Send RTCP packets via RtcpPacket callback

webrtc/modules/rtp_rtcp/source/rtcp_sender.cc

Index: webrtc/modules/rtp_rtcp/source/rtcp_sender.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtcp_sender.cc b/webrtc/modules/rtp_rtcp/source/rtcp_sender.cc
index eea1c81b79a06c0a094dab515f66e556c5cb9d2e..5add7cf3490cd64c7ed5a971fc7dfcf1b1e1dc82 100644
--- a/webrtc/modules/rtp_rtcp/source/rtcp_sender.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtcp_sender.cc
@@ -77,61 +77,61 @@ RTCPSender::FeedbackState::FeedbackState()
       module(nullptr) {
 }
 
-struct RTCPSender::RtcpContext {
-  RtcpContext(const FeedbackState& feedback_state,
-              int32_t nack_size,
-              const uint16_t* nack_list,
-              bool repeat,
-              uint64_t picture_id,
-              uint8_t* buffer,
-              uint32_t buffer_size)
-      : feedback_state(feedback_state),
-        nack_size(nack_size),
-        nack_list(nack_list),
-        repeat(repeat),
-        picture_id(picture_id),
-        buffer(buffer),
-        buffer_size(buffer_size),
-        ntp_sec(0),
-        ntp_frac(0),
-        position(0) {}
-
-  uint8_t* AllocateData(uint32_t bytes) {
-    RTC_DCHECK_LE(position + bytes, buffer_size);
-    uint8_t* ptr = &buffer[position];
-    position += bytes;
-    return ptr;
+class PacketContainer : public rtcp::Empty,
+                        public rtcp::RtcpPacket::PacketReadyCallback {
+ public:
+  explicit PacketContainer(Transport* transport)
+      : transport_(transport), bytes_sent_(0) {}
+  virtual ~PacketContainer() {
+    for (RtcpPacket* packet : appended_packets_)
+      delete packet;
   }
 
-  const FeedbackState& feedback_state;
-  int32_t nack_size;
-  const uint16_t* nack_list;
-  bool repeat;
-  uint64_t picture_id;
-  uint8_t* buffer;
-  uint32_t buffer_size;
-  uint32_t ntp_sec;
-  uint32_t ntp_frac;
-  uint32_t position;
-};
-
-// TODO(sprang): Once all builders use RtcpPacket, call SendToNetwork() here.
-class RTCPSender::PacketBuiltCallback
-    : public rtcp::RtcpPacket::PacketReadyCallback {
- public:
-  PacketBuiltCallback(RtcpContext* context) : context_(context) {}
-  virtual ~PacketBuiltCallback() {}
   void OnPacketReady(uint8_t* data, size_t length) override {
-    context_->position += length;
+    if (transport_->SendRtcp(data, length))
+      bytes_sent_ += length;
   }
-  bool BuildPacket(const rtcp::RtcpPacket& packet) {
-    return packet.BuildExternalBuffer(
-        &context_->buffer[context_->position],
-        context_->buffer_size - context_->position, this);
+
+  size_t SendPackets() {
+    rtcp::Empty::Build(this);
+    return bytes_sent_;
   }
 
  private:
-  RtcpContext* const context_;
+  Transport* transport_;
+  size_t bytes_sent_;
+};
+
+class RTCPSender::RtcpContext {
+ public:
+  RtcpContext(const FeedbackState& feedback_state,
+              int32_t nack_size,
+              const uint16_t* nack_list,
+              bool repeat,
+              uint64_t picture_id,
+              uint32_t ntp_sec,
+              uint32_t ntp_frac,
+              PacketContainer* container)
+      : feedback_state_(feedback_state),
+        nack_size_(nack_size),
+        nack_list_(nack_list),
+        repeat_(repeat),
+        picture_id_(picture_id),
+        ntp_sec_(ntp_sec),
+        ntp_frac_(ntp_frac),
+        container_(container) {}
+
+  virtual ~RtcpContext() {}
+
+  const FeedbackState& feedback_state_;
+  const int32_t nack_size_;
+  const uint16_t* nack_list_;
+  const bool repeat_;
+  const uint64_t picture_id_;
+  const uint32_t ntp_sec_;
+  const uint32_t ntp_frac_;
+
+  PacketContainer* const container_;
 };
 
 RTCPSender::RTCPSender(
@@ -474,15 +474,15 @@ int32_t RTCPSender::AddReportBlock(const RTCPReportBlock& report_block) {
   return 0;
 }
 
-RTCPSender::BuildResult RTCPSender::BuildSR(RtcpContext* ctx) {
+rtc::scoped_ptr<rtcp::RtcpPacket> RTCPSender::BuildSR(const RtcpContext& ctx) {
   for (int i = (RTCP_NUMBER_OF_SR - 2); i >= 0; i--) {
     // shift old
     last_send_report_[i + 1] = last_send_report_[i];
     last_rtcp_time_[i + 1] = last_rtcp_time_[i];
   }
 
