NLST: return paths relative to the working directory

[drakkan]

Based on RFC 959 NLST is intended to return information that can be used by a program to further process the files automatically.

More details here.

Returning absolute paths is simpler but it will break mget dir/*

[codecov]

Codecov Report

Base: 86.07% // Head: 86.25% // Increases project coverage by +0.17% 🎉

Coverage data is based on head (f289aa0) compared to base (df4aba0).
Patch coverage: 92.85% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #368      +/-   ##
==========================================
+ Coverage   86.07%   86.25%   +0.17%     
==========================================
  Files          11       11              
  Lines        1573     1600      +27     
==========================================
+ Hits         1354     1380      +26     
- Misses        151      152       +1     
  Partials       68       68              

Impacted Files	Coverage Δ
handle_dirs.go	89.04% <91.17%> (+0.56%)	⬆️
client_handler.go	86.82% <100.00%> (+0.28%)	⬆️

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[fclairamb]

LGTM

[drakkan]

@fclairamb thanks for reviewing/approving this PR so quickly. This code is already included in SFTPGo v2.3.5 (I had a security related release planned for this weekend) but I prefer to wait a few more days to get feedback from the user who reported the problem and to do another code review before merging here

[drakkan]

there is another subtle difference with ProFTPD. If you run a LIST command that points to a file not in the current directory, we return something like this:

ftp> ls dir/file.txt
200 PORT command successful
150 Using transfer connection
-rw-r--r-- 1 ftp ftp         4034 Sep 19 11:07 file.txt
226 Closing transfer connection

while ProFTPD returns this:

ftp> ls dir/file.txt
200 Comando PORT eseguito con successo
150 Apertura della connessione dati in modalità ASCII per file list 
-rw-r--r--   1 nicola   nicola       4034 Sep 19 09:07 dir/file.txt
226 Trasferimento completato

NLST for files and directories and LIST for directories now return ProFTPD-like output. I will submit a new PR if I have any reports of real issues related to this different behavior