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<h1>Writing a Cuberite plugin</h1>
<p>
This article will explain how to write a basic plugin. It details basic requirements
for a plugin, explains how to register a hook and bind a command, and gives plugin
standards details.
</p>
<p>
Let us begin. In order to begin development, we must firstly obtain a compiled copy
of MCServer, and make sure that the Core plugin is within the Plugins folder, and activated.
Core handles much of the Cuberite end-user experience and gameplay will be very bland without it.
</p>
<h2>Creating the basic template</h2>
<p>
Plugins are written in Lua. Therefore, create a new Lua file. You can create as many files as you wish, with
any filename - Cuberite bungs them all together at runtime, however, let us create a file called main.lua for now.
Format it like so:
</p>
<pre class="prettyprint lang-lua">
PLUGIN = nil
function Initialize(Plugin)
Plugin:SetName("NewPlugin")
Plugin:SetVersion(1)
-- Hooks
PLUGIN = Plugin -- NOTE: only needed if you want OnDisable() to use GetName() or something like that
-- Command Bindings
LOG("Initialised " .. Plugin:GetName() .. " v." .. Plugin:GetVersion())
return true
end
function OnDisable()
LOG(PLUGIN:GetName() .. " is shutting down...")
end
</pre>
<p>
Now for an explanation of the basics.
<ul>
<li><b>function Initialize</b> is called on plugin startup. It is the place where the plugin is set up.</li>
<li><b>Plugin:SetName</b> sets the name of the plugin.</li>
<li><b>Plugin:SetVersion</b> sets the revision number of the plugin. This must be an integer.</li>
<li><b>LOG</b> logs to console a message, in this case, it prints that the plugin was initialised.</li>
<li>The <b>PLUGIN</b> variable just stores this plugin's object, so GetName() can be called in OnDisable (as no Plugin parameter is passed there, contrary to Initialize).
This global variable is only needed if you want to know the plugin details (name, etc.) when shutting down.</li>
<li><b>function OnDisable</b> is called when the plugin is disabled, commonly when the server is shutting down. Perform cleanup and logging here.</li>
</ul>
Be sure to return true for this function, else Cuberite thinks you plugin had failed to initialise and prints a stacktrace with an error message.
</p>
<h2>Registering hooks</h2>
<p>
Hooks are things that Cuberite calls when an internal event occurs. For example, a hook is fired when a player places a block, moves,
logs on, eats, and many other things. For a full list, see <a href="index.html">the API documentation</a>.
</p>
<p>
A hook can be either informative or overridable. In any case, returning false will not trigger a response, but returning true will cancel
the hook and prevent it from being propagated further to other plugins. An overridable hook simply means that there is visible behaviour
to a hook's cancellation, such as a chest being prevented from being opened. There are some exceptions to this where only changing the value the
hook passes has an effect, and not the actual return value, an example being the HOOK_KILLING hook. See the API docs for details.
</p>
<p>
To register a hook, insert the following code template into the "-- Hooks" area in the previous code example.
</p>
<pre class="prettyprint lang-lua">
cPluginManager.AddHook(cPluginManager.HOOK_NAME_HERE, FunctionNameToBeCalled)
</pre>
<p>
What does this code do?
<ul>
<li><b>cPluginManager.AddHook</b> registers the hook. The hook name is the second parameter. See the previous API documentation link for a list of all hooks.</li>
</ul>
What about the third parameter, you ask? Well, it is the name of the function that Cuberite calls when the hook fires. It is in this
function that you should handle or cancel the hook.
</p>
<p>
So in total, this is a working representation of what we have so far covered.
</p>
<pre class="prettyprint lang-lua">
function Initialize(Plugin)
Plugin:SetName("DerpyPlugin")
Plugin:SetVersion(1)
cPluginManager.AddHook(cPluginManager.HOOK_PLAYER_MOVING, OnPlayerMoving)
LOG("Initialised " .. Plugin:GetName() .. " v." .. Plugin:GetVersion())
return true
end
function OnPlayerMoving(Player) -- See API docs for parameters of all hooks
return true -- Prohibit player movement, see docs for whether a hook is cancellable
end
</pre>
<p>
So, that code stops the player from moving. Not particularly helpful, but yes :P. Note that ALL documentation is available
on the main API docs page, so if ever in doubt, go there.
</p>
<h2>Binding a command</h2>
<h3>Format</h3>
<p>
So now we know how to hook into MCServer, how do we bind a command, such as /explode, for a player to type? That is more complicated.
We firstly add this template to the "-- Command bindings" section of the initial example:
</p>
<pre class="prettyprint lang-lua">
-- ADD THIS IF COMMAND DOES NOT REQUIRE A PARAMETER (/explode)
cPluginManager.BindCommand("/commandname", "permissionnode", FunctionToCall, " - Description of command")
-- ADD THIS IF COMMAND DOES REQUIRE A PARAMETER (/explode Notch)
cPluginManager.BindCommand("/commandname", "permissionnode", FunctionToCall, " ~ Description of command and parameter(s)")
</pre>
<p>
What does it do, and why are there two?
<ul>
<li><b>PluginManager:BindCommand</b> binds a command. It takes the command name (with a slash), the permission a player needs to execute the command, the function
to call when the command is executed, and a description of the command.</li>
</ul>
The command name is pretty self explanatory. The permission node is basically just a <b>string</b> that the player's group needs to have, so you can have anything in there,
though we recommend a style such as "derpyplugin.explode". The function to call is like the ones with Hooks, but with some fixed parameters which we will come on to later,
and the description is a description of the command which is shown when "/help" is typed.
