ACF mvc.lua example
Set the hostname with mvc.lua
In this example we will create a simple hostname-setting command-line application using mvc.lua. Once the controller/model are built, you can use the same code to set the hostname via the web with a web-based application controller.
For this example, we will assume you have root access on the linux box you are running on (preferably an alpine box!)
Get the mvc.lua module
svn "export" the mvc.lua module. Export will grab a copy without all the extra hidden "version control" stuff
svn export svn://svn.alpinelinux.org/acf/core/trunk/www/cgi-bin/mvc.lua
Create a model and controller
Create a file hostname-model.lua, defining the module functions to set and read the hostname. We return a table for each function including the value, error message and type of the value ("String" in the case of the hostname).
hostname-model.lua
-- Model functions for retrieving / setting the hostname
module ( ..., package.seeall )
-- All functions return a table with
-- A value, the type of the value, and a message if there was an error
local hosttype={ type="string" }
update= function ( name )
-- Check to make sure the name is valid
if (name == nil) then
hosttype.msg = "Hostname cannot be nil"
elseif (#name > 16) then
hosttype.msg = "Hostname must be less than 16 chars"
elseif (string.find(name, "[^%w%_%-]")) then
hosttype.msg = "Hostname can contain alphanumerics only"
end
-- If it is, set the hostname
if (hosttype.msg == nil ) then
local f = io.open("/etc/hostname", "w")
if f then
f:write(name .. "\n")
f:close()
end
f = io.popen ("/bin/hostname -F /etc/hostname")
f:close()
return read()
-- Otherwise, return the error message
else
hosttype.value = name
return hosttype
end
end
read= function ()
local f = io.popen ("/bin/hostname")
local n = f:read("*a") or "none"
f:close()
n=string.gsub(n, "\n$", "")
hosttype.value = n
return (hosttype)
end
Create a file hostname-controller.lua, defining the functions that an "end user" could run. We define Create Read Update Delete as standard actions:
hostname-controller.lua
-- hostname controller code
module ( ... , package.seeall )
create = function (self )
return self.model.update(self.clientdata.hostname)
end
read = function (self)
return self.model.read()
end
update = create
delete = function (self )
self.clientdata.hostname=""
return self.worker":create()
end
Optionally test the model code (without mvc.lua)
If you want, you can create a test.lua script to validate the model code works on its own:
test.lua
m=require("hostname-model")
print(m.update(arg[1]).msg)
print(m.read().value)
You can then test this with:
#lua test.lua "Alpine" nil Alpine
#lua test.lua "Invalid Name" Hostname can contain alphanumerics only Alpine
Make an MVC based application
To make the model and and controller work within the mvc.lua framework, we must do serveral things.
1. Create a configuration file. We'll call the application helloworld, so edit helloworld.conf and add:
appdir=helloworld/app/
2. Move the model and controller to the helloworld app directory:
mkdir -p helloworld/app mv helloworld-*.lua helloworld/app
3. Create an application level controller in the helloworld/app directory, named helloworld/app/app-controller.lua
module ( ..., package.seeall) -- application specific functions will go here
Nothing else needs to go in this controller for now.
4. Create a dispatch wrapper program, named helloworld.lua in the current directory:
-- Simple CLI based mvc application
-- this is to get around having to store
-- the config file in /etc/helloworld/helloworld.conf
ENV={}
ENV.HOME="."
-- load the module
require("mvc")
-- create an new "mvc object"
MVC=mvc:new()
-- load the config file so we can find the appdir
MVC:read_config("helloworld")
-- create an application container
APP=MVC:new("app")
-- dispatch the request
APP.clientdata.hostname=arg[2]
APP:dispatch( "", "hostname", (arg[1] or ""))
This application loads the "mvc.lua" framework, creates an mvc "object" named "MVC", then reads the helloworld.conf file to find out where the app dir is (helloworld/app/). It then loads the app-controller.lua into a new "application level" object named APP. Finally, it sets the clientdata and dispatches the hostname-controller/model pair.
5. Test the application:
# hostname Alpine # lua helloworld.lua no-such-function foo The following unhandled application error occured: controller: "hostname" does not have a "no-such-function" action. # hostname Alpine
# hostname Alpine # lua helloworld.lua update Alline Your controller and application did not specify a view resolver. The MVC framework has no view available. sorry. # hostname Alline
Note in the second case the hostname was changed, although the application does not know how to report success.
Create a view resolver and view formatter
The view resolver is a function that returns a function that processes the view. the second function (the one that is returned) receives input and processes the output.
