reworked & added interface IP for win & lin

Author: Atakan Çolak

.gitignore

@@ -0,0 +1,2 @@
+.vscode
+.idea

gateway.go

@@ -0,0 +1,23 @@
+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)
+)
+
+// DiscoverGateway is the OS independent function to get the default gateway
+func DiscoverGateway() (ip net.IP, err error) {
+	return discoverGatewayOSSpecific()
+}
+
+// DiscoverInterface is the OS independent function to call to get the default network interface IP that uses the default gateway
+func DiscoverInterface() (ip net.IP, err error) {
+	return discoverGatewayInterfaceOSSpecific()
+}

gateway_common.go

@@ -1,11 +1,13 @@
+// +build darwin
+
 package gateway
 
 import (
 	"net"
 	"os/exec"
 )
 
-func DiscoverGateway() (net.IP, error) {
+func discoverGatewayOSSpecific() (net.IP, error) {
 	routeCmd := exec.Command("/sbin/route", "-n", "get", "0.0.0.0")
 	output, err := routeCmd.CombinedOutput()
 	if err != nil {
@@ -14,3 +16,7 @@ func DiscoverGateway() (net.IP, error) {
 
 	return parseDarwinRouteGet(output)
 }
+
+func discoverGatewayInterfaceOSSpecific() (ip net.IP, err error) {
+	return nil, errNotImplemented
+}

gateway_darwin.go

@@ -1,11 +1,13 @@
+// +build freebsd
+
 package gateway
 
 import (
 	"net"
 	"os/exec"
 )
 
-func DiscoverGateway() (ip net.IP, err error) {
+func discoverGatewayOSSpecific() (ip net.IP, err error) {
 	routeCmd := exec.Command("netstat", "-rn")
 	output, err := routeCmd.CombinedOutput()
 	if err != nil {
@@ -14,3 +16,7 @@ func DiscoverGateway() (ip net.IP, err error) {
 
 	return parseBSDSolarisNetstat(output)
 }
+
+func discoverGatewayInterfaceOSSpecific() (ip net.IP, err error) {
+	return nil, errNotImplemented
+}

gateway_freebsd.go

@@ -1,3 +1,5 @@
+// +build linux
+
 package gateway
 
 import (
@@ -7,13 +9,12 @@ import (
 	"os"
 )
 
-
 const (
 	// See http://man7.org/linux/man-pages/man8/route.8.html
-	file  = "/proc/net/route"
+	file = "/proc/net/route"
 )
 
-func DiscoverGateway() (ip net.IP, err error) {
+func discoverGatewayOSSpecific() (ip net.IP, err error) {
 	f, err := os.Open(file)
 	if err != nil {
 		return nil, fmt.Errorf("Can't access %s", file)
@@ -24,7 +25,19 @@ func DiscoverGateway() (ip net.IP, err error) {
 	if err != nil {
 		return nil, fmt.Errorf("Can't read %s", file)
 	}
-	return parseLinuxProcNetRoute(bytes)
+	return parseLinuxGatewayIP(bytes)
 }
 
+func discoverGatewayInterfaceOSSpecific() (ip net.IP, err error) {
+	f, err := os.Open(file)
+	if err != nil {
+		return nil, fmt.Errorf("Can't access %s", file)
+	}
+	defer f.Close()
 
+	bytes, err := ioutil.ReadAll(f)
+	if err != nil {
+		return nil, fmt.Errorf("Can't read %s", file)
+	}
+	return parseLinuxInterfaceIP(bytes)
+}