-  last_rtcp_time_[0] = Clock::NtpToMs(ctx->ntp_sec, ctx->ntp_frac);
-  last_send_report_[0] = (ctx->ntp_sec << 16) + (ctx->ntp_frac >> 16);
+  last_rtcp_time_[0] = Clock::NtpToMs(ctx.ntp_sec_, ctx.ntp_frac_);
+  last_send_report_[0] = (ctx.ntp_sec_ << 16) + (ctx.ntp_frac_ >> 16);
 
   // The timestamp of this RTCP packet should be estimated as the timestamp of
   // the frame being captured at this moment. We are calculating that
@@ -491,67 +491,52 @@ RTCPSender::BuildResult RTCPSender::BuildSR(RtcpContext* ctx) {
   uint32_t rtp_timestamp =
       start_timestamp_ + last_rtp_timestamp_ +
       (clock_->TimeInMilliseconds() - last_frame_capture_time_ms_) *
-          (ctx->feedback_state.frequency_hz / 1000);
+          (ctx.feedback_state_.frequency_hz / 1000);
 
-  rtcp::SenderReport report;
-  report.From(ssrc_);
-  report.WithNtpSec(ctx->ntp_sec);
-  report.WithNtpFrac(ctx->ntp_frac);
-  report.WithRtpTimestamp(rtp_timestamp);
-  report.WithPacketCount(ctx->feedback_state.packets_sent);
-  report.WithOctetCount(ctx->feedback_state.media_bytes_sent);
+  rtcp::SenderReport* report = new rtcp::SenderReport();
+  report->From(ssrc_);
+  report->WithNtpSec(ctx.ntp_sec_);
+  report->WithNtpFrac(ctx.ntp_frac_);
+  report->WithRtpTimestamp(rtp_timestamp);
+  report->WithPacketCount(ctx.feedback_state_.packets_sent);
+  report->WithOctetCount(ctx.feedback_state_.media_bytes_sent);
 
   for (auto it : report_blocks_)
-    report.WithReportBlock(it.second);
-
-  PacketBuiltCallback callback(ctx);
-  if (!callback.BuildPacket(report))
-    return BuildResult::kTruncated;
+    report->WithReportBlock(it.second);
 
   report_blocks_.clear();
-  return BuildResult::kSuccess;
+
+  return rtc::scoped_ptr<rtcp::SenderReport>(report);
 }
 
-RTCPSender::BuildResult RTCPSender::BuildSDES(RtcpContext* ctx) {
+rtc::scoped_ptr<rtcp::RtcpPacket> RTCPSender::BuildSDES(
+    const RtcpContext& ctx) {
   size_t length_cname = cname_.length();
   RTC_CHECK_LT(length_cname, static_cast<size_t>(RTCP_CNAME_SIZE));
 
-  rtcp::Sdes sdes;
-  sdes.WithCName(ssrc_, cname_);
+  rtcp::Sdes* sdes = new rtcp::Sdes();
+  sdes->WithCName(ssrc_, cname_);
 
   for (const auto it : csrc_cnames_)
-    sdes.WithCName(it.first, it.second);
-
-  PacketBuiltCallback callback(ctx);
-  if (!callback.BuildPacket(sdes))
-    return BuildResult::kTruncated;
+    sdes->WithCName(it.first, it.second);
 
-  return BuildResult::kSuccess;
+  return rtc::scoped_ptr<rtcp::Sdes>(sdes);
 }
 
-RTCPSender::BuildResult RTCPSender::BuildRR(RtcpContext* ctx) {
-  rtcp::ReceiverReport report;
-  report.From(ssrc_);
+rtc::scoped_ptr<rtcp::RtcpPacket> RTCPSender::BuildRR(const RtcpContext& ctx) {
+  rtcp::ReceiverReport* report = new rtcp::ReceiverReport();
+  report->From(ssrc_);
   for (auto it : report_blocks_)
-    report.WithReportBlock(it.second);
-
-  PacketBuiltCallback callback(ctx);
-  if (!callback.BuildPacket(report))
-    return BuildResult::kTruncated;
+    report->WithReportBlock(it.second);
 
   report_blocks_.clear();
-
-  return BuildResult::kSuccess;
+  return rtc::scoped_ptr<rtcp::ReceiverReport>(report);
 }
 
-RTCPSender::BuildResult RTCPSender::BuildPLI(RtcpContext* ctx) {
-  rtcp::Pli pli;
-  pli.From(ssrc_);
-  pli.To(remote_ssrc_);
-
-  PacketBuiltCallback callback(ctx);
-  if (!callback.BuildPacket(pli))
-    return BuildResult::kTruncated;
+rtc::scoped_ptr<rtcp::RtcpPacket> RTCPSender::BuildPLI(const RtcpContext& ctx) {
+  rtcp::Pli* pli = new rtcp::Pli();
+  pli->From(ssrc_);
+  pli->To(remote_ssrc_);
 
