Re: Errors in p:try/p:catch yield little information when things go wrong

Hi David,

On 22.04.2020 06:48, david@thingbag.net wrote:
> Greetings,
> 
> I'm using p:load to load a doc and wrap it in a p:try/p:catch in XProc 
> (Calabash 1.22). When the document is malformed or unparsable, I get 
> very little information about the nature of the problem in the catch:
> 
> <c:errors xmlns:c="http://www.w3.org/ns/xproc-step">
>      <c:error xmlns:err="http://www.w3.org/ns/xproc-error" 
> code="err:XC0011"
>          href="file:/path/to/pdf.xpl"
>          line="6" column="65">Could not load
>          /path/to/Quinoa_Axe_Throwing_Specification.xml
>          (file:/path/to/pdf.xpl)
>          dtd-validate=false</c:error>
> </c:errors>

This error message is probably already as detailed as it gets, given 
that a program that uses an XML parser API does not see any difference 
whether the file is malformed or non-existent.

> 
> Likewise, when I wrap p:include in a try/catch, I only get an error code 
> indicating that it couldn't load a file and line numbers in the xpl:
> 
> <c:error href="file:/path/to/library.xpl" line="18" column="34">XProc 
> error err:XD0011</c:error>

That’s another story. I agree that the message should contain all the 
information that you see without try/catch.

I filed an issue: https://github.com/ndw/xmlcalabash1/issues/303

> 
> There's no information about which file or files couldn't be loaded for 
> example.
> 
> I was attempting to have the pipeline package up the error information 
> about why things fail and report it in a friendly way to my users. If I 
> were to load the same document as the source for the pipeline and not 
> use try/catch, Calabash would give me more information about why it 
> failed to parse the document, which xinclude couldn't be resolved, etc 
> but when I do that I have no way to recover gracefully from a failure 
> within the pipeline.
> 
> Am I going about things the wrong way? It seems that I have to put this 
> code in the layer that calls Calabash and scrape the unstructured 
> stderr/stdout info to let the user know what went wrong.

My experience with Calabash is also that it sometimes omits interesting 
parts of error messages. This is particularly the case if you run 
p:xslt. If you run Saxon standalone, you will get much more detailed 
error messages. The messages that Calabash displays are often misleading 
(often some info messages previously emitted by the stylesheet, but not 
the one that comes with the error). This might get worse when wrapped in 
p:try/p:catch. What you report about try/catch might or might not be 
related to the XSLT issue that I mentioned (since Calabash uses Saxon’s 
APIs for almost all lower-level operations, it might be related).

There’s already another error about accumulating messages in iterations: 
  https://github.com/ndw/xmlcalabash1/issues/259
Given Norm’s busy schedule, there is not much hope that he will be able 
to fix it soon. But compared to a couple years ago, Calabash’s 
diagnostic messages have already improved.

You might try Achim’s processor, Morgana XProc, either in the XProc 1.0 
or in the XProc 3.0 beta version.
https://www.xml-project.com/
Morgana has had more detailed error messages for quite some time.

Both implementors, in particular Norm, have pledged to make error 
messages (more) user friendly in the XProc 3.0 versions of their processors.

Gerrit

> 
> Regards,
> David
>

Received on Wednesday, 22 April 2020 07:41:38 UTC