Create skeleton of the rtcp transceiver.

RtcpTransceiver name reserved for thread-safe version that planned to
be wrapper of the RtcpTransceiverImpl

BUG=webrtc:8239

Change-Id: If8a3092eb1b8e4175e3efd23b52e1043cdabf19f
Reviewed-on: https://webrtc-review.googlesource.com/7920
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20414}

modules/rtp_rtcp/source/rtcp_transceiver_impl.cc

@@ -0,0 +1,96 @@
+/*
+ *  Copyright (c) 2017 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 "modules/rtp_rtcp/source/rtcp_transceiver_impl.h"
+
+#include <utility>
+#include <vector>
+
+#include "api/call/transport.h"
+#include "modules/rtp_rtcp/include/receive_statistics.h"
+#include "modules/rtp_rtcp/include/rtp_rtcp_defines.h"
+#include "modules/rtp_rtcp/source/rtcp_packet.h"
+#include "modules/rtp_rtcp/source/rtcp_packet/receiver_report.h"
+#include "modules/rtp_rtcp/source/rtcp_packet/report_block.h"
+#include "rtc_base/checks.h"
+
+namespace webrtc {
+namespace {
+
+// Helper to put several RTCP packets into lower layer datagram composing
+// Compound or Reduced-Size RTCP packet, as defined by RFC 5506 section 2.
+class PacketSender : public rtcp::RtcpPacket::PacketReadyCallback {
+ public:
+  PacketSender(Transport* transport, size_t max_packet_size)
+      : transport_(transport), max_packet_size_(max_packet_size) {
+    RTC_CHECK_LE(max_packet_size, IP_PACKET_SIZE);
+  }
+  ~PacketSender() override {
+    RTC_DCHECK_EQ(index_, 0) << "Unsent rtcp packet.";
+  }
+
+  // Appends a packet to pending compound packet.
+  // Sends rtcp compound packet if buffer was already full and resets buffer.
+  void AppendPacket(const rtcp::RtcpPacket& packet) {
+    packet.Create(buffer_, &index_, max_packet_size_, this);
+  }
+
+  // Sends pending rtcp compound packet.
+  void Send() {
+    if (index_ > 0) {
+      OnPacketReady(buffer_, index_);
+      index_ = 0;
+    }
+  }
+
+ private:
+  // Implements RtcpPacket::PacketReadyCallback
+  void OnPacketReady(uint8_t* data, size_t length) override {
+    transport_->SendRtcp(data, length);
+  }
+
+  Transport* const transport_;
+  const size_t max_packet_size_;
+  size_t index_ = 0;
+  uint8_t buffer_[IP_PACKET_SIZE];
+};
+
+}  // namespace
+
+RtcpTransceiverImpl::RtcpTransceiverImpl(const RtcpTransceiverConfig& config)
+    : config_(config) {
+  RTC_CHECK(config_.Validate());
+}
+
+RtcpTransceiverImpl::~RtcpTransceiverImpl() = default;
+
+void RtcpTransceiverImpl::SendCompoundPacket() {
+  PacketSender sender(config_.outgoing_transport, config_.max_packet_size);
+
+  rtcp::ReceiverReport rr;
+  rr.SetSenderSsrc(config_.feedback_ssrc);
+  if (config_.receive_statistics) {
+    // TODO(danilchap): Support sending more than
+    // |ReceiverReport::kMaxNumberOfReportBlocks| per compound rtcp packet.
+    std::vector<rtcp::ReportBlock> report_blocks =
+        config_.receive_statistics->RtcpReportBlocks(
+            rtcp::ReceiverReport::kMaxNumberOfReportBlocks);
+    // TODO(danilchap): Fill in LastSr/DelayLastSr fields of report blocks
+    // when RtcpTransceiver handles incoming sender reports.
+    rr.SetReportBlocks(std::move(report_blocks));
+  }
+  sender.AppendPacket(rr);
+  // TODO(danilchap): Append SDES to conform to the requirements on minimal
+  // compound RTCP packet.
+
+  sender.Send();
+}
+
+}  // namespace webrtc