SnappyCompressOutputStream.h

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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

/* vim: set ts=8 sts=2 et sw=2 tw=80: */

/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef mozilla_SnappyCompressOutputStream_h__

#define mozilla_SnappyCompressOutputStream_h__

#include "mozilla/Attributes.h"

#include "mozilla/UniquePtr.h"

#include "nsCOMPtr.h"

#include "nsIOutputStream.h"

#include "nsISupportsImpl.h"

#include "SnappyFrameUtils.h"

namespace mozilla {

class SnappyCompressOutputStream final : public nsIOutputStream,

                                         protected detail::SnappyFrameUtils {

 public:

  // Maximum compression block size.

  static const size_t kMaxBlockSize;

  // Construct a new blocking output stream to compress data to

  // the given base stream.  The base stream must also be blocking.

  // The compression block size may optionally be set to a value

  // up to kMaxBlockSize.

  explicit SnappyCompressOutputStream(nsIOutputStream* aBaseStream,

                                      size_t aBlockSize = kMaxBlockSize);

  // The compression block size.  To optimize stream performance

  // try to write to the stream in segments at least this size.

  size_t BlockSize() const;

 private:

  virtual ~SnappyCompressOutputStream();

  nsresult FlushToBaseStream();

  nsresult MaybeFlushStreamIdentifier();

  nsresult WriteAll(const char* aBuf, uint32_t aCount,

                    uint32_t* aBytesWrittenOut);

  nsCOMPtr<nsIOutputStream> mBaseStream;

  const size_t mBlockSize;

  // Buffer holding copied uncompressed data.  This must be copied here

  // so that the compression can be performed on a single flat buffer.

  mozilla::UniquePtr<char[]> mBuffer;

  // The next byte in the uncompressed data to copy incoming data to.

  size_t mNextByte;

  // Buffer holding the resulting compressed data.

  mozilla::UniquePtr<char[]> mCompressedBuffer;

  size_t mCompressedBufferLength;

  // The first thing written to the stream must be a stream identifier.

  bool mStreamIdentifierWritten;

 public:

  NS_DECL_THREADSAFE_ISUPPORTS

  NS_DECL_NSIOUTPUTSTREAM

};

}  // namespace mozilla

#endif  // mozilla_SnappyCompressOutputStream_h__