Allow twitch-cli to open default browser in Windows when run inside WSL

internal/login/login.go

@@ -14,6 +14,8 @@ import (
 	"net/url"
 	"os/exec"
 	"runtime"
+	"strings"
+	"syscall"
 	"time"
 
 	"github.com/spf13/viper"
@@ -115,7 +117,10 @@ func UserCredentialsLogin(p LoginParameters) (LoginResponse, error) {
 	u.RawQuery = q.Encode()
 
 	fmt.Println("Opening browser. Press Ctrl+C to cancel...")
-	openBrowser(u.String())
+	err = openBrowser(u.String())
+	if err != nil {
+		fmt.Printf("Unable to open default browser. You can manually navigate to this URL to complete the login: %s\n", u.String())
+	}
 
 	ur, err := userAuthServer()
 	if err != nil {
@@ -226,13 +231,38 @@ func generateState() (string, error) {
 	return base64.URLEncoding.EncodeToString(b), nil
 }
 
+// check for Windows Subsystem for Linux
+func isWsl(sc util.Syscall) bool {
+	// the common factor between WSL distros is the Microsoft-specific kernel version, so we check for that
+	// SUSE, WSLv1: 4.4.0-19041-Microsoft
+	// Ubuntu, WSLv2: 4.19.128-microsoft-standard
+	const wslIdentifier = "microsoft"
+	var uname syscall.Utsname
+	if err := sc.Uname(&uname); err == nil {
+		var kernel []byte
+		for _, b := range uname.Release {
+			if b == 0 {
+				break
+			}
+			kernel = append(kernel, byte(b))
+		}
+		return strings.Contains(strings.ToLower(string(kernel)), wslIdentifier)
+	}
+	return false
+}
+
 func openBrowser(url string) error {
+	const rundllParameters = "url.dll,FileProtocolHandler"
 	var err error
 	switch runtime.GOOS {
 	case "linux":
-		err = exec.Command("xdg-open", url).Start()
+		if isWsl(util.DefaultSyscall) {
+			err = exec.Command("rundll32.exe", rundllParameters, url).Start()
+		} else {
+			err = exec.Command("xdg-open", url).Start()
+		}
 	case "windows":
-		err = exec.Command("rundll32", "url.dll,FileProtocolHandler", url).Start()
+		err = exec.Command("rundll32", rundllParameters, url).Start()
 	case "darwin":
 		err = exec.Command("open", url).Start()
 	default:

internal/login/login_test.go

@@ -4,13 +4,16 @@ package login
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"net/http"
 	"net/http/httptest"
+	"syscall"
 	"testing"
 	"time"
 
 	"github.com/spf13/viper"
+	"github.com/stretchr/testify/assert"
 	"github.com/twitchdev/twitch-cli/internal/util"
 )
 
@@ -157,3 +160,40 @@ func TestUserAuthServer(t *testing.T) {
 	a.Equal(state, ur.State, "State mismatch")
 	a.Equal(code, ur.Code, "Code mismatch")
 }
+
+func TestIsWsl(t *testing.T) {
+	a := assert.New(t)
+
+	var (
+		// syscall.Utsname.Release value on various systems
+
+		// Ubuntu 20.04 on WSL2 on Windows 10 x64 20H2
+		ubuntu20Wsl2 = [65]int8{52, 46, 49, 57, 46, 49, 50, 56, 45, 109, 105, 99, 114, 111, 115, 111, 102, 116, 45, 115, 116, 97, 110, 100, 97, 114, 100, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
+
+		// Arch Linux on baremetal on 2021-04-02
+		archReal = [65]int8{53, 46, 49, 49, 46, 49, 49, 45, 97, 114, 99, 104, 49, 45, 49, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
+	)
+
+	result := isWsl(util.Syscall{
+		Uname: func(buf *syscall.Utsname) (err error) {
+			buf.Release = ubuntu20Wsl2
+			return nil
+		},
+	})
+	a.True(result)
+
+	result = isWsl(util.Syscall{
+		Uname: func(buf *syscall.Utsname) (err error) {
+			buf.Release = archReal
+			return nil
+		},
+	})
+	a.False(result)
+
+	result = isWsl(util.Syscall{
+		Uname: func(buf *syscall.Utsname) (err error) {
+			return errors.New("mocked error")
+		},
+	})
+	a.False(result)
+}

internal/util/syscall.go

@@ -0,0 +1,12 @@
+package util
+
+import "syscall"
+
+// Syscall wraps syscalls used in the application for unit testing purposes
+type Syscall struct {
+	Uname func(buf *syscall.Utsname) (err error)
+}
+
+var DefaultSyscall = Syscall{
+	Uname: syscall.Uname,
+}