Don't send receiver reports during simulcast probe

libwebrtc will stop sending SDES headers after the first receiver
report on a SSRC. This breaks probing if the receiver report is sent
before probing is completed. This change delays receiver reports for a
SSRC until the first non-probe packet is received.

interceptor/src/lib.rs

@@ -24,6 +24,9 @@ pub mod twcc;
 
 pub use error::Error;
 
+/// Attribute indicating the stream is probing incoming packets.
+pub const ATTR_READ_PROBE: usize = 2295978936;
+
 /// Attributes are a generic key/value store used by interceptors
 pub type Attributes = HashMap<usize, usize>;
 

interceptor/src/report/receiver/mod.rs

@@ -110,11 +110,11 @@ impl ReceiverReport {
                         m.values().cloned().collect()
                     };
                     for stream in streams {
-                        let pkt = stream.generate_report(now);
-
-                        let a = Attributes::new();
-                        if let Err(err) = rtcp_writer.write(&[Box::new(pkt)], &a).await{
-                            log::warn!("failed sending: {}", err);
+                        if let Some(pkt) = stream.generate_report(now) {
+                            let a = Attributes::new();
+                            if let Err(err) = rtcp_writer.write(&[Box::new(pkt)], &a).await{
+                                log::warn!("failed sending: {}", err);
+                            }
                         }
                     }
                 }
@@ -186,11 +186,17 @@ impl Interceptor for ReceiverReport {
         info: &StreamInfo,
         reader: Arc<dyn RTPReader + Send + Sync>,
     ) -> Arc<dyn RTPReader + Send + Sync> {
+        let wait_for_probe = info
+            .attributes
+            .get(&crate::ATTR_READ_PROBE)
+            .is_some_and(|v| *v != 0);
+
         let stream = Arc::new(ReceiverStream::new(
             info.ssrc,
             info.clock_rate,
             reader,
             self.internal.now.clone(),
+            wait_for_probe,
         ));
         {
             let mut streams = self.internal.streams.lock().await;

interceptor/src/report/receiver/receiver_stream.rs

@@ -13,6 +13,7 @@ struct ReceiverStreamInternal {
 
     packets: Vec<u64>,
     started: bool,
+    wait_for_probe: bool,
     seq_num_cycles: u16,
     last_seq_num: i32,
     last_report_seq_num: i32,
@@ -40,7 +41,7 @@ impl ReceiverStreamInternal {
         (self.packets[pos / 64] & (1 << (pos % 64))) != 0
     }
 
-    fn process_rtp(&mut self, now: SystemTime, pkt: &rtp::packet::Packet) {
+    fn process_rtp(&mut self, now: SystemTime, pkt: &rtp::packet::Packet, is_probe: bool) {
         if !self.started {
             // first frame
             self.started = true;
@@ -79,6 +80,7 @@ impl ReceiverStreamInternal {
 
         self.last_rtp_time_rtp = pkt.header.timestamp;
         self.last_rtp_time_time = now;
+        self.wait_for_probe &= is_probe;
     }
 
     fn process_sender_report(&mut self, now: SystemTime, sr: &rtcp::sender_report::SenderReport) {
@@ -158,6 +160,7 @@ impl ReceiverStream {
         clock_rate: u32,
         reader: Arc<dyn RTPReader + Send + Sync>,
         now: Option<FnTimeGen>,
+        wait_for_probe: bool,
     ) -> Self {
         let receiver_ssrc = rand::random::<u32>();
         ReceiverStream {
@@ -171,6 +174,7 @@ impl ReceiverStream {
 
                 packets: vec![0u64; 128],
                 started: false,
+                wait_for_probe,
                 seq_num_cycles: 0,
                 last_seq_num: 0,
                 last_report_seq_num: 0,
@@ -184,9 +188,9 @@ impl ReceiverStream {
         }
     }
 
-    pub(crate) fn process_rtp(&self, now: SystemTime, pkt: &rtp::packet::Packet) {
+    pub(crate) fn process_rtp(&self, now: SystemTime, pkt: &rtp::packet::Packet, is_probe: bool) {
         let mut internal = self.internal.lock();
-        internal.process_rtp(now, pkt);
+        internal.process_rtp(now, pkt, is_probe);
     }
 
     pub(crate) fn process_sender_report(
@@ -198,9 +202,17 @@ impl ReceiverStream {
         internal.process_sender_report(now, sr);
     }
 
