add vendor data

vendor/github.com/dunglas/httpsfv/key.go

@@ -0,0 +1,81 @@
+package httpsfv
+
+import (
+	"errors"
+	"fmt"
+	"io"
+)
+
+// ErrInvalidKeyFormat is returned when the format of a parameter or dictionary key is invalid.
+var ErrInvalidKeyFormat = errors.New("invalid key format")
+
+// isKeyChar checks if c is a valid key characters.
+func isKeyChar(c byte) bool {
+	if isLowerCaseAlpha(c) || isDigit(c) {
+		return true
+	}
+
+	switch c {
+	case '_', '-', '.', '*':
+		return true
+	}
+
+	return false
+}
+
+// checkKey checks if the given value is a valid parameter key according to
+// https://httpwg.org/specs/rfc9651.html#param.
+func checkKey(k string) error {
+	if len(k) == 0 {
+		return fmt.Errorf("a key cannot be empty: %w", ErrInvalidKeyFormat)
+	}
+
+	if !isLowerCaseAlpha(k[0]) && k[0] != '*' {
+		return fmt.Errorf("a key must start with a lower case alpha character or *: %w", ErrInvalidKeyFormat)
+	}
+
+	for i := 1; i < len(k); i++ {
+		if !isKeyChar(k[i]) {
+			return fmt.Errorf("the character %c isn't allowed in a key: %w", k[i], ErrInvalidKeyFormat)
+		}
+	}
+
+	return nil
+}
+
+// marshalKey serializes as defined in
+// https://httpwg.org/specs/rfc9651.html#ser-key.
+func marshalKey(b io.StringWriter, k string) error {
+	if err := checkKey(k); err != nil {
+		return err
+	}
+
+	_, err := b.WriteString(k)
+
+	return err
+}
+
+// parseKey parses as defined in
+// https://httpwg.org/specs/rfc9651.html#parse-key.
+func parseKey(s *scanner) (string, error) {
+	if s.eof() {
+		return "", &UnmarshalError{s.off, ErrInvalidKeyFormat}
+	}
+
+	c := s.data[s.off]
+	if !isLowerCaseAlpha(c) && c != '*' {
+		return "", &UnmarshalError{s.off, ErrInvalidKeyFormat}
+	}
+
+	start := s.off
+	s.off++
+
+	for !s.eof() {
+		if !isKeyChar(s.data[s.off]) {
+			break
+		}
+		s.off++
+	}
+
+	return s.data[start:s.off], nil
+}