add vendor data

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

@@ -0,0 +1,105 @@
+package httpsfv
+
+import (
+	"encoding/hex"
+	"errors"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+type DisplayString string
+
+var ErrInvalidDisplayString = errors.New("invalid display string type")
+
+var notVcharOrSp = &unicode.RangeTable{
+	R16: []unicode.Range16{
+		{0x0000, 0x001f, 1},
+		{0x007f, 0x00ff, 1},
+	},
+	LatinOffset: 2,
+}
+
+// marshalSFV serializes as defined in
+// https://httpwg.org/specs/rfc9651.html#ser-string.
+func (s DisplayString) marshalSFV(b *strings.Builder) error {
+	if _, err := b.WriteString(`%"`); err != nil {
+		return err
+	}
+
+	for i := 0; i < len(s); i++ {
+		if s[i] == '%' || s[i] == '"' || unicode.Is(notVcharOrSp, rune(s[i])) {
+			b.WriteRune('%')
+			b.WriteString(hex.EncodeToString([]byte{s[i]}))
+
+			continue
+		}
+
+		b.WriteByte(s[i])
+	}
+
+	b.WriteByte('"')
+
+	return nil
+}
+
+// parseDisplayString parses as defined in
+// https://httpwg.org/specs/rfc9651.html#parse-display.
+func parseDisplayString(s *scanner) (DisplayString, error) {
+	if s.eof() || len(s.data[s.off:]) < 2 || s.data[s.off:2] != `%"` {
+		return "", &UnmarshalError{s.off, ErrInvalidDisplayString}
+	}
+	s.off += 2
+
+	var b strings.Builder
+	for !s.eof() {
+		c := s.data[s.off]
+		s.off++
+
+		switch c {
+		case '%':
+			if len(s.data[s.off:]) < 2 {
+				return "", &UnmarshalError{s.off, ErrInvalidDisplayString}
+			}
+			c0 := unhex(s.data[s.off])
+			if c0 == 0 {
+				return "", &UnmarshalError{s.off, ErrInvalidDisplayString}
+			}
+
+			c1 := unhex(s.data[s.off+1])
+			if c1 == 0 {
+				return "", &UnmarshalError{s.off, ErrInvalidDisplayString}
+			}
+
+			b.WriteByte(c0<<4 | c1)
+			s.off += 2
+		case '"':
+			r := b.String()
+			if !utf8.ValidString(r) {
+				return "", ErrInvalidDisplayString
+			}
+
+			return DisplayString(r), nil
+
+		default:
+			if unicode.Is(notVcharOrSp, rune(c)) {
+				return "", &UnmarshalError{s.off, ErrInvalidDisplayString}
+			}
+
+			b.WriteByte(c)
+		}
+	}
+
+	return "", &UnmarshalError{s.off, ErrInvalidDisplayString}
+}
+
+func unhex(c byte) byte {
+	switch {
+	case '0' <= c && c <= '9':
+		return c - '0'
+	case 'a' <= c && c <= 'f':
+		return c - 'a' + 10
+	default:
+		return 0
+	}
+}