When I download files, the program crashes but I can't catch the exception

[lixiang365]

I have already used try-catch, but it still crashes.

using var ftp = new AsyncFtpClient(ip, username, password);
ftp.Config.ConnectTimeout = 30000;                        
ftp.Config.ReadTimeout = 60000;      
ftp.Config.DataConnectionConnectTimeout = 30000;  
ftp.Config.DataConnectionReadTimeout = 60000;    

.....
try{
var status = await ftp.DownloadFile(localFilePath, remoteFilePath,
                        FtpLocalExists.Resume,
                        FtpVerify.Delete | FtpVerify.Retry, progress);
}
catch{}

Application: BearCapture.UI.exe CoreCLR Version: 8.0.2526.11203 .NET Version: 8.0.25 Description: The process was terminated due to an unhandled exception. Exception Info: System.TimeoutException: Timed out trying to read data from the socket stream! at FluentFTP.FtpSocketStream.ReadAsync(Byte[] buffer, Int32 offset, Int32 count, CancellationToken token) at FluentFTP.FtpSocketStream.ReadLineAsync(Encoding encoding, CancellationToken token) at FluentFTP.Client.BaseClient.BaseFtpClient.FluentFTP.IInternalFtpClient.GetReplyInternal(CancellationToken token, String command, Boolean exhaustNoop, Int32 timeOut, Boolean useSema) at FluentFTP.Client.BaseClient.BaseFtpClient.FluentFTP.IInternalFtpClient.GetReplyInternal(CancellationToken token, String command) at FluentFTP.Client.BaseClient.BaseFtpClient.FluentFTP.IInternalFtpClient.CloseDataStreamInternal(FtpDataStream stream, CancellationToken token) at FluentFTP.Client.BaseClient.BaseFtpClient.FluentFTP.IInternalFtpClient.CloseDataStreamInternal(FtpDataStream stream, CancellationToken token) at FluentFTP.FtpDataStream.CloseAsync(CancellationToken token) at FluentFTP.FtpSocketStream.<>c__DisplayClass77_0.<b__0>d.MoveNext() --- End of stack trace from previous location --- at System.Threading.Tasks.Task.<>c.b__128_1(Object state) at System.Threading.ThreadPoolWorkQueue.Dispatch() at System.Threading.PortableThreadPool.WorkerThread.WorkerThreadStart()

I don't know if it has anything to do with my configuration.

[lixiang365]

Do I need to provide any more information? @FanDjango

[FanDjango]

Timed out trying to read data from the socket stream!

It could be anything. It could be TSL Session Resume failing. Does it always happen, does it only happen on this special file, or only with this server? Works with other servers? Do you think we are astrologers with a crystal ball?

I am sorry, but as a first step perhaps provide a log at detailed level. It might provide some more insight into the reason of the connection being suddenly dropped.

[lixiang365]

Timed out trying to read data from the socket stream!

It could be anything. It could be TSL Session Resume failing. Does it always happen, does it only happen on this special file, or only with this server? Works with other servers? Do you think we are astrologers with a crystal ball?

I am sorry, but as a first step perhaps provide a log at detailed level. It might provide some more insight into the reason of the connection being suddenly dropped.

I understand what you mean. Generally, this error occurs when there is an abnormal network connection. I'm not very familiar with c#. I don't understand why I couldn't catch this timeout exception when I used try catch? Could you help me analyze the code? @FanDjango

  var (code, fileName) = await Task.Run(() => _ftpService.DownloadFileAsync(
                    ctx.IpAddress,
                    ctx.Port,
                    filePath,
                    deleteOld: true));


        public async Task<(int errorCode, string fileName)> DownloadFileAsync(string ip, int port, string localDir, bool deleteOld = false)
        {
            
            try
            {
                string username = "anonymous"; 
                string password = "xx";

                using var ftp = new AsyncFtpClient(ip, username, password, port);
                ftp.Config.ConnectTimeout = 3000;
                ftp.Config.ReadTimeout = 5000;
                ftp.Config.DataConnectionConnectTimeout = 5000;
                ftp.Config.DataConnectionReadTimeout = 5000;
                ftp.Config.DataConnectionType = FtpDataConnectionType.PASV;
                ftp.Config.RetryAttempts = 3; 

                await ftp.AutoConnect();

