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 Linux box!)

Get the mvc.lua module

Get the mvc.lua module from the git repository.

wget https://gitlab.alpinelinux.org/acf/acf-core/-/blob/master/lua/mvc.lua

Create a model and controller

Create a file hostname-controller.lua, defining the functions that an "end user" could run. We will only create one action, edithostname, which will be used to read and update the hostname. Since the action makes changes to the system, it naturally takes the form of a 'form':

hostname-controller.lua

-- Controller for editing hostname
local mymodule = {} 

mymodule.edithostname = function (self)
        return self.handle_form(self, self.model.get_hostname, self.model.set_hostname, self.clientdata, "Update", "Edit Hostname", "Hostname Updated")
end                                   

return mymodule

Create a file hostname-model.lua, defining the model functions to get and set the hostname. We return a cfe table for each function including the form with the one entry for hostname:

hostname-model.lua

-- Model functions for retrieving / setting the hostname
local mymodule = {}

-- Create a cfe defining the form for editing the hostname and containing the current value
mymodule.get_hostname = function(self, clientdata)
        local retval = cfe({ type="group", value={}, label="Hostname" })

        -- Warning - io.popen has security risks, never pass user data to io.popen
        local f = io.popen ("/bin/hostname")
        local n = f:read("*a") or "none"
        f:close()
        n=string.gsub(n, "\n$", "")

        retval.value.hostname = cfe({ value=n, label="Hostname" })

        return retval
end

-- Set the hostname from the value contained in the cfe created by get_hostname
mymodule.set_hostname = function(self, hostnameform, action)
        local success = true

        -- Check to make sure the name is valid
        if (hostnameform.value.hostname.value == "") then
                success = false
                hostnameform.value.hostname.errtxt = "Hostname must not be blank"
        elseif (#hostnameform.value.hostname.value > 16) then
                success = false
                hostnameform.value.hostname.errtxt = "Hostname must be 16 characters or less"
        elseif (string.find(hostnameform.value.hostname.value, "[^%w%_%-]")) then
                success = false
                hostnameform.value.hostname.errtxt = "Hostname can contain alphanumerics only"
        end

        -- If it is valid, set the hostname
        if ( success ) then
                local f = io.open("/etc/hostname", "w")
                if f then
                        f:write(hostnameform.value.hostname.value .. "\n")
                        f:close()
                end
                -- Warning - io.popen has security risks, never pass user data to io.popen
                f = io.popen ("/bin/hostname -F /etc/hostname")
                f:close()
        else
                hostnameform.errtxt = "Failed to set hostname"
        end

        return hostnameform
end

return mymodule

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

require("mvc") -- Needed for cfe function definition
m=require("hostname-model")

local form = m.get_hostname()
form.value.hostname.value = arg[1] or ""
form = m.set_hostname(nil, form)

if form.errtxt then
        print("FAILED: "..form.value.hostname.errtxt or form.errtxt)
end
form = m.get_hostname()
print(form.value.hostname.value)

You can then test this with:

#lua test.lua "Alpine"
 Alpine

#lua test.lua "Invalid Name"
 FAILED: Hostname can contain alphanumerics only
 Alpine

Add the package to the ACF framework

To make the model and controller work within the ACF mvc.lua framework, we must do several things.

1. Install the ACF core package:

apk add acf-core

Optionally, you can add the entire web-based ACF framework:

setup-acf

2. Modify the ACF configuration file to look in /etc/acf/app/ for additional packages. Edit the /etc/acf/acf.conf file to add the /etc/acf/app/ directory to the appdir comma-separated list:

appdir=/etc/acf/app/,/usr/share/acf/app/

3. Move the model and controller to the new package directory. We will call the package "test":

mkdir -p /etc/acf/app/test
mv hostname-*.lua /etc/acf/app/test

4. Test the new package using the acf-cli application:

# acf-cli /test/hostname/edithostname
result = {}
result["label"] = "Edit Hostname"
result["option"] = "Edit"
result["type"] = "form"
result["value"] = {}
result["value"]["hostname"] = {}
result["value"]["hostname"]["label"] = "Hostname"
result["value"]["hostname"]["type"] = "text"
result["value"]["hostname"]["value"] = "Alpine"
# acf-cli /test/hostname/edithostname hostname=test submit=true
result = {}
result["descr"] = "Hostname Updated"
result["label"] = "Edit Hostname"
result["option"] = "Edit"
result["type"] = "form"
result["value"] = {}
result["value"]["hostname"] = {}
result["value"]["hostname"]["label"] = "Hostname"
result["value"]["hostname"]["type"] = "text"
result["value"]["hostname"]["value"] = "test"

