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Websocket - Why can't I send messages to a specific user?

Question:
Why am I being able to send messages to all users but not to a specific user? Am I missing something obvious here?
Problem:
My POC uses the following resources:
The official Spring Boot tutorial for sending messages to all users
This Baeldung tutorial for sending messages to specific users
I am currently using two endpoints:
The first one sends messages to all users and works fine.
Send to all users - working
#MessageMapping("/hello")
#SendTo("/topic/greetings")
public StompResponse greeting(StompRequest message) throws Exception {
Thread.sleep(1000); // simulated delay
return new StompResponse("Hello, " + HtmlUtils.htmlEscape(message.getName()) + "!");
}
The second one doesn't work. The method sendSpecific never gets called and I'm stuck trying to understand why.
Send to specific user - NOT working
/**
* Example of sending message to specific user using 'convertAndSendToUser()' and '/queue'
*/
#MessageMapping(Constants.SECURED_CHAT_ROOM)
public void sendSpecific(#Payload StompRequest message, Principal user, #Header("simpSessionId") String sessionId) throws Exception {
System.out.println("METHOD CALLED"); // This method never gets called
SimpMessageHeaderAccessor headerAccessor = SimpMessageHeaderAccessor.create(SimpMessageType.MESSAGE);
headerAccessor.setSessionId(sessionId);
headerAccessor.setLeaveMutable(true);
StompResponse out = new StompResponse(HtmlUtils.htmlEscape(message.getName()));
simpMessagingTemplate.convertAndSendToUser("hardcoded_username", Constants.SECURED_CHAT_SPECIFIC_USER, out, headerAccessor.getMessageHeaders());
}
Socket configuration:
#Configuration
#EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
#Override
public void configureMessageBroker(MessageBrokerRegistry config) {
config.enableSimpleBroker("/topic", Constants.SECURED_CHAT_SPECIFIC_USER);
config.setUserDestinationPrefix("/secured/user");
config.setApplicationDestinationPrefixes("/app");
}
#Override
public void registerStompEndpoints(StompEndpointRegistry registry) {
registry.addEndpoint("/connection-uri").withSockJS();
registry.addEndpoint(SECURED_CHAT_ROOM).withSockJS();
}
}
Client code:
const SocketConnection = function(l) {
const listener = l;
let sessionId;
const parseSessionId = (url) => {
console.log(stompClient.ws._transport.url);
url = url.replace("ws://localhost:8080" + Uri.CONNECTION_URI + "/", "");
url = url.replace("/websocket", "");
url = url.replace(/^[0-9]+\//, "");
console.log("Your current session is: " + url);
return url;
};
this.connect = () => {
const socket = new SockJS(Uri.CONNECTION_URI);
stompClient = Stomp.over(socket);
stompClient.connect({}, (frame) => {
listener.onSocketConnect(true);
console.log('Connected: ' + frame);
stompClient.subscribe(Uri.ALL_USERS, function (greeting) {
listener.onResponseReceived(JSON.parse(greeting.body).content);
});
// WIP
const url = stompClient.ws._transport.url
sessionId = parseSessionId(url);
console.log('SUBSCRIBING FOR SPECIFIC USER: ', Uri.SECURED_CHAT_SPECIFIC_USER)
// stompClient.subscribe(Uri.SECURED_CHAT_SPECIFIC_USER + sessionId, function (msgOut) {
stompClient.subscribe(Uri.SECURED_CHAT_SPECIFIC_USER + "-user" + sessionId, function (msgOut) {
// that.messageOut(JSON.parse(msgOut.body), opts);
console.log('SINGLE USER WORKS!!!!!!!',JSON.parse(msgOut.body))
});
});
}
this.disconnect = () => {
if (stompClient !== null) {
stompClient.disconnect();
}
listener.onSocketConnect(false);
console.log("Disconnected");
}
this.sendRequest = (uri) => {
stompClient.send(uri, {}, JSON.stringify({'name': $("#name").val()}));
}
};
Client initialization:
$(function () {
const socketClient = new SocketConnection(new FormUI());
$("form").on('submit', function (e) {
e.preventDefault();
});
$( "#connect" ).click(function() { socketClient.connect(); });
$( "#disconnect" ).click(function() { socketClient.disconnect(); });
$( "#send" ).click(function() {
socketClient.sendRequest(Uri.ALL_USERS);
socketClient.sendRequest(Uri.SECURED_CHAT_ROOM);
});
});

