feat: add support for custom server notifications

crates/rmcp/src/handler/client.rs

@@ -56,6 +56,9 @@ impl<H: ClientHandler> Service<RoleClient> for H {
             ServerNotification::PromptListChangedNotification(_notification_no_param) => {
                 self.on_prompt_list_changed(context).await
             }
+            ServerNotification::CustomNotification(notification) => {
+                self.on_custom_notification(notification, context).await
+            }
         };
         Ok(())
     }
@@ -166,6 +169,14 @@ pub trait ClientHandler: Sized + Send + Sync + 'static {
     ) -> impl Future<Output = ()> + Send + '_ {
         std::future::ready(())
     }
+    fn on_custom_notification(
+        &self,
+        notification: CustomNotification,
+        context: NotificationContext<RoleClient>,
+    ) -> impl Future<Output = ()> + Send + '_ {
+        let _ = (notification, context);
+        std::future::ready(())
+    }
 
     fn get_info(&self) -> ClientInfo {
         ClientInfo::default()

crates/rmcp/src/handler/server.rs

@@ -90,7 +90,7 @@ impl<H: ServerHandler> Service<RoleServer> for H {
             ClientNotification::RootsListChangedNotification(_notification) => {
                 self.on_roots_list_changed(context).await
             }
-            ClientNotification::CustomClientNotification(notification) => {
+            ClientNotification::CustomNotification(notification) => {
                 self.on_custom_notification(notification, context).await
             }
         };
@@ -230,7 +230,7 @@ pub trait ServerHandler: Sized + Send + Sync + 'static {
     }
     fn on_custom_notification(
         &self,
-        notification: CustomClientNotification,
+        notification: CustomNotification,
         context: NotificationContext<RoleServer>,
     ) -> impl Future<Output = ()> + Send + '_ {
         let _ = (notification, context);

crates/rmcp/src/model.rs

@@ -627,13 +627,13 @@ const_string!(CancelledNotificationMethod = "notifications/cancelled");
 pub type CancelledNotification =
     Notification<CancelledNotificationMethod, CancelledNotificationParam>;
 
-/// A catch-all notification the client can use to send custom messages to a server.
+/// A catch-all notification either side can use to send custom messages to its peer.
 ///
 /// This preserves the raw `method` name and `params` payload so handlers can
 /// deserialize them into domain-specific types.
 #[derive(Debug, Clone)]
 #[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
-pub struct CustomClientNotification {
+pub struct CustomNotification {
     pub method: String,
     pub params: Option<Value>,
     /// extensions will carry anything possible in the context, including [`Meta`]
@@ -643,7 +643,7 @@ pub struct CustomClientNotification {
     pub extensions: Extensions,
 }
 
-impl CustomClientNotification {
+impl CustomNotification {
     pub fn new(method: impl Into<String>, params: Option<Value>) -> Self {
         Self {
             method: method.into(),
@@ -1786,7 +1786,7 @@ ts_union!(
     | ProgressNotification
     | InitializedNotification
     | RootsListChangedNotification
-    | CustomClientNotification;
+    | CustomNotification;
 );
 
 ts_union!(
@@ -1817,7 +1817,8 @@ ts_union!(
     | ResourceUpdatedNotification
     | ResourceListChangedNotification
     | ToolListChangedNotification
-    | PromptListChangedNotification;
+    | PromptListChangedNotification
+    | CustomNotification;
 );
 
 ts_union!(
@@ -1907,7 +1908,7 @@ mod tests {
             serde_json::from_value(raw.clone()).expect("invalid notification");
         match &message {
             ClientJsonRpcMessage::Notification(JsonRpcNotification {
-                notification: ClientNotification::CustomClientNotification(notification),
+                notification: ClientNotification::CustomNotification(notification),
                 ..
             }) => {
                 assert_eq!(notification.method, "notifications/custom");
@@ -1927,6 +1928,38 @@ mod tests {
         assert_eq!(json, raw);
     }
 
+    #[test]
+    fn test_custom_server_notification_roundtrip() {
+        let raw = json!( {
+            "jsonrpc": JsonRpcVersion2_0,
+            "method": "notifications/custom-server",
+            "params": {"hello": "world"},
+        });
+
+        let message: ServerJsonRpcMessage =
+            serde_json::from_value(raw.clone()).expect("invalid notification");
+        match &message {
+            ServerJsonRpcMessage::Notification(JsonRpcNotification {
+                notification: ServerNotification::CustomNotification(notification),
+                ..
+            }) => {
+                assert_eq!(notification.method, "notifications/custom-server");
+                assert_eq!(
+                    notification
+                        .params
+                        .as_ref()
+                        .and_then(|p| p.get("hello"))
+                        .expect("hello present"),
+                    "world"
+                );
+            }
+            _ => panic!("Expected custom server notification"),
+        }
+
+        let json = serde_json::to_value(message).expect("valid json");
+        assert_eq!(json, raw);
+    }
+
     #[test]
     fn test_request_conversion() {
         let raw = json!( {

crates/rmcp/src/model/meta.rs

@@ -4,8 +4,8 @@ use serde::{Deserialize, Serialize};
 use serde_json::Value;
 
 use super::{
-    ClientNotification, ClientRequest, CustomClientNotification, Extensions, JsonObject,
-    JsonRpcMessage, NumberOrString, ProgressToken, ServerNotification, ServerRequest,
+    ClientNotification, ClientRequest, CustomNotification, Extensions, JsonObject, JsonRpcMessage,
+    NumberOrString, ProgressToken, ServerNotification, ServerRequest,
 };
 
 pub trait GetMeta {
@@ -18,7 +18,7 @@ pub trait GetExtensions {
     fn extensions_mut(&mut self) -> &mut Extensions;
 }
 
