Support SkyDNS' stubzones

This implements stubzones in the same way as SkyDNS. This
also works with multiple configured domains and has tests.
Also add more configuration parameters for TLS and path prefix and
enabling stubzones.  Run StubUpdates as a startup command to keep up to
date with the list in etcd.

middleware/etcd/stub_test.go

@@ -0,0 +1,145 @@
+// +build etcd
+
+package etcd
+
+import "testing"
+
+func TestStubLookup(t *testing.T) {
+	// e.updateStubZones()
+}
+
+/*
+func TestDNSStubForward(t *testing.T) {
+	s := newTestServer(t, false)
+	defer s.Stop()
+
+	c := new(dns.Client)
+	m := new(dns.Msg)
+
+	stubEx := &msg.Service{
+		// IP address of a.iana-servers.net.
+		Host: "199.43.132.53", Key: "a.example.com.stub.dns.skydns.test.",
+	}
+	stubBroken := &msg.Service{
+		Host: "127.0.0.1", Port: 5454, Key: "b.example.org.stub.dns.skydns.test.",
+	}
+	stubLoop := &msg.Service{
+		Host: "127.0.0.1", Port: Port, Key: "b.example.net.stub.dns.skydns.test.",
+	}
+	addService(t, s, stubEx.Key, 0, stubEx)
+	defer delService(t, s, stubEx.Key)
+	addService(t, s, stubBroken.Key, 0, stubBroken)
+	defer delService(t, s, stubBroken.Key)
+	addService(t, s, stubLoop.Key, 0, stubLoop)
+	defer delService(t, s, stubLoop.Key)
+
+	s.UpdateStubZones()
+
+	m.SetQuestion("www.example.com.", dns.TypeA)
+	resp, _, err := c.Exchange(m, "127.0.0.1:"+StrPort)
+	if err != nil {
+		// try twice
+		resp, _, err = c.Exchange(m, "127.0.0.1:"+StrPort)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+	if len(resp.Answer) == 0 || resp.Rcode != dns.RcodeSuccess {
+		t.Fatal("answer expected to have A records or rcode not equal to RcodeSuccess")
+	}
+	// The main diff. here is that we expect the AA bit to be set, because we directly
+	// queried the authoritative servers.
+	if resp.Authoritative != true {
+		t.Fatal("answer expected to have AA bit set")
+	}
+
+	// This should fail.
+	m.SetQuestion("www.example.org.", dns.TypeA)
+	resp, _, err = c.Exchange(m, "127.0.0.1:"+StrPort)
+	if len(resp.Answer) != 0 || resp.Rcode != dns.RcodeServerFailure {
+		t.Fatal("answer expected to fail for example.org")
+	}
+
+	// This should really fail with a timeout.
+	m.SetQuestion("www.example.net.", dns.TypeA)
+	resp, _, err = c.Exchange(m, "127.0.0.1:"+StrPort)
+	if err == nil {
+		t.Fatal("answer expected to fail for example.net")
+	} else {
+		t.Logf("succesfully failing %s", err)
+	}
+
+	// Packet with EDNS0
+	m.SetEdns0(4096, true)
+	resp, _, err = c.Exchange(m, "127.0.0.1:"+StrPort)
+	if err == nil {
+		t.Fatal("answer expected to fail for example.net")
+	} else {
+		t.Logf("succesfully failing %s", err)
+	}
+
+	// Now start another SkyDNS instance on a different port,
+	// add a stubservice for it and check if the forwarding is
+	// actually working.
+	oldStrPort := StrPort
+
+	s1 := newTestServer(t, false)
+	defer s1.Stop()
+	s1.config.Domain = "skydns.com."
+
+	// Add forwarding IP for internal.skydns.com. Use Port to point to server s.
+	stubForward := &msg.Service{
+		Host: "127.0.0.1", Port: Port, Key: "b.internal.skydns.com.stub.dns.skydns.test.",
+	}
+	addService(t, s, stubForward.Key, 0, stubForward)
+	defer delService(t, s, stubForward.Key)
+	s.UpdateStubZones()
+
+	// Add an answer for this in our "new" server.
+	stubReply := &msg.Service{
+		Host: "127.1.1.1", Key: "www.internal.skydns.com.",
+	}
+	addService(t, s1, stubReply.Key, 0, stubReply)
+	defer delService(t, s1, stubReply.Key)
+
+	m = new(dns.Msg)
+	m.SetQuestion("www.internal.skydns.com.", dns.TypeA)
+	resp, _, err = c.Exchange(m, "127.0.0.1:"+oldStrPort)
+	if err != nil {
+		t.Fatalf("failed to forward %s", err)
+	}
+	if resp.Answer[0].(*dns.A).A.String() != "127.1.1.1" {
+		t.Fatalf("failed to get correct reply")
+	}
+
+	// Adding an in baliwick internal domain forward.
+	s2 := newTestServer(t, false)
+	defer s2.Stop()
+	s2.config.Domain = "internal.skydns.net."
+
+	// Add forwarding IP for internal.skydns.net. Use Port to point to server s.
+	stubForward1 := &msg.Service{
+		Host: "127.0.0.1", Port: Port, Key: "b.internal.skydns.net.stub.dns.skydns.test.",
+	}
+	addService(t, s, stubForward1.Key, 0, stubForward1)
+	defer delService(t, s, stubForward1.Key)
+	s.UpdateStubZones()
+
+	// Add an answer for this in our "new" server.
+	stubReply1 := &msg.Service{
+		Host: "127.10.10.10", Key: "www.internal.skydns.net.",
+	}
+	addService(t, s2, stubReply1.Key, 0, stubReply1)
+	defer delService(t, s2, stubReply1.Key)
+
+	m = new(dns.Msg)
+	m.SetQuestion("www.internal.skydns.net.", dns.TypeA)
+	resp, _, err = c.Exchange(m, "127.0.0.1:"+oldStrPort)
+	if err != nil {
+		t.Fatalf("failed to forward %s", err)
+	}
+	if resp.Answer[0].(*dns.A).A.String() != "127.10.10.10" {
+		t.Fatalf("failed to get correct reply")
+	}
+}
+*/