gecko-dev/xpcom/io/nsStorageStream.h

/* -*- 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/. */

/*
 * The storage stream provides an internal buffer that can be filled by a
 * client using a single output stream.  One or more independent input streams
 * can be created to read the data out non-destructively.  The implementation
 * uses a segmented buffer internally to avoid realloc'ing of large buffers,
 * with the attendant performance loss and heap fragmentation.
 */

#ifndef _nsStorageStream_h_
#define _nsStorageStream_h_

#include "nsIStorageStream.h"
#include "nsIOutputStream.h"
#include "nsMemory.h"
#include "mozilla/Attributes.h"

#define NS_STORAGESTREAM_CID                       \
{ /* 669a9795-6ff7-4ed4-9150-c34ce2971b63 */       \
  0x669a9795,                                      \
  0x6ff7,                                          \
  0x4ed4,                                          \
  {0x91, 0x50, 0xc3, 0x4c, 0xe2, 0x97, 0x1b, 0x63} \
}

#define NS_STORAGESTREAM_CONTRACTID "@mozilla.org/storagestream;1"

class nsSegmentedBuffer;

class nsStorageStream final
  : public nsIStorageStream
  , public nsIOutputStream
{
public:
  nsStorageStream();

  NS_DECL_THREADSAFE_ISUPPORTS
  NS_DECL_NSISTORAGESTREAM
  NS_DECL_NSIOUTPUTSTREAM

  friend class nsStorageInputStream;

private:
  ~nsStorageStream();

  nsSegmentedBuffer* mSegmentedBuffer;
  uint32_t           mSegmentSize;       // All segments, except possibly the last, are of this size
                                         //   Must be power-of-2
  uint32_t           mSegmentSizeLog2;   // log2(mSegmentSize)
  bool               mWriteInProgress;   // true, if an un-Close'ed output stream exists
  int32_t            mLastSegmentNum;    // Last segment # in use, -1 initially
  char*              mWriteCursor;       // Pointer to next byte to be written
  char*              mSegmentEnd;        // Pointer to one byte after end of segment
                                         //   containing the write cursor
  uint32_t           mLogicalLength;     // Number of bytes written to stream

  nsresult Seek(int32_t aPosition);
  uint32_t SegNum(uint32_t aPosition)
  {
    return aPosition >> mSegmentSizeLog2;
  }
  uint32_t SegOffset(uint32_t aPosition)
  {
    return aPosition & (mSegmentSize - 1);
  }
};

#endif //  _nsStorageStream_h_