Re: [mosquitto-dev] Client receives PUBREC and MQTT disconnected

[Ian Craggs <icraggs@xxxxxxxxxxxxxxxxxxxxxxx>]

One reason could be that client library does not store MQTT state across 
application stops and restarts.

If the application is stopped when some MQTT QoS 2 exchanges are 
incomplete and the MQTT client library does not persist the inflight 
message state (to disk for example), there will be a mismatch between 
broker and client state.

The Paho Java and C (not embedded) clients do allow you to persist 
inflight data to disk, so that when the application is restarted, the 
state of inflight MQTT messages is restored, and this situation would 
not occur.

Ian

On 11/13/2015 01:50 AM, Khitai Pang wrote:
> Connecting with cleansession=true solved the problem, but all offline 
> messages are lost.
>
> Why is the client receiving a PUBREC that it doesn't know how to 
> handle?  What is going wrong here?
>
> Thanks
> Khitai
>
> On 2015/11/12 18:37, Ian Craggs wrote:
> > Have you tried connecting with cleansession=true to clean up the 
> > state for that client id?
> >
> > Ian
> >
> > On 11/12/2015 08:23 AM, Khitai Pang wrote:
> > > Here's what happened:
> > >
> > > _mosquitto_handle_pubrec handles the received PUBREC, then 
> > > _mosquitto_message_out_update updates the message's out status, but 
> > > in this function mosq->out_messages is NULL, so MOSQ_ERR_NOT_FOUND 
> > > is returned, _mosquitto_loop_rc_handle handles the response code, 
> > > since it's an error, finally _mosquitto_socket_close(mosq) is called.
> > >
> > > Regards
> > > Khitai
> > >
> > > On 2015/11/12 15:08, Khitai Pang wrote:
> > > > Got rc=6 in the ondisconenct callback.
> > > >
> > > > Regards
> > > > Khitai
> > > >
> > > > On 2015/11/12 14:43, Khitai Pang wrote:
> > > > > Hi,
> > > > >
> > > > > I am having problem with a particular MQTT client ID. When a 
> > > > > client connects to Mosquitto using this ID, it immediately 
> > > > > receives a PUBREC from the broker and then MQTT get disconnected:
> > > > >
> > > > > 2015-11-10 20:35:21.827 mqtt-test[58102:737651] === MQTT connected===
> > > > > 2015-11-10 20:35:22.329 mqtt-test[58102:737651] mosquitto log : 
> > > > > Client 362f23d0-8906-11e5-99da-005056355a83 received PUBREC (Mid: 58)
> > > > > 2015-11-10 20:35:22.454 mqtt-test[58102:737651] === MQTT 
> > > > > disconnected===
> > > > >
> > > > > Log on the broker side:
> > > > >
> > > > > ...
> > > > > testhost mosquitto[4911]: New client connected from ... as 
> > > > > 362f23d0-8906-11e5-99da-005056355a83 (c0, k120).
> > > > > testhost mosquitto[4911]: Socket error on client 
> > > > > 362f23d0-8906-11e5-99da-005056355a83, disconnecting.
> > > > > ...
> > > > >
> > > > > The broker is mosquitto 1.3.5.  The client uses libmosquitto in 
> > > > > mosquitto 1.4.4.
> > > > >
> > > > > Any help is appreciated.
> > > > >
> > > > >
> > > > > Regards,
> > > > > Khitai
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--
Ian Craggs
icraggs@xxxxxxxxxx                 IBM United Kingdom
Paho Project Lead; Committer on Mosquitto