From 4bf5c5358a4c00303938d4a88790d6a97ee6b0f0 Mon Sep 17 00:00:00 2001
From: Justin Spahr-Summers <justin@anthropic.com>
Date: Tue, 7 Jan 2025 14:13:47 +0000
Subject: [PATCH] Assert tool request handlers do not already exist

---
 src/server/index.ts    | 4 +++-
 src/shared/protocol.ts | 9 +++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/server/index.ts b/src/server/index.ts
index 77c5f5c7..a5345dd4 100644
--- a/src/server/index.ts
+++ b/src/server/index.ts
@@ -343,7 +343,9 @@ export class Server<
   }
 
   private setToolRequestHandlers() {
-    // TODO: Check that these handlers do not already exist
+    this.assertCanSetRequestHandler(ListToolsRequestSchema.shape.method.value);
+    this.assertCanSetRequestHandler(CallToolRequestSchema.shape.method.value);
+
     // TODO: Register tool capability
 
     this.setRequestHandler(ListToolsRequestSchema, (): ListToolsResult => ({
diff --git a/src/shared/protocol.ts b/src/shared/protocol.ts
index f430b319..9b4ba569 100644
--- a/src/shared/protocol.ts
+++ b/src/shared/protocol.ts
@@ -511,6 +511,15 @@ export abstract class Protocol<
     this._requestHandlers.delete(method);
   }
 
+  /**
+   * Asserts that a request handler has not already been set for the given method, in preparation for a new one being automatically installed.
+   */
+  protected assertCanSetRequestHandler(method: string): void {
+    if (this._requestHandlers.has(method)) {
+      throw new Error(`A request handler for ${method} already exists, which would be overridden`);
+    }
+  }
+
   /**
    * Registers a handler to invoke when this protocol object receives a notification with the given method.
    *