Multiple scripts in MySQL Proxy

MySQL Proxy is being beefed up, to make it ready for prime time. New features are being added, and old ones are improved and tested.
Testing the Proxy is an adventure in its own right. It's a tool that was designed to get in the middle of the scene and change things. Testing its features is more challenging than testing a straightforward application, even more complex like a database server. So the test suite for MySQL Proxy is much more complex and feature rich than the corresponding suite for the database server.
While researching to create the next edition of the test suite, able to cope with more features and corresponding testing requests, I developed a Lua script that enhances the current Proxy features and allows you to load several scripts, and use them all at once.
The script (load-multi.lua) is available in the latest Subversion tree. The usage is not difficult.
From any client, you need to send a query

PLOAD script_name;

The script you indicate will then be available to all the clients.
If your script contains functions that are used at session start (connect_server, read_handshake, read_auth, read_auth_result), they will be available when the next client connects. If your script uses read_query and read_query_result, they will be available immediately.
The mechanics of how this works is simple. You load one or more script containing one or more of the above mentioned functions that hook to the Proxy, and the load-multi module will stack each function in a list. For each hook, the load-multi module loops through the loaded functions, executes each one and tests the result. If the function returns a non null value, then that value is passed back to the Proxy.

This means that if you have two scripts that can handle a particular query, only the first one that has been loaded will get a chance to evaluate the query.
When loading modules, you must check the order in which you are loading them. If you load first a script that handles every query, such as a logging application, subsequent scripts would be just filling memory.
There are more goodies.
Your scripts can use some global functions that load-multi prepares for you. Each of these routines is in the proxy.global namespace, so they are available to all clients and their loaded scripts.
One first useful application that can be plugged to this module is a script that lists the status of loaded functions:

-- show_handlers.lua
function read_query (packet)
if packet:byte() ~= proxy.COM_QUERY then
 return
end
local query = packet:sub(2)
  if query:match('select pload status') then
      local header = { 'module', 'handler' }
      local rows = {}
      for id, lmodule in pairs(proxy.global.handler_status) do
          for i,h in pairs(lmodule) do
              table.insert(rows, { id, h.func } )
          end
      end
      return proxy.global.make_dataset(header,rows)
  end
end

Load this script with PLOAD show_handlers, and any client will be able to get a list of modules, with the function that each one introduced.

pload show_handlers;
+-------------------------------+
| info                          |
+-------------------------------+
| module "show_handlers" loaded |
+-------------------------------+
1 row in set (0.01 sec)

pload auth1;
+-----------------------+
| info                  |
+-----------------------+
| module "auth1" loaded |
+-----------------------+
1 row in set (0.03 sec)

select pload status;
+---------------+-------------------+
| module        | handler           |
+---------------+-------------------+
| show_handlers | read_query        |
| auth1         | read_auth         |
| auth1         | disconnect_client |
| auth1         | read_handshake    |
| auth1         | connect_server    |
| auth1         | read_auth_result  |
+---------------+-------------------+
6 rows in set (0.01 sec)

This new module has the ability of extending its own behavior. If you like playing with new features, you should try this one!