Re: SIMS and SFS, was: Re: Proposed XMPP Extension: Emoji Markup

Stephen Paul Weber <[email protected]> Sun, 26 Apr 2026 20:07:58 -0500

Newsgroups	gmane.network.jabber.standards-jig
Message-ID	<[email protected]>

>> Since this is most of the purpose of using sims or sfs (to get the
>> hash) it seems reasonable?
>
>I didn't know that was the main purpose of SIMS or SFS. Also surprises
>me, given that some implementation neither send nor process the hash.

I'm doing a details re-reading of SFS now and found these gems:

> It is RECOMMENDED that the file metadata specifies name, media-type, size 
> and one or multiple hash elements

If I'm not mistaked RECOMMENDED means SHOULD which means implementations are 
permitted to break if a hash is not present. This is very close to a MUST.

> On receive of a message including a <file-sharing/> element, the receiving 
> entity SHOULD lookup in a local storage, whether the file with any of the 
> proivded hashes has already been retrieved and is available

I agree, but difficult to do if there are not such hashes...

Interestingly, later:

>  If no <hash/> is provided or the <hash/> elements provided use 
>  unsupported algorithms, receiving clients MUST ignore any attached 
>  sources from other senders and only obtain the file from the sources 
>  announced by the original sender

Which now implies that no hashes is kind of ok, but nerfs source attaching.

BTW, would it make sense to give source attaching its own XEP? It takes up 
quite a lot of the space in this one for an advanced feature.

> If the disposition attribute is set to attachment, no <media-type/> is 
> provided or the <media-type/> indicates that the file can not be displayed 
> inline, i.e. when the media type is application/octet-stream, the 
> receiving entity SHOULD NOT display the file inline and instead offer to 
> download it or save it on the user's file system.

Does "display inline" here just mean "show a preview"? So if disposition is 
attachment I'm (almost) forbidden to show a preview of the file?

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