233 lines
6.4 KiB
Go
233 lines
6.4 KiB
Go
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package interfaces
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import (
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"bufio"
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"bytes"
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"errors"
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"fmt"
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"io"
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"log"
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"os"
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"os/exec"
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"runtime"
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"strings"
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"go4.org/mem"
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"inet.af/netaddr"
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"tailscale.com/syncs"
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"tailscale.com/util/lineread"
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)
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func init() {
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likelyHomeRouterIP = likelyHomeRouterIPLinux
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}
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var procNetRouteErr syncs.AtomicBool
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/*
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Parse 10.0.0.1 out of:
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$ cat /proc/net/route
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Iface Destination Gateway Flags RefCnt Use Metric Mask MTU Window IRTT
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ens18 00000000 0100000A 0003 0 0 0 00000000 0 0 0
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ens18 0000000A 00000000 0001 0 0 0 0000FFFF 0 0 0
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*/
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func likelyHomeRouterIPLinux() (ret netaddr.IP, ok bool) {
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if procNetRouteErr.Get() {
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// If we failed to read /proc/net/route previously, don't keep trying.
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// But if we're on Android, go into the Android path.
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if runtime.GOOS == "android" {
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return likelyHomeRouterIPAndroid()
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}
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return ret, false
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}
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lineNum := 0
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var f []mem.RO
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err := lineread.File("/proc/net/route", func(line []byte) error {
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lineNum++
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if lineNum == 1 {
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// Skip header line.
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return nil
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}
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f = mem.AppendFields(f[:0], mem.B(line))
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if len(f) < 4 {
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return nil
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}
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gwHex, flagsHex := f[2], f[3]
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flags, err := mem.ParseUint(flagsHex, 16, 16)
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if err != nil {
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return nil // ignore error, skip line and keep going
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}
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const RTF_UP = 0x0001
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const RTF_GATEWAY = 0x0002
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if flags&(RTF_UP|RTF_GATEWAY) != RTF_UP|RTF_GATEWAY {
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return nil
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}
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ipu32, err := mem.ParseUint(gwHex, 16, 32)
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if err != nil {
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return nil // ignore error, skip line and keep going
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}
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ip := netaddr.IPv4(byte(ipu32), byte(ipu32>>8), byte(ipu32>>16), byte(ipu32>>24))
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if isPrivateIP(ip) {
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ret = ip
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}
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return nil
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})
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if err != nil {
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procNetRouteErr.Set(true)
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if runtime.GOOS == "android" {
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return likelyHomeRouterIPAndroid()
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}
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log.Printf("interfaces: failed to read /proc/net/route: %v", err)
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}
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return ret, !ret.IsZero()
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}
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// Android apps don't have permission to read /proc/net/route, at
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// least on Google devices and the Android emulator.
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func likelyHomeRouterIPAndroid() (ret netaddr.IP, ok bool) {
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cmd := exec.Command("/system/bin/ip", "route", "show", "table", "0")
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out, err := cmd.StdoutPipe()
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if err != nil {
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return
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}
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if err := cmd.Start(); err != nil {
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log.Printf("interfaces: running /system/bin/ip: %v", err)
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return
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}
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// Search for line like "default via 10.0.2.2 dev radio0 table 1016 proto static mtu 1500 "
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lineread.Reader(out, func(line []byte) error {
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const pfx = "default via "
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if !mem.HasPrefix(mem.B(line), mem.S(pfx)) {
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return nil
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}
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line = line[len(pfx):]
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sp := bytes.IndexByte(line, ' ')
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if sp == -1 {
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return nil
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}
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ipb := line[:sp]
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if ip, err := netaddr.ParseIP(string(ipb)); err == nil && ip.Is4() {
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ret = ip
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log.Printf("interfaces: found Android default route %v", ip)
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}
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return nil
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})
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cmd.Process.Kill()
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cmd.Wait()
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return ret, !ret.IsZero()
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}
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// DefaultRouteInterface returns the name of the network interface that owns
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// the default route, not including any tailscale interfaces.
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func DefaultRouteInterface() (string, error) {
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v, err := defaultRouteInterfaceProcNet()
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if err == nil {
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return v, nil
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}
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if runtime.GOOS == "android" {
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return defaultRouteInterfaceAndroidIPRoute()
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}
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return v, err
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}
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var zeroRouteBytes = []byte("00000000")
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var procNetRoutePath = "/proc/net/route"
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func defaultRouteInterfaceProcNetInternal(bufsize int) (string, error) {
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f, err := os.Open(procNetRoutePath)
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if err != nil {
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return "", err
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}
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defer f.Close()
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br := bufio.NewReaderSize(f, bufsize)
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for {
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line, err := br.ReadSlice('\n')
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if err == io.EOF {
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return "", fmt.Errorf("no default routes found: %w", err)
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}
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if err != nil {
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return "", err
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}
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if !bytes.Contains(line, zeroRouteBytes) {
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continue
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}
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fields := strings.Fields(string(line))
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ifc := fields[0]
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ip := fields[1]
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netmask := fields[7]
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if strings.HasPrefix(ifc, "tailscale") ||
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strings.HasPrefix(ifc, "wg") {
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continue
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}
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if ip == "00000000" && netmask == "00000000" {
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// default route
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return ifc, nil // interface name
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}
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}
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}
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// returns string interface name and an error.
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// io.EOF: full route table processed, no default route found.
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// other io error: something went wrong reading the route file.
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func defaultRouteInterfaceProcNet() (string, error) {
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rc, err := defaultRouteInterfaceProcNetInternal(128)
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if rc == "" && (errors.Is(err, io.EOF) || err == nil) {
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// https://github.com/google/gvisor/issues/5732
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// On a regular Linux kernel you can read the first 128 bytes of /proc/net/route,
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// then come back later to read the next 128 bytes and so on.
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//
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// In Google Cloud Run, where /proc/net/route comes from gVisor, you have to
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// read it all at once. If you read only the first few bytes then the second
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// read returns 0 bytes no matter how much originally appeared to be in the file.
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//
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// At the time of this writing (Mar 2021) Google Cloud Run has eth0 and eth1
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// with a 384 byte /proc/net/route. We allocate a large buffer to ensure we'll
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// read it all in one call.
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return defaultRouteInterfaceProcNetInternal(4096)
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}
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return rc, err
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}
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// defaultRouteInterfaceAndroidIPRoute tries to find the machine's default route interface name
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// by parsing the "ip route" command output. We use this on Android where /proc/net/route
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// can be missing entries or have locked-down permissions.
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// See also comments in https://github.com/tailscale/tailscale/pull/666.
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func defaultRouteInterfaceAndroidIPRoute() (ifname string, err error) {
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cmd := exec.Command("/system/bin/ip", "route", "show", "table", "0")
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out, err := cmd.StdoutPipe()
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if err != nil {
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return "", err
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}
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if err := cmd.Start(); err != nil {
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log.Printf("interfaces: running /system/bin/ip: %v", err)
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return "", err
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}
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// Search for line like "default via 10.0.2.2 dev radio0 table 1016 proto static mtu 1500 "
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lineread.Reader(out, func(line []byte) error {
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const pfx = "default via "
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if !mem.HasPrefix(mem.B(line), mem.S(pfx)) {
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return nil
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}
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ff := strings.Fields(string(line))
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for i, v := range ff {
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if i > 0 && ff[i-1] == "dev" && ifname == "" {
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ifname = v
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}
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}
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return nil
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})
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cmd.Process.Kill()
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cmd.Wait()
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if ifname == "" {
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return "", errors.New("no default routes found")
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}
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return ifname, nil
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}
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