Sending response to client from within the request.post callback in koa - node.js

Question

I have this koa route /landing which is resulting in 404.
function* landing() {
//this.body = "response"; //1
var request = require('request');
request.post('http://url.com/resource',
{ json: { key: "post data"} },
function (error, response, body) {
if (!error && response.statusCode == 200) {
var token = body.data;
getListByToken(token, function(list){
this.body = list; //2
});
}
});
}
See comment in the top //1 - that is how you define body of a response in koa in a route. Instead of //1 I want to send response from //2 i.e. from within that request.get.
When a user is routed to /landing a post request has to fetch some data from a url. That fetched data is to be used by getListByToken to bring some other data, list, which should be sent to the user. The above code should have worked but it results in 404 Not Found response by koa.

Answer 1

We can use promises, simple and clean way of managing asynchronous codes.
var request = require('request-promise');
. . .
function* landing() {
try {
let response = yield request( {
method: 'POST',,
url: 'http://url.com/resource',
headers: { 'content-type': 'application/json' },
body: JSON.stringify( { json: { key: "post data"} } )
} );
this.body = yield new Promise( function( resolve, reject ) {
if ( response.statusCode == 200 ) {
getListByToken( response.body.token, function( list ) {
resolve( list );
} );
}
} );
} catch ( err ) {
/* do something with your errors */
}
}

Answer 2

Solved it with q. It makes koa hold response until yield happens.
var q = require('q');
function* landing() {
var deferred = q.defer();
var request = require('request');
request.post('http://url.com/resource',
{ json: { key: "post data"} },
function (error, response, body) {
if (!error && response.statusCode == 200) {
var token = body.data;
getListByToken(token, function(list){
deferred.resolve(repolist);
});
}
});
this.body = yield deferred.promise;
}
Thanks to https://stackoverflow.com/a/22159513/1128379