Request: Support MODE command

[tfranssen]

I want to use sFTPgo together with a Reolink camera. The camera sends a MODE S command before uploading a file. ftpserverlib does not recognize this and sends an error.

This is how the MODE should be implemented.

MODE FTP command
This command changes the transfer mode. The argument is a single Telnet character code specifying the data transfer modes described in the Section on Transmission Modes.

The following codes are assigned for transfer modes:
S – Stream
B – Block
C – Compressed
Z – Deflate
The default transfer mode is Stream. Mode Z (commonly referred to as “on-the-fly” compression) is defined in an IETF draft.

[tfranssen]

Added some logging:

Apr 26 12:27:18 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:18.847","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","clientIp":"*****:22432","message":"Client connected"}
Apr 26 12:27:18 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:18.849","sender":"FTP","connection_id":"FTP_0_7","message":"connection added, local address \"*****:21\", remote address \"*******:22432\", num open connections: 1"}
Apr 26 12:27:18 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:18.849","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"220 SFTPGo 2.5.6 ready","message":"Sending answer"}
Apr 26 12:27:18 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:18.973","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"AUTH TLS","message":"Received line"}
Apr 26 12:27:18 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:18.974","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"550 Cannot get a TLS config: no TLS certificate configured","message":"Sending answer"}
Apr 26 12:27:19 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:19.090","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"USER wildspotter","message":"Received line"}
Apr 26 12:27:19 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:19.091","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"331 OK","message":"Sending answer"}
Apr 26 12:27:19 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:19.208","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"PASS ****","message":"Received line"}
Apr 26 12:27:19 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:19.209","sender":"common","connection_id":"FTP_0_7","message":"connection swapped, close fs error: <nil>"}
Apr 26 12:27:19 ftpS3Gateway sftpgo[3542]: {"level":"info","time":"2024-04-26T12:27:19.209","sender":"FTP","connection_id":"FTP_0_7","message":"User \"wildspotter\" logged in with \"password\" from ip \"*****\""}
Apr 26 12:27:19 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:19.210","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"230 Password ok, continue","message":"Sending answer"}
Apr 26 12:27:19 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:19.344","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"PWD","message":"Received line"}
Apr 26 12:27:19 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:19.345","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"257 \"/\" is the current directory","message":"Sending answer"}
Apr 26 12:27:19 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:19.480","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"CWD wildspotter","message":"Received line"}
Apr 26 12:27:19 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:19.579","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"250 CD worked on /wildspotter","message":"Sending answer"}
Apr 26 12:27:19 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:19.708","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"CWD 2024","message":"Received line"}
Apr 26 12:27:19 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:19.755","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"250 CD worked on /wildspotter/2024","message":"Sending answer"}
Apr 26 12:27:19 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:19.887","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"CWD 04","message":"Received line"}
Apr 26 12:27:19 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:19.934","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"250 CD worked on /wildspotter/2024/04","message":"Sending answer"}
Apr 26 12:27:20 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:20.071","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"CWD 26","message":"Received line"}
Apr 26 12:27:20 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:20.142","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"250 CD worked on /wildspotter/2024/04/26","message":"Sending answer"}
Apr 26 12:27:20 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:20.271","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"TYPE A","message":"Received line"}
Apr 26 12:27:20 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:20.272","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"200 Type set to ASCII","message":"Sending answer"}
Apr 26 12:27:20 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:20.414","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"MODE S","message":"Received line"}
Apr 26 12:27:20 ftpS3Gateway sftpgo[3542]: {"level":"warn","time":"2024-04-26T12:27:20.414","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","command":"MODE","message":"Unknown command"}
Apr 26 12:27:20 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:20.415","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","line":"500 Unknown command \"MODE\"","message":"Sending answer"}
Apr 26 12:27:20 ftpS3Gateway sftpgo[3542]: {"level":"debug","time":"2024-04-26T12:27:20.547","sender":"ftpserverlib","server_id":"FTP_0","clientId":"7","clean":"false","message":"Client disconnected"}

[tfranssen]

Maybe just accepting MODE S would be enough for this. I will try to make the changes myself.

[fclairamb]

Deflate compression is part of the standard library so that should be fairly easy to support.