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fritz2 offers support for websockets you can use with different protocols. To use it, you first have to create a socket:

val websocket: Socket = websocket("ws://myserver:3333")

You can specify one or more protocols on creation. See these docs for more information.

Your socket is now ready to establish a Session with the server, using the method connect(). Messages can now be exchanged between socket and server, which looks like this:

val session: Session = websocket.connect()

// receiving messages from server
session.messages.body.onEach {
  window.alert("Server said: $it")
}.watch() // watch is needed because the message is not bound to html

// sending messages to server

As you can see, Session offers a Flow of MessageEvents in messages. When a new message from the server arrives, a new message pops up on the Flow. Get the content of the message with one of the following methods (depending on content type):

  • data: Flow<Any?>
  • body: Flow<String>
  • blob: Flow<Blob>
  • arrayBuffer: Flow<ArrayBuffer>

More information regarding the connection status is provided by the Session as Flows:

  • isConnecting: Flow<Boolean>
  • isOpen: Flow<Boolean>
  • isClosed: Flow<Boolean>
  • opens: Flow<Event>
  • closes: Flow<CloseEvent>

When you’re done, close the session client-side. Supplying a code and a reason is optional.

session.close(reason = "finished")

After the Session was closed by either client or server, no further messages can be sent, and trying to do so throws a SendException.

You can synchronize the content of a Store with a server via websockets. Use the function syncWith(socket: Socket, resource: Resource<T, I>) like in the following example:

data class Person(val name: String, val age: Int, val _id: String = uniqueId())

val personResource = Resource(Person::_id, PersonSerializer, Person("", 0))
val socket = websocket("ws://myserver:3333")

val entityStore = object : RootStore<Person>(personResource.emptyEntity) {
    init {
        syncWith(socket, personResource)
    // your handlers...

When the model in the Store changes, it will be sent to the server via Websockets, and vice versa of course. To get a full working example you can have a look at our Ktor Chat project.

That way fritz2 provides an easy way to synchronize your stores with a server. Want more? Keep on reading about Routing.

Distributed by a MIT license.