   TRACE_EVENT_INSTANT0(TRACE_DISABLED_BY_DEFAULT("webrtc_rtp"),
                        "RTCPSender::PLI");
@@ -559,21 +544,17 @@ RTCPSender::BuildResult RTCPSender::BuildPLI(RtcpContext* ctx) {
   TRACE_COUNTER_ID1(TRACE_DISABLED_BY_DEFAULT("webrtc_rtp"), "RTCP_PLICount",
                     ssrc_, packet_type_counter_.pli_packets);
 
-  return BuildResult::kSuccess;
+  return rtc::scoped_ptr<rtcp::Pli>(pli);
 }
 
-RTCPSender::BuildResult RTCPSender::BuildFIR(RtcpContext* ctx) {
-  if (!ctx->repeat)
+rtc::scoped_ptr<rtcp::RtcpPacket> RTCPSender::BuildFIR(const RtcpContext& ctx) {
+  if (!ctx.repeat_)
     ++sequence_number_fir_;  // Do not increase if repetition.
 
-  rtcp::Fir fir;
-  fir.From(ssrc_);
-  fir.To(remote_ssrc_);
-  fir.WithCommandSeqNum(sequence_number_fir_);
-
-  PacketBuiltCallback callback(ctx);
-  if (!callback.BuildPacket(fir))
-    return BuildResult::kTruncated;
+  rtcp::Fir* fir = new rtcp::Fir();
+  fir->From(ssrc_);
+  fir->To(remote_ssrc_);
+  fir->WithCommandSeqNum(sequence_number_fir_);
 
   TRACE_EVENT_INSTANT0(TRACE_DISABLED_BY_DEFAULT("webrtc_rtp"),
                        "RTCPSender::FIR");
@@ -581,7 +562,7 @@ RTCPSender::BuildResult RTCPSender::BuildFIR(RtcpContext* ctx) {
   TRACE_COUNTER_ID1(TRACE_DISABLED_BY_DEFAULT("webrtc_rtp"), "RTCP_FIRCount",
                     ssrc_, packet_type_counter_.fir_packets);
 
-  return BuildResult::kSuccess;
+  return rtc::scoped_ptr<rtcp::Fir>(fir);
 }
 
 /*
@@ -591,20 +572,16 @@ RTCPSender::BuildResult RTCPSender::BuildFIR(RtcpContext* ctx) {
    |            First        |        Number           | PictureID |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 */
-RTCPSender::BuildResult RTCPSender::BuildSLI(RtcpContext* ctx) {
-  rtcp::Sli sli;
-  sli.From(ssrc_);
-  sli.To(remote_ssrc_);
+rtc::scoped_ptr<rtcp::RtcpPacket> RTCPSender::BuildSLI(const RtcpContext& ctx) {
+  rtcp::Sli* sli = new rtcp::Sli();
+  sli->From(ssrc_);
+  sli->To(remote_ssrc_);
   // Crop picture id to 6 least significant bits.
-  sli.WithPictureId(ctx->picture_id & 0x3F);
-  sli.WithFirstMb(0);
-  sli.WithNumberOfMb(0x1FFF);  // 13 bits, only ones for now.
-
-  PacketBuiltCallback callback(ctx);
-  if (!callback.BuildPacket(sli))
-    return BuildResult::kTruncated;
+  sli->WithPictureId(ctx.picture_id_ & 0x3F);
+  sli->WithFirstMb(0);
+  sli->WithNumberOfMb(0x1FFF);  // 13 bits, only ones for now.
 
-  return BuildResult::kSuccess;
+  return rtc::scoped_ptr<rtcp::Sli>(sli);
 }
 
 /*
@@ -619,38 +596,32 @@ RTCPSender::BuildResult RTCPSender::BuildSLI(RtcpContext* ctx) {
 /*
 *    Note: not generic made for VP8
 */
-RTCPSender::BuildResult RTCPSender::BuildRPSI(RtcpContext* ctx) {
-  if (ctx->feedback_state.send_payload_type == 0xFF)
-    return BuildResult::kError;
-
-  rtcp::Rpsi rpsi;
-  rpsi.From(ssrc_);
-  rpsi.To(remote_ssrc_);
-  rpsi.WithPayloadType(ctx->feedback_state.send_payload_type);
-  rpsi.WithPictureId(ctx->picture_id);
-
-  PacketBuiltCallback callback(ctx);
-  if (!callback.BuildPacket(rpsi))
-    return BuildResult::kTruncated;
-
-  return BuildResult::kSuccess;
+rtc::scoped_ptr<rtcp::RtcpPacket> RTCPSender::BuildRPSI(
+    const RtcpContext& ctx) {
+  if (ctx.feedback_state_.send_payload_type == 0xFF)
+    return nullptr;
+
+  rtcp::Rpsi* rpsi = new rtcp::Rpsi();
+  rpsi->From(ssrc_);
+  rpsi->To(remote_ssrc_);
+  rpsi->WithPayloadType(ctx.feedback_state_.send_payload_type);
+  rpsi->WithPictureId(ctx.picture_id_);
+
+  return rtc::scoped_ptr<rtcp::Rpsi>(rpsi);
 }
 