I get this the error "Error: invalid address ...." while running my dapp

I'm developing a simple dapp for my private blockchain Quorum. I wrote my smart contract in Solidity and a script with JavaScript.
After running my blockchain and my JavaScript console, I did this:
and I get the error:
Error: invalid address
at web3.js:3930:15
at web3.js:3756:20
at web3.js:5025:28
at map ( < native code > )
at web3.js:5024:12
at web3.js:5050:18
at web3.js:5075:23
at web3.js:4137:16
My smart contract is this one:
pragma solidity >=0.4.0 <0.7.5;
contract MyContract {
int value;
constructor() public{
value=10;
}
function get() public view returns(int) {
return value;
}
function set(int value2) public {
value=value2;
}
}
And my script in javascript is this one:
a = eth.accounts[0]
web3.eth.defaultAccount = a;
// Risultato del comando > solcjs --bin --abi MyContract.sol
var abi = [{"inputs":[],"stateMutability":"nonpayable","type":"constructor"},{"inputs":[],"name":"get","outputs":[{"internalType":"int256","name":"","type":"int256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"int256","name":"value2","type":"int256"}],"name":"set","outputs":[],"stateMutability":"nonpayable","type":"function"}];
var bytecode = "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";
// Creazione del nuovo contratto con nome MyContract
var simpleContract = web3.eth.contract(abi);
var simple = simpleContract.new({from:web3.eth.accounts[0], data: bytecode, gas: 0x47b760, privateFor: ["QfeDAys9MPDs2XHExtc84jKGHxZg/aj52DTh0vtA3Xc="]}, function(e, contract) {
if (e) {
console.log("Error creating contract", e);
} else {
if (!contract.address) {
console.log("Contract transaction send: TransactionHash: " + contract.transactionHash + " waiting to be mined...");
} else {
console.log("Contract mined! Address: " + contract.address);
console.log(contract);
}
}
});
What can I try to resolve this?

I think the issue is that you have a small mistake in the ABI - the get() function should have "constant":true in the abi due to the function being labelled as view.
Without that, the get() function requires a from address to be defined for the transaction (i.e. you have to use private.get({"from": fromAddress}) or set the default account using web3.eth.defaultAccount = accountAddress).
If you correct the ABI then it should work.

