middleware/log: allows logging based on response classes (#325)

Add the ability to add a class of responses to be logged; success,
denial or error. The default is to log everything (all).

Fixes #258

middleware/pkg/response/typify.go

@@ -0,0 +1,96 @@
+package response
+
+import (
+	"fmt"
+
+	"github.com/miekg/dns"
+)
+
+// Type is the type of the message
+type Type int
+
+const (
+	// Success indicates a positive reply
+	NoError Type = iota
+	// NameError is a NXDOMAIN in header, SOA in auth.
+	NameError
+	// NoData indicated name found, but not the type: NOERROR in header, SOA in auth.
+	NoData
+	// Delegation is a msg with a pointer to another nameserver: NOERROR in header, NS in auth, optionally fluff in additional (not checked).
+	Delegation
+	// OtherError indicated any other error: don't cache these.
+	OtherError
+)
+
+func (t Type) String() string {
+	switch t {
+	case NoError:
+		return "NOERROR"
+	case NameError:
+		return "NXDOMAIN"
+	case NoData:
+		return "NODATA"
+	case Delegation:
+		return "DELEGATION"
+	case OtherError:
+		return "OTHERERROR"
+	}
+	return ""
+}
+
+// TypeFromString returns the type from the string s. If not type matches
+// the OtherError type and an error are returned.
+func TypeFromString(s string) (Type, error) {
+	switch s {
+	case "NOERROR":
+		return NoError, nil
+	case "NXDOMAIN":
+		return NameError, nil
+	case "NODATA":
+		return NoData, nil
+	case "DELEGATION":
+		return Delegation, nil
+	case "OTHERERROR":
+		return OtherError, nil
+	}
+	return NoError, fmt.Errorf("invalid Type: %s", s)
+}
+
+// Typify classifies a message, it returns the Type.
+func Typify(m *dns.Msg) (Type, *dns.OPT) {
+	opt := m.IsEdns0()
+
+	if len(m.Answer) > 0 && m.Rcode == dns.RcodeSuccess {
+		return NoError, opt
+	}
+
+	soa := false
+	ns := 0
+	for _, r := range m.Ns {
+		if r.Header().Rrtype == dns.TypeSOA {
+			soa = true
+			continue
+		}
+		if r.Header().Rrtype == dns.TypeNS {
+			ns++
+		}
+	}
+
+	// Check length of different sections, and drop stuff that is just to large? TODO(miek).
+	if soa && m.Rcode == dns.RcodeSuccess {
+		return NoData, opt
+	}
+	if soa && m.Rcode == dns.RcodeNameError {
+		return NameError, opt
+	}
+
+	if ns > 0 && ns == len(m.Ns) && m.Rcode == dns.RcodeSuccess {
+		return Delegation, opt
+	}
+
+	if m.Rcode == dns.RcodeSuccess {
+		return NoError, opt
+	}
+
+	return OtherError, opt
+}