feat: SSE handler, send y keepalive (issue 0011 fase 2)

functions/infra/sse_handler.go

@@ -0,0 +1,44 @@
+package infra
+
+import "net/http"
+
+// SSEHandler retorna un http.HandlerFunc que setea los headers SSE,
+// consume eventos del canal y los envia con flush. Cierra limpiamente
+// si el cliente se desconecta (context cancelado) o si el canal se cierra.
+//
+// Headers seteados:
+//   Content-Type: text/event-stream
+//   Cache-Control: no-cache
+//   Connection: keep-alive
+//   X-Accel-Buffering: no   (deshabilita buffering en nginx)
+func SSEHandler(events <-chan SSEEvent) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		flusher, ok := w.(http.Flusher)
+		if !ok {
+			http.Error(w, "streaming unsupported", http.StatusInternalServerError)
+			return
+		}
+
+		w.Header().Set("Content-Type", "text/event-stream")
+		w.Header().Set("Cache-Control", "no-cache")
+		w.Header().Set("Connection", "keep-alive")
+		w.Header().Set("X-Accel-Buffering", "no")
+		w.WriteHeader(http.StatusOK)
+		flusher.Flush()
+
+		ctx := r.Context()
+		for {
+			select {
+			case <-ctx.Done():
+				return
+			case ev, ok := <-events:
+				if !ok {
+					return
+				}
+				if err := SSESend(w, ev); err != nil {
+					return
+				}
+			}
+		}
+	}
+}