Execute Javascript on external url using HybridView, Xamarin cross platform

I have tried to execute JavaScript on an external url (ie: http://facebook.com) using WebView from Visual Studio Mac 2019, and so far no results.
To do so, I have tried to follow along with the official tutorial here https://learn.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/custom-renderer/hybridwebview, and also tried a simpler one here: https://xamarinhelp.com/xamarin-forms-webview-executing-javascript/
Here is what I did with explanations:
On my shared folder, I created an HybridWebView class with the following code:
public class HybridWebView : WebView
{
Action<string> action;
public static readonly BindableProperty UriProperty = BindableProperty.Create(
propertyName: "Uri",
returnType: typeof(Func<string, Task<string>>),
declaringType: typeof(HybridWebView),
defaultValue: default(string));
public string Uri
{
get => (string)GetValue(UriProperty);
set
{
SetValue(UriProperty, value);
}
}
public void RegisterAction(Action<string> callback)
{
action = callback;
}
public void Cleanup()
{
action = null;
}
public void InvokeAction(string data)
{
if (action == null || data == null)
{
return;
}
action.Invoke(data);
}
public Func<string, Task<string>> ExecuteJavascript
{
get { return (Func<string, Task<string>>)GetValue(UriProperty); }
set { SetValue(UriProperty, value); }
}
}
From The macOS project which I use to test my cross-platform app, I tried the following custom renderer:
public class HybridWebViewRenderer : ViewRenderer<HybridWebView, WKWebView>
{
protected override void OnElementChanged(ElementChangedEventArgs<HybridWebView> e)
{
base.OnElementChanged(e);
var webView = e.NewElement as HybridWebView;
if (webView != null)
{
Control.LoadRequest(new NSUrlRequest(new NSUrl(Element.ExecuteJavascript.ToString())));
}
}
}
To note that the following part wouldn't work:
var webView = e.NewElement as HybridWebView;
if (webView != null)
webView.ExecuteJavascript = (js) =>
{
return Task.FromResult(this.ExecuteJavascript(js)); // issue at ExecuteJavascript with following error ('HybridWebViewRenderer' does not contain a definition for 'ExecuteJavascript' ), hence replaced by Control.LoadRequest ...
};
From my ViewModel, I did the following:
public Func<string, Task<string>> EvaluateJavascript { get; set; }
public async Task OnConnectTapped()
{
Console.WriteLine("on connect tapped");
// passing the url onto a connection service
var hybridWebView = new HybridWebView
{
Uri = "https://facebook.com/"
};
//hybridWebView.InvokeAction("document.getElementById('td');");
//var result = await hybridWebView.RegisterAction(data => DisplayAlert("Alert", "Hello " + data, "OK"));
var result = await hybridWebView.ExecuteJavascript("document.cookie;");
Console.WriteLine("result is {0}", result);
}
Here is the error when trying to execute my code:
System.NullReferenceException: Object reference not set to an instance of an object
at MyApp.ViewModel.MainModel.OnConnectTapped () [0x00031] in .../../././/ViewModel/MainModel.cs:451
at .......<.ctor>g__c5|48_9 () [0x0001f] in /../../../.cs:143
at System.Runtime.CompilerServices.AsyncMethodBuilderCore+<>c.<ThrowAsync>b__7_0 (System.Object state) [0x00000] in /Users/builder/jenkins/workspace/xamarin-macios/xamarin-macios/external/mono/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/AsyncMethodBuilder.cs:1021
at Foundation.NSAsyncSynchronizationContextDispatcher.Apply () [0x00002] in /Library/Frameworks/Xamarin.Mac.framework/Versions/6.6.0.12/src/Xamarin.Mac/Foundation/NSAction.cs:178
at at (wrapper managed-to-native) AppKit.NSApplication.NSApplicationMain(int,string[])
at AppKit.NSApplication.Main (System.String[] args) [0x00040] in /Library/Frameworks/Xamarin.Mac.framework/Versions/6.6.0.12/src/Xamarin.Mac/AppKit/NSApplication.cs:100
at redacted.macOS.MainClass.Main (System.String[] args) [0x00017] in /Users/dom-bruise/Projects/redacted/redacted.macOS/Main.cs:11
For me, it could either be because I can't execute external pages, or the part where I replaced by the following messing up my attempt.
if (webView != null)
{
Control.LoadRequest(new NSUrlRequest(new NSUrl(Element.ExecuteJavascript.ToString())));
}
My main goal here is to have my app execute JavaScript underneath the hood on pages using WebView, and fill in forms automatically calling back C# from my app.

What is the alternative to `alert` in metro apps?

I created my first app on Windows 8 vs 2012 and it runs and works fine. But when I try to say "helloworld" from JavaScript like this:
alert("Hello World");
I get an error:
Unhandled exception at line 21,
column 13 in ms-appx://1af489cf-bac6-419b-8542-fdc18bdd2747/default.html
0x800a1391 - JavaScript runtime error: 'alert' is undefined
What is the alternative if alert is obsolete?

