Proposal for new wildcards for topic filtering

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Stefan Hupe

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May 10, 2014, 5:43:39 AM5/10/14
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Hi!

I have played around with topic filtering for a while and I think, that it would be really helpful, if we could add some new wildcards for topic filtering on broker side:

WILDCARDS: 
+, #, *, -


1. WILDCARD + (filter single section of a topic)

Just used. Example

Topics:
/a/b/c/d
/a/x/c/d
/a/x/y/d
/a/e/f/g
/a/h/f/i

client(id=123).subscribe.topic("/a/+/c/d")

Results:
/a/b/c/d
/a/x/c/d

client(id=123).subscribe.topic("/a/+/+/d")

Results:
/a/b/c/d
/a/x/c/d
/a/x/y/d

client(id=123).subscribe.topic("/a/+/f/+")

Results:
/a/e/f/g
/a/h/f/i
 

 2. WILDCARD # (for many sections at the end of a topic)

Just used. Example

client(id=123).subscribe.topic("/a/x/#")

Results:
/a/x/c/d
/a/x/y/d
 

3. WILDCARD # (for many sections IN a topic) 

Example:

Topics:
/a/b/c/d
/a/e/f/g 
/a/h/i/d
/a/k/l/m/d 
 
client(id=123).subscribe.topic("/a/#/d")

Results:
 
/a/b/c/d
/a/h/i/d
/a/k/l/m/d 

I have very often the use case, that I am interested in a special value, e.g. temperatures in a building, so I wanna subscribe to /house/#/temperature without the knowledge of alls the sections between /house and /temperature (because I the numbers of sections are different). 
 

4. WILDCARD * (single character in a topic section)

Example:

Topics:
/house/flat01/room01/temperature
/house/flat01/room02/temperature
/house/flat01/room13/temperature
/house/flat01/oven/temperature

client(id=123).subscribe.topic("/house/flat01/room0*/temperature")

Results:
 
/house/flat01/room01/temperature
/house/flat01/room02/temperature
 
 
5. WILDCARD + (many characters in topic section) 
 
client.(id=123).subscibe.topic("/house/flat01/room+/temperature") 
 
Results:
/house/flat01/room01/temperature
/house/flat01/room02/temperature
/house/flat01/room13/temperature
 

6. "WILDCARD" - (get messages without payload)

 I wanna get some information like
  • Is there currently a message for a specific topic in the queue of the broker?
  • How many messages for a specific topic are in the queue of the broker? (Should I download them now or later?)
  • What kind of topics are currently in the queue of the broker (like topic discovery)?
Example:

client(id=123).subscribe.topic("/house/#/-")

As a results I will get empty messages for those topics without any payload:

/house/flat01/room01/temperature
/house/flat01/room02/temperature
/house/flat01/room13/temperature
/house/flat01/oven/temperature

That I know, that currently messages for these topics are available and I can chosse, which topic I wanna subscribe to (discovery). 

client(id=123).subscibe.topic("/house/flat01/room04/temperature/-")

Result:

UNKNOWN TOPIC

client(id=123).subscribe.topic("/house/float01/room01/temperature/-")

Results:

 /house/flat01/room01/temperature
message 1
message 2
message 3
message 4 

So I know, that there are messages for this topics and that there are four messages. (E.g. I could decide to start the subscription later if there are enough messages in the queue.)

Why I don't use the filter with payload? I wanna let the messages in the queue. And I don't want to have all the network traffic for downloading large payloads I am not interested in, because I am only interested to know, what kind of topics exists and after that choose those one I wanna really subscribe to.

Any feedback?

Best

Stefan 
 
 
 
 

Stefan Hupe

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May 10, 2014, 6:02:58 AM5/10/14
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/-

will deliver all messages in the queue without payload

/--

will deliver only one message for each topic without payload
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