Note that the action string passed to acf-cli is of the form "/prefix/controller/action". The prefix is the path within /etc/acf/app where the controller may be found, so "/test/" for our case. The controller is determined from the controller file name, so "hostname" for our case. And, the action corresponds to the function within the controller to call, so "edithostname" for our case. Also note that, in the two examples above, the first case reads the existing hostname and the second case updates it. The output of the acf-cli application is a serialized version of the cfe form, which is good for testing but not too useful in real life.

Enable the package in the ACF web interface

1. Add the web-based ACF framework:

setup-acf

2. Configure all users to have access to the new hostname action. Edit "/etc/acf/app/test/hostname.roles" file and add GUEST permission for the edithostname action:

echo "GUEST=hostname/edithostname" > /etc/acf/app/test/hostname.roles

The new action should now be visible by browsing to https://IP-of-host/cgi-bin/acf/test/hostname/edithostname. Obviously you might want to reconsider providing GUEST access to this action, because this allows unauthenticated users to modify your hostname.

3. Add the new hostname action to the ACF menu. Edit "/etc/acf/app/test/hostname.menu" file and add a menu item:

echo "Test Hostname Edit edithostname" > /etc/acf/app/test/hostname.menu

You will need to log off from the ACF interface (or delete the session cookie) before the new menu item will be visible.

Make an MVC based application

You have two options for creating an MVC based application of your own.

1. Use the dispatch function. This is the method used by the web interface and the acf-cli application. The action to be dispatched is passed in a string format /prefix/controller/action and the input values are passed in as a clientinfo table. Output is determined by the view.

2. Use the new function to load the desired controller and then directly call the controller actions or model functions. Using the controller actions requires use of the clientdata structure to pass parameters. For calling the model functions, the application will call the get function to retrieve the form cfe, fill in the desired input values into the cfe, and then call the set function to submit the form and perform the desired action. The MVC application is responsible for any user interaction and display of the results.

Use the Dispatch method

test_dispatch

#!/usr/bin/lua
-- Simple CLI based mvc application

-- load the mvc module
mvc = require("acf.mvc")

-- create an new "mvc object"
MVC=mvc:new()

-- load the config file so we can find the appdir
MVC:read_config("acf")

-- dispatch the request
local clientdata = {hostname=arg[1], viewtype=arg[2], submit="Update"}
MVC:dispatch("/test/", "hostname", "edithostname", clientdata)

-- destroy the mvc object
MVC:destroy()

Test the application. As can be seen in the code above, the first argument is the new hostname and the second is a viewtype.

alpine:~# chmod 755 test_dispatch 
alpine:~# ./test_dispatch test
test:~# ./test_dispatch alpine
alpine:~#

Note that the application functions, but there is no output. This is because there is no viewtype supplied. There is built-in support for these standard viewtypes (not all apply): html, json, stream, serialized

alpine:~# ./test_dispatch test serialized
result = {}
result["descr"] = "Hostname Updated"
result["label"] = "Edit Hostname"
result["option"] = "Update"
result["type"] = "form"
result["value"] = {}
result["value"]["hostname"] = {}
result["value"]["hostname"]["label"] = "Hostname"
result["value"]["hostname"]["type"] = "text"
result["value"]["hostname"]["value"] = "test"
test:~# ./test_dispatch alpine json
{"type":"form","label":"Edit Hostname","value":{"hostname":{"value":"alpine","type":"text","label":"Hostname"}},"option":"Update","descr":"Hostname Updated"}
alpine:~#

You can also use a custom viewtype and/or view to customize the output. This relies on haserl to parse the view file, and haserl lua functions are only available when launched from haserl scripts (it would be nice if haserl were available as a standalone lua library). Haserl scripts expect to be launched by a web browser to handle CGI data, so passing input is trickier. I'm sure there is a better way to do this, but this is just an example:

test_haserl

#!/usr/bin/haserl-lua5.2 --shell=lua
<%
-- Simple CLI based mvc application

-- load the mvc module
mvc = require("acf.mvc")