-RTCPSender::BuildResult RTCPSender::BuildREMB(RtcpContext* ctx) {
-  rtcp::Remb remb;
-  remb.From(ssrc_);
+rtc::scoped_ptr<rtcp::RtcpPacket> RTCPSender::BuildREMB(
+    const RtcpContext& ctx) {
+  rtcp::Remb* remb = new rtcp::Remb();
+  remb->From(ssrc_);
   for (uint32_t ssrc : remb_ssrcs_)
-    remb.AppliesTo(ssrc);
-  remb.WithBitrateBps(remb_bitrate_);
-
-  PacketBuiltCallback callback(ctx);
-  if (!callback.BuildPacket(remb))
-    return BuildResult::kTruncated;
+    remb->AppliesTo(ssrc);
+  remb->WithBitrateBps(remb_bitrate_);
 
   TRACE_EVENT_INSTANT0(TRACE_DISABLED_BY_DEFAULT("webrtc_rtp"),
                        "RTCPSender::REMB");
 
-  return BuildResult::kSuccess;
+  return rtc::scoped_ptr<rtcp::Remb>(remb);
 }
 
 void RTCPSender::SetTargetBitrate(unsigned int target_bitrate) {
@@ -658,9 +629,10 @@ void RTCPSender::SetTargetBitrate(unsigned int target_bitrate) {
   tmmbr_send_ = target_bitrate / 1000;
 }
 
-RTCPSender::BuildResult RTCPSender::BuildTMMBR(RtcpContext* ctx) {
-  if (ctx->feedback_state.module == NULL)
-    return BuildResult::kError;
+rtc::scoped_ptr<rtcp::RtcpPacket> RTCPSender::BuildTMMBR(
+    const RtcpContext& ctx) {
+  if (ctx.feedback_state_.module == nullptr)
+    return nullptr;
   // Before sending the TMMBR check the received TMMBN, only an owner is
   // allowed to raise the bitrate:
   // * If the sender is an owner of the TMMBN -> send TMMBR
@@ -675,14 +647,14 @@ RTCPSender::BuildResult RTCPSender::BuildTMMBR(RtcpContext* ctx) {
   // will accuire criticalSectionRTCPReceiver_ is a potental deadlock but
   // since RTCPreceiver is not doing the reverse we should be fine
   int32_t lengthOfBoundingSet =
-      ctx->feedback_state.module->BoundingSet(tmmbrOwner, candidateSet);
+      ctx.feedback_state_.module->BoundingSet(tmmbrOwner, candidateSet);
 
   if (lengthOfBoundingSet > 0) {
     for (int32_t i = 0; i < lengthOfBoundingSet; i++) {
       if (candidateSet->Tmmbr(i) == tmmbr_send_ &&
           candidateSet->PacketOH(i) == packet_oh_send_) {
-        // do not send the same tuple
-        return BuildResult::kAborted;
+        // Do not send the same tuple.
+        return nullptr;
       }
     }
     if (!tmmbrOwner) {
@@ -693,124 +665,69 @@ RTCPSender::BuildResult RTCPSender::BuildTMMBR(RtcpContext* ctx) {
       int numCandidates = lengthOfBoundingSet + 1;
 
       // find bounding set
-      TMMBRSet* boundingSet = NULL;
+      TMMBRSet* boundingSet = nullptr;
       int numBoundingSet = tmmbr_help_.FindTMMBRBoundingSet(boundingSet);
       if (numBoundingSet > 0 || numBoundingSet <= numCandidates)
         tmmbrOwner = tmmbr_help_.IsOwner(ssrc_, numBoundingSet);
       if (!tmmbrOwner) {
-        // did not enter bounding set, no meaning to send this request
-        return BuildResult::kAborted;
+        // Did not enter bounding set, no meaning to send this request.
+        return nullptr;
       }
     }
   }
 
-  if (tmmbr_send_) {
-    rtcp::Tmmbr tmmbr;
-    tmmbr.From(ssrc_);
-    tmmbr.To(remote_ssrc_);
-    tmmbr.WithBitrateKbps(tmmbr_send_);
-    tmmbr.WithOverhead(packet_oh_send_);
+  if (!tmmbr_send_)
+    return nullptr;
 
