Missing user and group information for domain users

[gentooise]

Indicate project
libsysflow

Describe the bug
The user name is not reported for domain users.

To reproduce
Steps to reproduce the behavior (on a Ubuntu 22):

1. Setup LDAP (used local IP as LDAP server name): https://ubuntu.com/server/docs/install-and-configure-ldap
2. Enable TLS (required by SSSD): https://ubuntu.com/server/docs/ldap-and-transport-layer-security-tls
3. Setup SSSD with LDAP: https://ubuntu.com/server/docs/how-to-set-up-sssd-with-ldap
4. Login with newly created LDAP user and run commands (e.g. whoami, ls)

Expected behavior
Events are reported with the correct user name and group, like

Environment (please complete the following information):

• OS: Ubuntu 22.04, 5.15.0-69-generic
• SysFlow version: 0.6.3

Additional context
getpwuid and getgrgid standard C functions might be used to retrieve user/group information from uid/gid:

• https://pubs.opengroup.org/onlinepubs/009604499/functions/getpwuid.html
• https://pubs.opengroup.org/onlinepubs/009604499/functions/getgrgid.html
  Should fix also related issue: Missing user and group information #109

Files

****************************************************************
Header: Exporter , IP , File name 
Process: PID 103194 Creation Time, 1713946076546863602, Exe /usr/bin/whoami, Exe Args , User Name <NA>, Group Name <NA>, TTY 1
Proc Evt: TID 103194, OpFlags 2, Ret 0
****************************************************************
****************************************************************
Header: Exporter , IP , File name 
Process: PID 103195 Creation Time, 1713946077821078567, Exe /usr/bin/ls, Exe Args --color=auto, User Name <NA>, Group Name <NA>, TTY 1
Proc Evt: TID 103195, OpFlags 2, Ret 0
****************************************************************

[gentooise]

After analysis and workaround implementation on consumer side, I would like to share a piece of information if you plan to resolve this. The musl implementation of getpwuid differs from glibc and cannot be used to resolve the issue as I initially thought.

• musl just looks into /etc/passwd: https://github.com/rofl0r/musl/blob/master/src/passwd/getpw_r.c
• glibc leverages nss lookup: https://github.com/lattera/glibc/blob/master/pwd/getpwuid_r.c (https://en.wikipedia.org/wiki/Name_Service_Switch), so it also supports domain users

musl specifically does not use nss itself because it's not compatible with static linking and because loading arbitrary module libraries into the calling process's core is not safe and goes against best practices.