dom/media/XiphExtradata.cpp

   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 #include "XiphExtradata.h"
   8
   9 namespace mozilla {
  10
  11 bool XiphHeadersToExtradata(MediaByteBuffer* aCodecSpecificConfig,
  12                             const nsTArray<const unsigned char*>& aHeaders,
  13                             const nsTArray<size_t>& aHeaderLens) {
  14   size_t nheaders = aHeaders.Length();
  15   if (!nheaders || nheaders > 255) return false;
  16   aCodecSpecificConfig->AppendElement(nheaders - 1);
  17   for (size_t i = 0; i < nheaders - 1; i++) {
  18     size_t headerLen;
  19     for (headerLen = aHeaderLens[i]; headerLen >= 255; headerLen -= 255) {
  20       aCodecSpecificConfig->AppendElement(255);
  21     }
  22     aCodecSpecificConfig->AppendElement(headerLen);
  23   }
  24   for (size_t i = 0; i < nheaders; i++) {
  25     aCodecSpecificConfig->AppendElements(aHeaders[i], aHeaderLens[i]);
  26   }
  27   return true;
  28 }
  29
  30 bool XiphExtradataToHeaders(nsTArray<unsigned char*>& aHeaders,
  31                             nsTArray<size_t>& aHeaderLens, unsigned char* aData,
  32                             size_t aAvailable) {
  33   size_t total = 0;
  34   if (aAvailable < 1) {
  35     return false;
  36   }
  37   aAvailable--;
  38   int nHeaders = *aData++ + 1;
  39   for (int i = 0; i < nHeaders - 1; i++) {
  40     size_t headerLen = 0;
  41     for (;;) {
  42       // After this test, we know that (aAvailable - total > headerLen) and
  43       // (headerLen >= 0) so (aAvailable - total > 0). The loop decrements
  44       // aAvailable by 1 and total remains fixed, so we know that in the next
  45       // iteration (aAvailable - total >= 0). Thus (aAvailable - total) can
  46       // never underflow.
  47       if (aAvailable - total <= headerLen) {
  48         return false;
  49       }
  50       // Since we know (aAvailable > total + headerLen), this can't overflow
  51       // unless total is near 0 and both aAvailable and headerLen are within
  52       // 255 bytes of the maximum representable size. However, that is
  53       // impossible, since we would have had to have gone through this loop
  54       // more than 255 times to make headerLen that large, and thus decremented
  55       // aAvailable more than 255 times.
  56       headerLen += *aData;
  57       aAvailable--;
  58       if (*aData++ != 255) break;
  59     }
  60     // And this check ensures updating total won't cause (aAvailable - total)
  61     // to underflow.
  62     if (aAvailable - total < headerLen) {
  63       return false;
  64     }
  65     aHeaderLens.AppendElement(headerLen);
  66     // Since we know aAvailable >= total + headerLen, this can't overflow.
  67     total += headerLen;
  68   }
  69   aHeaderLens.AppendElement(aAvailable - total);
  70   for (int i = 0; i < nHeaders; i++) {
  71     aHeaders.AppendElement(aData);
  72     aData += aHeaderLens[i];
  73   }
  74   return true;
  75 }
  76
  77 }  // namespace mozilla