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Proposal and issues surrounding MustUnderstand faults

From: Glen Daniels <gdaniels@macromedia.com>
Date: Fri, 11 May 2001 19:24:20 -0400
Message-ID: <002e01c0da71$81d8c2c0$1600a8c0@c1vn>
To: <xml-dist-app@w3.org>
Hi folks!

On this week's conference call, I volunteered to take a crack at a proposal
for dealing with the difficulty of getting back useful information regarding
which headers in particular were the cause of a MustUnderstand fault.

This message proposes two possible solutions for the problem, and suggests a
bit more exploration into the issue of faults in general.

As background/context, you can read the description of the issue at [1].

** PROPOSAL 1 : Use the <Fault> element

This proposal involves EITHER extending the Fault element with another
sibling to <faultcode>,<faultactor>,etc. :

<faultcode>MustUnderstand</faultcode>
<faultheaders>
 <myNS:Header1 xmlns:myNS="http://some.com"/>
</faultheaders>

OR changing the rules of section 4.4 to allow the <detail> element to carry
information relating to headers, and adding the same <faultheaders> element
underneath <detail>.

** PROPOSAL 2 : Use the header

A similar proposal involves echoing back the offending headers in the
<SOAP-ENV:Header> section of the fault response:

<Envelope>
 <Header>
  <SOAP-EXT:MisunderstoodHeaders>
   <myNS:Header1 xmlns:myNS="http://some.com" mustUnderstand="1">
     Nobody understands me.
   </myNS:Header1>
  </SOAP-EXT:MisunderstoodHeaders>
 </Header>
 <Body>
  <Fault>
   <faultcode>MustUnderstand</faultcode>
  </Fault>
 </Body>
</Envelope>

The second one more cleanly fits the SOAP extensibility model, I think.  This
is potentially one of the "normative extensions" we could add to the spec,
since while not absolutely essential, it would be very handy if most processors
out there implemented this.

On a slightly broader note, I think in parallel with our discussion of the
potential symmetry and/or differences between headers and bodies, it would be
good to bring up how Faults are generated, and look carefully at the current
SOAP assumption that there is exactly one Fault per message, with a single
<faultcode>.  While convenient in some ways from a processing point of view,
this does generate a contended resource - and there may be ways in which fault
information can be orthogonally added to a message in the same way extension
data will be.  I don't want to go into this too deeply in this note, but did
want to sprout the seed of this discussion, which came up on the call.

--Glen

[1] http://lists.w3.org/Archives/Public/xml-dist-app/2001Apr/0097.html
Received on Friday, 11 May 2001 19:22:06 GMT

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