[fix] Use `req.connection` for all x-forward-* headers

lib/node-http-proxy.js

@@ -433,10 +433,10 @@ HttpProxy.prototype.proxyRequest = function (req, res, options) {
   // * `x-forwarded-proto`: Protocol of the original request
   // * `x-forwarded-port`: Port of the original request.
   //
-  if (options.enableXForwarded === true && req.connection) {
+  if (options.enableXForwarded === true && req.connection && req.connection.socket) {
     req.headers['x-forwarded-for']   = req.connection.remoteAddress || req.connection.socket.remoteAddress;
     req.headers['x-forwarded-port']  = req.connection.remotePort || req.connection.socket.remotePort;
-    req.headers['x-forwarded-proto'] = res.connection.pair ? 'https' : 'http';
+    req.headers['x-forwarded-proto'] = req.connection.pair ? 'https' : 'http';
   }
 
   //