[Standards] Re: [jdev] XEP-0115: Entity Capabilities
mridul at sun.com
Mon Jul 2 11:08:29 UTC 2007
Mridul Muralidharan wrote:
> Joe Hildebrand wrote:
>> On Jun 27, 2007, at 2:32 AM, Jacek Konieczny wrote:
>>> That is not true. Years ago I have proposed other solution: instead of
>>> announcing client name version and caps clients should announce digest
>>> (e.g. MD5 or SHA) of normalized set of supported features. The list
>>> would have to be obtained only once per feature set and it could be
>>> verified. The traffic would not be much bigger than with current
>>> solution and the 'cache taint' problem would be gone. And
>>> implementations could be simpler (no need for capability registry --
>>> namespace registry is enough) and less error-prone (when a new namespace
>>> is added the digest would change 'automatically'. Currently developers
>>> have to manually update version or capability string).
>>> I think the digest could be used with current specification too -- as
>>> the only capability string, bound with all the supported namespaces. But
>>> XEP-0115 is not optimized for such usage and says nothing about digest
>> The current spec could absolutely be used for this. The hardest part
>> is spec'ing how to generate a string that has all of the capabilities,
>> so that you can run the hash. Canonical XML is massive overkill, but,
>> for example, if we just said:
>> - For all sorting, use the Unicode Collation Algorithm
>> - Initialize an empty string E
>> - sort the identities by category, then type
>> - for each identity, append the category, then the type (if it exists)
>> to E (note: any information inside an identity will be ignored)
>> - sort the features by URI
>> - for each feature, append the URI to E (note: any information inside
>> a feature will be ignored)
>> - calculate the MD5 sum for E
>> - use this for the version number or extension name
>> Example (adapted from XEP-115, example 2):
>> <presence from='romeo at montague.net/home'>
>> <c xmlns='http://jabber.org/protocol/caps'
>> The receiving client SHOULD check the hashes, after doing the IQ/gets:
>> = 730c80b442e150dd5e19a31f8edfa8b1
>> = d6224a352df544cfde1fbce177301c67
>> md5(clientpchttp://jabber.org/protocol/xhtml-im) =
>> If the receiving client detects an inconsistency, it MUST NOT use the
>> information it received, and SHOULD show an error of some kind.
>> For backwards-compatibility, any version number that is not 32 octets
>> long consisting only of [0-9a-f] MUST be treated as if it does not
>> implement MD5 checking.
>> - Existing entities, both sending and receiving, should work fine
>> - Over time, we can phase in entities that send md5 versions and ext's
>> - Receiving clients that care about security can start checking MD5
> This sounds good enough to prevent polluting the client side cache.
Forgot to add, change name from ver & ext to verh and exth ?
Also, relationship between caps and pep :
If the server supports pep - then cant it not directly respond back to
the requester for caps disco queries ?
>> hashes of the features to check for poisoning.
>> - Downside: more bytes in presence than today.
> With server optimization implemented, wont this not be restricted to
> first time presence push to a contact ?
> So maybe not as bad ?
>> - Assertion: anything else we do will be at least this bad if not worse.
>> If we add these bits to -115, will everyone agree to never bring up
>> changing caps again, and to all agree on that the next time a n00b
>> comes around?
>> --Joe Hildebrand
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