Make publish_data wait until the DataChannel's bufferedAmount becomes low.

.nanpa/dc-buffered-amount-low-threshold.kdl

@@ -0,0 +1,6 @@
+patch type="added" package="libwebrtc" "Expose DataChannel.bufferedAmount property"
+patch type="fixed" package="livekit" "Wait for the buffered amount to become low before sending data during publish_data for Reliable Data Channel"
+patch type="added" package="livekit" "Add an API to set buffer_amount_low_threshold for DataChannel"
+patch type="added" package="livekit" "Update RoomInfo to contain buffer_amount_low_threshold for DataChannel"
+patch type="added" package="livekit-ffi" "Add an API to set buffer_amount_low_threshold for DataChannel"
+patch type="added" package="livekit-ffi" "Update RoomInfo to contain buffer_amount_low_threshold for DataChannel"

libwebrtc/src/data_channel.rs

@@ -97,6 +97,10 @@ impl DataChannel {
         self.handle.close()
     }
 
+    pub fn buffered_amount(&self) -> u64 {
+        self.handle.buffered_amount()
+    }
+
     pub fn on_state_change(&self, callback: Option<OnStateChange>) {
         self.handle.on_state_change(callback)
     }

libwebrtc/src/native/data_channel.rs

@@ -94,6 +94,10 @@ impl DataChannel {
         self.sys_handle.close();
     }
 
+    pub fn buffered_amount(&self) -> u64 {
+        self.sys_handle.buffered_amount()
+    }
+
     pub fn on_state_change(&self, handler: Option<OnStateChange>) {
         *self.observer.state_change_handler.lock() = handler;
     }

livekit-ffi/protocol/ffi.proto

@@ -116,6 +116,9 @@ message FfiRequest {
     SendStreamHeaderRequest send_stream_header = 44;
     SendStreamChunkRequest send_stream_chunk = 45;
     SendStreamTrailerRequest send_stream_trailer = 46;
+
+    // Data Channel
+    SetDataChannelBufferedAmountLowThresholdRequest set_data_channel_buffered_amount_low_threshold = 47;
   }
 }
 
@@ -178,6 +181,9 @@ message FfiResponse {
     SendStreamHeaderResponse send_stream_header = 43;
     SendStreamChunkResponse send_stream_chunk = 44;
     SendStreamTrailerResponse send_stream_trailer = 45;
+
+    // Data Channel
+    SetDataChannelBufferedAmountLowThresholdResponse set_data_channel_buffered_amount_low_threshold = 46;
   }
 }
 

livekit-ffi/protocol/room.proto

@@ -370,13 +370,16 @@ message RoomEvent {
     DataStreamHeaderReceived stream_header_received = 30;
     DataStreamChunkReceived stream_chunk_received = 31;
     DataStreamTrailerReceived stream_trailer_received = 32;
+    DataChannelBufferedAmountLowThresholdChanged data_channel_low_threshold_changed = 33;
   }
 }
 
 message RoomInfo {
   optional string sid = 1;
   required string name = 2;
   required string metadata = 3;
+  required uint64 lossy_dc_buffered_amount_low_threshold = 4;
+  required uint64 reliable_dc_buffered_amount_low_threshold = 5;
 }
 
 message OwnedRoom {
@@ -647,3 +650,17 @@ message SendStreamTrailerCallback {
   required uint64 async_id = 1;
   optional string error = 2;
 }
+
+message SetDataChannelBufferedAmountLowThresholdRequest {
+  required uint64 local_participant_handle = 1;
+  required uint64 threshold = 2;
+  required DataPacketKind kind = 3;
+}
+
+message SetDataChannelBufferedAmountLowThresholdResponse {
+}
+
+message DataChannelBufferedAmountLowThresholdChanged {
+  required DataPacketKind kind = 1;
+  required uint64 threshold = 2;
+}

