Function ServerSentEventSender

coderd/httpapi/httpapi.go:306–408

ServerSentEventSender establishes a Server-Sent Event connection and allows the consumer to send messages to the client. The function returned allows you to send a single message to the client, while the channel lets you listen for when the connection closes. As much as possible, this function sho

(rw http.ResponseWriter, r *http.Request)

// As much as possible, this function should be avoided in favor of using the
// OneWayWebSocket function. See OneWayWebSocket for more context.
func ServerSentEventSender(rw http.ResponseWriter, r *http.Request) (
	func(sse codersdk.ServerSentEvent) error,
	<-chan struct{},
	error,
) {
	h := rw.Header()
	h.Set("Content-Type", "text/event-stream")
	h.Set("Cache-Control", "no-cache")
	h.Set("Connection", "keep-alive")
	h.Set("X-Accel-Buffering", "no")

	f, ok := rw.(http.Flusher)
	if !ok {
		panic("http.ResponseWriter is not http.Flusher")
	}

	ctx := r.Context()
	closed := make(chan struct{})
	type sseEvent struct {
		payload []byte
		errC    chan error
	}
	eventC := make(chan sseEvent)

	// Synchronized handling of events (no guarantee of order).
	go func() {
		defer close(closed)
		ticker := time.NewTicker(HeartbeatInterval)
		defer ticker.Stop()

		for {
			var event sseEvent
			select {
			case <-ctx.Done():
				return
			case event = <-eventC:
			case <-ticker.C:
				event = sseEvent{
					payload: []byte(fmt.Sprintf("event: %s\n\n", codersdk.ServerSentEventTypePing)),
				}
			}

			_, err := rw.Write(event.payload)
			if event.errC != nil {
				event.errC <- err
			}
			if err != nil {
				return
			}
			f.Flush()
		}
	}()

	sendEvent := func(newEvent codersdk.ServerSentEvent) error {
		buf := &bytes.Buffer{}
		_, err := buf.WriteString(fmt.Sprintf("event: %s\n", newEvent.Type))
		if err != nil {
			return err