FluentFTP gets out of sync when server sends "150 Opening BINARY mode data connection for file list" response

[climam]

FTP OS: Unix

FluentFTP Version: 33.0.3

I am using FluentFTP high level API to upload files on a pretty old FTP server. This FTP server sends a response code 150 after execution of some commands such as NLST. Looking at the FTP specifications, FluentFTP should fetch another reply from the FTP server before sending a command. This is not the case and as a result, FluentFTP gets out of sync (see logs below).

See https://en.wikipedia.org/wiki/List_of_FTP_server_return_codes

1xx: Positive Preliminary reply The requested action is being initiated; expect another reply before proceeding with a new command. (The user-process sending another command before the completion reply would be in violation of protocol; but server-FTP processes should queue any commands that arrive while a preceding command is in progress.) This type of reply can be used to indicate that the command was accepted and the user-process may now pay attention to the data connections, for implementations where simultaneous monitoring is difficult. The server-FTP process may send at most, one 1xx reply per command.

-- | --

Logs :

# OpenPassiveDataStreamAsync(PASV, "NLST /__TESTS__", 0)
Command:  PASV
Response: 227 Entering Passive Mode (212,27,63,3,178,6).
Status:   Connecting to 212.27.63.3:45574
Command:  NLST /__TESTS__
Response: 150 Opening BINARY mode data connection for file list
Loaded '/usr/local/share/dotnet/shared/Microsoft.NETCore.App/2.2.7/System.Diagnostics.StackTrace.dll'. Module was built without symbols.
Loaded '/usr/local/share/dotnet/shared/Microsoft.NETCore.App/2.2.7/System.Reflection.Metadata.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.

# UploadAsync("__TESTS__/lastConnetion.txt", Append, True)

# FileExistsAsync("__TESTS__/lastConnetion.txt")

# GetWorkingDirectoryAsync()
Command:  PWD
Response: 226 Transfer complete.
Warning:  Failed to parse working directory from: Transfer complete.

# GetNameListingAsync("./__TESTS__")

# GetWorkingDirectoryAsync()
Command:  PWD
Response: 257 "/" is current directory.
Command:  TYPE I
Response: 257 "/" is current directory.

# OpenPassiveDataStreamAsync(PASV, "NLST /__TESTS__", 0)
Command:  PASV
Response: 200 Type set to I
Exception thrown: 'FluentFTP.FtpException' in System.Private.CoreLib.dll
Command:  QUIT
Response: 227 Entering Passive Mode (212,27,63,3,120,32).
Status:   Disposing FtpSocketStream...

# Dispose()
Status:   Disposing FtpClient object...
Status:   Disposing FtpSocketStream...

[robinrodricks]

We are not built to handle "preliminary replies". At present we support an error reply 5xx and the success reply 2xx. If you feel this is a good feature, you may contribute it and submit a PR we would happily accept.

[robinrodricks]

Added to the bucket list. We will pick this up as and when we have free time. Comment on this issue if you want us to prioritize it. Thanks!

[FanDjango]

This works fine since quite some time. Removed from bucket list.

[robinrodricks]

Awesome!