x/net/ipv6: add package example

LGTM=iant
R=iant
CC=golang-codereviews
https://golang.org/cl/176960043

ipv6/example_test.go

+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ipv6_test
+
+import (
+	"fmt"
+	"log"
+	"net"
+	"os"
+	"time"
+
+	"golang.org/x/net/internal/iana"
+	"golang.org/x/net/internal/icmp"
+	"golang.org/x/net/ipv6"
+)
+
+func ExampleConn_markingTCP() {
+	ln, err := net.Listen("tcp6", "[::]:1024")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer ln.Close()
+
+	for {
+		c, err := ln.Accept()
+		if err != nil {
+			log.Fatal(err)
+		}
+		go func(c net.Conn) {
+			defer c.Close()
+			p := ipv6.NewConn(c)
+			if err := p.SetTrafficClass(iana.DiffServAF11); err != nil {
+				log.Fatal(err)
+			}
+			if err := p.SetHopLimit(128); err != nil {
+				log.Fatal(err)
+			}
+			if _, err := c.Write([]byte("HELLO-R-U-THERE-ACK")); err != nil {
+				log.Fatal(err)
+			}
+		}(c)
+	}
+}
+
+func ExamplePacketConn_servingOneShotMulticastDNS() {
+	c, err := net.ListenPacket("udp6", "[::]:5353") // mDNS over UDP
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer c.Close()
+	p := ipv6.NewPacketConn(c)
+
+	en0, err := net.InterfaceByName("en0")
+	if err != nil {
+		log.Fatal(err)
+	}
+	mDNSLinkLocal := net.UDPAddr{IP: net.ParseIP("ff02::fb")}
+	if err := p.JoinGroup(en0, &mDNSLinkLocal); err != nil {
+		log.Fatal(err)
+	}
+	defer p.LeaveGroup(en0, &mDNSLinkLocal)
+	if err := p.SetControlMessage(ipv6.FlagDst|ipv6.FlagInterface, true); err != nil {
+		log.Fatal(err)
+	}
+
+	var wcm ipv6.ControlMessage
+	b := make([]byte, 1500)
+	for {
+		_, rcm, peer, err := p.ReadFrom(b)
+		if err != nil {
+			log.Fatal(err)
+		}
+		if !rcm.Dst.IsMulticast() || !rcm.Dst.Equal(mDNSLinkLocal.IP) {
+			continue
+		}
+		wcm.IfIndex = rcm.IfIndex
+		answers := []byte("FAKE-MDNS-ANSWERS") // fake mDNS answers, you need to implement this
+		if _, err := p.WriteTo(answers, &wcm, peer); err != nil {
+			log.Fatal(err)
+		}
+	}
+}
+
+func ExamplePacketConn_tracingIPPacketRoute() {
+	// Tracing an IP packet route to www.google.com.
+
+	const host = "www.google.com"
+	ips, err := net.LookupIP(host)
+	if err != nil {
+		log.Fatal(err)
+	}
+	var dst net.IPAddr
+	for _, ip := range ips {
+		if ip.To16() != nil && ip.To4() == nil {
+			dst.IP = ip
+			fmt.Printf("using %v for tracing an IP packet route to %s\n", dst.IP, host)
+			break
+		}
+	}
+	if dst.IP == nil {
+		log.Fatal("no AAAA record found")
+	}
+
+	c, err := net.ListenPacket(fmt.Sprintf("ip6:%d", iana.ProtocolIPv6ICMP), "::") // ICMP for IPv6
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer c.Close()
+	p := ipv6.NewPacketConn(c)
+
+	if err := p.SetControlMessage(ipv6.FlagHopLimit|ipv6.FlagSrc|ipv6.FlagDst|ipv6.FlagInterface, true); err != nil {
+		log.Fatal(err)
+	}
+	wm := icmp.Message{
+		Type: ipv6.ICMPTypeEchoRequest, Code: 0,
+		Body: &icmp.Echo{
+			ID:   os.Getpid() & 0xffff,
+			Data: []byte("HELLO-R-U-THERE"),
+		},
+	}
+	var f ipv6.ICMPFilter
+	f.SetAll(true)
+	f.Set(ipv6.ICMPTypeTimeExceeded, false)
+	f.Set(ipv6.ICMPTypeEchoReply, false)
+	if err := p.SetICMPFilter(&f); err != nil {
+		log.Fatal(err)
+	}
+
+	var wcm ipv6.ControlMessage
+	rb := make([]byte, 1500)
+	for i := 1; i <= 64; i++ { // up to 64 hops
+		wm.Body.(*icmp.Echo).Seq = i
+		wb, err := wm.Marshal(nil)
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		// In the real world usually there are several
+		// multiple traffic-engineered paths for each hop.
+		// You may need to probe a few times to each hop.
+		begin := time.Now()
+		wcm.HopLimit = i
+		if _, err := p.WriteTo(wb, &wcm, &dst); err != nil {
+			log.Fatal(err)
+		}
+		if err := p.SetReadDeadline(time.Now().Add(3 * time.Second)); err != nil {
+			log.Fatal(err)
+		}
+		n, rcm, peer, err := p.ReadFrom(rb)
+		if err != nil {
+			if err, ok := err.(net.Error); ok && err.Timeout() {
+				fmt.Printf("%v\t*\n", i)
+				continue
+			}
+			log.Fatal(err)
+		}
+		rm, err := icmp.ParseMessage(iana.ProtocolIPv6ICMP, rb[:n])
+		if err != nil {
+			log.Fatal(err)
+		}
+		rtt := time.Since(begin)
+
+		// In the real world you need to determine whether the
+		// received message is yours using ControlMessage.Src,
+		// ControlMesage.Dst, icmp.Echo.ID and icmp.Echo.Seq.
+		switch rm.Type {
+		case ipv6.ICMPTypeTimeExceeded:
+			names, _ := net.LookupAddr(peer.String())
+			fmt.Printf("%d\t%v %+v %v\n\t%+v\n", i, peer, names, rtt, rcm)
+		case ipv6.ICMPTypeEchoReply:
+			names, _ := net.LookupAddr(peer.String())
+			fmt.Printf("%d\t%v %+v %v\n\t%+v\n", i, peer, names, rtt, rcm)
+			return
+		}
+	}
+}
+
+func ExamplePacketConn_advertisingOSPFHello() {
+	c, err := net.ListenPacket(fmt.Sprintf("ip6:%d", iana.ProtocolOSPFIGP), "::") // OSPF for IPv6
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer c.Close()
+	p := ipv6.NewPacketConn(c)
+
+	en0, err := net.InterfaceByName("en0")
+	if err != nil {
+		log.Fatal(err)
+	}
+	allSPFRouters := net.IPAddr{IP: net.ParseIP("ff02::5")}
+	if err := p.JoinGroup(en0, &allSPFRouters); err != nil {
+		log.Fatal(err)
+	}
+	defer p.LeaveGroup(en0, &allSPFRouters)
+
+	hello := make([]byte, 24) // fake hello data, you need to implement this
+	ospf := make([]byte, 16)  // fake ospf header, you need to implement this
+	ospf[0] = 3               // version 3
+	ospf[1] = 1               // hello packet
+	ospf = append(ospf, hello...)
+	if err := p.SetChecksum(true, 12); err != nil {
+		log.Fatal(err)
+	}
+
+	cm := ipv6.ControlMessage{
+		TrafficClass: iana.DiffServCS6,
+		HopLimit:     1,
+		IfIndex:      en0.Index,
+	}
+	if _, err := p.WriteTo(ospf, &cm, &allSPFRouters); err != nil {
+		log.Fatal(err)
+	}
+}