[lwip-devel] [bug #48416] Problem with nonblocking connect

[Christian Prochaska]

URL:
  <http://savannah.nongnu.org/bugs/?48416>

                 Summary: Problem with nonblocking connect
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: cproc
            Submitted on: Tue 05 Jul 2016 06:29:25 PM GMT
                Category: sockets/netconn
                Severity: 3 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None
            lwIP version: git head

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Details:

I'm actually not using the most recent version, but from looking at the source
code the problem I'm having seems to still exist on the current git master
branch (4b136d631af0650247ab1bb21c7eb761d12960b6)

In 'lwip_netconn_do_connect()':

    ...

    case NETCONN_TCP:
      /* Prevent connect while doing any other action. */
      if (msg->conn->state == NETCONN_CONNECT) {
        msg->err = ERR_ALREADY;
      } else if (msg->conn->state != NETCONN_NONE) {
        msg->err = ERR_ISCONN;
      } else {
        setup_tcp(msg->conn);
        msg->err = tcp_connect(msg->conn->pcb.tcp,
API_EXPR_REF(msg->msg.bc.ipaddr),
          msg->msg.bc.port, lwip_netconn_do_connected);
        if (msg->err == ERR_OK) {
          u8_t non_blocking = netconn_is_nonblocking(msg->conn);
          msg->conn->state = NETCONN_CONNECT;

    ...

The problem occurred when the function was called for the second time when the
connection was already established. I would have expected an 'ERR_ISCONN'
status code, but instead tcp_connect() got called for a second time and
printed a 'tcp_connect: can only connect from state CLOSED' error message (the
actual state was ESTABLISHED).

The reason for the repeated call of 'tcp_connect()' was that
'msg->conn->state' was NETCONN_NONE, as set in 'lwip_netconn_do_connected()'
after the connection was established.

Perhaps a new netconn state 'NETCONN_CONNECTED' would be needed here, but I'm
not too familiar with lwip interna to be sure about that.




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