Move dummy DNS server to integration/internal/network

Signed-off-by: Rob Murray <rob.murray@docker.com>

integration/internal/network/dns.go

@@ -0,0 +1,66 @@
+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(0644)
+	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() })
+}

integration/networking/resolvconf_test.go

@@ -1,8 +1,6 @@
 package networking
 
 import (
-	"net"
-	"os"
 	"strings"
 	"testing"
 
@@ -10,29 +8,11 @@ import (
 	"github.com/docker/docker/integration/internal/container"
 	"github.com/docker/docker/integration/internal/network"
 	"github.com/docker/docker/testutil/daemon"
-	"github.com/miekg/dns"
 	"gotest.tools/v3/assert"
 	is "gotest.tools/v3/assert/cmp"
 	"gotest.tools/v3/skip"
 )
 
-// writeTempResolvConf writes a resolv.conf that only contains a single
-// nameserver line, with address addr.
-// It returns the name of the temp file.
-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(0644)
-	assert.NilError(t, err)
-	f.Write([]byte("nameserver " + addr + "\n"))
-	return f.Name()
-}
-
 // Regression test for https://github.com/moby/moby/issues/46968
 func TestResolvConfLocalhostIPv6(t *testing.T) {
 	// No "/etc/resolv.conf" on Windows.
@@ -40,7 +20,7 @@ func TestResolvConfLocalhostIPv6(t *testing.T) {
 
 	ctx := setupTest(t)
 
-	tmpFileName := writeTempResolvConf(t, "127.0.0.53")
+	tmpFileName := network.WriteTempResolvConf(t, "127.0.0.53")
 
 	d := daemon.New(t, daemon.WithEnvVars("DOCKER_TEST_RESOLV_CONF_PATH="+tmpFileName))
 	d.StartWithBusybox(ctx, t, "--experimental", "--ip6tables")
@@ -81,43 +61,6 @@ options ndots:0
 `))
 }
 
-const dnsRespAddr = "10.11.12.13"
-
-// startDaftDNS starts and returns a really, really daft DNS server that only
-// responds to type-A requests, and always with address dnsRespAddr.
-func startDaftDNS(t *testing.T, addr string) *dns.Server {
-	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()
-	}()
-
-	return server
-}
-
 // Check that when a container is connected to an internal network, DNS
 // requests sent to daemon's internal DNS resolver are not forwarded to
 // an upstream resolver listening on a localhost address.
@@ -128,11 +71,10 @@ func TestInternalNetworkDNS(t *testing.T) {
 	ctx := setupTest(t)
 
 	// Start a DNS server on the loopback interface.
-	server := startDaftDNS(t, "127.0.0.1")
+	network.StartDaftDNS(t, "127.0.0.1")
-	defer server.Shutdown()
 
 	// Set up a temp resolv.conf pointing at that DNS server, and a daemon using it.
-	tmpFileName := writeTempResolvConf(t, "127.0.0.1")
+	tmpFileName := network.WriteTempResolvConf(t, "127.0.0.1")
 	d := daemon.New(t, daemon.WithEnvVars("DOCKER_TEST_RESOLV_CONF_PATH="+tmpFileName))
 	d.StartWithBusybox(ctx, t, "--experimental", "--ip6tables")
 	defer d.Stop(t)
@@ -160,7 +102,7 @@ func TestInternalNetworkDNS(t *testing.T) {
 	res, err := container.Exec(ctx, c, ctrId, []string{"nslookup", "test.example"})
 	assert.NilError(t, err)
 	assert.Check(t, is.Equal(res.ExitCode, 0))
-	assert.Check(t, is.Contains(res.Stdout(), dnsRespAddr))
+	assert.Check(t, is.Contains(res.Stdout(), network.DNSRespAddr))
 
 	// Connect the container to the internal network as well.
 	// External DNS should still be used.
@@ -169,7 +111,7 @@ func TestInternalNetworkDNS(t *testing.T) {
 	res, err = container.Exec(ctx, c, ctrId, []string{"nslookup", "test.example"})
 	assert.NilError(t, err)
 	assert.Check(t, is.Equal(res.ExitCode, 0))
-	assert.Check(t, is.Contains(res.Stdout(), dnsRespAddr))
+	assert.Check(t, is.Contains(res.Stdout(), network.DNSRespAddr))
 
 	// Disconnect from the external network.
 	// Expect no access to the external DNS.
@@ -187,5 +129,5 @@ func TestInternalNetworkDNS(t *testing.T) {
 	res, err = container.Exec(ctx, c, ctrId, []string{"nslookup", "test.example"})
 	assert.NilError(t, err)
 	assert.Check(t, is.Equal(res.ExitCode, 0))
-	assert.Check(t, is.Contains(res.Stdout(), dnsRespAddr))
+	assert.Check(t, is.Contains(res.Stdout(), network.DNSRespAddr))
 }