VALUES not passed to SERVICE in federated queries

[Martynas Jusevičius]

Hi,

I have two Fuseki 4.6.1 instances in a Docker network (fuseki-admin
and fuseki-end-user) that federate SPARQL queries between each other.

When I execute this query on fuseki-admin:

PREFIX  rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX  acl:  <http://www.w3.org/ns/auth/acl#>
PREFIX  sioc: <http://rdfs.org/sioc/ns#>

SELECT  *
FROM <urn:x-arq:UnionGraph>
WHERE
  { VALUES ( ?this ?Container ) {
      ( <https://localhost:4443/whateverest/> <https://localhost:4443/> )
    }
    SERVICE <http://fuseki-end-user:3030/ds/>
      { GRAPH ?Container
          { ?Container  a  ?Type }
      }
  }

then I can see the ?Container binding was injected into the query
string executed on fuseki-end-user:

Query = SELECT  * WHERE   { GRAPH <https://localhost:4443/>       {
<https://localhost:4443/>                   a  ?Type       }   }

However when I add FILTER NOT EXISTS to the federated part

PREFIX  rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX  acl:  <http://www.w3.org/ns/auth/acl#>
PREFIX  sioc: <http://rdfs.org/sioc/ns#>

SELECT  *
FROM <urn:x-arq:UnionGraph>
WHERE
  { VALUES (?this ?Container) { (<https://localhost:4443/whateverest/>
<https://localhost:4443/>) }
    SERVICE <http://fuseki-end-user:3030/ds/>
      {  GRAPH ?Container
              {
                ?Container  a  ?Type
              }
            FILTER NOT EXISTS { GRAPH ?this
                                  { ?this
sioc:has_parent|sioc:has_container  ?Container }
                              }
      }
  }

I see a single request in fuseki-end-user but none of the variables
are bound to anything:

Query =  Query = SELECT  * WHERE   { GRAPH ?Container       {
?Container  a  ?Type }     FILTER NOT EXISTS { GRAPH ?this
              { ?this
<http://rdfs.org/sioc/ns#has_parent>|<http://rdfs.org/sioc/ns#has_container>
?Container }

This looks plain wrong because without bindings it eliminates too many
(positive) results, and the final result on fuseki-end-user comes out
empty.

Is this a bug or am I misunderstanding something about VALUES and/or SERVICE?

Martynas