[feat] implementation for nack generator module

src/rtcp/nack.h

@@ -0,0 +1,56 @@
+/*
+ *  Copyright (c) 2015 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 MODULES_RTP_RTCP_SOURCE_RTCP_PACKET_NACK_H_
+#define MODULES_RTP_RTCP_SOURCE_RTCP_PACKET_NACK_H_
+
+#include <vector>
+
+#include "common_header.h"
+#include "rtp_feedback.h"
+
+namespace webrtc {
+namespace rtcp {
+class Nack : public RtpFeedback {
+ public:
+  static constexpr uint8_t kFeedbackMessageType = 1;
+  Nack();
+  Nack(const Nack&);
+  ~Nack() override;
+
+  // Parse assumes header is already parsed and validated.
+  bool Parse(const CommonHeader& packet);
+
+  void SetPacketIds(const uint16_t* nack_list, size_t length);
+  void SetPacketIds(std::vector<uint16_t> nack_list);
+  const std::vector<uint16_t>& packet_ids() const { return packet_ids_; }
+
+  size_t BlockLength() const override;
+
+  bool Create(uint8_t* packet, size_t* index, size_t max_length,
+              PacketReadyCallback callback) const override;
+
+ private:
+  static constexpr size_t kNackItemLength = 4;
+  struct PackedNack {
+    uint16_t first_pid;
+    uint16_t bitmask;
+  };
+
+  void Pack();    // Fills packed_ using packed_ids_. (used in SetPacketIds).
+  void Unpack();  // Fills packet_ids_ using packed_. (used in Parse).
+
+  std::vector<PackedNack> packed_;
+  std::vector<uint16_t> packet_ids_;
+};
+
+}  // namespace rtcp
+}  // namespace webrtc
+#endif  // MODULES_RTP_RTCP_SOURCE_RTCP_PACKET_NACK_H_