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moby--moby/libnetwork/resolver_test.go
Deep Debroy 20faf0adf0 Retry other external DNS servers on ServFail
Signed-off-by: Deep Debroy <ddebroy@docker.com>
2018-03-23 10:22:04 -07:00

270 lines
6.9 KiB
Go

package libnetwork
import (
"bytes"
"net"
"syscall"
"testing"
"time"
"github.com/miekg/dns"
)
// a simple/null address type that will be used to fake a local address for unit testing
type tstaddr struct {
net string
}
func (a *tstaddr) Network() string { return "tcp" }
func (a *tstaddr) String() string { return "127.0.0.1" }
// a simple writer that implements dns.ResponseWriter for unit testing purposes
type tstwriter struct {
msg *dns.Msg
}
func (w *tstwriter) WriteMsg(m *dns.Msg) (err error) {
w.msg = m
return nil
}
func (w *tstwriter) Write(m []byte) (int, error) { return 0, nil }
func (w *tstwriter) LocalAddr() net.Addr { return new(tstaddr) }
func (w *tstwriter) RemoteAddr() net.Addr { return new(tstaddr) }
func (w *tstwriter) TsigStatus() error { return nil }
func (w *tstwriter) TsigTimersOnly(b bool) {}
func (w *tstwriter) Hijack() {}
func (w *tstwriter) Close() error { return nil }
func (w *tstwriter) GetResponse() *dns.Msg { return w.msg }
func (w *tstwriter) ClearResponse() { w.msg = nil }
func checkNonNullResponse(t *testing.T, m *dns.Msg) {
if m == nil {
t.Fatal("Null DNS response found. Non Null response msg expected.")
}
}
func checkNullResponse(t *testing.T, m *dns.Msg) {
if m != nil {
t.Fatal("Non Null DNS response found. Null response msg expected.")
}
}
func checkDNSAnswersCount(t *testing.T, m *dns.Msg, expected int) {
answers := len(m.Answer)
if answers != expected {
t.Fatalf("Expected number of answers in response: %d. Found: %d", expected, answers)
}
}
func checkDNSResponseCode(t *testing.T, m *dns.Msg, expected int) {
if m.MsgHdr.Rcode != expected {
t.Fatalf("Expected DNS response code: %d. Found: %d", expected, m.MsgHdr.Rcode)
}
}
func checkDNSRRType(t *testing.T, actual, expected uint16) {
if actual != expected {
t.Fatalf("Expected DNS Rrtype: %d. Found: %d", expected, actual)
}
}
func TestDNSIPQuery(t *testing.T) {
c, err := New()
if err != nil {
t.Fatal(err)
}
defer c.Stop()
n, err := c.NewNetwork("bridge", "dtnet1", "", nil)
if err != nil {
t.Fatal(err)
}
defer func() {
if err := n.Delete(); err != nil {
t.Fatal(err)
}
}()
ep, err := n.CreateEndpoint("testep")
if err != nil {
t.Fatal(err)
}
sb, err := c.NewSandbox("c1")
if err != nil {
t.Fatal(err)
}
defer func() {
if err := sb.Delete(); err != nil {
t.Fatal(err)
}
}()
// we need the endpoint only to populate ep_list for the sandbox as part of resolve_name
// it is not set as a target for name resolution and does not serve any other purpose
err = ep.Join(sb)
if err != nil {
t.Fatal(err)
}
// add service records which are used to resolve names. These are the real targets for the DNS querries
n.(*network).addSvcRecords("ep1", "name1", "svc1", net.ParseIP("192.168.0.1"), net.IP{}, true, "test")
w := new(tstwriter)
// the unit tests right now will focus on non-proxyed DNS requests
r := NewResolver(resolverIPSandbox, false, sb.Key(), sb.(*sandbox))
// test name1's IP is resolved correctly with the default A type query
q := new(dns.Msg)
q.SetQuestion("name1", dns.TypeA)
r.(*resolver).ServeDNS(w, q)
resp := w.GetResponse()
checkNonNullResponse(t, resp)
t.Log("Response: ", resp.String())
checkDNSResponseCode(t, resp, dns.RcodeSuccess)
checkDNSAnswersCount(t, resp, 1)
checkDNSRRType(t, resp.Answer[0].Header().Rrtype, dns.TypeA)
