static new ThreadLocal<SS> readHttpPageLinewise_extraHeaders;

static CloseableIterableIterator<S> readHttpPageLinewise(S url) ctex {
  SS extraHeaders = getAndClearThreadLocal(readHttpPageLinewise_extraHeaders);
  URLConnection con = openConnection(url);
  for (S key : keys(extraHeaders))
    con.setRequestProperty(key, extraHeaders.get(key));
  ret linesFromReader(utf8BufferedReader(con.getInputStream()));
}