Add a ParseHeader method to RtcpPacket, for parsing common RTCP header.

webrtc/modules/rtp_rtcp/source/rtcp_packet.cc

Index: webrtc/modules/rtp_rtcp/source/rtcp_packet.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtcp_packet.cc b/webrtc/modules/rtp_rtcp/source/rtcp_packet.cc
index 8cb6fb0833644077c3aed6f60475b56e9f23b2cc..75f670d2fb58185fdc4f28bcc7b7bc0e1c66ac43 100644
--- a/webrtc/modules/rtp_rtcp/source/rtcp_packet.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtcp_packet.cc
@@ -729,6 +729,8 @@ size_t RtcpPacket::HeaderLength() const {
   return ((length_in_bytes + 3) / 4) - 1;
 }
 
+RtcpPacket::CommonHeader::CommonHeader()
+    : count_or_format(0), payload_type(0), payload_size_bytes(0) {}
 // From RFC 3550, RTP: A Transport Protocol for Real-Time Applications.
 //
 // RTP header format.
@@ -743,7 +745,7 @@ void RtcpPacket::CreateHeader(
     uint8_t packet_type,
     size_t length,
     uint8_t* buffer,
-    size_t* pos) const {
+    size_t* pos) {
   assert(length <= 0xffff);
   const uint8_t kVersion = 2;
   AssignUWord8(buffer, pos, (kVersion << 6) + count_or_format);
@@ -751,6 +753,58 @@ void RtcpPacket::CreateHeader(
   AssignUWord16(buffer, pos, length);
 }
 
+bool RtcpPacket::ParseHeader(const uint8_t* packet,
+                             size_t index,
+                             size_t max_length,
+                             CommonHeader* header) {

[åsapersson, 2015/09/03 08:57:20]

Looks like RTCPUtility::RTCPParseCommonHeader can be used?

[sprang_webrtc, 2015/09/04 14:12:50]

I've merged this into RTCPUtility.

+  DCHECK(header != nullptr);
+  size_t length = max_length - index;
+  const size_t kHeaderLength = 4;
+  if (length < kHeaderLength) {
+    LOG(LS_WARNING) << "Too little data (" << length << " byte"
+                    << (length != 1 ? "s" : "")
+                    << ") remaining in buffer to parse RTCP header (4 bytes).";
+    return false;
+  }
+
+  const uint8_t kRtcpVersion = 2;
+  uint8_t version = packet[index] >> 6;
+  if (version != kRtcpVersion) {
+    LOG(LS_WARNING) << "Invalid RTCP header: Version must be " << kRtcpVersion
+                    << " but was " << version;
+    return false;
+  }
+
+  size_t packet_size_words =
+      ByteReader<uint16_t>::ReadBigEndian(&packet[index + 2]) + 1;
+  if (length < packet_size_words * 4) {
+    LOG(LS_WARNING) << "Buffer too small (" << length
+                    << " bytes) to fit a FeedbackPacket of "
+                    << packet_size_words << " 32bit words.";
+    return false;
+  }
+
+  bool has_padding = (packet[index] & 0x20) != 0;
+  size_t payload_size = packet_size_words * 4;
+  if (has_padding) {
+    uint8_t padding_bytes = packet[index + payload_size - 1];
+    if (kHeaderLength + padding_bytes > payload_size) {
+      LOG(LS_WARNING) << "Invalid RTCP header: Too many padding bytes ("
+                      << padding_bytes << ") for a packet size of "
+                      << payload_size << "bytes.";
+      return false;
+    }
+    payload_size -= padding_bytes;
+  }
+  payload_size -= kHeaderLength;
+
+  header->payload_size_bytes = payload_size;
+  header->count_or_format = packet[index] & 0x1F;
+  header->payload_type = packet[index + 1];
+
+  return true;
+}
+
 bool Empty::Create(uint8_t* packet,
                    size_t* index,
                    size_t max_length,