livekit-ffi/src/conversion/room.rs

@@ -252,6 +252,12 @@ impl From<&FfiRoom> for proto::RoomInfo {
             sid: room.maybe_sid().map(|x| x.to_string()),
             name: room.name(),
             metadata: room.metadata(),
+            lossy_dc_buffered_amount_low_threshold: room
+                .data_channel_options(DataPacketKind::Lossy)
+                .buffered_amount_low_threshold,
+            reliable_dc_buffered_amount_low_threshold: room
+                .data_channel_options(DataPacketKind::Reliable)
+                .buffered_amount_low_threshold,
         }
     }
 }

livekit-ffi/src/livekit.proto.rs

@@ -1,5 +1,4 @@
 // @generated
-// This file is @generated by prost-build.
 #[allow(clippy::derive_partial_eq_without_eq)]
 #[derive(Clone, PartialEq, ::prost::Message)]
 pub struct FrameCryptor {
@@ -2635,7 +2634,7 @@ pub struct OwnedBuffer {
 pub struct RoomEvent {
     #[prost(uint64, required, tag="1")]
     pub room_handle: u64,
-    #[prost(oneof="room_event::Message", tags="2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32")]
+    #[prost(oneof="room_event::Message", tags="2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33")]
     pub message: ::core::option::Option<room_event::Message>,
 }
 /// Nested message and enum types in `RoomEvent`.
@@ -2707,6 +2706,8 @@ pub mod room_event {
         StreamChunkReceived(super::DataStreamChunkReceived),
         #[prost(message, tag="32")]
         StreamTrailerReceived(super::DataStreamTrailerReceived),
+        #[prost(message, tag="33")]
+        DataChannelLowThresholdChanged(super::DataChannelBufferedAmountLowThresholdChanged),
     }
 }
 #[allow(clippy::derive_partial_eq_without_eq)]
@@ -2718,6 +2719,10 @@ pub struct RoomInfo {
     pub name: ::prost::alloc::string::String,
     #[prost(string, required, tag="3")]
     pub metadata: ::prost::alloc::string::String,
+    #[prost(uint64, required, tag="4")]
+    pub lossy_dc_buffered_amount_low_threshold: u64,
+    #[prost(uint64, required, tag="5")]
+    pub reliable_dc_buffered_amount_low_threshold: u64,
 }
 #[allow(clippy::derive_partial_eq_without_eq)]
 #[derive(Clone, PartialEq, ::prost::Message)]
@@ -3217,6 +3222,28 @@ pub struct SendStreamTrailerCallback {
     #[prost(string, optional, tag="2")]
     pub error: ::core::option::Option<::prost::alloc::string::String>,
 }
+#[allow(clippy::derive_partial_eq_without_eq)]
+#[derive(Clone, PartialEq, ::prost::Message)]
+pub struct SetDataChannelBufferedAmountLowThresholdRequest {
+    #[prost(uint64, required, tag="1")]
+    pub local_participant_handle: u64,
+    #[prost(uint64, required, tag="2")]
+    pub threshold: u64,
+    #[prost(enumeration="DataPacketKind", required, tag="3")]
+    pub kind: i32,
+}
+#[allow(clippy::derive_partial_eq_without_eq)]
+#[derive(Clone, PartialEq, ::prost::Message)]
+pub struct SetDataChannelBufferedAmountLowThresholdResponse {
+}
+#[allow(clippy::derive_partial_eq_without_eq)]
+#[derive(Clone, PartialEq, ::prost::Message)]
+pub struct DataChannelBufferedAmountLowThresholdChanged {
+    #[prost(enumeration="DataPacketKind", required, tag="1")]
+    pub kind: i32,
+    #[prost(uint64, required, tag="2")]
+    pub threshold: u64,
+}
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, PartialOrd, Ord, ::prost::Enumeration)]
 #[repr(i32)]
 pub enum IceTransportType {
@@ -3989,7 +4016,7 @@ pub struct RpcMethodInvocationEvent {
 #[allow(clippy::derive_partial_eq_without_eq)]
 #[derive(Clone, PartialEq, ::prost::Message)]
 pub struct FfiRequest {
-    #[prost(oneof="ffi_request::Message", tags="2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46")]
+    #[prost(oneof="ffi_request::Message", tags="2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47")]
     pub message: ::core::option::Option<ffi_request::Message>,
 }
 /// Nested message and enum types in `FfiRequest`.
@@ -4094,13 +4121,16 @@ pub mod ffi_request {
         SendStreamChunk(super::SendStreamChunkRequest),
         #[prost(message, tag="46")]
         SendStreamTrailer(super::SendStreamTrailerRequest),
+        /// Data Channel
+        #[prost(message, tag="47")]
+        SetDataChannelBufferedAmountLowThreshold(super::SetDataChannelBufferedAmountLowThresholdRequest),
     }
 }
 /// This is the output of livekit_ffi_request function.
 #[allow(clippy::derive_partial_eq_without_eq)]
 #[derive(Clone, PartialEq, ::prost::Message)]
 pub struct FfiResponse {
-    #[prost(oneof="ffi_response::Message", tags="2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45")]
+    #[prost(oneof="ffi_response::Message", tags="2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46")]
     pub message: ::core::option::Option<ffi_response::Message>,
 }
 /// Nested message and enum types in `FfiResponse`.
@@ -4203,6 +4233,9 @@ pub mod ffi_response {
         SendStreamChunk(super::SendStreamChunkResponse),
         #[prost(message, tag="45")]
         SendStreamTrailer(super::SendStreamTrailerResponse),
+        /// Data Channel
+        #[prost(message, tag="46")]
+        SetDataChannelBufferedAmountLowThreshold(super::SetDataChannelBufferedAmountLowThresholdResponse),
     }
 }
 /// To minimize complexity, participant events are not included in the protocol.

