How can I broadcast a message to all clients connected to an Undertow websocket server?

This is my current setup for an Undertow websocket server:

    Undertow server = Undertow.builder()
            .addHttpListener(8080, "localhost")
            .setHandler(path()
                    .addPrefixPath("/", websocket((exchange, channel) -> {
                        channel.getReceiveSetter().set(new AbstractReceiveListener() {
                            @Override
                            protected void onFullTextMessage(WebSocketChannel channel, BufferedTextMessage message) {
                                final String messageData = message.getData();
                                for (WebSocketChannel session : channel.getPeerConnections()) {
                                    WebSockets.sendText(messageData, session, null);
                                }
                            }
                        });
                        channel.resumeReceives();
                    }))).build();

This is copied from one of their demo files. I believe onFullTextMessage here broadcasts any messages it receives to all clients.

I want to be able to trigger this behavior on demand. So instead of having to receive a message and using an event handler to send out more messages, I want to be able to arbitrarily do server.send() and send a message to all connected clients.

I’ve looked around and haven’t found anything that seems capable of achieving this. I don’t relish the idea of tracking all WebSocketChannels and sending to each client manually. Surely, there’s a method somewhere that I’ve overlooked?

I’d appreciate some pointers if it’s not something that’s just not possible!

Answer

You can broadcast the message to all the clients on the channel by getting all the connections to this canal and sending the message :

channel.getPeerConnections().forEach(connection -> {
    WebSockets.sendText(messageData, connection, null);
});

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Answer