Automatic handling of logging level (#882)

Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com>

src/server/index.ts

@@ -32,6 +32,9 @@ import {
   ServerRequest,
   ServerResult,
   SUPPORTED_PROTOCOL_VERSIONS,
+  LoggingLevel,
+  SetLevelRequestSchema,
+  LoggingLevelSchema
 } from "../types.js";
 import Ajv from "ajv";
 
@@ -108,8 +111,36 @@ export class Server<
     this.setNotificationHandler(InitializedNotificationSchema, () =>
       this.oninitialized?.(),
     );
+
+    if (this._capabilities.logging) {
+        this.setRequestHandler(SetLevelRequestSchema, async (request, extra) => {
+            const transportSessionId: string | undefined = extra.sessionId || extra.requestInfo?.headers['mcp-session-id'] as string || undefined;
+            const { level } = request.params;
+            const parseResult = LoggingLevelSchema.safeParse(level);
+            if (transportSessionId && parseResult.success) {
+                this._loggingLevels.set(transportSessionId, parseResult.data);
+            }
+            return {};
+        })
+    }
   }
 
+  // Map log levels by session id
+  private _loggingLevels = new Map<string, LoggingLevel>();
+
+  // Map LogLevelSchema to severity index
+  private readonly LOG_LEVEL_SEVERITY = new Map(
+    LoggingLevelSchema.options.map((level, index) => [level, index])
+  );
+
+  // Is a message with the given level ignored in the log level set for the given session id?
+  private isMessageIgnored = (level: LoggingLevel, sessionId: string): boolean => {
+    const currentLevel = this._loggingLevels.get(sessionId);
+    return (currentLevel)
+        ? this.LOG_LEVEL_SEVERITY.get(level)! < this.LOG_LEVEL_SEVERITY.get(currentLevel)!
+        : false;
+  };
+
   /**
    * Registers new capabilities. This can only be called before connecting to a transport.
    *
@@ -121,7 +152,6 @@ export class Server<
         "Cannot register capabilities after connecting to transport",
       );
     }
-
     this._capabilities = mergeCapabilities(this._capabilities, capabilities);
   }
 
@@ -324,10 +354,10 @@ export class Server<
     if (result.action === "accept" && result.content) {
       try {
         const ajv = new Ajv();
-        
+
         const validate = ajv.compile(params.requestedSchema);
         const isValid = validate(result.content);
-        
+
         if (!isValid) {
           throw new McpError(
             ErrorCode.InvalidParams,
@@ -359,8 +389,19 @@ export class Server<
     );
   }
 
-  async sendLoggingMessage(params: LoggingMessageNotification["params"]) {
-    return this.notification({ method: "notifications/message", params });
+    /**
+     * Sends a logging message to the client, if connected.
+     * Note: You only need to send the parameters object, not the entire JSON RPC message
+     * @see LoggingMessageNotification
+     * @param params
+     * @param sessionId optional for stateless and backward compatibility
+     */
+    async sendLoggingMessage(params: LoggingMessageNotification["params"], sessionId?: string) {
+      if (this._capabilities.logging) {
+          if (!sessionId || !this.isMessageIgnored(params.level, sessionId)) {
+              return this.notification({method: "notifications/message", params})
+          }
+      }
   }
 
   async sendResourceUpdated(params: ResourceUpdatedNotification["params"]) {

src/server/mcp.ts

@@ -41,6 +41,7 @@ import {
   ServerRequest,
   ServerNotification,
   ToolAnnotations,
+  LoggingMessageNotification,
 } from "../types.js";
 import { Completable, CompletableDef } from "./completable.js";
 import { UriTemplate, Variables } from "../shared/uriTemplate.js";
@@ -822,7 +823,7 @@ export class McpServer {
   /**
    * Registers a tool taking either a parameter schema for validation or annotations for additional metadata.
    * This unified overload handles both `tool(name, paramsSchema, cb)` and `tool(name, annotations, cb)` cases.
-   * 
+   *
    * Note: We use a union type for the second parameter because TypeScript cannot reliably disambiguate
    * between ToolAnnotations and ZodRawShape during overload resolution, as both are plain object types.
    */
@@ -834,9 +835,9 @@ export class McpServer {
 
   /**
    * Registers a tool `name` (with a description) taking either parameter schema or annotations.
-   * This unified overload handles both `tool(name, description, paramsSchema, cb)` and 
+   * This unified overload handles both `tool(name, description, paramsSchema, cb)` and
    * `tool(name, description, annotations, cb)` cases.
-   * 
+   *
    * Note: We use a union type for the third parameter because TypeScript cannot reliably disambiguate
    * between ToolAnnotations and ZodRawShape during overload resolution, as both are plain object types.
    */
@@ -1047,6 +1048,16 @@ export class McpServer {
     return this.server.transport !== undefined
   }
 
+  /**
+   * Sends a logging message to the client, if connected.
+   * Note: You only need to send the parameters object, not the entire JSON RPC message
+   * @see LoggingMessageNotification
+   * @param params
+   * @param sessionId optional for stateless and backward compatibility
+   */
+  async sendLoggingMessage(params: LoggingMessageNotification["params"], sessionId?: string) {
+    return this.server.sendLoggingMessage(params, sessionId);
+  }
   /**
    * Sends a resource list changed event to the client, if connected.
    */