livekit-ffi/src/server/requests.rs

@@ -905,6 +905,20 @@ fn on_rpc_method_invocation_response(
     Ok(proto::RpcMethodInvocationResponseResponse { error })
 }
 
+fn on_set_data_channel_buffered_amount_low_threshold(
+    server: &'static FfiServer,
+    set_data_channel_buffered_amount_low_threshold: proto::SetDataChannelBufferedAmountLowThresholdRequest,
+) -> FfiResult<proto::SetDataChannelBufferedAmountLowThresholdResponse> {
+    let ffi_participant = server
+        .retrieve_handle::<FfiParticipant>(
+            set_data_channel_buffered_amount_low_threshold.local_participant_handle,
+        )?
+        .clone();
+    Ok(ffi_participant.room.set_data_channel_buffered_amount_low_threshold(
+        set_data_channel_buffered_amount_low_threshold,
+    ))
+}
+
 #[allow(clippy::field_reassign_with_default)] // Avoid uggly format
 pub fn handle_request(
     server: &'static FfiServer,
@@ -1078,6 +1092,11 @@ pub fn handle_request(
                 server, request,
             )?)
         }
+        proto::ffi_request::Message::SetDataChannelBufferedAmountLowThreshold(request) => {
+            proto::ffi_response::Message::SetDataChannelBufferedAmountLowThreshold(
+                on_set_data_channel_buffered_amount_low_threshold(server, request)?,
+            )
+        }
     });
 
     Ok(res)

livekit-ffi/src/server/room.rs

@@ -774,6 +774,17 @@ impl RoomInner {
     ) -> Option<oneshot::Sender<Result<String, RpcError>>> {
         return self.rpc_method_invocation_waiters.lock().remove(&invocation_id);
     }
+
+    pub fn set_data_channel_buffered_amount_low_threshold(
+        &self,
+        request: proto::SetDataChannelBufferedAmountLowThresholdRequest,
+    ) -> proto::SetDataChannelBufferedAmountLowThresholdResponse {
+        let _ = self.room.local_participant().set_data_channel_buffered_amount_low_threshold(
+            request.threshold,
+            request.kind().into(),
+        );
+        proto::SetDataChannelBufferedAmountLowThresholdResponse {}
+    }
 }
 
