Notes/NoteHub.cs

using BinaryDad.Notes.Services;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.SignalR;

namespace BinaryDad.Notes
{
    [Authorize]
    public class NoteHub : Hub
    {
        private readonly INoteService noteService;

        public NoteHub(INoteService noteService)
        {
            this.noteService = noteService;
        }

        public override Task OnConnectedAsync()
        {
            var noteName = Context.GetHttpContext().Request.Query["noteName"];

            NoteContext.ClientNotes[Context.ConnectionId] = noteName;

            return base.OnConnectedAsync();
        }

        public async Task SaveNote(string content, string noteName)
        {
            noteService.SaveNote(content, noteName);

            // find all other connections except for the current one
            var clientConnections = NoteContext.ClientNotes
                .Where(c => c.Value == noteName && c.Key != Context.ConnectionId)
                .Select(c => c.Key)
                .ToList();

            // update note for all other clients
            await Clients
                .Clients(clientConnections)
                .SendAsync("updateNote", content);
        }
    }
}