Debug library not accessible: attempt to index a nil value (global 'debug')

[ashvinsharma]

I am trying to use lua-http in vector, but I got this error-

ERROR vector::topology::builder: Configuration error. error=Transform "my_transform_id": Cannot evaluate Lua code in "source": runtime error: /usr/local/share/lua/5.4/http/bit.lua:14: attempt to index a nil value (global 'debug')
stack traceback:
    [C]: in metamethod 'index'
    /usr/local/share/lua/5.4/http/bit.lua:14: in main chunk
    [C]: in function 'require'
    /usr/local/share/lua/5.4/http/h2_connection.lua:7: in main chunk
    [C]: in function 'require'
    /usr/local/share/lua/5.4/http/client.lua:8: in main chunk
    [C]: in function 'require'
    /usr/local/share/lua/5.4/http/request.lua:5: in main chunk
    [C]: in function 'require'
    /etc/vector-lua-scripts/test.lua:2: in function 'test'
    /etc/vector-lua-scripts/test.lua:36: in main chunk
    [C]: in function 'require'
    [string "src/transforms/lua/v2/mod.rs:263:17"]:1: in main chunk

    [C]: in function 'require'

    (command line):1: in main chunk

    [C]: in ?

I debugged a little and found it broke at this line

-- file: http/bit.lua
local info = debug.getinfo(1, "Sl")

Can I do anything to make mlua have access to debug std library?

NOTE

I tried to run this lua-http library in a clean docker image containing lua5.4 and it runs perfectly fine. Here's that dockerfile-

FROM timberio/vector:0.34.1-debian

RUN apt-get update -y && \
    apt-get upgrade -y && \
    apt-get install -y lua5.4 liblua5.4-dev libssl-dev build-essential wget && \
    apt-get clean && \
    rm -rf /var/lib/apt/lists/*

RUN wget https://luarocks.org/releases/luarocks-3.8.0.tar.gz --no-check-certificate && \
    tar zxpf luarocks-3.8.0.tar.gz && cd luarocks-3.8.0 && \
    ./configure --lua-version=5.4 && \
    make && make install

RUN luarocks install http --lua-version=5.4 --tree=/usr/local
RUN ["vector", "--version"]

ENTRYPOINT ["/usr/bin/vector"]

And I ran the following commands

root@a4cfc0f2e9eb:/# lua5.4
Lua 5.4.4  Copyright (C) 1994-2022 Lua.org, PUC-Rio
> request = require "http.request"
> req = request.new_from_uri("http://google.com")
> for k, v in req.headers:each() do
        print(k, v)
    end
:method	GET
:authority	google.com
:path	/
:scheme	http
user-agent	lua-http/0.4
> print(debug)
table: 0xaaaad1f8e770

This would otherwise break on the first line with mlua.

[khvzak]

Can I do anything to make mlua have access to debug std library?

debug library is unsafe and improper use can cause segfaults on Rust side. This is the reason why it's not available by default. You need to create a Lua instance using Lua::unsafe_new to load debug library.

[ashvinsharma]

But this means I have to modify vector’s source code for this change, right? I think i will switch my library instead 😅.

[khvzak]

Seems vector explicitly disabled debug library:
See:

        // In order to support loading C modules in Lua, we need to create unsafe instance
        // without debug library.
        let lua = unsafe {
            mlua::Lua::unsafe_new_with(mlua::StdLib::ALL_SAFE, mlua::LuaOptions::default())
        };

https:/vectordotdev/vector/blob/9693f5253c2ce306de3cfa40d0c52439df98fc71/src/transforms/lua/v1/mod.rs#L115-L119

However you can try the following workaround (mocking debug library):

debug = {
  getinfo = function()
     return {
         currentline = 0,
         source = "?"
    }
  end
}

The lua-http library does not really require debug to be functional

[ashvinsharma]

Okay I will try this. I have seen debug getting called multiple times in that library though. I’m not well equipped with lua skills to handle if something breaks. 😅