Unable to use interpolated strings for endpoints with GraphQL source

[tmc-yuval-naveh]

Hi,
I have 3 downstream services - one JSON schema (using loadJSONSchemaSubgraph) and the others are GraphQL (using loadGraphQLHTTPSubgraph).
All endpoints use interpolated strings.

   sourceHandler: loadJSONSchemaSubgraph('XXProducts', {
      endpoint: '{env.XX_API_PRODUCTS_ENDPOINT}'
   }
   
  sourceHandler: loadGraphQLHTTPSubgraph('XXEvents', {
      endpoint: '{env.XX_EVENTS_ENDPOINT}'
    })

The JSON schema source works fine. The endpoint string reads from env and query comes back as expected.
The GraphQL sources do not work - queries fail with an error

 "extensions": {
                "code": "DOWNSTREAM_SERVICE_ERROR",
                "serviceName": "XXEvents",
                "request": {
                    "method": "GET",
                    "url": "/%7Benv.XX_EVENTS_ENDPOINT%7D?query=<HIDDEN by me>"
                },
                "response": {
                    "status": 404,
                    "statusText": "Not Found",
                    "body": "404 page not found\n"
                }
            }
        }

When I use the literal value (not interpolated string) then the query works fine.
The url above shows the the problem: %7Benv.XX_EVENTS_ENDPOINT%7D

Any ideas? workarounds? Is this a bug?

I looked at the implementation of loadGraphQLHTTPSubgraph and couldn't spot an issue/

export function loadGraphQLHTTPSubgraph(
  subgraphName: string,
  {
    endpoint,
    method,
    useGETForQueries,

    operationHeaders,
    credentials,
    retry,
    timeout,

    source,
    schemaHeaders,

    federation = false,

    transportKind = 'http',
  }: GraphQLSubgraphLoaderHTTPConfiguration,
): MeshComposeCLISourceHandlerDef {
  return (ctx: LoaderContext) => {
    let schema$: MaybePromise<GraphQLSchema>;
    const interpolationData = {
      env: process.env,
    };
    const interpolatedEndpoint = stringInterpolator.parse(endpoint, interpolationData);
    const interpolatedSource = stringInterpolator.parse(source, interpolationData);

UPDATE: logged the graphql source handler and can see that the endpoint value was replaced with the env var value.
The supergraph.graphql file has the uninterpolated string (i.e. template) as expected. I guess the loading of the schema has to work or the build phase would have failed. So this seems to be a runtime issue, with hive gateway not interpolating the endpoint.

XX_EVENTS @join__graph(name: "XXEvents", url: "{env.XX_EVENTS_ENDPOINT}")

[tmc-yuval-naveh]

It's not the same, but similar:
ardatan/graphql-mesh#5403
ardatan/graphql-mesh#5296

[tmc-yuval-naveh]

I created an issue and a demo project
#1016

[enisdenjo]

Ok cool, thanks. We can continue the discussion there.