Initial checkin.

Copied from

https://github.com/jackpal/Taipei-Torrent/blob/master/torrent/gateway.go

Split into OS-specific versions.

Author: jackpal

LICENSE

@@ -0,0 +1,27 @@
+// Copyright (c) 2010 Jack Palevich. All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//    * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//    * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//    * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

gateway_darwin.go

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+package gateway
+
+import (
+	"bytes"
+	"io/ioutil"
+	"net"
+	"os/exec"
+)
+
+func DiscoverGateway() (ip net.IP, err error) {
+	routeCmd := exec.Command("route", "-n", "get", "0.0.0.0")
+	stdOut, err := routeCmd.StdoutPipe()
+	if err != nil {
+		return
+	}
+	if err = routeCmd.Start(); err != nil {
+		return
+	}
+	output, err := ioutil.ReadAll(stdOut)
+	if err != nil {
+		return
+	}
+
+	// Darwin route out format is always like this:
+	//    route to: default
+	// destination: default
+	//        mask: default
+	//     gateway: 192.168.1.1
+	outputLines := bytes.Split(output, []byte("\n"))
+	for _, line := range outputLines {
+		if bytes.Contains(line, []byte("gateway:")) {
+			gatewayFields := bytes.Fields(line)
+			ip = net.ParseIP(string(gatewayFields[1]))
+			break
+		}
+	}
+
+	err = routeCmd.Wait()
+	return
+}

gateway_linux.go

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+package gateway
+
+import (
+	"bytes"
+	"io/ioutil"
+	"net"
+	"os/exec"
+)
+
+func DiscoverGateway() (ip net.IP, err error) {
+	routeCmd := exec.Command("route", "-n")
+	stdOut, err := routeCmd.StdoutPipe()
+	if err != nil {
+		return
+	}
+	if err = routeCmd.Start(); err != nil {
+		return
+	}
+	output, err := ioutil.ReadAll(stdOut)
+	if err != nil {
+		return
+	}
+
+	// Linux route out format is always like this:
+	// Kernel IP routing table
+	// Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
+	// 0.0.0.0         192.168.1.1     0.0.0.0         UG    0      0        0 eth0
+	outputLines := bytes.Split(output, []byte("\n"))
+	for _, line := range outputLines {
+		if bytes.Contains(line, []byte("0.0.0.0")) {
+			ipFields := bytes.Fields(line)
+			ip = net.ParseIP(string(ipFields[1]))
+			break
+		}
+	}
+	err = routeCmd.Wait()
+	return
+}

gateway_windows.go

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+package gateway
+
+import (
+	"bytes"
+	"io/ioutil"
+	"net"
+	"os/exec"
+)
+
+func DiscoverGateway() (ip net.IP, err error) {
+	routeCmd := exec.Command("route", "print", "0.0.0.0")
+	stdOut, err := routeCmd.StdoutPipe()
+	if err != nil {
+		return
+	}
+	if err = routeCmd.Start(); err != nil {
+		return
+	}
+	output, err := ioutil.ReadAll(stdOut)
+	if err != nil {
+		return
+	}
+
+	// Windows route output format is always like this:
+	// ===========================================================================
+	// 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
+	// ===========================================================================
+	// I'm trying to pick the active route,
+	// then jump 2 lines and pick the third IP
+	// Not using regex because output is quite standard from Windows XP to 8 (NEEDS TESTING)
+	outputLines := bytes.Split(output, []byte("\n"))
+	for idx, line := range outputLines {
+		if bytes.Contains(line, []byte("Active Routes:")) {
+			ipFields := bytes.Fields(outputLines[idx+2])
+			ip = net.ParseIP(string(ipFields[2]))
+			break
+		}
+	}
+	err = routeCmd.Wait()
+	return
+}