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Re: [paho-dev] Mqtt Paho - Trying to publish while broker is unreachable

Hi Roger,

just FYI, in RSMB I used an "update" or command file, with the same syntax as the config file. This would be looked for every 5 seconds, executed if it existed, then deleted. I considered using an $SYS admin topic but didn't have good security at the time, so that seemed like too big a risk.

I like the method of issuing commands via MQTT to a $SYS admin topic. That way you can use any MQTT client.


On 23/01/14 12:52, Roger Light wrote:
Hi Ian,

Dynamic bridges in mosquitto - yes definitely. I've not done it before
because I was considering what control mechanism to use.



On Thu, Jan 23, 2014 at 10:51 AM, Ian Craggs
<icraggs@xxxxxxxxxxxxxxxxxxxxxxx> wrote:

my RSMB broker (for which the code is in the Mosquitto project) has dynamic
bridges (and has had for several years).

Your suggestion is interesting.  If we published to a broker topic (possibly
prefixed by a $ as alternative behaviour is allowed in the 3.1.1 spec), then
a normal MQTT application could listen for any such message, and set up a
dynamic bridge to the remote system.  You can do this with RSMB today
(except that RSMB does not persist messages to disk so messages are lost
over a restart).

Dynamic bridges is a feature I was thinking of asking if Roger wanted to add
to Mosquitto.

This is an option I had previously thought of rather than implementing
offline buffering in the clients.  But given that very simple offline
buffering should be easy to add, both approaches could have their place.
Do you agree?


On 22/01/14 12:50, Paul Fremantle wrote:


That brings up an interesting question: If I do the model you suggest, then
the local mosquitto broker must have a hard-coded definition of the remote
broker. That is ok in many cases, but in general it might be nice to have a
way of specifying the address of the broker in the topic name:

e.g. instead of just topicA/topicB, put mqtt://
at which point my local broker will know this needs to go to the broker

This then becomes a bit like SMTP, where I config my local mail client to
talk to my well-known, trusted, available SMTP server, and it then does the
onward forwarding of my mail to the correct SMTP server for the recipient.


On 22 January 2014 09:32, Ian Craggs <icraggs@xxxxxxxxxxxxxxxxxxxxxxx>
Hi Pablo,

the short answer is that you have to handle the situation by yourself.
Having some buffering capability in the client is something that you are not
alone in asking for.  I'll make sure to add that to our requirements.

One way you can address this, is, as you point out, with a local Mosquitto
broker and a bridge.


On 21/01/14 21:31, Pablo Lopez wrote:

Hi all paho-dev members.

This is my first (baby) step in the "Internet of things" world, and I'm
having a hard time with it :)

Let me introduce myself : I'm Pablo, a french developer who is trying to
connect raspberry pi sensors to a central server to process sensors values.

But I'm having a hard time handling WiFi instability in my environment.

So I'm copying here a message I already put in the open on StackOverflow

Thank you for any help you could provide.

I'm going back to the Java Paho source code to try answering my question
by myself ;)

I'm begininng to use Mqtt and I have a hard time with handling an
unreliable network. I'm using a Paho Java Client (in groovy) to publish
messages to a distant Mosquitto Broker.

Is there a way, when the broker is unreachable, to have the Paho client
persist the message and automatically re-connect to the broker and publish
the locally stored messages ? Do I have to handle everything myself, using
for example a local broker ?

Here is my client building code

     String pe
Dir = config['persistence-dir'] ?: System.getProperty('')
     def persistence = new MqttDefaultFilePersistence(persistenceDir)
     client = new MqttClient(uri, clientId, persistence)
     options = new MqttConnectOptions()
     if (config.password) {
         options.setPassword(config.password as

And my publish code

   def message = new MqttMessage(Json.encode(outgoingMessage).getBytes())
     try {
     def topic = client.getTopic('processMsg')
     def token = topic.publish(message)
     if (client) {


Pablo Lopez
email & gtalk : plopez@xxxxxxxx / mob: +33-
Xebia, Software Development Done Right.

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Paul Fremantle
Part-time PhD student - School of Computing
email: paul.fremantle@xxxxxxxxxx, paul@xxxxxxxxxxxxx
twitter: pzfreo / skype: paulfremantle / blog:
CTO and Co-Founder, WSO2
OASIS WS-RX TC Co-chair, Apache Member
07740 199 729

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