Advertise client capabilities to SFU

.changeset/sdk_capabilities.md

@@ -0,0 +1,6 @@
+---
+livekit-api: patch
+livekit-uniffi: patch
+---
+
+Add advertising of SDK client capabilities - #1022 (@chenosaurus)

livekit-api/src/access_token.rs

@@ -336,6 +336,7 @@ mod tests {
             agents: vec![livekit_protocol::RoomAgentDispatch {
                 agent_name: "test-agent".to_string(),
                 metadata: "test-metadata".to_string(),
+                ..Default::default()
             }],
             ..Default::default()
         };

livekit-api/src/signal_client/mod.rs

@@ -54,6 +54,10 @@ const REGION_FETCH_TIMEOUT: Duration = Duration::from_secs(3);
 const VALIDATE_TIMEOUT: Duration = Duration::from_secs(3);
 pub const PROTOCOL_VERSION: u32 = 17;
 
+/// Capabilities the Rust SDK advertises to the SFU at connect time.
+const CLIENT_CAPABILITIES: &[proto::client_info::Capability] =
+    &[proto::client_info::Capability::CapPacketTrailer];
+
 #[derive(Error, Debug)]
 pub enum SignalError {
     #[error("ws failure: {0}")]
@@ -580,6 +584,7 @@ fn create_join_request_param(
         os,
         os_version,
         device_model,
+        capabilities: CLIENT_CAPABILITIES.iter().map(|c| *c as i32).collect(),
         ..Default::default()
     };
 
@@ -683,6 +688,13 @@ fn get_livekit_url(
             lk_url.query_pairs_mut().append_pair("version", sdk_version.as_str());
         }
 
+        // parse client capabilities
+        if !CLIENT_CAPABILITIES.is_empty() {
+            let caps =
+                CLIENT_CAPABILITIES.iter().map(|c| c.as_str_name()).collect::<Vec<_>>().join(",");
+            lk_url.query_pairs_mut().append_pair("capabilities", &caps);
+        }
+
         // For reconnects in v0 path, add reconnect and sid as separate query parameters
         if reconnect {
             lk_url
@@ -802,6 +814,24 @@ mod tests {
         assert_eq!(validate_url.scheme(), "https");
     }
 
+    #[test]
+    fn livekit_url_includes_client_capabilities() {
+        let io = SignalOptions::default();
+        let lk_url = get_livekit_url("wss://localhost:7880", &io, false, false, None, "").unwrap();
+
+        let capabilities = lk_url
+            .query_pairs()
+            .find_map(|(key, value)| (key == "capabilities").then(|| value.into_owned()))
+            .unwrap();
+        let expected = CLIENT_CAPABILITIES
+            .iter()
+            .map(|capability| capability.as_str_name())
+            .collect::<Vec<_>>()
+            .join(",");
+
+        assert_eq!(capabilities, expected);
+    }
+
     /// Regression test for https://github.com/livekit/rust-sdks/issues/1042.
     ///
     /// Prior to the fix, `SignalInner::validate` issued an auth-less GET to