How to call removeEDNSOptionFromOPT in dnsdist.conf ?

[hi-glenn]

How to call int removeEDNSOptionFromOPT(char* optStart, size_t* optLen, const uint16_t optionCodeToRemove) function by lua in dnsdist.conf

My dns server is too old to support edns-cookie. I want to use dnsdist as a proxy to remove edns-cookie on query.

How should I write the lua script ?

[rgacogne]

There is currently no binding to make this function available to Lua, so it's not possible. You could patch dnsdist yourself, to add a Lua binding for this function, but you would need to be careful: removeEDNSOptionFromOPT only works as expected if there is no RR after the OPT one, which is usually the case but might not be true with TSIG, for example.
I would personally rather investigate upgrading/replacing a DNS server that chokes on DNS cookies (which should not be the case, a server that does not understand an EDNS option should just ignore it) than working around it, but I guess that might not be an option for you.