                var items = await ftp.GetListing(RemoteDir);
                if (items == null || items.Length == 0)
                {
                    
                    return (-2, string.Empty);
                }

                var orderItems = items
                    .Where(x => x.Type == FtpObjectType.File && x.Name.EndsWith(".mp4", StringComparison.OrdinalIgnoreCase))
                    .OrderByDescending(x => x.Name)
                    .ToList();

                if (!orderItems.Any())
                {
                    
                    return (-2, string.Empty);
                }

                var latestFile = orderItems[0];
                

                string localFilePath = Path.Combine(localDir, latestFile.Name);
                string remoteFilePath = $"{RemoteDir}/{latestFile.Name}";

                int lastProgress = -1;
                var progress = new Progress<FtpProgress>(p =>
                {
                    int percent = (int)p.Progress;
                    if (percent % 10 == 0 && percent != lastProgress)
                    {
                        
                        lastProgress = percent;
                    }
                });

                var startTime = DateTime.Now;
                var status = await ftp.DownloadFile(localFilePath, remoteFilePath, FtpLocalExists.Resume, FtpVerify.Retry, progress);

                if (status == FtpStatus.Success || status == FtpStatus.Skipped)
                {
                    
                    if (deleteOld)
                    {
                       
                        for (int i = 0; i < orderItems.Count; i++)
                        {
                            try
                            {
                                await ftp.DeleteFile($"{RemoteDir}/{orderItems[i].Name}");
                                
                            }
                            catch (Exception ex)
                            {
                                Debug.WriteLine($"[FtpService] ip: {ip} port:{port},  {orderItems[i].Name} | {ex.Message}");
                            }
                        }
                    }
                    else
                    {
                        
                        if (orderItems.Count > 5)
                        {
                            for (int i = 5; i < orderItems.Count; i++) 
                            {
                                try
                                {
                                    await ftp.DeleteFile($"{RemoteDir}/{orderItems[i].Name}");
                                    Debug.WriteLine($"[FtpService] ip: {ip} port:{port},  {orderItems[i].Name}");
                                }
                                catch (Exception ex)
                                {
                                    Debug.WriteLine($"[FtpService] ip: {ip} port:{port},  {orderItems[i].Name} | {ex.Message}");
                                }
                            }
                        }
                    }

                    return (0, latestFile.Name);
                }

                
                return (-1, latestFile.Name);
            }
            catch (Exception ex)
            {
                
                return (-3, string.Empty);
            }
            
        }

output

14:23:30:443 [FtpService] ip: 192.168.3.101 port:21, 下载进度: 10% | 速度: 5.19 MB/s
14:23:30:940 [FtpService] ip: 192.168.3.101 port:21, 下载进度: 20% | 速度: 5.17 MB/s
14:23:30:940 [FtpService] ip: 192.168.3.101 port:21, 下载进度: 20% | 速度: 5.17 MB/s
14:23:36:450 引发的异常:“FluentFTP.Exceptions.FtpException”(位于 System.Private.CoreLib.dll 中)
14:23:41:497 [FtpService] ip: 192.168.3.101 port:21, 下载异常: Error while downloading the file from the server. See InnerException for more info.
14:23:41:497 “BearCapture.UI.exe”(Win32): 已加载“C:\Windows\System32\version.dll”。包含/排除设置已禁用符号加载。
14:23:41:497 “System.TimeoutException”类型的未经处理的异常在 System.Private.CoreLib.dll 中发生
14:23:41:497 Timed out trying to read data from the socket stream!
14:23:41:497

[FanDjango]

I have already used try-catch, but it still crashes.

I misunderstood. You nowhere really indicated the I don't understand why I couldn't catch this timeout exception when I used try catch?

Sorry.

I found this SO that refers to this kind of problem:

https://stackoverflow.com/questions/69966157/exception-thrown-in-async-method-is-not-caught-why

First, try to reduce your code to the minimum. But:
It is even possible that internally in FluentFTP there is a missing await?

var status = await ftp.DownloadFile(localFilePath, remoteFilePath, FtpLocalExists.Resume, FtpVerify.Retry, progress);

This looks correct, this is where the exception occurs.

Perhaps this SO link also helps to find the reason:

https://stackoverflow.com/questions/19865523/why-cant-i-catch-an-exception-from-async-code

[lixiang365]