Messages not getting sent via ZMQ - php

Question

Currently, i am trying a simple code of sending/receiving messages using ZMQ. The code is as below
/* Create new queue object, there needs to be a server at the other end */
$queue = new ZMQSocket(new ZMQContext(), ZMQ::SOCKET_REQ);
$queue->connect("tcp://127.0.0.1:5555");
/* Assign socket 1 to the queue, send and receive */
$retries = 5;
$sending = true;
/* Start a loop */
do {
try {
/* Try to send / receive */
if ($sending) {
echo "Sending message\n";
$queue->send("This is a message", ZMQ::MODE_NOBLOCK);
$sending = false;
} else {
echo "Got response: " . $queue->recv(ZMQ::MODE_NOBLOCK) . "\n";
echo 'Complete';
break;
}
} catch (ZMQSocketException $e) {
/* EAGAIN means that the operation would have blocked, retry */
if ($e->getCode() === ZMQ::ERR_EAGAIN) {
echo " - Got EAGAIN, retrying ($retries)\n";
} else {
die(" - Error: " . $e->getMessage());
}
}
/* Sleep a bit between operations */
usleep(5);
} while (--$retries);
When i run this script in console, my output is
Sending message
Got response:
Complete
I believe that though there are no errors thrown, but still my message is not actually sent. I also ran netstat command but i didn't found any process listening on port 5555. Ideally there should be one(current). But no exception is thrown while making connection.
Is there something which i am missing?

Answer 1

When you say no process is listening on port 5555, it probably means that your server is not up and running. Your client will not throw any errors even if there is no server, it just sets up and waits for the server to come online (with your particular setup here, at least).
In this case, since you're using non-blocking mode, it'll send your message on the first pass through the loop (why are you sending the message in the loop at all?), but it won't actually send anything because the server isn't there. Then it'll attempt to receive on the second pass through the loop, but since the socket isn't ready to receive it looks like it'll just fail silently, without throwing an exception. Since no exception is thrown, it gets to your break statement, quits the loop, and you're done.
First things first, your send call should happen before the loop, it's something you want to do only once.
Then, when you recv, store the result in a variable and test for emptiness. Leave the try/catch code. The result should be something like this:
/* Create new queue object, there needs to be a server at the other end */
$queue = new ZMQSocket(new ZMQContext(), ZMQ::SOCKET_REQ);
$queue->connect("tcp://127.0.0.1:5555");
/* Assign socket 1 to the queue, send and receive */
$retries = 5;
echo "Sending message\n";
$queue->send("This is a message", ZMQ::MODE_NOBLOCK);
/* Start a loop */
do {
try {
/* Try to receive */
$response = $queue->recv(ZMQ::MODE_NOBLOCK);
if (!empty($response)) {
echo "Got response: " . $response . "\n";
echo 'Complete';
break;
}
else {
echo "we probably haven't even sent the original request yet, retrying ($retries)\n";
}
}
catch (ZMQSocketException $e) {
/* EAGAIN means that the operation would have blocked, retry */
if ($e->getCode() === ZMQ::ERR_EAGAIN) {
echo " - Got EAGAIN, retrying ($retries)\n";
} else {
die(" - Error: " . $e->getMessage());
}
}
/* Sleep a bit between operations */
usleep(5);
} while (--$retries);
echo "END OF LINE";
... keep in mind this is a minor fix to the client code that makes it behave a little more rationally, I still believe your actual problem is that the server isn't running.

Answer 2

Please add the server code. You are showing the client code. Since the problem seems to be in the server, and you also state that the server is not visible with netstat, the problem is most probably there.