Bug 1191114 (Part 2) - Add support for creating an anonymous metadata decoder, for use in tests. r=tn

--HG--
extra : rebase_source : 465523f87fda3ac80484fd368c9bbfe3daca2afc

image/DecoderFactory.cpp

@@ -215,5 +215,30 @@ DecoderFactory::CreateAnonymousDecoder(DecoderType aType,
   return decoder.forget();
 }
 
+/* static */ already_AddRefed<Decoder>
+DecoderFactory::CreateAnonymousMetadataDecoder(DecoderType aType,
+                                               SourceBuffer* aSourceBuffer)
+{
+  if (aType == DecoderType::UNKNOWN) {
+    return nullptr;
+  }
+
+  nsRefPtr<Decoder> decoder =
+    GetDecoder(aType, /* aImage = */ nullptr, /* aIsRedecode = */ false);
+  MOZ_ASSERT(decoder, "Should have a decoder now");
+
+  // Initialize the decoder.
+  decoder->SetMetadataDecode(true);
+  decoder->SetIterator(aSourceBuffer->Iterator());
+  decoder->SetIsFirstFrameDecode();
+
+  decoder->Init();
+  if (NS_FAILED(decoder->GetDecoderError())) {
+    return nullptr;
+  }
+
+  return decoder.forget();
+}
+
 } // namespace image
 } // namespace mozilla

image/DecoderFactory.h

@@ -101,11 +101,37 @@ public:
                         int aSampleSize,
                         const gfx::IntSize& aResolution);
 
+  /**
+   * Creates and initializes an anonymous decoder (one which isn't associated
+   * with an Image object). Only the first frame of the image will be decoded.
+   *
+   * @param aType Which type of decoder to create - JPEG, PNG, etc.
+   * @param aSourceBuffer The SourceBuffer which the decoder will read its data
+   *                      from.
+   * @param aFlags Flags specifying what type of output the decoder should
+   *               produce; see GetDecodeFlags() in RasterImage.h.
+   */
   static already_AddRefed<Decoder>
   CreateAnonymousDecoder(DecoderType aType,
                          SourceBuffer* aSourceBuffer,
                          uint32_t aFlags);
 
+  /**
+   * Creates and initializes an anonymous metadata decoder (one which isn't
+   * associated with an Image object). This decoder will only decode the image's
+   * header, extracting metadata like the size of the image. No actual image
+   * data will be decoded and no surfaces will be allocated.
+   *
+   * @param aType Which type of decoder to create - JPEG, PNG, etc.
+   * @param aSourceBuffer The SourceBuffer which the decoder will read its data
+   *                      from.
+   * @param aFlags Flags specifying what type of output the decoder should
+   *               produce; see GetDecodeFlags() in RasterImage.h.
+   */
+  static already_AddRefed<Decoder>
+  CreateAnonymousMetadataDecoder(DecoderType aType,
+                                 SourceBuffer* aSourceBuffer);
+
 private:
   virtual ~DecoderFactory() = 0;