confusing error message when (S)FTP accounts file has malformed URL

[zooko]

A user on IRC was setting up FUSE↔sshfs↔Tahoe-SFTP-server↔LAFS. He connected to the Tahoe-SFTP-server with the "sftp" client, issued the command "ls", and got this error message:

remote readdir("/"): Permission denied

It finally turned out to be that the dir cap in his accounts file had a trailing "/" character on it. Removing that made the error message go away and the SFTP server start working. To close this ticket, make it so that the error message in a case like this gives the user a clue that something is wrong with the cap.

(This might actually be hard to accomplish, if there isn't a way to send back an arbitrary error message in the SFTP protocol in response to the SFTP client's "ls" command.)

[ClashTheBunny]

Why not just handle this in the Tahoe-SFTP server? When would a trailing slash not be good to ignore and just give the user the directory? This isn't an API, this is where we should use heuristics to shield users.

[zooko]

Replying to ClashTheBunny:

Why not just handle this in the Tahoe-SFTP server? When would a trailing slash not be good to ignore and just give the user the directory? This isn't an API, this is where we should use heuristics to shield users.

I guess we should have two tickets: one to usefully report malformed caps in the SFTP accounts file, and the other to accept a broader range of plausible caps (e.g. don't mind trailing slashes on dir caps).