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)
                        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, name )
        return self.model.update(name)
end

read = function (self)
        return self.model.read()
end

update = function (self, name )
         return self:create(name)
end 

delete = function (self, name)
        return self: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