ZeroMQ Lost Messages with PHP Subscriber

Question

i'm using zeromq with php bindings to connect to the zmq module in Freeswitch (a VOIP Software Switch).

Short: i'm loosing Events. Long: The zmq module in Freeswitch is implemented in c++ as publisher. My PHP Code is as follows:

<?php
  $context = new ZMQContext();

  echo "connect to freeswitch zmq module...";
  $sub = new ZMQSocket($context, ZMQ::SOCKET_SUB);
  $sub->setSockOpt(ZMQ::SOCKOPT_SUBSCRIBE,"");
  $sub->connect("tcp://192.168.20.73:5556");
  $hwm = $sub->getSockOpt(ZMQ::SOCKOPT_HWM);
  echo "ok.hwm: $hwm\n";

  echo "looping\n";
  while(1) {
  $data = $sub->recv();
  $d = json_decode($sub->recv(),TRUE);
  $event = $d["Event-Name"];
  $date = $d["Event-Date-Local"];
  $ts = $d["Event-Date-Timestamp"];
  $msgnr = $d["ZMQ-Msg-Cnt"];
  echo "PHP: $date msg# $msgnr $ts received $event\n";
}
?>

ZMQ-Msg-Cnt is a sequence number i've build into the zmq module in freeswitch. I can see that every 2nd message is lost. tcpdump shows that the message is received by zmq.

I've converted the PHP Code into C and now i'm able to receive every message. C:

#include "zhelpers.h"
#include "cJSON.h"

int main (void)
{
    void *context = zmq_init (1);

    void *subscriber = zmq_socket (context, ZMQ_SUB);
    zmq_connect (subscriber, "tcp://192.168.20.73:5556");
    zmq_setsockopt (subscriber, ZMQ_SUBSCRIBE, "", 0);

    while (1) {
        char *string = s_recv (subscriber);

        cJSON *root = cJSON_Parse(string);
        int msgcnt = cJSON_GetObjectItem(root,"ZMQ-Msg-Cnt")->valueint;

        printf("C: %s msg# %s %s received %s\n",
            cJSON_GetObjectItem(root,"Event-Date-Local")->valuestring,
            cJSON_GetObjectItem(root,"ZMQ-Msg-Cnt")->valuestring,
            cJSON_GetObjectItem(root,"Event-Date-Timestamp")->valuestring,
            cJSON_GetObjectItem(root,"Event-Name")->valuestring
        );
        cJSON_Delete(root);
        free (string);
    }

zmq_close (subscriber);
zmq_term (context);
return 0;
}

Is there anything wrong with the PHP Code ? Are there any tricks/must-do/hints for PHP ?

Thanks in advance, gerald weber

Answer 1

You are calling the recv function twice, thus it is loading one message, skipping any processing on it, then loading the second one:

$data = $sub->recv();
// This is your first message, called in a blocking mode

$d = json_decode($sub->recv(),TRUE);
// and here's your second one, called in a non-blocking mode

Change these two lines to just one:

$d = json_decode($sub->recv());