Fixing out of order error in gopacket linux routing

v2/pkg/routing/router_linux.go

@@ -1,30 +1,251 @@
 //go:build linux
 
+// 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.
+
+// Package routing provides a very basic but mostly functional implementation of
+// a routing table for IPv4/IPv6 addresses.  It uses a routing table pulled from
+// the kernel via netlink to find the correct interface, gateway, and preferred
+// source IP address for packets destined to a particular location.
+//
+// The routing package is meant to be used with applications that are sending
+// raw packet data, which don't have the benefit of having the kernel route
+// packets for them.
 package routing
 
 import (
+	"bytes"
+	"errors"
+	"fmt"
 	"net"
-
-	"github.com/google/gopacket/routing"
+	"sort"
+	"strings"
+	"syscall"
+	"unsafe"
 )
 
-// New creates a https://github.com/google/gopacket instance for Linux
-func New() (Router, error) {
-	router, err := routing.New()
-	if err != nil {
-		return nil, err
+// 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
+}
+
+// rtInfo contains information on a single route.
+type rtInfo struct {
+	Src, Dst         *net.IPNet
+	Gateway, PrefSrc net.IP
+	// We currently ignore the InputIface.
+	InputIface, OutputIface uint32
+	Priority                uint32
+}
+
+// routeSlice implements sort.Interface to sort routes by Priority.
+type routeSlice []*rtInfo
+
+func (r routeSlice) Len() int {
+	return len(r)
+}
+func (r routeSlice) Less(i, j int) bool {
+	return r[i].Priority < r[j].Priority
+}
+func (r routeSlice) Swap(i, j int) {
+	r[i], r[j] = r[j], r[i]
+}
+
+type router struct {
+	ifaces map[int]*net.Interface
+	addrs  map[int]ipAddrs
+	v4, v6 routeSlice
+}
+
+func (r *router) String() string {
+	strs := []string{"ROUTER", "--- V4 ---"}
+	for _, route := range r.v4 {
+		strs = append(strs, fmt.Sprintf("%+v", *route))
 	}
-	return RouterLinux{router: router}, nil
+	strs = append(strs, "--- V6 ---")
+	for _, route := range r.v6 {
+		strs = append(strs, fmt.Sprintf("%+v", *route))
+	}
+	return strings.Join(strs, "\n")
 }
 
-type RouterLinux struct {
-	router routing.Router
+type ipAddrs struct {
+	v4, v6 net.IP
 }
 
-func (r RouterLinux) Route(dst net.IP) (iface *net.Interface, gateway, preferredSrc net.IP, err error) {
-	return r.router.Route(dst)
+func (r *router) Route(dst net.IP) (iface *net.Interface, gateway, preferredSrc net.IP, err error) {
+	return r.RouteWithSrc(nil, nil, dst)
 }
 
-func (r RouterLinux) RouteWithSrc(input net.HardwareAddr, src, dst net.IP) (iface *net.Interface, gateway, preferredSrc net.IP, err error) {
-	return r.router.RouteWithSrc(input, src, dst)
+func (r *router) RouteWithSrc(input net.HardwareAddr, src, dst net.IP) (iface *net.Interface, gateway, preferredSrc net.IP, err error) {
+	var ifaceIndex int
+	switch {
+	case dst.To4() != nil:
+		ifaceIndex, gateway, preferredSrc, err = r.route(r.v4, input, src, dst)
+	case dst.To16() != nil:
+		ifaceIndex, gateway, preferredSrc, err = r.route(r.v6, input, src, dst)
+	default:
+		err = errors.New("IP is not valid as IPv4 or IPv6")
+	}
+
+	if err != nil {
+		return
+	}
+
+	iface = r.ifaces[ifaceIndex]
+
+	if preferredSrc == nil {
+		switch {
+		case dst.To4() != nil:
+			preferredSrc = r.addrs[ifaceIndex].v4
+		case dst.To16() != nil:
+			preferredSrc = r.addrs[ifaceIndex].v6
+		}
+	}
+	return
+}
+
+func (r *router) route(routes routeSlice, input net.HardwareAddr, src, dst net.IP) (iface int, gateway, preferredSrc net.IP, err error) {
+	var inputIndex uint32
+	if input != nil {
+		for i, iface := range r.ifaces {
+			if bytes.Equal(input, iface.HardwareAddr) {
+				inputIndex = uint32(i)
+				break
+			}
+		}
+	}
+	var defaultGateway *rtInfo = nil
+	for _, rt := range routes {
+		if rt.InputIface != 0 && rt.InputIface != inputIndex {
+			continue
+		}
+		if rt.Src == nil && rt.Dst == nil {
+			defaultGateway = rt
+			continue
+		}
+		if rt.Src != nil && !rt.Src.Contains(src) {
+			continue
+		}
+		if rt.Dst != nil && !rt.Dst.Contains(dst) {
+			continue
+		}
+		return int(rt.OutputIface), rt.Gateway, rt.PrefSrc, nil
+	}
+
+	if defaultGateway != nil {
+		return int(defaultGateway.OutputIface), defaultGateway.Gateway, defaultGateway.PrefSrc, nil
+	}
+	err = fmt.Errorf("no route found for %v", dst)
+	return
+}
+
+// New creates a new router object.  The router returned by New currently does
+// not update its routes after construction... care should be taken for
+// long-running programs to call New() regularly to take into account any
+// changes to the routing table which have occurred since the last New() call.
+func New() (Router, error) {
+	rtr := &router{
+		ifaces: make(map[int]*net.Interface),
+		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
+			}
+			switch rt.Family {
+			case syscall.AF_INET:
+				rtr.v4 = append(rtr.v4, &routeInfo)
+			case syscall.AF_INET6:
+				rtr.v6 = append(rtr.v6, &routeInfo)
+			default:
+				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]))
+				}
+			}
+		}
+	}
+	sort.Sort(rtr.v4)
+	sort.Sort(rtr.v6)
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+	for _, tmp := range ifaces {
+		iface := tmp
+		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
 }