Dart - websocket.on()

import 'package:nitric_sdk/nitric.dart';

final socket = Nitric.websocket("socket");

socket.onConnect((ctx) async {
  // handle connections
});

socket.onDisconnect((ctx) async {
  // handle disconnections
});

socket.onMessage((ctx) async {
  // handle messages
});

Parameters

Name
handler
Type
WebsocketHandler
Description
The middleware function to use as handlers for the Websocket events.

Examples

The `connect` event

The connect event can be used to permit or deny new connections. Until the connect handler returns a successful response the client will be unable to send or receive messages via the websocket. If you need to perform any sort of client authentication before accepting the connection this is where it should be done.

Unlike the other websocket events the connect event has access to the query parameters provided during the connection request. This allows the client to provide relevant information needed to validate and establish the connection.

Additionally, the connectionId provided during this event will be used for all future communication with the client via this connection, it should be persisted in your application until the connection is terminated.

import 'package:nitric_sdk/nitric.dart';

final socket = Nitric.websocket("socket");

socket.onConnect((ctx) async {
  if (!isValidConnection(ctx.req.query)) {
    // deny the connection
    ctx.res.reject = true;
    return ctx;
  }

  registerConnection(ctx.req.connectionId);
});

Managing websocket connections

Websocket connections need to be managed. This can be done using any persistent data store you like. One approach is to use a Nitric key value store.

import 'package:nitric_sdk/nitric.dart';

final socket = Nitric.websocket("socket");
final connections = Nitric.kv("connections").allow([
  KeyValueStorePermission.get,
  KeyValueStorePermission.set,
  KeyValueStorePermission.delete,
]);

socket.onConnect((ctx) async {
  await connections.set(ctx.req.connectionId, {
    // add metadata
    "creation_time": DateTime.now(),
  });

  return ctx;
});

socket.onDisconnect((ctx) async {
  await connections.delete(ctx.req.connectionId);
});

Register a handler for message events

socket.onMessage((ctx) async {
  // handle messages
  print("new message from ${ctx.req.connectionId} ${ctx.req.message}");
});