http-echo is an HTTP server for examining request headers sent by HTTP clients.
Running http-echo with no arguments will start an HTTP server listening on port 8000 on all available network interfaces.
$ http-echo
2020/12/05 23:05:46 http-echo
2020/12/05 23:05:46 Listening on :8000...
A specific network address to listen on can be specified using the -http command line argument.
$ http-echo -http 127.0.0.1:8080
2020/12/05 23:05:46 http-echo
2020/12/05 23:05:46 Listening on 127.0.0.1:8080...