[erlang-questions] SFTPD, directory listing and file attributes

[Karolis Petrauskas]

Hi all,

I'm trying to use the ssh_sftpd server and found strange behaviour
when listing files:

    sftp> ls -l /c/
    data.csv
    data.txt
    some.xxx

File permissions and gid/uid are not shown with the -l option.

If listing the files with the -n option the file attributes are shown
as expected:

    sftp> ls -n /c/
    -rw-rw-r--    0 1000     1000            0 Dec 27 20:11 /c/data.csv
    -rw-rw-r--    0 1000     1000            0 Dec 27 20:12 /c/data.txt
    -rw-rw-r--    0 1000     1000            0 Dec 27 19:12 /c/some.xxx

The attributes are also shown if the files are listed using wildcard:

    sftp> ls -l /c/*
    -rw-rw-r--    0 1000     1000            0 Dec 27 20:12 /c/data.txt
    -rw-rw-r--    0 1000     1000            0 Dec 27 20:11 /c/data.csv
    -rw-rw-r--    0 1000     1000            0 Dec 27 19:12 /c/some.xxx

But in this case, the sftp client asks for file attributes for each
file explicitly. In the client debug, I see the calls similar to the
following, repeated three times in this case:

    debug3: Sent message fd 3 T:7 I:20
    debug3: Received stat reply T:105 I:20


I work on linux, Ubuntu xenial.
I use Erlang/OTP 20.1 for the server.
The client is openssh sftp, version="OpenSSH_7.2p2 Ubuntu-4ubuntu2.2,
OpenSSL 1.0.2g  1 Mar 2016".
The server and the client agrees on the sftp version 3, as the client
implements it.

I tried to look at the ssh_sftp server sources. It looks like
ssh_xfer:encode_name/3 is incorrect, because long file name is not
included in the protocol version 3
(https://tools.ietf.org/html/draft-ietf-secsh-filexfer-03#page-26, see
SSH_FXP_NAME).
As I quick test, I tried to change the Vsn ranges here, but in that
case the server started to report corrupted frames.

I would be apprieciated for any pointers.

Maybe there is a way to log the sftp messages (decrypted) on the
client, it would help to compare responses from the erlang server and
the openssh server (the latter provides the attributes correctly).

--
Karolis Petrauskas