Like socketpair, but for Golang, and TCP instead of Unix sockets

connpair.go

package connpair

import (
	"net"
)

func ConnPair() (serverConn, clientConn net.Conn, err error) {
	l, err := net.Listen("tcp", "localhost:0")
	if err != nil {
		return
	}
	defer l.Close()

	addr := l.Addr()

	var err2 error

	done := make(chan struct{})

	go func() {
		defer close(done)
		clientConn, err2 = net.Dial(addr.Network(), addr.String())
	}()

	serverConn, err = l.Accept()
	<-done

	if err == nil {
		err = err2
	}

	if err != nil {
		if clientConn != nil {
			clientConn.Close()
		}
		if serverConn != nil {
			serverConn.Close()
		}
	}

	return
}