Add android os (#25)

* Add android os

Allthough android is linux the 'ip route' command doesn't return 'default' line.
Android has only one interface active at any time.

GNUmakefile

@@ -55,7 +55,7 @@ doc::
 
 world::
 	@set -e; \
-	for os in solaris darwin freebsd linux windows; do \
+	for os in solaris darwin freebsd linux windows android; do \
 		for arch in amd64; do \
 			printf "Building on %s-%s\n" "$${os}" "$${arch}" ; \
 			env GOOS="$${os}" GOARCH="$${arch}" go build -o /dev/null; \

cmd/sockaddr/GNUmakefile

@@ -26,4 +26,4 @@ test::	$(BIN)
 .PHONY: world
 world::
 	mkdir -p bin
-	gox -os="solaris darwin freebsd linux windows" -arch="386 amd64 arm" -output="bin/sockaddr_{{.OS}}_{{.Arch}}" .
+	gox -os="solaris darwin freebsd linux windows android" -arch="386 amd64 arm" -output="bin/sockaddr_{{.OS}}_{{.Arch}}" .

ifaddrs.go

@@ -1197,23 +1197,46 @@ func parseDefaultIfNameFromRoute(routeOut string) (string, error) {
 // parseDefaultIfNameFromIPCmd parses the default interface from ip(8) for
 // Linux.
 func parseDefaultIfNameFromIPCmd(routeOut string) (string, error) {
+	parsedLines := parseIfNameFromIPCmd(routeOut)
+	for _, parsedLine := range parsedLines {
+		if parsedLine[0] == "default" &&
+			parsedLine[1] == "via" &&
+			parsedLine[3] == "dev" {
+			ifName := strings.TrimSpace(parsedLine[4])
+			return ifName, nil
+		}
+	}
+
+	return "", errors.New("No default interface found")
+}
+
+// parseDefaultIfNameFromIPCmdAndroid parses the default interface from ip(8) for
+// Android.
+func parseDefaultIfNameFromIPCmdAndroid(routeOut string) (string, error) {
+	parsedLines := parseIfNameFromIPCmd(routeOut)
+	if (len(parsedLines) > 0) {
+		ifName := strings.TrimSpace(parsedLines[0][4])
+		return ifName, nil
+	}
+
+	return "", errors.New("No default interface found")
+}
+
+
+// parseIfNameFromIPCmd parses interfaces from ip(8) for
+// Linux.
+func parseIfNameFromIPCmd(routeOut string) [][]string {
 	lines := strings.Split(routeOut, "\n")
 	re := whitespaceRE.Copy()
+	parsedLines := make([][]string, 0, len(lines))
 	for _, line := range lines {
 		kvs := re.Split(line, -1)
 		if len(kvs) < 5 {
 			continue
 		}
-
-		if kvs[0] == "default" &&
-			kvs[1] == "via" &&
-			kvs[3] == "dev" {
-			ifName := strings.TrimSpace(kvs[4])
-			return ifName, nil
-		}
+		parsedLines = append(parsedLines, kvs)
 	}
-
-	return "", errors.New("No default interface found")
+	return parsedLines
 }
 
 // parseDefaultIfNameWindows parses the default interface from `netstat -rn` and

route_info_android.go

@@ -0,0 +1,34 @@
+package sockaddr
+
+import (
+	"errors"
+	"os/exec"
+)
+
+type routeInfo struct {
+	cmds map[string][]string
+}
+
+// NewRouteInfo returns a Android-specific implementation of the RouteInfo
+// interface.
+func NewRouteInfo() (routeInfo, error) {
+	return routeInfo{
+		cmds: map[string][]string{"ip": {"/system/bin/ip", "route", "get", "8.8.8.8"}},
+	}, nil
+}
+
+// GetDefaultInterfaceName returns the interface name attached to the default
+// route on the default interface.
+func (ri routeInfo) GetDefaultInterfaceName() (string, error) {
+	out, err := exec.Command(ri.cmds["ip"][0], ri.cmds["ip"][1:]...).Output()
+	if err != nil {
+		return "", err
+	}
+
+
+	var ifName string
+	if ifName, err = parseDefaultIfNameFromIPCmdAndroid(string(out)); err != nil {
+		return "", errors.New("No default interface found")
+	}
+	return ifName, nil
+}

route_info_linux.go

@@ -1,3 +1,5 @@
+// +build !android
+
 package sockaddr
 
 import (