I'm solving the problem of passing data to and from Lua-side with the implementation of two custom functions gl.DataToTable and gl.TableToData

...

and pass to gl.BufferData().

Consider Lua's flexibility. You don't have to enforce strict GL api, and then fight with it by adding more functions.

In my toy engine I'm trying to express GL/D3D api at higher level. Don't prepare data to fill buffer, just create new vbo, and hide conversions from scripts.

For example:

local mesh = vao {
    vbo {
        pos = vec3f {0,0,0, ......},
        normal = vec3f {0,1,0, ....}
    },
    live_colors = vbo {
        color = vec4b {255,255,255,255, ....}
    },
    vbo {
        index = {0,1,2,2,3,0,....}
    }
}

It looks clean, expressive, you can bind that object as vao - it hides details about GL's VAO or D3D's vertex declaration, and it allows automatic binding of vertex streams to shader attribs.

You can assing new data as simple as this:

-- alter single semantic
mesh[1].normal = vec3f {... new normals}

-- replace one buffer in vao with completely new data of different format
mesh.live_colors = vbo { colors = vec3f {1.0,1.0,1.0,...} }

Same with shaders. It's much more convenient to assign values to uniforms with "shader_obj.uniform_name = {1,2,3,0}" than bind/ask uniform location then use acquired indices to actually write data.

vec3f/vec4f/vec4b doesn't convert data, it only alters passed table by inserting fields identifying desired data type and vector size, and is actually lua function.