Email MCP

import { Client } from '@modelcontextprotocol/sdk/client/index.js' import { SSEClientTransport } from '@modelcontextprotocol/sdk/client/sse.js' import { Server } from '@modelcontextprotocol/sdk/server/index.js' import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js' import type { JSONRPCMessage, JSONRPCRequest, ClientCapabilities, Implementation, } from '@modelcontextprotocol/sdk/types.js' import { z } from 'zod' import { getVersion } from '../lib/getVersion.js' import { Logger } from '../types.js' import { onSignals } from '../lib/onSignals.js' export interface SseToStdioArgs { sseUrl: string logger: Logger headers: Record<string, string> } let sseClient: Client | undefined const newInitializeSseClient = ({ message }: { message: JSONRPCRequest }) => { const clientInfo = message.params?.clientInfo as Implementation | undefined const clientCapabilities = message.params?.capabilities as | ClientCapabilities | undefined return new Client( { name: clientInfo?.name ?? 'supergateway', version: clientInfo?.version ?? getVersion(), }, { capabilities: clientCapabilities ?? {}, }, ) } const newFallbackSseClient = async ({ sseTransport, }: { sseTransport: SSEClientTransport }) => { const fallbackSseClient = new Client( { name: 'supergateway', version: getVersion(), }, { capabilities: {}, }, ) await fallbackSseClient.connect(sseTransport) return fallbackSseClient } export async function sseToStdio(args: SseToStdioArgs) { const { sseUrl, logger, headers } = args logger.info(` - sse: ${sseUrl}`) logger.info( ` - Headers: ${Object.keys(headers).length ? JSON.stringify(headers) : '(none)'}`, ) logger.info('Connecting to SSE...') onSignals({ logger }) const sseTransport = new SSEClientTransport(new URL(sseUrl), { eventSourceInit: { fetch: (...props: Parameters<typeof fetch>) => { const [url, init = {}] = props return fetch(url, { ...init, headers: { ...init.headers, ...headers } }) }, }, requestInit: { headers, }, }) sseTransport.onerror = (err) => { logger.error('SSE error:', err) } sseTransport.onclose = () => { logger.error('SSE connection closed') process.exit(1) } const stdioServer = new Server( { name: 'supergateway', version: getVersion(), }, { capabilities: {}, }, ) const stdioTransport = new StdioServerTransport() await stdioServer.connect(stdioTransport) const wrapResponse = (req: JSONRPCRequest, payload: object) => ({ jsonrpc: req.jsonrpc || '2.0', id: req.id, ...payload, }) stdioServer.transport!.onmessage = async (message: JSONRPCMessage) => { const isRequest = 'method' in message && 'id' in message if (isRequest) { logger.info('Stdio → SSE:', message) const req = message as JSONRPCRequest let result try { if (!sseClient) { if (message.method === 'initialize') { sseClient = newInitializeSseClient({ message, }) const originalRequest = sseClient.request sseClient.request = async function (...args) { result = await originalRequest.apply(this, args) return result } await sseClient.connect(sseTransport) sseClient.request = originalRequest } else { logger.info('SSE client not initialized, creating fallback client') sseClient = await newFallbackSseClient({ sseTransport }) } logger.info('SSE connected') } else { result = await sseClient.request(req, z.any()) } } catch (err) { logger.error('Request error:', err) const errorCode = err && typeof err === 'object' && 'code' in err ? (err as any).code : -32000 let errorMsg = err && typeof err === 'object' && 'message' in err ? (err as any).message : 'Internal error' const prefix = `MCP error ${errorCode}:` if (errorMsg.startsWith(prefix)) { errorMsg = errorMsg.slice(prefix.length).trim() } const errorResp = wrapResponse(req, { error: { code: errorCode, message: errorMsg, }, }) process.stdout.write(JSON.stringify(errorResp) + '\n') return } const response = wrapResponse( req, result.hasOwnProperty('error') ? { error: { ...result.error } } : { result: { ...result } }, ) logger.info('Response:', response) process.stdout.write(JSON.stringify(response) + '\n') } else { logger.info('SSE → Stdio:', message) process.stdout.write(JSON.stringify(message) + '\n') } } logger.info('Stdio server listening') }