import type { Transport } from '@modelcontextprotocol/sdk/shared/transport.js'
import type { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js'
import type { JSONRPCMessage } from '@modelcontextprotocol/sdk/types.js'
import * as fs from 'node:fs'
import * as path from 'node:path'
/**
* A wrapper transport that logs all MCP communication to a file
*/
export class LoggingTransport implements Transport {
private wrapped: StdioServerTransport
private logStream: fs.WriteStream
private logFile: string
sessionId?: string
constructor(wrapped: StdioServerTransport, logFile: string) {
// Store wrapped transport
this.wrapped = wrapped
// Set up logging
this.logFile = logFile
// Create log directory if it doesn't exist
const logDir = path.dirname(this.logFile)
if (!fs.existsSync(logDir)) {
fs.mkdirSync(logDir, { recursive: true })
}
// Create log stream
this.logStream = fs.createWriteStream(this.logFile, { flags: 'a' })
// Log initial connection information
this.log({
type: 'connection_info',
timestamp: new Date().toISOString(),
message: 'LoggingTransport initialized',
})
// Set up forwarding of events
this.wrapped.onmessage = (message: JSONRPCMessage) => {
this.log({
type: 'received',
timestamp: new Date().toISOString(),
message,
})
if (this.onmessage) this.onmessage(message)
}
this.wrapped.onerror = (error: Error) => {
this.log({
type: 'error',
timestamp: new Date().toISOString(),
error: error.message,
stack: error.stack,
})
if (this.onerror) this.onerror(error)
}
this.wrapped.onclose = () => {
this.log({
type: 'close',
timestamp: new Date().toISOString(),
message: 'Connection closed',
})
if (this.onclose) this.onclose()
// Close the log stream when the connection closes
this.logStream.end()
}
}
// Implementation of Transport interface
onclose?: () => void
onerror?: (error: Error) => void
onmessage?: (message: JSONRPCMessage) => void
async start(): Promise<void> {
return this.wrapped.start()
}
async close(): Promise<void> {
return this.wrapped.close()
}
async send(message: JSONRPCMessage): Promise<void> {
this.log({
type: 'sent',
timestamp: new Date().toISOString(),
message,
})
return this.wrapped.send(message)
}
private log(data: any): void {
try {
this.logStream.write(`${JSON.stringify(data)}\n`)
} catch (error) {
console.error('Failed to write to log file:', error)
}
}
}
