jackpal / gateway

A golang library for discovering the address of a LAN gateway.

gateway

A simple library for discovering the IP address of the default gateway.

Example:

package main

import (
    "fmt"

    "github.com/jackpal/gateway"
)

func main() {
    gateway, err := gateway.DiscoverGateway()
    if err != nil {
        fmt.Println(err)
    } else {
        fmt.Println("Gateway:", gateway.String())
   }
}

Provides implementations for:

• Darwin (macOS)
• Dragonfly
• FreeBSD
• Linux
• NetBSD
• OpenBSD
• Solaris and illumos
• Windows

Other platforms use an implementation that always returns an error.

Pull requests for other OSs happily considered!

Versions

v1.0.15

Update dependencies to latest versions. This was done to squelch a github security alert caused by depending upon an old version of x/net. This is the first time I've updated module versions, the tests pass, so hopefully everything's good.

v1.0.14

• Fix panic when interface not set in Solaris netstat -rn output.

v1.0.13

• Add tools/check-cross-compile.sh to check that the code compiles for various OSs.
• Fix compilation errors exposed by tools/check-cross-compile.sh.

v1.0.12

• If there are multiple default gateways, Windows now returns the gateway with the lowest metric.
• Fix solaris build break. (In theory, IDK how to test this easily.)
• Upgrade to golang 1.21
• Upgrade golang.org/x/net version, makes dependabot happy. Probably was not any actual security issue because gateway doesn't use any of the APIs of golang.org/x/net that had security issues.

v1.0.11

• Implement DiscoverInterface for BSD-like OSes.

v1.0.10

• Fix non-BSD-based builds.

v1.0.9

• Add go.mod and go.sum files.
• Use "golang.org/x/net/route" to implement all BSD variants.
  • As a side effect this adds support for Dragonfly and NetBSD.
• Add example to README.
• Remove broken continuous integration.

v1.0.8

• Add support for OpenBSD
• Linux parser now supports gateways with an IP address of 0.0.0.0
• Fall back to netstat on darwin systems if route fails.
• Simplify Linux /proc/net/route parsers.

gateway's Issues

Will not working on windows of non-Englisht language

In gateway_common.go:

func parseWindowsRoutePrint(output []byte) (net.IP, error) {
	lines := strings.Split(string(output), "\n")
	for idx, line := range lines {
		if strings.HasPrefix(line, "Active Routes:") {
			if len(lines) <= idx+2 {
				return nil, errNoGateway
			}
...

If default language is non-English, "Active Routes" will be translated.

don't hardcode paths for linux

ip and routes are in a different path on some of my machines and I modified the code to do the following in gateway_linux.go.

func binPath(execName string) string {
    cmd := exec.Command("which", execName)
    buf, _ := cmd.Output()
    return strings.Trim(string(buf), "\n")
}

func DiscoverGateway() (ip net.IP, err error) {
    ip, err = discoverGatewayUsingRoute()
    if err != nil {
        ip, err = discoverGatewayUsingIp()
    }
    return
}

func discoverGatewayUsingIp() (net.IP, error) {
    routeCmd := exec.Command(binPath("ip"), "route", "show")
    output, err := routeCmd.CombinedOutput()
    if err != nil {
        return nil, err
    }

    return parseLinuxIPRoute(output)
}

func discoverGatewayUsingRoute() (net.IP, error) {
    routeCmd := exec.Command(binPath("route"), "-n")
    output, err := routeCmd.CombinedOutput()
    if err != nil {
        return nil, err
    }

    return parseLinuxRoute(output)
}

You'd probably want to memoize the paths and check on errors but I think the direction is something this pkg should consider.

tests now hang in limited debian chroot

Hello!

I don't know if this is related to the newely merged commit, but the tests hang on my machine.

Here is the output:

    go test -v github.com/jackpal/gateway
=== RUN   TestGateway

//cc @calmh

better BSD detection without calling external commands

My full example. Feel free to implement in your package.

package main

import (
    "net"
    "fmt"
    "errors"
    "syscall"
    "golang.org/x/net/route"
)

var (
    errNoGateway = errors.New("No gateway")
)

func GetGateway() (ip net.IP, err error) {
    rib, err := route.FetchRIB(syscall.AF_INET, syscall.NET_RT_DUMP, 0)
    if err != nil {
	return nil, err
    }

    msgs, err := route.ParseRIB(syscall.NET_RT_DUMP, rib)
    if err != nil {
	return nil, err
    }

    for _, m := range msgs {
	switch m := m.(type) {
	case *route.RouteMessage:
		var ip net.IP
		switch sa := m.Addrs[syscall.RTAX_GATEWAY].(type) {
		case *route.Inet4Addr:
		    ip = net.IPv4(sa.IP[0], sa.IP[1], sa.IP[2], sa.IP[3])
		    return ip, nil
		case *route.Inet6Addr:
		    ip = make(net.IP, net.IPv6len)
		    copy(ip, sa.IP[:])
		    return ip, nil
		}
	}
    }
    return nil, errNoGateway
}

func main() {
    gateway, err := GetGateway()
    if err != nil {
	fmt.Println(err)
    } else {
	fmt.Println("Gateway:", gateway.String())
    }
}

Retrieving router on OSX no longer working

I'm using this package for one of my CLI tools..

