning promise.
+    if (m_allowed_to_start) {
+        TRY_OR_THROW_OOM(vm, m_pending_promises.try_append(promise));
+        TRY_OR_THROW_OOM(vm, m_pending_resume_promises.try_append(promise));
+    }
+
+    // 6. Set the [[control thread state]] on the AudioContext to running.
+    set_control_state(Bindings::AudioContextState::Running);
+
+    // 7. Queue a control message to resume the AudioContext.
+    // FIXME: Implement control message queue to run following steps on the rendering thread
+
+    // FIXME: 7.1: Attempt to acquire system resources.
+
+    // 7.2: Set the [[rendering thread state]] on the AudioContext to running.
+    set_rendering_state(Bindings::AudioContextState::Running);
+
+    // 7.3: Start rendering the audio graph.
+    if (!start_rendering_audio_graph()) {
+        // 7.4: In case of failure, queue a media element task to execute the following steps:
+        queue_a_media_element_task([&realm, this]() {
+            // 7.4.1: Reject all promises from [[pending resume promises]] in order, then clear [[pending resume promises]].
+            for (auto const& promise : m_pending_resume_promises) {
+                WebIDL::reject_promise(realm, promise, JS::js_null());
+            }
+            m_pending_resume_promises.clear();
+
+            // FIXME: 7.4.2: Additionally, remove those promises from [[pending promises]].
+        });
+    }
+
+    // 7.5: queue a media element task to execute the following steps:
+    queue_a_media_element_task([&realm, &promise, this]() {
+        // 7.5.1: Resolve all promises from [[pending resume promises]] in order.
+        for (auto const& promise : m_pending_resume_promises) {
+            *promise->resolve();
+        }
+
+        // 7.5.2: Clear [[pending resume promises]].
+        m_pending_resume_promises.clear();
+
+        // FIXME: Additionally, remove those promises from [[pending promises]].
+
+        // 7.5.3: Resolve promise.
+        *promise->resolve();
+
+        // 7.5.4: If the state attribute of the AudioContext is not already "running":
+        if (state() != Bindings::AudioContextState::Running) {
+            // 7.5.4.1: Set the state attribute of the AudioContext to "running".
+            set_control_state(Bindings::AudioContextState::Running);
+
+            // 7.5.4.2: queue a media element task to fire an event named statechange at the AudioContext.
+            queue_a_media_element_task([&realm, this]() {
+                this->dispatch_event(DOM::Event::create(realm, HTML::EventNames::statechange).release_value_but_fixme_should_propagate_errors());
+            });
+        }
+    });
+
+    // 8. Return promise.
+    return JS::NonnullGCPtr { verify_cast<JS::Promise>(*promise->promise()) };
+}
+
+// https://www.w3.org/TR/webaudio/#dom-audiocontext-suspend
+WebIDL::ExceptionOr<JS::NonnullGCPtr<JS::Promise>> AudioContext::suspend()
+{
+    auto& realm = this->realm();
+    auto& vm = realm.vm();
+
+    // FIXME: 1. If this's relevant global object's associated Document is not fully active then return a promise rejected with "InvalidStateError" DOMException.
+
+    // 2. Let promise be a new Promise.
+    auto promise = WebIDL::create_promise(realm);
+
+    // 3. If the [[control thread state]] on the AudioContext is closed reject the promise with InvalidStateError, abort these steps, returning promise.
+    if (state() == Bindings::AudioContextState::Closed) {
+        WebIDL::reject_promise(realm, promise, WebIDL::InvalidStateError::create(realm, "Audio context is already closed."));
+        return JS::NonnullGCPtr { verify_cast<JS::Promise>(*promise->promise()) };
+    }
+
+    // 4. Append promise to [[pending promises]].
+    TRY_OR_THROW_OOM(vm, m_pending_promises.try_append(promise));
+
+    // 5. Set [[suspended by user]] to true.
+    m_suspended_by_user = true;
+
+    // 6. Set the [[control thread state]] on the AudioContext to suspended.
+    set_control_state(Bindings::AudioContextState::Suspended);
+
+    // 7. Queue a control message to suspend the AudioContext.
+    // FIXME: Implement control message queue to run following steps on the rendering thread
+
+    // FIXME: 7.1: Attempt to release system resources.
+
+    // 7.2: Set the [[rendering thread state]] on the AudioContext to suspended.
+    set_rendering_state(Bindings::AudioContextState::Suspended);
+
+    // 7.3: queue a media element task to execute the following steps:
+    queue_a_media_element_task([&realm, &promise, this]() {
+        // 7.3.1: Resolve promise.
+        *promise->resolve();
+
+        // 7.3.2: If the state attribute of the AudioContext is not already "suspended":
+        if (state() != Bindings::AudioContextState::Suspended) {
+            // 7.3.2.1: Set the state attribute of the AudioContext to "suspended".
+            set_control_state(Bindings::AudioContextState::Suspended);
+
+            // 7.3.2.2: queue a media element task to fire an event named statechange at the AudioContext.
+            queue_a_media_element_task([&realm, this]() {
+                this->dispatch_event(DOM::Event::create(realm, HTML::EventNames::statechange).release_value_but_fixme_should_propagate_errors());
+            });
+        }
+    });
+
+    // 8. Return promise.
+    return JS::NonnullGCPtr { verify_cast<JS::Promise>(*promise->promise()) };
+}
+
+// https://www.w3.org/TR/webaudio/#dom-audiocontext-close
+WebIDL::ExceptionOr<JS::NonnullGCPtr<JS::Promise>> AudioContext::close()
+{
+    auto& realm = this->realm();
+
+    // FIXME: 1. If this's relevant global object's associated Document is not fully active then return a promise rejected with "InvalidStateError" DOMException.
+
+    // 2. Let promise be a new Promise.
+    auto promise = WebIDL::create_promise(realm);
+
+    // 3. If the [[control thread state]] flag on the AudioContext is closed reject the promise with InvalidStateError, abort these steps, returning promise.
+    if (state() == Bindings::AudioContextState::Closed) {
+        WebIDL::reject_promise(realm, promise, WebIDL::InvalidStateError::create(realm, "Audio context is already closed."));
+        return JS::NonnullGCPtr { verify_cast<JS::Promise>(*promise->promise()) };
+    }
+
+    // 4. Set the [[control thread state]] flag on the AudioContext to closed.
+    set_control_state(Bindings::AudioContextState::Closed);
+
+    // 5. Queue a control message to close the AudioContext.
+    // FIXME: Implement control message queue to run following steps on the rendering thread
+
+    // FIXME: 5.1: Attempt to release system resources.
+
+    // 5.2: Set the [[rendering thread state]] to "suspended".
+    set_rendering_state(Bindings::AudioContextState::Suspended);
+
+    // FIXME: 5.3: If this control message is being run in a reaction to the document being unloaded, abort this algorithm.
+
+    // 5.4: queue a media element task to execute the following steps:
+    queue_a_media_element_task([&realm, &promise, this]() {
+        // 5.4.1: Resolve promise.
+        *promise->resolve();
+
+        // 5.4.2: If the state attribute of the AudioContext is not already "closed":
+        if (state() != Bindings::AudioContextState::Closed) {
+            // 5.4.2.1: Set the state attribute of the AudioContext to "closed".
+            set_control_state(Bindings::AudioContextState::Closed);
+        }
+
+        // 5.4.2.2: queue a media element task to fire an event named statechange at the AudioContext.
+        // FIXME: Attempting to queue another task in here causes an assertion fail at Vector.h:148
+        this->dispatch_event(DOM::Event::create(realm, HTML::EventNames::statechange).release_value_but_fixme_should_propagate_errors());
+    });
+
+    // 6. Return promise
+    return JS::NonnullGCPtr { verify_cast<JS::Promise>(*promise->promise()) };
+}
+
+void AudioContext::queue_a_media_element_task(JS::SafeFunction<void()> steps)
+{
+    auto task = HTML::Task::create(m_media_element_event_task_source.source, HTML::current_settings_object().responsible_document(), move(steps));
+    HTML::main_thread_event_loop().task_queue().add(move(task));
+}
+
+// FIXME: Actually implement the rendering thread
+bool AudioContext::start_rendering_audio_graph()
+{
+    bool render_result = true;
+    return render_result;
+}
+
 }

