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Re: [paho-dev] Mqtt Paho - Trying to publish while broker is unreachable 
Alex,
I'm not sure that we need a working group for this, at least to start with. The bridges in question here can act as perfectly normal MQTT clients, so a different protocol is not necessary. The changes I made to the protocol for bridging could be useful, but aren't essential. The control mechanisms could be broker specific, so not part of the protocol. I would be happy to join in any discussion though.
Just in case anyone was wondering why we didn't do buffering in the first place, it's because even a simple approach throws up these design questions:
1. what happens if you publish with a client object which has never connected, and never could connect because the uri was wrong? 
2. how often do you try reconnecting and when?
3. how do you manage the store of unprocessed messages?
Just thinking that a buffered layer could be built over the basic client... that could work well... 

Ian


On 23/01/14 13:08, Alexandros Kritikos wrote:

Since there is a lot of interest in this and people are eager to start discussing ways to do it, why don’t we set up an OASIS TC / eclipse group / whatever for bridging in general, to be released in the future as a supplementary certification? A control mechanism could be an MQTT based / namespace based / other ?

Alex

On 23 Ιαν 2014, at 2:52 μ.μ., Roger Light <roger@xxxxxxxxxx> wrote:


Hi Ian,

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

Cheers,

Roger

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

Paul,

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?

Ian


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

Ian

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://broker.freo.me/topicA/topicB
at which point my local broker will know this needs to go to the broker
broker.freo.me

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.

Paul


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

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.

Ian


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


http://stackoverflow.com/questions/21269331/mqtt-paho-trying-to-publish-while-broker-is-unreachable

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
rsistence
Dir = config['persistence-dir'] ?: System.getProperty('java.io.tmpdir')
    def persistence = new MqttDefaultFilePersistence(persistenceDir)
    client = new MqttClient(uri, clientId, persistence)
    client.setCallback(this)
    options = new MqttConnectOptions()
    if (config.password) {
        options.setPassword(config.password as
char[])
        options.setUserName(config.user)
    }
    options.setCleanSession(false)
    client.connect(options)

And my publish code

  def message = new MqttMessage(Json.encode(outgoingMessage).getBytes())
    try {
    client?.connect(options)
    def topic = client.getTopic('processMsg')
    message.setQos(1)
    def token = topic.publish(message)
    if (client) {
        client.disconnect()
    }

Thanks



--
Pablo Lopez
email & gtalk : plopez@xxxxxxxx / mob: +33-6.07.56.04.64
Xebia, Software Development Done Right.
http://blog.xebia.fr


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


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