[admax88q]

That honestly sounds more complicated. FTP isn't that difficult of a protocol, especially if you only need to support one known client, you can take all sort of shortcuts.

If you deploy an existing FTP server, and _then_ integrate with it at the filesystem level you now have two components, and your sysadmin requirements grow. Now you gotta administrate an FTP server that's probably written for classic UNIX single server usage, gotta handle filesystem permissions, gotta somehow hook up your distributed locks to the filesystem, sanitize filenames for your chosen filesystem.

Honestly filesystems suck, there's so many gotchas from a security perspective, when all you really want is to pipe binary data in this side, and out the other side.

I implemented an IRC bot in a few hours in javascript one day. Those classic IETF text based protocols are actually really fun and easy to implement, especially in a language that makes strings safe and easy (i.e. not C).

I could easily see figuring out all the deployment concerns around integrating with an existing FTP server end up taking way longer than just integrating the subset needed for this use case.

[stjohnswarts]

Strings in c aren't that bad with stuff like bstring or glib. Just gotta be careful with deallocations so you don't get leaks. Much better than all the security issues with std strings. I mean not anywhere close to python/ruby/javascript easy but it's not as bad as HN likes to declare it.

[recursive]

Active mode is pretty weird. Coordinating a single client across two ports sounds difficult to me, but I've never implemented it. If that's not a difficult protocol, then what is?

[tuwtuwtuwtuw]

Http3, IMAP, Caldav and MAPI?

Cordinating a client across two ports sounds trivial compared to for example properly implementing client and server versions of IMAP search commands when no client or server follows the specification.

[pixl97]

Until you realize that the two ports commonly involve dealing with middleware that cant handle it properly.

[tuwtuwtuwtuw]

You will have similar issues with other protocols as well. I have seen physical bandwidth limiters, windows drivers, corrupt winsock LSPs etc mess with IMAP traffic. I have seen middleware replacing SMTP commands sent from a client to server for no good reason, such as replacing "EHLO hostname" with "EHLO **".

[winrid]

The lock would be handled by something like Redis or a DB.

But yeah, if you only need to support one client, I can see the reasoning. It would never have flied at any of the places I've worked, though, having to support tons of clients.

[admax88q]

Yeah totally I hear you. If you have to support many external clients using an existing ftp implementation makes lot more sense.