EventSource

Server-Sent Events for iOS, watchOS, tvOS and macOS

This library is deprecated, slated to become unmaintained in July 2021. LaunchDarkly's iOS SDK has moved to using a new Swift SSE library as a replacement.

For details on Server Sent Events, see the Specification

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:, onMessage, 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

To make the initial connection to the streaming event server, call open on the event source. That gives you control over when events start arriving.

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

Reconnection attempts are automatic and seamless, even if the server goes down. How frequently reconnection attempts are made is controlled by the server by setting the retry key on its events. If the server doesn't send a retry, the default is 1 second intervals.

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.

Installation

EventSource supports multiple methods for installing the library in a project.

Installation with CocoaPods

CocoaPods is a dependency manager for Objective-C, which automates and simplifies the process of using 3rd-party libraries like EventSource in your projects. You can install it with the following command:

$ gem install cocoapods

Podfile

To integrate EventSource into your Xcode project using CocoaPods, specify it in your Podfile:

source 'https://github.com/CocoaPods/Specs.git'
platform :ios, '8.0'

target 'TargetName' do
pod 'DarklyEventSource', '~> 4.1.1'
end

Then, run the following command:

$ pod install

Installation with Carthage

Carthage is a decentralized dependency manager that builds your dependencies and provides you with binary frameworks.

You can install Carthage with Homebrew using the following command:

$ brew update
$ brew install carthage

To integrate EventSource into your Xcode project using Carthage, specify it in your Cartfile:

github "launchdarkly/ios-eventsource" >= 4.1.1

Run carthage to build the framework and drag the built EventSource.framework into your Xcode project.

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.

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.