var nf int64 // Size of fragment
		holeStart, holeEnd := sr.sp[0].Offset, sr.sp[0].endOffset()
		if sr.pos < holeStart { // In a data fragment
			nf = holeStart - sr.pos
			nf, err = io.CopyN(ws, sr.fr, nf)
		} else { // In a hole fragment
			nf = holeEnd - sr.pos
			if sr.physicalRemaining() == 0 {
				writeLastByte = true
				nf--
			}
			_, err = ws.Seek(nf, io.SeekCurrent)
		}

			if sw.physicalRemaining() == 0 {
				readLastByte = true
				nf--
			}
			_, err = rs.Seek(nf, io.SeekCurrent)
		} else { // In a data fragment
			nf = dataEnd - sw.pos
			nf, err = io.CopyN(sw.fw, rs, nf)
		}
		sw.pos += nf
		if sw.pos >= dataEnd && len(sw.sp) > 1 {
			sw.sp = sw.sp[1:] // Ensure last fragment always remains
		}
	}

	// Copy file to f, but also into h to double-check hash.
	if _, err := file.Seek(0, 0); err != nil {
		f.Truncate(0)
		return err
	}
	h := sha256.New()
	w := io.MultiWriter(f, h)
	if _, err := io.CopyN(w, file, size-1); err != nil {
		f.Truncate(0)
		return err
	}
	// Check last byte before writing it; writing it will make the size match
	// what other processes expect to find and might cause them to start

func (d *dotWriter) copyUntil(w io.Writer, buf *bytes.Buffer, sep string) error {
	i := bytes.Index(buf.Bytes(), []byte(sep))
	if i == -1 {
		return fmt.Errorf("couldn't find dot sep %q", sep)
	}
	_, err := io.CopyN(w, buf, int64(i+len(sep)))
	return err
}

type htmlFuncPrinter struct {
	w io.Writer
}

func (p htmlFuncPrinter) header(f *Func) {}