You should use Windows.UI.Popups.MessageDialog:
(new Windows.UI.Popups.MessageDialog("Content", "Title")).showAsync().done();
However, you should be aware that:
This is not blocking like the familiar alert
Because it's not blocking you may try to show them multiple messages boxes; this isn't allow.
I answered another question like this here. Here's the code to allow you to call alert, and have multiple messages in flight:
(function () {
var alertsToShow = [];
var dialogVisible = false;
function showPendingAlerts() {
if (dialogVisible || !alertsToShow.length) {
return;
}
dialogVisible = true;
(new Windows.UI.Popups.MessageDialog(alertsToShow.shift())).showAsync().done(function () {
dialogVisible = false;
showPendingAlerts();
})
}
window.alert = function (message) {
if (window.console && window.console.log) {
window.console.log(message);
}
alertsToShow.push(message);
showPendingAlerts();
}
})();

Remember that alert is not a JavaScript function, it's a browser (host) function, therefore, it's not available in non browser environments.
This link tells you to do the following
Replace all alert functions with firing an event window.external.notify("message");
Use scriptnotify event in webview to get that message.
Show metro own dialog: MessageDialog

javascript：
(function () {
window.alert = function (message) {
window.external.notify( message);
}
//do some test
alert("a");
alert("b");
alert("c");
window.setInterval(function () {
alert("e");
alert("f");
}, 5000);
window.setInterval(function () {
alert("d");
alert("2");
}, 10000);
})();
C#:
//register ScriptNotify event
webView2.ScriptNotify += webView2_ScriptNotify;
async void webView2_ScriptNotify(object sender, NotifyEventArgs e)
{
MSG.Alert(e.Value);
}
public class MSG
{
static List<string> messages = new List<string>();
public static void Alert(string message)
{
messages.Add(message);
if (messages.Count == 1)
{
Show(messages.First());
}
}
private static async Task Show(string message)
{
MessageDialog md = new MessageDialog(message, "Title");
md.Commands.Add(
new UICommand("OK", new UICommandInvokedHandler((cmd) =>
{
messages.RemoveAt(0);
})));
await md.ShowAsync();
while (messages.Count > 0)
{
await Show(messages.First());
}
}
}

memory leak in ajax - setInterval

I have an ajax code which causes memory leak (especially in IE).
function setStatus() {
var formInput=$(this).serialize();
$.getJSON('CheckStatus.action', formInput, function(data) {
if(data == false) {
function getEventsPeriodicaly() {
getEvents();
};
var timer = setInterval(function () {getEventsPeriodicaly();}, 5000);
}
}
);
}
function getEvents() {
var formInput=$(this).serialize();
$.getJSON('StartEP.action', formInput,function(data) {
var txt = $("#txtEventsArea");
if(data != null && data.toString().length!=0) {
txt.val(data.join('\n') + '\n' + txt.val());
data=null;
}
}
)}
StartEP
public String startEP() throws Exception {
logger.info("[EP] In startEP");
try {
synchronized(status) {
if(!getStatus()) {
EventProcessor amiep = EventProcessor.getInstance();
amiep.addObserver(this);
new Thread(amiep).start();
setStatus(true);
}
}
} catch (Exception ex) {
logger.error("Unable to start EP", ex);
return ERROR;
}
logger.info("[EP] In startEP, before loop");
while(!gotNewData) {
Thread.sleep(4000);
}
gotNewData = false;
logger.info("[EP] Out startEP");
return SUCCESS;
}
The StartEP action returns messages (about 5KB on each request). First I thought it concerned with setting text to textarea, but after some tests got that it is not the reason. Could it be setInterval method?
Is there any considerations?
thanks

I would say this looks pretty suspect:
while(!gotNewData) {
Thread.sleep(4000);
}
Where is gotNewData set? If you call the web service once and set gotNewData to true and then call another web service and set gotNewData to false I don't think there is a guarantee that you're setting the variable within the same instance of the application. Therefore, if you are not, then every time you're hitting the web service you are starting a new thread and then continually putting it back to sleep.