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
Get the mvc.lua module from the git repository.
wget http://git.alpinelinux.org/cgit/acf-core/plain/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 for 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.update_hostname, self.clientdata, "Edit", "Edit Hostname", "Hostname Updated")
end
return mymodule
Create a file hostname-model.lua, defining the model functions to get and update 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 = {}
local f = io.popen ("/bin/hostname")
local n = f:read("*a") or "none"
f:close()
n=string.gsub(n, "\n$", "")
retval.hostname = cfe({ value=n, label="Hostname" })
return cfe({ type="group", value=retval, label="Hostname" })
end
-- Update the hostname from the value contained in the cfe created by get_hostname
mymodule.update_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 less than 16 chars"
elseif (string.find(hostnameform.value.hostname.value, "[^%w%_%-]")) then
success = false
hostnameform.value.hostname.errtxt = "Hostname can contain alphanumerics only"
end
-- If it is, 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
f = io.popen ("/bin/hostname -F /etc/hostname")
f:close()
else
hostnameform.errtxt = "Failed to update 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.update_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 first case read the existing hostname and the second case updated 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
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 ""))
-- destroy the mvc objects APP:destroy() MVC:destroy()
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 returned function receives input from the controller and generates the output to be displayed.
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 in the view.
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.
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