Server-sent events

Server-Sent Events (SSE) is a server push technology enabling a client to receive automatic updates from a server via an HTTP connection, and describes how servers can initiate data transmission towards clients once an initial client connection has been established. They are commonly used to send message updates or continuous data streams to a browser client and designed to enhance native, cross-browser streaming through a JavaScript API called EventSource, through which a client requests a particular URL in order to receive an event stream. The Server-Sent Events EventSource API is standardized as part of HTML5^[1] by the W3C.

History

The WHATWG Web Applications 1.0 proposal^[2] included a mechanism to push content to the client. On September 1, 2006, the Opera web browser implemented this new experimental technology in a feature called "Server-Sent Events".^[3]^[4]

Browser support

Web browser support for Server-Sent Events
Browser	Supported	Notes
Internet Explorer	No	^[5]
Mozilla Firefox	Yes	Starting with Firefox 6 ^[5]
Google Chrome	Yes	Starting with Chrome 6 ^[5]
Opera	Yes	Starting with Opera 11.5 ^[5]
Safari	Yes	Starting with Safari 5.0 ^[5]
Microsoft Edge	Yes	Starting with Edge 79 ^[5]

Libraries

.NET

Service Stack EventSource library with both server and client implementations.

ASP.NET

SignalR - Transparent implementation for ASP.NET.

C

HaSSEs Asynchronous server-side SSE daemon written in C (It uses one thread for all connected clients).

Erlang

Lasse EventSource server handler for Erlang's cowboy
Shotgun EventSource client in Erlang

Go

eventsource EventSource library for Go.
go-sse SSE implementation for Go.
go-rfc/sse Optimised SSE decoder for Go

Java

jEaSSE - Server-side asynchronous implementation for Java servlets and Vert.x
Akka HTTP has SSE support since version 10.0.8
alpakka Event Source Connector EventSource library for alpakka which supports reconnection
Spring WebFlux Server and client side Java implementation built on reactive streams and non-blocking servers
Jersey has a full implementation of JAX-RS support for Server Sent Events as defined in JSR-370
Micronaut HTTP server supports emitting Server Sent Events
JeSSE - Server-side library with user/session management, group broadcast, and authentication
Armeria has server and client-side asynchronous SSE implementation built on top of Netty and Reactive Streams
Play Framework Event Source for server-sent event emission

Node.js

sse-stream - Node.js/Browserify implementation (client and server).
total.js - web application framework for Node.js - example + supports WebSockets (RFC 6455)
eventsource-node - EventSource client for Node.js
Thread-SSE - A library for Node.js and web browser to develop security and high-performance SSE.

Objective C

TRVSEventSource - EventSource implementation in Objective-C for iOS and macOS using NSURLSession.

Perl

Mojolicious - Perl real-time web framework.

PHP

Hoa\Eventsource - Server implementation.

Python

Python SSE Client - EventSource client library for Python using Requests library.
Server Side Events (SSE) client for Python - EventSource client library for Python using Requests or urllib3 library.
django-eventstream - Server-Sent Events for Django.
flask-sse - A simple Flask extension powered by Redis.
sse
SSE protocol for Starlette - server sent events for starlette and FastApi
event-source-library - Implementation in python2 with Tornado. Client and server implementations.

Ruby

Faye - Simple pub/sub messaging for the web.

Rust

Warp A super-easy, composable, web server framework for warp speeds.

Scala

Akka HTTP has SSE support since version 10.0.8
alpakka Event Source Connector EventSource library for alpakka which supports reconnection

Swift

EventSource - EventSource implementation using NSURLSession.

References

^ "Server-Sent Events". W3C. 17 July 2013.
^ "Web Applications 1.0 specification".
^ "Event Streaming to Web Browsers".
^ Stream Updates with Server-Sent Events, Eric Bidelman, HTML5Rocks website.
^ ^a ^b ^c ^d ^e ^f When can I use... Server-sent DOM events

External links

Server-Sent Events. W3C Recommendation.
HTML5 Server-push Technologies, Part 1. Introduction into HTML5 Server-push Technologies. Part 1 covers ServerSent Events.
Using Server-Sent Events. A concise example of how to use server-sent events, on the Mozilla Developer Network.
EventSource reference on MDN
Django push: Using Server-Sent Events and WebSocket with Django Django push: Using Server-Sent Events and WebSocket with Django.
Server-Sent Events Example in Spring
Server-Sent Events vs WebSockets

[1] "Server-Sent Events". W3C. 17 July 2013.

[2] "Web Applications 1.0 specification".

[3] "Event Streaming to Web Browsers".

[tutorial-4] Stream Updates with Server-Sent Events, Eric Bidelman, HTML5Rocks website.

[caniuse.com-5] ^ ^a ^b ^c ^d ^e ^f When can I use... Server-sent DOM events

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