libct: use strings.CutPrefix where possible

Using strings.CutPrefix (available since Go 1.20) instead of
strings.HasPrefix and/or strings.TrimPrefix makes the code
a tad more straightforward.

No functional change.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/cgroups/devices/systemd.go

@@ -224,8 +224,7 @@ func findDeviceGroup(ruleType devices.Type, ruleMajor int64) (string, error) {
 			continue
 		}
 
-		group := strings.TrimPrefix(line, ruleMajorStr)
-		if len(group) < len(line) { // got it
+		if group, ok := strings.CutPrefix(line, ruleMajorStr); ok {
 			return prefix + group, nil
 		}
 	}

libcontainer/cgroups/file.go

@@ -151,8 +151,8 @@ func openFile(dir, file string, flags int) (*os.File, error) {
 	if prepareOpenat2() != nil {
 		return openFallback(path, flags, mode)
 	}
-	relPath := strings.TrimPrefix(path, cgroupfsPrefix)
-	if len(relPath) == len(path) { // non-standard path, old system?
+	relPath, ok := strings.CutPrefix(path, cgroupfsPrefix)
+	if !ok { // Non-standard path, old system?
 		return openFallback(path, flags, mode)
 	}
 

libcontainer/cgroups/fs2/freezer.go

@@ -104,9 +104,7 @@ func waitFrozen(dirPath string) (cgroups.FreezerState, error) {
 		if i == maxIter {
 			return cgroups.Undefined, fmt.Errorf("timeout of %s reached waiting for the cgroup to freeze", waitTime*maxIter)
 		}
-		line := scanner.Text()
-		val := strings.TrimPrefix(line, "frozen ")
-		if val != line { // got prefix
+		if val, ok := strings.CutPrefix(scanner.Text(), "frozen "); ok {
 			if val[0] == '1' {
 				return cgroups.Frozen, nil
 			}

libcontainer/cgroups/systemd/user.go

@@ -61,8 +61,7 @@ func DetectUID() (int, error) {
 	scanner := bufio.NewScanner(bytes.NewReader(b))
 	for scanner.Scan() {
 		s := strings.TrimSpace(scanner.Text())
-		if strings.HasPrefix(s, "OwnerUID=") {
-			uidStr := strings.TrimPrefix(s, "OwnerUID=")
+		if uidStr, ok := strings.CutPrefix(s, "OwnerUID="); ok {
 			i, err := strconv.Atoi(uidStr)
 			if err != nil {
 				return -1, fmt.Errorf("could not detect the OwnerUID: %w", err)

libcontainer/cgroups/utils.go

@@ -332,8 +332,8 @@ func getHugePageSizeFromFilenames(fileNames []string) ([]string, error) {
 
 	for _, file := range fileNames {
 		// example: hugepages-1048576kB
-		val := strings.TrimPrefix(file, "hugepages-")
-		if len(val) == len(file) {
+		val, ok := strings.CutPrefix(file, "hugepages-")
+		if !ok {
 			// Unexpected file name: no prefix found, ignore it.
 			continue
 		}

libcontainer/configs/validate/rootless.go

@@ -56,7 +56,7 @@ func rootlessEUIDMount(config *configs.Config) error {
 		// Check that the options list doesn't contain any uid= or gid= entries
 		// that don't resolve to root.
 		for _, opt := range strings.Split(mount.Data, ",") {
-			if str := strings.TrimPrefix(opt, "uid="); len(str) < len(opt) {
+			if str, ok := strings.CutPrefix(opt, "uid="); ok {
 				uid, err := strconv.Atoi(str)
 				if err != nil {
 					// Ignore unknown mount options.
@@ -65,9 +65,9 @@ func rootlessEUIDMount(config *configs.Config) error {
 				if _, err := config.HostUID(uid); err != nil {
 					return fmt.Errorf("cannot specify uid=%d mount option for rootless container: %w", uid, err)
 				}
+				continue
 			}
-
-			if str := strings.TrimPrefix(opt, "gid="); len(str) < len(opt) {
+			if str, ok := strings.CutPrefix(opt, "gid="); ok {
 				gid, err := strconv.Atoi(str)
 				if err != nil {
 					// Ignore unknown mount options.

libcontainer/specconv/spec_linux.go

@@ -685,8 +685,8 @@ func initSystemdProps(spec *specs.Spec) ([]systemdDbus.Property, error) {
 	var sp []systemdDbus.Property
 
 	for k, v := range spec.Annotations {
-		name := strings.TrimPrefix(k, keyPrefix)
-		if len(name) == len(k) { // prefix not there
+		name, ok := strings.CutPrefix(k, keyPrefix)
+		if !ok { // prefix not there
 			continue
 		}
 		if err := checkPropertyName(name); err != nil {

libcontainer/utils/utils.go

@@ -88,8 +88,8 @@ func stripRoot(root, path string) string {
 func SearchLabels(labels []string, key string) (string, bool) {
 	key += "="
 	for _, s := range labels {
-		if strings.HasPrefix(s, key) {
-			return s[len(key):], true
+		if val, ok := strings.CutPrefix(s, key); ok {
+			return val, true
 		}
 	}
 	return "", false