SignalR 将用户 ID 从 controller 映射到连接 ID

Question

I am building an ASP.NET Core application with Angular, and I am trying to implement a basic, one-on-one chat functionality using SignalR.

Since I want to allow one-on-one chatting and make chat messages persistent at some point, I'd like to be able to map User Id to SignalR Connection Id and send messages directly to a user based on their Id.

Now, all the examples I've seen use code within a Hub, which makes sense since Hub keeps track of Clients and their connection ids. But other logic that I'll have starts and ends inside my Controller, of course, and I can't call a hub directly from a controller.

Since SignalR is supposed to be relying on Identity by default, his is what I've tried so far:

[Route("send")]
    [HttpPost]
    public async Task<IActionResult> SendRequest([FromBody] Chat.Models.Message message)
    {
        var userId = Guid.Parse(User.FindFirstValue(ClaimTypes.NameIdentifier)); // I'd like to register this (current) userId with SignalR connection Id somehow
        
        var sender = new ChatSender { Id= userId, Name = user.FullName };

        await _hubContext.Clients.All.SendAsync("ReceiveMessage", sender, message.MessageText); // can't extend this, nor access hub directly

        //var recipient = _hubContext.Clients.User(message.To); // message.To is a Guid of a recepient
        //await recipient.SendAsync("ReceiveMessage", sender, message.MessageText);
        return Ok();
    }

The code above works as a broadcast, but if I replace the _hubContext.Clients.All.SendAsync with two commented out lines below, it does nothing.

Any suggestions?

Answer 1

SignalR mapping User Id to Connection Id

To map the user id /name with the connection id, you need to use the Hub's OnConnectedAsync method to get the userid/username and the connection id, then insert them into database. Code like below:

[Authorize]
public class ChatHub : Hub
{
    private readonly ApplicationDbContext _context;
    public ChatHub(ApplicationDbContext context)
    {
        _context = context;
    }
    public override async Task OnConnectedAsync()
    {
        //get the connection id
        var connectionid = Context.ConnectionId;
        //get the username or userid
        var username = Context.User.Identity.Name;
        var userId = Guid.Parse(Context.User.FindFirstValue(ClaimTypes.NameIdentifier));

        //insert or updatde them into database.
        var CId = _context.UserIdToCId.Find(userId);
        CId.ConnectionId = connectionid;
        _context.Update(CId);
        await _context.SaveChangesAsync();
        await base.OnConnectedAsync();
    }

map User Id to SignalR Connection Id and send messages directly to a user based on their Id.

You can pass your receiver id or name from your client to the SendRequest method, according to the receiver id or name to find the signalr connection id from database. After find the receiver's connection id, then use the following code to send message:

await _hubContext.Clients.Client("{receiver connection id}").SendAsync("ReceiveMessage", message);

the more code you can refer to:

 public class HomeController : Controller
    {
        private readonly IHubContext<ChatHub> _hubContext;
        private readonly ApplicationDbContext _context;
        public HomeController( IHubContext<ChatHub> hubContext, ApplicationDbContext context)
        {               
            _hubContext = hubContext;
            _context = context;
        }
         ...
        /// <summary>
        /// 
        /// </summary>
        /// <param name="receiver">receiver id or name</param>
        /// <param name="message">message </param>
        /// <returns></returns>
        [Route("send")]
        [HttpPost]
        public async Task<IActionResult> SendRequest([FromBody] string receiver, Message message)
        {
            //1. according to the receiver id or name to find the signalr connection id
                //To map the user id /name with the connection id, you need to use the Hub's OnConnectedAsync method to get the userid/username and the connection id.
                //then insert them into database
            //2. After find the receiver's connection id, then use the following code to send message.
            await _hubContext.Clients.Client("{receiver connection id}").SendAsync("ReceiveMessage", message);
             
            return Ok();
        } 

Note When the receiver is disconnected,remember to delete the receiver's connection id from database, avoid sending error.

Besides, you can refer to How can I make one to one chat system in Asp.Net.Core Mvc Signalr? to know more.