Userland/Libraries/LibWeb/WebAudio/AudioContext.h

@@ -6,23 +6,55 @@
 
 #pragma once
 
+#include <LibWeb/Bindings/AudioContextPrototype.h>
+#include <LibWeb/HighResolutionTime/DOMHighResTimeStamp.h>
 #include <LibWeb/WebAudio/BaseAudioContext.h>
 
 namespace Web::WebAudio {
 
+struct AudioContextOptions {
+    Bindings::AudioContextLatencyCategory latency_hint = Bindings::AudioContextLatencyCategory::Interactive;
+    Optional<float> sample_rate;
+};
+
+struct AudioTimestamp {
+    double context_time { 0 };
+    double performance_time { 0 };
+};
+
 // https://webaudio.github.io/web-audio-api/#AudioContext
 class AudioContext final : public BaseAudioContext {
     WEB_PLATFORM_OBJECT(AudioContext, BaseAudioContext);
 
 public:
-    static WebIDL::ExceptionOr<JS::NonnullGCPtr<AudioContext>> construct_impl(JS::Realm&);
+    static WebIDL::ExceptionOr<JS::NonnullGCPtr<AudioContext>> construct_impl(JS::Realm&, AudioContextOptions const& context_options = {});
 
     virtual ~AudioContext() override;
 
