Disconnects from server every 60 seconds when using FTP and FTPS

[petejfh]

I'm doing a recursive delete of a folder which contains ~4000 files split over ~60 subfolders and have noticed that FileZilla is being disconnected every 60 seconds. It re-establishes the connection and continues the delete, but the disconnection pattern continues. The server is hosted remotely to the client.

FileZilla version: 3.65.0 on Windows 11
Protocol: FTPS (TLS 1.3)
Server Host: Linux Rocky el9
Server Host .NET version: 8

Output from the FileZilla log shows:

• 2024-01-22 19:37:57 32424 1 Error: Connection closed by server
• 2024-01-22 19:38:57 32424 1 Error: Connection closed by server
• 2024-01-22 19:39:57 32424 1 Error: Connection closed by server
• 2024-01-22 19:40:57 32424 1 Error: Connection closed by server
• 2024-01-22 19:41:57 32424 1 Error: Connection closed by server
• 2024-01-22 19:42:57 32424 1 Error: Connection closed by server
• 2024-01-22 19:43:57 32424 1 Error: Connection closed by server

Example output from the FTP server shows for one of these events:

• Jan 22 19:40:57 Stopped sending responses, from FubarDev.FtpServer.FtpConnection
• Jan 22 19:40:57 Stopped reading command, from FubarDev.FtpServer.FtpConnection
• Jan 22 19:40:57 Sending the response cancelled: 426 Connection closed; transfer aborted, from FubarDev.FtpServer.Commands.DefaultFtpCommandDispatcher
• Jan 22 19:40:57 Connection closed, from FubarDev.FtpServer.FtpConnection

Any ideas on why these disconnects are happening every 60 seconds?

I see the same behaviour with .NET 6 too.

[petejfh]

I'm also seeing the same behaviour using plain FTP (i.e. non-FTPS).

[fubar-coder]

I'll have to look into this, but I assume that some kind of idle connection timer is kicking in.

[tjipke-fg]

We had this same issue and I investigated it and came to the following conclusion: By default FtpConnectionIdleCheck is registered as a singleton (for IFtpConnectionCheck). However the code in it assumes it is instantiated for each connection.
I found a workaround for it, by first calling DisableIdleCheck on the builder (in AddFtpServer ) to remove that existing Singleton registration and then registering the FtpConnectionIdleCheck again but now as Scoped.

So my code now looks like this:

            // Add FTP server services
            services
               .AddFtpServer(
                    builder =>
                    {
                        // fix bug in FTPConnectionidleCheck being resolved as Singleton, where it should be Scoped
                        builder.DisableIdleCheck()
                            .Services.AddScoped<IFtpConnectionCheck, FtpConnectionIdleCheck>();
...

And this seems to work correct

[tjipke-fg]

Extra info: the disconnects happened only after the FTP server was running for at least 5:00 minutes after the first FTP connection was made (since the default timeout is 5 mins and the idle check was registered on the first FTP connection)