SSE "data" field not being received by Dart http.client - flutter

Question

I'm building a Flutter app that receives SSE from a server and translates them to specific notifications. The server is a Spring Boot app returning events containing "event:" and "data:" fields:
public void pushNotification(String username, PushEvent event) {
var emitter = emitters.get(username);
if (emitter == null) {
return;
}
try {
emitter.send(event.toSseEvent());
} catch (IOException e) {
log.debug("Could not send event for user " + username);
emitters.remove(username);
}
}
public class PushEvent {
private String type;
private Map<String, Object> body;
public SseEmitter.SseEventBuilder toSseEvent() {
return SseEmitter.event().name(type).data(body);
}
}
On the Flutter app, I use the Dart http package to open a Stream and receive the events:
Future<void> subscribe() async {
if (!_userModel.hasAuthentication()) {
return;
}
var user = _userModel.user as AuthenticatedUser;
var username = user.username;
var token = _userModel.getToken();
var uri = Uri.https(ApiUtils.API_BASE, '/api/push/subscribe/$username');
try {
var client = http.Client();
_client = client;
var request = new http.Request("GET", uri);
request.headers["Accept"] = "text/event-stream";
request.headers["Cache-Control"] = "no-cache";
request.headers["Authorization"] = token;
var response = await client.send(request);
if (response.statusCode == 200) {
_isSubscribed = true;
response.stream.toStringStream().forEach((value) {
var event = ServerEvent.parse(value);
_handleEvents(event);
}).onError((error, stackTrace) {
log.info("Connection closed");
log.info(error);
log.info(stackTrace);
unsubscribe();
}).whenComplete(() {
log.info("Connection completed");
unsubscribe();
subscribe();
});
} else {
_isSubscribed = false;
}
notifyListeners();
} catch (e) {
unsubscribe();
log.warning("Could not subscribe to notifications");
log.warning(e);
}
}
However, when I receive an event containing data from the server, the data does not show on the log:
I/flutter (14779): event:FRIEND_REQUEST
I/flutter (14779): data:
I am certain the data is being sent by the server since the React app on the same domain decodes the SSE and shows the notifications as intended:
const subscribePush = () => {
const username = sessionStorage.getItem('loggedUsername');
const token = sessionStorage.getItem('token');
var es = new EventSourcePolyfill(
'/api/push/subscribe/' + username,
{
headers: {
"Authorization": token,
}
}
);
es.onerror = () => es.close();
es.addEventListener("FRIEND_REQUEST", e => handleFriendRequestEvent(e));
es.addEventListener("FRIEND_ACCEPT", e => handleFriendAcceptEvent(e));
}
const handleFriendRequestEvent = function (event) {
const username = sessionStorage.getItem("loggedUsername");
const data = JSON.parse(event.data);
const source = data.source;
if (source !== username) {
var note = `${source} solicitou sua amizade!`;
var newNotifs = notifications.concat(note);
setNotifications(newNotifs);
setNewNotifications(newNotifications + 1);
}
}
Could something be missing from the request on the Flutter app, or is it possibly a bug?

Answer 1

Your implementation looks strangely similar to this one:
https://github.com/stevenroose/dart-eventsource
Take a look at the client implementation and how the response in decoded using the decoder.dart file.