how to handle error?

[Isma399]

Hello,
thanks for this lib.
We try to use it to localize mail sender, testing step was ok with some ips.
But passing it in prod breaks.
Is there a way to handle error when IP is in mmdb but not data :

# cat test.lua
local mm = require 'maxminddb'
local db = mm.open('/var/lib/libmaxminddb/GeoLite2-City.mmdb')

function geoip(ip)
    local res, status = db:lookup(ip)
    return res:get("country", "iso_code")
end

for k, ip in pairs({'8.8.8.8', '165.72.200.98'}) do
    print(ip, geoip(ip))
end

Script breaks on 165.72.200.98 :

# lua test.lua
8.8.8.8 US
lua: The lookup path does not match the data (key that doesn't exist, array index bigger than the array, expected array or map where none exists)
stack traceback:
        [C]: in function 'get'
        test.lua:6: in function 'geoip'
        test.lua:10: in main chunk
        [C]: ?

[fabled]

You can use standard lua error handling via pcall, e.g. something like:

function geoip(ip)
    local ok, res, status = pcall(db.lookup, db, ip)
    if not ok then return nil end
    local ok, val = pcall(res.get, res, "country", "iso_code")
    if not ok then return nil end
    return val
end

Though it might make sense to add or modify the methods to not generate hard error on "not found" error, but instead return nil.

[Isma399]

Thank you, that works very well!
I don't event expect that you answer me so thanks again.
I've also thought to modify line82 of maxminddb.c to return nil.
But I don't know of to write that in C.