Server-Sent Events for iOS and Mac

What does it do?

It creates a long-lived, unidirectional HTTP channel between your Cocoa app and a web server so that your app can receive events from the server.

Listening for Named Events

Subscribing to a named event is done via the addEventListener:handler: method, as shown below:

NSURL *serverURL = [NSURL URLWithString:@"http://127.0.0.1:8000/"];
EventSource *source = [EventSource eventSourceWithURL:serverURL];
[source addEventListener:@"hello_event" handler:^(Event *e) {
    NSLog(@"%@: %@", e.event, e.data);
}];

It's super simple and will be familiar to anyone who has seen any Server-Sent Events JavaScript code.

Listening for All Events

There's a onMessage: method that will receive all message events from the server.

NSURL *serverURL = [NSURL URLWithString:@"http://127.0.0.1:8000/"];
EventSource *source = [EventSource eventSourceWithURL:serverURL];
[source onMessage:^(Event *e) {
    NSLog(@"%@: %@", e.event, e.data);
}];

Listening for Connection State Changes

Additionally, there are onOpen:, onError:, and onReadyStateChanged: methods to receive connection state events.

NSURL *serverURL = [NSURL URLWithString:@"http://127.0.0.1:8000/"];
EventSource *source = [EventSource eventSourceWithURL:serverURL];
[source onError:^(Event *e) {
    NSLog(@"ERROR: %@", e.data);
}];

With the exception of the onError:, the event and data properties for these events will be null. Check the readyState property on the event.

Graceful Connection Handling

Reconnection attempts are automatic and seamless, even if the server goes go. How frequently reconnection attempts are made is controlled by the server by setting the retry key on its events.

Server Code

This is a simple Node.js app that will generate the Server-Sent Events. The events are created at a rate of one per second.

var http = require('http');

http.createServer(function (req, res) {
    res.writeHead(200, { 'Transfer-Encoding': 'chunked', 'Content-Type': 'text/event-stream' });

    setInterval(function() { 
        var now = new Date().getTime();
        var payload = 'event: hello_event\ndata: {"message":"' + now + '"}\n\n'; 
        res.write(payload); 
    }, 1000);
}).listen(8000);

The payload above doesn't include an id parameter, but if you include one it will be available in the Event object in your Cocoa code.

There is also a simple Go Server-Sent Events server.

Installation

The easiest way to get started is to use Carthage. Just add the following line to your Cartfile and the run carthage update from your terminal:

github "neilco/EventSource"

If you prefer Cocoapods, add this to your Podfile and then run pod install from your terminal:

pod 'EventSource'

Otherwise, just include the contents of the EventSource directory manually to your project.

Other bits

Contact

I'm @neilco on GitHub and I'm @neilco on Twitter.

License

MIT license

Copyright (c) 2013 Neil Cowburn (http://github.com/neilco/)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.