-impl GetExtensions for CustomClientNotification {
+impl GetExtensions for CustomNotification {
     fn extensions(&self) -> &Extensions {
         &self.extensions
     }
@@ -27,7 +27,7 @@ impl GetExtensions for CustomClientNotification {
     }
 }
 
-impl GetMeta for CustomClientNotification {
+impl GetMeta for CustomNotification {
     fn get_meta_mut(&mut self) -> &mut Meta {
         self.extensions_mut().get_or_insert_default()
     }
@@ -104,7 +104,7 @@ variant_extension! {
         ProgressNotification
         InitializedNotification
         RootsListChangedNotification
-        CustomClientNotification
+        CustomNotification
     }
 }
 
@@ -117,6 +117,7 @@ variant_extension! {
         ResourceListChangedNotification
         ToolListChangedNotification
         PromptListChangedNotification
+        CustomNotification
     }
 }
 #[derive(Debug, Serialize, Deserialize, Clone, Default, PartialEq)]

crates/rmcp/src/model/serde_impl.rs

@@ -3,7 +3,7 @@ use std::borrow::Cow;
 use serde::{Deserialize, Serialize};
 
 use super::{
-    CustomClientNotification, Extensions, Meta, Notification, NotificationNoParam, Request,
+    CustomNotification, Extensions, Meta, Notification, NotificationNoParam, Request,
     RequestNoParam, RequestOptionalParam,
 };
 #[derive(Serialize, Deserialize)]
@@ -249,7 +249,7 @@ where
     }
 }
 
-impl Serialize for CustomClientNotification {
+impl Serialize for CustomNotification {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
         S: serde::Serializer,
@@ -277,7 +277,7 @@ impl Serialize for CustomClientNotification {
     }
 }
 
-impl<'de> Deserialize<'de> for CustomClientNotification {
+impl<'de> Deserialize<'de> for CustomNotification {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
         D: serde::Deserializer<'de>,
@@ -294,7 +294,7 @@ impl<'de> Deserialize<'de> for CustomClientNotification {
         if let Some(meta) = _meta {
             extensions.insert(meta);
         }
-        Ok(CustomClientNotification {
+        Ok(CustomNotification {
             extensions,
             method: body.method,
             params,

crates/rmcp/tests/test_message_schema/client_json_rpc_message_schema.json

@@ -396,8 +396,8 @@
         "content"
       ]
     },
-    "CustomClientNotification": {
-      "description": "A catch-all notification the client can use to send custom messages to a server.\n\nThis preserves the raw `method` name and `params` payload so handlers can\ndeserialize them into domain-specific types.",
+    "CustomNotification": {
+      "description": "A catch-all notification either side can use to send custom messages to its peer.\n\nThis preserves the raw `method` name and `params` payload so handlers can\ndeserialize them into domain-specific types.",
       "type": "object",
       "properties": {
         "method": {
@@ -651,7 +651,7 @@
           "$ref": "#/definitions/NotificationNoParam2"
         },
         {
-          "$ref": "#/definitions/CustomClientNotification"
+          "$ref": "#/definitions/CustomNotification"
         }
       ],
       "required": [

crates/rmcp/tests/test_message_schema/client_json_rpc_message_schema_current.json

@@ -396,8 +396,8 @@
         "content"
       ]
     },
-    "CustomClientNotification": {
-      "description": "A catch-all notification the client can use to send custom messages to a server.\n\nThis preserves the raw `method` name and `params` payload so handlers can\ndeserialize them into domain-specific types.",
+    "CustomNotification": {
+      "description": "A catch-all notification either side can use to send custom messages to its peer.\n\nThis preserves the raw `method` name and `params` payload so handlers can\ndeserialize them into domain-specific types.",
       "type": "object",
       "properties": {
         "method": {
@@ -651,7 +651,7 @@
           "$ref": "#/definitions/NotificationNoParam2"
         },
         {
-          "$ref": "#/definitions/CustomClientNotification"
+          "$ref": "#/definitions/CustomNotification"
         }
       ],
       "required": [

crates/rmcp/tests/test_message_schema/server_json_rpc_message_schema.json

@@ -392,6 +392,19 @@
         "content"
       ]
     },
+    "CustomNotification": {
+      "description": "A catch-all notification either side can use to send custom messages to its peer.\n\nThis preserves the raw `method` name and `params` payload so handlers can\ndeserialize them into domain-specific types.",
+      "type": "object",
+      "properties": {
+        "method": {
+          "type": "string"
+        },
+        "params": true
+      },
+      "required": [
+        "method"
+      ]
+    },
     "CancelledNotificationMethod": {
       "type": "string",
       "format": "const",
@@ -977,6 +990,9 @@
         },
         {
           "$ref": "#/definitions/NotificationNoParam3"
+        },
+        {
+          "$ref": "#/definitions/CustomNotification"
         }
       ],
       "required": [

crates/rmcp/tests/test_message_schema/server_json_rpc_message_schema_current.json

@@ -392,6 +392,19 @@
         "content"
       ]
     },
+    "CustomNotification": {
+      "description": "A catch-all notification either side can use to send custom messages to its peer.\n\nThis preserves the raw `method` name and `params` payload so handlers can\ndeserialize them into domain-specific types.",
+      "type": "object",
+      "properties": {
+        "method": {
+          "type": "string"
+        },
+        "params": true
+      },
+      "required": [
+        "method"
+      ]
+    },
     "CancelledNotificationMethod": {
       "type": "string",
       "format": "const",
@@ -977,6 +990,9 @@
         },
         {
           "$ref": "#/definitions/NotificationNoParam3"
+        },
+        {
+          "$ref": "#/definitions/CustomNotification"
         }
       ],
       "required": [