Add decodeMetadata() method to ImageDecoder.

Allows API users with ReadableStreams as input to know when they can
start using the metadata fields on the ImageDecoder.

R=sandersd

Bug: 1073995
Change-Id: I6d32fcf7e2dda5927e62cd370c50238cb96d5074
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2254455
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Auto-Submit: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Dan Sanders <sandersd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#780531}

third_party/blink/renderer/modules/webcodecs/image_decoder.idl

@@ -23,23 +23,29 @@
   Promise<ImageFrame> decode(optional unsigned long frameIndex = 0,
                              optional boolean completeFramesOnly = true);
 
+  // Decodes only the metadata for an image; resolves the promise when metadata
+  // can be decoded. Normally this is done automatically at construction time.
+  // However when using a ReadableStream, there may not be enough data to decode
+  // metadata at the time of construction.
+  Promise<void> decodeMetadata();
+
   // The number of frames in the image.
   //
   // When decoding a ReadableStream the value will be 0 until enough data to
-  // decode the frame count has been received. If the format has no fixed count,
-  // the value will increase as frames are received by the decoder.
+  // decode metadata has been received. If the format has no fixed count, the
+  // value will increase as frames are received by the decoder.
   readonly attribute unsigned long frameCount;
 
   // The detected mime type for the decoded image.
   //
   // When decoding a ReadableStream the value will be an empty string until
-  // enough data to detect the mime type has been received.
+  // enough data to decode metadata has been received.
   readonly attribute USVString type;
 
   // The image's preferred repetition count.
   //
   // When decoding a ReadableStream the value will be 0 until enough data to
-  // decode the repetition count has been received.
+  // decode metadata has been received.
   readonly attribute unsigned long repetitionCount;
 
   // True if all available frames have been received by the decoder.

third_party/blink/renderer/modules/webcodecs/image_decoder_external.cc

@@ -88,23 +88,23 @@ ImageDecoderExternal::ImageDecoderExternal(ScriptState* script_state,
   // TODO: Data is owned by the caller who may be free to manipulate it. We will
   // probably need to make a copy to our own internal data or neuter the buffers
   // as seen by JS.
-  auto sr = SegmentReader::CreateFromSkData(
+  segment_reader_ = SegmentReader::CreateFromSkData(
       SkData::MakeWithoutCopy(buffer.Data(), buffer.ByteLengthAsSizeT()));
-  if (!sr) {
+  if (!segment_reader_) {
     exception_state.ThrowDOMException(DOMExceptionCode::kConstraintError,
                                       "Failed to read image data");
     return;
   }
 
   data_complete_ = true;
-  MaybeCreateImageDecoder(std::move(sr));
+  MaybeCreateImageDecoder();
   if (!decoder_) {
     exception_state.ThrowDOMException(DOMExceptionCode::kConstraintError,
                                       "Failed to create image decoder");
     return;
   }
 
-  UpdateFrameAndRepetitionCount();
+  MaybeUpdateMetadata();
   if (decoder_->Failed()) {
     exception_state.ThrowDOMException(DOMExceptionCode::kOperationError,
                                       "Image decoding failed");
@@ -128,6 +128,16 @@ ScriptPromise ImageDecoderExternal::decode(uint32_t frame_index,
   return promise;
 }
 
+ScriptPromise ImageDecoderExternal::decodeMetadata() {
+  DVLOG(1) << __func__;
+
+  auto* resolver = MakeGarbageCollected<ScriptPromiseResolver>(script_state_);
+  auto promise = resolver->Promise();
+  pending_metadata_decodes_.push_back(resolver);
+  MaybeSatisfyPendingMetadataDecodes();
+  return promise;
+}
+
 uint32_t ImageDecoderExternal::frameCount() const {
   return frame_count_;
 }
@@ -165,11 +175,11 @@ void ImageDecoderExternal::OnStateChange() {
 
     data_complete_ = result == BytesConsumer::Result::kDone;
     if (!decoder_)
-      MaybeCreateImageDecoder(nullptr);
+      MaybeCreateImageDecoder();
     else
       decoder_->SetData(stream_buffer_, data_complete_);
 
-    UpdateFrameAndRepetitionCount();
+    MaybeUpdateMetadata();
     MaybeSatisfyPendingDecodes();
   }
 }
@@ -182,6 +192,7 @@ void ImageDecoderExternal::Trace(Visitor* visitor) const {
   visitor->Trace(script_state_);
   visitor->Trace(consumer_);
   visitor->Trace(pending_decodes_);
+  visitor->Trace(pending_metadata_decodes_);
   visitor->Trace(init_data_);
   visitor->Trace(options_);
   ScriptWrappable::Trace(visitor);
@@ -268,8 +279,15 @@ void ImageDecoderExternal::MaybeSatisfyPendingDecodes() {
       static_cast<wtf_size_t>(new_end - pending_decodes_.begin()));
 }
 
-void ImageDecoderExternal::MaybeCreateImageDecoder(
-    scoped_refptr<SegmentReader> sr) {
+void ImageDecoderExternal::MaybeSatisfyPendingMetadataDecodes() {
+  DCHECK(decoder_);
+  DCHECK(decoder_->Failed() || frame_count_ > 0);
+  for (auto& resolver : pending_metadata_decodes_)
+    resolver->Resolve();
+  pending_metadata_decodes_.clear();
+}
+
+void ImageDecoderExternal::MaybeCreateImageDecoder() {
   // TODO: This does not handle SVG Images since they use another "decoder." It
   // is highly coupled with the DOM today, so isn't suitable for this API.
 
