Sequa AI

import type { Transport } from '@modelcontextprotocol/sdk/shared/transport.js' import { isInitializeRequest } from '@modelcontextprotocol/sdk/types.js' import { fatalLog, getTimestamp, log, sleep } from './utils.js' export class McpProxy { public static async createProxy( localTransport: Transport, connectToRemote: () => Promise<Transport>, onShutdown: () => void, ) { const proxy = new McpProxy(localTransport, connectToRemote, onShutdown) await proxy.initialize() return proxy } private running = true private currentRemote: Transport | undefined = undefined private initMessage: any | undefined = undefined constructor( private readonly localTransport: Transport, private readonly connectToRemote: () => Promise<Transport>, private readonly onShutdown: () => void, ) {} public async initialize() { this.running = true await this.initializeRemote() } private async initializeRemote() { if (!this.running) { return } if (this.currentRemote) { log('Reconnecting to remote') this.currentRemote.onmessage = undefined this.currentRemote.onclose = undefined this.currentRemote.onerror = undefined } let retryCount = 0 while (true) { try { this.currentRemote = await this.connectToRemote() await this.currentRemote.start() if (this.initMessage) { await this.currentRemote.send(this.initMessage) } break } catch (error) { if (retryCount > 3) { await this.shutdown() throw error } retryCount++ fatalLog('Error connecting to remote:', error) await sleep(2000) } } this.localTransport.onmessage = this.handleClientMessage.bind(this) this.currentRemote.onmessage = this.handleServerMessage.bind(this) this.localTransport.onclose = this.handleClientClose.bind(this) this.currentRemote.onclose = this.handleServerClose.bind(this) this.localTransport.onerror = this.handleClientError.bind(this) this.currentRemote.onerror = this.handleServerError.bind(this) } private async handleClientMessage(message: any) { if (!this.currentRemote) { throw new Error('Remote transport is not initialized') } try { log(`[${getTimestamp()}] Client -> Server: ${JSON.stringify(message)}`) await this.currentRemote.send(message) if (isInitializeRequest(message)) { this.initMessage = message } } catch (error) { log('Error forwarding message to server:', error) const maxAttempts = 3 for (let i = 0; i < maxAttempts; i++) { try { log(`Retrying to send message ${i + 1}/${maxAttempts}`) await this.initializeRemote() await this.currentRemote.send(message) break } catch (error) { fatalLog(`Error sending retry message`, error) await sleep(2000) } } } } private async handleServerMessage(message: any) { try { log(`[${getTimestamp()}] Server -> Client: ${JSON.stringify(message)}`) await this.localTransport.send(message) } catch (error) { log('Error forwarding message to client:', error) void this.shutdown() } } private async handleClientClose() { log('Client connection closed') await this.shutdown() } private async handleServerClose() { log('Server connection closed') await this.initializeRemote() } private async handleClientError(error: Error) { log('Client error received', error) await this.shutdown() } private async handleServerError(error: Error) { log('Server error received', error) } private async shutdown(): Promise<void> { if (this.running) { this.running = false await this.safeClose(this.currentRemote) await this.safeClose(this.localTransport) this.onShutdown() } } private async safeClose(transport: Transport | undefined): Promise<void> { if (!transport) { return } try { await transport.close() } catch {} } }