I tried the module on GeoIP2-Anonymous-database from maxmind (tried couple of latest versions)

i got assert error, "wrong key type" on the line below.
https://github.com/daurnimator/mmdblua/blob/master/mmdb/init.lua#L258

I prefer if function returns error instead raise Lua errors.
E.g. if i get info from untrasted source I want return either info or error message.
Now I have to use pcall for such thing.
I like way how it was implemented in cjson library.
It just provide 2 module cjson and cjson.safe.

Suggestions for the right way to do this? I think that file:seek() would work.

I have system where I have ffi.abi('le') false, but mmdb file has such endian.
So as result I have wrong value in record_size.
I suggest detect endian based on e.g. IP version format. It can be either 6 or 4.

At the moment we use some hacky routines to read/write doubles: https://github.com/daurnimator/mmdblua/blob/f0644b7478ec91fd8a7d85a9f0f259f444ba20cd/IEEE-754.lua
As well as some simple routines to read ints:

Lua 5.3 brings with it new function string.unpack which can be used to tidy this up.
compat-5.3 can be used to bring this functionality to lua 5.1 and 5.2. Preferably we stay compatible with Roberto's struct library too.

https://en.wikipedia.org/wiki/IPv6#IPv4-mapped_IPv6_addresses

e.g. ::ffff:192.0.2.128

It would be nice if you would consider adding proper source release tarballs,
as GitHub auto-generated tarballs are not immutable. This is an issue [1] for
operating systems creating packages for mmdblua. Thanks in advance.

[1] https://marc.info/?l=openbsd-ports&m=151973450514279&w=2

hi buddy, you wrote a very nice useful module, thank!
but is there any way that i can integrate your module without luarocks?

Care to make a luarocks release?