feat: add server/discover model types

Add the SEP-2575 server/discover request and result model,
wire it into the JSON-RPC request/result unions, and cover basic serde routing.

Fixes #869

Author: howardjohn

crates/rmcp/src/handler/server.rs

@@ -27,6 +27,9 @@ impl<H: ServerHandler> Service<RoleServer> for H {
         // `context` is moved into the dispatch below, so read the negotiated version first.
         let protocol_version = context.protocol_version();
         let result = match request {
+            ClientRequest::DiscoverRequest(_request) => {
+                Err(McpError::method_not_found::<DiscoverRequestMethod>())
+            }
             ClientRequest::InitializeRequest(request) => self
                 .initialize(request.params, context)
                 .await

crates/rmcp/src/model.rs

@@ -808,6 +808,55 @@ impl CustomRequest {
     }
 }
 
+const_string!(DiscoverRequestMethod = "server/discover");
+
+/// Sent from the client to discover server identity, capabilities, and supported protocol versions.
+pub type DiscoverRequest = Request<DiscoverRequestMethod, EmptyObject>;
+
+#[derive(Debug, Serialize, Deserialize, Clone, PartialEq)]
+#[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
+#[non_exhaustive]
+pub struct DiscoverResult {
+    pub supported_versions: Vec<ProtocolVersion>,
+    pub capabilities: ServerCapabilities,
+    pub server_info: Implementation,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub instructions: Option<String>,
+    #[serde(rename = "_meta", skip_serializing_if = "Option::is_none")]
+    pub meta: Option<Meta>,
+}
+
+impl DiscoverResult {
+    pub fn new(
+        supported_versions: impl Into<Vec<ProtocolVersion>>,
+        capabilities: ServerCapabilities,
+    ) -> Self {
+        Self {
+            supported_versions: supported_versions.into(),
+            capabilities,
+            server_info: Implementation::from_build_env(),
+            instructions: None,
+            meta: None,
+        }
+    }
+
+    pub fn with_server_info(mut self, server_info: Implementation) -> Self {
+        self.server_info = server_info;
+        self
+    }
+
+    pub fn with_instructions(mut self, instructions: impl Into<String>) -> Self {
+        self.instructions = Some(instructions.into());
+        self
+    }
+
+    pub fn with_meta(mut self, meta: Meta) -> Self {
+        self.meta = Some(meta);
+        self
+    }
+}
+
 const_string!(InitializeResultMethod = "initialize");
 /// # Initialization
 /// This request is sent from the client to the server when it first connects, asking it to begin initialization.
@@ -3572,6 +3621,7 @@ macro_rules! ts_union {
 
 ts_union!(
     export type ClientRequest =
+    | DiscoverRequest
     | PingRequest
     | InitializeRequest
     | CompleteRequest
@@ -3595,6 +3645,7 @@ ts_union!(
 impl ClientRequest {
     pub fn method(&self) -> &str {
         match &self {
+            ClientRequest::DiscoverRequest(r) => r.method.as_str(),
             ClientRequest::PingRequest(r) => r.method.as_str(),
             ClientRequest::InitializeRequest(r) => r.method.as_str(),
             ClientRequest::CompleteRequest(r) => r.method.as_str(),
@@ -3669,6 +3720,7 @@ ts_union!(
 
 ts_union!(
     export type ServerResult =
+    | DiscoverResult
     | InitializeResult
     | CompleteResult
     | GetPromptResult

crates/rmcp/src/model/meta.rs

@@ -138,6 +138,7 @@ macro_rules! variant_extension {
 
 variant_extension! {
     ClientRequest {
+        DiscoverRequest
         PingRequest
         InitializeRequest
         CompleteRequest