-    PacketBuiltCallback callback(ctx);
-    if (!callback.BuildPacket(tmmbr))
-      return BuildResult::kTruncated;
-  }
-  return BuildResult::kSuccess;
+  rtcp::Tmmbr* tmmbr = new rtcp::Tmmbr();
+  tmmbr->From(ssrc_);
+  tmmbr->To(remote_ssrc_);
+  tmmbr->WithBitrateKbps(tmmbr_send_);
+  tmmbr->WithOverhead(packet_oh_send_);
+
+  return rtc::scoped_ptr<rtcp::Tmmbr>(tmmbr);
 }
 
-RTCPSender::BuildResult RTCPSender::BuildTMMBN(RtcpContext* ctx) {
+rtc::scoped_ptr<rtcp::RtcpPacket> RTCPSender::BuildTMMBN(
+    const RtcpContext& ctx) {
   TMMBRSet* boundingSet = tmmbr_help_.BoundingSetToSend();
-  if (boundingSet == NULL)
-    return BuildResult::kError;
+  if (boundingSet == nullptr)
+    return nullptr;
 
-  rtcp::Tmmbn tmmbn;
-  tmmbn.From(ssrc_);
+  rtcp::Tmmbn* tmmbn = new rtcp::Tmmbn();
+  tmmbn->From(ssrc_);
   for (uint32_t i = 0; i < boundingSet->lengthOfSet(); i++) {
     if (boundingSet->Tmmbr(i) > 0) {
-      tmmbn.WithTmmbr(boundingSet->Ssrc(i), boundingSet->Tmmbr(i),
-                      boundingSet->PacketOH(i));
+      tmmbn->WithTmmbr(boundingSet->Ssrc(i), boundingSet->Tmmbr(i),
+                       boundingSet->PacketOH(i));
     }
   }
 
-  PacketBuiltCallback callback(ctx);
-  if (!callback.BuildPacket(tmmbn))
-    return BuildResult::kTruncated;
-
-  return BuildResult::kSuccess;
+  return rtc::scoped_ptr<rtcp::Tmmbn>(tmmbn);
 }
 
-RTCPSender::BuildResult RTCPSender::BuildAPP(RtcpContext* ctx) {
-  rtcp::App app;
-  app.From(ssrc_);
-  app.WithSubType(app_sub_type_);
-  app.WithName(app_name_);
-  app.WithData(app_data_.get(), app_length_);
+rtc::scoped_ptr<rtcp::RtcpPacket> RTCPSender::BuildAPP(const RtcpContext& ctx) {
+  rtcp::App* app = new rtcp::App();
+  app->From(ssrc_);
+  app->WithSubType(app_sub_type_);
+  app->WithName(app_name_);
+  app->WithData(app_data_.get(), app_length_);
 
-  PacketBuiltCallback callback(ctx);
-  if (!callback.BuildPacket(app))
-    return BuildResult::kTruncated;
-
-  return BuildResult::kSuccess;
+  return rtc::scoped_ptr<rtcp::App>(app);
 }
 
-RTCPSender::BuildResult RTCPSender::BuildNACK(RtcpContext* ctx) {
-  // sanity
-  if (ctx->position + 16 >= IP_PACKET_SIZE) {
-    LOG(LS_WARNING) << "Failed to build NACK.";
-    return BuildResult::kTruncated;
-  }
-
-  // int size, uint16_t* nack_list
-  // add nack list
-  uint8_t FMT = 1;
-  *ctx->AllocateData(1) = 0x80 + FMT;
-  *ctx->AllocateData(1) = 205;
-
-  *ctx->AllocateData(1) = 0;
-  int nack_size_pos_ = ctx->position;
-  *ctx->AllocateData(1) = 3;  // setting it to one kNACK signal as default
-
-  // Add our own SSRC
-  ByteWriter<uint32_t>::WriteBigEndian(ctx->AllocateData(4), ssrc_);
-
-  // Add the remote SSRC
-  ByteWriter<uint32_t>::WriteBigEndian(ctx->AllocateData(4), remote_ssrc_);
-
-  // Build NACK bitmasks and write them to the RTCP message.
-  // The nack list should be sorted and not contain duplicates if one
-  // wants to build the smallest rtcp nack packet.
-  int numOfNackFields = 0;
-  int maxNackFields =
-      std::min<int>(kRtcpMaxNackFields, (IP_PACKET_SIZE - ctx->position) / 4);
-  int i = 0;
-  while (i < ctx->nack_size && numOfNackFields < maxNackFields) {
-    uint16_t nack = ctx->nack_list[i++];
-    uint16_t bitmask = 0;
-    while (i < ctx->nack_size) {
-      int shift = static_cast<uint16_t>(ctx->nack_list[i] - nack) - 1;
-      if (shift >= 0 && shift <= 15) {
-        bitmask |= (1 << shift);
-        ++i;
-      } else {
-        break;
-      }
-    }
-    // Write the sequence number and the bitmask to the packet.
-    assert(ctx->position + 4 < IP_PACKET_SIZE);
-    ByteWriter<uint16_t>::WriteBigEndian(ctx->AllocateData(2), nack);
-    ByteWriter<uint16_t>::WriteBigEndian(ctx->AllocateData(2), bitmask);
-    numOfNackFields++;
-  }
-  ctx->buffer[nack_size_pos_] = static_cast<uint8_t>(2 + numOfNackFields);
-
-  if (i != ctx->nack_size)
-    LOG(LS_WARNING) << "Nack list too large for one packet.";
+rtc::scoped_ptr<rtcp::RtcpPacket> RTCPSender::BuildNACK(
+    const RtcpContext& ctx) {
+  rtcp::Nack* nack = new rtcp::Nack();
+  nack->From(ssrc_);
+  nack->To(remote_ssrc_);
+  nack->WithList(ctx.nack_list_, ctx.nack_size_);
 
