Topic Wildcards
Tobias Oberstein
Specifically, the spec talks about wildcards being
"The multi-level wildcard and single-level wildcard can be used for
subscriptions, but they cannot be used within a topic by the publisher
of a message."
I.e.
PUBLISH: not allowed
SUBSCRIBE: allowed
UNSUBSCRIBE: ??
all other msgs: not allowed
?
For example, given a client has subscribed to
finance/stock/ibm/#
and receives messages for (fully qualified) topics
finance/stock/ibm
finance/stock/ibm/closingprice
finance/stock/ibm/currentprice
...
how does the client unsubscribe?
The set of topics for a subscription using a wildcard
is open ended, since topics used for publications are not
"preregistered", right?
So even unsubscribing from the 3 qualified topics
finance/stock/ibm
finance/stock/ibm/closingprice
finance/stock/ibm/currentprice
won't suffice, since
finance/stock/ibm/dayavgprice
might still be received.
How does that work?
Thanks,
\Tobias
Nicholas O'Leary
yes, wildcards may be used in UNSUBSCRIBE messages.
So a subscription to finance/stock/ibm/# is removed by unsubscribing
to exactly the same topic string - finance/stock/ibm/#
Regards,
Nick
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Tobias Oberstein
> yes, wildcards may be used in UNSUBSCRIBE messages.
>
> So a subscription to finance/stock/ibm/# is removed by unsubscribing
> to exactly the same topic string - finance/stock/ibm/#
Just to get that right .. is the following correct?
1)
Client subscribes "finance/stock/ibm/#" and
unsubscribes "finance/stock/ibm/closingprice"
The unsubscribe for "finance/stock/ibm/closingprice" is silenty
ignored (was never subscribed on that very "topic subsc. string")
It will still receive msgs for "finance/stock/ibm/closingprice"
since it is still subscribed to "finance/stock/ibm/#"
2)
Client subscribes "finance/stock/ibm/closingprice" and
unsubscribes "finance/stock/ibm/#"
The unsubscribe for "finance/stock/ibm/#" is silenty
ignored (was never subscribed on that very "topic subsc. string")
It will still receive msgs for "finance/stock/ibm/closingprice"
since it is still subscribed to "finance/stock/ibm/closingprice"
3)
Client subsribes "finance/stock/ibm/#" and
subscribes "finance/stock/ibm/closingprice"
Client will receive msgs published to "finance/stock/ibm/closingprice"
_twice_
==
In other words, "topic subscription strings" are interpreted merely
syntactically and have no "set semantics"?
[Dont know how to express that better .. hope you get it from ctx above]
Thanks!
\Tobias
Roger Light
> 1)
> Client subscribes "finance/stock/ibm/#" and
> unsubscribes "finance/stock/ibm/closingprice"
>
> The unsubscribe for "finance/stock/ibm/closingprice" is silenty
> ignored (was never subscribed on that very "topic subsc. string")
>
> It will still receive msgs for "finance/stock/ibm/closingprice"
> since it is still subscribed to "finance/stock/ibm/#"
This is correct.
> 2)
> Client subscribes "finance/stock/ibm/closingprice" and
> unsubscribes "finance/stock/ibm/#"
>
> The unsubscribe for "finance/stock/ibm/#" is silenty
> ignored (was never subscribed on that very "topic subsc. string")
>
> It will still receive msgs for "finance/stock/ibm/closingprice"
> since it is still subscribed to "finance/stock/ibm/closingprice"
This is correct.
> 3)
> Client subsribes "finance/stock/ibm/#" and
> subscribes "finance/stock/ibm/closingprice"
>
> Client will receive msgs published to "finance/stock/ibm/closingprice"
> _twice_
As Nick already mentioned in another email, overlapping subscriptions
should not result in a message being received more than one. This is
however an outstanding bug in mosquitto - you will receive the message
twice in the above situation.
Cheers,
Roger