url.c

    /* This was formerly done in transfer.c, but we better do it here */
    if((CURLE_SEND_ERROR == result) && conn->bits.reuse) {
      /* This was a re-use of a connection and we got a write error in the
       * DO-phase. Then we DISCONNECT this connection and have another attempt
       * to CONNECT and then DO again! The retry cannot possibly find another
       * connection to re-use, since we only keep one possible connection for
       * each.  */

      infof(data, "Re-used connection seems dead, get a new one\n");

      conn->bits.close = TRUE; /* enforce close of this connection */
      result = Curl_done(&conn, result, FALSE); /* we are so done with this */

      /* conn may no longer be a good pointer */

      /*
       * According to bug report #1330310. We need to check for
       * CURLE_SEND_ERROR here as well. I figure this could happen when the
       * request failed on a FTP connection and thus Curl_done() itself tried
       * to use the connection (again). Slight Lack of feedback in the report,
       * but I don't think this extra check can do much harm.
       */
      if((CURLE_OK == result) || (CURLE_SEND_ERROR == result)) {
        bool async;
        bool protocol_done = TRUE;

        /* Now, redo the connect and get a new connection */
        result = Curl_connect(data, connp, &async, &protocol_done);
        if(CURLE_OK == result) {
          /* We have connected or sent away a name resolve query fine */

          conn = *connp; /* setup conn to again point to something nice */
          if(async) {
            /* Now, if async is TRUE here, we need to wait for the name
               to resolve */
            result = Curl_wait_for_resolv(conn, NULL);
            if(result)
              return result;

            /* Resolved, continue with the connection */
            result = Curl_async_resolved(conn, &protocol_done);
            if(result)
              return result;
          }

          /* ... finally back to actually retry the DO phase */
          result = conn->handler->do_it(conn, done);
        }
      }
    }

    if((result == CURLE_OK) && *done)
      /* do_complete must be called after the protocol-specific DO function */
      do_complete(conn);
  }
  return result;
}

CURLcode Curl_do_more(struct connectdata *conn)
{
  CURLcode result=CURLE_OK;

  if(conn->handler->do_more)
    result = conn->handler->do_more(conn);

  if(result == CURLE_OK)
    /* do_complete must be called after the protocol-specific DO function */
    do_complete(conn);

  return result;
}

/* Called on connect, and if there's already a protocol-specific struct
   allocated for a different connection, this frees it that it can be setup
   properly later on. */
void Curl_reset_reqproto(struct connectdata *conn)
{
  struct SessionHandle *data = conn->data;
  if(data->state.proto.generic && data->state.current_conn != conn) {
    free(data->state.proto.generic);
    data->state.proto.generic = NULL;
  }
  data->state.current_conn = conn;
}