middleware/auto: add (#333)

Add auto-load middleware that automatically picks up zones.

Every X seconds it will scan for new zones.
Add tests and documentation.

Make 'make test' use -race.

middleware/auto/auto.go

@@ -0,0 +1,99 @@
+// Package auto implements an on-the-fly loading file backend.
+package auto
+
+import (
+	"errors"
+	"regexp"
+	"time"
+
+	"github.com/miekg/coredns/middleware"
+	"github.com/miekg/coredns/middleware/file"
+	"github.com/miekg/coredns/request"
+
+	"github.com/miekg/dns"
+	"golang.org/x/net/context"
+)
+
+type (
+	// Auto holds the zones and the loader configuration for automatically loading zones.
+	Auto struct {
+		Next middleware.Handler
+		*Zones
+
+		loader
+	}
+
+	loader struct {
+		directory string
+		template  string
+		re        *regexp.Regexp
+
+		// In the future this should be something like ZoneMeta that contains all this stuff.
+		transferTo []string
+		noReload   bool
+
+		duration time.Duration
+	}
+)
+
+// ServeDNS implements the middleware.Handle interface.
+func (a Auto) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	state := request.Request{W: w, Req: r}
+	if state.QClass() != dns.ClassINET {
+		return dns.RcodeServerFailure, errors.New("can only deal with ClassINET")
+	}
+	qname := state.Name()
+
+	// TODO(miek): match the qname better in the map
+
+	// Precheck with the origins, i.e. are we allowed to looks here.
+	zone := middleware.Zones(a.Zones.Origins()).Matches(qname)
+	if zone == "" {
+		if a.Next != nil {
+			return a.Next.ServeDNS(ctx, w, r)
+		}
+		return dns.RcodeServerFailure, errors.New("no next middleware found")
+	}
+
+	// Now the real zone.
+	zone = middleware.Zones(a.Zones.Names()).Matches(qname)
+
+	a.Zones.RLock()
+	z, ok := a.Zones.Z[zone]
+	a.Zones.RUnlock()
+
+	if !ok {
+		return a.Next.ServeDNS(ctx, w, r)
+	}
+	if z == nil {
+		return dns.RcodeServerFailure, nil
+	}
+
+	if state.QType() == dns.TypeAXFR || state.QType() == dns.TypeIXFR {
+		xfr := file.Xfr{Zone: z}
+		return xfr.ServeDNS(ctx, w, r)
+	}
+
+	answer, ns, extra, result := z.Lookup(qname, state.QType(), state.Do())
+
+	m := new(dns.Msg)
+	m.SetReply(r)
+	m.Authoritative, m.RecursionAvailable, m.Compress = true, true, true
+	m.Answer, m.Ns, m.Extra = answer, ns, extra
+
+	switch result {
+	case file.Success:
+	case file.NoData:
+	case file.NameError:
+		m.Rcode = dns.RcodeNameError
+	case file.Delegation:
+		m.Authoritative = false
+	case file.ServerFailure:
+		return dns.RcodeServerFailure, nil
+	}
+
+	state.SizeAndDo(m)
+	m, _ = state.Scrub(m)
+	w.WriteMsg(m)
+	return dns.RcodeSuccess, nil
+}