Hi Roger,
Thanks for your example, it gave me helpful clues to improve my code
elsewhere.
I totally agree with you, it depends on the requirements. Maybe it is
better to state my requirements more precisely:
In your example your client's publish depends on the "on_message event".
In my client publish and subscribe should be independent of each other
but they should share the same loop-method (in other words, the same
connection to the broker). The client should listen on its socket for
inbound messages but the listener should not halt the whole program. If
a message arrives, my on_message-callback-function transfers this
message to an external message-handler object, which interprets the
content and does further processing, but this is not relevant for the
client. And finally, an external event (function call) should always be
able to trigger a publish.
A pattern would be the IA91 Java client provided by IBM. The client
connects to the broker, topics can be subscribed and while the client is
publishing messages other messages from the broker can be received.
So, my client should only be responsible for receiving and sending
messages but it should be able to do both at the same time. External
modules can trigger a publish by calling the client's publish-method
(together with a reference to a message-object) and inbound messages get
transferred to another module, let's call it MessageHandler. And for the
final step of the project it is necessary to run the whole client in at
least one thread independent from the main process. Because my client is
only a smaller part of a project und should not affect the other
modules. Therefore an exclusive usage of the main() isn't possible.
I know this is not a very technical description, but rather a first
approach to summarize the functionallity in writing. Please tell me, if
something needs further explanation (perhaps with UML).
Rene
Am 05.03.2012 10:42, schrieb Roger Light:
Hi Rene,
How you create a client that does both publish and subscribe really
depends on what you need to achieve. I've created a simple C++ example
that does both publish and subscribe. It subscribes to a celsius
temperature feed, converts the temperature into farenheit and
republishes the same data. You can see this example at
https://bitbucket.org/oojah/mosquitto/src/d22f87ef34f0/examples/temperature_conversion
Cheers,
Roger
On Sat, Mar 3, 2012 at 1:49 PM, Rene Lösch<[email protected]> wrote:
Hello,
I'm looking for some help building a MQTT client which combines both,
subscription-functionality and publish-functionality. I'm using the
mosquitto C++ wrapper for mosquitto lib and I have already a prototype which
is able to do that. The client-loop-method together with the do-while-loop
is processed by a separated thread, but I'm unsure if that is the right way.
My only clues are Roger's sources for a single pub_client and sub_client
written in C.
Does someone have a "construction manual" for me or provide a small
setp-by-step guide how to build such a client?
Any advice on ways how to combine these functionalities is welcome, also for
language C.
Thanks,
Rene
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