dotcloud/docker

package network

import (
    "net"
    "os"
    "testing"

    "github.com/miekg/dns"
    "gotest.tools/v3/assert"
)

const DNSRespAddr = "10.11.12.13"

// WriteTempResolvConf writes a resolv.conf that only contains a single
// nameserver line, with address addr.
// It returns the name of the temp file. The temp file will be deleted
// automatically by a t.Cleanup().
func WriteTempResolvConf(t *testing.T, addr string) string {
    t.Helper()
    // Not using t.TempDir() here because in rootless mode, while the temporary
    // directory gets mode 0777, it's a subdir of an 0700 directory owned by root.
    // So, it's not accessible by the daemon.
    f, err := os.CreateTemp("", "resolv.conf")
    assert.NilError(t, err)
    t.Cleanup(func() { os.Remove(f.Name()) })
    err = f.Chmod(0o644)
    assert.NilError(t, err)
    f.Write([]byte("nameserver " + addr + "\n"))
    return f.Name()
}

// StartDaftDNS starts and returns a really, really daft DNS server that only
// responds to type-A requests, and always with address dnsRespAddr.
// The DNS server will be stopped automatically by a t.Cleanup().
func StartDaftDNS(t *testing.T, addr string) {
    serveDNS := func(w dns.ResponseWriter, query *dns.Msg) {
        if query.Question[0].Qtype == dns.TypeA {
            resp := &dns.Msg{}
            resp.SetReply(query)
            answer := &dns.A{
                Hdr: dns.RR_Header{
                    Name:   query.Question[0].Name,
                    Rrtype: dns.TypeA,
                    Class:  dns.ClassINET,
                    Ttl:    600,
                },
            }
            answer.A = net.ParseIP(DNSRespAddr)
            resp.Answer = append(resp.Answer, answer)
            _ = w.WriteMsg(resp)
        }
    }

    conn, err := net.ListenUDP("udp", &net.UDPAddr{
        IP:   net.ParseIP(addr),
        Port: 53,
    })
    assert.NilError(t, err)

    server := &dns.Server{Handler: dns.HandlerFunc(serveDNS), PacketConn: conn}
    go func() {
        _ = server.ActivateAndServe()
    }()

    t.Cleanup(func() { server.Shutdown() })
}