Whisking Functions with Promises

Last few weeks I was learning and enhancing my skills around the new buzz word “serverless” and trying to understand whats the buzz is all about.  As ardent Open Source developer, I was looking for platform where I can develop and deploy the serverless functions, which is when i stumbled up on Apache OpenWhisk.

In this blog we will see how to build a simple nodejs function that can do a reverse geocoding using GoogleMaps API.,and deploy the functions on to OpenWhisk .

The context of the blog was to show building an Apache OpenWhisk JavaScript action which involves a callback.  As most of us are familiar with GoogleMaps API , which has lots of callbacks I thought use it for this blog example.

The source code of this blog is available on my github repository.

I am being a newbie to nodejs development I did several mistakes around configuration, function definition and invoking  the function.  The blog is more of explaining what I did wrong and what I did to make the function working as expected.

OK with context set, lets start writing the function (first of the wrong way ;)) that does the reverse geocoding for us using the GoogleMaps API :

	'use strict';
	const gmap = require('@google/maps');
	function location(params) {
	const latlng = JSON.parse(JSON.stringify(params.coords))
	const gmapClient = gmap.createClient({
	key: process.env.GOOGLE_MAPS_API_KEY
	})
	gmapClient.reverseGeocode({
	"latlng": latlng,
	"result_type": "postal_code"
	},function(function(results, status){
	if (status === 'OK'){
	return {status: 'Err',location: response.json.results[0].formatted_address}
	}else{
	return {status: status,location: 'Unknown'}
	}
	})
	return {status: status,location: 'Unknown'}
	}
	global.main = location;

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ow_promise_blog_notworking.js

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For the sake of brevity and sticking to context of the blog, I am skipping details of source repo and related npm scripts.   Rest of this blog we just need  know:

• build is npm run build
• action deploy is npm run deploy
• action invoke is npm run dev

After we build npm run build, deploy  npm run deploy  the function, we invoke the action via npm run dev  always returning the result as :

{status: status,location: ‘Unknown‘}

I did not have any clue on why that did not work 😦 , with bit of research and consulting the OpenWhisk actions document I found that I was not properly handling the callback function of googlemap client’s  “reverseGeocode” method. I then decided to wrap the callback within Promise and return a Promise as response of the OpenWhisk nodejs Action.

Following the OpenWhisk actions documentation I tried updating the code as:

	'use strict';
	const gmap = require('@google/maps');
	function location(params) {
	const latlng = JSON.parse(JSON.stringify(params.coords))
	const gmapClient = gmap.createClient({
	key: process.env.GOOGLE_MAPS_API_KEY
	})
	return new Promise(function (resolve, reject) {
	gmapClient.reverseGeocode({
	"latlng": latlng,
	"result_type": "postal_code"
	}, function (results, status) {
	let respStatus = response.json.status
	if (respStatus === 'OK') {
	resolve({ status: respStatus, location: response.json.results[0].formatted_address })
	} else {
	reject({ status: respStatus, location: "" })
	}
	})
	});
	}
	global.main = location;

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ow_promise_blog_blocked.js

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Invoking the action post doing npm run build took me from bad to worse 😦 with action hung and no response.

Polling the OpenWhisk logs via wsk activation poll showed the following lines :

Activation: ‘location-finder’ (750f66bd750d426d8f66bd750d026d2a)[
“2018-02-23T05:27:06.453Z stderr: There was an issue while collecting your logs. Data might be missing.”
]

With further analysis and debug, I found  that I need to make the google map client promise aware.

Did the further and final modification to the function as :

	'use strict';
	const gmap = require('@google/maps');
	function location(params) {
	const latlng = JSON.parse(JSON.stringify(params.coords))
	const gmapClient = gmap.createClient({
	key: process.env.GOOGLE_MAPS_API_KEY,
	Promise: Promise
	})
	return gmapClient.reverseGeocode({
	"latlng": latlng,
	"result_type": "postal_code"
	}).asPromise()
	.then((response) => {
	let status = response.json.status
	let location = ""
	if (status === 'OK') {
	location = response.json.results[0].formatted_address
	}
	return { status: status, location: location }
	}).catch((err) => {
	console.log("Err: ", err)
	return { status: err, location: "unknown" }
	})
	}
	global.main = location;

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ow_promise_blog_working.js

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Two important changes :

• Line#11, where I created the google maps client to promise aware
• modified the way of the node function to return the promise from the location function via asPromise() method.

Doing a rebuild, deploy and run returned the expected response:

{
“location”: “New Row, London WC2N 4LH, UK”,
“status”: “OK”
}

In this example we saw how Promise can be configured on the google map client, if you are using similar functions from other API, then you need to check on how to hook on to  API call that can give you a handle to a Promise.

In summary the crucial learnings is how to return a Promise the right way from an Apache OpenWhisk JavaScript action, so that when invoking OpenWhisk action returns the response which will be part of the future(Promise) and does not exit the function immediately after the main function ends.