add vendor data

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

@@ -0,0 +1,88 @@
+package httpsfv
+
+import (
+	"errors"
+	"strings"
+	"unicode"
+)
+
+// ErrInvalidStringFormat is returned when a string format is invalid.
+var ErrInvalidStringFormat = errors.New("invalid string format")
+
+// marshalString serializes as defined in
+// https://httpwg.org/specs/rfc9651.html#ser-string.
+func marshalString(b *strings.Builder, s string) error {
+	if err := b.WriteByte('"'); err != nil {
+		return err
+	}
+
+	for i := 0; i < len(s); i++ {
+		if s[i] <= '\u001F' || s[i] >= unicode.MaxASCII {
+			return ErrInvalidStringFormat
+		}
+
+		switch s[i] {
+		case '"', '\\':
+			if err := b.WriteByte('\\'); err != nil {
+				return err
+			}
+		}
+
+		if err := b.WriteByte(s[i]); err != nil {
+			return err
+		}
+	}
+
+	if err := b.WriteByte('"'); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// parseString parses as defined in
+// https://httpwg.org/specs/rfc9651.html#parse-string.
+func parseString(s *scanner) (string, error) {
+	if s.eof() || s.data[s.off] != '"' {
+		return "", &UnmarshalError{s.off, ErrInvalidStringFormat}
+	}
+	s.off++
+
+	var b strings.Builder
+
+	for !s.eof() {
+		c := s.data[s.off]
+		s.off++
+
+		switch c {
+		case '\\':
+			if s.eof() {
+				return "", &UnmarshalError{s.off, ErrInvalidStringFormat}
+			}
+
+			n := s.data[s.off]
+			if n != '"' && n != '\\' {
+				return "", &UnmarshalError{s.off, ErrInvalidStringFormat}
+			}
+			s.off++
+
+			if err := b.WriteByte(n); err != nil {
+				return "", err
+			}
+
+			continue
+		case '"':
+			return b.String(), nil
+		default:
+			if c <= '\u001F' || c >= unicode.MaxASCII {
+				return "", &UnmarshalError{s.off, ErrInvalidStringFormat}
+			}
+
+			if err := b.WriteByte(c); err != nil {
+				return "", err
+			}
+		}
+	}
+
+	return "", &UnmarshalError{s.off, ErrInvalidStringFormat}
+}