if !owned {
		header = w.handlerHeader
	}
	var excludeHeader map[string]bool
	delHeader := func(key string) {
		if owned {
			header.Del(key)
			return
		}
		if _, ok := header[key]; !ok {
			return
		}
		if excludeHeader == nil {
			excludeHeader = make(map[string]bool)
		}
		excludeHeader[key] = true
	}
	var setHeader extraHeader

	if !ok {
		return r
	}
	return &excludedReader{r, 0, int64(cmd.Dataoff), int64(cmd.Dataoff + cmd.Datasize)}
}

// excludedReader wraps an io.Reader. Reading from it returns the bytes from
// the underlying reader, except that when the byte offset is within the
// range between start and end, it returns zero bytes.
type excludedReader struct {
	r          io.Reader
	off        int64 // current offset

		{12, 24, []string{"0123456789", "ab\x00\x00\x00\x00\x00\x00\x00\x00", "\x00\x00\x00\x00"}},   // end
	}
	p := make([]byte, 10)
	for _, test := range tests {
		r := &excludedReader{strings.NewReader(s), 0, test.start, test.end}
		for _, res := range test.results {
			n, err := r.Read(p)
			if err != nil {
				t.Errorf("read failed: %v", err)
			}
			if n != len(res) {