nginx version: openresty/1.15.8.1rc0
built by gcc 7.3.0 (Ubuntu 7.3.0-27ubuntu1~18.04)
built with OpenSSL 1.1.0j  20 Nov 2018
TLS SNI support enabled

I am experiencing random segfaults when passing invalid data to base64url (and base64 in general seems)
This seems to be caused by a race condition of some sorts, since adding some debugging in ngx.base64
sometimes makes the problem disappear.

Minimal test to reproduce:

local u64d = require "ngx.base64".decode_base64url

for i=1,1000 do
        local x = u64d(("x"):rep(i))
end

$ resty segfault.lua ; echo $?
0
$ resty segfault.lua ; echo $?
139