How can we be sure that a message has been sent

[amqp-node]

How can we be sure that a message has been sent

[squaremo]

You can use a feature of RabbitMQ called "confirmations" to find out if messages have arrived: http://www.rabbitmq.com/confirms.html

amqplib supports confirmations via ConfirmChannels. With a ConfirmChannel, #publish and #sendToQueue return a promise which is resolved when the message is acknowledged by the server (or rejected if it's nacked).

var ok = api.connect('amqp://localhost');
ok = ok.then(function(conn) {
    return conn.createConfirmChannel();
});
ok = ok.then(function(ch) {
    return ch.publish(...).then(function() { console.log("Acknowledged!"); });
});
ok.then(null, console.warn);

(That's in the current release. For future releases I've changed it so that #publish and #sendToQueue take a callback, rather than returning a promise)

[michaelklishin]

No other client has two separate functions for channel creation. Maybe it should be possible to enable confirms on a channel, like all other clients do? E.g. with Bunny

ch = conn.create_channel
ch.confirm_select

[squaremo]

No other client has two separate functions for channel creation. Maybe it should be possible to enable confirms on a channel, like all other clients do?

My reasoning is that you're either going to want to have confirms on or off from the get-go. The same goes for transactions, though I haven't implemented them.

[charlyz]

Thanks so much for you quick answer. My main concern is that if the channel is not found (or "cannot be used for whatever reasons") but try to publish something anyway, the channel error handler is triggered. If I understand correctly, I should keep track of all the messages I send. If a message is acknowledged then I can stop worrying about it. And if the channel error handler is triggered, I should re-send all the messages which have not been acknowledged. Am I right?

[michaelklishin]

@charlyz RabbitMQ log should be pretty clear about what causes the channel exception.

[charlyz]

@michaelklishin I guess :) My point is that it would be easier not to resolve the publish() promise if something goes wrong (channel closed, connection closed, earthquake, etc.) instead of triggering the channel error handler.

[squaremo]

And if the channel error handler is triggered, I should re-send all the messages which have not been acknowledged. Am I right?

Yes, although not getting an acknowledgment doesn't mean it hasn't been sent: the channel may have broken before the acknowledgment could be received. So it really depends on whether you are happier with the possibility of duplicates, or of missing messages.

[charlyz]

I see. We are not a banking company it should make it. Thanks for your help guys.