MTP Streaming: Readahead Buffer

chrome/browser/media_galleries/fileapi/readahead_file_stream_reader.h

+// Copyright 2014 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 CHROME_BROWSER_MEDIA_GALLERIES_FILEAPI_READAHEAD_FILE_STREAM_READER_H_
+#define CHROME_BROWSER_MEDIA_GALLERIES_FILEAPI_READAHEAD_FILE_STREAM_READER_H_
+
+#include <queue>
+
+#include "base/memory/weak_ptr.h"
+#include "net/base/io_buffer.h"
+#include "webkit/browser/blob/file_stream_reader.h"
+
+// Wraps a source FileStreamReader with a readahead buffer.
+class ReadaheadFileStreamReader
+    : public NON_EXPORTED_BASE(webkit_blob::FileStreamReader) {
+ public:
+  // Takes ownership of |source|.
+  explicit ReadaheadFileStreamReader(webkit_blob::FileStreamReader* source);
+
+  virtual ~ReadaheadFileStreamReader();
+
+  // FileStreamReader overrides.
+  virtual int Read(net::IOBuffer* buf, int buf_len,
+                   const net::CompletionCallback& callback) OVERRIDE;
+  virtual int64 GetLength(
+      const net::Int64CompletionCallback& callback) OVERRIDE;
+
+ private:
+  // Returns the number of bytes consumed from the internal cache into |sink|.
+  // Returns an error code if we are out of cache, hit an error, or hit EOF.
+  int FinishReadFromCacheOrStoredError(net::DrainableIOBuffer* sink);
+
+  // Reads into a new buffer from the source reader. This calls
+  // OnFinishReadFromSource when it completes (either synchronously or
+  // asynchronously).
+  void ReadFromSourceIfNeeded();
+  void OnFinishReadFromSource(net::IOBuffer* buffer, int result);
+
+  // This is reset to NULL upon encountering a read error or EOF.
+  scoped_ptr<webkit_blob::FileStreamReader> source_;
+
+  // This stores the error or EOF from the source FileStreamReader. Its
+  // value is undefined if |source_| is non-NULL.
+  int source_error_;
+  bool source_has_pending_read_;
+
+  // This contains a queue of buffers filled from |source_|, waiting to be
+  // consumed.
+  std::queue<scoped_refptr<net::DrainableIOBuffer> > buffers_;
+
+  // The read buffer waiting for the source FileStreamReader to finish
+  // reading and fill the cache.
+  scoped_refptr<net::DrainableIOBuffer> pending_sink_buffer_;
+  net::CompletionCallback pending_read_callback_;
+
+  base::WeakPtrFactory<ReadaheadFileStreamReader> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(ReadaheadFileStreamReader);
+};
+
+#endif  // CHROME_BROWSER_MEDIA_GALLERIES_FILEAPI_READAHEAD_FILE_STREAM_READER_H_