DOKK / manpages / debian 12 / libresolv-wrapper / resolv_wrapper.1.en
RESOLV_WRAPPER(1)   RESOLV_WRAPPER(1)

resolv_wrapper - A wrapper for dns name resolving or dns faking.

LD_PRELOAD=libresolv_wrapper.so RESOLV_WRAPPER_CONF="/path/to/resolv.conf" ./myapplication

resolv_wrapper makes it possible on most UNIX platforms to contact your own DNS implementation in your test environment. It requires socket_wrapper to be able to contact it. If it doesn’t work on a special platform the wrapper is able to fake DNS queries and return valid responses to your application.

•Redirects name queries to the nameservers specified in your resolv.conf

•Can fake DNS queries using a simple formatted DNS hosts file.

RESOLV_WRAPPER_CONF

This is used to specify the resolv.conf to use. The format of the resolv.conf file is defined in the manpage resolv.conf(5). Currently only the namserver directive is supported.

In order that this works with socket_wrapper. The res_* symbols need to be in a separate libresolv library. If they are part of libc this wont work. This is the case with glibc >= 2.34.

RESOLV_WRAPPER_HOSTS

This environment variable is used for faking DNS queries. It must point to a hosts-like text file that specifies fake records for custom queries. The format of the file looks like this: 

TYPE    RECORD_NAME RECORD_VALUE

For example:

A       dc.cwrap.org 127.0.0.10
AAAA    dc.cwrap.org fd00::5357:5f0a
CNAME   kerberos.cwrap.org dc.cwrap.org
SRV     _kerberos._tcp.cwrap.org kerberos.cwrap.org 88
URI     _vpn.cwrap.org https://vpn.cwrap.org/VPN
TXT     cwrap.org v=spf1 mx

RESOLV_WRAPPER_DEBUGLEVEL

If you need to see what is going on in resolv_wrapper itself or try to find a bug, you can enable logging support in resolv_wrapper if you built it with debug symbols.

•0 = ERROR

•1 = WARNING

•2 = DEBUG

•3 = TRACE

RESOLV_WRAPPER_DISABLE_DEEPBIND

This allows you to disable deep binding in resolv_wrapper. This is useful for running valgrind tools or sanitizers like (address, undefined, thread).

The following command would trick kinit(1) into using DNS servers from "./resolv.conf" for Kerberos service resolution:

$ LD_PRELOAD=libresolv_wrapper.so RESOLV_WRAPPER_CONF="./resolv.conf" kinit user@EXAMPLE.COM

The Samba Team

Author.
2020-01-31