transfer.c

              int writesockindex,  /* socket index to write to, it may very
                                      well be the same we read from. -1
                                      disables */
              curl_off_t *writecountp /* return number of bytes written or
                                       NULL */
              )
{
  struct connectdata *conn = (struct connectdata *)c_conn;
  if(!conn)
    return CURLE_BAD_FUNCTION_ARGUMENT;

  curlassert(sockindex <= 1);

  /* now copy all input parameters */
  conn->sockfd = sockindex==-1?-1:conn->sock[sockindex];
  conn->size = size;
  conn->bits.getheader = getheader;
  conn->bytecountp = bytecountp;
  conn->writesockfd = writesockindex==-1?-1:conn->sock[writesockindex];
  conn->writebytecountp = writecountp;

  return CURLE_OK;

}