fix: accept namespaced discovery server information (#1039)

Author: tsarlandie-oai

crates/rmcp/src/model.rs

@@ -1089,6 +1089,42 @@ impl InitializeResult {
 pub type ServerInfo = InitializeResult;
 pub type ClientInfo = InitializeRequestParams;
 
+/// Information learned about a server by a client.
+///
+/// Legacy initialization requires [`server_info`](Self::server_info), while
+/// the modern discovery lifecycle carries it as optional, self-reported result
+/// metadata. The remaining fields are available in both lifecycle modes.
+#[derive(Debug, Serialize, Deserialize, Clone, PartialEq)]
+#[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
+#[non_exhaustive]
+pub struct ServerPeerInfo {
+    /// The negotiated protocol version.
+    pub protocol_version: ProtocolVersion,
+    /// The capabilities advertised by the server.
+    pub capabilities: ServerCapabilities,
+    /// Optional, self-reported server implementation identity.
+    pub server_info: Option<Implementation>,
+    /// Optional human-readable instructions about using the server.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub instructions: Option<String>,
+    /// Protocol-level response metadata.
+    #[serde(rename = "_meta", skip_serializing_if = "Option::is_none")]
+    pub meta: Option<MetaObject>,
+}
+
+impl From<ServerInfo> for ServerPeerInfo {
+    fn from(info: ServerInfo) -> Self {
+        Self {
+            protocol_version: info.protocol_version,
+            capabilities: info.capabilities,
+            server_info: Some(info.server_info),
+            instructions: info.instructions,
+            meta: info.meta,
+        }
+    }
+}
+
 const_string!(DiscoverRequestMethod = "server/discover");
 
 /// Parameters for [`DiscoverRequest`].
@@ -1120,7 +1156,7 @@ impl schemars::JsonSchema for DiscoverRequestParams {
 pub type DiscoverRequest = Request<DiscoverRequestMethod, DiscoverRequestParams>;
 
 /// The server's response to a [`DiscoverRequest`].
-#[derive(Debug, Serialize, Deserialize, Clone, PartialEq)]
+#[derive(Debug, Serialize, Clone, PartialEq)]
 #[serde(rename_all = "camelCase")]
 #[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 #[non_exhaustive]
@@ -1131,8 +1167,6 @@ pub struct DiscoverResult {
     pub supported_versions: Vec<ProtocolVersion>,
     /// Capabilities provided by this server.
     pub capabilities: ServerCapabilities,
-    /// Information about the server implementation.
-    pub server_info: Implementation,
     /// Optional guidance for using the server.
     #[serde(skip_serializing_if = "Option::is_none")]
     pub instructions: Option<String>,
@@ -1145,18 +1179,77 @@ pub struct DiscoverResult {
     pub meta: Option<MetaObject>,
 }
 
+impl<'de> Deserialize<'de> for DiscoverResult {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        #[derive(Deserialize)]
+        #[serde(rename_all = "camelCase")]
+        struct Helper {
+            result_type: ResultType,
+            supported_versions: Vec<ProtocolVersion>,
+            capabilities: ServerCapabilities,
+            server_info: Option<serde_json::Value>,
+            instructions: Option<String>,
+            ttl_ms: u64,
+            cache_scope: CacheScope,
+            #[serde(rename = "_meta")]
+            meta: Option<MetaObject>,
+        }
+
+        let mut helper = Helper::deserialize(deserializer)?;
+        let has_canonical_server_info = helper
+            .meta
+            .as_ref()
+            .is_some_and(|metadata| metadata.0.contains_key(MetaObject::META_KEY_SERVER_INFO));
+        if !has_canonical_server_info
+            && let Some(server_info) = helper
+                .server_info
+                .and_then(|value| serde_json::from_value::<Implementation>(value).ok())
+        {
+            helper
+                .meta
+                .get_or_insert_with(MetaObject::new)
+                .set_server_info(server_info);
+        }
+
+        Ok(Self {
+            result_type: helper.result_type,
+            supported_versions: helper.supported_versions,
+            capabilities: helper.capabilities,
+            instructions: helper.instructions,
+            ttl_ms: helper.ttl_ms,
+            cache_scope: helper.cache_scope,
+            meta: helper.meta,
+        })
+    }
+}
+
 impl DiscoverResult {
     /// Create a non-cacheable private discovery result.
     pub fn new(
         supported_versions: Vec<ProtocolVersion>,
         capabilities: ServerCapabilities,
         server_info: Implementation,
+    ) -> Self {
+        Self::new_without_server_info(supported_versions, capabilities)
+            .with_server_info(server_info)
+    }
+
+    /// Create a non-cacheable private discovery result without a server identity.
+    ///
+    /// Server identity is optional display-only metadata. Servers should normally
+    /// use [`DiscoverResult::new`], but this constructor supports peers that do
+    /// not advertise an implementation name and version.
+    pub fn new_without_server_info(
+        supported_versions: Vec<ProtocolVersion>,
+        capabilities: ServerCapabilities,
     ) -> Self {
         Self {
             result_type: ResultType::COMPLETE,
             supported_versions,
             capabilities,
-            server_info,
             instructions: None,
             ttl_ms: 0,
             cache_scope: CacheScope::Private,
@@ -1178,10 +1271,30 @@ impl DiscoverResult {
         } = server_info;
         let mut result = Self::new(supported_versions, capabilities, server_info);
         result.instructions = instructions;
-        result.meta = meta;
+        if let Some(meta) = meta {
+            result.meta.get_or_insert_with(MetaObject::new).extend(meta);
+        }
         result
     }
 
