Maintenance: error wrapping of alpine package

cmd/gluetun/main.go

@@ -49,6 +49,7 @@ var (
 
 var (
 	errSetupRouting = errors.New("cannot setup routing")
+	errCreateUser   = errors.New("cannot create user")
 )
 
 func main() {
@@ -177,7 +178,7 @@ func _main(ctx context.Context, buildInfo models.BuildInformation,
 	const defaultUsername = "nonrootuser"
 	nonRootUsername, err := alpineConf.CreateUser(defaultUsername, puid)
 	if err != nil {
-		return err
+		return fmt.Errorf("%w: %s", errCreateUser, err)
 	}
 	if nonRootUsername != defaultUsername {
 		logger.Info("using existing username %s corresponding to user id %d", nonRootUsername, puid)

internal/alpine/users.go

@@ -1,35 +1,47 @@
 package alpine
 
 import (
+	"errors"
 	"fmt"
 	"os"
 	"os/user"
+	"strconv"
+)
+
+var (
+	ErrUserAlreadyExists = errors.New("user already exists")
 )
 
 // CreateUser creates a user in Alpine with the given UID.
 func (c *configurator) CreateUser(username string, uid int) (createdUsername string, err error) {
-	UIDStr := fmt.Sprintf("%d", uid)
+	UIDStr := strconv.Itoa(uid)
 	u, err := c.osUser.LookupID(UIDStr)
 	_, unknownUID := err.(user.UnknownUserIdError)
 	if err != nil && !unknownUID {
-		return "", fmt.Errorf("cannot create user: %w", err)
+		return "", err
-	} else if u != nil {
+	}
+
+	if u != nil {
 		if u.Username == username {
 			return "", nil
 		}
 		return u.Username, nil
 	}
+
 	u, err = c.osUser.Lookup(username)
 	_, unknownUsername := err.(user.UnknownUserError)
 	if err != nil && !unknownUsername {
-		return "", fmt.Errorf("cannot create user: %w", err)
+		return "", err
-	} else if u != nil {
-		return "", fmt.Errorf("cannot create user: user with name %s already exists for ID %s instead of %d",
-			username, u.Uid, uid)
 	}
+
+	if u != nil {
+		return "", fmt.Errorf("%w: with name %s for ID %s instead of %d",
+			ErrUserAlreadyExists, username, u.Uid, uid)
+	}
+
 	file, err := c.openFile("/etc/passwd", os.O_APPEND|os.O_WRONLY, 0644)
 	if err != nil {
-		return "", fmt.Errorf("cannot create user: %w", err)
+		return "", err
 	}
 	s := fmt.Sprintf("%s:x:%d:::/dev/null:/sbin/nologin\n", username, uid)
 	_, err = file.WriteString(s)
@@ -37,5 +49,6 @@ func (c *configurator) CreateUser(username string, uid int) (createdUsername str
 		_ = file.Close()
 		return "", err
 	}
+
 	return username, file.Close()
 }