[fix] Only set `x-forward-*` headers if req.connection and req.connection.socket

lib/node-http-proxy/http-proxy.js

@@ -126,10 +126,10 @@ HttpProxy.prototype.proxyRequest = function (req, res, buffer) {
   // * `x-forwarded-proto`: Protocol of the original request
   // * `x-forwarded-port`: Port of the original request.
   //
-  if (this.enable.xforward) {
+  if (this.enable.xforward && 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';
   }
 
   //