[Standards] What is the size limit of node and item ids in XEP-0060: Publish-Subscribe?

Peter Saint-Andre stpeter at stpeter.im
Thu Mar 1 14:10:17 UTC 2018


On 3/1/18 1:07 AM, Jonas Wielicki wrote:
> On Donnerstag, 1. März 2018 08:52:29 CET Florian Schmaus wrote:
>> On 01.03.2018 01:17, Peter Saint-Andre wrote:
>>> On 2/28/18 3:18 PM, Timothée Jaussoin wrote:
>>>> Hi,
>>>>
>>>> I came across a database limitation while implementing Pubsub in Movim.
>>>>
>>>> I'd like to know if we have a limitation for the size of the node and
>>>> items ids in Pubsub (like we have for the JIDs). Also do we have some
>>>> specific forbid characters, basically what is the format of such
>>>> attributes? If noting is already specificed I think that it would be
>>>> wise to update the 0060 to do so.> 
>>> My inclination is to specify a length of 1023 octets
>>
>> Which would break applications and protocols using JIDs as node or item
>> identifier. This includes for example MIX. If we want to allow this, we
>> need at least (3x1023)+2 octets, and then I would probably go for 4096
>> octets.
> 
> This is bikeshedding territory. But given that databases have limits on the 
> size of keys, using as many as needed and as few as possible octets (the 3071 
> you quoted) is probably sensible.
> 
> Do those protocols use bare or full JIDs? If they only use bare and if we 
> agree that full JIDs (due to their transience) do not make sense, the limit 
> could conceivably be as low as 2047, which is probably comfortable for 
> databases to handle.

A full, especially non-client JID need not be transient, so I suppose
we'd set it to 3071 (not sure why we'd need 4096 other than the fact
it's a power of 2):

https://tools.ietf.org/html/rfc7622#section-3.1

Peter

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