xpcom/io/nsStorageStream.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 /*
   8  * The storage stream provides an internal buffer that can be filled by a
   9  * client using a single output stream.  One or more independent input streams
  10  * can be created to read the data out non-destructively.  The implementation
  11  * uses a segmented buffer internally to avoid realloc'ing of large buffers,
  12  * with the attendant performance loss and heap fragmentation.
  13  */
  14
  15 #ifndef _nsStorageStream_h_
  16 #define _nsStorageStream_h_
  17
  18 #include "nsIStorageStream.h"
  19 #include "nsIOutputStream.h"
  20 #include "nsMemory.h"
  21 #include "mozilla/Attributes.h"
  22
  23 #define NS_STORAGESTREAM_CID                       \
  24 { /* 669a9795-6ff7-4ed4-9150-c34ce2971b63 */       \
  25   0x669a9795,                                      \
  26   0x6ff7,                                          \
  27   0x4ed4,                                          \
  28   {0x91, 0x50, 0xc3, 0x4c, 0xe2, 0x97, 0x1b, 0x63} \
  29 }
  30
  31 #define NS_STORAGESTREAM_CONTRACTID "@mozilla.org/storagestream;1"
  32
  33 class nsSegmentedBuffer;
  34
  35 class nsStorageStream MOZ_FINAL
  36   : public nsIStorageStream
  37   , public nsIOutputStream
  38 {
  39 public:
  40   nsStorageStream();
  41
  42   NS_DECL_THREADSAFE_ISUPPORTS
  43   NS_DECL_NSISTORAGESTREAM
  44   NS_DECL_NSIOUTPUTSTREAM
  45
  46   friend class nsStorageInputStream;
  47
  48 private:
  49   ~nsStorageStream();
  50
  51   nsSegmentedBuffer* mSegmentedBuffer;
  52   uint32_t           mSegmentSize;       // All segments, except possibly the last, are of this size
  53                                          //   Must be power-of-2
  54   uint32_t           mSegmentSizeLog2;   // log2(mSegmentSize)
  55   bool               mWriteInProgress;   // true, if an un-Close'ed output stream exists
  56   int32_t            mLastSegmentNum;    // Last segment # in use, -1 initially
  57   char*              mWriteCursor;       // Pointer to next byte to be written
  58   char*              mSegmentEnd;        // Pointer to one byte after end of segment
  59                                          //   containing the write cursor
  60   uint32_t           mLogicalLength;     // Number of bytes written to stream
  61
  62   NS_METHOD Seek(int32_t aPosition);
  63   uint32_t SegNum(uint32_t aPosition)
  64   {
  65     return aPosition >> mSegmentSizeLog2;
  66   }
  67   uint32_t SegOffset(uint32_t aPosition)
  68   {
  69     return aPosition & (mSegmentSize - 1);
  70   }
  71 };
  72
  73 #endif //  _nsStorageStream_h_