SSE vs WebSockets in Go

Use WebSockets for full-duplex, low-latency bidirectional communication and Server-Sent Events (SSE) for unidirectional server-to-client streaming. WebSockets require a third-party library like gorilla/websocket to handle the protocol upgrade, while SSE uses the standard net/http package and relies on ResponseWriter.Flush() for streaming. For a simple server-to-client notification system, SSE is the easiest implementation:

func handler(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "text/event-stream")
    w.Header().Set("Cache-Control", "no-cache")
    w.Header().Set("Connection", "keep-alive")
    flusher, _ := w.(http.Flusher)
    for {
        fmt.Fprintf(w, "data: %s\n\n", "Hello")
        flusher.Flush()
        time.Sleep(1 * time.Second)
    }
}

For bidirectional chat, use gorilla/websocket to upgrade the connection:

import "github.com/gorilla/websocket"

var upgrader = websocket.Upgrader{CheckOrigin: func(r *http.Request) bool { return true }}

func handler(w http.ResponseWriter, r *http.Request) {
    conn, _ := upgrader.Upgrade(w, r, nil)
    for {
        _, msg, _ := conn.ReadMessage()
        conn.WriteMessage(websocket.TextMessage, msg)
    }
}

Use Server-Sent Events (SSE) when your server needs to push updates to a client, like a live news feed or stock ticker, because it is simple and uses standard HTTP. Choose WebSockets when you need two-way communication where the client and server send messages back and forth instantly, like in a chat app or multiplayer game. Think of SSE as a radio broadcast (one-way) and WebSockets as a telephone call (two-way).