Avoid using strings.Split

dnssec_keyscan.go

@@ -37,7 +37,8 @@ func (k *DNSKEY) ReadPrivateKey(q io.Reader, file string) (crypto.PrivateKey, er
 		return nil, ErrPrivKey
 	}
 	// TODO(mg): check if the pubkey matches the private key
-	algo, err := strconv.ParseUint(strings.SplitN(m["algorithm"], " ", 2)[0], 10, 8)
+	algoStr, _, _ := strings.Cut(m["algorithm"], " ")
+	algo, err := strconv.ParseUint(algoStr, 10, 8)
 	if err != nil {
 		return nil, ErrPrivKey
 	}

generate.go

@@ -35,17 +35,17 @@ func (zp *ZoneParser) generate(l lex) (RR, bool) {
 		token = token[:i]
 	}
 
-	sx := strings.SplitN(token, "-", 2)
-	if len(sx) != 2 {
+	startStr, endStr, ok := strings.Cut(token, "-")
+	if !ok {
 		return zp.setParseError("bad start-stop in $GENERATE range", l)
 	}
 
-	start, err := strconv.ParseInt(sx[0], 10, 64)
+	start, err := strconv.ParseInt(startStr, 10, 64)
 	if err != nil {
 		return zp.setParseError("bad start in $GENERATE range", l)
 	}
 
-	end, err := strconv.ParseInt(sx[1], 10, 64)
+	end, err := strconv.ParseInt(endStr, 10, 64)
 	if err != nil {
 		return zp.setParseError("bad stop in $GENERATE range", l)
 	}
@@ -54,7 +54,7 @@ func (zp *ZoneParser) generate(l lex) (RR, bool) {
 	}
 
 	// _BLANK
-	l, ok := zp.c.Next()
+	l, ok = zp.c.Next()
 	if !ok || l.value != zBlank {
 		return zp.setParseError("garbage after $GENERATE range", l)
 	}
@@ -211,15 +211,16 @@ func (r *generateReader) ReadByte() (byte, error) {
 func modToPrintf(s string) (string, int64, string) {
 	// Modifier is { offset [ ,width [ ,base ] ] } - provide default
 	// values for optional width and type, if necessary.
-	var offStr, widthStr, base string
-	switch xs := strings.Split(s, ","); len(xs) {
-	case 1:
-		offStr, widthStr, base = xs[0], "0", "d"
-	case 2:
-		offStr, widthStr, base = xs[0], xs[1], "d"
-	case 3:
-		offStr, widthStr, base = xs[0], xs[1], xs[2]
-	default:
+	offStr, s, ok0 := strings.Cut(s, ",")
+	widthStr, s, ok1 := strings.Cut(s, ",")
+	base, _, ok2 := strings.Cut(s, ",")
+	if !ok0 {
+		widthStr = "0"
+	}
+	if !ok1 {
+		base = "d"
+	}
+	if ok2 {
 		return "", 0, "bad modifier in $GENERATE"
 	}
 
@@ -234,8 +235,8 @@ func modToPrintf(s string) (string, int64, string) {
 		return "", 0, "bad offset in $GENERATE"
 	}
 
-	width, err := strconv.ParseInt(widthStr, 10, 64)
-	if err != nil || width < 0 || width > 255 {
+	width, err := strconv.ParseUint(widthStr, 10, 8)
+	if err != nil {
 		return "", 0, "bad width in $GENERATE"
 	}
 