+    double base_latency() const { return m_base_latency; };
+    double output_latency() const { return m_output_latency; };
+    AudioTimestamp get_output_timestamp();
+    WebIDL::ExceptionOr<JS::NonnullGCPtr<JS::Promise>> resume();
+    WebIDL::ExceptionOr<JS::NonnullGCPtr<JS::Promise>> suspend();
+    WebIDL::ExceptionOr<JS::NonnullGCPtr<JS::Promise>> close();
+
 private:
-    explicit AudioContext(JS::Realm&);
+    explicit AudioContext(JS::Realm&, AudioContextOptions const& context_options);
 
     virtual JS::ThrowCompletionOr<void> initialize(JS::Realm&) override;
+    virtual void visit_edges(Cell::Visitor&) override;
+
+    double m_base_latency { 0 };
+    double m_output_latency { 0 };
+
+    bool m_allowed_to_start = true;
+    Vector<JS::NonnullGCPtr<WebIDL::Promise>> m_pending_promises;
+    Vector<JS::NonnullGCPtr<WebIDL::Promise>> m_pending_resume_promises;
+    bool m_suspended_by_user = false;
+    HTML::UniqueTaskSource m_media_element_event_task_source {};
+
+    void queue_a_media_element_task(JS::SafeFunction<void()> steps);
+    bool start_rendering_audio_graph();
 };
 
 }

Userland/Libraries/LibWeb/WebAudio/AudioContext.idl

@@ -1,8 +1,31 @@
 #import <WebAudio/BaseAudioContext.idl>
 
+// https://www.w3.org/TR/webaudio/#enumdef-audiocontextlatencycategory
+enum AudioContextLatencyCategory { "balanced", "interactive", "playback" };
+
 // https://webaudio.github.io/web-audio-api/#AudioContext
 [Exposed=Window]
 interface AudioContext : BaseAudioContext {
-    // FIXME: Should be constructor (optional AudioContextOptions contextOptions = {});
+    constructor(optional AudioContextOptions contextOptions = {});
-    constructor();
+    readonly attribute double baseLatency;
+    readonly attribute double outputLatency;
+    AudioTimestamp getOutputTimestamp ();
+    Promise<undefined> resume ();
+    Promise<undefined> suspend ();
+    Promise<undefined> close ();
+    // FIXME: MediaElementAudioSourceNode createMediaElementSource (HTMLMediaElement mediaElement);
+    // FIXME: MediaStreamAudioSourceNode createMediaStreamSource (MediaStream mediaStream);
+    // FIXME: MediaStreamTrackAudioSourceNode createMediaStreamTrackSource (MediaStreamTrack mediaStreamTrack);
+    // FIXME: MediaStreamAudioDestinationNode createMediaStreamDestination ();
+};
+
+dictionary AudioContextOptions {
+  AudioContextLatencyCategory latencyHint = "interactive";
+  float sampleRate;
+};
+
+dictionary AudioTimestamp {
+  double contextTime;
+  // FIXME: Should be DOMHighResTimeStamp, but DOMHighResTimeStamp doesn't get parsed as a double during codegen
+  double performanceTime;
 };

Userland/Libraries/LibWeb/WebAudio/BaseAudioContext.cpp

@@ -5,6 +5,7 @@
  */
 
 #include <LibWeb/Bindings/Intrinsics.h>
+#include <LibWeb/HTML/EventNames.h>
 #include <LibWeb/WebAudio/BaseAudioContext.h>
 
 namespace Web::WebAudio {
@@ -24,4 +25,14 @@ JS::ThrowCompletionOr<void> BaseAudioContext::initialize(JS::Realm& realm)
     return {};
 }
 
+void BaseAudioContext::set_onstatechange(WebIDL::CallbackType* event_handler)
+{
+    set_event_handler_attribute(HTML::EventNames::statechange, event_handler);
+}
+
+WebIDL::CallbackType* BaseAudioContext::onstatechange()
+{
+    return event_handler_attribute(HTML::EventNames::statechange);
+}
+
 }

