init

.gitignore

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+.vscode
+.idea

.travis.yml

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+language: go
+go:
+    - 1.18
+script:
+    - go test -v ./...

LICENSE

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+The MIT License
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+

README.md

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+# go-gateway
+
+A simple library for discovering the IP address of the default gateway.
+
+
+[![Build Status](https://travis-ci.org/net-byte/go-gateway.svg)](https://travis-ci.org/net-byte/go-gateway)
+
+Provides implementations for:
+
++ Linux
++ MacOS 
++ Windows
+
+Other platforms use an implementation that always returns an error.

gateway.go

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+package gateway
+
+import (
+	"errors"
+	"net"
+	"runtime"
+)
+
+var (
+	errNoGateway      = errors.New("no gateway found")
+	errCantParse      = errors.New("can't parse string output")
+	errNotImplemented = errors.New("not implemented for OS: " + runtime.GOOS)
+)
+
+// DiscoverGatewayIPv4 is the OS independent function to get the default ipv4 gateway
+func DiscoverGatewayIPv4() (ip net.IP, err error) {
+	return discoverGatewayOSSpecificIPv4()
+}
+
+// DiscoverGatewayIPv6 is the OS independent function to get the default ipv6 gateway
+func DiscoverGatewayIPv6() (ip net.IP, err error) {
+	return discoverGatewayOSSpecificIPv6()
+}

gateway_darwin.go

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+//go:build darwin
+// +build darwin
+
+package gateway
+
+import (
+	"net"
+	"os/exec"
+)
+
+func discoverGatewayOSSpecificIPv4() (ip net.IP, err error) {
+	ipstr := execCmd("sh", "-c", "route -n get default | grep 'gateway' | awk 'NR==1{print $2}'")
+	ipv4 := net.ParseIP(ipstr)
+	if ipv4 == nil {
+		return nil, errCantParse
+	}
+	return ipv4, nil
+}
+
+func discoverGatewayOSSpecificIPv6() (ip net.IP, err error) {
+	ipstr := execCmd("sh", "-c", "route -6 -n get default | grep 'gateway' | awk 'NR==1{print $2}'")
+	ipv6 := net.ParseIP(ipstr)
+	if ipv6 == nil {
+		return nil, errCantParse
+	}
+	return ipv6, nil
+}

gateway_linux.go

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+//go:build linux
+// +build linux
+
+package gateway
+
+import (
+	"net"
+)
+
+func discoverGatewayOSSpecificIPv4() (ip net.IP, err error) {
+	ipstr := execCmd("sh", "-c", "route -n | grep 'UG[ \t]' | awk 'NR==1{print $2}'")
+	ipv4 := net.ParseIP(ipstr)
+	if ipv4 == nil {
+		return nil, errCantParse
+	}
+	return ipv4, nil
+}
+
+func discoverGatewayOSSpecificIPv6() (ip net.IP, err error) {
+	ipstr := execCmd("sh", "-c", "route -6 -n | grep 'UG[ \t]' | awk 'NR==1{print $2}'")
+	ipv6 := net.ParseIP(ipstr)
+	if ipv6 == nil {
+		return nil, errCantParse
+	}
+	return ipv6, nil
+}