crates/rmcp/tests/test_deserialization.rs

@@ -1,4 +1,50 @@
-use rmcp::model::{JsonRpcResponse, ServerJsonRpcMessage, ServerResult};
+use rmcp::model::{
+    ClientJsonRpcMessage, ClientRequest, JsonRpcResponse, ServerJsonRpcMessage, ServerResult,
+};
+use serde_json::json;
+
+#[test]
+fn test_discover_request() {
+    let message: ClientJsonRpcMessage = serde_json::from_value(json!({
+        "jsonrpc": "2.0",
+        "id": 1,
+        "method": "server/discover",
+        "params": {}
+    }))
+    .unwrap();
+
+    assert!(matches!(
+        message,
+        ClientJsonRpcMessage::Request(r)
+            if matches!(r.request, ClientRequest::DiscoverRequest(_))
+    ));
+}
+
+#[test]
+fn test_discover_result() {
+    let message: ServerJsonRpcMessage = serde_json::from_value(json!({
+        "jsonrpc": "2.0",
+        "id": 1,
+        "result": {
+            "supportedVersions": ["2026-07-28", "2025-11-25"],
+            "capabilities": {},
+            "serverInfo": {
+                "name": "test-server",
+                "version": "1.0.0"
+            }
+        }
+    }))
+    .unwrap();
+
+    assert!(matches!(
+        message,
+        ServerJsonRpcMessage::Response(JsonRpcResponse {
+            result: ServerResult::DiscoverResult(_),
+            ..
+        })
+    ));
+}
+
 #[test]
 fn test_tool_list_result() {
     let json = std::fs::read("tests/test_deserialization/tool_list_result.json").unwrap();

