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dnstest.go
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dnstest.go
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package dnstest
import (
"context"
"fmt"
"net"
"testing"
"time"
"github.com/miekg/dns"
)
// Replaces net.DefaultResolver with a resolver that resolves
// configured names to 127.0.0.1 and fails to resolve any other name.
// Uses t.Cleanup to restore resolver after the test.
func LoopbackNames(t *testing.T, first string, rest ...string) {
mux := dns.NewServeMux()
mux.HandleFunc(".", newDnsHandler(append(rest, first)))
s, err := startServer(mux)
if err != nil {
t.Fatal(err)
return
}
defaultResolver := net.DefaultResolver
net.DefaultResolver = serverResolver(s)
t.Cleanup(func() {
net.DefaultResolver = defaultResolver
s.Shutdown()
})
}
type dnsHandler struct {
names map[string]struct{}
}
func newDnsHandler(names []string) func(w dns.ResponseWriter, r *dns.Msg) {
h := &dnsHandler{
names: make(map[string]struct{}),
}
for _, name := range names {
h.names[dns.CanonicalName(name)] = struct{}{}
}
return h.handle
}
func (h *dnsHandler) handle(w dns.ResponseWriter, r *dns.Msg) {
if r.MsgHdr.Opcode != dns.OpcodeQuery {
h.nameError(w, r)
return
}
q := r.Question[0]
if q.Qtype != dns.TypeA || q.Qclass != dns.ClassINET {
h.nameError(w, r)
return
}
qname := dns.CanonicalName(q.Name)
if _, ok := h.names[qname]; !ok {
h.nameError(w, r)
return
}
reply := new(dns.Msg)
reply.SetRcode(r, dns.RcodeSuccess)
reply.Answer = append(reply.Answer, &dns.A{
Hdr: dns.RR_Header{
Name: qname,
Rrtype: dns.TypeA,
Class: dns.ClassINET,
Ttl: 9999,
},
A: net.IPv4(127, 0, 0, 1),
})
w.WriteMsg(reply)
}
func (h *dnsHandler) nameError(w dns.ResponseWriter, r *dns.Msg) {
reply := new(dns.Msg)
reply.SetRcode(r, dns.RcodeNameError)
w.WriteMsg(reply)
}
func startServer(handler dns.Handler) (*dns.Server, error) {
ready := make(chan error, 1)
server := &dns.Server{
Addr: ":0",
Net: "udp",
Handler: handler,
NotifyStartedFunc: func() { ready <- nil },
}
go func() { ready <- server.ListenAndServe() }()
return server, <-ready
}
func serverResolver(server *dns.Server) *net.Resolver {
return &net.Resolver{
PreferGo: true,
StrictErrors: true,
Dial: func(ctx context.Context, network, addr string) (net.Conn, error) {
if network != "udp" {
return nil, fmt.Errorf("unsupported network: %s", network)
}
dialer := net.Dialer{Timeout: 1 * time.Second}
return dialer.DialContext(ctx, network, server.PacketConn.LocalAddr().String())
},
}
}