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1. Rails 4 & Server-Sent Events
Piotr Karbownik

2. SSE - EventSource API
Server-Sent Events (SSE) is a HTML5 standard
describing how servers can initiate data
transmission towards clients once an initial
client connection has been established.
Browsers: Firefox, Chrome, Opera, Safari

3. SSE != Websockets
• SSE connections can only push data to the
browser.
• It’s still HTTP - no new protocol
• Automatic reconnection

4. SSE - applications
• Notifications
• Continuous data streams
• News feeds

5. SSE – on the frontend
function newStream(){
var source = new EventSource('/streaming');
source.addEventListener('update', function(e) {
//do stuff
});
}

6. SSE – on the frontend
function newStream(){
var source = new EventSource('/streaming');
source.onmessage (function(e) {
//do stuff
});
}

7. EventSource Object Methods
onopen -When a connection to the server is
opened
onmessage - When a message is received
onerror - When an error occurs

8. SSE – message format
Sample:
event: my_event
data: {"username": „Peter"}
event - The event's type. If this is specified, an event will be
dispatched on the browser to the listener for the specified event
name.
data - field for the message.
id - the event ID to set the EventSource object's last event ID value
retry - The reconnection time to use when attempting to send the
event.

9. Rails 4 - ActionController::Live
Live Streaming: the ability to send partial
responses to the client immediately.

10. What about the server?
Server must support:
• Long running requests
• Live streaming
• Concurrency
• Examples: Puma, Rainbows, Thin

11. Config
environments /development.rb:
• config.cache_classes = true
• config.eager_load = true
database.yml
• pool == server max threads
• for Puma default is 16

12. Sample code - 1

13. Sample code

14. Sample code - 2

16. Summary
• Easy to implement
• Real time
• Good for notifications
• Problems with client connections amount and
status.

17. …and the end
Sample apps:
https://github.com/cynamonium/srug-
streamapp-2/
https://github.com/cynamonium/srug-
streamapp-1