crates/rmcp/tests/test_message_schema/client_json_rpc_message_schema.json

@@ -530,6 +530,11 @@
     "CustomResult": {
       "description": "A catch-all response either side can use for custom requests."
     },
+    "DiscoverRequestMethod": {
+      "type": "string",
+      "format": "const",
+      "const": "server/discover"
+    },
     "ElicitResult": {
       "description": "The result returned by a client in response to an elicitation request.\n\nContains the user's decision (accept/decline/cancel) and optionally their input data\nif they chose to accept the request.",
       "type": "object",
@@ -1038,10 +1043,10 @@
       },
       "anyOf": [
         {
-          "$ref": "#/definitions/RequestNoParam"
+          "$ref": "#/definitions/Request"
         },
         {
-          "$ref": "#/definitions/Request"
+          "$ref": "#/definitions/RequestNoParam"
         },
         {
           "$ref": "#/definitions/Request2"
@@ -1052,6 +1057,9 @@
         {
           "$ref": "#/definitions/Request4"
         },
+        {
+          "$ref": "#/definitions/Request5"
+        },
         {
           "$ref": "#/definitions/RequestOptionalParam"
         },
@@ -1061,9 +1069,6 @@
         {
           "$ref": "#/definitions/RequestOptionalParam3"
         },
-        {
-          "$ref": "#/definitions/Request5"
-        },
         {
           "$ref": "#/definitions/Request6"
         },
@@ -1073,20 +1078,23 @@
         {
           "$ref": "#/definitions/Request8"
         },
+        {
+          "$ref": "#/definitions/Request9"
+        },
         {
           "$ref": "#/definitions/RequestOptionalParam4"
         },
         {
-          "$ref": "#/definitions/Request9"
+          "$ref": "#/definitions/Request10"
         },
         {
           "$ref": "#/definitions/RequestOptionalParam5"
         },
         {
-          "$ref": "#/definitions/Request10"
+          "$ref": "#/definitions/Request11"
         },
         {
-          "$ref": "#/definitions/Request11"
+          "$ref": "#/definitions/Request12"
         },
         {
           "$ref": "#/definitions/CustomRequest"
@@ -1426,10 +1434,10 @@
       "type": "object",
       "properties": {
         "method": {
-          "$ref": "#/definitions/InitializeResultMethod"
+          "$ref": "#/definitions/DiscoverRequestMethod"
         },
         "params": {
-          "$ref": "#/definitions/InitializeRequestParams"
+          "$ref": "#/definitions/EmptyObject"
         }
       },
       "required": [
@@ -1438,6 +1446,22 @@
       ]
     },
     "Request10": {
+      "description": "Represents a JSON-RPC request with method, parameters, and extensions.\n\nThis is the core structure for all MCP requests, containing:\n- `method`: The name of the method being called\n- `params`: The parameters for the method\n- `extensions`: Additional context data (similar to HTTP headers)",
+      "type": "object",
+      "properties": {
+        "method": {
+          "$ref": "#/definitions/GetTaskMethod"
+        },
+        "params": {
+          "$ref": "#/definitions/GetTaskParams"
+        }
+      },
+      "required": [
+        "method",
+        "params"
+      ]
+    },
+    "Request11": {
       "description": "Represents a JSON-RPC request with method, parameters, and extensions.\n\nThis is the core structure for all MCP requests, containing:\n- `method`: The name of the method being called\n- `params`: The parameters for the method\n- `extensions`: Additional context data (similar to HTTP headers)",
       "type": "object",
       "properties": {
@@ -1453,7 +1477,7 @@
         "params"
       ]
     },
-    "Request11": {
+    "Request12": {
       "description": "Represents a JSON-RPC request with method, parameters, and extensions.\n\nThis is the core structure for all MCP requests, containing:\n- `method`: The name of the method being called\n- `params`: The parameters for the method\n- `extensions`: Additional context data (similar to HTTP headers)",
       "type": "object",
       "properties": {
@@ -1474,10 +1498,10 @@
       "type": "object",
       "properties": {
         "method": {
-          "$ref": "#/definitions/CompleteRequestMethod"
+          "$ref": "#/definitions/InitializeResultMethod"
         },
         "params": {
-          "$ref": "#/definitions/CompleteRequestParams"
+          "$ref": "#/definitions/InitializeRequestParams"
         }
       },
       "required": [
@@ -1490,10 +1514,10 @@
       "type": "object",
       "properties": {
         "method": {
-          "$ref": "#/definitions/SetLevelRequestMethod"
+          "$ref": "#/definitions/CompleteRequestMethod"
         },
         "params": {
-          "$ref": "#/definitions/SetLevelRequestParams"
+          "$ref": "#/definitions/CompleteRequestParams"
         }
       },
       "required": [
@@ -1506,10 +1530,10 @@
       "type": "object",
       "properties": {
         "method": {
-          "$ref": "#/definitions/GetPromptRequestMethod"
+          "$ref": "#/definitions/SetLevelRequestMethod"
         },
         "params": {
-          "$ref": "#/definitions/GetPromptRequestParams"
+          "$ref": "#/definitions/SetLevelRequestParams"
         }
       },
       "required": [
@@ -1522,10 +1546,10 @@
       "type": "object",
       "properties": {
         "method": {
-          "$ref": "#/definitions/ReadResourceRequestMethod"
+          "$ref": "#/definitions/GetPromptRequestMethod"
         },
         "params": {
-          "$ref": "#/definitions/ReadResourceRequestParams"
+          "$ref": "#/definitions/GetPromptRequestParams"
         }
       },
       "required": [
@@ -1538,10 +1562,10 @@
       "type": "object",
       "properties": {
         "method": {
-          "$ref": "#/definitions/SubscribeRequestMethod"
+          "$ref": "#/definitions/ReadResourceRequestMethod"
         },
         "params": {
-          "$ref": "#/definitions/SubscribeRequestParams"
+          "$ref": "#/definitions/ReadResourceRequestParams"
         }
       },
       "required": [
@@ -1554,10 +1578,10 @@
       "type": "object",
       "properties": {
         "method": {
-          "$ref": "#/definitions/UnsubscribeRequestMethod"
+          "$ref": "#/definitions/SubscribeRequestMethod"
         },
         "params": {
-          "$ref": "#/definitions/UnsubscribeRequestParams"
+          "$ref": "#/definitions/SubscribeRequestParams"
         }
       },
       "required": [
@@ -1570,10 +1594,10 @@
       "type": "object",
       "properties": {
         "method": {
-          "$ref": "#/definitions/CallToolRequestMethod"
+          "$ref": "#/definitions/UnsubscribeRequestMethod"
         },
         "params": {
-          "$ref": "#/definitions/CallToolRequestParams"
+          "$ref": "#/definitions/UnsubscribeRequestParams"
         }
       },
       "required": [
@@ -1586,10 +1610,10 @@
       "type": "object",
       "properties": {
         "method": {
-          "$ref": "#/definitions/GetTaskMethod"
+          "$ref": "#/definitions/CallToolRequestMethod"
         },
         "params": {
-          "$ref": "#/definitions/GetTaskParams"
+          "$ref": "#/definitions/CallToolRequestParams"
         }
       },
       "required": [