Re: [mosquitto-dev] Interoperability between V3.1 and V5

[Ben Hardill <hardillb@xxxxxxxxx>]

Shared subscriptions while being part of the V5 spec doesn't actually 
require anything client side, it's all down to the broker.So as long as 
your clients subscribe with the correct topic prefix it should just work 
iirc.

In fact there are a couple brokers with their own slightly different 
prefix implementations available before v5 became available.

On 04/08/2021 20:21, Steve Prior wrote:
> Thanks,
>
> I actually did figure that out  after being confused about "P2" meaning 
> v3.1.1.
>
> What I'm most interested in at the moment is the shared 
> subscription/load balancing feature.  I thought I might have seen 
> mention that this might work with a v3.1.1 client as long as the 
> mosquitto broker supports it - is this true?  I've got Arduino/ESP8266 
> IOT devices which use the PubSub library which does not have v5 and 
> won't soon.  It's possible that I'd want some of them to publish to a 
> topic that is subscribed to from load balanced handlers, though also it 
> sounds like the $share/group/topic might only need to be done by the 
> subscriber and the publisher might just need to publish to topic and 
> could still be v3.1.1?
>
> Steve
>
> On 8/4/2021 12:29 PM, Roger Light wrote:
> > Hi Steve,
> >
> > The log message on connect is:
> >
> > New client connected from <ip>:<port> as <client id> (p<protocol>,
> > c<clean session/start>, k<keepalive>, u'<username>')
> >
> > The protocol value currently shows: 5 for MQTT v5.0, 2 for MQTT
> > v3.1.1, and 1 for MQTT v3.1. I'm fixing that so it will be 5, 4, and 3
> > respectively to match the protocol assigned number.
> >
> > Regards,
> >
> > Roger
> >
> >
> > On Sun, 1 Aug 2021 at 06:08, Steve Prior <sprior@xxxxxxxxxxxx> wrote:
> > > With log_type all on a test mosquitto server I don't see any way to 
> > > determine
> > > what protocol version a client used to connect to the broker.  Is 
> > > there any way
> > > on the server to verify that a client is using a given protocol 
> > > version? This
> > > will become important to me later when I try to change the protocol 
> > > version in
> > > the c library from SWI-Prolog.
> > >
> > > Steve
> > >
> > > On 7/29/2021 5:39 AM, Roger Light wrote:
> > > > Hi Steve,
> > > >
> > > > That's correct. The only caveat is that when MQTT v5 clients publish
> > > > messages that have MQTT v5 properties attached those properties won't
> > > > be passed to the v3.1/v3.1.1 clients of course.
> > > >
> > > > Regards,
> > > >
> > > > Roger
> > > >
> > > > On Thu, 29 Jul 2021 at 06:28, Steve Prior <sprior@xxxxxxxxxxxx> wrote:
> > > > > I'm starting to move from v3.1 to v5 and wanted to confirm that 
> > > > > v3.1 clients can
> > > > > interoperate with v5 clients through Mosquitto (both sides can 
> > > > > publish and
> > > > > subscribe to the other versions messages), correct?
> > > > >
> > > > > Steve
> > > > >
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