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
12static 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
37namespace media {
38namespace mp2t {
39
40TsSectionPsi::TsSectionPsi()
41    : wait_for_pusi_(true),
42      leading_bytes_to_discard_(0) {
43}
44
45TsSectionPsi::~TsSectionPsi() {
46}
47
48bool 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
116void TsSectionPsi::Flush() {
117}
118
119void TsSectionPsi::Reset() {
120  ResetPsiSection();
121  ResetPsiState();
122}
123
124void 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