Set response header in a custom rust plugin using ControlFlow::Continue

[Meemaw]

Hey,

Is it possible to set a response header in a custom rust plugin when using ControlFlow::Continue? Its obviously possible to do so when using ControlFlow::Break when a new response is built, but unsure about Continue.

[garypen]

You could set the header and it will be propagated through to the subgraphs. However, I think that you are looking for a header to be propagated back to the client.

I'd implement this by setting a key in context when you know you are continuing and then check if the key is present in one of the response services (router or supergraph would be good choices). If the context key is present, then set the header there from the context value. You could do this in rhai or in your custom plugin.

[Meemaw]

Hey @garypen thanks for the help. Came up with something like this, does this looks rougly okay?

    .map_response(|mut response: supergraph::Response| {
        let context_value: Result<Option<String>, BoxError> =
            response.context.get(header);

        if let Ok(Some(remaining_tokens)) = context_value {
            let header = HeaderValue::from_str(&remaining_tokens);
            if let Ok(header_value) = header {
                response
                    .response
                    .headers_mut()
                    .append(header, header_value);
            }
        }
        response
    })

Actually, while at it, I have a question on how to test that this header is present in the response. Testing the plugin using TestHarness + oneshot, but the graphql::Response doesn't seem to expose headers?

[bnjjj]

For the test, if you're using something like this:

let service_stack = YourPlugin::new(PluginInit::try_builder().config(config).supergraph_sdl(Default::default()).build().unwrap())
    .await
    .unwrap()
    .supergraph_service(mock_service.boxed());
let res = service_stack
    .oneshot(request)
    .await
    .unwrap();

// Access headers via res.response.headers();