IPCamAppBar/IPCamAppBar/CameraStream.cs

using System;
using System.Drawing;
using System.IO;
using System.Net;
using System.Threading;
using System.Threading.Tasks;

namespace IPCamAppBar
{
    public class FrameEventArgs : EventArgs
    {
        public Image Image { get; set; }
    }

    public class StreamExceptionEventArgs : EventArgs
    {
        public Exception Exception { get; set; }
    }


    public delegate void FrameEvent(object sender, FrameEventArgs args);
    public delegate void StreamExceptionEvent(object sender, StreamExceptionEventArgs args);


    internal abstract class CameraStream : IDisposable
    {
        public event FrameEvent Frame;
        public event StreamExceptionEvent StreamException;

        private readonly CancellationTokenSource cancelTaskTokenSource = new CancellationTokenSource();
        private Task streamTask;
        private DataMonitor dataMonitor;

        protected CameraStream()
        {
        }


        public void Start(string url)
        {
            if (streamTask != null)
                throw new InvalidOperationException("CameraStream already started");

            streamTask = Task.Run(() => Fetch(url, cancelTaskTokenSource.Token));
        }


        public void Dispose()
        {
            cancelTaskTokenSource.Cancel();

            try
            {
                streamTask?.Wait();
            }
            catch (AggregateException e)
            {
                if (e.InnerExceptions.Count == 1 && e.InnerExceptions[0] is TaskCanceledException)
                    return;

                throw;
            }
            catch (TaskCanceledException) { }
        }


        private async Task Fetch(string url, CancellationToken cancellationToken)
        {
            while (!cancellationToken.IsCancellationRequested)
            {
                var uri = new Uri(url);
                var request = WebRequest.CreateHttp(uri);

                if (!string.IsNullOrEmpty(uri.UserInfo))
                {
                    var parts = uri.UserInfo.Split(':');
                    request.Credentials = new NetworkCredential(parts[0], parts.Length > 1 ? parts[1] : "");
                }

                request.ReadWriteTimeout = 10;

                try
                {
                    HttpWebResponse response;

                    using (cancellationToken.Register(() => request.Abort(), false))
                    {
                        response = (HttpWebResponse)await request.GetResponseAsync();
                        cancellationToken.ThrowIfCancellationRequested();
                    }


                    if (response.StatusCode != HttpStatusCode.OK)
                        throw new WebException(response.StatusDescription);

                    using (var responseStream = response.GetResponseStream())
                    {
                        var dataMonitorCancellationTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
                        dataMonitor = new DataMonitor(dataMonitorCancellationTokenSource, TimeSpan.FromSeconds(15));

                        try
                        { 
                            await ReadFrames(responseStream, dataMonitorCancellationTokenSource.Token);
                        }
                        catch (TaskCanceledException)
                        {
                            if (!dataMonitorCancellationTokenSource.IsCancellationRequested)
                                throw;
                        }
                    }
                }
                catch (TaskCanceledException)
                {
                }
                catch (Exception e)
                {
                    if (cancellationToken.IsCancellationRequested)
                        break;

                    OnStreamException(new StreamExceptionEventArgs
                    {
                        Exception = e
                    });

                    await Task.Delay(5000, cancellationToken);
                }
            }
        }


        protected abstract Task ReadFrames(Stream stream, CancellationToken cancellationToken);


        protected virtual void OnFrame(FrameEventArgs args)
        {
            dataMonitor.Reset();
            Frame?.Invoke(this, args);
        }


        protected virtual void OnStreamException(StreamExceptionEventArgs args)
        {
            StreamException?.Invoke(this, args);
        }
    }


    internal static class BufferExtensions
    {
        public static int Find(this byte[] buffer, byte[] pattern, int limit = int.MaxValue, int startAt = 0)
        {
            var patternIndex = 0;
            var bufferIndex = 0;

            for (bufferIndex = startAt; bufferIndex < buffer.Length && patternIndex < pattern.Length && bufferIndex < limit; bufferIndex++)
            {
                if (buffer[bufferIndex] == pattern[patternIndex])
                {
                    patternIndex++;
                }
                else
                {
                    patternIndex = 0;
                }
            }

            if (patternIndex == pattern.Length)
                return bufferIndex - pattern.Length;

            return -1;
        }
    }


    internal class DataMonitor
    {
        private readonly CancellationTokenSource cancellationTokenSource;
        private readonly long timeout;

        private readonly Timer timeoutTimer;


        public DataMonitor(CancellationTokenSource cancellationTokenSource, TimeSpan timeout)
        {
            this.cancellationTokenSource = cancellationTokenSource;
            this.timeout = (long)timeout.TotalMilliseconds;

            timeoutTimer = new Timer(Tick, null, this.timeout, -1);
        }


        public void Reset()
        {
            timeoutTimer.Change(timeout, -1);
        }


        private void Tick(object state)
        {
            cancellationTokenSource.Cancel();
        }
    }
}