import type { Transport } from '@modelcontextprotocol/sdk/shared/transport.js'
import { getTimestamp, log } from './utils.js'
export class McpProxy {
public static async createProxy(
transportToClient: Transport,
transportToServer: Transport,
onShutdown: () => Promise<void> = async () => {},
) {
const proxy = new McpProxy(transportToClient, transportToServer, onShutdown)
await proxy.initialize()
return proxy
}
private running = true
constructor(
private readonly transportToClient: Transport,
private readonly transportToServer: Transport,
private readonly onShutdown: () => Promise<void>,
) {}
public async initialize() {
this.transportToClient.onmessage = this.handleClientMessage.bind(this)
this.transportToServer.onmessage = this.handleServerMessage.bind(this)
this.transportToClient.onclose = this.handleClientClose.bind(this)
this.transportToServer.onclose = this.handleServerClose.bind(this)
this.transportToClient.onerror = this.handleClientError.bind(this)
this.transportToServer.onerror = this.handleServerError.bind(this)
}
private async handleClientMessage(message: any) {
if (!this.running) {
return
}
try {
log(`[${getTimestamp()}] Client -> Server: ${JSON.stringify(message)}`)
await this.transportToServer.send(message).catch((error) => {
log('Error forwarding message to server:', error)
this.handleServerError(error instanceof Error ? error : new Error(String(error)))
})
} catch (error) {
await this.handleClientError(error instanceof Error ? error : new Error(String(error)))
}
}
private async handleServerMessage(message: any) {
if (!this.running) {
return
}
try {
log(`[${getTimestamp()}] Server -> Client: ${JSON.stringify(message)}`)
await this.transportToClient.send(message).catch((error) => {
log('Error forwarding message to client:', error)
this.handleClientError(error instanceof Error ? error : new Error(String(error)))
})
} catch (error) {
await this.handleServerError(error instanceof Error ? error : new Error(String(error)))
}
}
private async handleClientClose() {
if (!this.running) {
return
}
log('Client connection closed')
await this.shutdown()
}
private async handleServerClose() {
if (!this.running) {
return
}
log('Server connection closed')
await this.shutdown()
}
private async handleClientError(error: Error) {
if (!this.running) {
return
}
log('Client error received', error)
await this.shutdown()
}
private async handleServerError(error: Error) {
if (!this.running) {
return
}
log('Server error received', error)
await this.shutdown()
}
private async shutdown(): Promise<void> {
if (this.running) {
this.running = false
await this.safeClose(this.transportToClient)
await this.safeClose(this.transportToServer)
await this.onShutdown()
}
}
private async safeClose(transport: Transport): Promise<void> {
try {
await transport.close()
} catch {}
}
}
