We Keep Coding

Signalr - It's possible to wait reponse from client?

I am a beginner in using Signalr and am checking out some examples.
Is it possible to send a message to the client from the server and wait for a return from it? Or is it possible to guarantee that after the answer the same session will be used?
My question is because in a given process, within a transaction, I need to ask the user if he wants to continue with the changes. I have not been able to ask this question before because validations should be done in the same session where changes have been made (but not yet confirmed).

Reiterating the comment from Jaime Yule, WebSockets are bidirectional communication and do not follow the Request/Response architecture for messaging. Given the very fluid nature of communication around WebSockets, these bullet points are good to keep in mind for your current (& future) scenarios:
SignalR is great if you're going to use it for fire & forget (Display a pop-up to a user and that's it)
It's not designed around request-response like you're asking, and trying to use it as such is an anti-pattern
Messages may be sent from either end of the connection at any time,
and there is no native support for one message to indicate it is
related to another
This makes the protocol poorly suited for transactional requirements

It is possible, but i would not recommend (relying on) it.
And it's not a pretty solution (using a static event and being pretty complex for such a simple thing).
Story goes like this:
Make sure client and server know the connectionId - They probably know that already, but i could not figure out a way to access it.
Await NotificationService.ConfirmAsync
... which will call confirm on the client
... which will await the user supplied answer
... and send it back to the server using Callback from The hub.
... which will notify the Callback from the NotificationService over a static event
... which will hand off the message back to ConfirmAsync (using a AutoResetEvent)
... which is hopefully still waiting :)
Client and server both have a 10 second timeout set.
The hub:
// Setup as /notification-hub
public class NotificationHub : Hub {
public string ConnectionId() => Context.ConnectionId;
public static event Action<string, string> Response;
public void Callback(string connectionId, string message) {
Response?.Invoke(connectionId, message);
}
}
Service:
// Wire it up using DI
public class NotificationService {
private readonly IHubContext<NotificationHub> _notificationHubContext;
public NotificationService(IHubContext<NotificationHub> notificationHubContext) {
_notificationHubContext = notificationHubContext;
}
public async Task<string> ConfirmAsync(string connectionId, string text, IEnumerable<string> choices) {
await _notificationHubContext.Clients.Client(connectionId)
.SendAsync("confirm", text, choices);
var are = new AutoResetEvent(false);
string response = null;
void Callback(string connId, string message) {
if (connectionId == connId) {
response = message;
are.Set();
}
}
NotificationHub.Response += Callback;
are.WaitOne(TimeSpan.FromSeconds(10));
NotificationHub.Response -= Callback;
return response;
}
}
Client side js:
var conn = new signalR.HubConnectionBuilder().withUrl("/notification-hub").build();
var connId;
// using Noty v3 (https://ned.im/noty/)
function confirm(text, choices) {
return new Promise(function (resolve, reject) {
var n = new Noty({
text: text,
timeout: 10000,
buttons: choices.map(function (b) {
return Noty.button(b, 'btn', function () {
resolve(b);
n.close();
});
})
});
n.show();
});
}
conn.on('confirm', function(text, choices) {
confirm(text, choices).then(function(choice) {
conn.invoke("Callback", connId, choice);
});
});
conn.start().then(function() {
conn.invoke("ConnectionId").then(function (connectionId) {
connId = connectionId;
// Picked up by a form and posted to the server
document.querySelector(".connection-id-input").value = connectionId;
});
});
For me this is way to complex to put it into the project i am working on.
It really looks like something that will come back and bite you later...

Is it possible to send a message to the client from the server and wait for a return from it? Or is it possible to guarantee that after the answer the same session will be used?
None of this is possible. Currently there's no way to wait for the client's response or even to get to know if the client received the message. There's some discussion implementing this on GitHub. Also here's the feature request.
Until then, the workaround is to send a "notification" from the server with a fire and forget attitude and let the client get the required data via a HTTP request to the server.