</p>
<p>
So why are there two? Standards. A plugin that accepts a parameter MUST use a format for the description of " ~ Description of command and parms"
whereas a command that doesn't accept parameters MUST use " - Description of command" instead. Be sure to put a space before the tildes or dashes.
Additionally, try to keep the description brief and on one line on the client.
</p>
<h3>Parameters</h3>
<p>
What parameters are in the function Cuberite calls when the command is executed? A 'Split' array and a 'Player' object.
</p>
<h4>The Split Array</h4>
<p>
The Split array is an array of all text submitted to the server, including the actual command. Cuberite automatically splits the text into the array,
so plugin authors do not need to worry about that. An example of a Split array passed for the command, "/derp zubby explode" would be:<br /><br />
   /derp (Split[1])<br />
   zubby (Split[2])<br />
   explode (Split[3])<br />
<br />
   The total amount of parameters passed were: 3 (#Split)
</p>
<h4>The Player Object and sending them messages</h4>
<p>
The Player object is basically a pointer to the player that has executed the command. You can do things with them, but most common is sending
a message. Again, see the API documentation for fuller details. But, you ask, how <i>do</i> we send a message to the client?
</p>
<p>
There are dedicated functions used for sending a player formatted messages. By format, I refer to coloured prefixes/coloured text (depending on configuration)
that clearly categorise what type of message a player is being sent. For example, an informational message has a yellow coloured [INFO] prefix, and a warning message
has a rose coloured [WARNING] prefix. A few of the most used functions are listed here, but see the API docs for more details. Look in the cRoot, cWorld, and cPlayer sections
for functions that broadcast to the entire server, the whole world, and a single player, respectively.
</p>
<pre class="prettyprint lang-lua">
-- Format: §yellow[INFO] §white%text% (yellow [INFO], white text following it)
-- Use: Informational message, such as instructions for usage of a command
Player:SendMessageInfo("Usage: /explode [player]")
-- Format: §green[INFO] §white%text% (green [INFO] etc.)
-- Use: Success message, like when a command executes successfully
Player:SendMessageSuccess("Notch was blown up!")
-- Format: §rose[INFO] §white%text% (rose coloured [INFO] etc.)
-- Use: Failure message, like when a command was entered correctly but failed to run, such as when the destination player wasn't found in a /tp command
Player:SendMessageFailure("Player Salted was not found")
</pre>
<p>
Those are the basics. If you want to output text to the player for a reason other than the three listed above, and you want to colour the text, simply concatenate
"cChatColor.*colorhere*" with your desired text, concatenate being "..". See the API docs for more details of all colours, as well as details on logging to console with
LOG("Text").
</p>
<h2>Final example and conclusion</h2>
<p>
So, a working example that checks the validity of a command, and blows up a player, and also refuses pickup collection to players with >100ms ping.
</p>
<pre class="prettyprint lang-lua">
function Initialize(Plugin)
Plugin:SetName("DerpyPluginThatBlowsPeopleUp")
Plugin:SetVersion(9001)
cPluginManager.BindCommand("/explode", "derpyplugin.explode", Explode, " ~ Explode a player");
cPluginManager:AddHook(cPluginManager.HOOK_COLLECTING_PICKUP, OnCollectingPickup)
LOG("Initialised " .. Plugin:GetName() .. " v." .. Plugin:GetVersion())
return true
end
function Explode(Split, Player)
if (#Split ~= 2) then
-- There was more or less than one argument (excluding the "/explode" bit)
-- Send the proper usage to the player and exit
Player:SendMessage("Usage: /explode [playername]")
return true
end
-- Create a callback ExplodePlayer with parameter Explodee, which Cuberite calls for every player on the server
local HasExploded = false
local ExplodePlayer = function(Explodee)
-- If the player we are currently at is the one we specified as the parameter
if (Explodee:GetName() == Split[2]) then
-- Create an explosion at the same position as they are; see <a href="cWorld.html">API docs</a> for further details of this function
Player:GetWorld():DoExplosionAt(Explodee:GetPosX(), Explodee:GetPosY(), Explodee:GetPosZ(), false, esPlugin)
Player:SendMessageSuccess(Split[2] .. " was successfully exploded")
HasExploded = true;
return true -- Signalize to Cuberite that we do not need to call this callback for any more players
end
end
-- Tell Cuberite to loop through all players and call the callback above with the Player object it has found
cRoot:Get():FindAndDoWithPlayer(Split[2], ExplodePlayer)
if not(HasExploded) then
-- We have not broken out so far, therefore, the player must not exist, send failure
Player:SendMessageFailure(Split[2] .. " was not found")
end
return true
end
function OnCollectingPickup(Player, Pickup) -- Again, see the API docs for parameters of all hooks. In this case, it is a Player and Pickup object
if (Player:GetClientHandle():GetPing() > 100) then -- Get ping of player, in milliseconds
return true -- Discriminate against high latency - you don't get drops :D
else
return false -- You do get the drops! Yay~
end
end
</pre>
<p>
Make sure to read the comments for a description of what everything does. Also be sure to return true for all <b>command</b> handlers, unless you want Cuberite to print out an "Unknown command" message
when the command gets executed :P. Make sure to follow standards - use CoreMessaging.lua functions for messaging, dashes for no parameter commands and tildes for vice versa,
and finally, <a href="index.html">the API documentation</a> is your friend!
</p>
<p>
Happy coding ;)
</p>
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