dev-server/lib/proxy.js

const http = require('http');
const debug = require('debug')('dev-server:proxy');

module.exports = function(app) {
  app.proxy = function(url, config) {
    app.use(url, function(req, res) {
      var httpPath = (config.path || '') + req.path;
      var headers = {};

      Object.keys(req.headers).forEach(function(name) {
        if (name !== 'host' && name !== 'connection') headers[name] = req.headers[name];
      });

      headers.host = config.hostname || config.host;

      var client = http.request(
        {
          host: config.host,
          hostname: config.hostname,
          port: config.port,
          localAddress: config.localAddress,
          socketPath: config.socketPath || config.socket,
          method: req.method,
          path: httpPath,
        },
        function(proxyres) {
          debug('server connection - response');

          res.statusCode = proxyres.statusCode;
          if (proxyres.headers['content-type'])
            res.setHeader('content-type', proxyres.headers['content-type']);

          proxyres.on('data', function(data) {
            res.write(data);
          });

          proxyres.on('end', function() {
            debug('res end');
            res.end();
          });

          proxyres.on('error', function() {
            debug('PROXY ERROR');
            res.statusCode = 500;
            res.end();
          });
        }
      );

      req.setEncoding('utf8');

      req.on('data', function(data) {
        client.write(data);
      });

      req.on('end', function() {
        debug('req end');
        client.end();
      });
    });
  };
};