@@ -298,7 +316,6 @@ void ImageDecoderExternal::MaybeCreateImageDecoder(
     if (!ImageDecoder::HasSufficientDataToSniffImageType(*stream_buffer_))
       return;
 
-    DCHECK(!sr);
     decoder_ = ImageDecoder::Create(
         stream_buffer_, data_complete_, premultiply_alpha,
         ImageDecoder::kHighBitDepthToHalfFloat, color_behavior,
@@ -308,18 +325,20 @@ void ImageDecoderExternal::MaybeCreateImageDecoder(
 
   DCHECK(data_complete_);
   decoder_ = ImageDecoder::Create(
-      std::move(sr), data_complete_, premultiply_alpha,
+      segment_reader_, data_complete_, premultiply_alpha,
       ImageDecoder::kHighBitDepthToHalfFloat, color_behavior,
       ImageDecoder::OverrideAllowDecodeToYuv::kDeny, desired_size);
 }
 
-void ImageDecoderExternal::UpdateFrameAndRepetitionCount() {
+void ImageDecoderExternal::MaybeUpdateMetadata() {
   if (!decoder_)
     return;
 
   const size_t decoded_frame_count = decoder_->FrameCount();
-  if (decoder_->Failed())
+  if (decoder_->Failed()) {
+    MaybeSatisfyPendingMetadataDecodes();
     return;
+  }
 
   // TODO: Is this useful? We should have each decoder indicate its own mime
   // type then.
@@ -332,6 +351,8 @@ void ImageDecoderExternal::UpdateFrameAndRepetitionCount() {
   const int decoded_repetition_count = decoder_->RepetitionCount();
   if (decoded_repetition_count > 0)
     repetition_count_ = decoded_repetition_count;
+
+  MaybeSatisfyPendingMetadataDecodes();
 }
 
 }  // namespace blink

third_party/blink/renderer/modules/webcodecs/image_decoder_external.h

@@ -39,6 +39,7 @@ class MODULES_EXPORT ImageDecoderExternal final : public ScriptWrappable,
 
   // image_decoder.idl implementation.
   ScriptPromise decode(uint32_t frame_index, bool complete_frames_only);
+  ScriptPromise decodeMetadata();
   uint32_t frameCount() const;
   String type() const;
   uint32_t repetitionCount() const;
@@ -53,8 +54,9 @@ class MODULES_EXPORT ImageDecoderExternal final : public ScriptWrappable,
 
  private:
   void MaybeSatisfyPendingDecodes();
-  void MaybeCreateImageDecoder(scoped_refptr<SegmentReader> sr);
-  void UpdateFrameAndRepetitionCount();
+  void MaybeSatisfyPendingMetadataDecodes();
+  void MaybeCreateImageDecoder();
+  void MaybeUpdateMetadata();
 
   Member<ScriptState> script_state_;
 
@@ -62,6 +64,9 @@ class MODULES_EXPORT ImageDecoderExternal final : public ScriptWrappable,
   Member<ReadableStreamBytesConsumer> consumer_;
   scoped_refptr<SharedBuffer> stream_buffer_;
 
+  // Used when all data is provided at construction time.
+  scoped_refptr<SegmentReader> segment_reader_;
+
   // Construction parameters.
   Member<const ImageDecoderInit> init_data_;
   Member<const ImageBitmapOptions> options_;
@@ -86,6 +91,7 @@ class MODULES_EXPORT ImageDecoderExternal final : public ScriptWrappable,
     bool complete = false;
   };
   HeapVector<Member<DecodeRequest>> pending_decodes_;
+  HeapVector<Member<ScriptPromiseResolver>> pending_metadata_decodes_;
 
   // When decode() of incomplete frames has been requested, we need to track the
   // generation id for each SkBitmap that we've handed out. So that we can defer

third_party/blink/renderer/modules/webcodecs/image_decoder_init.idl

@@ -7,5 +7,9 @@
 typedef (ArrayBuffer or ArrayBufferView or ReadableStream) ImageBufferSource;
 dictionary ImageDecoderInit {
   required ImageBufferSource data;
+
+  // Options to use when creating ImageBitmap objects from decoded frames. The
+  // resize width and height are additionally used to facilitate reduced
+  // resolution decoding.
   ImageBitmapOptions options;
 };

third_party/blink/web_tests/http/tests/serviceworker/webexposed/global-interface-listing-service-worker-expected.txt

@@ -795,6 +795,7 @@ interface ImageDecoder
     getter type
     method constructor
     method decode
+    method decodeMetadata
 interface InstallEvent : ExtendableEvent
     attribute @@toStringTag
     method constructor

third_party/blink/web_tests/webexposed/global-interface-listing-dedicated-worker-expected.txt

@@ -738,6 +738,7 @@ Starting worker: resources/global-interface-listing-worker.js
 [Worker]     getter type
 [Worker]     method constructor
 [Worker]     method decode
+[Worker]     method decodeMetadata
 [Worker] interface Lock
 [Worker]     attribute @@toStringTag
 [Worker]     getter mode

third_party/blink/web_tests/webexposed/global-interface-listing-expected.txt

@@ -4544,6 +4544,7 @@ interface ImageDecoder
     getter type
     method constructor
     method decode
+    method decodeMetadata
 interface Ink
     attribute @@toStringTag
     method constructor

third_party/blink/web_tests/webexposed/global-interface-listing-shared-worker-expected.txt

@@ -725,6 +725,7 @@ Starting worker: resources/global-interface-listing-worker.js
 [Worker]     getter type
 [Worker]     method constructor
 [Worker]     method decode
+[Worker]     method decodeMetadata
 [Worker] interface Lock
 [Worker]     attribute @@toStringTag
 [Worker]     getter mode