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      1 // Copyright 2014 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include "media/formats/mp2t/ts_section_psi.h"
      6 
      7 #include "base/basictypes.h"
      8 #include "base/logging.h"
      9 #include "media/base/bit_reader.h"
     10 #include "media/formats/mp2t/mp2t_common.h"
     11 
     12 static bool IsCrcValid(const uint8* buf, int size) {
     13   uint32 crc = 0xffffffffu;
     14   const uint32 kCrcPoly = 0x4c11db7;
     15 
     16   for (int k = 0; k < size; k++) {
     17     int nbits = 8;
     18     uint32 data_msb_aligned = buf[k];
     19     data_msb_aligned <<= (32 - nbits);
     20 
     21     while (nbits > 0) {
     22       if ((data_msb_aligned ^ crc) & 0x80000000) {
     23         crc <<= 1;
     24         crc ^= kCrcPoly;
     25       } else {
     26         crc <<= 1;
     27       }
     28 
     29       data_msb_aligned <<= 1;
     30       nbits--;
     31     }
     32   }
     33 
     34   return (crc == 0);
     35 }
     36 
     37 namespace media {
     38 namespace mp2t {
     39 
     40 TsSectionPsi::TsSectionPsi()
     41     : wait_for_pusi_(true),
     42       leading_bytes_to_discard_(0) {
     43 }
     44 
     45 TsSectionPsi::~TsSectionPsi() {
     46 }
     47 
     48 bool TsSectionPsi::Parse(bool payload_unit_start_indicator,
     49                              const uint8* buf, int size) {
     50   // Ignore partial PSI.
     51   if (wait_for_pusi_ && !payload_unit_start_indicator)
     52     return true;
     53 
     54   if (payload_unit_start_indicator) {
     55     // Reset the state of the PSI section.
     56     ResetPsiState();
     57 
     58     // Update the state.
     59     wait_for_pusi_ = false;
     60     DCHECK_GE(size, 1);
     61     int pointer_field = buf[0];
     62     leading_bytes_to_discard_ = pointer_field;
     63     buf++;
     64     size--;
     65   }
     66 
     67   // Discard some leading bytes if needed.
     68   if (leading_bytes_to_discard_ > 0) {
     69     int nbytes_to_discard = std::min(leading_bytes_to_discard_, size);
     70     buf += nbytes_to_discard;
     71     size -= nbytes_to_discard;
     72     leading_bytes_to_discard_ -= nbytes_to_discard;
     73   }
     74   if (size == 0)
     75     return true;
     76 
     77   // Add the data to the parser state.
     78   psi_byte_queue_.Push(buf, size);
     79   int raw_psi_size;
     80   const uint8* raw_psi;
     81   psi_byte_queue_.Peek(&raw_psi, &raw_psi_size);
     82 
     83   // Check whether we have enough data to start parsing.
     84   if (raw_psi_size < 3)
     85     return true;
     86   int section_length =
     87       ((static_cast<int>(raw_psi[1]) << 8) |
     88        (static_cast<int>(raw_psi[2]))) & 0xfff;
     89   if (section_length >= 1021)
     90     return false;
     91   int psi_length = section_length + 3;
     92   if (raw_psi_size < psi_length) {
     93     // Don't throw an error when there is not enough data,
     94     // just wait for more data to come.
     95     return true;
     96   }
     97 
     98   // There should not be any trailing bytes after a PMT.
     99   // Instead, the pointer field should be used to stuff bytes.
    100   DVLOG_IF(1, raw_psi_size > psi_length)
    101       << "Trailing bytes after a PSI section: "
    102       << psi_length << " vs " << raw_psi_size;
    103 
    104   // Verify the CRC.
    105   RCHECK(IsCrcValid(raw_psi, psi_length));
    106 
    107   // Parse the PSI section.
    108   BitReader bit_reader(raw_psi, raw_psi_size);
    109   bool status = ParsePsiSection(&bit_reader);
    110   if (status)
    111     ResetPsiState();
    112 
    113   return status;
    114 }
    115 
    116 void TsSectionPsi::Flush() {
    117 }
    118 
    119 void TsSectionPsi::Reset() {
    120   ResetPsiSection();
    121   ResetPsiState();
    122 }
    123 
    124 void TsSectionPsi::ResetPsiState() {
    125   wait_for_pusi_ = true;
    126   psi_byte_queue_.Reset();
    127   leading_bytes_to_discard_ = 0;
    128 }
    129 
    130 }  // namespace mp2t
    131 }  // namespace media
    132 
    133