1// Copyright 2012 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package ipv4_test
6
7import (
8	"fmt"
9	"log"
10	"net"
11	"os"
12	"runtime"
13	"time"
14
15	"golang.org/x/net/icmp"
16	"golang.org/x/net/ipv4"
17)
18
19func ExampleConn_markingTCP() {
20	ln, err := net.Listen("tcp", "0.0.0.0:1024")
21	if err != nil {
22		log.Fatal(err)
23	}
24	defer ln.Close()
25
26	for {
27		c, err := ln.Accept()
28		if err != nil {
29			log.Fatal(err)
30		}
31		go func(c net.Conn) {
32			defer c.Close()
33			if c.RemoteAddr().(*net.TCPAddr).IP.To4() != nil {
34				p := ipv4.NewConn(c)
35				if err := p.SetTOS(0x28); err != nil { // DSCP AF11
36					log.Fatal(err)
37				}
38				if err := p.SetTTL(128); err != nil {
39					log.Fatal(err)
40				}
41			}
42			if _, err := c.Write([]byte("HELLO-R-U-THERE-ACK")); err != nil {
43				log.Fatal(err)
44			}
45		}(c)
46	}
47}
48
49func ExamplePacketConn_servingOneShotMulticastDNS() {
50	c, err := net.ListenPacket("udp4", "0.0.0.0:5353") // mDNS over UDP
51	if err != nil {
52		log.Fatal(err)
53	}
54	defer c.Close()
55	p := ipv4.NewPacketConn(c)
56
57	en0, err := net.InterfaceByName("en0")
58	if err != nil {
59		log.Fatal(err)
60	}
61	mDNSLinkLocal := net.UDPAddr{IP: net.IPv4(224, 0, 0, 251)}
62	if err := p.JoinGroup(en0, &mDNSLinkLocal); err != nil {
63		log.Fatal(err)
64	}
65	defer p.LeaveGroup(en0, &mDNSLinkLocal)
66	if err := p.SetControlMessage(ipv4.FlagDst, true); err != nil {
67		log.Fatal(err)
68	}
69
70	b := make([]byte, 1500)
71	for {
72		_, cm, peer, err := p.ReadFrom(b)
73		if err != nil {
74			log.Fatal(err)
75		}
76		if !cm.Dst.IsMulticast() || !cm.Dst.Equal(mDNSLinkLocal.IP) {
77			continue
78		}
79		answers := []byte("FAKE-MDNS-ANSWERS") // fake mDNS answers, you need to implement this
80		if _, err := p.WriteTo(answers, nil, peer); err != nil {
81			log.Fatal(err)
82		}
83	}
84}
85
86func ExamplePacketConn_tracingIPPacketRoute() {
87	// Tracing an IP packet route to www.google.com.
88
89	const host = "www.google.com"
90	ips, err := net.LookupIP(host)
91	if err != nil {
92		log.Fatal(err)
93	}
94	var dst net.IPAddr
95	for _, ip := range ips {
96		if ip.To4() != nil {
97			dst.IP = ip
98			fmt.Printf("using %v for tracing an IP packet route to %s\n", dst.IP, host)
99			break
100		}
101	}
102	if dst.IP == nil {
103		log.Fatal("no A record found")
104	}
105
106	c, err := net.ListenPacket("ip4:1", "0.0.0.0") // ICMP for IPv4
107	if err != nil {
108		log.Fatal(err)
109	}
110	defer c.Close()
111	p := ipv4.NewPacketConn(c)
112
113	if err := p.SetControlMessage(ipv4.FlagTTL|ipv4.FlagSrc|ipv4.FlagDst|ipv4.FlagInterface, true); err != nil {
114		log.Fatal(err)
115	}
116	wm := icmp.Message{
117		Type: ipv4.ICMPTypeEcho, Code: 0,
118		Body: &icmp.Echo{
119			ID:   os.Getpid() & 0xffff,
120			Data: []byte("HELLO-R-U-THERE"),
121		},
122	}
123
124	rb := make([]byte, 1500)
125	for i := 1; i <= 64; i++ { // up to 64 hops
126		wm.Body.(*icmp.Echo).Seq = i
127		wb, err := wm.Marshal(nil)
128		if err != nil {
129			log.Fatal(err)
130		}
131		if err := p.SetTTL(i); err != nil {
132			log.Fatal(err)
133		}
134
135		// In the real world usually there are several
136		// multiple traffic-engineered paths for each hop.