This is now possible with .NET 7 using Client Results.
Today, I've highlighted this issue in dotnet's Github page and got a good response from one of the developers of SignalR.
This requires the server to use ISingleClientProxy.InvokeAsync to be able to make request to the client and wait for response.
Quote from the documentation
In addition to making calls to clients, the server can request a
result from a client. This requires the server to use
ISingleClientProxy.InvokeAsync and the client to return a result from
its .On handler.
From the client (js/ts)
hubConnection.on("GetMessage", async () => {
let promise = new Promise((resolve, reject) => {
setTimeout(() => {
resolve(new { data: "message" });
}, 100);
});
return promise;
});
From the server (C#)
//By calling Client(...) on an instance of IHubContext<T>
async Task<object> SomeMethod(IHubContext<MyHub> context)
{
string result = await context.Clients.Client(connectionID).InvokeAsync<string>(
"GetMessage");
return result;
}
//---------------------------//
//Or by calling Client(...) or Caller on the Clients property in a Hub method
public class ChatHub : Hub
{
public async Task<string> WaitForMessage(string connectionId)
{
var message = await Clients.Client(connectionId).InvokeAsync<string>(
"GetMessage");
return message;
}
}

Using the following form with Invoke waits for and returns the response directly (just like a "real" synchronous method call)
var persons = hubProxy.Invoke<IEnumerable<Person>>("GetPersonsSynchronous", SearchCriteria, noteFields).Result;
foreach (Person person in persons)
{
Console.WriteLine($"{person.LastName}, {person.FirstName}");
}

SignalR - Pushing notification to servers

When I try to broadcast a message to all clients, I can trigger client's javascript code from server and get the job done.
But this time my aim is to trigger a method in all servers. For example, when roles of a user changed in one server, I want to warn other servers about this operation and I want to make other servers retrieve updated user role list for particular user.
Is it possible to do this with SignalR? Can a server behave like a client (browser)?

Yes you can do that.
Let's say you have the following hub:
public class TheHub : Hub
{
public void RoleChanged(int userId)
{
Clients.All.roleChanged(userId);
}
}
On all the listening servers, you'd have to do:
var _connection = new HubConnection("http://localhost:1234/signalr");
var _theHub = _connection.CreateHubProxy("TheHub");
_myHub.On<int>("RoleChanged", userId =>
{
System.Diagnostics.Debug.WriteLine("Changed user's Id: " + userId);
});
_connection.Start().Wait();
To invoke the RoleChanged event, do:
_myHub.Invoke("RoleChanged").Wait();

Redirect to a different aspx page and run the next code in background (.NET 4.5.2)

