code: public void readHeaderTo(OutputStream os) throws IOException {
          position = 0;
          byte[] buf = new byte[(int)responseBodyStart];
          int c = read(buf,0,buf.length);
          if(c != -1) {
              os.write(buf,0,c);
          }
      }
docs: /*
  Like 'readFullyTo', but only reads the header-part.
  Starts from the beginning each time it is called.