More robust IP discovery, attempted fix for #17

Author: shayne

go.mod

@@ -1,6 +1,6 @@
 module github.com/shayne/go-wsl2-host
 
-go 1.12
+go 1.14
 
 require (
 	github.com/stretchr/testify v1.4.0

pkg/wslcli/wslcli.go

@@ -5,8 +5,10 @@ import (
 	"errors"
 	"fmt"
 	"io/ioutil"
+	"math/bits"
 	"os/exec"
 	"regexp"
+	"strconv"
 	"strings"
 
 	"golang.org/x/text/encoding/unicode"
@@ -41,10 +43,105 @@ func ListAll() (string, error) {
 	return decoded, nil
 }
 
+func netmaskToBits(mask uint32) int {
+	return bits.OnesCount32(mask)
+}
+func hexToUint32LE(hex string) (uint32, error) {
+	i, err := strconv.ParseInt(hex[6:8]+hex[4:6]+hex[2:4]+hex[0:2], 16, 64)
+	if err != nil {
+		return 0, err
+	}
+	return uint32(i), nil
+}
+
+type routeInfo struct {
+	net  uint32
+	mask uint32
+}
+
+func getRouteInfo(name string) (*routeInfo, error) {
+	cmd := exec.Command("wsl.exe", "-d", name, "--", "cat", "/proc/net/route")
+	out, err := cmd.Output()
+	if err != nil {
+		return nil, err
+	}
+	ri := &routeInfo{}
+	sout := string(out)
+	sout = strings.TrimSpace(sout)
+	lines := strings.Split(sout, "\n")
+	lines = lines[1:]
+	for _, line := range lines {
+		fs := strings.Fields(line)
+		if ri.mask > 0 && ri.net > 0 {
+			break
+		}
+		if fs[0] != "eth0" {
+			continue
+		}
+		if fs[1] != "00000000" {
+			net, err := hexToUint32LE(fs[1])
+			if err != nil {
+				return nil, fmt.Errorf("failed to convert network to Uint32: %w", err)
+			}
+			ri.net = net
+		}
+		if fs[7] != "00000000" {
+			mask, err := hexToUint32LE(fs[7])
+			if err != nil {
+				return nil, fmt.Errorf("failed to convert netmask to Uint32: %w", err)
+			}
+			ri.mask = mask
+		}
+	}
+
+	return ri, nil
+}
+
+func isIPInRange(ri *routeInfo, ip uint32) bool {
+	return (ri.net & ri.mask) == (ip & ri.mask)
+}
+
+func ipToUint32(ip string) (uint32, error) {
+	octets := strings.Split(ip, ".")
+	if len(octets) != 4 {
+		return 0, errors.New("invalid IP address")
+	}
+
+	var io uint32
+
+	o1, err := strconv.Atoi(octets[0])
+	if err != nil {
+		return 0, fmt.Errorf("failed to parse IP address, %s: %w", ip, err)
+	}
+	io += uint32(o1 << 24)
+	o2, err := strconv.Atoi(octets[1])
+	if err != nil {
+		return 0, fmt.Errorf("failed to parse IP address, %s: %w", ip, err)
+	}
+	io += uint32(o2 << 16)
+	o3, err := strconv.Atoi(octets[2])
+	if err != nil {
+		return 0, fmt.Errorf("failed to parse IP address, %s: %w", ip, err)
+	}
+	io += uint32(o3 << 8)
+	o4, err := strconv.Atoi(octets[3])
+	if err != nil {
+		return 0, fmt.Errorf("failed to parse IP address, %s: %w", ip, err)
+	}
+	io += uint32(o4)
+
+	return io, nil
+}
+
 // GetIP returns the IP address of the given distro
 // Suggest check if running before calling this function as
 // it has the side-effect of starting the distro
 func GetIP(name string) (string, error) {
+	ri, err := getRouteInfo(name)
+	if err != nil {
+		return "", err
+	}
+
 	cmd := exec.Command("wsl.exe", "-d", name, "--", "cat", "/proc/net/fib_trie")
 	out, err := cmd.Output()
 	if err != nil {
@@ -56,13 +153,17 @@ func GetIP(name string) (string, error) {
 		return "", errors.New("invalid output from fib_trie")
 	}
 	lines := strings.Split(sout, "\n")
-	for i, line := range lines {
+	for i := len(lines) - 1; i >= 0; i-- {
+		line := lines[i]
 		if strings.Index(line, "32 host LOCAL") != -1 {
-			if i > 0 && strings.Index(lines[i-1], "127.0.0.1") == -1 {
-				if fs := strings.Fields(lines[i-1]); len(fs) > 1 {
-					return strings.TrimSpace(fs[1]), nil
-				}
-				break
+			fs := strings.Fields(lines[i-1])
+			ipstr := strings.TrimSpace(fs[1])
+			ip, err := ipToUint32(ipstr)
+			if err != nil {
+				return "", fmt.Errorf("failed to convert ip, %s: %w", ipstr, err)
+			}
+			if isIPInRange(ri, ip) {
+				return ipstr, nil
 			}
 		}
 	}