I am working on an ASP.NET Webform project (legacy code).On my button_click event i am sending sms message to all the datas populated in this.
var customerSMS = BusinessLayer.SMS.SmsSetup.GetAllCustomerSMS(OfficeId);
This takes around 15seconds to do all the computing and get the data(1000rows)
from the Db.And for each data it runs through the loop and does validation and
sends the sms and it does take time.I want to do this task in background and
redirect the user to the index page and the background process continues till it
gets out of the loop.I am new to this and still learning this beautiful
language C#.I did go through this amazing Asynchronous Programming async/await
and Multithreading approach and got hold of it only in simple WindowsForm
applications.Any reference/code snippet/best approach with a simple explanation for my case would be helpful.
My button click event code :
protected void ReturntoDashboard_Click(object sender, EventArgs e)
{
sms = Everest.Net.BusinessLayer.SMS.SmsSetup.GetSmsSetUp(OfficeId);
if (sms.EnableSmsData && sms.SmsCount > 0)
{
#region Loan Section
var smsLoan = Everest.Net.BusinessLayer.SMS.SmsSetup.GetLoanId(s.Sms_AccountNumber);
var loanId =
BusinessLayer.SMS.SmsSetup.GetLoanIdValue(s.Sms_AccountNumber);
var dateexceeded =
BusinessLayer.SMS.SmsSetup.IsDateExceeded(loanId);
if (smsLoan != null && dateexceeded == true)
{
foreach (Common.SMS.SMSSetup sm in smsLoan)
{
var smsClosingBalanceLoan = BusinessLayer.SMS.SmsSetup.GetAmountForLoanAlert( sm.LoanId,
BusinessLayer.Core.DateConversion
.GetCurrentServerDate()
.AddDays(sms.DaysbeforeLoanalerts).ToString());
if (smsClosingBalanceLoan != null)
{
if (smsClosingBalanceLoan.LoanAmountToPay > 0)
{
int smsSentAlertCount = sms.LoanAlertCount;
var logCount = BusinessLayer.SMS.SmsSetup.GetLoanSmsAlertSentCount(DateTime.Now.AddDays(-smsSentAlertCount).ToString("yyyy-MM-dd"), DateTime.Now.ToString("yyyy-MM-dd"), sm.LoanAccountNumber);
if (logCount < smsSentAlertCount)
{
smsLog = new Everest.Net.Common.SMS.SMSSetup();
finalMessage = "Dear Member, Your Loan accnt " + sm.LoanAccountNumber + " with Principal"+ "+" + "Int Amnt: Rs." + smsClosingBalanceLoan.LoanAmountToPay + " need to be payed.Thank You," + officeName.OfficeName;
smsLog.LogServiceType = "Loan";
smsLog.LogSmsType = s.Sms_SmsType;
smsLog.LogSmsMessage = finalMessage;
smsLog.LogCustomerId = s.CustomerId.ToString();
smsLog.LogAccountNumber = s.Sms_AccountNumber;
smsLog.LogAccountType = s.Sms_AccountType;
smsLog.LogSmsSentDate = BusinessLayer.Core.DateConversion.GetCurrentServerDate();
smsLog.LogSmsFailedDate = "";
smsLog.LogSentStatus = true;
smsLog.LogUserId = UserId;
smsLog.LogSmsFailedMessage = "";
try
{
var result = Everest.Net.BusinessLayer.SMS.smsParameters.SendSMS(sms.FromNum, sms.Token, sms.Url, cellNum, finalMessage);
}
catch (Exception ex)
{
smsLog.LogSmsFailedDate = System.DateTime.Now.ToString("MM/dd/yyyy HHmmss");
smsLog.LogSentStatus = false;
smsLog.LogSmsFailedMessage = ex.Message;
Everest.Net.BusinessLayer.SMS.SmsSetup.InsertSMSLog(smsLog);
}
sms = Everest.Net.BusinessLayer.SMS.SmsSetup.GetSmsSetUp(OfficeId);
sms.SmsCount = sms.SmsCount - 1;
Everest.Net.BusinessLayer.SMS.SmsSetup.UpdateSmsSetup(sms);
Everest.Net.BusinessLayer.SMS.SmsSetup.InsertSMSLog(smsLog);
}
}
}
}
}
}
}
}
catch (Exception ex)

The ideal solution would remove the responsibility of sending the SMS from the web application itself. Instead, the web application should create a database record containing the message and recipient addresses, and a separate background job (e.g. a Windows Service) should poll the database and send SMS messages when neeeded. This is the best solution in terms of fault tolerance and auditability, because there is a permanent record of the messaging job which can be resumed if the system fails.
That being said, maybe you don't want to go to all that trouble. If you feel strongly that you wish to send the SMS directly from the ASP.NET application, you will need to create a Task and queue it to run using QueueBackgroundWorkitem. You will need to refactor your code a bit.
Move all the logic for sending the SMS into a separate function that accepts all the information needed as parameters. For example,
static void SendSMS(string[] addresses, string messagetext)
{
//Put your SMS code here
}
When you need to call the function, queue it as a background item
HostingEnvironment.QueueBackgroundWorkItem(a => SendSMS(addresses, messageText));
If your worker task needs to access its own cancellation token (e.g. if it is supposed to loop until cancelled), it is passed as an argument to the lambda expression. So you could modify the prototype
static void SendSMS(string[] addresses, string messagetext, CancellationToken token)
{
while (!token.IsCancellationRequested)
{
//Put your code here
}
}
and pass it thus:
HostingEnvironment.QueueBackgroundWorkItem(token => SendSMS(addresses, messageText, token));
Placing the task in the background queue ensures that ASP.NET keeps track of the thread, doesn't try to garbage collect it, and shuts it down properly when the application pool needs to shut down.
After queuing the background operation, your page can render is content per usual and conclude the HTTP response while the task continues to execute.

