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[paho-dev] MQTT C client for Embedded Systems

Hello all,

I've started putting together some notes around the design of an MQTT C client for embedded systems, as we're starting to be asked for such a thing.  Examples environments are mbed ( and FreeRTOS (

I'm using a wiki page at:

Any input welcome.

To Frank in particular, some questions/observations.

1) API style.  The FreeRTOS guy we've talked to named the async API as most natural for that OS.  As a result, I was thinking that we could go with async only, but you brought up the sync API too.  The sync API could run as a layer over the async API (do operation, then wait for completion), but that wouldn't necessarily help if the goal was to be single-threaded.  Is that what you are suggesting with a synchronous API - no background threads?

2) Memory allocation.  The current C client already redefines malloc/free to its own functions.  We could use the same approach and implement our own de/allocation from a static buffer if static memory only was allowed.  (On the other hand, if we could minimize or eliminate dynamic allocation entirely, that would be even better.  I think some experiments are in order).

3) The API has to be able to pass the needed data to the underlying layer that implements say networking.  If the needs of one layer are different from another, we may need different parameters at the MQTT API layer - I'm thinking about create/connect in particular here.  Any particular strategies for handling this?  (void pointers to an arbitrary structures seem a bit abstract).


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