Koa.js在竞争条件下产生值

Question

I have an app that uses koa.js , and for context I am in the process of interfacing an external system that doesn't strictly follow request/responses pattern. IE. after a "request", it may or may not answer.

I am able to match my requests to these responses, but then I am unable to put that into the koa.js response :

r.get('/...', *function() {

    // (1) cannot yield since it will block and never call (2) ?
    callbacks.storeCb(howToMatchAnEventualResponse, function(err, resp) {  // may never get called depending about how the external system answers
        console.log("I should answer the http req now"); // how to answer the request from here ?
    });

    // has to be done after storingCb, this may or may not trigger the callback above
    externalSystem.sendMessage(msg); // (2)

    // something similar will have to be done in the callback instead
    this.body = {
        success : true,
        response : ''
    };

});

So my question is, how do I answer the http request using koa in my callback (or something similar), and how can I send an empty answer when the callback is not called (ie. after a delay maybe) ?

I am guessing that I am looking for something similar to Promise.race() , but for koa , so using yield .

Answer 1

Well in the end I was able to use bluebird's Promise.race() .

I would still be interested into a solution using generators.