diff --git a/packages/core/src/tools/mcp-client.ts b/packages/core/src/tools/mcp-client.ts index 3773aae5f2..1b268e6de1 100644 --- a/packages/core/src/tools/mcp-client.ts +++ b/packages/core/src/tools/mcp-client.ts @@ -42,6 +42,7 @@ import { AuthProviderType } from '../config/config.js'; import { GoogleCredentialProvider } from '../mcp/google-auth-provider.js'; import { ServiceAccountImpersonationProvider } from '../mcp/sa-impersonation-provider.js'; import { DiscoveredMCPTool } from './mcp-tool.js'; +import { XcodeMcpBridgeFixTransport } from './xcode-mcp-fix-transport.js'; import type { CallableTool, FunctionCall, Part, Tool } from '@google/genai'; import { basename } from 'node:path'; @@ -1871,7 +1872,7 @@ export async function createTransport( } if (mcpServerConfig.command) { - const transport = new StdioClientTransport({ + let transport: Transport = new StdioClientTransport({ command: mcpServerConfig.command, args: mcpServerConfig.args || [], env: sanitizeEnvironment( @@ -1894,14 +1895,38 @@ export async function createTransport( cwd: mcpServerConfig.cwd, stderr: 'pipe', }); + + // Fix for Xcode 26.3 mcpbridge non-compliant responses + // It returns JSON in `content` instead of `structuredContent` + if ( + mcpServerConfig.command === 'xcrun' && + mcpServerConfig.args?.includes('mcpbridge') + ) { + transport = new XcodeMcpBridgeFixTransport(transport); + } + if (debugMode) { - transport.stderr!.on('data', (data) => { - const stderrStr = data.toString().trim(); - debugLogger.debug( - `[DEBUG] [MCP STDERR (${mcpServerName})]: `, - stderrStr, - ); - }); + // The `XcodeMcpBridgeFixTransport` wrapper hides the underlying `StdioClientTransport`, + // which exposes `stderr` for debug logging. We need to unwrap it to attach the listener. + + const underlyingTransport = + transport instanceof XcodeMcpBridgeFixTransport + ? // eslint-disable-next-line @typescript-eslint/no-explicit-any + (transport as any).transport + : transport; + + if ( + underlyingTransport instanceof StdioClientTransport && + underlyingTransport.stderr + ) { + underlyingTransport.stderr.on('data', (data) => { + const stderrStr = data.toString().trim(); + debugLogger.debug( + `[DEBUG] [MCP STDERR (${mcpServerName})]: `, + stderrStr, + ); + }); + } } return transport; } diff --git a/packages/core/src/tools/xcode-mcp-fix-transport.test.ts b/packages/core/src/tools/xcode-mcp-fix-transport.test.ts new file mode 100644 index 0000000000..76cd21864f --- /dev/null +++ b/packages/core/src/tools/xcode-mcp-fix-transport.test.ts @@ -0,0 +1,120 @@ +/** + * @license + * Copyright 2026 Google LLC + * SPDX-License-Identifier: Apache-2.0 + */ +import { describe, it, expect } from 'vitest'; +import { EventEmitter } from 'node:events'; +import { XcodeMcpBridgeFixTransport } from './xcode-mcp-fix-transport.js'; +import type { Transport } from '@modelcontextprotocol/sdk/shared/transport.js'; +import type { JSONRPCMessage } from '@modelcontextprotocol/sdk/types.js'; + +// Mock Transport that simulates the mcpbridge behavior +class MockBadMcpBridgeTransport extends EventEmitter implements Transport { + onclose?: () => void; + onerror?: (error: Error) => void; + onmessage?: (message: JSONRPCMessage) => void; + + async start() {} + async close() {} + async send(_message: JSONRPCMessage) {} + + // eslint-disable-next-line @typescript-eslint/no-explicit-any + emitMessage(msg: any) { + this.onmessage?.(msg); + } +} + +describe('Xcode MCP Bridge Fix', () => { + it('intercepts and fixes the non-compliant mcpbridge response', async () => { + const mockTransport = new MockBadMcpBridgeTransport(); + const fixTransport = new XcodeMcpBridgeFixTransport(mockTransport); + + // We need to capture what the fixTransport emits to its listeners + // eslint-disable-next-line @typescript-eslint/no-explicit-any + const messages: any[] = []; + fixTransport.onmessage = (msg) => { + messages.push(msg); + }; + + await fixTransport.start(); + + // SCENARIO 1: Bad response from Xcode + // It has `content` stringified JSON, but misses `structuredContent` + const badPayload = { + jsonrpc: '2.0', + id: 1, + result: { + content: [ + { + type: 'text', + text: JSON.stringify({ + windows: [{ title: 'HelloWorld', path: '/path/to/project' }], + }), + }, + ], + // Missing: structuredContent + }, + }; + + mockTransport.emitMessage(badPayload); + + // Verify the message received by the client (listener of fixTransport) + const fixedMsg = messages.find((m) => m.id === 1); + expect(fixedMsg).toBeDefined(); + expect(fixedMsg.result.structuredContent).toBeDefined(); + expect(fixedMsg.result.structuredContent.windows[0].title).toBe( + 'HelloWorld', + ); + + // SCENARIO 2: Good response (should be untouched) + const goodPayload = { + jsonrpc: '2.0', + id: 2, + result: { + content: [{ type: 'text', text: 'normal text' }], + structuredContent: { some: 'data' }, + }, + }; + mockTransport.emitMessage(goodPayload); + + const goodMsg = messages.find((m) => m.id === 2); + expect(goodMsg).toBeDefined(); + expect(goodMsg.result.structuredContent).toEqual({ some: 'data' }); + }); + + it('ignores responses that cannot be parsed as JSON', async () => { + const mockTransport = new MockBadMcpBridgeTransport(); + const fixTransport = new XcodeMcpBridgeFixTransport(mockTransport); + + // eslint-disable-next-line @typescript-eslint/no-explicit-any + const messages: any[] = []; + fixTransport.onmessage = (msg) => { + messages.push(msg); + }; + + await fixTransport.start(); + + const nonJsonPayload = { + jsonrpc: '2.0', + id: 3, + result: { + content: [ + { + type: 'text', + text: "Just some plain text that isn't JSON", + }, + ], + }, + }; + + mockTransport.emitMessage(nonJsonPayload); + + const msg = messages.find((m) => m.id === 3); + expect(msg).toBeDefined(); + expect(msg.result.structuredContent).toBeUndefined(); + expect(msg.result.content[0].text).toBe( + "Just some plain text that isn't JSON", + ); + }); +}); diff --git a/packages/core/src/tools/xcode-mcp-fix-transport.ts b/packages/core/src/tools/xcode-mcp-fix-transport.ts new file mode 100644 index 0000000000..d7936e7e09 --- /dev/null +++ b/packages/core/src/tools/xcode-mcp-fix-transport.ts @@ -0,0 +1,101 @@ +/** + * @license + * Copyright 2025 Google LLC + * SPDX-License-Identifier: Apache-2.0 + */ + +import type { Transport } from '@modelcontextprotocol/sdk/shared/transport.js'; +import type { + JSONRPCMessage, + JSONRPCResponse, +} from '@modelcontextprotocol/sdk/types.js'; +import { EventEmitter } from 'node:events'; + +/** + * A wrapper transport that intercepts messages from Xcode's mcpbridge and fixes + * non-compliant responses. + * + * Issue: Xcode 26.3's mcpbridge returns tool results in `content` but misses + * `structuredContent` when the tool has an output schema. + * + * Fix: Parse the text content as JSON and populate `structuredContent`. + */ +export class XcodeMcpBridgeFixTransport + extends EventEmitter + implements Transport +{ + constructor(private readonly transport: Transport) { + super(); + + // Forward messages from the underlying transport + this.transport.onmessage = (message) => { + this.handleMessage(message); + }; + + this.transport.onclose = () => { + this.onclose?.(); + }; + + this.transport.onerror = (error) => { + this.onerror?.(error); + }; + } + + // Transport interface implementation + onclose?: () => void; + onerror?: (error: Error) => void; + onmessage?: (message: JSONRPCMessage) => void; + + async start(): Promise { + await this.transport.start(); + } + + async close(): Promise { + await this.transport.close(); + } + + async send(message: JSONRPCMessage): Promise { + await this.transport.send(message); + } + + private handleMessage(message: JSONRPCMessage) { + if (this.isJsonResponse(message)) { + this.fixStructuredContent(message); + } + this.onmessage?.(message); + } + + private isJsonResponse(message: JSONRPCMessage): message is JSONRPCResponse { + return 'result' in message || 'error' in message; + } + + private fixStructuredContent(response: JSONRPCResponse) { + if (!('result' in response)) return; + + // We can cast because we verified 'result' is in response, + // but TS might still be picky if the type is a strict union. + // Let's treat it safely. + // eslint-disable-next-line @typescript-eslint/no-explicit-any + const result = response.result as any; + + // Check if we have content but missing structuredContent + if ( + result.content && + Array.isArray(result.content) && + result.content.length > 0 && + !result.structuredContent + ) { + const firstItem = result.content[0]; + if (firstItem.type === 'text' && typeof firstItem.text === 'string') { + try { + // Attempt to parse the text as JSON + const parsed = JSON.parse(firstItem.text); + // If successful, populate structuredContent + result.structuredContent = parsed; + } catch (_) { + // Ignored: Content is likely plain text, not JSON. + } + } + } + } +}