source: binary-improvements2/WebServer/src/SSE/AbsEvent.cs@ 399

using System;
using System.Collections.Generic;
using System.IO;
using System.Net.Sockets;
using System.Text;
using AllocsFixes.JSON;
using Webserver.UrlHandlers;
using HttpListenerResponse = SpaceWizards.HttpListener.HttpListenerResponse;

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<HttpListenerResponse> openStreams = new List<HttpListenerResponse> ();

                private readonly BlockingQueue<(string _eventName, object _data)> sendQueue =
                        new BlockingQueue<(string _eventName, object _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 (HttpListenerResponse _resp) {
                        totalOpened++;
                        currentlyOpen++;

                        openStreams.Add (_resp);
                }

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


                public void ProcessSendQueue () {
                        while (sendQueue.HasData ()) {
                                (string eventName, object data) = sendQueue.Dequeue ();
                                
                                stringBuilder.Append ("event: ");
                                stringBuilder.AppendLine (eventName);
                                stringBuilder.Append ("data: ");
                                
                                switch (data) {
                                        case string dataString:
                                                stringBuilder.AppendLine (dataString);
                                                break;
                                        case JsonNode dataJson:
                                                dataJson.ToString (stringBuilder);
                                                stringBuilder.AppendLine ("");
                                                break;
                                        default:
                                                logError ("Data is neither string nor JSON.", false);
                                                continue;
                                }
                                
                                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) {
                                                logError ("Exception while encoding data for output, most likely exceeding buffer size:", false);
                                                Log.Exception (e);
                                                return;
                                        }
                                } else {
                                        buf = Encoding.UTF8.GetBytes (output);
                                        bytesToSend = buf.Length;
                                }

                                for (int i = openStreams.Count - 1; i >= 0; i--) {
                                        HttpListenerResponse resp = openStreams [i];
                                        try {
                                                if (resp.OutputStream.CanWrite) {
                                                        resp.OutputStream.Write (buf, 0, bytesToSend);
                                                        resp.OutputStream.Flush ();
                                                } else {
                                                        currentlyOpen--;
                                                        totalClosed++;

                                                        logError ("Can not write to endpoint, closing", true);
                                                        openStreams.RemoveAt (i);
                                                        resp.Close ();
                                                }
                                        } catch (IOException e) {
                                                currentlyOpen--;
                                                totalClosed++;

                                                openStreams.RemoveAt (i);

                                                if (e.InnerException is SocketException se) {
                                                        if (se.SocketErrorCode != SocketError.ConnectionAborted && se.SocketErrorCode != SocketError.Shutdown) {
                                                                logError ($"SocketError ({se.SocketErrorCode}) while trying to write", true);
                                                        }
                                                } else {
                                                        logError ("IOException while trying to write:", true);
                                                        Log.Exception (e);
                                                }
                                        } catch (Exception e) {
                                                currentlyOpen--;
                                                totalClosed++;

                                                openStreams.RemoveAt (i);
                                                logError ("Exception while trying to write:", true);
                                                Log.Exception (e);
                                                resp.Close ();
                                        }
                                }
                        }
                }

                protected void logError (string _message, bool _printConnections) {
                        Log.Error (_printConnections
                                ? $"[Web] [SSE] '{Name}': {_message} (Left open: {currentlyOpen}, total opened: {totalOpened}, closed: {totalClosed})"
                                : $"[Web] [SSE] '{Name}': {_message}");
                }

                public virtual int DefaultPermissionLevel () {
                        return 0;
                }
        }
}