Re: [paho-dev] Persistence (C Language)

[Ian Craggs <icraggs@xxxxxxxxxxxxxxxxxxxxxxx>]

Hi Jaspar,

when you use the MQTTCLIENT_PERSISTENCE_DEFAULT persistence option, the persistence_context should be set to a directory to use.  That's it.  The persistence capability is all done for you, you don't need to make any calls to the persistence layer yourself.

The MQTTCLIENT_PERSISTENCE_USER option is provided if you want to use another persistence library.  Here is an example of using Redis (https://bugs.eclipse.org/bugs/show_bug.cgi?id=410419).  In that case, you would implement the persistence interface, but you still wouldn't make the actual calls yourself, that would still be done by the Paho library.

I hope that is a good explanation.

Ian

On 12/30/2016 10:29 AM, Jaspar Löchte wrote:
> Hello there,
>
> I don’t know, if this is the “right” place to get help for using MQTT Paho.
>
> I am doing some research on persistent messaging with MQTT. I use the open source Mosquitto Broker in combination with MQTT-Paho for C language.
>
> I just set up a publisher (able to publish various messages on a topic) and a subscriber (to receive them).
>
> Now I wanted to get persistence mode. I tried to figure out how to use the functions from the MQTTClientPersistence.h Header.
>
> There is no example for using persistence header. I thought I need to use the client, then I thought about a void pointer.
> The other thing I am not sure about is, what to use as a persistence type?
> If I use MQTTCLIENT_PERSISTENCE_DEFAULT the paho script is doing everything for me and I dont need to open an own PersistenceClient? And for MQTTCLIENT_PERSISTENCE_USER I need to set up everything on my own? (with opening, and saving messages and all the stuff?)
>
> What ever I try, I get SIGSEGV in the Persistence_open function.
>
>
> void* handle;
> MQTTClient client;
> MQTTClient_persistence persist;
> MQTTClient_create(&client, config->host, config->cid, MQTTCLIENT_PERSISTENCE_DEFAULT, dir);
>
> // some connection options …
>
> //persist.popen((void**)&handle, config->cid, config->host, dir);
> persist.popen(&client, config->cid, config->host, dir);
>
> Thank you
>
> Jaspar Löchte
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--
Ian Craggs
icraggs@xxxxxxxxxx                 IBM United Kingdom
Paho Project Lead; Committer on Mosquitto