sS md5OfStream(InputStream in) ctex {
  if (in == null) ret "-";
  temp in;
  
  MessageDigest md5 = MessageDigest.getInstance("MD5");

  byte[] buf = new[65536];
  int l;
  while (true) {
    l = in.read(buf);
    if (l <= 0) break;
    md5.update(buf, 0, l);
  }
  
  ret bytesToHex(md5.digest());
}

Began life as a copy of #1016251