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How do I send messages from Java program to a Javascript STOMP client using ActiveMQ-Artemis?

I'm trying to communicate back and forth between a Java process and a browser UI. To do this, I configured a multicast address in Artemis. The messages from the Java process are not making it to the browser subscribers, which are implemented using StompJS.
To test, I wrote a Hello World type of program in Java and in Javascript to simplify the probelm as much as I could. Both programs will start consumers on the address and then send 100 messages to the address. The consumers just log that they received the message.
The Java program receives all the messages that it produced and all the messages that the Javascript program produced. The Javascript program receives all the messages that it produced, but none of the messages that the Java program produced.
When I use the Artemis Console to look at the queue the STOMP client has created, it shows 200 messages added, 100 acknowledged, and 100 stuck in delivering.
If I use the Artemis Console to send a message to that address, that message is received by both the Java and Javascript programs.
Any ideas what I'm doing wrong here?
Javascript program
import { Client } from "#stomp/stompjs"
let client;
export function testStomp() {
client = new Client();
client.brokerURL = "ws://messaging-host:7961";
client.onConnect = handleConnected;
client.activate();
}
function handleConnected() {
client.subscribe("broadcastMessage", message => console.log(message.body));
const message = { destination: "broadcastMessage" };
for (let i = 0; i < 100; i++) {
message.body = "Message from javascript " + i;
client.publish(message);
}
}
Java program:
package com.whatever;
import org.apache.activemq.artemis.api.core.*;
import org.apache.activemq.artemis.api.core.client.*;
import java.util.UUID;
public class TestArtemis {
public static void main(String[] args) throws Exception {
String url = "tcp://messaging-host:7961";
ServerLocator serverLocator = ActiveMQClient.createServerLocator(url);
ClientSession session = serverLocator.createSessionFactory().createSession();
startConsumer(session);
ClientProducer producer = session.createProducer();
for (int i = 0; i < 100; i++) {
String payload = "Message from java " + i;
ClientMessage message = session.createMessage(false);
message.getBodyBuffer().writeBytes(payload.getBytes());
producer.send("broadcastMessage", message);
Thread.sleep(1000);
}
}
private static void startConsumer(ClientSession session) throws Exception{
session.start();
String queueName = UUID.randomUUID().toString();
session.createQueue(new QueueConfiguration(queueName)
.setAddress("broadcastMessage")
.setDurable(false)
.setRoutingType(RoutingType.MULTICAST)
.setTemporary(true));
ClientConsumer consumer = session.createConsumer(queueName);
consumer.setMessageHandler(message -> {
byte[] bytes = new byte[message.getBodyBuffer().readableBytes()];
message.getDataBuffer().readBytes(bytes);
System.out.println("Received " + new String(bytes));
});
}
}

ActiveMQ Artemis uses the content-length header to detect if the STOMP message type is binary or text.
To use text STOMP message type the Javascript program has to skip the content-length header and the Java program has to produce messages with text type i.e.
Javascript program changes:
const message = { destination: "broadcastMessage", skipContentLengthHeader: true };
Java program:
ClientMessage message = session.createMessage(Message.TEXT_TYPE, false);
message.getBodyBuffer().writeNullableSimpleString(SimpleString.toSimpleString(payload));
To use binary STOMP message type the Java program has to produce messages with the content-length header i.e.
String payload = "Message from java " + i;
byte[] payloadBytes = payload.getBytes();
ClientMessage message = session.createMessage(false);
message.putIntProperty("content-length", payloadBytes.length);
message.getBodyBuffer().writeBytes(payloadBytes);

C# Websocket The remote party closed the WebSocket connection without completing the close handshake

