How to use the http-proxy/lib/http-proxy/common.setupSocket function in http-proxy

proxyReq.on('upgrade', function(proxyRes, proxySocket, proxyHead) {
    proxySocket.on('error', onOutgoingError);

    // Allow us to listen when the websocket has completed
    proxySocket.on('end', function () {
      server.emit('close', proxyRes, proxySocket, proxyHead);
    });

    // The pipe below will end proxySocket if socket closes cleanly, but not
    // if it errors (eg, vanishes from the net and starts returning
    // EHOSTUNREACH). We need to do that explicitly.
    socket.on('error', function () {
      proxySocket.end();
    });

    common.setupSocket(proxySocket);

    if (proxyHead && proxyHead.length) proxySocket.unshift(proxyHead);

    // Remark: Handle writing the headers to the socket when switching protocols
    // Also handles when a header is an array
    socket.write(createHttpHeader(
      'HTTP/1.1 101 Switching Protocols',
      proxyRes.headers
    ));

    let proxyStream = proxySocket;

    if (options.createWsServerTransformStream) {
      const wsServerTransformStream = options.createWsServerTransformStream(
        req,
        proxyReq,

const createHttpHeader = function(line, headers) {
    return Object.keys(headers).reduce(function (head, key) {
      const value = headers[key];
      if (!Array.isArray(value)) {
        head.push(`${key}: ${value}`);
        return head;
      }
      for (let i = 0; i < value.length; i++) {
        head.push(`${key}: ${value[i]}`);
      }
      return head;
    }, [line])
      .join(CRLF) + `${CRLF}${CRLF}`;
  };

  common.setupSocket(socket);

  if (head && head.length) socket.unshift(head);

  const protocol = common.isSSL.test(options.target.protocol) ? https : http;

  const proxyReq = protocol.request(
    common.setupOutgoing(options.ssl || {}, options, req)
  );

  // Enable developers to modify the proxyReq before headers are sent
  if (server) {
    server.emit('proxyReqWs', proxyReq, req, socket, options, head);
  }

  // Error Handler
  proxyReq.on('error', onOutgoingError);