| Re: [paho-dev] When to send publish acknowledgements |
"Allan Stockdill-Mander" <asm@xxxxxxxxxx> writes: > I've had a PR for the v5 golang client > https://github.com/eclipse/paho.golang/pull/52 that changes the > behaviour so that Publish messages are only acknowledged (the puback > or pubrec sent) after the associated message handlers have been > invoked and returned. I can see a benefit to doing this for the > application as you effectively don't need to have incoming message > persistence, until you have processed the message if the client dies > and reconnects the server should resend any unacked messages. I don't see that spec bit as being about this question. The real question is if the ack is supposed to come from the MQTT processing step or from a client having done something and committed the results to stable storage. An analog is TCP acks: the TCP implementation (typically in kernel) acks bytes, nad merely places them in a buffer for the process to read or not get around to reading. So the big Q is what does the spec stay about when something should be acked: when the MQTT code has received it when it has been read/accessed by some user code when that user code has decided that it has finished the processing that it wants to do My overall sense, very very fuzzy and take it with a big grain of salt, is that pub/ack is about network loss only, and is not meant to support some sort of transaction commit all the way to the processing code. It is then a good question how to build a system that does what you want, and perhaps the answer is to send a higher-level ack as an MQTT message. Hope this helps at least explain why I'm not quite following you.
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