Is there a hook to customize HTTP requests to downstream Gql servers?

[joffrey-bion]

Is there a hook to customize HTTP requests to downstream Gql servers?

[sachindshinde]

Yep, you can place the structured context object in the extensions property of the JSON body in HTTP GraphQL requests and responses.

The steps are as follows:

• In the gateway's server constructor, you pass in a context function that extracts the context object from the gateway request and adds it to the gateway context, e.g.

const server = new ApolloServer({
  gateway: /* gateway constructor */ ,
  subscriptions: false,
  context: ({ req }) => {
    const contextObject = /* Parse the context object from req.body */ ;
    // Add the context object to the gateway context
    return { contextObject };
  },
});

• In the gateway constructor, you pass in a buildService function that creates a RemoteGraphQLDataSource sub-class that defines a willSendRequest() callback to take the context object out of the gateway context and embed it in request.extensions and a didReceiveResponse() callback to take the context object out of response.extensions and add it to the gateway context. This looks like:

const server = new ApolloServer({
  gateway: new ApolloGateway({
    serviceList: /* service list */ ,
    buildService: ({ url }) => {
      return new ContextObjectDataSource({ url });
    },
  }),
  subscriptions: false,
  context: /* context function */ ,
});

class ContextObjectDataSource extends RemoteGraphQLDataSource {
  willSendRequest({ request, context }) {
    if (context.contextObject) {
      request.extensions = {
        ...request.extensions,
        contextObject: context.contextObject,
      };
    }
  }

  didReceiveResponse({ response, context }) {
    if (response.extensions && response.extensions.contextObject) {
      context.contextObject = response.extensions.contextObject;
    }
    return response;
  }
};

• In the implementing service's server constructor, you pass in a plugin that defines a requestDidStart() callback to take the context object out of request.extensions and add it to the implementing service context and a willSendResponse() callback to take the context object out of the implementing service context and embed it in response.extensions. This looks like:

const server = new ApolloServer({
  schema: /* implementing service schema */ ,
  plugins: [{
    requestDidStart: ({ request, context }) => {
      if (request.extensions && request.extensions.contextObject) {
        context.contextObject = request.extensions.contextObject;
      }

      return {
        willSendResponse: ({ context, response }) => {
          response.extensions = {
            ...response.extensions,
            contextObject: context.contextObject,
          };
        },
      };
    },
  }],
});

[joffrey-bion]

Hi, thanks a lot for the detailed answer.

I'm sorry it was probably not clear in my question, but I had seen it was possible in the NodeJS version.
My question was about whether this was possible with this apollofederation-jvm project, in Java, sorry for the confusion 😥

[joffrey-bion]

Wait, maybe I got confused.

I thought this project was meant to build a federation gateway instead of the nodeJS federation gateway.
But I believe I was wrong and this is not the case. Is this project instead meant to be used for downstream GraphQL servers, just so that they expose their schema in a federation-compliant way?

If this is the case, then please feel free to close this issue as irrelevant.

[sachindshinde]

But I believe I was wrong and this is not the case. Is this project instead meant to be used for downstream GraphQL servers, just so that they expose their schema in a federation-compliant way?

Yep, that's exactly right, it's a thin layer around graphql-java to make it federation-compliant.

If this is the case, then please feel free to close this issue as irrelevant.

Sounds good, I'll close out the issue. If you end up having any troubles with Apollo Gateway, feel free to file an issue on their GitHub page.