sort.Strings(features)
	sort.Strings(required)

	take := func(sl *[]string) string {
		s := (*sl)[0]
		*sl = (*sl)[1:]
		return s
	}

	for len(features) > 0 || len(required) > 0 {
		switch {
		case len(features) == 0 || (len(required) > 0 && required[0] < features[0]):
			feature := take(&required)
			if exceptionSet[feature] {
				// An "unfortunate" case: the feature was once

	if len(b) == 0 {
		return 0, nil
	}
	if len(f.ops) == 0 {
		return 0, errors.New("unexpected Write operation")
	}
	s, ok := f.ops[0].(string)
	if !ok {
		return 0, errors.New("unexpected Write operation")
	}

	if !strings.HasPrefix(s, string(b)) {
		return 0, testError{fmt.Errorf("got Write(%q), want Write(%q)", b, s)}
	}
	if len(s) > len(b) {
		f.ops[0] = s[len(b):]
	} else {
		f.ops = f.ops[1:]
	}

			eb.uint64(h.offset)
			h.Extra = append(h.Extra, buf[:]...)
		} else {
			b.uint32(h.CompressedSize)
			b.uint32(h.UncompressedSize)
		}

		b.uint16(uint16(len(h.Name)))
		b.uint16(uint16(len(h.Extra)))
		b.uint16(uint16(len(h.Comment)))
		b = b[4:] // skip disk number start and internal file attr (2x uint16)
		b.uint32(h.ExternalAttrs)
		if h.offset > uint32max {
			b.uint32(uint32max)
		} else {