spf-discuss
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Re: considering XML

2004-01-21 19:49:52
On Wed, Jan 21, 2004 at 01:43:05PM -0500, Meng Weng Wong wrote:
A significant stakeholder is in favour of using an XML encoding for SPF.

How do you guys feel about that?

Good god, that's an abomination.

However, a canonical mapping might be nice: All extensions could get a
prefix, defined at the end of the SPF string as URIs, so the whole thing can
be converted into XML, RDF or whatever W3C-compliant data model is being
used at the moment.  Use a designated subdomain for namespace
declarations:

domain IN TXT "v=spf1 a mx foo#bar:DEADBEEF baz#bar:<elem/> 
xmlnsdom=_xmlns.domain"
_xmlns.domain IN TXT "foo=http://foo.org/spf/extensions# base64"
_xmlns.domain IN TXT "baz=http://baz.org/spf/extensions# inline"

and 


<spf xmlns='http://spf.pobox.com/1'
        xmlns:foo='http://foo.org/spf/extensions#'>
        <a/>
        <mx/>
        <foo:bar>DEADBEEF</foo:bar>
        <baz:bar><elem/></baz:bar>
</spf>

It's a compact encoding, special-purpose, but easy to understand.
Downsides? Needs a registrar.  Makes SPF too large to fit in DNS well.
Use ten extensions, no matter how compact, and the URIs will eat your
SPF record for lunch.

XML is too verbose to fit much data into the constraints of a single
512-byte UDP packet.

It's an abomination, but might satisfy.

I personally think having a registrar for prefixes for spf mechanisms
makes more sense -- avoid the completely arbitrary syntax of XML.  We
already have a tree-shaped structure, DNS, we really don't need to add
the complexity of XML to SPF, too.

Ari

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