   // Report stats.
   NACKStringBuilder stringBuilder;
-  for (int idx = 0; idx < i; ++idx) {
-    stringBuilder.PushNACK(ctx->nack_list[idx]);
-    nack_stats_.ReportRequest(ctx->nack_list[idx]);
+  for (int idx = 0; idx < ctx.nack_size_; ++idx) {
+    stringBuilder.PushNACK(ctx.nack_list_[idx]);
+    nack_stats_.ReportRequest(ctx.nack_list_[idx]);
   }
   packet_type_counter_.nack_requests = nack_stats_.requests();
   packet_type_counter_.unique_nack_requests = nack_stats_.unique_requests();
@@ -822,70 +739,59 @@ RTCPSender::BuildResult RTCPSender::BuildNACK(RtcpContext* ctx) {
   TRACE_COUNTER_ID1(TRACE_DISABLED_BY_DEFAULT("webrtc_rtp"), "RTCP_NACKCount",
                     ssrc_, packet_type_counter_.nack_packets);
 
-  return BuildResult::kSuccess;
+  return rtc::scoped_ptr<rtcp::Nack>(nack);
 }
 
-RTCPSender::BuildResult RTCPSender::BuildBYE(RtcpContext* ctx) {
-  rtcp::Bye bye;
-  bye.From(ssrc_);
+rtc::scoped_ptr<rtcp::RtcpPacket> RTCPSender::BuildBYE(const RtcpContext& ctx) {
+  rtcp::Bye* bye = new rtcp::Bye();
+  bye->From(ssrc_);
   for (uint32_t csrc : csrcs_)
-    bye.WithCsrc(csrc);
-
-  PacketBuiltCallback callback(ctx);
-  if (!callback.BuildPacket(bye))
-    return BuildResult::kTruncated;
+    bye->WithCsrc(csrc);
 
-  return BuildResult::kSuccess;
+  return rtc::scoped_ptr<rtcp::Bye>(bye);
 }
 
-RTCPSender::BuildResult RTCPSender::BuildReceiverReferenceTime(
-    RtcpContext* ctx) {
-
+rtc::scoped_ptr<rtcp::RtcpPacket> RTCPSender::BuildReceiverReferenceTime(
+    const RtcpContext& ctx) {
   if (last_xr_rr_.size() >= RTCP_NUMBER_OF_SR)
     last_xr_rr_.erase(last_xr_rr_.begin());
   last_xr_rr_.insert(std::pair<uint32_t, int64_t>(
-      RTCPUtility::MidNtp(ctx->ntp_sec, ctx->ntp_frac),
-      Clock::NtpToMs(ctx->ntp_sec, ctx->ntp_frac)));
+      RTCPUtility::MidNtp(ctx.ntp_sec_, ctx.ntp_frac_),
+      Clock::NtpToMs(ctx.ntp_sec_, ctx.ntp_frac_)));
 
-  rtcp::Xr xr;
-  xr.From(ssrc_);
+  rtcp::Xr* xr = new rtcp::Xr();
+  xr->From(ssrc_);
 
   rtcp::Rrtr rrtr;
-  rrtr.WithNtpSec(ctx->ntp_sec);
-  rrtr.WithNtpFrac(ctx->ntp_frac);
+  rrtr.WithNtpSec(ctx.ntp_sec_);
+  rrtr.WithNtpFrac(ctx.ntp_frac_);
 
-  xr.WithRrtr(&rrtr);
+  xr->WithRrtr(&rrtr);
 
   // TODO(sprang): Merge XR report sending to contain all of RRTR, DLRR, VOIP?
 