Hello I'm currently implementing a websocket component to my very basic site. I'm running .NET Core 3.1 HTTP Listener for serving html, I've been stumped by implementing websockets.
I've worked with TCP in C# before and understand the flow of everything but websockets are a new thing to me. Here is the C# code for accepting websockets
[Route("/socket", "GET")]
public static async Task upgrade(HttpListenerContext c)
{
if (!c.Request.IsWebSocketRequest)
{
c.Response.StatusCode = 400;
c.Response.Close();
return;
}
try
{
var sock = (await c.AcceptWebSocketAsync(null)).WebSocket;
byte[] buff = new byte[1024];
var r = await sock.ReceiveAsync(buff, System.Threading.CancellationToken.None);
}
catch (Exception x)
{
Console.WriteLine($"Got exception: {x}");
}
//WebSocketHandler.AddSocket(sock);
}
I've added var r = await sock.ReceiveAsync(buff, System.Threading.CancellationToken.None); to this function because originally I was getting the exception in my WebSocketHandler class, so I moved the code to the one function to test.
Here is the client:
<script>
let socket = new WebSocket("ws://localhost:3000/socket");
socket.onopen = function (event) {
console.log("[ OPENED ] - Opened Websocket!");
};
socket.onclose = function (event) {
console.log("[ CLOSED ] - Socket closed");
};
socket.onerror = function (error) {
console.log("[ ERROR ] - Got websocket error:");
console.error(error);
};
socket.onmessage = function (event) {
// This function will be responsible for handling events
console.log("[ MESSAGE ] - Message received: ");
const content = JSON.parse(event.data);
console.log(content);
};
</script>
Here is the output in the console for the client:
Navigated to http://127.0.0.1:5500/index.html
index.html:556 [ OPENED ] - Opened Websocket!
index.html:569 [ CLOSED ] - Socket closed
And here is the exception from the C# server:
Got exception: System.Net.WebSockets.WebSocketException (997): The remote party closed the WebSocket connection without completing the close handshake.
at System.Net.WebSockets.WebSocketBase.WebSocketOperation.Process(Nullable`1 buffer, CancellationToken cancellationToken)
at System.Net.WebSockets.WebSocketBase.ReceiveAsyncCore(ArraySegment`1 buffer, CancellationToken cancellationToken)
at SwissbotCore.HTTP.Routes.UpgradeWebsocket.upgrade(HttpListenerContext c) in C:\Users\plynch\source\repos\SwissbotCore\SwissbotCore\HTTP\Routes\UpgradeWebsocket.cs:line 29
I can provide the http requests that the client sends if need be but I am completely stumped on this, any help will be greatly appreciated.

You might want to read up on The Close Handshake in Section 1.4 in RFC 6455 and also Close the WebSocket Connection in Section 7.1.1 in RFC 6455.
Essentially, you need to let the WebSocket endpoint know you are going to close the socket, before you terminate the socket.
For your server side, you should probably be catching this exception, as this can also happen in production scenarios when network issues occur.

I'm not sure why, but, if you change the code inside try block to this:
try
{
var sock = (await c.AcceptWebSocketAsync(null)).WebSocket;
byte[] buff = new byte[1024];
await Listen(sock);
}
catch (Exception x)
{
Console.WriteLine($"Got exception: {x}");
}
private async Task Listen(WebSocket sock)
{
return new Task(async () =>
{
while(sock.State == WebSocketState.Open)
{
var r = await sock.ReceiveAsync(buff, System.Threading.CancellationToken.None);
}
});
}
it's gonna work out fine.

How to send message from node.js server to Android app?