We will build a very simple view resolver and view processor for our application. Add this to the end of helloworld/app/hostname-controller.lua
local private = {}
private.view = function (f)
if (f.msg) then
print( (f.value or "") .. " is not a valid hostname ")
else
print ("Hostname is currently " .. f.value )
end
end
view_resolver = function (self)
return private.view
end
Now we can test:
# lua helloworld.lua update "1 2 3" 1 2 3 is not a valid hostname # lua helloworld.lua update is not a valid hostname # lua helloworld.lua update Alpine Hostname is currently Alpine
But we have two problems:
1. We now have to make a view resolver and view function for every controller. If we add a date setting controller, we'll have to make a view resolver and view function for it, and so on.
2. Perhaps more importantly, view_resolver is now an "action" in our appliction. Recall that invalid actions are captured, but try this:
# lua helloworld.lua no_such_action Alpine
The following unhandled application error occured:
controller: "hostname" does not have a "no_such_action" action.
# lua helloworld.lua view_resolver Alpine
The following unhandled application error occured:
./helloworld/app/hostname-controller.lua:27: attempt to index local 'f' (a function value)
stack traceback:
./helloworld/app/hostname-controller.lua:27: in function 'viewfunc'
./mvc.lua:139: in function <./mvc.lua:90>
[C]: in function 'xpcall'
./mvc.lua:90: in function 'dispatch'
helloworld.lua:23: in main chunk
[C]: ?
Because view_resolver is an action in the worker table, the mvc.lua runs it; but it returns a function, not a table, and causes an unhandled exception.
Move the view resolver to the application level
The solution to both problems is to move the view resolver and the view function out of the controller's worker table, into the next higher level, in this case, the application's worker table:
1. Delete the private.view and view_resolver functions from helloworld/app/hostname-controller.lua
2. Add the following to helloworld/app/app-controller.lua
local private = {}
private.view = function ( controller, action, viewtable )
io.write(string.format("Controller: %s Action: %s\n",
controller or "", action or ""))
io.write ("Returned a table with the following values:\n")
for k,v in pairs(viewtable) do
io.write(string.format("%s\t%s\n", k, v))
end
end
view_resolver = function (self)
return function (viewtable)
return private.view (self.conf.controller, self.conf.action, viewtable)
end
end
This creates a more "generic" view, but one that will work for any controller - not just hostname.
Now things work as they should:
# lua helloworld.lua update "one two" Controller: hostname Action: update Returned a table with the following values: value one two type string msg Hostname can contain alphanumerics only # lua helloworld.lua view_resolver "Alpine" The following unhandled application error occured: controller: "hostname" does not have a "view_resolver" action.
The mvc table
The mvc.lua module has a provision for executing code on module load, prior to executing the controller's action, and just after executing the controller's action.
This is done with the mvc table in the controller. To demonstrate, let's add a few functions to helloworld/app/app-controller.lua
mvc = {}
mvc.on_load = function (self, parent)
print ("This is the app controller's on_load function")
end
mvc.pre_exec = function (self)
print ("This is the app controller's pre_exec function")
end
mvc.post_exec = function (self)
print ("This is the app controller's post_exec function")
end
Now running our script shows when the functions get called:
# lua helloworld.lua update "Alpine" This is the app controller's on_load function This is the app controller's pre_exec function This is the app controller's post_exec function Controller: hostname Action: update Returned a table with the following values: value Alpine type string
We can add mvc functions to a specific controller, as well. Add this to helloworld/app/hostname-controller.lua
mvc = {}
mvc.on_load = function (self, parent )
print ("This is the hostname controller's on_load function")
end
mvc.pre_exec = function (self)
print ("This is the hostname controller's pre_exec function")
end
mvc.post_exec = function (self)
print ("This is the hostname controller's post_exec function")
end
And this happens:
# lua helloworld.lua update "Alpine" This is the app controller's on_load function This is the hostname controller's on_load function This is the hostname controller's pre_exec function This is the hostname controller's post_exec function Controller: hostname Action: update Returned a table with the following values: value Alpine type string
Note that both the app and hostname on_load functions were run, but only the hostname pre_exec and post_exec functions ran. This is because the pre and post exec functions are run as part of the "action", and the dispatch function looks in the lowest-level controller for the pre/post_exec function. Since hostname now defines those functions, it runs them.
To run both the hostname and app pre_exec function, you must arrange for the hostname pre_exec function to call it's parent pre_exec: