Developing software in the Real World

CORS and OpenWhisk web actions

By default, OpenWhisk will handle the relevant responses for CORS. Specifically, it will respond to an OPTIONS request with these headers:

If you need to change what is sent or you don't want to send these headers at all, then you need to do set the annotation web-custom-options to true and handle the OPTIONS header yourself. Note that if you don't set this annotation, you must not set any of these headers yourself as… continue reading.

Creating an OpenWhisk Alexa skill

In a previous post, I looked at the mechanics of how to create an Alexa skill to tell me which colour bin I needed to put out next. I'll now look at how I chose to implement it in OpenWhisk, using Swift. An Alexa skill consists of a number of intents and you register a single end point to handle them all. As I'm using OpenWhisk, I have direct web access to my actions without… continue reading.

POSTing data using KituraNet

I had a need to send a POST request with a JSON body from Swift and as I had KituraNet and SwiftyJSON already around, it proved to reasonably easy. To send a POST request using KituraNet, I wrote this code:

As you can see, I've liberally commented it, so it should be easy to follow. Let's look at some interesting bits. SwiftJSON is convenient SwiftyJSON does all the heavy lifting of converting dictionaries. As… continue reading.

Detecting OpenWhisk web actions

I've already written about OpenWhisk web actions and how they allow you to send a status code and HTTP headers to the client by returning a dictionary with the keys status, headers and body from your main() method:

If this test action is in the default namespace, then we create it with wsk action update test test.swift -a web-export true to enable web action support and access it via curl:

However, when you… continue reading.

Calling an OpenWhisk action in Swift

As OpenWhisk is a Functions as a Service system, it makes sense to create actions that do one thing and call other actions when they want other work done. As an example, in DrinksChooser, the choose action calls the incrementDrinkCount action which increments the count of the recommended drink in Redis. This way, choose doesn't have to know anything about Redis as that's not its job. In OpenWhisk's Swift environment, there's the Whisk.invoke() method to… continue reading.

Passing secrets to your OpenWhisk action

There is only one way to pass data into your OpenWhisk action: parameters. Your function receives a dictionary of parameters and returns one. Let's explore how you can set these parameters. Parameters passed to the action You can see this by creating this action: test.swift

Add the action to OpenWhisk with: wsk action update params params.swift -a web-export true and test:

If you use a Web Action (unauthenticated HTTP requests), then OpenWhisk will… continue reading.

Error handling in OpenWhisk actions

With a standard OpenWhisk action, we return a dictionary of the data and let OpenWhisk deal with converting it to JSON etc. OpenWhisk will also set the correct 200 status code. How do we handle an error though? It turns out that if there is a key called "error" in our returned dictionary, then all the other data is ignored and an error is sent back. To show this, consider this action:

If we… continue reading.

OpenWhisk web actions

The first way that you learn to call your OpenWhisk action over HTTP is a POST request that is authenticated using your API key. This key allows all sorts of write access to your account, so you never release it. If you want to access the action over HTTP without the API key, you have two choices: Web Actions or API Gateway. This article discusses how to use Web Actions as they are very useful… continue reading.

Serverless Swift on OpenWhisk

I'm interested in serverless computing and as I write Swift, the OpenWhisk platform comes up high when you Google. This turns out to be a really good choice as OpenWhisk is Open Source so I can read the source code (and have done!). In principle, I can also run my own instance of it if I need to to for regulatory reasons, or just to avoid vendor lock-in. Commercially, the whole point of Serverless (aka… continue reading.

A Kitura tutorial

Swift only became interesting to me when it was released as Open Source with an open development model. I'm exploring using it on Linux for APIs and as worker processes at the end of a queue, such as RabbitMQ or beanstalkd. To this end, I've been playing with Kitura, a web framework for Swift 3 by the Swift@IBM team. It's inspired by Express and so the basic operation is familiar to me. As is my… continue reading.