+    /// Return the optional self-reported server identity from result metadata.
+    pub fn server_info(&self) -> Option<Implementation> {
+        self.meta.as_ref().and_then(MetaObject::server_info)
+    }
+
+    /// Set the self-reported server identity in canonical result metadata.
+    pub fn set_server_info(&mut self, server_info: Implementation) {
+        self.meta
+            .get_or_insert_with(MetaObject::new)
+            .set_server_info(server_info);
+    }
+
+    /// Set the self-reported server identity in canonical result metadata.
+    pub fn with_server_info(mut self, server_info: Implementation) -> Self {
+        self.set_server_info(server_info);
+        self
+    }
+
     /// Set the cache lifetime hint in milliseconds.
     pub fn with_ttl_ms(mut self, ttl_ms: u64) -> Self {
         self.ttl_ms = ttl_ms;

crates/rmcp/src/model/meta.rs

@@ -253,6 +253,8 @@ pub struct MetaObject(pub JsonObject);
 pub use self::MetaObject as Meta;
 
 impl MetaObject {
+    /// Reserved result metadata key for the server implementation identity.
+    pub const META_KEY_SERVER_INFO: &'static str = "io.modelcontextprotocol/serverInfo";
     /// Reserved `_meta` key for the W3C Trace Context `traceparent` value (SEP-414).
     const TRACEPARENT_FIELD: &str = "traceparent";
     /// Reserved `_meta` key for the W3C Trace Context `tracestate` value (SEP-414).
@@ -322,6 +324,19 @@ impl MetaObject {
         self.0.extend(other.0);
     }
 
+    /// Get the self-reported server implementation identity, if present and valid.
+    ///
+    /// This value is intended for display, logging, and debugging. Callers must
+    /// not use it for behavioral or security decisions.
+    pub fn server_info(&self) -> Option<Implementation> {
+        self.decode_value(Self::META_KEY_SERVER_INFO)
+    }
+
+    /// Set the self-reported server implementation identity.
+    pub fn set_server_info(&mut self, server_info: Implementation) {
+        self.insert_serialized(Self::META_KEY_SERVER_INFO, server_info);
+    }
+
     fn decode_value<T>(&self, key: &str) -> Option<T>
     where
         T: for<'de> Deserialize<'de>,

