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Server Sent Events (SSE): EventSource implementation on Swift.

Andres Canal wrote this on May 28, 2015 under dev, eventsource, ios, open, server-sent-events, sse, swift .

We are pretty used to develop apps that consume REST APIs. We ask the server to perform an action and that's it. But this it's not always the best way to go in some scenarios. What happens if you need to get real time events from a server? The first thing that comes to our head is just set a timer and poll the server with a GET every 30 seconds or so, but this is not a good approach at all, lots of overhead, polling even if server has nothing to return and some other negative impacts on the server too.

So what's the way of doing this? The answer is Server Sent Events. This is an API standarized as part of HTML5 by the W3C. But if this is web technology why I'm talking about it on a iOS post? Because we can stil use it, we can consume those events, we just need to know how to do it or use a library that follows the standard.

Here you can read the latest library specification. Basically SSE works opening a connection and keeping that connection opened for ever, when the server has something to send it just sends the data over that connection. The stream of data follows a convention so everybody knows what to expect, if the connection drops you reconnect and that's it. Pretty easy.

Where can I apply this?

Well, the answer would be: 'every time you need to get data from a server not knowing when that data is going to be available'. For example a chat, you need to get the message when the message is sent, you don't want to have to ask the server for it, you want it now! Another example would be an app that tracks a vehicle in a map, you want to know where the vehicle is as the vehicle reports it's location.

How do I use it?

1- Download the library, drag the EventSource.swift file to your project or you can install this using cocoapods.

pod 'IKEventSource'

2- Create a new EventSource object:

var eventSource: eventSource = EventSource(url: server, headers: ["Authorization" : basicAuthAuthorization])

3- Subscribe to the different events:

eventSource.onOpen {
    // When opened

  eventSource.onError { (error) in
    // When errors

  eventSource.onMessage { (id, event, data) in
    // Here you get an event without event name!

  eventSource.addEventListener("event-name") { (id, event, data) in
    // Here you get an event 'event-name'

And that's it. You can close the connection when you don't need it anymore:


Checkout our github page for IKEventSource: IKEventSource