Re: [mosquitto-dev] Order of "topic" rules in bridge definitions

[Ian Craggs <icraggs@xxxxxxxxxxxxxxxxxxxxxxx>]

Hi Jos,

if it's anything like when I "designed" this in RSMB, then the ordering 
should be significant, for two reasons:

1) it's simpler to implement
2) it provides predictable behaviour -- the first topic item in the list 
takes precedence

Not sophisticated, but it's meant for low footprint servers.

Ian

On 01/21/2015 11:56 AM, Jos Vos wrote:
> Hi,
>
> I'm doing some experiments with bridging.  When doing this, one question
> remained unanswered from the documentation: how are multiple topic rules
> in a bridge definition interpreted if their patterns are not mutually
> exclusive?
>
> What I have: 3 mosquitto servers, think of them as the left, middle
> and right server, and the middle server is setting up a bridge to
> both the left and right server.  I first tried this:
>
>    connection leftbridge
>    address 127.0.0.1:1883
>    cleansession true
>    topic # in 0 bridged/fromleft/ ""
>    topic # out 0 "" bridged/frommiddle/
>
>    connection rightbridge
>    address 127.0.0.1:9883
>    cleansession true
>    topic # in 0 bridged/fromright/ ""
>    topic # out 0 "" bridged/frommiddle/
>
> This works, that is, all messages appear on all servers and are
> prefixed by every bridge path they have passed.  So, left messages
> in "tst" arrive at the right as "bridged/frommiddle/bridged/fromleft/tst".
>
> Now I wanted to avoid the double prefixes and, after some attempts, I
> ended up with this config:
>
>    connection leftbridge
>    address 127.0.0.1:1883
>    cleansession true
>    topic # in 0 bridged/fromleft/ ""
>    topic # out 0 bridged/fromright/ bridged/fromright/
>    topic # out 0 "" bridged/frommiddle/
>
>    connection rightbridge
>    address 127.0.0.1:9883
>    cleansession true
>    topic # in 0 bridged/fromright/ ""
>    topic # out 0 bridged/fromleft/ bridged/fromleft/
>    topic # out 0 "" bridged/frommiddle/
>
> Now this seems to work, but as soon as I exchange the "out" rules in
> each bridge, I see the old behavior, so the order does matter.
>
> My question is: can I rely on the matching order for topics (the
> first match determines the policy) and in this way safely list
> exceptions *before* the generic "" rule?
>
> Thx,
>
> --
> --    Jos Vos <jos@xxxxxx>
> --    X/OS Experts in Open Systems BV   |   Phone: +31 20 6938364
> --    Amsterdam, The Netherlands        |     Fax: +31 20 6948204
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--
Ian Craggs
icraggs@xxxxxxxxxx                 IBM United Kingdom
Paho Project Lead; Committer on Mosquitto