Im trying to make a simple application. That is When I write a word at edittext in android app such as "Hi", Then android app send message "Hi" to node.js server and node.js server send message "Hi has sent successflly" to android app. This is just a example, actually my object is android send a data(message) to server, and receive another data(message) from server.
The problem is this. When I write a word at android app and press button, the message transmitted successfully(I can confirm by console at node.js). But I cant send message to android from node.js .. When I press send button, My android app shut down..
What android says is "java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.Activity.runOnUiThread(java.lang.Runnable)' on a null object reference" ..
Yesterday, this error didn't happened and another error occured. "cannot cast string to JSONObject."
I will show you my code.
Server Side(Node.js)
var app = require('express')();
var http = require('http').Server(app);
var io = require('socket.io')(http);
var port = 12000;
app.get('/', function(req, res) {
res.sendFile('index.html');
})
io.on('connection', function(socket) {
console.log('Android device has been connected');
socket.on('message', function(data) {
console.log('message from Android : ' + data);
Object.keys(io.sockets.sockets);
Object.keys(io.sockets.sockets).forEach(function (id) {
console.log("ID : ", id );
io.to(id).emit('message', data);
console.log(data + ' has sent successfully');
})
/*if (data != null) {
io.emit('message', {message : data + ' has received successfully'});
}*/
})
socket.on('disconnect', function() {
console.log('Android device has been disconnected');
})
})
http.listen(port, function() {
console.log('Server Start at port number ' + port);
})
Client Side (Android)
private Emitter.Listener handleIncomingMessages = new Emitter.Listener(){
#Override
public void call(final Object... args){
getActivity().runOnUiThread(new Runnable() {
#Override
public void run() {
JSONObject data = (JSONObject) args[0];
String message;
try {
message = data.getString("text").toString();
Log.i("result", message);
addMessage(message);
} catch (JSONException e) {
Log.e("result", "Error : JSONException");
return;
} catch (ClassCastException e) {
Log.e("result", "Error : ClassCastException");
e.printStackTrace();
return;
}
}
});
}
};
private void sendMessage(){
String message = mInputMessageView.getText().toString().trim();
mInputMessageView.setText("");
addMessage(message);
JSONObject sendText = new JSONObject();
try{
sendText.put("text", message);
socket.emit("message", message);
}catch(JSONException e){
}
}
private void addMessage(String message) {
mMessages.add(new Message.Builder(Message.TYPE_MESSAGE)
.message(message).build());
// mAdapter = new MessageAdapter(mMessages);
mAdapter = new MessageAdapter( mMessages);
mAdapter.notifyItemInserted(0);
scrollToBottom();
}
private void scrollToBottom() {
mMessagesView.scrollToPosition(mAdapter.getItemCount() - 1);
}
I already searched similar problems that other people asked, but It didn't give me solution. Please help me. Thank you for reading long question.
p.s Because Im not English speaker, Im not good at English .. There will be many problems at grammar and writing skills. Thanks for understanding...

Reason this happens is because method getActivity() returns null. This might happen if you run this on a fragment after it is detached from an activity or activity is no longer visible. I would do a normal null check before like:
Activity activity = getActivity();
if(activity != null) {
activity.runOnUiThread(new Runnable() {...}
}
I'm not familiar with socket.emit() method but it might throw network exception since it's running on UI thread and you are not allowed to do that. I recommend using RxJava/RxAndroid if you want to do this on another thread.
If you want to do network operation just use it like this:
Observable
.fromRunnable(new Runnable {
void run() {
// here do your work
}
})
.subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Subscriber<Void>() {
#Override
public void onCompleted() {
// not really needed here
}
#Override
public void onError(Throwable e) {
// handle errors on UI thread
}
#Override
public void onNext(Void void) {
// do something on UI thread after run is done
}
});
Basically what it does it calls method call from Callable you just made on separate thread and when it's over it invokes onNext method if no exception was thrown or onError method if exception was thrown from Subscriber class.
Note that Response class isn't part of the RxJava/RxAndroid API and you can make it if you want. You can make it a simple POJO class or anything else you need it to be. If you don't need to have response you can use Runnable instead of Callable and it will work just fine.
In order for this to work you need to add this dependencies to your modules Gradle file:
dependencies {
compile 'io.reactivex:rxandroid:1.2.1'
compile 'io.reactivex:rxjava:1.1.6'
}

