# HowTo: Write Modules

See [online wiki](https://github.com/openwrt/luci/wiki/ModulesHowTo) for latest version.

**Note:** If you plan to integrate your module into LuCI, you should read the [Module Reference](./Modules.md) in advance.

This tutorial describes how to write your own modules for the LuCI WebUI.
For this tutorial we refer to your LuCI installation directory as `lucidir` (`/usr/lib/lua/luci` on your OpenWRT device) and assume your LuCI installation is reachable through your webserver via `http://192.168.1.1/cgi-bin/luci`.

The recommended way to set up development environment:

Install OpenWRT on your router/device (You could use a QEMU or VirtualBox image instead)

Install SSHFS on your host

Mount your routers' root (/) someplace on your development host (eg. /mnt/router)

Then open /mnt/router/(lucidir) in your favorite development studio

Extra: Add configurations to your dev studio which will delete the luci cache (detailed below) and then open a browser window to your routers' configuration page in order to see your module/application.


When testing, if you have edited index files, be sure to remove the folder `/tmp/luci-modulecache/*` and the file(s) `/tmp/luci-indexcache*`, then refresh the LUCI page to see your edits.

## Show me the way (The dispatching process)
To write a module you need to understand the basics of the dispatching process in LuCI.
LuCI uses a dispatching tree that will be built by executing the index-Function of every available controller.
The CGI-environment variable `PATH_INFO` will be used as the path in this dispatching tree, e.g.: `/cgi-bin/luci/foo/bar/baz`
will be resolved to `foo.bar.baz`

To register a function in the dispatching tree, you can use the `entry`-function of `luci.dispatcher`. It takes 4 arguments (2 are optional):
```lua
entry(path, target, title=nil, order=nil)
```

* `path` is a table that describes the position in the dispatching tree: For example a path of `{"foo", "bar", "baz"}` would insert your node in `foo.bar.baz`.
* `target` describes the action that will be taken when a user requests the node. There are several predefined ones of which the 3 most important (call, template, cbi) are described later on this page
* `title` defines the title that will be visible to the user in the menu (optional)
* `order` is a number with which nodes on the same level will be sorted in the menu (optional)

You can assign more attributes by manipulating the node table returned by the entry-function. A few example attributes:

* `i18n` defines which translation file should be automatically loaded when the page gets requested
* `dependent` protects plugins to be called out of their context if a parent node is missing
* `leaf` stops parsing the request at this node and goes no further in the dispatching tree
* `sysauth` requires the user to authenticate with a given system user account


# It's all about names (Naming and the module file)
Now that you know the basics about dispatching, we can start writing modules. Now, choose the category and name of your new digital child.

Let's assume you want to create a new application `myapp` with a module `mymodule`.

So you have to create a new sub-directory `lucidir/controller/myapp` with a file `mymodule.lua` with the following content:
```lua
module("luci.controller.myapp.mymodule", package.seeall)

function index()

end
```

The first line is required for Lua to correctly identify the module and create its scope.
The `index`-Function will be used to register actions in the dispatching tree.



## Teaching your new child (Actions)
So it has a name, but no actions.

We assume you want to reuse your module myapp.mymodule that you began in the last step.


### Actions
Reopen `lucidir/controller/myapp/mymodule.lua` and just add a function to it with:
```lua
module("luci.controller.myapp.mymodule", package.seeall)

function index()
    entry({"click", "here", "now"}, call("action_tryme"), "Click here", 10).dependent=false
end
 
function action_tryme()
    luci.http.prepare_content("text/plain")
    luci.http.write("Haha, rebooting now...")
    luci.sys.reboot()
end
```

And now visit the path `/cgi-bin/luci/click/here/now` (`http://192.168.1.1/luci/click/here/now` if you are using the development environment) in your browser.

These action functions simply have to be added to a dispatching entry.

As you may or may not know: CGI specification requires you to send a `Content-Type` header before you can send your content. You will find several shortcuts (like the one used above) as well as redirecting functions in the module `luci.http`

### Views
If you only want to show the user text or some interesting family photos, it may be enough to use an HTML-template.
These templates can also include some Lua code but be aware that writing whole office-suites by only using these templates might be considered "dirty" by other developers.

Now let's create a little template `lucidir/view/myapp-mymodule/helloworld.htm` with the content:

```html
<%+header%>
<h1><%:Hello World%></h1> 
<%+footer%>
```


and add the following line to the `index`-Function of your module file.
```lua
entry({"my", "new", "template"}, template("myapp-mymodule/helloworld"), "Hello world", 20).dependent=false
```

Now visit the path `/cgi-bin/luci/my/new/template` (`http://192.168.1.1/luci/my/new/template`) in your browser.

You may notice those special `<% %>`-Tags, these are [template markups](./Templates.md) used by the LuCI template processor.
It is always good to include header and footer at the beginning and end of a template as those create the default design and menu.

### CBI models
The CBI is one of the coolest features of LuCI.
It creates a formulae based user interface and saves its contents to a specific UCI config file.
You only have to describe the structure of the configuration file in a CBI model file and Luci does the rest of the work.
This includes generating, parsing and validating an XHTML form and reading and writing the UCI file.

So let's be serious at least for this paragraph and create a practical example `lucidir/model/cbi/myapp-mymodule/netifaces.lua` with the following contents:

```lua
m = Map("network", "Network") -- We want to edit the uci config file /etc/config/network

s = m:section(TypedSection, "interface", "Interfaces") -- Especially the "interface"-sections
s.addremove = true -- Allow the user to create and remove the interfaces
function s:filter(value)
   return value ~= "loopback" and value -- Don't touch loopback
end 
s:depends("proto", "static") -- Only show those with "static"
s:depends("proto", "dhcp") -- or "dhcp" as protocol and leave PPPoE and PPTP alone

p = s:option(ListValue, "proto", "Protocol") -- Creates an element list (select box)
p:value("static", "static") -- Key and value pairs
p:value("dhcp", "DHCP")
p.default = "static"

s:option(Value, "ifname", "interface", "the physical interface to be used") -- This will give a simple textbox

s:option(Value, "ipaddr", translate("ip", "IP Address")) -- Yes, this is an i18n function ;-)

s:option(Value, "netmask", "Netmask"):depends("proto", "static") -- You may remember this "depends" function from above

mtu = s:option(Value, "mtu", "MTU")
mtu.optional = true -- This one is very optional

dns = s:option(Value, "dns", "DNS-Server")
dns:depends("proto", "static")
dns.optional = true
function dns:validate(value) -- Now, that's nifty, eh?
    return value:match("[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+") -- Returns nil if it doesn't match otherwise returns match
end

gw = s:option(Value, "gateway", "Gateway")
gw:depends("proto", "static")
gw.rmempty = true -- Remove entry if it is empty

return m -- Returns the map
```

and of course remember to add something like this to your module's `index`-Function.
```lua
entry({"admin", "network", "interfaces"}, cbi("myapp-mymodule/netifaces"), "Network interfaces", 30).dependent=false
```

There are many more features. See [the CBI reference](./CBI.md) and the modules shipped with LuCI.