preserve Upgrade header

end request in hijack mode

Author: schummar

lib/modem.js

@@ -227,7 +227,7 @@ Modem.prototype.dial = function (options, callback) {
 
   if (options.hijack) {
     optionsf.headers.Connection = 'Upgrade';
-    optionsf.headers.Upgrade = 'tcp';
+    optionsf.headers.Upgrade ??= 'tcp';
   }
 
   if (this.socketPath) {
@@ -366,7 +366,7 @@ Modem.prototype.buildRequest = function (options, context, data, callback) {
     data.pipe(req);
   }
 
-  if (!context.hijack && !context.openStdin && (typeof data === 'string' || data === undefined || Buffer.isBuffer(data))) {
+  if (!context.openStdin && (typeof data === 'string' || data === undefined || Buffer.isBuffer(data))) {
     req.end();
   }
 };