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Hi Pat, Mark,<br>
<br>
As web client developer, I indeed appreciate when I can have
something else than a XML<br>
document to parse in case of query error. I already have the
possibility to get some errors in<br>
JSON, and apparently Rubin already accept text errors.<br>
<br>
On the other hand, I'd also understand if a service cannot supply
the error in multiple formats.<br>
It is not always easy or possible to do. Because of this, I agree
with the approach stating<br>
that the error documents <i>should</i> be provided, <i>as much as
possible</i>, in the requested format.<br>
Then, we should probably say that the fallback standard format <i>must</i>
be VOTable. This way,<br>
it is a safe format that a generic client can rely on. So, in a
word, I agree.<br>
<br>
Anyway, I am a bit lost. Where do you plan to apply a fix?<br>
DALI, TAP, UWS?<br>
If DALI, is it expected in the upcoming DALI-1.2?<br>
<br>
Cheers,<br>
Grégory<br>
<br>
<br>
<div class="moz-cite-prefix">On 17/09/2025 18:12, Mark Taylor via
dal wrote:<br>
</div>
<blockquote type="cite"
cite="mid:3852fd55-7988-819-dabe-ce67e39b1ad0@andromeda.star.bris.ac.uk">
<pre wrap="" class="moz-quote-pre">The impossible-to-provide-VOTable point doesn't apply in this context.
TAP 1.1 sec 3.3 does talk about errors in the use of the HTTP protocol,
which would lead to non-VOTable error responses, but the case I'm
talking about here is an error document retrieved from the UWS
error document endpoint /async/<jobid>/error:
"Error documents should be in a format that matches the requested format
where possible; see DALI for details. If the error document is being
retrieved from the /async/<jobid>/error resource (specified by UWS)
after an asynchronous query, the HTTP status code should be 200."
So where a VOTable result is implicitly or explicitly requested
it is possible to supply a VOTable response; the TAP 1.0->1.1
inconsistency is the "should" which used to be a "must".
On Wed, 17 Sep 2025, Patrick Dowler wrote:
</pre>
<blockquote type="cite">
<pre wrap="" class="moz-quote-pre">At this point it has been written/advertised that way for years, so we
should consider whether it is something to fix or just something to
accept and adapt to... I know it is not always possible to adhere to
the strict "error must be VOTable" because some errors happen before
handling the request gets anywhere near the code that can feasibly
write a VOTable.
--
Patrick Dowler
Canadian Astronomy Data Centre
Victoria, BC, Canada
On Wed, 17 Sept 2025 at 02:51, Mark Taylor <a class="moz-txt-link-rfc2396E" href="mailto:m.b.taylor@bristol.ac.uk"><m.b.taylor@bristol.ac.uk></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="" class="moz-quote-pre">
It might be the spirit, but between TAP 1.1 and DALI 1.1 the text does
seem to allow a plain text error document, which is what Rubin are
currently doing, though I haven't encountered it in other services.
So I think that means that clients and validators have to be prepared
for that (topcat and taplint currently are not; I don't know about
other TAP clients).
Unless we consider this Erratum fodder?
On Mon, 15 Sep 2025, Patrick Dowler wrote:
</pre>
<blockquote type="cite">
<pre wrap="" class="moz-quote-pre">iirc, it was deliberate to change from "must be VOTable" to be able to
play nice with other formats, so it probably should have been as close
to "must be in the requested format" as possible. But of course, not
all tabular output formats can carry error messages, so it gets kind
of tricky in the details.
The spirit is still definitely that if the client expects a VOTable
response they get that for both success and error, but the DALI quote
shown is much too vague... I think that is where the
clarification/detail is needed.
--
Patrick Dowler
Canadian Astronomy Data Centre
Victoria, BC, Canada
On Mon, 15 Sept 2025 at 06:41, Mark Taylor via dal <a class="moz-txt-link-rfc2396E" href="mailto:dal@ivoa.net"><dal@ivoa.net></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="" class="moz-quote-pre">
Hi DAL.
Following a taplint query by Stelios, I've just noticed the following
inconsistency between TAP 1.0 and TAP 1.1 as regards the format of
UWS error documents resulting from failed async TAP queries:
TAP 1.0 Sec 2.7.3:
"Error documents for TAP errors must be VOTable documents;
any result-format specified in the request is ignored."
TAP 1.1 Sec 3.3:
"Error documents should be in a format that matches the requested
format where possible; see DALI for details."
DALI 1.1 Sec 4.2:
"An error document describing errors in use of the DAL service
protocol may be a VOTable document (...) or a plain text document."
For an expected VOTable result, this is effectively a downgrade of a
MUST to a SHOULD for VOTable as the format of the error document.
So a TAP 1.0 client will expect a VOTable error document from a failed
async TAP query, but may get tripped up by receiving instead a plain
text error document. This change is not explicitly noted in
Appendix A of TAP 1.1 "Changes from TAP-1.0 to TAP-1.1",
though A.1 says, somewhat misleadingly, "Removed text that duplicates
material from DALI.".
This looks to me like an oversight since it is (from the client's
point of view) a backwardly incompatible behaviour change from TAP 1.0
to TAP 1.1.
Has anybody come across this before, or remember whether it was
deliberate?
Mark
--
Mark Taylor Astronomical Programmer Physics, Bristol University, UK
<a class="moz-txt-link-abbreviated" href="mailto:m.b.taylor@bristol.ac.uk">m.b.taylor@bristol.ac.uk</a> <a class="moz-txt-link-freetext" href="https://www.star.bristol.ac.uk/mbt/">https://www.star.bristol.ac.uk/mbt/</a>
</pre>
</blockquote>
<pre wrap="" class="moz-quote-pre">
</pre>
</blockquote>
<pre wrap="" class="moz-quote-pre">
--
Mark Taylor Astronomical Programmer Physics, Bristol University, UK
<a class="moz-txt-link-abbreviated" href="mailto:m.b.taylor@bristol.ac.uk">m.b.taylor@bristol.ac.uk</a> <a class="moz-txt-link-freetext" href="https://www.star.bristol.ac.uk/mbt/">https://www.star.bristol.ac.uk/mbt/</a>
</pre>
</blockquote>
<pre wrap="" class="moz-quote-pre">
</pre>
</blockquote>
<pre wrap="" class="moz-quote-pre">
--
Mark Taylor Astronomical Programmer Physics, Bristol University, UK
<a class="moz-txt-link-abbreviated" href="mailto:m.b.taylor@bristol.ac.uk">m.b.taylor@bristol.ac.uk</a> <a class="moz-txt-link-freetext" href="https://www.star.bristol.ac.uk/mbt/">https://www.star.bristol.ac.uk/mbt/</a>
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