This sample application provides a simple echo server that sends clients back whatever data they send it. Invoke it using one of the following syntaxes:
swift run NIOEchoServer # Binds the server on ::1, port 9999.
swift run NIOEchoServer 9899 # Binds the server on ::1, port 9899
swift run NIOEchoServer /path/to/unix/socket # Binds the server using the given UNIX socket
swift run NIOEchoServer 192.168.0.5 9899 # Binds the server on 192.168.0.5:9899