MVC CORE SignalR send messages specific user only - asp.net-core-mvc

Question

Im using SignalR Core and ASPNET Core 2.2 and try to to send message to single user. for all user it's working fine.
Csharp code
[HubMethodName("SendMessageToUser")]
public Task DirectMessage(string user, string message)
{
//eg.user = abcd#gmail.com
return Clients.User(user).SendAsync("ReceiveMessage", message);
}
JS code
connection.on("ReceiveMessage", function (user, message) {
var msg = message.replace(/&/g, "&").replace(/</g,"<").replace(/>/g, ">");
var encodedMsg = user + " says " + msg;
var li = document.createElement("li");
li.textContent = encodedMsg;
document.getElementById("messagesList").appendChild(li);
});

Answer 1

You can send message to specific user using their connection id so
I need to create a hub like this. The GetConnectionId will return the connect id of that user when they connect to signalR hub
public class ConnectionHub : Hub
{
public async Task Send(string userId)
{
var message = $"Send message to you with user id {userId}";
await Clients.Client(userId).SendAsync("ReceiveMessage", message);
}
public string GetConnectionId()
{
return Context.ConnectionId;
}
}
Then in startup.cs
services.AddSignalR();
app.UseSignalR(routes =>
{
routes.MapHub<ConnectionHub>("/connectionHub");
});
Then the client side code
(function () {
var connection = new signalR.HubConnectionBuilder().withUrl("/connectionHub").build();
connection.start().then(function () {
console.log("connected");
connection.invoke('getConnectionId')
.then(function (connectionId) {
sessionStorage.setItem('conectionId', connectionId);
// Send the connectionId to controller
}).catch(err => console.error(err.toString()));;
});
$("#sendmessage").click(function () {
var connectionId = sessionStorage.getItem('conectionId');
connection.invoke("Send", connectionId);
});
connection.on("ReceiveMessage", function (message) {
console.log(message);
});
})();
First I invoke getConnectionId in the hub to get user connection id then I can send message to specific user using their connection id.
Hope that help