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()

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:

# lua helloworld.lua no-such-function foo
The following unhandled application error occured:
 
controller: "hostname" does not have a "no-such-function" action.