Sending binary data by socket between C# and Js

I'm trying to send binary data between server (C#) application and client (js-application -- made by WebSocket). Connection between server and client is established and handshake is OK. Messages from client are receiving by server, but when I'm trying to send binary data to client, the event "onmessage" doesn't work.
This is fragments of my C# code. Sending binary data in "sendFile" function.
class Listener
{
private IPAddress ip;
private int port;
private TcpListener server;
private TcpClient client;
private NetworkStream stream;
private bool isSuccHandshaked;
public Listener()
{
ip = IPAddress.Loopback;
port = 8080;
server = new TcpListener(ip, port);
isSuccHandshaked = false;
}
private void makeHandshake()
{
//...
}
private String decodeMessage(Byte[] bytes)
{
//...
}
private void sendFile()
{
Byte[] dataToSend = File.ReadAllBytes("test.txt");
stream.Write(datatosend, 0, datatosend.Length);
stream.Flush();
}
public void startListen()
{
server.Start();
Console.WriteLine("Server has started on {0}. Port: {1}. {2}Waiting for a connection...", ip, port, Environment.NewLine);
client = server.AcceptTcpClient();
Console.WriteLine("A client connected.");
stream = client.GetStream();
while (!isSuccHandshaked)
{
makeHandshake();
}
while (true)
{
if (client.Available > 0)
{
Byte[] bytes = new Byte[client.Available];
stream.Read(bytes, 0, bytes.Length);
String message = decodeMessage(bytes);
sendFile();
}
}
}
}
}
and js-code:
var address = 'ws://localhost:8080';
var socket = new WebSocket( address );
socket.binaryType = "arraybuffer";
socket.onopen = function () {
alert( 'handshake successfully established. May send data now...' );
socket.send( "Aff" );
};
socket.onclose = function () {
alert( 'connection closed' );
};
socket.onmessage = function ( evt ) {
console.log( "Receive message!" );
console.log( "Got ws message: " + evt.data );
}
Maybe there is some peculiar properties in receiving data with WebSocket protocol? Wich useful approaches to send binary data from C# code to js you can recommend?

A websocket is not a raw TCP socket. It uses HTTP negotiation and its own framing protocol you have to comply with. If you are interested in writing your own server in C# take a look at this.
However if you only want to use them, you can either use the default Microsoft implementation with IIS, or you can use one of the many standalone websockets components. I maintain one named WebSocketListener.

node.js eventListener not listen

i'm a noob of node.js and i'm following the examples on "Node.js in action".
I've a question about one example :
The following code implements a simple chat server via telnet. When i write a message, the script should send message to all connected client.
var events = require('events');
var net = require('net');
var channel = new events.EventEmitter();
channel.clients = {};
channel.subscriptions = {};
channel.on('join',function(id,client){
this.clients[id] = client;
this.subscriptions[id] = function(senderId,message){
if(id != senderId){
this.clients[id].write(message);
}
};
this.on('broadcast',this.subscriptions);
});
var server = net.createServer(function(client){
var id = client.remoteAddress+':'+client.remotePort;
client.on('connect',function(){
channel.emit('join',id,client);
});
client.on('data',function(data){
data = data.toString();
channel.emit('broadcast',id,data);
});
});
server.listen(8888);
But when i try to connect via telnet and send a message it doesn't work.
Thanks

A couple issues I noticed. See the comments in the code.
var events = require('events');
var net = require('net');
var channel = new events.EventEmitter();
channel.clients = {};
channel.subscriptions = {};
channel.on('join',function(id, client) {
this.clients[id] = client;
this.subscriptions[id] = function(senderId,message) {
if(id != senderId)
this.clients[id].write(message);
};
//added [id] to "this.subscriptions"
//Before you were passing in the object this.subscriptions
//which is not a function. So that would have actually thrown an exception.
this.on('broadcast',this.subscriptions[id]);
});
var server = net.createServer(function(client) {
//This function is called whenever a client connects.
//So there is no "connect" event on the client object.
var id = client.remoteAddress+':'+client.remotePort;
channel.emit('join', id, client);
client.on('data',function(data) {
data = data.toString();
channel.emit('broadcast',id,data);
});
});
server.listen(8888);
Also note: If a client disconnects and another client sends a message then this.clients[id].write(message); will throw an exception. This is because, as of now, you're not listening for the disconnect event and removing clients which are no longer connected. So you'll attempt to write to a client which is no longer connected which will throw an exception. I assume you just haven't gotten there yet, but I wanted to mention it.