xpcom/io/SnappyCompressOutputStream.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozilla_SnappyCompressOutputStream_h__
   8 #define mozilla_SnappyCompressOutputStream_h__
   9
  10 #include "mozilla/Attributes.h"
  11 #include "mozilla/UniquePtr.h"
  12 #include "nsCOMPtr.h"
  13 #include "nsIOutputStream.h"
  14 #include "nsISupportsImpl.h"
  15 #include "SnappyFrameUtils.h"
  16
  17 namespace mozilla {
  18
  19 class SnappyCompressOutputStream final : public nsIOutputStream,
  20                                          protected detail::SnappyFrameUtils {
  21  public:
  22   // Maximum compression block size.
  23   static const size_t kMaxBlockSize;
  24
  25   // Construct a new blocking output stream to compress data to
  26   // the given base stream.  The base stream must also be blocking.
  27   // The compression block size may optionally be set to a value
  28   // up to kMaxBlockSize.
  29   explicit SnappyCompressOutputStream(nsIOutputStream* aBaseStream,
  30                                       size_t aBlockSize = kMaxBlockSize);
  31
  32   // The compression block size.  To optimize stream performance
  33   // try to write to the stream in segments at least this size.
  34   size_t BlockSize() const;
  35
  36  private:
  37   virtual ~SnappyCompressOutputStream();
  38
  39   nsresult FlushToBaseStream();
  40   nsresult MaybeFlushStreamIdentifier();
  41   nsresult WriteAll(const char* aBuf, uint32_t aCount,
  42                     uint32_t* aBytesWrittenOut);
  43
  44   nsCOMPtr<nsIOutputStream> mBaseStream;
  45   const size_t mBlockSize;
  46
  47   // Buffer holding copied uncompressed data.  This must be copied here
  48   // so that the compression can be performed on a single flat buffer.
  49   mozilla::UniquePtr<char[]> mBuffer;
  50
  51   // The next byte in the uncompressed data to copy incoming data to.
  52   size_t mNextByte;
  53
  54   // Buffer holding the resulting compressed data.
  55   mozilla::UniquePtr<char[]> mCompressedBuffer;
  56   size_t mCompressedBufferLength;
  57
  58   // The first thing written to the stream must be a stream identifier.
  59   bool mStreamIdentifierWritten;
  60
  61  public:
  62   NS_DECL_THREADSAFE_ISUPPORTS
  63   NS_DECL_NSIOUTPUTSTREAM
  64 };
  65
  66 }  // namespace mozilla
  67
  68 #endif  // mozilla_SnappyCompressOutputStream_h__