source: binary-improvements/MapRendering/Web/SSE/SseHandler.cs@ 430

using System;
using System.Net;
using System.Collections.Generic;
using System.Reflection;
using System.Threading;
using AllocsFixes.NetConnections.Servers.Web.Handlers;

// Implemented following HTML spec
// https://html.spec.whatwg.org/multipage/server-sent-events.html

namespace AllocsFixes.NetConnections.Servers.Web.SSE {
        public class SseHandler : PathHandler {
                private readonly Dictionary<string, EventBase> events = new CaseInsensitiveStringDictionary<EventBase> ();
                
                private ThreadManager.ThreadInfo queueThead;
                private readonly AutoResetEvent evSendRequest = new AutoResetEvent (false);
                private bool shutdown;

                public SseHandler (string _moduleName = null) : base (_moduleName) {
                        Type[] ctorTypes = {typeof (SseHandler)};
                        object[] ctorParams = {this};

                        foreach (Type t in Assembly.GetExecutingAssembly ().GetTypes ()) {
                                if (!t.IsAbstract && t.IsSubclassOf (typeof (EventBase))) {
                                        ConstructorInfo ctor = t.GetConstructor (ctorTypes);
                                        if (ctor != null) {
                                                EventBase apiInstance = (EventBase) ctor.Invoke (ctorParams);
                                                addEvent (apiInstance.Name, apiInstance);
                                        }
                                }
                        }
                }

                public override void SetBasePathAndParent (Web _parent, string _relativePath) {
                        base.SetBasePathAndParent (_parent, _relativePath);
                        
                        queueThead = ThreadManager.StartThread ("SSE-Processing_" + urlBasePath, QueueProcessThread, ThreadPriority.BelowNormal,
                                _useRealThread: true);
                }

                public override void Shutdown () {
                        base.Shutdown ();
                        shutdown = true;
                        SignalSendQueue ();
                }

                private void addEvent (string _eventName, EventBase _eventInstance) {
                        events.Add (_eventName, _eventInstance);
                        WebPermissions.Instance.AddKnownModule ("webevent." + _eventName, _eventInstance.DefaultPermissionLevel ());
                }

                public override void HandleRequest (HttpListenerRequest _req, HttpListenerResponse _resp, WebConnection _user,
                        int _permissionLevel) {
                        string eventName = _req.Url.AbsolutePath.Remove (0, urlBasePath.Length);

                        if (!events.TryGetValue (eventName, out EventBase eventInstance)) {
                                Log.Out ($"Error in {nameof (SseHandler)}.HandleRequest(): No handler found for event \"{eventName}\"");
                                _resp.StatusCode = (int) HttpStatusCode.NotFound;
                                return;
                        }

                        if (!AuthorizeForEvent (eventName, _permissionLevel)) {
                                _resp.StatusCode = (int) HttpStatusCode.Forbidden;
                                if (_user != null) {
                                        //Log.Out ($"{nameof(SseHandler)}: user '{user.SteamID}' not allowed to access '{eventName}'");
                                }

                                return;
                        }

                        try {
                                eventInstance.AddListener (_resp);

                                // Keep the request open
                                _resp.SendChunked = true;

                                _resp.AddHeader ("Content-Type", "text/event-stream");
                                _resp.OutputStream.Flush ();
                        } catch (Exception e) {
                                Log.Error ($"Error in {nameof (SseHandler)}.HandleRequest(): Handler {eventInstance.Name} threw an exception:");
                                Log.Exception (e);
                                _resp.StatusCode = (int) HttpStatusCode.InternalServerError;
                        }
                }

                private bool AuthorizeForEvent (string _eventName, int _permissionLevel) {
                        return WebPermissions.Instance.ModuleAllowedWithLevel ("webevent." + _eventName, _permissionLevel);
                }

                private void QueueProcessThread (ThreadManager.ThreadInfo _threadInfo) {
                        try {
                                while (!shutdown && !_threadInfo.TerminationRequested ()) {
                                        evSendRequest.WaitOne (500);

                                        foreach (KeyValuePair<string, EventBase> kvp in events) {
                                                kvp.Value.ProcessSendQueue ();
                                        }
                                }
                        } catch (Exception e) {
                                Log.Error ("SSE: Error processing send queue");
                                Log.Exception (e);
                        }
                }

                public void SignalSendQueue () {
                        evSendRequest.Set ();
                }
        }
}