fix: accept namespaced discovery server information (#1039)

Author: tsarlandie-oai

crates/rmcp/src/model.rs

@@ -1113,7 +1113,7 @@ 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]
@@ -1124,7 +1124,8 @@ pub struct DiscoverResult {
     pub supported_versions: Vec<ProtocolVersion>,
     /// Capabilities provided by this server.
     pub capabilities: ServerCapabilities,
-    /// Information about the server implementation.
+    /// Information about the server implementation. Also accepted from
+    /// `_meta["io.modelcontextprotocol/serverInfo"]` during deserialization.
     pub server_info: Implementation,
     /// Optional guidance for using the server.
     #[serde(skip_serializing_if = "Option::is_none")]
@@ -1138,6 +1139,53 @@ 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<Implementation>,
+            instructions: Option<String>,
+            ttl_ms: u64,
+            cache_scope: CacheScope,
+            #[serde(rename = "_meta")]
+            meta: Option<MetaObject>,
+        }
+
+        let helper = Helper::deserialize(deserializer)?;
+        let server_info = match helper.server_info {
+            Some(server_info) => server_info,
+            None => {
+                let metadata_server_info = helper
+                    .meta
+                    .as_ref()
+                    .and_then(|metadata| metadata.0.get("io.modelcontextprotocol/serverInfo"))
+                    .ok_or_else(|| serde::de::Error::missing_field("serverInfo"))?;
+
+                serde_json::from_value(metadata_server_info.clone())
+                    .map_err(serde::de::Error::custom)?
+            }
+        };
+
+        Ok(Self {
+            result_type: helper.result_type,
+            supported_versions: helper.supported_versions,
+            capabilities: helper.capabilities,
+            server_info,
+            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(

crates/rmcp/tests/test_server_discover.rs

@@ -74,6 +74,110 @@ fn discover_result_deserializes_to_typed_variant() {
     );
 }
 
+#[test]
+fn discover_result_accepts_server_info_in_namespaced_metadata() {
+    let message: ServerJsonRpcMessage = serde_json::from_value(json!({
+        "jsonrpc": "2.0",
+        "id": 1,
+        "result": {
+            "resultType": "complete",
+            "supportedVersions": ["2026-07-28"],
+            "capabilities": {},
+            "ttlMs": 0,
+            "cacheScope": "private",
+            "_meta": {
+                "io.modelcontextprotocol/serverInfo": {
+                    "name": "conformance-mock-server",
+                    "version": "1.0.0"
+                },
+                "unrelated": { "preserved": true }
+            }
+        }
+    }))
+    .expect("discovery response with namespaced server info should deserialize");
+
+    let ServerJsonRpcMessage::Response(JsonRpcResponse { result, .. }) = message else {
+        panic!("expected response");
+    };
+    let ServerResult::DiscoverResult(result) = result else {
+        panic!("expected discovery response, not a tool-call result");
+    };
+
+    assert_eq!(result.server_info.name, "conformance-mock-server");
+    assert_eq!(result.server_info.version, "1.0.0");
+
+    let metadata = result.meta.expect("discovery metadata should be preserved");
+    assert_eq!(
+        metadata.0.get("io.modelcontextprotocol/serverInfo"),
+        Some(&json!({
+            "name": "conformance-mock-server",
+            "version": "1.0.0"
+        }))
+    );
+    assert_eq!(
+        metadata.0.get("unrelated"),
+        Some(&json!({ "preserved": true }))
+    );
+}
+
+#[test]
+fn discover_result_prefers_top_level_server_info_over_namespaced_metadata() {
+    let result: DiscoverResult = serde_json::from_value(json!({
+        "resultType": "complete",
+        "supportedVersions": ["2026-07-28"],
+        "capabilities": {},
+        "serverInfo": {
+            "name": "top-level-server",
+            "version": "2.0.0"
+        },
+        "ttlMs": 0,
+        "cacheScope": "private",
+        "_meta": {
+            "io.modelcontextprotocol/serverInfo": {
+                "name": "metadata-server",
+                "version": "1.0.0"
+            },
+            "unrelated": true
+        }
+    }))
+    .expect("top-level server info should remain supported");
+
+    assert_eq!(result.server_info.name, "top-level-server");
+    assert_eq!(result.server_info.version, "2.0.0");
+    assert_eq!(
+        result
+            .meta
+            .as_ref()
+            .and_then(|metadata| metadata.0.get("unrelated")),
+        Some(&json!(true))
+    );
+}
+
+#[test]
+fn discover_result_requires_valid_top_level_or_namespaced_server_info() {
+    let result = json!({
+        "resultType": "complete",
+        "supportedVersions": ["2026-07-28"],
+        "capabilities": {},
+        "ttlMs": 0,
+        "cacheScope": "private",
+        "_meta": { "unrelated": true }
+    });
+
+    assert!(serde_json::from_value::<DiscoverResult>(result).is_err());
+
+    let malformed_server_info = json!({
+        "resultType": "complete",
+        "supportedVersions": ["2026-07-28"],
+        "capabilities": {},
+        "ttlMs": 0,
+        "cacheScope": "private",
+        "_meta": { "io.modelcontextprotocol/serverInfo": { "name": "missing-version" } }
+    });
+
+    assert!(serde_json::from_value::<DiscoverResult>(malformed_server_info).is_err());
+}
+
 #[test]
 fn unsupported_protocol_version_error_matches_draft_schema() {
     let error = ErrorData::unsupported_protocol_version(