gateway_parsers.go

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+package gateway
+
+import (
+	"log"
+	"net"
+	"os/exec"
+	"strings"
+)
+
+type windowsRouteStructIPv4 struct {
+	Destination string
+	Netmask     string
+	Gateway     string
+	Interface   string
+	Metric      string
+}
+
+type windowsRouteStructIPv6 struct {
+	If          string
+	Metric      string
+	Destination string
+	Gateway     string
+}
+
+func parseToWindowsRouteStructIPv4(output []byte) (windowsRouteStructIPv4, error) {
+	// Windows route output format is always like this:
+	// ===========================================================================
+	// Interface List
+	// 8 ...00 12 3f a7 17 ba ...... Intel(R) PRO/100 VE Network Connection
+	// 1 ........................... Software Loopback Interface 1
+	// ===========================================================================
+	// IPv4 Route Table
+	// ===========================================================================
+	// Active Routes:
+	// Network Destination        Netmask          Gateway       Interface  Metric
+	//           0.0.0.0          0.0.0.0      192.168.1.1    192.168.1.100     20
+	// ===========================================================================
+	//
+	// Windows commands are localized, so we can't just look for "Active Routes:" string
+	// I'm trying to pick the active route,
+	// then jump 2 lines and get the row
+	// Not using regex because output is quite standard from Windows XP to 8 (NEEDS TESTING)
+	lines := strings.Split(string(output), "\n")
+	sep := 0
+	for idx, line := range lines {
+		if sep == 3 {
+			// We just entered the 2nd section containing "Active Routes:"
+			if len(lines) <= idx+2 {
+				return windowsRouteStructIPv4{}, errNoGateway
+			}
+
+			fields := strings.Fields(lines[idx+2])
+			if len(fields) < 5 {
+				return windowsRouteStructIPv4{}, errCantParse
+			}
+
+			return windowsRouteStructIPv4{
+				Destination: fields[0],
+				Netmask:     fields[1],
+				Gateway:     fields[2],
+				Interface:   fields[3],
+				Metric:      fields[4],
+			}, nil
+		}
+		if strings.HasPrefix(line, "=======") {
+			sep++
+			continue
+		}
+	}
+	return windowsRouteStructIPv4{}, errNoGateway
+}
+
+func parseToWindowsRouteStructIPv6(output []byte) (windowsRouteStructIPv6, error) {
+
+	lines := strings.Split(string(output), "\n")
+	sep := 0
+	for idx, line := range lines {
+		if sep == 3 {
+			// We just entered the 2nd section containing "Active Routes:"
+			if len(lines) <= idx+2 {
+				return windowsRouteStructIPv6{}, errNoGateway
+			}
+
+			fields := strings.Fields(lines[idx+2])
+			if len(fields) < 5 {
+				return windowsRouteStructIPv6{}, errCantParse
+			}
+
+			return windowsRouteStructIPv6{
+				If:          fields[0],
+				Metric:      fields[1],
+				Destination: fields[2],
+				Gateway:     fields[3],
+			}, nil
+		}
+		if strings.HasPrefix(line, "=======") {
+			sep++
+			continue
+		}
+	}
+	return windowsRouteStructIPv6{}, errNoGateway
+}
+
+func parseWindowsGatewayIPv4(output []byte) (net.IP, error) {
+	parsedOutput, err := parseToWindowsRouteStructIPv4(output)
+	if err != nil {
+		return nil, err
+	}
+
+	ip := net.ParseIP(parsedOutput.Gateway)
+	if ip == nil {
+		return nil, errCantParse
+	}
+	return ip, nil
+}
+
+func parseWindowsGatewayIPv6(output []byte) (net.IP, error) {
+	parsedOutput, err := parseToWindowsRouteStructIPv6(output)
+	if err != nil {
+		return nil, err
+	}
+
+	ip := net.ParseIP(parsedOutput.Gateway)
+	if ip == nil {
+		return nil, errCantParse
+	}
+	return ip, nil
+}
+
+func execCmd(c string, args ...string) string {
+	cmd := exec.Command(c, args...)
+	out, err := cmd.Output()
+	if err != nil {
+		log.Println("failed to exec cmd:", err)
+	}
+	if len(out) == 0 {
+		return ""
+	}
+	s := string(out)
+	return strings.ReplaceAll(s, "\n", "")
+}

gateway_unimplemented.go

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+//go:build !darwin && !linux && !windows && !solaris && !freebsd
+// +build !darwin,!linux,!windows,!solaris,!freebsd
+
+package gateway
+
+import (
+	"net"
+)
+
+func discoverGatewayOSSpecificIPv4() (ip net.IP, err error) {
+	return ip, errNotImplemented
+}
+
+func discoverGatewayOSSpecificIPv6() (ip net.IP, err error) {
+	return ip, errNotImplemented
+}

gateway_windows.go

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+//go:build windows
+// +build windows
+
+package gateway
+
+import (
+	"net"
+	"os/exec"
+	"syscall"
+)
+
+func discoverGatewayOSSpecificIPv4() (ip net.IP, err error) {
+	routeCmd := exec.Command("route", "print", "0.0.0.0")
+	routeCmd.SysProcAttr = &syscall.SysProcAttr{HideWindow: true}
+	output, err := routeCmd.CombinedOutput()
+	if err != nil {
+		return nil, err
+	}
+
+	return parseWindowsGatewayIPv4(output)
+}
+
+func discoverGatewayOSSpecificIPv6() (ip net.IP, err error) {
+	routeCmd := exec.Command("route", "print","-6" "::/0")
+	routeCmd.SysProcAttr = &syscall.SysProcAttr{HideWindow: true}
+	output, err := routeCmd.CombinedOutput()
+	if err != nil {
+		return nil, err
+	}
+
+	return parseWindowsGatewayIPv6(output)
+}

go.mod

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+module github.com/net-byte/go-gateway
+
+go 1.18