[rtp_rtcp] rtcp header structure copied from RTCPUtility and extended

webrtc/modules/rtp_rtcp/source/rtcp_packet/common_header.cc

+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "webrtc/modules/rtp_rtcp/source/rtcp_packet/common_header.h"
+
+#include "webrtc/base/logging.h"
+#include "webrtc/modules/rtp_rtcp/source/byte_io.h"
+
+namespace webrtc {
+namespace rtcp {
+//    0                   1           1       2                   3
+//    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+// 0 |V=2|P|   C/F   |
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+// 1                 |  Packet Type  |
+//   ----------------+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+// 2                                 |             length            |
+//   --------------------------------+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//
+// Common header for all RTCP packets, 4 octets.
+bool CommonHeader::Parse(const uint8_t* buffer, size_t size_bytes) {
+  const size_t kHeaderSizeBytes = 4;
+  const uint8_t kVersion = 2;
+
+  if (size_bytes < kHeaderSizeBytes) {
+    LOG(LS_WARNING) << "Too little data (" << size_bytes << " byte"
+                    << (size_bytes != 1 ? "s" : "")
+                    << ") remaining in buffer to parse RTCP header (4 bytes).";
+    return false;
+  }
+
+  uint8_t version = buffer[0] >> 6;
+  if (version != kVersion) {
+    LOG(LS_WARNING) << "Invalid RTCP header: Version must be "
+                    << static_cast<int>(kVersion) << " but was "
+                    << static_cast<int>(version);
+    return false;
+  }
+
+  bool has_padding = (buffer[0] & 0x20) != 0;
+  count_or_format_ = buffer[0] & 0x1F;
+  packet_type_ = buffer[1];
+  payload_size_ = ByteReader<uint16_t>::ReadBigEndian(&buffer[2]) * 4;
+  payload_ = buffer + kHeaderSizeBytes;
+  padding_size_ = 0;
+
+  if (size_bytes < kHeaderSizeBytes + payload_size_) {
+    LOG(LS_WARNING) << "Buffer too small (" << size_bytes
+                    << " bytes) to fit an RtcpPacket with a header and "
+                    << payload_size_ << " bytes.";
+    return false;
+  }
+
+  if (has_padding) {
+    if (payload_size_ == 0) {
+      LOG(LS_WARNING) << "Invalid RTCP header: Padding bit set but 0 payload "
+                         "size specified.";
+      return false;
+    }
+
+    padding_size_ = payload_[payload_size_ - 1];
+    if (padding_size_ > payload_size_) {
+      LOG(LS_WARNING) << "Invalid RTCP header: Too many padding bytes ("
+                      << padding_size_ << ") for a packet payload size of "
+                      << payload_size_ << " bytes.";
+      return false;
+    }
+    payload_size_ -= padding_size_;
+  }
+  return true;
+}
+}  // namespace rtcp
+}  // namespace webrtc