initial prototype

.gitignore

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+/realm
+*.zone

Makefile

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+realm: ./cmd/realm/main.go ./server.go ./zone.go
+	go build ./cmd/realm
+
+clean:
+	rm -f ./realm
+
+run:
+	go run ./cmd/realm/main.go
+
+.PHONY: clean run

cmd/realm/main.go

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+package main
+
+import (
+	"log"
+
+	"github.com/brettlangdon/realm"
+	"github.com/codegangsta/cli"
+)
+
+func main() {
+	var app *cli.App = cli.NewApp()
+	app.Name = "realm"
+	app.Version = "0.1.0"
+	app.Author = "Brett Langdon"
+	app.Email = "me@brett.is"
+	app.Flags = []cli.Flag{
+		cli.StringFlag{
+			Name:   "zone, z",
+			EnvVar: "REALM_ZONE",
+			Usage:  "location to DNS zone file [required]",
+		},
+		cli.StringFlag{
+			Name:   "bind, b",
+			EnvVar: "REALM_BIND",
+			Value:  ":53",
+			Usage:  "'[<host>]:<port>' to bind too",
+		},
+	}
+	app.Action = func(c *cli.Context) {
+		var filename string = c.String("zone")
+		if filename == "" {
+			log.Fatal("must supply zone file via \"--zone\" flag or \"REALM_ZONE\" environment variable")
+		}
+
+		var zone *realm.Zone
+		var err error
+		log.Printf("parsing zone file \"%s\"\n", filename)
+		zone, err = realm.ParseZone(filename)
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		var bind string = c.String("bind")
+		log.Printf("starting the server on \"%s\"\n", bind)
+		var server *realm.Server = realm.NewServer(bind, zone)
+		log.Fatal(server.ListenAndServe())
+	}
+
+	app.RunAndExitOnError()
+}

server.go

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+package realm
+
+import "github.com/miekg/dns"
+
+type Server struct {
+	server *dns.Server
+	zone   *Zone
+}
+
+func NewServer(listen string, zone *Zone) *Server {
+	var server *Server = &Server{zone: zone}
+	server.server = &dns.Server{
+		Addr:    listen,
+		Net:     "udp",
+		Handler: server,
+	}
+	return server
+}
+
+func (server *Server) ListenAndServe() error {
+	return server.server.ListenAndServe()
+}
+
+func (server *Server) ServeDNS(w dns.ResponseWriter, request *dns.Msg) {
+	var response *dns.Msg = &dns.Msg{}
+	response.SetReply(request)
+	response.Compress = true
+
+	for _, question := range request.Question {
+		var records []dns.RR = server.zone.Lookup(question.Name, question.Qtype, question.Qclass)
+		response.Answer = append(response.Answer, records...)
+	}
+
+	w.WriteMsg(response)
+}

zone.go

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+package realm
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/miekg/dns"
+)
+
+type Zone struct {
+	records []dns.RR
+}
+
+func ParseZone(filename string) (*Zone, error) {
+	var zone *Zone
+	var err error
+	zone = &Zone{
+		records: make([]dns.RR, 0),
+	}
+
+	var file *os.File
+	file, err = os.Open(filename)
+	if err != nil {
+		return nil, fmt.Errorf("could not parse zone file \"%s\": \"%s\"", filename, err)
+	}
+	defer file.Close()
+
+	var tokens chan *dns.Token
+	tokens = dns.ParseZone(file, "", "")
+	for token := range tokens {
+		if token.Error != nil {
+			return nil, fmt.Errorf("could not parse zone file \"%s\": \"%s\"", filename, token.Error)
+		}
+
+		zone.records = append(zone.records, token.RR)
+	}
+	return zone, nil
+}
+
+func (zone *Zone) Lookup(name string, reqType uint16, reqClass uint16) []dns.RR {
+	name = dns.Fqdn(name)
+	var records []dns.RR = make([]dns.RR, 0)
+	for _, record := range zone.records {
+		var header *dns.RR_Header = record.Header()
+		if header.Name != name || (header.Class != reqClass && reqClass != dns.ClassANY) {
+			continue
+		}
+
+		if reqType == dns.TypeANY || reqType == header.Rrtype {
+			records = append(records, record)
+		} else if header.Rrtype == dns.TypeCNAME {
+			records = append(records, record)
+			var cname *dns.CNAME = record.(*dns.CNAME)
+			var cnameRecords []dns.RR = zone.Lookup(dns.Fqdn(cname.Target), reqType, reqClass)
+			records = append(records, cnameRecords...)
+		}
+	}
+	return records
+}