[zeromq-dev] SocketMonitor receives connection events after close event

[Auer, Jens]

Hi,

I am using a socket monitor to generate logging output for socket state events such as connection retries and disconnects. It basically works fine, but I am seeing connection retry events after receiving a close event. Is that correct? It feels strange that the socket tries to reconnect after it has been closed.

I have modified the example from the man page to be closer to my case. It basically opens a REQ socket, sends a message and then zmq_polls for an answer for 500ms. After that, the socket is closed and the monitor is read in a loop until ZMQ_EVENT_MONITOR_STOPPED is received. The events are logged to stdout as hex values:
./monitor
event: 2
event: 80
event: 4
event: 2
event: 80
event: 4
event: 2
event: 80
event: 4
event: 2
event: 80
event: 4
event: 400

>From what I see, the monitor receives multiple close events (80) and after the close event still connection retried (4) and connect delayed (2) events. Finally it receives the monitor close event. Is this expected?

The test code is:

#include <zmq.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>

//  Read one event off the monitor socket; return value and address
//  by reference, if not null, and event number by value. Returns -1
//  in case of error.

static int
get_monitor_event (void *monitor, int *value, char **address)
{
    //  First frame in message contains event number and value
    zmq_msg_t msg;
    zmq_msg_init (&msg);
    if (zmq_msg_recv (&msg, monitor, 0) == -1)
        return -1;              //  Interrupted, presumably
    assert (zmq_msg_more (&msg));

    uint8_t *data = (uint8_t *) zmq_msg_data (&msg);
    uint16_t event = *(uint16_t *) (data);
    if (value)
        *value = *(uint32_t *) (data + 2);

    //  Second frame in message contains event address
    zmq_msg_init (&msg);
    if (zmq_msg_recv (&msg, monitor, 0) == -1)
        return -1;              //  Interrupted, presumably
    assert (!zmq_msg_more (&msg));

    if (address) {
        uint8_t *data = (uint8_t *) zmq_msg_data (&msg);
        size_t size = zmq_msg_size (&msg);
        *address = (char *) malloc (size + 1);
        memcpy (*address, data, size);
        (*address)[size] = 0;
    }
    return event;
}

int main (void)
{
    void *ctx = zmq_ctx_new ();
    assert (ctx);

    //  We'll monitor these two sockets
    void *client = zmq_socket (ctx, ZMQ_REQ);
    assert (client);
    int reconnectivl = 100;
    int zero=0;
    zmq_setsockopt(client, ZMQ_RECONNECT_IVL, &reconnectivl, sizeof(int) );
zmq_setsockopt(client, ZMQ_LINGER, &reconnectivl, sizeof(int) );

    //  Socket monitoring only works over inproc://
    int rc = zmq_socket_monitor (client, "tcp://127.0.0.1:10099", ZMQ_EVENT_ALL);
    assert (rc == -1);
    assert (zmq_errno () == EPROTONOSUPPORT);

    //  Monitor all events on client and server sockets
    rc = zmq_socket_monitor (client, "inproc://monitor-client", ZMQ_EVENT_ALL);
    assert (rc == 0);

    //  Create two sockets for collecting monitor events
    void *client_mon = zmq_socket (ctx, ZMQ_PAIR);
zmq_setsockopt(client_mon, ZMQ_LINGER, &zero, sizeof(int) );
    assert (client_mon);

    //  Connect these to the inproc endpoints so they'll get events
    rc = zmq_connect (client_mon, "inproc://monitor-client");
    assert (rc == 0);

    //  Now do a basic ping test
    rc = zmq_connect (client, "tcp://127.0.0.1:10099");
    assert (rc == 0);

{
    zmq_msg_t msg;
    zmq_msg_init_size(&msg, 100);
    zmq_msg_send( &msg, client, ZMQ_SNDMORE);
}
{
    zmq_msg_t msg;
    zmq_msg_init_size(&msg, 100);
    zmq_msg_send( &msg, client, 0);
}

zmq_pollitem_t p[] = { {client, -1, ZMQ_POLLIN | ZMQ_POLLOUT | ZMQ_POLLERR, 0} };
zmq_poll(p, 1, 500);

    //  Close client and server
    zmq_close(client);

    //  Now collect and check events from both sockets
    int event = 0;
    do
    {
        event = get_monitor_event (client_mon, NULL, NULL);
        printf("event: %x\n", event);
    }
    while (event != ZMQ_EVENT_MONITOR_STOPPED);

    //  Close down the sockets
    zmq_close(client_mon);
    zmq_ctx_term (ctx);

    return 0 ; }

Best wishes,
  Jens

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Jens Auer | CGI | Software-Engineer
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