Add endpoint for sse server-sent events

README.md

@@ -191,6 +191,36 @@ Set-Cookie: hello=world
 
 </details>
 
+
+<details>
+<summary><code>/sse</code> Server-Sent Events (SSE) endpoint that sends a message every second.</summary>
+</details>
+
+#### Responses
+
+| Status | Description            |
+| ------ | ---------------------- |
+| 200 OK | Server is operational. |
+
+
+#### Example
+
+Server will respond with `Content-Type: text/event-stream` with the following content:
+
+```http
+HTTP/1.1 200 OK
+Cache-Control: no-cache
+Connection: keep-alive
+Content-Type: text/event-stream
+Date: Wed, 19 Feb 2025 10:10:15 GMT
+Transfer-Encoding: chunked
+
+data: { "counter": "1", "timestamp": "2025-02-19T12:10:15+02:00" }
+
+data: { "counter": "2", "timestamp": "2025-02-19T12:10:16+02:00" }
+...
+```
+
 <details>
 <summary><code>/apps/</code> Returns a list of available applications.</summary>
 </details>
@@ -245,7 +275,7 @@ Example commands in the descriptions are given using the
 To build and run the echoserver locally, use the following commands:
 
 ```sh
-make build
+make
 ./echoserver
 ```
 

handler.go

@@ -31,6 +31,8 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		h.statusHandler(w, r)
 	case strings.HasPrefix(r.URL.Path, "/apps/"):
 		h.templateHandler(w, r)
+	case r.URL.Path == "/sse":
+		h.serverSentEventHandler(w, r)
 	default:
 		h.echoHandler(w, r)
 	}
@@ -303,3 +305,38 @@ func (h *Handler) templateHandler(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "Error executing template", http.StatusInternalServerError)
 	}
 }
+
+// serverSentEventHandler implements a long polling server that periodically sends "ping" messages.
+func (h *Handler) serverSentEventHandler(w http.ResponseWriter, r *http.Request) {
+	slog.Info("Handling stream request", "url", r.URL.String())
+	w.Header().Set("Content-Type", "text/event-stream")
+	w.Header().Set("Cache-Control", "no-cache")
+	w.Header().Set("Connection", "keep-alive")
+
+	ticker := time.NewTicker(1 * time.Second)
+	defer ticker.Stop()
+
+	ctx := r.Context()
+	counter := 0
+
+	for {
+		select {
+		case <-ticker.C:
+			timestamp := time.Now().Format(time.RFC3339)
+			counter++
+			message := fmt.Sprintf("data: { \"timestamp\": \"%s\", \"counter\": \"%d\" }\n\n", timestamp, counter)
+			_, err := w.Write([]byte(message))
+			if err != nil {
+				slog.Error("Error writing to stream", "error", err)
+				return
+			}
+
+			if f, ok := w.(http.Flusher); ok {
+				f.Flush()
+			}
+		case <-ctx.Done():
+			slog.Info("Client disconnected")
+			return
+		}
+	}
+}