scan.go

@@ -1216,42 +1216,34 @@ func stringToCm(token string) (e, m uint8, ok bool) {
 	if token[len(token)-1] == 'M' || token[len(token)-1] == 'm' {
 		token = token[0 : len(token)-1]
 	}
-	s := strings.SplitN(token, ".", 2)
-	var meters, cmeters, val int
-	var err error
-	switch len(s) {
-	case 2:
-		if cmeters, err = strconv.Atoi(s[1]); err != nil {
-			return
-		}
+
+	var (
+		meters, cmeters, val int
+		err                  error
+	)
+	mStr, cmStr, hasCM := strings.Cut(token, ".")
+	if hasCM {
 		// There's no point in having more than 2 digits in this part, and would rather make the implementation complicated ('123' should be treated as '12').
 		// So we simply reject it.
 		// We also make sure the first character is a digit to reject '+-' signs.
-		if len(s[1]) > 2 || s[1][0] < '0' || s[1][0] > '9' {
+		cmeters, err = strconv.Atoi(cmStr)
+		if err != nil || len(cmStr) > 2 || cmStr[0] < '0' || cmStr[0] > '9' {
 			return
 		}
-		if len(s[1]) == 1 {
+		if len(cmStr) == 1 {
 			// 'nn.1' must be treated as 'nn-meters and 10cm, not 1cm.
 			cmeters *= 10
 		}
-		if s[0] == "" {
-			// This will allow omitting the 'meter' part, like .01 (meaning 0.01m = 1cm).
-			break
-		}
-		fallthrough
-	case 1:
-		if meters, err = strconv.Atoi(s[0]); err != nil {
-			return
-		}
+	}
+	// This slighly ugly condition will allow omitting the 'meter' part, like .01 (meaning 0.01m = 1cm).
+	if !hasCM || mStr != "" {
+		meters, err = strconv.Atoi(mStr)
 		// RFC1876 states the max value is 90000000.00.  The latter two conditions enforce it.
-		if s[0][0] < '0' || s[0][0] > '9' || meters > 90000000 || (meters == 90000000 && cmeters != 0) {
+		if err != nil || mStr[0] < '0' || mStr[0] > '9' || meters > 90000000 || (meters == 90000000 && cmeters != 0) {
 			return
 		}
-	case 0:
-		// huh?
-		return 0, 0, false
 	}
-	ok = true
+
 	if meters > 0 {
 		e = 2
 		val = meters
@@ -1263,8 +1255,7 @@ func stringToCm(token string) (e, m uint8, ok bool) {
 		e++
 		val /= 10
 	}
-	m = uint8(val)
-	return
+	return e, uint8(val), true
 }
 
 func toAbsoluteName(name, origin string) (absolute string, ok bool) {

svcb.go

@@ -314,10 +314,11 @@ func (s *SVCBMandatory) unpack(b []byte) error {
 }
 
 func (s *SVCBMandatory) parse(b string) error {
-	str := strings.Split(b, ",")
-	codes := make([]SVCBKey, 0, len(str))
-	for _, e := range str {
-		codes = append(codes, svcbStringToKey(e))
+	codes := make([]SVCBKey, 0, strings.Count(b, ",")+1)
+	for len(b) > 0 {
+		var key string
+		key, b, _ = strings.Cut(b, ",")
+		codes = append(codes, svcbStringToKey(key))
 	}
 	s.Code = codes
 	return nil
@@ -613,19 +614,24 @@ func (s *SVCBIPv4Hint) String() string {
 }
 
 func (s *SVCBIPv4Hint) parse(b string) error {
+	if b == "" {
+		return errors.New("dns: svcbipv4hint: empty hint")
+	}
 	if strings.Contains(b, ":") {
 		return errors.New("dns: svcbipv4hint: expected ipv4, got ipv6")
 	}
-	str := strings.Split(b, ",")
-	dst := make([]net.IP, len(str))
-	for i, e := range str {
+
+	hint := make([]net.IP, 0, strings.Count(b, ",")+1)
+	for len(b) > 0 {
+		var e string
+		e, b, _ = strings.Cut(b, ",")
 		ip := net.ParseIP(e).To4()
 		if ip == nil {
 			return errors.New("dns: svcbipv4hint: bad ip")
 		}
-		dst[i] = ip
+		hint = append(hint, ip)
 	}
-	s.Hint = dst
+	s.Hint = hint
 	return nil
 }
 
@@ -733,19 +739,24 @@ func (s *SVCBIPv6Hint) String() string {
 }
 
 func (s *SVCBIPv6Hint) parse(b string) error {
-	str := strings.Split(b, ",")
-	dst := make([]net.IP, len(str))
-	for i, e := range str {
+	if b == "" {
+		return errors.New("dns: svcbipv6hint: empty hint")
+	}
+
+	hint := make([]net.IP, 0, strings.Count(b, ",")+1)
+	for len(b) > 0 {
+		var e string
+		e, b, _ = strings.Cut(b, ",")
 		ip := net.ParseIP(e)
 		if ip == nil {
 			return errors.New("dns: svcbipv6hint: bad ip")
 		}
 		if ip.To4() != nil {
 			return errors.New("dns: svcbipv6hint: expected ipv6, got ipv4-mapped-ipv6")
 		}
-		dst[i] = ip
+		hint = append(hint, ip)
 	}
-	s.Hint = dst
+	s.Hint = hint
 	return nil
 }