Server-Sent Events (SSE) is a technology that enables the server to send real-time updates to a client over a single, persistent HTTP connection. Unlike traditional HTTP requests where the client must request data from the server, SSE allows the server to automatically push updates to the client as they become available. This makes it ideal for applications like live notifications, stock market tickers, or social media feeds, where updates are constantly being generated and need to be shown in real time without any delay.
The key advantage of SSE is its simplicity and efficiency. Once the client establishes the initial connection, the server can continuously send data in the form of text-based events, keeping the client updated without additional requests. SSE operates over HTTP, which makes it easy to implement and works well in situations where one-way communication (from server to client) is sufficient. It provides a lightweight solution for real-time data updates with minimal overhead, unlike WebSockets, which allow for two-way communication.
Header Parameters for SSE:
To establish an SSE connection, the client typically sends a GET request with the appropriate headers, and the server responds with an HTTP stream containing the events. Some key headers include:
-
Accept: text/event-stream– This header tells the server that the client expects an SSE stream. -
Cache-Control: no-cache– Prevents the browser from caching the response. -
Connection: keep-alive– Ensures the connection remains open for continuous data streaming. -
Content-Type: text/event-stream– Tells the client the format of the incoming data stream.
SSE Event Flow:
-
Client opens a connection to the server using
GET /events(or another endpoint). -
Server responds with a
Content-Type: text/event-streamheader and keeps the connection open, sending data continuously. -
Client processes the events as they arrive.