Merge pull request #315 from koic/support_roots

Add `roots/list` and `notifications/roots/list_changed` support

lib/mcp/methods.rb

@@ -73,14 +73,12 @@ module MCP
           require_capability!(method, capabilities, :completions)
         when ROOTS_LIST
           require_capability!(method, capabilities, :roots)
-        when NOTIFICATIONS_ROOTS_LIST_CHANGED
-          require_capability!(method, capabilities, :roots)
-          require_capability!(method, capabilities, :roots, :listChanged)
         when SAMPLING_CREATE_MESSAGE
           require_capability!(method, capabilities, :sampling)
         when ELICITATION_CREATE
           require_capability!(method, capabilities, :elicitation)
-        when INITIALIZE, PING, NOTIFICATIONS_INITIALIZED, NOTIFICATIONS_PROGRESS, NOTIFICATIONS_CANCELLED, NOTIFICATIONS_ELICITATION_COMPLETE
+        when INITIALIZE, PING, NOTIFICATIONS_INITIALIZED, NOTIFICATIONS_ROOTS_LIST_CHANGED,
+             NOTIFICATIONS_PROGRESS, NOTIFICATIONS_CANCELLED, NOTIFICATIONS_ELICITATION_COMPLETE
           # No specific capability required.
         end
       end

lib/mcp/server.rb

@@ -121,6 +121,7 @@ module MCP
         Methods::PING => ->(_) { {} },
         Methods::NOTIFICATIONS_INITIALIZED => ->(_) {},
         Methods::NOTIFICATIONS_PROGRESS => ->(_) {},
+        Methods::NOTIFICATIONS_ROOTS_LIST_CHANGED => ->(_) {},
         Methods::COMPLETION_COMPLETE => ->(_) { DEFAULT_COMPLETION_RESULT },
         Methods::LOGGING_SET_LEVEL => method(:configure_logging_level),
 
@@ -218,6 +219,14 @@ module MCP
       report_exception(e, { notification: "log_message" })
     end
 
+    # Sets a handler for `notifications/roots/list_changed` notifications.
+    # Called when a client notifies the server that its filesystem roots have changed.
+    #
+    # @yield [params] The notification params (typically `nil`).
+    def roots_list_changed_handler(&block)
+      @handlers[Methods::NOTIFICATIONS_ROOTS_LIST_CHANGED] = block
+    end
+
     # Sets a custom handler for `resources/read` requests.
     # The block receives the parsed request params and should return resource
     # contents. The return value is set as the `contents` field of the response.

lib/mcp/server_context.rb

@@ -30,6 +30,15 @@ module MCP
       @notification_target.notify_log_message(data: data, level: level, logger: logger, related_request_id: @related_request_id)
     end
 
+    # Delegates to the session so the request is scoped to the originating client.
+    def list_roots
+      if @notification_target.respond_to?(:list_roots)
+        @notification_target.list_roots(related_request_id: @related_request_id)
+      else
+        raise NoMethodError, "undefined method 'list_roots' for #{self}"
+      end
+    end
+
     # Delegates to the session so the request is scoped to the originating client.
     # Falls back to `@context` (via `method_missing`) when `@notification_target`
     # does not support sampling.

lib/mcp/server_session.rb

@@ -41,6 +41,15 @@ module MCP
       @client_capabilities || @server.client_capabilities
     end
 
+    # Sends a `roots/list` request scoped to this session.
+    def list_roots(related_request_id: nil)
+      unless client_capabilities&.dig(:roots)
+        raise "Client does not support roots."
+      end
+
+      send_to_transport_request(Methods::ROOTS_LIST, nil, related_request_id: related_request_id)
+    end
+
     # Sends a `sampling/createMessage` request scoped to this session.
     def create_sampling_message(related_request_id: nil, **kwargs)
       params = @server.build_sampling_params(client_capabilities, **kwargs)