 // Task used to publish data without blocking the client thread
@@ -1246,6 +1257,14 @@ async fn forward_event(
                 proto::DataStreamTrailerReceived { trailer: trailer.into(), participant_identity },
             ));
         }
+        RoomEvent::DataChannelBufferedAmountLowThresholdChanged { kind, threshold } => {
+            let _ = send_event(proto::room_event::Message::DataChannelLowThresholdChanged(
+                proto::DataChannelBufferedAmountLowThresholdChanged {
+                    kind: proto::DataPacketKind::from(kind).into(),
+                    threshold,
+                },
+            ));
+        }
         _ => {
             log::warn!("unhandled room event: {:?}", event);
         }

livekit/src/room/mod.rs

@@ -43,7 +43,7 @@ use crate::{
     prelude::*,
     rtc_engine::{
         EngineError, EngineEvent, EngineEvents, EngineOptions, EngineResult, RtcEngine,
-        SessionStats,
+        SessionStats, INITIAL_BUFFERED_AMOUNT_LOW_THRESHOLD,
     },
 };
 
@@ -196,6 +196,10 @@ pub enum RoomEvent {
     },
     Reconnecting,
     Reconnected,
+    DataChannelBufferedAmountLowThresholdChanged {
+        kind: DataPacketKind,
+        threshold: u64,
+    },
 }
 
 #[derive(Debug, Clone, Copy, Eq, PartialEq)]
@@ -360,6 +364,19 @@ impl Debug for Room {
 struct RoomInfo {
     metadata: String,
     state: ConnectionState,
+    lossy_dc_options: DataChannelOptions,
+    reliable_dc_options: DataChannelOptions,
+}
+
+#[derive(Clone)]
+pub struct DataChannelOptions {
+    pub buffered_amount_low_threshold: u64,
+}
+
+impl Default for DataChannelOptions {
+    fn default() -> Self {
+        Self { buffered_amount_low_threshold: INITIAL_BUFFERED_AMOUNT_LOW_THRESHOLD }
+    }
 }
 
 pub(crate) struct RoomSession {
@@ -506,6 +523,8 @@ impl Room {
             info: RwLock::new(RoomInfo {
                 state: ConnectionState::Disconnected,
                 metadata: room_info.metadata,
+                lossy_dc_options: Default::default(),
+                reliable_dc_options: Default::default(),
             }),
             remote_participants: Default::default(),
             active_speakers: Default::default(),
@@ -623,6 +642,13 @@ impl Room {
     pub fn e2ee_manager(&self) -> &E2eeManager {
         &self.inner.e2ee_manager
     }
+
+    pub fn data_channel_options(&self, kind: DataPacketKind) -> DataChannelOptions {
+        match kind {
+            DataPacketKind::Lossy => self.inner.info.read().lossy_dc_options.clone(),
+            DataPacketKind::Reliable => self.inner.info.read().reliable_dc_options.clone(),
+        }
+    }
 }
 
 impl RoomSession {
@@ -741,6 +767,9 @@ impl RoomSession {
             EngineEvent::DataStreamTrailer { trailer, participant_identity } => {
                 self.handle_data_stream_trailer(trailer, participant_identity);
             }
+            EngineEvent::DataChannelBufferedAmountLowThresholdChanged { kind, threshold } => {
+                self.handle_data_channel_buffered_low_threshold_change(kind, threshold);
+            }
             _ => {}
         }
 
@@ -1278,6 +1307,24 @@ impl RoomSession {
         self.dispatcher.dispatch(&event);
     }
 
+    fn handle_data_channel_buffered_low_threshold_change(
+        &self,
+        kind: DataPacketKind,
+        threshold: u64,
+    ) {
+        let mut info = self.info.write();
+        match kind {
+            DataPacketKind::Lossy => {
+                info.lossy_dc_options.buffered_amount_low_threshold = threshold;
+            }
+            DataPacketKind::Reliable => {
+                info.reliable_dc_options.buffered_amount_low_threshold = threshold;
+            }
+        }
+        let event = RoomEvent::DataChannelBufferedAmountLowThresholdChanged { kind, threshold };
+        self.dispatcher.dispatch(&event);
+    }
+
     /// Create a new participant
     /// Also add it to the participants list
     fn create_participant(