Support MCP StreamableHTTPClientTransport (#1014)

packages/core/src/config/config.ts

@@ -45,6 +45,8 @@ export class MCPServerConfig {
     readonly cwd?: string,
     // For sse transport
     readonly url?: string,
+    // For streamable http transport
+    readonly httpUrl?: string,
     // For websocket transport
     readonly tcp?: string,
     // Common

packages/core/src/tools/mcp-client.ts

@@ -7,12 +7,12 @@
 import { Client } from '@modelcontextprotocol/sdk/client/index.js';
 import { StdioClientTransport } from '@modelcontextprotocol/sdk/client/stdio.js';
 import { SSEClientTransport } from '@modelcontextprotocol/sdk/client/sse.js';
+import { StreamableHTTPClientTransport } from '@modelcontextprotocol/sdk/client/streamableHttp.js';
 import { parse } from 'shell-quote';
 import { MCPServerConfig } from '../config/config.js';
 import { DiscoveredMCPTool } from './mcp-tool.js';
 import { CallableTool, FunctionDeclaration, mcpToTool } from '@google/genai';
 import { ToolRegistry } from './tool-registry.js';
-import { WebSocketClientTransport } from './websocket-client-transport.js';
 
 export const MCP_DEFAULT_TIMEOUT_MSEC = 10 * 60 * 1000; // default to 10 minutes
 
@@ -163,10 +163,12 @@ async function connectAndDiscover(
   updateMCPServerStatus(mcpServerName, MCPServerStatus.CONNECTING);
 
   let transport;
-  if (mcpServerConfig.url) {
+  if (mcpServerConfig.httpUrl) {
+    transport = new StreamableHTTPClientTransport(
+      new URL(mcpServerConfig.httpUrl),
+    );
+  } else if (mcpServerConfig.url) {
     transport = new SSEClientTransport(new URL(mcpServerConfig.url));
-  } else if (mcpServerConfig.tcp) {
-    transport = new WebSocketClientTransport(new URL(mcpServerConfig.tcp));
   } else if (mcpServerConfig.command) {
     transport = new StdioClientTransport({
       command: mcpServerConfig.command,
@@ -180,7 +182,7 @@ async function connectAndDiscover(
     });
   } else {
     console.error(
-      `MCP server '${mcpServerName}' has invalid configuration: missing url (for SSE), tcp (for websocket), and command (for stdio). Skipping.`,
+      `MCP server '${mcpServerName}' has invalid configuration: missing httpUrl (for Streamable HTTP), url (for SSE), and command (for stdio). Skipping.`,
     );
     // Update status to disconnected
     updateMCPServerStatus(mcpServerName, MCPServerStatus.DISCONNECTED);
@@ -260,7 +262,7 @@ async function connectAndDiscover(
       if (
         transport instanceof StdioClientTransport ||
         transport instanceof SSEClientTransport ||
-        transport instanceof WebSocketClientTransport
+        transport instanceof StreamableHTTPClientTransport
       ) {
         await transport.close();
       }
@@ -321,7 +323,7 @@ async function connectAndDiscover(
     if (
       transport instanceof StdioClientTransport ||
       transport instanceof SSEClientTransport ||
-      transport instanceof WebSocketClientTransport
+      transport instanceof StreamableHTTPClientTransport
     ) {
       await transport.close();
     }
@@ -341,7 +343,7 @@ async function connectAndDiscover(
     if (
       transport instanceof StdioClientTransport ||
       transport instanceof SSEClientTransport ||
-      transport instanceof WebSocketClientTransport
+      transport instanceof StreamableHTTPClientTransport
     ) {
       await transport.close();
       // Update status to disconnected

packages/core/src/tools/websocket-client-transport.ts

@@ -1,97 +0,0 @@
-/**
- * @license
- * Copyright 2025 Google LLC
- * SPDX-License-Identifier: Apache-2.0
- */
-
-import WebSocket from 'ws';
-import {
-  Transport,
-  TransportSendOptions,
-} from '@modelcontextprotocol/sdk/shared/transport.js';
-import { JSONRPCMessage } from '@modelcontextprotocol/sdk/types.js';
-import { AuthInfo } from '@modelcontextprotocol/sdk/server/auth/types.js';
-
-export class WebSocketClientTransport implements Transport {
-  private socket: WebSocket | null = null;
-  onclose?: () => void;
-  onerror?: (error: Error) => void;
-  onmessage?: (
-    message: JSONRPCMessage,
-    extra?: { authInfo?: AuthInfo },
-  ) => void;
-
-  constructor(private readonly url: URL) {}
-
-  async start(): Promise<void> {
-    return new Promise((resolve, reject) => {
-      const handshakeTimeoutDuration = 10000;
-      let connectionTimeout: NodeJS.Timeout | null = null;
-
-      try {
-        this.socket = new WebSocket(this.url.toString(), {
-          handshakeTimeout: handshakeTimeoutDuration,
-        });
-
-        connectionTimeout = setTimeout(() => {
-          this.socket?.close();
-          reject(
-            new Error(
-              `WebSocket connection timed out after ${handshakeTimeoutDuration}ms`,
-            ),
-          );
-        }, handshakeTimeoutDuration);
-
-        this.socket.on('open', () => {
-          clearTimeout(connectionTimeout!);
-          resolve();
-        });
-
-        this.socket.on('message', (data) => {
-          try {
-            const parsedMessage: JSONRPCMessage = JSON.parse(data.toString());
-            this.onmessage?.(parsedMessage, { authInfo: undefined }); // Auth unsupported currently
-          } catch (error: unknown) {
-            this.onerror?.(
-              error instanceof Error ? error : new Error(String(error)),
-            );
-          }
-        });
-
-        this.socket.on('error', (error) => {
-          clearTimeout(connectionTimeout!);
-          this.onerror?.(error);
-          reject(error);
-        });
-
-        this.socket.on('close', () => {
-          clearTimeout(connectionTimeout!);
-          this.onclose?.();
-          this.socket = null;
-        });
-      } catch (error: unknown) {
-        clearTimeout(connectionTimeout!);
-        reject(error instanceof Error ? error : new Error(String(error)));
-      }
-    });
-  }
-
-  async close(): Promise<void> {
-    if (this.socket) {
-      this.socket.close();
-      this.socket = null;
-    }
-  }
-
-  async send(
-    message: JSONRPCMessage,
-    _options?: TransportSendOptions,
-  ): Promise<void> {
-    if (!this.socket || this.socket.readyState !== WebSocket.OPEN) {
-      throw new Error(
-        'WebSocket is not connected or not open. Cannot send message.',
-      );
-    }
-    this.socket.send(JSON.stringify(message));
-  }
-}