MQTT Service
# helpr
RobvanLopik
05/08/2023, 11:30 AMI wanted to use the Datacake package as an example for writing a general MQTT service. It turns out the Datacake code is much more complicated than I expected, especially the Networkmodule part. Could someone (@kasperl ?) explain to me the rationale for this. Second question: how would you implement subscribing to topics and receiving answers?
k
kasperl
05/08/2023, 3:48 PMYeah, the complexity in the implementation is a valid point. I wanted to build a service that would connect on demand and the NetworkModule handles that well. We use it for net.open/close.
kasperl
05/08/2023, 3:48 PMSo if two separate clients start at the same time, the share one connection to Datacake.
kasperl
05/08/2023, 3:49 PMOnce the last one goes away, we close down the connection.
kasperl
05/08/2023, 3:53 PMThere are multiple options for subscribing to topics and receiving answers. One is a polling approach and one is a pushing approach. It is probably nice to subscribe on the client and then maintain a simple map in the service (topic -> resource) and use the notification mechanism to push data to the clients that want the data.
kasperl
05/08/2023, 3:55 PMSo https://github.com/kasperl/toit-datacake/blob/main/src/service.toit#L164 is the resource you can call
notify_r
RobvanLopik
05/09/2023, 8:29 AMThanks for the info. The resource/notify is what I also came up with. For the complexity I will have to decide whether to try to understand it, or think of something simpler.
f
floitsch
05/09/2023, 8:44 AMThe Datacake package is a bit more sophisticated (as Kasper explained for several reasons).
If you just want to use MQTT, or have a simple example for using a different broker, then have a look at the Adafruit example: https://github.com/toitware/mqtt/blob/main/examples/adafruit.toit
r
RobvanLopik
05/09/2023, 9:14 AMThat stage I already passed; see: https://github.com/robvanlopik/toit-pharo
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floitsch
05/09/2023, 9:17 AMI see.
Nice.
r
RobvanLopik
05/09/2023, 9:19 AMNow I specifically want to have a base container to do the MQTT stuff and load different containers with services that talk to my Pharo systems through MQTT. In toit-pharo I expose for example I2C to the Pharo side, where I have code to run different I2C devices, but it makes more sense to move that over to the ESP32 side.
f
floitsch
05/09/2023, 9:20 AMSounds good.