When I run networker ls, I get the following error:

failed to list devices: failed to get router: failed to discover gateway: no gateway found.

Error comes from here.

I'd like to submit a PR for this.

DiscoverInterface not in go package

Expected

• get your code from https://pkg.go.dev/github.com/jackpal/gateway using go get
• try to use the exported function DiscoverInterface

What I got

• DiscoverInterface not defined in gateway

How to fix

• FOR THE USER

• clone the repository into your project (I did it under ext/gateway for my project https://github.com/bachittle/ping-go)
• route your go.mod to the local repository using 'replace' function
  

• FOR THE OWNER

• keep https://pkg.go.dev/github.com/jackpal/gateway up to date with this repository.
• If you are the owner, then update the goproxy, if not then contact the real owner

Win32 API version

Just sharing my implementation incase you feel to incorporate it someday (IPv4 only though).
Feel free to copy it and modify it in any shape or form, you can ignore the license completely.

calmh/syncthing@6a6ec72

I have no clue how to check which one is the default one though 💃
Stackoverflow suggests: https://msdn.microsoft.com/en-us/library/windows/desktop/aa365924(v=vs.85).aspx

Please create a new (dot) release

Please tag a v1.0.6 release such that users of your library get the improvements since the latest release (e.g. https://github.com/jackpal/gateway/pull/20/files) - thanks.

Update solaris and freebsd code to have full paths to their executables.

Otherwise there's the potential that the PATH does not include the directory where the executable lives, or that the PATH is set so that some other executable with the same name is found first.

No longer compiles with older Go versions

$ /usr/lib/go-1.19/bin/go build
gateway_parsers.go:14:2: package slices is not in GOROOT (/usr/lib/go-1.19/src/slices)

v1.0.9 build error on linux

branch: v1.0.9 (v1.0.8 has no error)
error:

go: downloading github.com/modern-go/concurrent v0.0.0-20180228061459-e0a39a4cb421
package client
	imports github.com/jackpal/gateway
	imports golang.org/x/net/route: build constraints exclude all Go files in /home/ubuntu/go/pkg/mod/golang.org/x/[email protected]/route

Windows implementation doesn't consider multiple default GW with different MTUs

Real example:

> route print 0.0.0.0
===========================================================================
Interface List
 19...00 05 9a 3c 7a 00 ......Cisco AnyConnect Secure Mobility Client Virtual Miniport Adapter for Windows x64
 37...00 15 5d 0e 76 41 ......Hyper-V Virtual Ethernet Adapter
 21...cc 15 31 1e 58 08 ......Microsoft Wi-Fi Direct Virtual Adapter
  9...ce 15 31 1e 58 07 ......Microsoft Wi-Fi Direct Virtual Adapter #2
  6...cc 15 31 1e 58 07 ......Intel(R) Wi-Fi 6 AX201 160MHz
 17...cc 15 31 1e 58 0b ......Bluetooth Device (Personal Area Network)
  1...........................Software Loopback Interface 1
===========================================================================

IPv4 Route Table
===========================================================================
Active Routes:
Network Destination        Netmask          Gateway       Interface  Metric
          0.0.0.0          0.0.0.0    192.168.100.1   192.168.100.74     50
          0.0.0.0          0.0.0.0       10.21.38.1      10.21.38.97      2
===========================================================================
Persistent Routes:
  None

IPv6 Route Table
===========================================================================
Active Routes:
  None
Persistent Routes:
  None

I think in this case some metric comparison needed

Please tag new release

I got the fork/exec /usr/bin/ip: no such file or directory error. But now I see this is already fixed. But using go get I get the very old 1.0.4 release :/

Panics on Windows when there is no default gateway

It tries to index into rows of output from "route print" that don't necessarily exist:

panic: runtime error: index out of range
goroutine 38788 [running]:
panic(0xb76840, 0xc082002020)
    c:/go/src/runtime/panic.go:481 +0x3f4
github.com/syncthing/syncthing/vendor/github.com/jackpal/gateway.DiscoverGateway(0x0, 0x0, 0x0, 0x0, 0x0)
    c:/jenkins/workspace/syncthing-release-windows/src/github.com/syncthing/syncthing/vendor/github.com/jackpal/gateway/gateway_windows.go:37 +0x4e6
github.com/syncthing/syncthing/lib/pmp.Discover(0x1a3185c5000, 0x2540be400, 0x0, 0x0, 0x0)
    c:/jenkins/workspace/syncthing-release-windows/src/github.com/syncthing/syncthing/lib/pmp/pmp.go:25 +0x48
github.com/syncthing/syncthing/lib/nat.discoverAll.func1(0x1a3185c5000, 0x2540be400, 0xc082218cc0, 0x30e3218, 0xc082e7a740, 0xdd8aa0)
    c:/jenkins/workspace/syncthing-release-windows/src/github.com/syncthing/syncthing/lib/nat/registry.go:32 +0x4c
created by github.com/syncthing/syncthing/lib/nat.discoverAll
    c:/jenkins/workspace/syncthing-release-windows/src/github.com/syncthing/syncthing/lib/nat/registry.go:36 +0x1bb

(syncthing/syncthing#3142)

please tag and version this project

Hello,

Can you please tag and version this project?

I am the Debian Maintainer for gateway and versioning would help Debian keep up with development.