-- create an new "mvc object"
MVC=mvc:new()

-- load the config file so we can find the appdir
MVC:read_config("acf")

-- dispatch the request
local clientdata = {hostname=FORM.hostname, viewtype=FORM.viewtype, submit="Update"}
MVC:dispatch("/test/", "hostname", "edithostname", clientdata)

-- destroy the mvc object
MVC:destroy()
%>

/etc/acf/app/test/hostname-edithostname-text.lsp

<%
local data, viewlibrary, page_info, session = ... 

if data.errtxt then
        print(data:print_errtxt())
else
        print(data.descr)
end
%>

Test the application

test:~# chmod 755 test_haserl 
test:~# QUERY_STRING='hostname=alpine&viewtype=text' REQUEST_METHOD=GET ./test_haserl
Hostname Updated
alpine:~# QUERY_STRING='hostname=asdfasdfasdfasdfasdf&viewtype=text' REQUEST_METHOD=GET ./test_haserl
Failed to set hostname
hostname: Hostname must be 16 characters or less
alpine:~#

You can further customize the application by creating your own application-specific controller. This is how the web interface and the acf-cli application are written. In both cases, a simple application is written to load not just an mvc:new() reference, but an application-specific controller to wrap the mvc:new() object. The dispatch function is then called on the application-specific controller object, which can override any function in mvc.lua to add a customized implementation. For example, both applications override the handle_clientdata function to customize the way input data is provided in the clientdata structure, and the web interface-specific controller contains a lot of code to handle features such as menus, templates, skins, authentication, redirection, ... The best way to understand this is to just read the code.

Web application
- Application - acf
- Controller - acf_www-controller.lua
acf-cli
- Application - acf-cli
- Controller - acf_cli-controller.lua

Use the New method

test_new

#!/usr/bin/lua
-- Simple CLI based mvc application

-- load the mvc module
mvc = require("acf.mvc")

-- create an new "mvc object"
MVC=mvc:new()

-- load the config file so we can find the appdir
MVC:read_config("acf")

-- load the hostname controller
HOSTNAME=MVC:new("/test/hostname")

local hostname

-- METHOD 1 - controller action
HOSTNAME.clientdata = {hostname=arg[1], submit="Update"}
hostname = HOSTNAME:edithostname()

-- METHOD 2 - model functions
hostname = HOSTNAME.model:get_hostname()
hostname.value.hostname.value = arg[1]
hostname = HOSTNAME.model:set_hostname(hostname)

if hostname.errtxt then
        print(hostname:print_errtxt())
else
        print(hostname.descr or "Hostname Updated")
end

HOSTNAME:destroy()
MVC:destroy()

Once you have a hostname controller object, you can access its actions, passing data through clientdata, or you can directly access the get/set functions of the model. Test the app:

test:~# chmod 755 test_new
test:~# ./test_new alpine
Hostname Updated
alpine:~# ./test_new asdfasdfasdfasdfasdf
Failed to set hostname
hostname: Hostname must be 16 characters or less
alpine:~#

This material is obsolete ...

Please feel free to help us make an up-to-date version. (Discuss)

mvc load & exec special functions

The mvc.lua module has a provision for executing code on module load, prior to executing the controller's action, just after executing the controller's action, and on module unload.

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

mvc.on_unload = function (self)
        print ("This is the app controller's on_unload 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
  This is the app controller's on_unload function

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

mvc.on_unload = function (self)
        print ("This is the hostname controller's on_unload 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
  This is the hostname controller's on_unload function
  Controller: hostname  Action: update
  Returned a table with the following values:
  value   Alpine
  type    string
  This is the app controller's on_unload function

Note that both the app and hostname on_load and on_unload 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:

mvc = {}
mvc.on_load = function (self, parent)
       print ("This is the hostname controller's on_load function")
       mvc.parent_pre_exec = parent.worker.mvc.pre_exec
end

mvc.pre_exec = function (self)
        mvc.parent_pre_exec (self)
        print ("This is the hostname controller's pre_exec function")
end