add comments

cmd/realm/main.go

@@ -8,6 +8,7 @@ import (
 )
 
 func main() {
+	// Setup our CLI app
 	var app *cli.App = cli.NewApp()
 	app.Name = "realm"
 	app.Version = "0.1.0"
@@ -26,12 +27,16 @@ func main() {
 			Usage:  "'[<host>]:<port>' to bind too",
 		},
 	}
+
+	// This action is called for all commands
 	app.Action = func(c *cli.Context) {
+		// Ensure that a zone filename was provided
 		var filename string = c.String("zone")
 		if filename == "" {
 			log.Fatal("must supply zone file via \"--zone\" flag or \"REALM_ZONE\" environment variable")
 		}
 
+		// Load and parse the zone file
 		var zone *realm.Zone
 		var err error
 		log.Printf("parsing zone file \"%s\"\n", filename)
@@ -40,11 +45,13 @@ func main() {
 			log.Fatal(err)
 		}
 
+		// Create and start the server
 		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())
 	}
 
+	// Parse command arguments and run `app.Action`
 	app.RunAndExitOnError()
 }

server.go

@@ -2,34 +2,45 @@ package realm
 
 import "github.com/miekg/dns"
 
+// A Server listens for DNS requests over UDP and responds with answers from the provided Zone.
 type Server struct {
 	server *dns.Server
 	zone   *Zone
 }
 
+// NewServer returns a new initialized *Server that will bind to listen and will look up answers from zone.
 func NewServer(listen string, zone *Zone) *Server {
-	var server *Server = &Server{zone: zone}
-	server.server = &dns.Server{
+	var server *Server
+	s = &Server{zone: zone}
+	s.server = &dns.Server{
 		Addr:    listen,
 		Net:     "udp",
 		Handler: server,
 	}
-	return server
+	return s
 }
 
-func (server *Server) ListenAndServe() error {
+// ListenAndServe will start the nameserver on the configured address.
+func (s *Server) ListenAndServe() error {
 	return server.server.ListenAndServe()
 }
 
-func (server *Server) ServeDNS(w dns.ResponseWriter, request *dns.Msg) {
-	var response *dns.Msg = &dns.Msg{}
+// ServeDNS will be called for every DNS request to this server.
+// It will attempt to provide answers to all questions from the configured zone.
+func (s *Server) ServeDNS(w dns.ResponseWriter, request *dns.Msg) {
+	// Setup the default response
+	var response *dns.Msg
+	response = &dns.Msg{}
 	response.SetReply(request)
 	response.Compress = true
 
+	// Lookup answers to any of the questions
 	for _, question := range request.Question {
-		var records []dns.RR = server.zone.Lookup(question.Name, question.Qtype, question.Qclass)
+		var records []dns.RR
+		records = s.zone.Lookup(question.Name, question.Qtype, question.Qclass)
 		response.Answer = append(response.Answer, records...)
 	}
 
+	// Respond to the request
 	w.WriteMsg(response)
 }

zone.go

@@ -7,10 +7,13 @@ import (
 	"github.com/miekg/dns"
 )
 
+// A Zone a container for records parsed from a zone file.
 type Zone struct {
 	records []dns.RR
 }
 
+// ParseZone will attempt to parse a zone file from the provided filename and return a Zone.
+// ParseZone will return an error if the file provided does not exist or could not be properly parsed.
 func ParseZone(filename string) (*Zone, error) {
 	var zone *Zone
 	var err error
@@ -18,6 +21,7 @@ func ParseZone(filename string) (*Zone, error) {
 		records: make([]dns.RR, 0),
 	}
 
+	// Open the file
 	var file *os.File
 	file, err = os.Open(filename)
 	if err != nil {
@@ -25,6 +29,7 @@ func ParseZone(filename string) (*Zone, error) {
 	}
 	defer file.Close()
 
+	// Parse the file into records
 	var tokens chan *dns.Token
 	tokens = dns.ParseZone(file, "", "")
 	for token := range tokens {
@@ -37,21 +42,32 @@ func ParseZone(filename string) (*Zone, error) {
 	return zone, nil
 }
 
+// Lookup will find all records which we should respond with for the given name, request type, and request class.
 func (zone *Zone) Lookup(name string, reqType uint16, reqClass uint16) []dns.RR {
 	name = dns.Fqdn(name)
-	var records []dns.RR = make([]dns.RR, 0)
+	var records []dns.RR
+	records = make([]dns.RR, 0)
 	for _, record := range zone.records {
-		var header *dns.RR_Header = record.Header()
+		var header *dns.RR_Header
+		header = record.Header()
+
+		// Skip this record if the name or class do not match
 		if header.Name != name || (header.Class != reqClass && reqClass != dns.ClassANY) {
 			continue
 		}
 
+		// Collect this record if the types match or this record is a CNAME
 		if reqType == dns.TypeANY || reqType == header.Rrtype {
 			records = append(records, record)
 		} else if header.Rrtype == dns.TypeCNAME {
+			// Append this CNAME record as a response
 			records = append(records, record)
-			var cname *dns.CNAME = record.(*dns.CNAME)
-			var cnameRecords []dns.RR = zone.Lookup(dns.Fqdn(cname.Target), reqType, reqClass)
+
+			// Attempt to resolve this CNAME record
+			var cname *dns.CNAME
+			cname = record.(*dns.CNAME)
+			var cnameRecords []dns.RR
+			cnameRecords = zone.Lookup(dns.Fqdn(cname.Target), reqType, reqClass)
 			records = append(records, cnameRecords...)
 		}
 	}