fix: #699 Forward fetch parameter to SSEClientTransport in MCPServerSSE (#700)

Author: aasullivan

.changeset/brave-regions-hug.md

@@ -0,0 +1,5 @@
+---
+'@openai/agents-core': patch
+---
+
+fix: #699 Forward fetch parameter to SSEClientTransport in MCPServerSSE

packages/agents-core/src/mcp.ts

@@ -603,6 +603,9 @@ export interface MCPServerSSEOptions {
   authProvider?: any;
   // RequestInit
   requestInit?: any;
+  // Custom fetch implementation used for all network requests.
+  // import { FetchLike } from '@modelcontextprotocol/sdk/shared/transport.js';
+  fetch?: any;
   // import { SSEReconnectionOptions } from '@modelcontextprotocol/sdk/client/sse.js';
   eventSourceInit?: any;
   // ----------------------------------------------------

packages/agents-core/src/shims/mcp-server/node.ts

@@ -200,6 +200,7 @@ export class NodeMCPServerSSE extends BaseMCPServerSSE {
         authProvider: this.params.authProvider,
         requestInit: this.params.requestInit,
         eventSourceInit: this.params.eventSourceInit,
+        fetch: this.params.fetch,
       });
       this.session = new Client({
         name: this._name,

packages/agents-core/test/shims/mcp-server/node.test.ts

@@ -1,5 +1,8 @@
 import { describe, test, expect, vi, afterAll, beforeAll } from 'vitest';
-import { NodeMCPServerStdio } from '../../../src/shims/mcp-server/node';
+import {
+  NodeMCPServerStdio,
+  NodeMCPServerSSE,
+} from '../../../src/shims/mcp-server/node';
 import { TransportSendOptions } from '@modelcontextprotocol/sdk/shared/transport';
 import { JSONRPCMessage } from '@modelcontextprotocol/sdk/types';
 
@@ -86,3 +89,104 @@ class MockClient {
     return Promise.resolve();
   }
 }
+
+let capturedFetch: any = undefined;
+
+class MockSSEClientTransport {
+  url: URL;
+  options: {
+    authProvider?: any;
+    requestInit?: any;
+    eventSourceInit?: any;
+    fetch?: any;
+  };
+
+  constructor(
+    url: URL,
+    options: {
+      authProvider?: any;
+      requestInit?: any;
+      eventSourceInit?: any;
+      fetch?: any;
+    },
+  ) {
+    this.url = url;
+    this.options = options;
+    capturedFetch = options.fetch;
+  }
+
+  start(): Promise<void> {
+    return Promise.resolve();
+  }
+
+  send(
+    _message: JSONRPCMessage,
+    _options?: TransportSendOptions,
+  ): Promise<void> {
+    return Promise.resolve();
+  }
+
+  close(): Promise<void> {
+    return Promise.resolve();
+  }
+}
+
+describe('NodeMCPServerSSE', () => {
+  beforeAll(() => {
+    vi.mock(
+      '@modelcontextprotocol/sdk/client/sse.js',
+      async (importOriginal) => {
+        return {
+          ...(await importOriginal()),
+          SSEClientTransport: MockSSEClientTransport,
+        };
+      },
+    );
+    vi.mock(
+      '@modelcontextprotocol/sdk/client/index.js',
+      async (importOriginal) => {
+        return {
+          ...(await importOriginal()),
+          Client: MockClient,
+        };
+      },
+    );
+  });
+
+  test('should forward custom fetch to SSEClientTransport', async () => {
+    const customFetch = vi.fn(async (_input, _init) => {
+      return new Response('{}', { status: 200 });
+    });
+
+    const server = new NodeMCPServerSSE({
+      url: 'https://example.com/sse',
+      name: 'test-sse-server',
+      fetch: customFetch,
+    });
+
+    expect(server).toBeDefined();
+    expect(server.name).toBe('test-sse-server');
+
+    await server.connect();
+
+    expect(capturedFetch).toBe(customFetch);
+
+    await server.close();
+  });
+
+  test('should accept SSE server without custom fetch', async () => {
+    const server = new NodeMCPServerSSE({
+      url: 'https://example.com/sse',
+      name: 'test-sse-server-no-fetch',
+    });
+
+    expect(server).toBeDefined();
+    await server.connect();
+    await server.close();
+  });
+
+  afterAll(() => {
+    vi.clearAllMocks();
+    capturedFetch = undefined;
+  });
+});