source: TFP-WebServer/WebServer/src/SSE/AbsEvent.cs@ 500

using System;
using System.Collections.Generic;
using System.Text;
using Webserver.UrlHandlers;

namespace Webserver.SSE {
        public abstract class AbsEvent {
                private const int encodingBufferSize = 1024 * 1024;

                private readonly SseHandler parent;
                public readonly string Name;

                private readonly byte[] encodingBuffer;
                private readonly StringBuilder stringBuilder = new StringBuilder ();

                private readonly List<SseClient> openClients = new List<SseClient> ();

                private readonly BlockingQueue<(string _eventName, string _data)> sendQueue =
                        new BlockingQueue<(string _eventName, string _data)> ();

                private int currentlyOpen;
                private int totalOpened;
                private int totalClosed;

                protected AbsEvent (SseHandler _parent, bool _reuseEncodingBuffer = true, string _name = null) {
                        Name = _name ?? GetType ().Name;
                        parent = _parent;
                        if (_reuseEncodingBuffer) {
                                encodingBuffer = new byte[encodingBufferSize];
                        }
                }

                public void AddListener (SseClient _client) {
                        totalOpened++;
                        currentlyOpen++;

                        openClients.Add (_client);
                        
                        logConnectionState ("Connection opened", _client);
                }

                protected void SendData (string _eventName, string _data) {
                        sendQueue.Enqueue ((_eventName, _data));
                        parent.SignalSendQueue ();
                }

                public void ProcessSendQueue () {
                        while (sendQueue.HasData ()) {
                                (string eventName, string data) = sendQueue.Dequeue ();
                                
                                stringBuilder.Append ("event: ");
                                stringBuilder.AppendLine (eventName);
                                stringBuilder.Append ("data: ");
                                stringBuilder.AppendLine (data);
                                
                                stringBuilder.AppendLine ("");

                                string output = stringBuilder.ToString ();
                                stringBuilder.Clear ();

                                byte[] buf;
                                int bytesToSend;
                                if (encodingBuffer != null) {
                                        buf = encodingBuffer;
                                        try {
                                                bytesToSend = Encoding.UTF8.GetBytes (output, 0, output.Length, buf, 0);
                                        } catch (ArgumentException e) {
                                                Log.Error ($"[Web] [SSE] '{Name}': Exception while encoding data for output, most likely exceeding buffer size:");
                                                Log.Exception (e);
                                                return;
                                        }
                                } else {
                                        buf = Encoding.UTF8.GetBytes (output);
                                        bytesToSend = buf.Length;
                                }

                                sendBufToListeners (buf, bytesToSend);
                        }
                }

                private void sendBufToListeners (byte[] _bytes, int _bytesToSend) {
                        for (int i = openClients.Count - 1; i >= 0; i--) {
                                openClients [i].Write (_bytes, _bytesToSend);
                        }
                }

                public virtual int DefaultPermissionLevel () => 0;

                private void logConnectionState (string _message, SseClient _client) {
                        Log.Out ($"[Web] [SSE] '{Name}': {_message} from {_client.RemoteEndpoint} (Left open: {currentlyOpen}, total opened: {totalOpened}, closed: {totalClosed})");
                }

                public void ClientClosed (SseClient _client) {
                        if (openClients.Remove (_client)) {
                                currentlyOpen--;
                                totalClosed++;

                                logConnectionState ("Closed connection", _client);
                        }
                }
        }
}