feat: support version negotiation

Author: =

crates/rmcp/src/model.rs

@@ -30,7 +30,6 @@ pub fn object(value: serde_json::Value) -> JsonObject {
     }
 }
 
-
 /// Use this macro just like [`serde_json::json!`]
 #[cfg(feature = "macros")]
 #[macro_export]
@@ -103,6 +102,23 @@ impl ProtocolVersion {
     pub const LATEST: Self = Self::V_2025_03_26;
 }
 
+impl PartialOrd for ProtocolVersion {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        fn parse(s: &str) -> Option<(u16, u16, u16)> {
+            let (s_year, rest) = s.split_once('-')?;
+            let (s_month, rest) = rest.split_once('-')?;
+            let s_day = rest;
+            let year = s_year.parse::<u16>().ok()?;
+            let month = s_month.parse::<u16>().ok()?;
+            let day = s_day.parse::<u16>().ok()?;
+            Some((year, month, day))
+        }
+        let self_date = parse(self.0.as_ref())?;
+        let other_date = parse(other.0.as_ref())?;
+        Some(self_date.cmp(&other_date))
+    }
+}
+
 impl Serialize for ProtocolVersion {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -1135,4 +1151,11 @@ mod tests {
 
         assert_eq!(server_response_json, raw_response_json);
     }
+
+    #[test]
+    fn test_protocol_version_order() {
+        let v1 = ProtocolVersion::V_2024_11_05;
+        let v2 = ProtocolVersion::V_2025_03_26;
+        assert!(v1 < v2);
+    }
 }

crates/rmcp/src/service/server.rs

@@ -6,9 +6,10 @@ use crate::model::{
     ClientRequest, ClientResult, CreateMessageRequest, CreateMessageRequestParam,
     CreateMessageResult, ListRootsRequest, ListRootsResult, LoggingMessageNotification,
     LoggingMessageNotificationParam, ProgressNotification, ProgressNotificationParam,
-    PromptListChangedNotification, ResourceListChangedNotification, ResourceUpdatedNotification,
-    ResourceUpdatedNotificationParam, ServerInfo, ServerJsonRpcMessage, ServerNotification,
-    ServerRequest, ServerResult, ToolListChangedNotification,
+    PromptListChangedNotification, ProtocolVersion, ResourceListChangedNotification,
+    ResourceUpdatedNotification, ResourceUpdatedNotificationParam, ServerInfo,
+    ServerJsonRpcMessage, ServerNotification, ServerRequest, ServerResult,
+    ToolListChangedNotification,
 };
 
 #[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
@@ -65,11 +66,11 @@ where
     T: IntoTransport<RoleServer, E, A>,
     E: std::error::Error + From<std::io::Error> + Send + Sync + 'static,
 {
+    const SUPPORTED_HIGHEST_VERSION: ProtocolVersion = ProtocolVersion::LATEST;
     let (sink, stream) = transport.into_transport();
     let mut sink = Box::pin(sink);
     let mut stream = Box::pin(stream);
     let id_provider = <Arc<AtomicU32RequestIdProvider>>::default();
-
     // service
     let (request, id) = stream
         .next()
@@ -90,7 +91,21 @@ where
         )
         .into());
     };
-    let init_response = service.get_info();
+
+    let protocol_version = match peer_info
+        .params
+        .protocol_version
+        .partial_cmp(&SUPPORTED_HIGHEST_VERSION)
+        .ok_or(std::io::Error::new(
+            std::io::ErrorKind::InvalidData,
+            "unsupported protocol version",
+        ))? {
+        std::cmp::Ordering::Less => peer_info.params.protocol_version.clone(),
+        _ => SUPPORTED_HIGHEST_VERSION,
+    };
+
+    let mut init_response = service.get_info();
+    init_response.protocol_version = protocol_version;
     sink.send(ServerJsonRpcMessage::response(
         ServerResult::InitializeResult(init_response),
         id,