Use strings.Cut() instead of string.SplitN() (#4049)

strings.Cut() generates less garbage as it does not allocate the slice to hold parts.

baggage/baggage.go

@@ -289,45 +289,37 @@ func parseMember(member string) (Member, error) {
 		props      properties
 	)
 
-	parts := strings.SplitN(member, propertyDelimiter, 2)
-	switch len(parts) {
-	case 2:
+	keyValue, properties, found := strings.Cut(member, propertyDelimiter)
+	if found {
 		// Parse the member properties.
-		for _, pStr := range strings.Split(parts[1], propertyDelimiter) {
+		for _, pStr := range strings.Split(properties, propertyDelimiter) {
 			p, err := parseProperty(pStr)
 			if err != nil {
 				return newInvalidMember(), err
 			}
 			props = append(props, p)
 		}
-		fallthrough
-	case 1:
-		// Parse the member key/value pair.
+	}
+	// Parse the member key/value pair.
 
-		// Take into account a value can contain equal signs (=).
-		kv := strings.SplitN(parts[0], keyValueDelimiter, 2)
-		if len(kv) != 2 {
-			return newInvalidMember(), fmt.Errorf("%w: %q", errInvalidMember, member)
-		}
-		// "Leading and trailing whitespaces are allowed but MUST be trimmed
-		// when converting the header into a data structure."
-		key = strings.TrimSpace(kv[0])
-		var err error
-		value, err = url.QueryUnescape(strings.TrimSpace(kv[1]))
-		if err != nil {
-			return newInvalidMember(), fmt.Errorf("%w: %q", err, value)
-		}
-		if !keyRe.MatchString(key) {
-			return newInvalidMember(), fmt.Errorf("%w: %q", errInvalidKey, key)
-		}
-		if !valueRe.MatchString(value) {
-			return newInvalidMember(), fmt.Errorf("%w: %q", errInvalidValue, value)
-		}
-	default:
-		// This should never happen unless a developer has changed the string
-		// splitting somehow. Panic instead of failing silently and allowing
-		// the bug to slip past the CI checks.
-		panic("failed to parse baggage member")
+	// Take into account a value can contain equal signs (=).
+	k, v, found := strings.Cut(keyValue, keyValueDelimiter)
+	if !found {
+		return newInvalidMember(), fmt.Errorf("%w: %q", errInvalidMember, member)
+	}
+	// "Leading and trailing whitespaces are allowed but MUST be trimmed
+	// when converting the header into a data structure."
+	key = strings.TrimSpace(k)
+	var err error
+	value, err = url.QueryUnescape(strings.TrimSpace(v))
+	if err != nil {
+		return newInvalidMember(), fmt.Errorf("%w: %q", err, value)
+	}
+	if !keyRe.MatchString(key) {
+		return newInvalidMember(), fmt.Errorf("%w: %q", errInvalidKey, key)
+	}
+	if !valueRe.MatchString(value) {
+		return newInvalidMember(), fmt.Errorf("%w: %q", errInvalidValue, value)
 	}
 
 	return Member{key: key, value: value, properties: props, hasData: true}, nil