137		// You may need to probe a few times to each hop.
138		begin := time.Now()
139		if _, err := p.WriteTo(wb, nil, &dst); err != nil {
140			log.Fatal(err)
141		}
142		if err := p.SetReadDeadline(time.Now().Add(3 * time.Second)); err != nil {
143			log.Fatal(err)
144		}
145		n, cm, peer, err := p.ReadFrom(rb)
146		if err != nil {
147			if err, ok := err.(net.Error); ok && err.Timeout() {
148				fmt.Printf("%v\t*\n", i)
149				continue
150			}
151			log.Fatal(err)
152		}
153		rm, err := icmp.ParseMessage(1, rb[:n])
154		if err != nil {
155			log.Fatal(err)
156		}
157		rtt := time.Since(begin)
158
159		// In the real world you need to determine whether the
160		// received message is yours using ControlMessage.Src,
161		// ControlMessage.Dst, icmp.Echo.ID and icmp.Echo.Seq.
162		switch rm.Type {
163		case ipv4.ICMPTypeTimeExceeded:
164			names, _ := net.LookupAddr(peer.String())
165			fmt.Printf("%d\t%v %+v %v\n\t%+v\n", i, peer, names, rtt, cm)
166		case ipv4.ICMPTypeEchoReply:
167			names, _ := net.LookupAddr(peer.String())
168			fmt.Printf("%d\t%v %+v %v\n\t%+v\n", i, peer, names, rtt, cm)
169			return
170		default:
171			log.Printf("unknown ICMP message: %+v\n", rm)
172		}
173	}
174}
175
176func ExampleRawConn_advertisingOSPFHello() {
177	c, err := net.ListenPacket("ip4:89", "0.0.0.0") // OSPF for IPv4
178	if err != nil {
179		log.Fatal(err)
180	}
181	defer c.Close()
182	r, err := ipv4.NewRawConn(c)
183	if err != nil {
184		log.Fatal(err)
185	}
186
187	en0, err := net.InterfaceByName("en0")
188	if err != nil {
189		log.Fatal(err)
190	}
191	allSPFRouters := net.IPAddr{IP: net.IPv4(224, 0, 0, 5)}
192	if err := r.JoinGroup(en0, &allSPFRouters); err != nil {
193		log.Fatal(err)
194	}
195	defer r.LeaveGroup(en0, &allSPFRouters)
196
197	hello := make([]byte, 24) // fake hello data, you need to implement this
198	ospf := make([]byte, 24)  // fake ospf header, you need to implement this
199	ospf[0] = 2               // version 2
200	ospf[1] = 1               // hello packet
201	ospf = append(ospf, hello...)
202	iph := &ipv4.Header{
203		Version:  ipv4.Version,
204		Len:      ipv4.HeaderLen,
205		TOS:      0xc0, // DSCP CS6
206		TotalLen: ipv4.HeaderLen + len(ospf),
207		TTL:      1,
208		Protocol: 89,
209		Dst:      allSPFRouters.IP.To4(),
210	}
211
212	var cm *ipv4.ControlMessage
213	switch runtime.GOOS {
214	case "darwin", "ios", "linux":
215		cm = &ipv4.ControlMessage{IfIndex: en0.Index}
216	default:
217		if err := r.SetMulticastInterface(en0); err != nil {
218			log.Fatal(err)
219		}
220	}
221	if err := r.WriteTo(iph, ospf, cm); err != nil {
222		log.Fatal(err)
223	}
224}
225