SOA & MINFO compression length mismatch

[tmthrgd]

The following two newly created test cases fail:

func TestMsgCompressMINFO(t *testing.T) {
	msg := new(Msg)
	msg.Compress = true
	msg.SetQuestion("www.example.com.", TypeSRV)
	msg.Answer = append(msg.Answer, &MINFO{
		Hdr:   RR_Header{Name: "www.example.com.", Class: 1, Rrtype: TypeSRV, Ttl: 0x3c},
		Rmail: "mail.example.org.",
		Email: "mail.example.org.",
	})

	predicted := msg.Len()
	buf, err := msg.Pack()
	if err != nil {
		t.Error(err)
	}
	if predicted != len(buf) {
		t.Fatalf("predicted compressed length is wrong: predicted %d, actual %d", predicted, len(buf))
	}
}

func TestMsgCompressSOA(t *testing.T) {
	msg := new(Msg)
	msg.Compress = true
	msg.SetQuestion("www.example.com.", TypeSRV)
	msg.Answer = append(msg.Answer, &SOA{
		Hdr:  RR_Header{Name: "www.example.com.", Class: 1, Rrtype: TypeSRV, Ttl: 0x3c},
		Ns:   "ns.example.org.",
		Mbox: "mail.example.org.",
	})

	predicted := msg.Len()
	buf, err := msg.Pack()
	if err != nil {
		t.Error(err)
	}
	if predicted != len(buf) {
		t.Fatalf("predicted compressed length is wrong: predicted %d, actual %d", predicted, len(buf))
	}
}

with:

--- FAIL: TestMsgCompressMINFO (0.00s)
    length_test.go:402: predicted compressed length is wrong: predicted 81, actual 65
--- FAIL: TestMsgCompressSOA (0.00s)
    length_test.go:422: predicted compressed length is wrong: predicted 99, actual 88

I believe the compressedLen code isn't handling matches between the two compressed domains properly, whereas the PackDomainName code is.

/cc @miekg

[miekg]

Do you know off hand what isn't compressed here?

[tmthrgd]

In the first test, the second "mail.example.org." isn't being compressed into the first. While in the second test, "example.org." from "mail.example.org." isn't being compressed into "ns.example.org.".

I think they're both the same bug and honestly I don't understand what's wrong with the current code. I have managed to fix it in rewriting the compressed length code which I'll upload shortly.