crates/rmcp/src/service/client.rs

@@ -25,7 +25,7 @@ use crate::{
         NumberOrString, PaginatedRequestParams, ProgressNotification, ProgressNotificationParam,
         ProtocolVersion, ReadResourceRequest, ReadResourceRequestParams, ReadResourceResponse,
         ReadResourceResult, Reference, RequestId, RequestMetaObject, RootsListChangedNotification,
-        ServerInfo, ServerJsonRpcMessage, ServerNotification, ServerRequest, ServerResult,
+        ServerJsonRpcMessage, ServerNotification, ServerPeerInfo, ServerRequest, ServerResult,
         SetLevelRequest, SetLevelRequestParams, SubscribeRequest, SubscribeRequestParams,
         SubscriptionFilter, SubscriptionsListenRequest, SubscriptionsListenRequestParams,
         SubscriptionsListenResult, UnsubscribeRequest, UnsubscribeRequestParams, UpdateTaskParams,
@@ -188,7 +188,7 @@ impl ServiceRole for RoleClient {
     type PeerResp = ServerResult;
     type PeerNot = ServerNotification;
     type Info = ClientInfo;
-    type PeerInfo = ServerInfo;
+    type PeerInfo = ServerPeerInfo;
     type InitializeError = ClientInitializeError;
     const IS_CLIENT: bool = true;
 
@@ -751,7 +751,7 @@ where
     let ServerResult::InitializeResult(initialize_result) = response else {
         return Err(ClientInitializeError::ExpectedInitResult(Some(response)));
     };
-    peer.set_peer_info(initialize_result);
+    peer.set_peer_info(initialize_result.into());
 
     // send notification
     let notification = ClientJsonRpcMessage::notification(
@@ -821,10 +821,11 @@ where
                         server_supported: result.supported_versions,
                     });
                 };
-                peer.set_peer_info(ServerInfo {
+                let server_info = result.server_info();
+                peer.set_peer_info(ServerPeerInfo {
                     protocol_version: selected.clone(),
                     capabilities: result.capabilities,
-                    server_info: result.server_info,
+                    server_info,
                     instructions: result.instructions,
                     meta: result.meta,
                 });

crates/rmcp/tests/test_client_lifecycle_modes.rs

@@ -60,6 +60,51 @@ async fn discover_startup_accepts_stringified_numeric_response_id() {
     server_task.await.expect("server task");
 }
 
+#[tokio::test]
+async fn discover_startup_accepts_anonymous_server() {
+    let (server_transport, client_transport) = tokio::io::duplex(4096);
+    let mut server = IntoTransport::<rmcp::RoleServer, _, _>::into_transport(server_transport);
+    let server_task = tokio::spawn(async move {
+        let ClientJsonRpcMessage::Request(request) =
+            server.receive().await.expect("expected discover request")
+        else {
+            panic!("expected discover request");
+        };
+        let result: DiscoverResult = serde_json::from_value(serde_json::json!({
+            "resultType": "complete",
+            "supportedVersions": ["2026-07-28"],
+            "capabilities": {},
+            "ttlMs": 0,
+            "cacheScope": "private"
+        }))
+        .expect("anonymous discovery result");
+        server
+            .send(ServerJsonRpcMessage::response(
+                ServerResult::DiscoverResult(result),
+                request.id,
+            ))
+            .await
+            .expect("send discover response");
+    });
+
+    let client = DiscoverClient
+        .serve_with_lifecycle(
+            client_transport,
+            ClientLifecycleMode::Discover {
+                preferred_versions: vec![ProtocolVersion::V_2026_07_28],
+            },
+        )
+        .await
+        .expect("anonymous server should remain discoverable");
+    let peer = client
+        .peer_info()
+        .expect("discovery should store peer state");
+    assert_eq!(peer.protocol_version, ProtocolVersion::V_2026_07_28);
+    assert_eq!(peer.server_info, None);
+    client.cancel().await.expect("cancel client");
+    server_task.await.expect("server task");
+}
+
 #[tokio::test]
 async fn high_level_server_accepts_discover_startup_without_initialize() {
     let (server_transport, client_transport) = tokio::io::duplex(4096);

crates/rmcp/tests/test_mrtr_behavior.rs

@@ -316,7 +316,7 @@ where
             let client = serve_directly::<RoleClient, _, _, _, _>(
                 MrtrClient,
                 client_transport,
-                Some(client_peer_info),
+                Some(client_peer_info.into()),
             );
 
             let result = body(client).await;
@@ -580,7 +580,7 @@ async fn request_state_codec_seals_and_verifies_through_the_loop() -> anyhow::Re
             let client = serve_directly::<RoleClient, _, _, _, _>(
                 MrtrClient,
                 client_transport,
-                Some(server_info(ProtocolVersion::V_2026_07_28)),
+                Some(server_info(ProtocolVersion::V_2026_07_28).into()),
             );
 
             let result = client