add vendor data

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

@@ -0,0 +1,41 @@
+package httpsfv
+
+import (
+	"errors"
+	"io"
+	"time"
+)
+
+var ErrInvalidDateFormat = errors.New("invalid date format")
+
+// marshalDate serializes as defined in
+// https://httpwg.org/specs/rfc9651.html#ser-date.
+func marshalDate(b io.StringWriter, i time.Time) error {
+	_, err := b.WriteString("@")
+	if err != nil {
+		return err
+	}
+
+	return marshalInteger(b, i.Unix())
+}
+
+// parseDate parses as defined in
+// https://httpwg.org/specs/rfc9651.html#parse-date.
+func parseDate(s *scanner) (time.Time, error) {
+	if s.eof() || s.data[s.off] != '@' {
+		return time.Time{}, &UnmarshalError{s.off, ErrInvalidDateFormat}
+	}
+	s.off++
+
+	n, err := parseNumber(s)
+	if err != nil {
+		return time.Time{}, &UnmarshalError{s.off, ErrInvalidDateFormat}
+	}
+
+	i, ok := n.(int64)
+	if !ok {
+		return time.Time{}, &UnmarshalError{s.off, ErrInvalidDateFormat}
+	}
+
+	return time.Unix(i, 0), nil
+}