add Plan 9 support

Add an implementation for Plan 9. The unit test passes with IPv4 and
IPv6.

netroute_plan9.go

+// Generate a local routing table structure following the code at
+// https://github.com/google/gopacket/blob/master/routing/routing.go
+//
+// Plan 9 networking is described here: http://9p.io/magic/man2html/3/ip
+
+package netroute
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"net"
+	"strconv"
+	"strings"
+
+	"github.com/google/gopacket/routing"
+)
+
+const netdir = "/net"
+
+func New() (routing.Router, error) {
+	rtr := &router{}
+	rtr.ifaces = make(map[int]net.Interface)
+	rtr.addrs = make(map[int]ipAddrs)
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return nil, fmt.Errorf("could not get interfaces: %v", err)
+	}
+	for _, iface := range ifaces {
+		rtr.ifaces[iface.Index] = iface
+		var addrs ipAddrs
+		ifaceAddrs, err := iface.Addrs()
+		if err != nil {
+			return nil, err
+		}
+		for _, addr := range ifaceAddrs {
+			if inet, ok := addr.(*net.IPNet); ok {
+				// Go has a nasty habit of giving you IPv4s as ::ffff:1.2.3.4 instead of 1.2.3.4.
+				// We want to use mapped v4 addresses as v4 preferred addresses, never as v6
+				// preferred addresses.
+				if v4 := inet.IP.To4(); v4 != nil {
+					if addrs.v4 == nil {
+						addrs.v4 = v4
+					}
+				} else if addrs.v6 == nil {
+					addrs.v6 = inet.IP
+				}
+			}
+		}
+		rtr.addrs[iface.Index] = addrs
+	}
+
+	rtr.v4, rtr.v6, err = parseIPRoutes()
+	if err != nil {
+		return nil, err
+	}
+	return rtr, nil
+}
+
+func parseIPRoutes() (v4, v6 routeSlice, err error) {
+	buf, err := ioutil.ReadFile(netdir + "/iproute")
+	if err != nil {
+		return nil, nil, err
+	}
+
+	for {
+		i := bytes.IndexRune(buf, '\n')
+		if i <= 0 {
+			break
+		}
+		f := strings.Fields(string(buf[:i]))
+		buf = buf[i+1:]
+
+		if len(f) < 8 {
+			return nil, nil, fmt.Errorf("iproute entry contains %d fields", len(f))
+		}
+		flags, rt, err := parseRoute(f)
+		if err != nil {
+			return nil, nil, err
+		}
+		if rt.Dst != nil {
+			// If gateway for destination 127.0.0.1/32 is 127.0.0.1, set it to nil.
+			if m, n := rt.Dst.Mask.Size(); n > 0 && m == n && rt.Dst.IP.Equal(rt.Gateway) {
+				rt.Gateway = nil
+			}
+		}
+		if strings.ContainsRune(flags, '4') { // IPv4
+			v4 = append(v4, rt)
+		}
+		if strings.ContainsRune(flags, '6') { // IPv6
+			v6 = append(v6, rt)
+		}
+	}
+	return v4, v6, nil
+}
+
+func parseRoute(f []string) (flags string, rt *rtInfo, err error) {
+	rt = new(rtInfo)
+	isV4 := strings.ContainsRune(f[3], '4') // flags
+
+	rt.PrefSrc, rt.Src, err = parsePlan9CIDR(f[6], f[7], isV4)
+	if err != nil {
+		return "", nil, err
+	}
+	_, rt.Dst, err = parsePlan9CIDR(f[0], f[1], isV4)
+	if err != nil {
+		return "", nil, err
+	}
+	rt.Gateway = net.ParseIP(f[2])
+
+	n, err := strconv.ParseUint(f[5], 10, 32)
+	if err != nil {
+		return "", nil, err
+	}
+	rt.InputIface = 0
+	rt.OutputIface = uint32(n) + 1 // starts at 0, so net package adds 1
+	rt.Priority = 0
+	return f[3], rt, nil
+}
+
+func parsePlan9CIDR(addr, mask string, isV4 bool) (net.IP, *net.IPNet, error) {
+	if len(mask) == 0 || mask[0] != '/' {
+		return nil, nil, fmt.Errorf("invalid CIDR mask %v", mask)
+	}
+	n, err := strconv.ParseUint(mask[1:], 10, 32)
+	if err != nil {
+		return nil, nil, err
+	}
+	ip := net.ParseIP(addr)
+	iplen := net.IPv6len
+	if isV4 {
+		// Plan 9 uses IPv6 mask for IPv4 addresses
+		n -= 8 * (net.IPv6len - net.IPv4len)
+		iplen = net.IPv4len
+	}
+	if n == 0 && ip.IsUnspecified() {
+		return nil, nil, nil
+	}
+	m := net.CIDRMask(int(n), 8*iplen)
+	return ip, &net.IPNet{IP: ip.Mask(m), Mask: m}, nil
+}

netroute_test.go

@@ -44,10 +44,10 @@ func TestRoute(t *testing.T) {
 		t.Fatal(err)
 	}
 	if gw != nil || !src.Equal(localAddr) {
-		t.Fatalf("Did not expect gateway to localhost: %v", gw)
+		t.Fatalf("Did not expect gateway for %v->%v: %v", src, localAddr, gw)
 	}
 
-	// Route to somewher external should.
+	// Route to somewhere external should.
 	_, gw, _, err = r.Route(net.IPv4(8, 8, 8, 8))
 	if err != nil {
 		t.Fatal(err)