-  PacketBuiltCallback callback(ctx);
-  if (!callback.BuildPacket(xr))
-    return BuildResult::kTruncated;
-
-  return BuildResult::kSuccess;
+  return rtc::scoped_ptr<rtcp::Xr>(xr);
 }
 
-RTCPSender::BuildResult RTCPSender::BuildDlrr(RtcpContext* ctx) {
-  rtcp::Xr xr;
-  xr.From(ssrc_);
+rtc::scoped_ptr<rtcp::RtcpPacket> RTCPSender::BuildDlrr(
+    const RtcpContext& ctx) {
+  rtcp::Xr* xr = new rtcp::Xr();
+  xr->From(ssrc_);
 
   rtcp::Dlrr dlrr;
-  const RtcpReceiveTimeInfo& info = ctx->feedback_state.last_xr_rr;
+  const RtcpReceiveTimeInfo& info = ctx.feedback_state_.last_xr_rr;
   dlrr.WithDlrrItem(info.sourceSSRC, info.lastRR, info.delaySinceLastRR);
 
-  xr.WithDlrr(&dlrr);
-
-  PacketBuiltCallback callback(ctx);
-  if (!callback.BuildPacket(xr))
-    return BuildResult::kTruncated;
+  xr->WithDlrr(&dlrr);
 
-  return BuildResult::kSuccess;
+  return rtc::scoped_ptr<rtcp::Xr>(xr);
 }
 
 // TODO(sprang): Add a unit test for this, or remove if the code isn't used.
-RTCPSender::BuildResult RTCPSender::BuildVoIPMetric(RtcpContext* ctx) {
-  rtcp::Xr xr;
-  xr.From(ssrc_);
+rtc::scoped_ptr<rtcp::RtcpPacket> RTCPSender::BuildVoIPMetric(
+    const RtcpContext& context) {
+  rtcp::Xr* xr = new rtcp::Xr();
+  xr->From(ssrc_);
 
   rtcp::VoipMetric voip;
   voip.To(remote_ssrc_);
@@ -910,13 +816,9 @@ RTCPSender::BuildResult RTCPSender::BuildVoIPMetric(RtcpContext* ctx) {
   voip.JbMax(xr_voip_metric_.JBmax);
   voip.JbAbsMax(xr_voip_metric_.JBabsMax);
 
-  xr.WithVoipMetric(&voip);
+  xr->WithVoipMetric(&voip);
 
-  PacketBuiltCallback callback(ctx);
-  if (!callback.BuildPacket(xr))
-    return BuildResult::kTruncated;
-
-  return BuildResult::kSuccess;
+  return rtc::scoped_ptr<rtcp::Xr>(xr);
 }
 
 int32_t RTCPSender::SendRTCP(const FeedbackState& feedback_state,
@@ -932,43 +834,59 @@ int32_t RTCPSender::SendRTCP(const FeedbackState& feedback_state,
 
 int32_t RTCPSender::SendCompoundRTCP(
     const FeedbackState& feedback_state,
-    const std::set<RTCPPacketType>& packetTypes,
+    const std::set<RTCPPacketType>& packet_types,
     int32_t nack_size,
     const uint16_t* nack_list,
     bool repeat,
     uint64_t pictureID) {
+  PacketContainer container(transport_);
   {
     CriticalSectionScoped lock(critical_section_rtcp_sender_.get());
     if (method_ == RtcpMode::kOff) {
       LOG(LS_WARNING) << "Can't send rtcp if it is disabled.";
       return -1;
     }
-  }
-  uint8_t rtcp_buffer[IP_PACKET_SIZE];
-  int rtcp_length =
-      PrepareRTCP(feedback_state, packetTypes, nack_size, nack_list, repeat,
-                  pictureID, rtcp_buffer, IP_PACKET_SIZE);
 
-  // Sanity don't send empty packets.
-  if (rtcp_length <= 0)
-    return -1;
+    // We need to send our NTP even if we haven't received any reports.
+    uint32_t ntp_sec;
+    uint32_t ntp_frac;
+    clock_->CurrentNtp(ntp_sec, ntp_frac);
+    RtcpContext context(feedback_state, nack_size, nack_list, repeat, pictureID,
+                        ntp_sec, ntp_frac, &container);
+
+    PrepareReport(packet_types, feedback_state);
+
+    auto it = report_flags_.begin();
+    while (it != report_flags_.end()) {
+      auto builder_it = builders_.find(it->type);
+      RTC_DCHECK(builder_it != builders_.end());
+      if (it->is_volatile) {
+        report_flags_.erase(it++);
+      } else {
+        ++it;
+      }
 
-  return SendToNetwork(rtcp_buffer, static_cast<size_t>(rtcp_length));
-}
+      BuilderFunc func = builder_it->second;
+      rtc::scoped_ptr<rtcp::RtcpPacket> packet = (this->*func)(context);
+      if (packet.get() == nullptr)
+        return -1;
+      container.Append(packet.release());
+    }
 
