Re: HTTP requests, databases and how to transmit SHACL validation reports

Good question, good timing.

On 22/03/2020 16:23, Håvard Ottestad wrote:
> Hi,
> 
> I’m a committer over at Eclipse RDF4J and am currently looking at how we can extend our RDF4J Server to respond to the client with the SHACL validation report if the user's request could not be processed due to a violation.
> 
> An example:
> 
> We have a database of users with some SHACL rules that among other things specify that a user needs to have exactly one password.
> 
> The client tries to add a user, but the user didn’t specify a password, so the request gets rejected by the database. This should naturally have been detected on the client side first - but you know… lazy developers and the like :P
> 
> Anyway, since this is happening over HTTP we need to send an appropriate response to the client so that the client can tell the user to provide a password. This response should contain the SHACL validation report, we don’t want to reinvent the wheel.
> 
> For the actual HTTP response we have a few things to consider:
> 
>   - Status and status line. Currently considering 409 - Conflict

Loos good.

While some 4xx and 5xx are errors specific to the HTTP protocol (e.g. 
406 "Not Acceptable"), 409 does say the current state of the resource 
conflicts with the request which seems appropriate here.

>   - Content-type header. Currently considering this to be "application/n-quads" to reflect the serialisation of the SHACL validation report

Yes - but to me application/shacl-validation-report+n-quads is better.

Realistically, the "x+y" thing isn't well supported by client-side 
toolkits but mist do expose the whole Content-type of the response.

>   - Custom header. Currently considering "Eclipse-RDF4J-Exception: ShaclSailValidationException” to tell the client that this response is due to a ShaclSailValidationException

Custom headers can be inconvenient depending on the client-side HTTP 
library being used.  To be useful the app is going to look in the body 
so I'm not sure this adds much over the "Content-type" option.

> 
> We have other options too:
> 
>   - "Content-type: application/n-quads+shacl-validation-report” similar to how json-ld is handled

Yes, though the other way round:

application/shacl-validation-report+n-quads

c.f

rdf+xml
sparql-results+json
ld+json

and
application/shacl-validation-report+turtle

if you must:
text/shacl-validation-report+turtle

(always did think text/turtle was a bit strange)

>   - Custom status: 409 - SHACL violation

HTTP/2 and HTTP/3 don't carry the message part of HTTP/1.1 status line.
https://tools.ietf.org/html/rfc7540#section-8.1.2.4

>   - Magic numbers train of thought with the first line of the response being something like “SHACL validation report”.

That would be a new MIME type?

I prefer application/shacl-validation-report+turtle

> 
> 
> What I’m wondering is: How are other databases solving this particular problem?
> 
> And: Did the SHACL Working Group discuss this issue? Maybe in light of the SPARQL protocol?
> 
> Best regards,
> Håvard M. Ottestad
>

Received on Sunday, 22 March 2020 18:26:07 UTC