Reverse proxy for monitoring RPC requests to a local anvil server

anvil-reverse-proxy.ts

import { createWriteStream, writeFileSync } from 'node:fs';
import { createServer, request } from 'node:http';

// Settings //

const TARGET_HOST = '127.0.0.1';
const TARGET_PORT = 8545;
const PROXY_PORT = 8546;

// Server //

const server = createServer((req, res) => {
  let body = '';
  req.on('data', (chunk) => (body += chunk));
  req.on('end', async () => {
    // Log the request
    log('RPC Request:', JSON.parse(body));

    // Forward the request to Anvil
    const proxyReq = request(
      {
        hostname: TARGET_HOST,
        port: TARGET_PORT,
        path: req.url,
        method: req.method,
        headers: req.headers,
      },
      (proxyRes) => {
        // Log the response
        let body = '';
        proxyRes.on('data', (chunk) => (body += chunk));
        proxyRes.on('end', () => log('RPC Response:', JSON.parse(body)));

        // Send response back to client
        res.writeHead(proxyRes.statusCode || 200, proxyRes.headers);
        proxyRes.pipe(res);
      }
    );
    proxyReq.on('error', (err) => {
      log('Proxy Error:', err);
      res.writeHead(500);
      res.end('Proxy error');
    });
    proxyReq.write(body);
    proxyReq.end();
  });
});

// Start server
server.listen(PROXY_PORT, () =>
  console.log(
    `Proxy server running at: ${`http://127.0.0.1:${PROXY_PORT}`}`
  )
);

// Logger //

const timestamp = new Date().toISOString();
const logFileName = `requests-${timestamp}.log`;

// Reset log file
writeFileSync(logFileName, '');

// Create a write stream to log file
const logStream = createWriteStream(logFileName, {
  flags: 'a', // Append mode
});

// Log to the log file and console
function log(...args: any[]) {
  const timestamp = new Date().toISOString();
  const message = formatArgs(...args);
  const logLine = `[${timestamp}] ${message}\n`;
  logStream.write(logLine);
  console.log(logLine);
}

function formatArgs(...args: any[]) {
  return args.map(formatArg).join(' ');
}

function formatArg(arg: any) {
  if (typeof arg === 'object') {
    return JSON.stringify(arg, bigintReplacer, 2);
  }
  return arg;
}

function bigintReplacer(_: string, value: any) {
  if (typeof value === 'bigint') {
    return value.toString();
  }
  return value;
}