modules/lua/docs/writing-handlers.txt

mod_lua always looks to invoke a function for the handler, rather than
just evaluating a script body CGI style. A handler function looks
something like this:

    -- example.lua --
    require "string"

    function handle_something(r)
        r.content_type = "text/plain"
        r:puts("Hello Lua World!\n")
    
        if r.method == 'GET' then
            for k, v in pairs( r:parseargs() ) do
                r:puts( string.format("%s: %s", k, v) )
            end
        elseif r.method == 'POST' then
            for k, v in pairs( r:parsebody() ) do
                r:puts( string.format("%s: %s", k, v) )
            end
        else
            r:puts("unknown HTTP method " .. r.method)
        end 
    end

This handler function just prints out the uri or form encoded
arguments to a plaintext page.

This means (and in fact encourages) that you can have multiple
handlers (or hooks, or filters) in the same script.

Data Structures:
    request_rec:
        the request_rec is mapped in as a userdata. It has a metatable
        which lets you do useful things with it. For the most part it
        has the same fields as the request_rec struct (see httpd.h 
        until we get better docs here) many of which are writeable as
        well as readable, and has (at least) the following methods:
        
        r:puts("hello", " world", "!") -- print to response body
        
        -- logging functions
        r:debug("This is a debug log message")
        r:info("This is an info log message")
        r:notice("This is an notice log message")
        r:warn("This is an warn log message")
        r:err("This is an err log message")
        r:alert("This is an alert log message")
        r:crit("This is an crit log message")
        r:emerg("This is an emerg log message")