Userland/Libraries/LibWeb/WebAudio/BaseAudioContext.h

@@ -6,6 +6,7 @@
 
 #pragma once
 
+#include <LibWeb/Bindings/BaseAudioContextPrototype.h>
 #include <LibWeb/DOM/EventTarget.h>
 
 namespace Web::WebAudio {
@@ -17,10 +18,28 @@ class BaseAudioContext : public DOM::EventTarget {
 public:
     virtual ~BaseAudioContext() override;
 
+    float sample_rate() const { return m_sample_rate; };
+    double current_time() const { return m_current_time; };
+    Bindings::AudioContextState state() const { return m_control_thread_state; };
+
+    void set_onstatechange(WebIDL::CallbackType*);
+    WebIDL::CallbackType* onstatechange();
+
+    void set_sample_rate(float sample_rate) { m_sample_rate = sample_rate; };
+    void set_control_state(Bindings::AudioContextState state) { m_control_thread_state = state; };
+    void set_rendering_state(Bindings::AudioContextState state) { m_rendering_thread_state = state; };
+
 protected:
     explicit BaseAudioContext(JS::Realm&);
 
     virtual JS::ThrowCompletionOr<void> initialize(JS::Realm&) override;
+
+private:
+    float m_sample_rate { 0 };
+    double m_current_time { 0 };
+
+    Bindings::AudioContextState m_control_thread_state = Bindings::AudioContextState::Suspended;
+    Bindings::AudioContextState m_rendering_thread_state = Bindings::AudioContextState::Suspended;
 };
 
 }

Userland/Libraries/LibWeb/WebAudio/BaseAudioContext.idl

@@ -1,6 +1,43 @@
 #import <DOM/EventTarget.idl>
+#import <DOM/EventHandler.idl>
+
+// https://www.w3.org/TR/webaudio/#enumdef-audiocontextstate
+enum AudioContextState { "suspended", "running", "closed" };
+
+// FIXME: callback DecodeErrorCallback = undefined (DOMException error);
+
+// FIXME: callback DecodeSuccessCallback = undefined (AudioBuffer decodedData);
 
 // https://webaudio.github.io/web-audio-api/#BaseAudioContext
 [Exposed=Window]
 interface BaseAudioContext : EventTarget {
+    // FIXME: readonly attribute AudioDestinationNode destination;
+    readonly attribute float sampleRate;
+    readonly attribute double currentTime;
+    // FIXME: readonly attribute AudioListener listener;
+    readonly attribute AudioContextState state;
+    // FIXME: [SameObject, SecureContext]
+    // readonly attribute AudioWorklet audioWorklet;
+    attribute EventHandler onstatechange;
+
+    // FIXME: AnalyserNode createAnalyser ();
+    // FIXME: BiquadFilterNode createBiquadFilter ();
+    // FIXME: AudioBuffer createBuffer (unsigned long numberOfChannels, unsigned long length, float sampleRate);
+    // FIXME: AudioBufferSourceNode createBufferSource ();
+    // FIXME: ChannelMergerNode createChannelMerger (optional unsigned long numberOfInputs = 6);
+    // FIXME: ChannelSplitterNode createChannelSplitter (optional unsigned long numberOfOutputs = 6);
+    // FIXME: ConstantSourceNode createConstantSource ();
+    // FIXME: ConvolverNode createConvolver ();
+    // FIXME: DelayNode createDelay (optional double maxDelayTime = 1.0);
+    // FIXME: DynamicsCompressorNode createDynamicsCompressor ();
+    // FIXME: GainNode createGain ();
+    // FIXME: IIRFilterNode createIIRFilter (sequence<double> feedforward, sequence<double> feedback);
+    // FIXME: OscillatorNode createOscillator ();
+    // FIXME: PannerNode createPanner ();
+    // FIXME: PeriodicWave createPeriodicWave (sequence<float> real, sequence<float> imag, optional PeriodicWaveConstraints constraints = {});
+    // FIXME: ScriptProcessorNode createScriptProcessor(optional unsigned long bufferSize = 0, optional unsigned long numberOfInputChannels = 2, optional unsigned long numberOfOutputChannels = 2);
+    // FIXME: StereoPannerNode createStereoPanner ();
+    // FIXME: WaveShaperNode createWaveShaper ();
+
+    // FIXME: Promise<AudioBuffer> decodeAudioData (ArrayBuffer audioData, optional DecodeSuccessCallback? successCallback, optional DecodeErrorCallback? errorCallback);
 };