How to use websockets?
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You can declare a dependency on Cask with the following using directive:
//> using dep com.lihaoyi::cask::0.10.2
In your build.sbt, you can add a dependency on Cask:
lazy val example = project.in(file("example"))
.settings(
scalaVersion := "3.4.2",
libraryDependencies += "com.lihaoyi" %% "cask" % "0.10.2",
fork := true
)
In your build.sc, you can add a dependency on Cask:
object example extends RootModule with ScalaModule {
def scalaVersion = "3.4.2"
def ivyDeps = Agg(
ivy"com.lihaoyi::cask::0.10.2"
)
}
You can create a WebSocket endpoint with the @cask.websocket annotation. The endpoint method should return a
cask.WsHandler instance defining how the communication should take place. It can also return a cask.Response, which rejects the
attempt at forming a WebSocket connection.
The connection can also be closed by sending a cask.Ws.close() message through the WebSocket channel.
Create an HTML file named websockets.html with the following content and place it in the resources directory.
<!DOCTYPE html>
<html>
<body>
<div>
<input type="text" id="input" placeholder="Provide city name">
<button onclick="sendMessage()">Send</button>
</div>
<div id="time"></div>
<script>
const ws = new WebSocket('ws://localhost:8080/websocket');
ws.onmessage = function(event) {
receiveMessage(event.data);
};
ws.onclose = function(event) {
receiveMessage('The connection has been closed');
};
function sendMessage() {
const inputElement = document.getElementById('input');
const message = inputElement.value;
ws.send(message);
}
function receiveMessage(message) {
const timeElement = document.getElementById('time');
timeElement.textContent = message;
}
</script>
</body>
</html>
The JavaScript code opens a WebSocket connection using the ws://localhost:8080/websocket endpoint. The ws.onmessage
event handler is executed when the server pushes a message to the browser and ws.onclose when the connection is closed.
Create an endpoint for serving static files using the @cask.staticResources annotation and an endpoint for handling
the WebSocket connection.
@cask.staticResources("/static")
def static() = "."
private def getZoneIdForCity(city: String): Option[ZoneId] = {
import scala.jdk.CollectionConverters._
ZoneId.getAvailableZoneIds.asScala.find(_.endsWith("/" + city)).map(ZoneId.of)
}
@cask.websocket("/websocket")
def websocket(): cask.WsHandler = {
cask.WsHandler { channel =>
cask.WsActor {
case cask.Ws.Text("") => channel.send(cask.Ws.Close())
case cask.Ws.Text(city) =>
val text = getZoneIdForCity(city) match {
case Some(zoneId) => s"Current date is: ${ZonedDateTime.now().withZoneSameInstant(zoneId)}"
case None => s"Couldn't find time zone for city $city"
}
channel.send(cask.Ws.Text(text))
}
}
}
initialize()
@cask.staticResources("/static")
def static() = "."
private def getZoneIdForCity(city: String): Option[ZoneId] =
import scala.jdk.CollectionConverters.*
ZoneId.getAvailableZoneIds.asScala.find(_.endsWith("/" + city)).map(ZoneId.of)
@cask.websocket("/websocket")
def websocket(): cask.WsHandler =
cask.WsHandler { channel =>
cask.WsActor {
case cask.Ws.Text("") => channel.send(cask.Ws.Close())
case cask.Ws.Text(city) =>
val text = getZoneIdForCity(city) match
case Some(zoneId) => s"Current date is: ${ZonedDateTime.now().withZoneSameInstant(zoneId)}"
case None => s"Couldn't find time zone for city $city"
channel.send(cask.Ws.Text(text))
}
}
initialize()
In the cask.WsHandler we define a cask.WsActor. It reacts to events (of type cask.util.Ws.Event) and uses the
WebSocket channel to send messages. In this example, we receive the name of a city and return the current time there. If the server
receives an empty message, the connection is closed.