[rtp_rtcp] rtcp header structure copied from RTCPUtility and extended

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

+/*
+ *  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.
+ */
+#ifndef WEBRTC_MODULES_RTP_RTCP_SOURCE_RTCP_PACKET_COMMON_HEADER_H_
+#define WEBRTC_MODULES_RTP_RTCP_SOURCE_RTCP_PACKET_COMMON_HEADER_H_
+
+#include "webrtc/base/basictypes.h"
+
+namespace webrtc {
+namespace rtcp {
+class CommonHeader {
+ public:
+  CommonHeader() {}
+  CommonHeader(const CommonHeader&) = default;
+  CommonHeader& operator =(const CommonHeader&) = default;
+
+  bool Parse(const uint8_t* buffer, size_t size_bytes);
+
+  uint8_t type() const { return packet_type_; }
+  // Depending on packet type same header field can be used either as count or
+  // as feedback message type (fmt). Caller expected to know how it is used.
+  uint8_t fmt() const { return count_or_format_; }
+  uint8_t count() const { return count_or_format_; }
+  size_t payload_size_bytes() const { return payload_size_; }
+  const uint8_t* payload() const { return payload_; }
+  // Returns pointer to the next RTCP packet in compound packet.
+  const uint8_t* NextPacket() const {
+    return payload_ + payload_size_ + padding_size_;
+  }
+
+ private:
+  uint8_t packet_type_ = 0;
+  uint8_t count_or_format_ = 0;
+  uint8_t padding_size_ = 0;
+  uint32_t payload_size_ = 0;
+  const uint8_t* payload_ = nullptr;
+};
+}  // namespace rtcp
+}  // namespace webrtc
+#endif  // WEBRTC_MODULES_RTP_RTCP_SOURCE_RTCP_PACKET_COMMON_HEADER_H_