if answer, ok := resp.Answer[0].(*dns.A); ok {
if !bytes.Equal(answer.A, net.ParseIP("192.168.0.1")) {
t.Fatalf("IP response in Answer %v does not match 192.168.0.1", answer.A)
}
} else {
t.Fatal("Answer of type A not found")
}
w.ClearResponse()
// test MX query with name1 results in Success response with 0 answer records
q = new(dns.Msg)
q.SetQuestion("name1", dns.TypeMX)
r.(*resolver).ServeDNS(w, q)
resp = w.GetResponse()
checkNonNullResponse(t, resp)
t.Log("Response: ", resp.String())
checkDNSResponseCode(t, resp, dns.RcodeSuccess)
checkDNSAnswersCount(t, resp, 0)
w.ClearResponse()
// test MX query with non existent name results in ServFail response with 0 answer records
// since this is a unit test env, we disable proxying DNS above which results in ServFail rather than NXDOMAIN
q = new(dns.Msg)
q.SetQuestion("nonexistent", dns.TypeMX)
r.(*resolver).ServeDNS(w, q)
resp = w.GetResponse()
checkNonNullResponse(t, resp)
t.Log("Response: ", resp.String())
checkDNSResponseCode(t, resp, dns.RcodeServerFailure)
w.ClearResponse()
}
func newDNSHandlerServFailOnce(requests *int) func(w dns.ResponseWriter, r *dns.Msg) {
return func(w dns.ResponseWriter, r *dns.Msg) {
m := new(dns.Msg)
m.SetReply(r)
m.Compress = false
if *requests == 0 {
m.SetRcode(r, dns.RcodeServerFailure)
}
*requests = *requests + 1
w.WriteMsg(m)
}
}
func waitForLocalDNSServer(t *testing.T) {
retries := 0
maxRetries := 10
for retries < maxRetries {
t.Log("Try connecting to DNS server ...")
// this test and retry mechanism only works for TCP. With UDP there is no
// connection and the test becomes inaccurate leading to unpredictable results
tconn, err := net.DialTimeout("tcp", "127.0.0.1:53", 10*time.Second)
retries = retries + 1
if err != nil {
if oerr, ok := err.(*net.OpError); ok {
// server is probably initializing
if oerr.Err == syscall.ECONNREFUSED {
continue
}
} else {
// something is wrong: we should stop for analysis
t.Fatal(err)
}
}
if tconn != nil {
tconn.Close()
break
}
}
}
func TestDNSProxyServFail(t *testing.T) {
c, err := New()
if err != nil {
t.Fatal(err)
}
defer c.Stop()
n, err := c.NewNetwork("bridge", "dtnet2", "", nil)
if err != nil {
t.Fatal(err)
}
defer func() {
if err := n.Delete(); err != nil {
t.Fatal(err)
}
}()
sb, err := c.NewSandbox("c1")
if err != nil {
t.Fatal(err)
}
defer func() {
if err := sb.Delete(); err != nil {
t.Fatal(err)
}
}()
var nRequests int
// initialize a local DNS server and configure it to fail the first query
dns.HandleFunc(".", newDNSHandlerServFailOnce(&nRequests))
// use TCP for predictable results. Connection tests (to figure out DNS server initialization) don't work with UDP
server := &dns.Server{Addr: ":53", Net: "tcp"}
go server.ListenAndServe()
defer server.Shutdown()
waitForLocalDNSServer(t)
t.Log("DNS Server can be reached")
w := new(tstwriter)
r := NewResolver(resolverIPSandbox, true, sb.Key(), sb.(*sandbox))
q := new(dns.Msg)
q.SetQuestion("name1.", dns.TypeA)
var localDNSEntries []extDNSEntry
extTestDNSEntry := extDNSEntry{IPStr: "127.0.0.1", HostLoopback: true}
// configure two external DNS entries and point both to local DNS server thread
localDNSEntries = append(localDNSEntries, extTestDNSEntry)
localDNSEntries = append(localDNSEntries, extTestDNSEntry)
// this should generate two requests: the first will fail leading to a retry
r.(*resolver).SetExtServers(localDNSEntries)
r.(*resolver).ServeDNS(w, q)
if nRequests != 2 {
t.Fatalf("Expected 2 DNS querries. Found: %d", nRequests)
}
t.Logf("Expected number of DNS requests generated")
}