feat: add Default and constructors to ServerSseMessage (#794)

* feat: add Default and constructors to ServerSseMessage

* fix: add tests, missing feature gates, small test issues

Author: erenatas

crates/rmcp/src/transport/common/http_header.rs

@@ -65,8 +65,10 @@ pub(crate) fn extract_scope_from_header(header: &str) -> Option<String> {
 
 #[cfg(test)]
 mod tests {
+    #[cfg(feature = "client-side-sse")]
     use super::*;
 
+    #[cfg(feature = "client-side-sse")]
     #[test]
     fn extract_scope_quoted() {
         let header = r#"Bearer error="insufficient_scope", scope="files:read files:write""#;
@@ -76,6 +78,7 @@ mod tests {
         );
     }
 
+    #[cfg(feature = "client-side-sse")]
     #[test]
     fn extract_scope_unquoted() {
         let header = r#"Bearer scope=read:data, error="insufficient_scope""#;
@@ -85,12 +88,14 @@ mod tests {
         );
     }
 
+    #[cfg(feature = "client-side-sse")]
     #[test]
     fn extract_scope_missing() {
         let header = r#"Bearer error="invalid_token""#;
         assert_eq!(extract_scope_from_header(header), None);
     }
 
+    #[cfg(feature = "client-side-sse")]
     #[test]
     fn extract_scope_empty_header() {
         assert_eq!(extract_scope_from_header("Bearer"), None);

crates/rmcp/src/transport/common/server_side_http.rs

@@ -57,7 +57,7 @@ impl sse_stream::Timer for TokioTimer {
     }
 }
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, Default)]
 #[non_exhaustive]
 pub struct ServerSseMessage {
     /// The event ID for this message. When set, clients can use this ID
@@ -71,6 +71,37 @@ pub struct ServerSseMessage {
     pub retry: Option<Duration>,
 }
 
+impl ServerSseMessage {
+    /// Create a message carrying a JSON-RPC response/notification with an event ID.
+    pub fn new(event_id: impl Into<String>, message: ServerJsonRpcMessage) -> Self {
+        Self {
+            event_id: Some(event_id.into()),
+            message: Some(Arc::new(message)),
+            retry: None,
+        }
+    }
+
+    /// Wrap a JSON-RPC message without an event ID or retry hint.
+    pub fn from_message(message: ServerJsonRpcMessage) -> Self {
+        Self {
+            event_id: None,
+            message: Some(Arc::new(message)),
+            retry: None,
+        }
+    }
+
+    /// Create a priming event that tells the client to reconnect after `retry`
+    /// if the connection drops.
+    /// See [SEP-1699](https://github.com/modelcontextprotocol/modelcontextprotocol/issues/1699).
+    pub fn priming(event_id: impl Into<String>, retry: Duration) -> Self {
+        Self {
+            event_id: Some(event_id.into()),
+            message: None,
+            retry: Some(retry),
+        }
+    }
+}
+
 pub(crate) fn sse_stream_response(
     stream: impl futures::Stream<Item = ServerSseMessage> + Send + Sync + 'static,
     keep_alive: Option<Duration>,
@@ -169,3 +200,49 @@ where
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::model::{EmptyResult, JsonRpcResponse, JsonRpcVersion2_0, RequestId, ServerResult};
+
+    fn dummy_message() -> ServerJsonRpcMessage {
+        ServerJsonRpcMessage::Response(JsonRpcResponse {
+            jsonrpc: JsonRpcVersion2_0,
+            id: RequestId::Number(1),
+            result: ServerResult::EmptyResult(EmptyResult {}),
+        })
+    }
+
+    #[test]
+    fn default_has_all_none() {
+        let msg = ServerSseMessage::default();
+        assert!(msg.event_id.is_none());
+        assert!(msg.message.is_none());
+        assert!(msg.retry.is_none());
+    }
+
+    #[test]
+    fn new_sets_event_id_and_message() {
+        let msg = ServerSseMessage::new("42", dummy_message());
+        assert_eq!(msg.event_id.as_deref(), Some("42"));
+        assert!(msg.message.is_some());
+        assert!(msg.retry.is_none());
+    }
+
+    #[test]
+    fn from_message_has_no_event_id() {
+        let msg = ServerSseMessage::from_message(dummy_message());
+        assert!(msg.event_id.is_none());
+        assert!(msg.message.is_some());
+        assert!(msg.retry.is_none());
+    }
+
+    #[test]
+    fn priming_sets_event_id_and_retry() {
+        let msg = ServerSseMessage::priming("0", Duration::from_secs(5));
+        assert_eq!(msg.event_id.as_deref(), Some("0"));
+        assert!(msg.message.is_none());
+        assert_eq!(msg.retry, Some(Duration::from_secs(5)));
+    }
+}

