media: Add MojoDecoderBuffer{Reader|Writer}

media/mojo/common/mojo_decoder_buffer_converter.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef MEDIA_MOJO_COMMON_MOJO_DECODER_BUFFER_CONVERTER_

[alokp, 2016/06/27 20:18:21]

nit: Since this file contains implementations of Reader and Writer, renaming it
to mojo_decoder_buffer_io.h may be more appropriate?

[xhwang, 2016/06/28 01:11:48]

I still like converter better (the same reason why I use Convert* as function
name originally. These two classes not only read/write the data part, but also
does a full "conversion" between media::mojom::DecoderBuffer and
media::DecoderBuffer. It's very similar to the traditional mojo type converters,
so I'd like make the name consistent as well.

+#define MEDIA_MOJO_COMMON_MOJO_DECODER_BUFFER_CONVERTER_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "media/base/demuxer_stream.h"
+#include "media/mojo/interfaces/media_types.mojom.h"
+#include "mojo/public/cpp/system/data_pipe.h"
+
+namespace media {
+
+class DecoderBuffer;
+
+// A helper class that converts mojom::DecoderBuffer to media::DecoderBuffer.
+// The data part of the DecoderBuffer is read from a DataPipe.
+class MojoDecoderBufferReader {
+ public:
+  // Creates a MojoDecoderBufferReader of |type| and set the |producer_handle|.
+  static std::unique_ptr<MojoDecoderBufferReader> Create(
+      DemuxerStream::Type type,
+      mojo::ScopedDataPipeProducerHandle* producer_handle);
+
+  // Hold the consumer handle to read DecoderBuffer data.
+  explicit MojoDecoderBufferReader(
+      mojo::ScopedDataPipeConsumerHandle consumer_handle);
+
+  ~MojoDecoderBufferReader();
+
+  // Converts |buffer| into a DecoderBuffer (read data from DataPipe if needed).

[alokp, 2016/06/27 20:18:21]

nit: Change "Converts" to "Reads decoder buffer data".

nit2: Perhaps rename this function to ReadDecoderBufferData to make it clearer.

Ditto for the writer.

[xhwang, 2016/06/28 01:11:48]

See comment above. This function not only read the decoder buffer data, but also
do a full conversion (including other fields like timestamp etc).

+  // Returns the result DecoderBuffer. Returns null in case of an error.
+  scoped_refptr<DecoderBuffer> ReadDecoderBuffer(
+      const mojom::DecoderBufferPtr& buffer);
+
+ private:
+  // For reading the data section of a DecoderBuffer.
+  mojo::ScopedDataPipeConsumerHandle consumer_handle_;
+
+  DISALLOW_COPY_AND_ASSIGN(MojoDecoderBufferReader);
+};
+
+// A helper class that converts media::DecoderBuffer to mojom::DecoderBuffer.
+// The data part of the DecoderBuffer is written into a DataPipe.
+class MojoDecoderBufferWriter {
+ public:
+  // Creates a MojoDecoderBufferWriter of |type| and set the |consumer_handle|.
+  static std::unique_ptr<MojoDecoderBufferWriter> Create(
+      DemuxerStream::Type type,
+      mojo::ScopedDataPipeConsumerHandle* consumer_handle);
+
+  // Hold the producer handle to write DecoderBuffer data.
+  explicit MojoDecoderBufferWriter(
+      mojo::ScopedDataPipeProducerHandle producer_handle);
+
+  ~MojoDecoderBufferWriter();
+
+  // Converts a DecoderBuffer into mojo DecoderBuffer, writing data into
+  // DataPipe if needed. Returns null if conversion failed.
+  mojom::DecoderBufferPtr WriteDecoderBuffer(
+      const scoped_refptr<DecoderBuffer>& media_buffer);
+
+ private:
+  // For writing the data section of DecoderBuffer into DataPipe.
+  mojo::ScopedDataPipeProducerHandle producer_handle_;
+
+  DISALLOW_COPY_AND_ASSIGN(MojoDecoderBufferWriter);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_MOJO_COMMON_MOJO_DECODER_BUFFER_CONVERTER_