feat: Sse server auto ping (#74)

1. auto ping in sse stream every second to make cursor happy
2. configurable sse keep alive

---------

Co-authored-by: = <=>

crates/rmcp/src/transport/sse_server.rs

@@ -1,4 +1,4 @@
-use std::{collections::HashMap, net::SocketAddr, sync::Arc};
+use std::{collections::HashMap, io, net::SocketAddr, sync::Arc, time::Duration};
 
 use axum::{
     Json, Router,
@@ -6,12 +6,11 @@ use axum::{
     http::StatusCode,
     response::{
         Response,
-        sse::{Event, Sse},
+        sse::{Event, KeepAlive, Sse},
     },
     routing::{get, post},
 };
-use futures::{Sink, SinkExt, Stream, StreamExt};
-use tokio::io;
+use futures::{Sink, SinkExt, Stream};
 use tokio_stream::wrappers::ReceiverStream;
 use tokio_util::sync::{CancellationToken, PollSender};
 use tracing::Instrument;
@@ -26,28 +25,33 @@ type TxStore =
     Arc<tokio::sync::RwLock<HashMap<SessionId, tokio::sync::mpsc::Sender<ClientJsonRpcMessage>>>>;
 pub type TransportReceiver = ReceiverStream<RxJsonRpcMessage<RoleServer>>;
 
+const DEFAULT_AUTO_PING_INTERVAL: Duration = Duration::from_secs(15);
+
 #[derive(Clone)]
 struct App {
     txs: TxStore,
     transport_tx: tokio::sync::mpsc::UnboundedSender<SseServerTransport>,
     post_path: Arc<str>,
+    sse_ping_interval: Duration,
 }
 
 impl App {
     pub fn new(
         post_path: String,
+        sse_ping_interval: Duration,
     ) -> (
         Self,
         tokio::sync::mpsc::UnboundedReceiver<SseServerTransport>,
     ) {
-        let (transport_tx, tranport_rx) = tokio::sync::mpsc::unbounded_channel();
+        let (transport_tx, transport_rx) = tokio::sync::mpsc::unbounded_channel();
         (
             Self {
                 txs: Default::default(),
                 transport_tx,
                 post_path: post_path.into(),
+                sse_ping_interval,
             },
-            tranport_rx,
+            transport_rx,
         )
     }
 }
@@ -87,7 +91,7 @@ async fn sse_handler(
 ) -> Result<Sse<impl Stream<Item = Result<Event, io::Error>>>, Response<String>> {
     let session = session_id();
     tracing::info!(%session, "sse connection");
-    use tokio_stream::wrappers::ReceiverStream;
+    use tokio_stream::{StreamExt, wrappers::ReceiverStream};
     use tokio_util::sync::PollSender;
     let (from_client_tx, from_client_rx) = tokio::sync::mpsc::channel(64);
     let (to_client_tx, to_client_rx) = tokio::sync::mpsc::channel(64);
@@ -108,11 +112,12 @@ async fn sse_handler(
     if transport_send_result.is_err() {
         tracing::warn!("send transport out error");
         let mut response =
-            Response::new("fail to send out trasnport, it seems server is closed".to_string());
+            Response::new("fail to send out transport, it seems server is closed".to_string());
         *response.status_mut() = StatusCode::INTERNAL_SERVER_ERROR;
         return Err(response);
     }
     let post_path = app.post_path.as_ref();
+    let ping_interval = app.sse_ping_interval;
     let stream = futures::stream::once(futures::future::ok(
         Event::default()
             .event("endpoint")
@@ -124,7 +129,7 @@ async fn sse_handler(
             Err(e) => Err(io::Error::new(io::ErrorKind::InvalidData, e)),
         }
     }));
-    Ok(Sse::new(stream))
+    Ok(Sse::new(stream).keep_alive(KeepAlive::new().interval(ping_interval)))
 }
 
 pub struct SseServerTransport {
@@ -190,6 +195,7 @@ impl Stream for SseServerTransport {
         mut self: std::pin::Pin<&mut Self>,
         cx: &mut std::task::Context<'_>,
     ) -> std::task::Poll<Option<Self::Item>> {
+        use futures::StreamExt;
         self.stream.poll_next_unpin(cx)
     }
 }
@@ -200,6 +206,7 @@ pub struct SseServerConfig {
     pub sse_path: String,
     pub post_path: String,
     pub ct: CancellationToken,
+    pub sse_keep_alive: Option<Duration>,
 }
 
 #[derive(Debug)]
@@ -215,6 +222,7 @@ impl SseServer {
             sse_path: "/sse".to_string(),
             post_path: "/message".to_string(),
             ct: CancellationToken::new(),
+            sse_keep_alive: None,
         })
         .await
     }
@@ -240,7 +248,10 @@ impl SseServer {
     /// Warning: This function creates a new SseServer instance with the provided configuration.
     /// `App.post_path` may be incorrect if using `Router` as an embedded router.
     pub fn new(config: SseServerConfig) -> (SseServer, Router) {
-        let (app, transport_rx) = App::new(config.post_path.clone());
+        let (app, transport_rx) = App::new(
+            config.post_path.clone(),
+            config.sse_keep_alive.unwrap_or(DEFAULT_AUTO_PING_INTERVAL),
+        );
         let router = Router::new()
             .route(&config.sse_path, get(sse_handler))
             .route(&config.post_path, post(post_event_handler))

examples/servers/src/axum_router.rs

@@ -24,6 +24,7 @@ async fn main() -> anyhow::Result<()> {
         sse_path: "/sse".to_string(),
         post_path: "/message".to_string(),
         ct: tokio_util::sync::CancellationToken::new(),
+        sse_keep_alive: None,
     };
 
     let (sse_server, router) = SseServer::new(config);