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<h1>Writing a MCServer 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 MCServer end-user experience and is a necessary component of
plugin development, as necessary plugin components depend on sone of its functions.
</p>
<p>
Next, we must obtain a copy of CoreMessaging.lua. This can be found
<a href="https://raw.github.com/mc-server/MCServer/master/MCServer/Plugins/MagicCarpet/coremessaging.lua">here.</a>
This is used to provide messaging support that is compliant with MCServer standards.
</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 - MCServer 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">
local PLUGIN
function Initialize(Plugin)
Plugin:SetName("DerpyPlugin")
Plugin:SetVersion(1)
PLUGIN = Plugin
-- Hooks
local PluginManager = cPluginManager:Get()
-- 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).</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 MCS 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 MCServer 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 MCServer 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)
local PluginManager = cPluginManager:Get()
-- Command bindings
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)
PluginManager:BindCommand("/commandname", "permissionnode", FunctionToCall, " - Description of command")
-- ADD THIS IF COMMAND DOES REQUIRE A PARAMETER (/explode Notch)
PluginManager: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 MCServer 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. MCServer 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>
Remember that copy of CoreMessaging.lua that we downloaded earlier? Make sure that file is in your plugin folder, along with the main.lua file you are typing
your code in. Since MCS brings all the files together on JIT compile, we don't need to worry about requiring any files or such. Simply follow the below examples:
</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
SendMessage(Player, "Usage: /explode [player]")
-- Format: §green[INFO] §white%text% (green [INFO] etc.)
-- Use: Success message, like when a command executes successfully
SendMessageSuccess(Player, "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
SendMessageFailure(Player, "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)
local PluginManager = cPluginManager:Get()
PluginManager: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
SendMessage(Player, "Usage: /explode [playername]")
return true
end
-- Create a callback ExplodePlayer with parameter Explodee, which MCS 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)
SendMessageSuccess(Player, Split[2] .. " was successfully exploded")
HasExploded = true;
return true -- Signalize to MCS that we do not need to call this callback for any more players
end
end
-- Tell MCS 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
SendMessageFailure(Player, 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 MCS 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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