EventSource

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.

Client Code

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.

There's a onMessage: method that will receive all message events from the server. Additionally, there are onOpen: and onError: methods to receive open and error events.

Re-connections to the server are automatic and graceful, even if the server goes go.

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.

Contact

Neil Cowburn
@neilco

License

MIT license

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.