Validates sending RTCP before RTP.

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 37ea6922f78b770a1d13a3ca17090df371c7a8ea..5c3d03ec59744ef69d120503fe7c7ef7125e68ab 100644
--- a/webrtc/modules/rtp_rtcp/source/rtcp_sender.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtcp_sender.cc
@@ -485,6 +485,8 @@ rtc::scoped_ptr<rtcp::RtcpPacket> RTCPSender::BuildSR(const RtcpContext& ctx) {
   last_rtcp_time_[0] = Clock::NtpToMs(ctx.ntp_sec_, ctx.ntp_frac_);
   last_send_report_[0] = (ctx.ntp_sec_ << 16) + (ctx.ntp_frac_ >> 16);
 
+  // Timestamp shouldn't be esitmated before frame was received.
+  RTC_DCHECK_GE(last_frame_capture_time_ms_, 0);
   // The timestamp of this RTCP packet should be estimated as the timestamp of
   // the frame being captured at this moment. We are calculating that
   // timestamp as the last frame's timestamp + the time since the last frame
@@ -823,6 +825,28 @@ int32_t RTCPSender::SendCompoundRTCP(
       LOG(LS_WARNING) << "Can't send rtcp if it is disabled.";
       return -1;
     }
+    // Add all flags as volatile. Non volatile entries will not be overwritten.
+    // All new volatile flags added will be consumed by the end of this call.
+    SetFlags(packet_types, true);
+
+    // Prevent sending streams to send SR before any media has been sent.
+    const bool can_calculate_rtp_timestamp = (last_frame_capture_time_ms_ >= 0);
+    if (sending_ && !can_calculate_rtp_timestamp) {
+      bool consumed_report_flag = ConsumeFlag(kRtcpReport);
+      bool consumed_sr_flag = ConsumeFlag(kRtcpSr);
+      bool sender_report = consumed_report_flag || consumed_sr_flag;
+      if (sender_report && AllVolatileFlagsConsumed()) {
+        // This call was for Sender Report and nothing else.
+        return 0;
+      }
+      if (method_ == RtcpMode::kCompound) {
+        // Not allowed to send any RTCP packet without sender report.
+        return -1;
+      }
+    }
+
+    if (packet_type_counter_.first_packet_time_ms == -1)
+      packet_type_counter_.first_packet_time_ms = clock_->TimeInMilliseconds();
 
     // We need to send our NTP even if we haven't received any reports.
     uint32_t ntp_sec;
@@ -831,7 +855,7 @@ int32_t RTCPSender::SendCompoundRTCP(
     RtcpContext context(feedback_state, nack_size, nack_list, repeat, pictureID,
                         ntp_sec, ntp_frac, &container);
 
-    PrepareReport(packet_types, feedback_state);
+    PrepareReport(feedback_state);
 
     auto it = report_flags_.begin();
     while (it != report_flags_.end()) {
@@ -862,15 +886,7 @@ int32_t RTCPSender::SendCompoundRTCP(
   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);
-
-  if (packet_type_counter_.first_packet_time_ms == -1)
-    packet_type_counter_.first_packet_time_ms = clock_->TimeInMilliseconds();
-
+void RTCPSender::PrepareReport(const FeedbackState& feedback_state) {
   bool generate_report;
   if (IsFlagPresent(kRtcpSr) || IsFlagPresent(kRtcpRr)) {
     // Report type already explicitly set, don't automatically populate.