Add a DNS lookup of the servername. Only listen on that IPv6 address.

Signed-off-by: Jeff Carr <jcarr@wit.com>

server/Makefile

@@ -2,7 +2,10 @@ DNSNAME = $(shell hostname -f)
 
 # check if DNSNAME is a FQDN
 
-all:
+run:
+	go run *.go
+
+gaper:
 	# 'gaper' is a simple and smart golang tool that just rebuilds every time you change a file
 	# go get -u github.com/maxcnunes/gaper
 	gaper

server/dnstrace.go

@@ -0,0 +1,146 @@
+// inspired from github.com/rs/dnstrace/main.go
+
+package main
+
+import "flag"
+import "fmt"
+import "log"
+import "net"
+import "os"
+import "strings"
+import "time"
+
+import "github.com/miekg/dns"
+import "github.com/rs/dnstrace/client"
+
+const (
+	cReset    = 0
+	cBold     = 1
+	cRed      = 31
+	cGreen    = 32
+	cYellow   = 33
+	cBlue     = 34
+	cMagenta  = 35
+	cCyan     = 36
+	cGray     = 37
+	cDarkGray = 90
+)
+
+func colorize(s interface{}, color int, enabled bool) string {
+	if !enabled {
+		return fmt.Sprintf("%v", s)
+	}
+	return fmt.Sprintf("\x1b[%dm%v\x1b[0m", color, s)
+}
+
+func dnstrace(hostname string, qtypestr string) dns.RR {
+	color := flag.Bool("color", true, "Enable/disable colors")
+
+	qname := dns.Fqdn(hostname)
+	// qtype := dns.TypeA
+	qtype := dns.StringToType[qtypestr]
+
+	col := func(s interface{}, c int) string {
+		return colorize(s, c, *color)
+	}
+
+	m := &dns.Msg{}
+	m.SetQuestion(qname, qtype)
+	// Set DNSSEC opt to better emulate the default queries from a nameserver.
+	o := &dns.OPT{
+		Hdr: dns.RR_Header{
+			Name:   ".",
+			Rrtype: dns.TypeOPT,
+		},
+	}
+	o.SetDo()
+	o.SetUDPSize(dns.DefaultMsgSize)
+	m.Extra = append(m.Extra, o)
+
+	c := client.New()
+	c.Client.Timeout = 500 * time.Millisecond
+	t := client.Tracer{
+		GotIntermediaryResponse: func(i int, m *dns.Msg, rs client.Responses, rtype client.ResponseType) {
+			fr := rs.Fastest()
+			var r *dns.Msg
+			if fr != nil {
+				r = fr.Msg
+			}
+			qname := m.Question[0].Name
+			qtype := dns.TypeToString[m.Question[0].Qtype]
+			if i > 1 {
+				fmt.Println()
+			}
+			fmt.Printf("%d - query %s %s", i, qtype, qname)
+			if r != nil {
+				fmt.Printf(": %s", strings.Replace(strings.Replace(r.MsgHdr.String(), ";; ", "", -1), "\n", ", ", -1))
+			}
+			fmt.Println()
+			for _, pr := range rs {
+				ln := 0
+				if pr.Msg != nil {
+					ln = pr.Msg.Len()
+				}
+				rtt := float64(pr.RTT) / float64(time.Millisecond)
+				lrtt := "0ms (from cache)"
+				if pr.Server.HasGlue {
+					lrtt = "0ms (from glue)"
+				} else if pr.Server.LookupRTT > 0 {
+					lrtt = fmt.Sprintf("%.2fms", float64(pr.Server.LookupRTT)/float64(time.Millisecond))
+				}
+				fmt.Printf(col("  - %d bytes in %.2fms + %s lookup on %s(%s)", cDarkGray), ln, rtt, lrtt, pr.Server.Name, pr.Addr)
+				if pr.Err != nil {
+					err := pr.Err
+					if oerr, ok := err.(*net.OpError); ok {
+						err = oerr.Err
+					}
+					fmt.Printf(": %v", col(err, cRed))
+				}
+				fmt.Print("\n")
+			}
+
+			switch rtype {
+			case client.ResponseTypeDelegation:
+				var label string
+				for _, rr := range r.Ns {
+					if ns, ok := rr.(*dns.NS); ok {
+						label = ns.Header().Name
+						break
+					}
+				}
+				_, ns := c.DCache.Get(label)
+				for _, s := range ns {
+					var glue string
+					if s.HasGlue {
+						glue = col("glue: "+strings.Join(s.Addrs, ","), cDarkGray)
+					} else {
+						glue = col("no glue", cYellow)
+					}
+					fmt.Printf("%s %d NS %s (%s)\n", label, s.TTL, s.Name, glue)
+				}
+			case client.ResponseTypeCNAME:
+				for _, rr := range r.Answer {
+					fmt.Println(rr)
+				}
+			}
+		},
+		FollowingCNAME: func(domain, target string) {
+			fmt.Printf(col("\n~ following CNAME %s -> %s\n", cBlue), domain, target)
+		},
+	}
+	r, rtt, err := c.RecursiveQuery(m, t)
+	if err != nil {
+		fmt.Printf(col("*** error: %v\n", cRed), err)
+		os.Exit(1)
+	}
+
+	fmt.Println()
+	fmt.Printf(col(";; Cold best path time: %s\n\n", cGray), rtt)
+	for _, rr := range r.Answer {
+		log.Println(rr)
+	}
+	for _, rr := range r.Answer {
+		return rr
+	}
+	return nil
+}

server/server.go

@@ -15,6 +15,13 @@ import "strings"
 import "time"
 import "log"
 
+// will try to get this hosts FQDN
+import "github.com/Showmax/go-fqdn"
+
+import "github.com/miekg/dns"
+
+import "github.com/davecgh/go-spew/spew"
+
 const MIN = 1
 const MAX = 100
 
@@ -25,8 +32,20 @@ const (
 )
 
 func main() {
-	// // Listen for incoming connections.
-	l, err := net.Listen(CONN_TYPE, CONN_HOST+":"+CONN_PORT)
+	hostname := fqdn.Get()
+	log.Println("FQDN hostname is", hostname)
+
+	// lookup the IP address from DNS
+	dnsRR := dnstrace(hostname, "AAAA")
+	spew.Dump(dnsRR)
+	ipaddr := dns.Field(dnsRR, 1)
+	log.Println("ipaddr", ipaddr)
+
+	listenstr :=  "[" + ipaddr + "]:" + CONN_PORT
+	log.Println("listenstr", listenstr)
+
+	// // Listen for incoming connections on the IPv6 address only
+	l, err := net.Listen(CONN_TYPE, listenstr)
 	if err != nil {
 		log.Println("Error listening:", err.Error())
 		return
@@ -35,7 +54,7 @@ func main() {
 	// Close the listener when the application closes.
 	defer l.Close()
 
-	log.Println("Listening on " + CONN_HOST + ":" + CONN_PORT)
+	log.Println("Listening on " + listenstr)
 
 	rand.Seed(time.Now().Unix())