HangFire Server Enable - Disable manually

During development of HangFire application with C# ASP.NET, and I decided to implement functionally where Admin can manage state of Server, jobs.
List item
Server Enable Disable state. Using Enable Button click event Admin
can start JOB server so all the Fire and Forget and Recurrent job can
performed. And Disable button stop all the activities of JOB.
Retrieve the current state of Server
I want to retrieve current state of JOB server, So I can show is
server is on or Off.
Retrieve state and enable / disable state of Jobs (Only recurrent).

If you want to manage Server/Job created by Hangfire, you can use MonitoringApi or JobStorage to get there statuses.
Sample Codes :
var _jobStorage = JobStorage.Current;
// How to get recurringjobs
using (var connection = _jobStorage.GetConnection())
{
var storageConnection = connection as JobStorageConnection;
if (storageConnection != null)
{
var recurringJob = storageConnection.GetRecurringJobs();
foreach(var job in recurringJob)
{
// do you stuff
}
}
}
// How to get Servers
var monitoringApi = _jobStorage.GetMonitoringApi();
var serverList = monitoringApi.Servers();
foreach( var server in serverList)
{
// do you stuff with the server
// you can use var connection = _jobStorage.GetConnection()
// to remove server
}
From here you can play around with Hangfire.

Listening to Events in the calendar from more than one person using EWS API

Simply I would like to receive a notification every time someone added a new appointment or made any changes on what he/she has.
The only way I know how to do it , is by using
service.SubscribeToStreamingNotifications
but the problem here that it only listens to the account that the service is bound to like in this way
var service = new ExchangeService(ExchangeVersion.Exchange2010_SP2)
{
Credentials = new WebCredentials(userName, password)
};
service.SubscribeToStreamingNotifications(new FolderId[]
{
WellKnownFolderName.Calendar
}, EventType.FreeBusyChanged, EventType.Deleted);
I have solved this problem by creating a list of services each service is bounded to different user and the application should listen to each of them.
The problem with this way is that I need to have the password of each account I wont to listen to its events, which is not possible in real world.
so is there any way to deal with that ?

I have solved this problem, by creating a list of services, all the services are a clone of the main ExchangeService, with the same credentials for the admin account, but they are impersonated to the other accounts.
NOTE: You need to setup the server so it allows impersonation.
private void ImpersonateUsers(ICollection<string> userSmtps)
{
if (userSmtps != null)
if (userSmtps.Count > 0)
{
foreach (var userSmtp in userSmtps)
{
if (_services.ContainsKey(userSmtp)) continue;
var newService = new ExchangeService(ExchangeVersion.Exchange2010_SP2);
try
{
var serviceCred = ((System.Net.NetworkCredential)(((WebCredentials)(_services.First().Value.Credentials)).Credentials));
newService.Credentials = new WebCredentials(serviceCred.UserName, serviceCred.Password, serviceCred.Domain);
newService.AutodiscoverUrl(serviceCred.UserName + "#" + serviceCred.Domain, RedirectionUrlValidationCallback);
newService.ImpersonatedUserId = new ImpersonatedUserId(ConnectingIdType.SmtpAddress, userSmtp);
}
catch (Exception ex)
{
System.Diagnostics.Debug.WriteLine(ex.Message);
}
_services.Add(userSmtp, newService);
}
}
}
Where userSmtps is a list of the email addresses I want to impersonate and _services is the dictionary of services where the first member is the main service.

you will have to create a service instance per user. There is no way to subscribe to other users folder.
But instead of StreamingNotifications you can use Pull and Push-Subscriptions too.
Something like this:
List<FolderId> folders = new List<FolderId>();
folders.Add(new FolderId(WellKnownFolderName.Calendar));
PullSubscription subscription = = service.SubscribeToPullNotifications(folders, 1440, watermark, EventType.Created, EventType.Deleted, EventType.Modified, EventType.Moved, EventType.NewMail);
Some time later....
GetEventsResults currentevents = m_subscription .GetEvents();