-int RTCPSender::PrepareRTCP(const FeedbackState& feedback_state,
-                            const std::set<RTCPPacketType>& packetTypes,
-                            int32_t nack_size,
-                            const uint16_t* nack_list,
-                            bool repeat,
-                            uint64_t pictureID,
-                            uint8_t* rtcp_buffer,
-                            int buffer_size) {
-  CriticalSectionScoped lock(critical_section_rtcp_sender_.get());
+    if (packet_type_counter_observer_ != nullptr) {
+      packet_type_counter_observer_->RtcpPacketTypesCounterUpdated(
+          remote_ssrc_, packet_type_counter_);
+    }
 
-  RtcpContext context(feedback_state, nack_size, nack_list, repeat, pictureID,
-                      rtcp_buffer, buffer_size);
+    RTC_DCHECK(AllVolatileFlagsConsumed());
+  }
 
+  size_t bytes_sent = container.SendPackets();
+  return bytes_sent == 0 ? -1 : 0;
+}
+
+void RTCPSender::PrepareReport(const std::set<RTCPPacketType>& packetTypes,
+                               const FeedbackState& feedback_state) {
   // Add all flags as volatile. Non volatile entries will not be overwritten
   // and all new volatile flags added will be consumed by the end of this call.
   SetFlags(packetTypes, true);
@@ -992,9 +910,6 @@ int RTCPSender::PrepareRTCP(const FeedbackState& feedback_state,
   if (IsFlagPresent(kRtcpSr) || (IsFlagPresent(kRtcpRr) && !cname_.empty()))
     SetFlag(kRtcpSdes, true);
 
-  // We need to send our NTP even if we haven't received any reports.
-  clock_->CurrentNtp(context.ntp_sec, context.ntp_frac);
-
   if (generate_report) {
     if (!sending_ && xr_send_receiver_reference_time_enabled_)
       SetFlag(kRtcpXrReceiverReferenceTime, true);
@@ -1028,8 +943,8 @@ int RTCPSender::PrepareRTCP(const FeedbackState& feedback_state,
     if (!statisticians.empty()) {
       for (auto it = statisticians.begin(); it != statisticians.end(); ++it) {
         RTCPReportBlock report_block;
-        if (PrepareReport(feedback_state, it->first, it->second,
-                          &report_block)) {
+        if (PrepareReportBlock(feedback_state, it->first, it->second,
+                               &report_block)) {
           // TODO(danilchap) AddReportBlock may fail (for 2 different reasons).
           // Probably it shouldn't be ignored.
           AddReportBlock(report_block);
@@ -1037,48 +952,12 @@ int RTCPSender::PrepareRTCP(const FeedbackState& feedback_state,
       }
     }
   }
-
-  auto it = report_flags_.begin();
-  while (it != report_flags_.end()) {
-    auto builder = builders_.find(it->type);
-    RTC_DCHECK(builder != builders_.end());
-    if (it->is_volatile) {
-      report_flags_.erase(it++);
-    } else {
-      ++it;
-    }
-
-    uint32_t start_position = context.position;
-    BuildResult result = (this->*(builder->second))(&context);
-    switch (result) {
-      case BuildResult::kError:
-        return -1;
-      case BuildResult::kTruncated:
-        return context.position;
-      case BuildResult::kAborted:
-        context.position = start_position;
-        FALLTHROUGH();
-      case BuildResult::kSuccess:
-        continue;
-      default:
-        abort();
-    }
-  }
-
-  if (packet_type_counter_observer_ != NULL) {
-    packet_type_counter_observer_->RtcpPacketTypesCounterUpdated(
-        remote_ssrc_, packet_type_counter_);
-  }
-
-  RTC_DCHECK(AllVolatileFlagsConsumed());
-
-  return context.position;
 }
 
-bool RTCPSender::PrepareReport(const FeedbackState& feedback_state,
-                               uint32_t ssrc,
-                               StreamStatistician* statistician,
-                               RTCPReportBlock* report_block) {
+bool RTCPSender::PrepareReportBlock(const FeedbackState& feedback_state,
+                                    uint32_t ssrc,
+                                    StreamStatistician* statistician,
+                                    RTCPReportBlock* report_block) {
   // Do we have receive statistics to send?
   RtcpStatistics stats;
   if (!statistician->GetStatistics(&stats, true))
@@ -1116,12 +995,6 @@ bool RTCPSender::PrepareReport(const FeedbackState& feedback_state,
   return true;
 }
 
-int32_t RTCPSender::SendToNetwork(const uint8_t* dataBuffer, size_t length) {
-  if (transport_->SendRtcp(dataBuffer, length))
-    return 0;
-  return -1;
-}
-
 void RTCPSender::SetCsrcs(const std::vector<uint32_t>& csrcs) {
   assert(csrcs.size() <= kRtpCsrcSize);
   CriticalSectionScoped lock(critical_section_rtcp_sender_.get());