1// Generate a local routing table structure following the code at
2// https://github.com/google/gopacket/blob/master/routing/routing.go
3//
4// Plan 9 networking is described here: http://9p.io/magic/man2html/3/ip
5
6package netroute
7
8import (
9	"bytes"
10	"fmt"
11	"io/ioutil"
12	"net"
13	"strconv"
14	"strings"
15
16	"github.com/google/gopacket/routing"
17)
18
19const netdir = "/net"
20
21func New() (routing.Router, error) {
22	rtr := &router{}
23	rtr.ifaces = make(map[int]net.Interface)
24	rtr.addrs = make(map[int]ipAddrs)
25	ifaces, err := net.Interfaces()
26	if err != nil {
27		return nil, fmt.Errorf("could not get interfaces: %v", err)
28	}
29	for _, iface := range ifaces {
30		rtr.ifaces[iface.Index] = iface
31		var addrs ipAddrs
32		ifaceAddrs, err := iface.Addrs()
33		if err != nil {
34			return nil, err
35		}
36		for _, addr := range ifaceAddrs {
37			if inet, ok := addr.(*net.IPNet); ok {
38				// Go has a nasty habit of giving you IPv4s as ::ffff:1.2.3.4 instead of 1.2.3.4.
39				// We want to use mapped v4 addresses as v4 preferred addresses, never as v6
40				// preferred addresses.
41				if v4 := inet.IP.To4(); v4 != nil {
42					if addrs.v4 == nil {
43						addrs.v4 = v4
44					}
45				} else if addrs.v6 == nil {
46					addrs.v6 = inet.IP
47				}
48			}
49		}
50		rtr.addrs[iface.Index] = addrs
51	}
52
53	rtr.v4, rtr.v6, err = parseIPRoutes()
54	if err != nil {
55		return nil, err
56	}
57	return rtr, nil
58}
59
60func parseIPRoutes() (v4, v6 routeSlice, err error) {
61	buf, err := ioutil.ReadFile(netdir + "/iproute")
62	if err != nil {
63		return nil, nil, err
64	}
65
66	for {
67		i := bytes.IndexRune(buf, '\n')
68		if i <= 0 {
69			break
70		}
71		f := strings.Fields(string(buf[:i]))
72		buf = buf[i+1:]
73
74		if len(f) < 8 {
75			return nil, nil, fmt.Errorf("iproute entry contains %d fields", len(f))
76		}
77		flags, rt, err := parseRoute(f)
78		if err != nil {
79			return nil, nil, err
80		}
81		if rt.Dst != nil {
82			// If gateway for destination 127.0.0.1/32 is 127.0.0.1, set it to nil.
83			if m, n := rt.Dst.Mask.Size(); n > 0 && m == n && rt.Dst.IP.Equal(rt.Gateway) {
84				rt.Gateway = nil
85			}
86		}
87		if strings.ContainsRune(flags, '4') { // IPv4
88			v4 = append(v4, rt)
89		}
90		if strings.ContainsRune(flags, '6') { // IPv6
91			v6 = append(v6, rt)
92		}
93	}
94	return v4, v6, nil
95}
96
97func parseRoute(f []string) (flags string, rt *rtInfo, err error) {
98	rt = new(rtInfo)
99	isV4 := strings.ContainsRune(f[3], '4') // flags
100
101	rt.PrefSrc, rt.Src, err = parsePlan9CIDR(f[6], f[7], isV4)
102	if err != nil {
103		return "", nil, err
104	}
105	_, rt.Dst, err = parsePlan9CIDR(f[0], f[1], isV4)
106	if err != nil {
107		return "", nil, err
108	}
109	rt.Gateway = net.ParseIP(f[2])
110
111	n, err := strconv.ParseUint(f[5], 10, 32)
112	if err != nil {
113		return "", nil, err
114	}
115	rt.InputIface = 0
116	rt.OutputIface = uint32(n) + 1 // starts at 0, so net package adds 1
117	rt.Priority = 0
118	return f[3], rt, nil
119}
120
121func parsePlan9CIDR(addr, mask string, isV4 bool) (net.IP, *net.IPNet, error) {
122	if len(mask) == 0 || mask[0] != '/' {
123		return nil, nil, fmt.Errorf("invalid CIDR mask %v", mask)
124	}
125	n, err := strconv.ParseUint(mask[1:], 10, 32)
126	if err != nil {
127		return nil, nil, err
128	}
129	ip := net.ParseIP(addr)
130	iplen := net.IPv6len
131	if isV4 {
132		// Plan 9 uses IPv6 mask for IPv4 addresses
133		n -= 8 * (net.IPv6len - net.IPv4len)
134		iplen = net.IPv4len
135	}
136	if n == 0 && ip.IsUnspecified() {
137		return nil, nil, nil
138	}
139	m := net.CIDRMask(int(n), 8*iplen)
140	return ip, &net.IPNet{IP: ip.Mask(m), Mask: m}, nil
141}
142