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netroute_linux.go
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netroute_linux.go
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// Copyright 2012 Google, Inc. All rights reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the LICENSE file in the root of the source
// tree.
//go:build linux
// Generate a local routing table structure following the code at
// https://github.com/google/gopacket/blob/master/routing/routing.go
package netroute
import (
"net"
"sort"
"syscall"
"unsafe"
"github.com/google/gopacket/routing"
)
// Pulled from http://man7.org/linux/man-pages/man7/rtnetlink.7.html
// See the section on RTM_NEWROUTE, specifically 'struct rtmsg'.
type routeInfoInMemory struct {
Family byte
DstLen byte
SrcLen byte
TOS byte
Table byte
Protocol byte
Scope byte
Type byte
Flags uint32
}
func New() (routing.Router, error) {
rtr := &router{}
rtr.ifaces = make(map[int]net.Interface)
rtr.addrs = make(map[int]ipAddrs)
tab, err := syscall.NetlinkRIB(syscall.RTM_GETROUTE, syscall.AF_UNSPEC)
if err != nil {
return nil, err
}
msgs, err := syscall.ParseNetlinkMessage(tab)
if err != nil {
return nil, err
}
loop:
for _, m := range msgs {
switch m.Header.Type {
case syscall.NLMSG_DONE:
break loop
case syscall.RTM_NEWROUTE:
rt := (*routeInfoInMemory)(unsafe.Pointer(&m.Data[0]))
routeInfo := rtInfo{}
attrs, err := syscall.ParseNetlinkRouteAttr(&m)
if err != nil {
return nil, err
}
if rt.Family != syscall.AF_INET && rt.Family != syscall.AF_INET6 {
continue loop
}
for _, attr := range attrs {
switch attr.Attr.Type {
case syscall.RTA_DST:
routeInfo.Dst = &net.IPNet{
IP: net.IP(attr.Value),
Mask: net.CIDRMask(int(rt.DstLen), len(attr.Value)*8),
}
case syscall.RTA_SRC:
routeInfo.Src = &net.IPNet{
IP: net.IP(attr.Value),
Mask: net.CIDRMask(int(rt.SrcLen), len(attr.Value)*8),
}
case syscall.RTA_GATEWAY:
routeInfo.Gateway = net.IP(attr.Value)
case syscall.RTA_PREFSRC:
routeInfo.PrefSrc = net.IP(attr.Value)
case syscall.RTA_IIF:
routeInfo.InputIface = *(*uint32)(unsafe.Pointer(&attr.Value[0]))
case syscall.RTA_OIF:
routeInfo.OutputIface = *(*uint32)(unsafe.Pointer(&attr.Value[0]))
case syscall.RTA_PRIORITY:
routeInfo.Priority = *(*uint32)(unsafe.Pointer(&attr.Value[0]))
}
}
if routeInfo.Dst == nil && routeInfo.Src == nil && routeInfo.Gateway == nil {
continue loop
}
switch rt.Family {
case syscall.AF_INET:
rtr.v4 = append(rtr.v4, &routeInfo)
case syscall.AF_INET6:
rtr.v6 = append(rtr.v6, &routeInfo)
default:
// should not happen.
continue loop
}
}
}
sort.Sort(rtr.v4)
sort.Sort(rtr.v6)
ifaces, err := net.Interfaces()
if err != nil {
return nil, 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
}
return rtr, nil
}