-    pub(crate) fn generate_report(&self, now: SystemTime) -> rtcp::receiver_report::ReceiverReport {
+    pub(crate) fn generate_report(
+        &self,
+        now: SystemTime,
+    ) -> Option<rtcp::receiver_report::ReceiverReport> {
         let mut internal = self.internal.lock();
-        internal.generate_report(now)
+
+        if internal.wait_for_probe {
+            return None;
+        }
+
+        Some(internal.generate_report(now))
     }
 }
 
@@ -213,14 +225,16 @@ impl RTPReader for ReceiverStream {
         buf: &mut [u8],
         a: &Attributes,
     ) -> Result<(rtp::packet::Packet, Attributes)> {
+        let is_probe = a.get(&crate::ATTR_READ_PROBE).is_some_and(|v| *v != 0);
+
         let (pkt, attr) = self.parent_rtp_reader.read(buf, a).await?;
 
         let now = if let Some(f) = &self.now {
             f()
         } else {
             SystemTime::now()
         };
-        self.process_rtp(now, &pkt);
+        self.process_rtp(now, &pkt, is_probe);
 
         Ok((pkt, attr))
     }

interceptor/src/report/receiver/receiver_test.rs

@@ -58,6 +58,73 @@ async fn test_receiver_interceptor_before_any_packet() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test(start_paused = true)]
+async fn test_receiver_interceptor_read_probe() -> Result<()> {
+    let mt = Arc::new(MockTime::default());
+    let time_gen = {
+        let mt = Arc::clone(&mt);
+        Arc::new(move || mt.now())
+    };
+
+    let icpr: Arc<dyn Interceptor + Send + Sync> = ReceiverReport::builder()
+        .with_interval(Duration::from_millis(50))
+        .with_now_fn(time_gen)
+        .build("")?;
+
+    let stream = MockStream::new(
+        &StreamInfo {
+            ssrc: 123456,
+            clock_rate: 90000,
+            attributes: [(crate::ATTR_READ_PROBE, 1)].into_iter().collect(),
+            ..Default::default()
+        },
+        icpr,
+    )
+    .await;
+
+    // no report initially
+    tokio::time::timeout(Duration::from_millis(60), stream.written_rtcp())
+        .await
+        .expect_err("expected no report");
+
+    stream
+        .receive_rtp(rtp::packet::Packet {
+            header: rtp::header::Header {
+                sequence_number: 7,
+                ..Default::default()
+            },
+            ..Default::default()
+        })
+        .await;
+
+    let pkts = stream.written_rtcp().await.unwrap();
+    assert_eq!(pkts.len(), 1);
+    if let Some(rr) = pkts[0]
+        .as_any()
+        .downcast_ref::<rtcp::receiver_report::ReceiverReport>()
+    {
+        assert_eq!(rr.reports.len(), 1);
+        assert_eq!(
+            rr.reports[0],
+            rtcp::reception_report::ReceptionReport {
+                ssrc: 123456,
+                last_sequence_number: 7,
+                last_sender_report: 0,
+                fraction_lost: 0,
+                total_lost: 0,
+                delay: 0,
+                jitter: 0,
+            }
+        )
+    } else {
+        panic!();
+    }
+
+    stream.close().await?;
+
+    Ok(())
+}
+
 #[tokio::test]
 async fn test_receiver_interceptor_after_rtp_packets() -> Result<()> {
     let mt = Arc::new(MockTime::default());

webrtc/src/peer_connection/peer_connection_internal.rs

@@ -1072,23 +1072,30 @@ impl PeerConnectionInternal {
             None => return Err(Error::ErrInterceptorNotBind),
         };
 
-        let stream_info = create_stream_info(
+        let mut stream_info = create_stream_info(
             "".to_owned(),
             ssrc,
             params.codecs[0].payload_type,
             params.codecs[0].capability.clone(),
             &params.header_extensions,
             None,
         );
+
+        // indicate this stream starts with probing
+        stream_info
+            .attributes
+            .insert(interceptor::ATTR_READ_PROBE, 1);
+
         let (rtp_read_stream, rtp_interceptor, rtcp_read_stream, rtcp_interceptor) = self
             .dtls_transport
             .streams_for_ssrc(ssrc, &stream_info, &icpr)
             .await?;
 
-        let a = Attributes::new();
         for _ in 0..=SIMULCAST_PROBE_COUNT {
             if mid.is_empty() || (rid.is_empty() && rsid.is_empty()) {
-                let (pkt, _) = rtp_interceptor.read(&mut buf, &a).await?;
+                let (pkt, a) = rtp_interceptor
+                    .read(&mut buf, &stream_info.attributes)
+                    .await?;
                 let (m, r, rs, _) = handle_unknown_rtp_packet(
                     &pkt.header,
                     mid_extension_id as u8,