Forward fetch response headers to Apollo graphql response - express

Question

I have an apollo-datasource-rest data source setup on an Apollo/Graphql
Expressjs server. I'd like to forward a few headers from the fetch response to the /graphql response.
Here is the flow:
POST /graphql
Graphql makes fetch request using this.get('http://example.com/api')
Response from this fetch contains the header "cache-status"
Response from /graphql
I'd like to include the "cache-status" header from the example.com/api response here in the /graphql response
I see the header in the didReceiveResponse() method of the rest datasource class. I'm not sure this is the right place to access and store it. How do I include the "cache-status" header in the POST /graphql response?

Answer 1

Assuming you're RESTDataSource from apollo-datasource-rest, you can override the didReceiveResponse to intercept the response and return a custom return value.
Here's a code snippet in Typescript, it can be easily converted to Javascript if need be by removing the parameter/return types and access modifiers.
class MyRestDataSource extends RESTDataSource {
public constructor(baseUrl: string) {
super();
this.baseURL = baseUrl;
}
public async getSomething(): Promise<any & { headers?: { [key: string]: string } }> {
// make the get request
return this.get('path/to/something');
}
// intercept response after receiving it
protected async didReceiveResponse(response: Response, _request: Request) {
// get the value that is returned by default, by calling didReceiveResponse from the base class
const defaultReturnValue = await super.didReceiveResponse(response, _request);
// check if it makes sense to replace return value for this type of request
if (_request.url.endsWith('path/to/something')) {
// if yes get the headers from response headers and add it to the returned value
return {
...defaultReturnValue,
headers: { headerValue: response.headers.get('header_name') },
};
}
return defaultReturnValue;
}
}

Answer 2

I think you can utilize formatResponse of ApolloServerLambda()
And respond with proper headers. I have not tried it myself. But looking at the document I feel it should be helpful
formatResponse?: (
response: GraphQLResponse,
requestContext: GraphQLRequestContext<TContext>,
) => GraphQLResponse | null;