MeSH SPARQL endpoint does not seem to return HTTP Content-Type header

[yayamamo]

When issuing a SPARQL query to the endpoint by a curl tool, I've noticed that the response header didn't include an HTTP Content-Type header.
This may cause inappropriate behavior of a SPARQL client.

Below is the one I encountered. The query is a Construct SPARQL query.

% curl -vLH 'Accept: application/rdf+xml' --data-urlencode query@query.rq https://id.nlm.nih.gov/mesh/sparql 
...
> POST /mesh/sparql HTTP/1.1
> Host: id.nlm.nih.gov
> User-Agent: curl/7.64.1
> Accept: application/rdf+xml
> Content-Length: 365
> Content-Type: application/x-www-form-urlencoded
> 
* upload completely sent off: 365 out of 365 bytes
< HTTP/1.1 200 
< Date: Wed, 18 Nov 2020 05:05:07 GMT
< Server: Apache/2.4.6 (CentOS)
< X-Frame-Options: SAMEORIGIN
< X-Forwarded-Proto: https
< Access-Control-Allow-Origin: *
< Access-Control-Allow-Methods: GET, POST, PUT
< Access-Control-Allow-Headers: Cache-Control, Pragma, Origin, Authorization, Content-Type, X-Requested-With
< Access-Control-Max-Age: 1800
< Set-Cookie: JSESSIONID=4D5D6794B67A0483E64DC70F07CFDFF2; Path=/mesh; Secure; HttpOnly
< Cache-Control: no-cache,no-store
< X-XSS-Protection: 1; mode=lock
< Transfer-Encoding: chunked
< X-count: 2
< X-VIP-Info: 130.14.16.63:443
< X-Pool-Info: /Common/id_pool 10.1.5.126 80
< Strict-Transport-Security: max-age=31536000; includeSubDomains; preload
< 
...

In addition, when trying a query at MeSH RDF API, I noticed that there was mismatch between Response content type and the one in the Response headers.
I set it to application/ld+json, but the response was content-type: application/rdf+xml;charset=utf-8.
Moreover, text/turtle and application/rdf+n3 also set no content-type as in the case of application/rdf+xml.

[danizen]

Thank you; these are errors that may be upstream in Lodestar, or at least in the version of Lodestar upon which we base MeSH RDF. I will follow-up shortly, at least by the time we have updated MeSH RDF so that 2021 is current and no longer interim.

[danizen]

I wonder whether your Accept request header matches the SPARQL query. When I do a simple SELECT query I get Content-Type application/sparql-results+xml;charset=utf-8 as the response. If I then manually set the Accept request header to application/rdf+xml, then the Content-Type is missing on the response.

The content type returned is conceptually able to specified by the Accept request header (e.g. should support Content-Negotiation). In practice you have to be careful to match the Content-Type to what is returned via the Query Editor as you select the various formats.

If that explains the what you experienced, let me know and I will close this Github issue.

[yayamamo]

What I got was a SPARQL CONSTRUCT query response without an HTTP Content-Type header, which should be RDF, and therefore application/rdf+xml was a valid response of Content-Type.
( https://www.w3.org/TR/sparql11-protocol/#construct-simple )
For example, the response to the query CONSTRUCT WHERE { <http://id.nlm.nih.gov/mesh/C000612320> ?pred ?obj . } should have an HTTP Content-Type header of Content-Type: application/rdf+xml when its HTTP Accept request header is Accept: application/rdf+xml.
This issue (i.e., no Content-Type header in a response) happens in the case of Accept: text/turtle, too.
However, that response header IS included when I set the Accept request header of Accept: text/html or Accept: text/plain, whose headers of response are Content-Type: application/rdf+xml;charset=utf-8 and Content-Type: text/plain;charset=utf-8, respectively.

[danizen]

Thanks, I'll look into that.