MinimalWebApplicationSSE

Minimal .NET 6 WebAPI - Server-Sent Events (SSE)

Event

The Event interface represents an event which takes place in the DOM.

-- https://developer.mozilla.org/en-US/docs/Web/API/Event

Server-sent events

Traditionally, a web page has to send a request to the server to receive new data. That is, the page requests data from the server. With server-sent events, it's possible for a server to send new data to a web page at any time, by pushing messages to the web page. These incoming messages can be treated as Events + data inside the web page.

-- https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events

Using server-sent events

Developing a web application that uses server-sent events is straightforward. You'll need a bit of code on the server to stream events to the front-end, but the client side code works almost identically to websockets in part of handling incoming events. This is a one-way connection, so you can't send events from a client to a server.

-- https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events

EventSource

The EventSource interface is web content's interface to server-sent events. An EventSource instance opens a persistent connection to an HTTP server, which sends events in text/event-stream format. The connection remains open until closed by calling EventSource.close().

Once the connection is opened, incoming messages from the server are delivered to your code in the form of events. If there is an event field in the incoming message, the triggered event is the same as the event field value. If no event field is present, then a generic message event is fired.

Unlike WebSockets, server-sent events are unidirectional; that is, data messages are delivered in one direction, from the server to the client (such as a user's web browser). That makes them an excellent choice when there's no need to send data from the client to the server in message form. For example, EventSource is a useful approach for handling things like social media status updates, news feeds, or delivering data into a client-side storage mechanism like IndexedDB or web storage.

-- https://developer.mozilla.org/en-US/docs/Web/API/EventSource