port property
int portReturns the port that the server is listening on. This can be used to get the actual port used when a value of 0 for port is specified in the bind or bindSecure call.
Source
int get port;© 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
https://api.dartlang.org/stable/1.24.3/dart-io/HttpServer/port.html