TelegramWebHook.cs

using System;
using System.Net;
using System.IO;
using Newtonsoft.Json;
using Telegram.Bot.Types;

namespace StackExBot
{
    class WebHook
    {
        private readonly HttpListener WebHookReceiver = new HttpListener();
        private string Token;
        private bool Stopped = false;
        
        public string Url { get; private set; }

        public WebHook(string fqdn, int port, string token)
        {
            Token = token;
            Url = $"https://{fqdn}:{port}/{token}";
            WebHookReceiver.Prefixes.Add($"https://{fqdn}:{port}/");
        }
        public void Start()
        {
            if (Stopped) throw new ObjectDisposedException("HttpListener");
            WebHookReceiver.Start();
            WebHookReceiver.BeginGetContext(WebHookContextReceived, null);
        }
        public void StopAndClose()
        {
            if (!Stopped)
            {
                Stopped = true;
                if (WebHookReceiver.IsListening)
                    WebHookReceiver.Stop();
                WebHookReceiver.Close();
            }
        }

        private void WebHookContextReceived(IAsyncResult AR)
        {
            HttpListenerContext context = WebHookReceiver.EndGetContext(AR);
            WebHookReceiver.BeginGetContext(WebHookContextReceived, null);
            OnWebHookContext(context);
        }

        private void OnWebHookContext(HttpListenerContext context)
        {
            if (context.Request.HttpMethod.ToLower() != "post")
            {
                RespondWithCode(context, HttpStatusCode.MethodNotAllowed);
                return;
            }

            if (!context.Request.Url.AbsolutePath.TrimEnd('/').EndsWith(Token))
            {
                RespondWithCode(context, HttpStatusCode.Forbidden);
                return;
            }
            
            try
            {
                string json;
                using (StreamReader sr = new StreamReader(context.Request.InputStream))
                    json = sr.ReadToEnd();

                Update update = JsonConvert.DeserializeObject<Update>(json);
                if (update == null)
                {
                    RespondWithCode(context, HttpStatusCode.BadRequest);
                }
                else
                {
                    OnUpdate?.BeginInvoke(this, update, OnInvokeEnd, null);
                    RespondWithCode(context, HttpStatusCode.OK);
                }
            }
            catch
            {
                RespondWithCode(context, HttpStatusCode.BadRequest);
            }
        }

        private void RespondWithCode(HttpListenerContext context, HttpStatusCode errorCode)
        {
            context.Response.StatusCode = (int)errorCode;
            context.Response.OutputStream.Close();
        }

        private void OnInvokeEnd(IAsyncResult AR)
        {
            OnUpdate?.EndInvoke(AR);
        }

        public event EventHandler<Update> OnUpdate;
    }
}