coredns/plugin/pkg/dnstest/server.go

package dnstest

import (
	"net"

	"github.com/miekg/dns"
)

// A Server is an DNS server listening on a system-chosen port on the local
// loopback interface, for use in end-to-end DNS tests.
type Server struct {
	Addr string // Address where the server listening.

	s1 *dns.Server // udp
	s2 *dns.Server // tcp
}

// NewServer starts and returns a new Server. The caller should call Close when
// finished, to shut it down.
func NewServer(f dns.HandlerFunc) *Server {
	dns.HandleFunc(".", f)

	ch1 := make(chan bool)
	ch2 := make(chan bool)

	l, _ := net.Listen("tcp", ":0")
	if l == nil {
		return nil
	}
	p, _ := net.ListenPacket("udp", l.Addr().String())
	if p == nil {
		l.Close()
		return nil // yes, this may crash some test, but this is better than hanging
	}

	s1 := &dns.Server{PacketConn: p}
	s2 := &dns.Server{Listener: l}
	s1.NotifyStartedFunc = func() { close(ch1) }
	s2.NotifyStartedFunc = func() { close(ch2) }
	go s1.ActivateAndServe()
	go s2.ActivateAndServe()

	<-ch1
	<-ch2

	return &Server{s1: s1, s2: s2, Addr: p.LocalAddr().String()}
}

// Close shuts down the server.
func (s *Server) Close() {
	s.s1.Shutdown()
	s.s2.Shutdown()
}