crates/rmcp/src/transport/streamable_http_server/session/local.rs

@@ -1,7 +1,6 @@
 use std::{
     collections::{HashMap, HashSet, VecDeque},
     num::ParseIntError,
-    sync::Arc,
     time::Duration,
 };
 
@@ -222,21 +221,13 @@ impl CachedTx {
 
     async fn send(&mut self, message: ServerJsonRpcMessage) {
         let event_id = self.next_event_id();
-        let message = ServerSseMessage {
-            event_id: Some(event_id.to_string()),
-            message: Some(Arc::new(message)),
-            retry: None,
-        };
+        let message = ServerSseMessage::new(event_id.to_string(), message);
         self.cache_and_send(message).await;
     }
 
     async fn send_priming(&mut self, retry: Duration) {
         let event_id = self.next_event_id();
-        let message = ServerSseMessage {
-            event_id: Some(event_id.to_string()),
-            message: None,
-            retry: Some(retry),
-        };
+        let message = ServerSseMessage::priming(event_id.to_string(), retry);
         self.cache_and_send(message).await;
     }
 

crates/rmcp/src/transport/streamable_http_server/tower.rs

@@ -499,11 +499,7 @@ where
                 .map_err(internal_error_response("create standalone stream"))?;
             // Prepend priming event if sse_retry configured
             let stream = if let Some(retry) = self.config.sse_retry {
-                let priming = ServerSseMessage {
-                    event_id: Some("0".into()),
-                    message: None,
-                    retry: Some(retry),
-                };
+                let priming = ServerSseMessage::priming("0", retry);
                 futures::stream::once(async move { priming })
                     .chain(stream)
                     .left_stream()
@@ -609,11 +605,7 @@ where
                             .map_err(internal_error_response("get session"))?;
                         // Prepend priming event if sse_retry configured
                         let stream = if let Some(retry) = self.config.sse_retry {
-                            let priming = ServerSseMessage {
-                                event_id: Some("0".into()),
-                                message: None,
-                                retry: Some(retry),
-                            };
+                            let priming = ServerSseMessage::priming("0", retry);
                             futures::stream::once(async move { priming })
                                 .chain(stream)
                                 .left_stream()
@@ -687,20 +679,11 @@ where
                     .initialize_session(&session_id, message)
                     .await
                     .map_err(internal_error_response("create stream"))?;
-                let stream = futures::stream::once(async move {
-                    ServerSseMessage {
-                        event_id: None,
-                        message: Some(Arc::new(response)),
-                        retry: None,
-                    }
-                });
+                let stream =
+                    futures::stream::once(async move { ServerSseMessage::from_message(response) });
                 // Prepend priming event if sse_retry configured
                 let stream = if let Some(retry) = self.config.sse_retry {
-                    let priming = ServerSseMessage {
-                        event_id: Some("0".into()),
-                        message: None,
-                        retry: Some(retry),
-                    };
+                    let priming = ServerSseMessage::priming("0", retry);
                     futures::stream::once(async move { priming })
                         .chain(stream)
                         .left_stream()
@@ -774,11 +757,7 @@ where
                         // SSE mode (default): original behaviour preserved unchanged
                         let stream = ReceiverStream::new(receiver).map(|message| {
                             tracing::trace!(?message);
-                            ServerSseMessage {
-                                event_id: None,
-                                message: Some(Arc::new(message)),
-                                retry: None,
-                            }
+                            ServerSseMessage::from_message(message)
                         });
                         Ok(sse_stream_response(
                             stream,

crates/rmcp/tests/test_inflight_response_drain.rs

@@ -1,4 +1,4 @@
-#![cfg(not(feature = "local"))]
+#![cfg(all(feature = "client", feature = "server", not(feature = "local")))]
 // cargo test --test test_inflight_response_drain --features "client server"
 
 use std::{