factorio-clusterio/docs/writing-plugins.md

# Writing Plugins

Plugins for Clusterio are classes written in JavaScript that run under Node.js.
The plugin classes have pre-defined hooks that are called during various stages and operations of Clusterio.


## Contents

- [Plugin Structure](#plugin-structure)
- [Defining the plugin class](#defining-the-plugin-class)
- [Logging Messages](#logging-messages)
- [Plugin Configuration](#plugin-configuration)
- [Communicating with Factorio](#communicating-with-factorio)
- [Defining Link Messages](#defining-link-messages)
    - [Defining Events](#defining-events)
    - [Defining Requests](#defining-requests)
- [Sending Link Messages](#sending-link-messages)
    - [Handling connection events](#handling-connection-events)
- [Collecting Statistics](#collecting-statistics)
- [Adding Custom Commands to clusterioctl](#adding-custom-commands-to-clusterioctl)


## Plugin Structure

The basic file structure of a plugin is the following.

    plugin_name/
      +- info.js
      +- package.json
      +- controller.js
      +- instance.js
      +- control.js
      +- test/
      |  +- plugin.js
      +- module/
         +- module.json
         +- plugin.lua

Clusterio plugins are Node.js packages that can be published on npm for ease of installation and distribution.
The usual guides for creating such packages apply.
At minimum the `package.json` file must contain a version entry.

A possible workflow for developing plugins is to place the plugin in a sub-directory of where clusterio has been installed, and rely on Node.js searching up the folder heirarchy for it to find `@clusterio/lib`.
To add it to `plugin-list.json` so that it gets loaded use the `plugin add <path>` sub-command to either clusteriocontroller, clusteriohost or clusterioctl.
Note that it's important that the path starts with ./ or ../ (use .\ or ..\ on Windows).

For a plugin the most important file is the `info.js` file.
Without it the plugin will not recognized by Clusterio.
Here's an example of it:

```js
const { libLink } = require("@clusterio/lib"); // For messages

module.exports = {
    name: "foo_frobber",
    title: "Foo Frobber",
    description: "Does advanced frobnication",
    instanceEntrypoint: "instance",
    controllerEntrypoint: "controller",
    messages: {
        /* See below */
    },
};
```

The following properties are recognized:

**name**:
    Internal name of the plugin.
    Must be the same as the plugin's directory name

**title**:
    Name of the plugin as shown to users.
    Currently not used.

**description**:
    Brief description of what the plugin does.
    Currently not used.

**instanceEntrypoint**:
    Path to a Node.js module relative to the plugin directory which contains the InstancePlugin class definition for this plugin.
    This is an optional paramater.
    A plugin may have code only for instances but it must still be loaded on the controller in order for it to be possible to load it on an instance.

**InstanceConfigGroup**:
    Subclass of `PluginConfigGroup` for defining the per instance configuration fields for this plugin.
    See [Plugin Configuration](#plugin-configuration)

**controllerEntrypoint**:
    Path to a Node.js module relative to the plugin directory which contains the ControllerPlugin class definiton for this plugin.
    This is an optional parameter.
    A plugin can be made that only runs on the controller.

**ControllerConfigGroup**:
    Subclass of `PluginConfigGroup` for defining the controller configuration fields for this plugin.
    See [Plugin Configuration](#plugin-configuration)

**controlEntrypoint**:
    Path to a Node.js module relative to the plugin directory which contains the ControlPlugin class definition for this plugin.
    This is an optional paramater.
    A plugin can be made that only runs on the clusterioctl side.

**messages**:
    Object with link messages definitions for this plugin.
    See guide for [defining link messages](#defining-link-messages) below.

The optional module folder contains a Clusterio module that will be patched into the save when the plugin is loaded.
See the section on [Clusterio Modules](developing-for-clusterio.md) in the Developing for Clusterio document.
The only restriction imposed on modules embedded into plugins is that they must be named the same as the plugin.

While there is no standard for how to organize a plugin it's recommended to put the ControllerPlugin class definition into controller.js and the InstancePlugin class definition into instance.js.
You can put them into whatever file you want (even the same one for both).

For both instanceEntrypoint and controllerEntrypoint the path should not end with .js and it should use forward slashes for directory separators if any.


## Defining the plugin class

The plugin class should derive from its respective base class defined in `lib/plugin`.
For example, to define a ControllerPlugin class the following code can be used:

```js
const libPlugin = require("@clusterio/lib/plugin");

class ControllerPlugin extends libPlugin.BaseControllerPlugin {
    async init() {
        this.foo = 42;
        await this.startFrobnication();
    }

    // ...
}

module.exports = {
    ControllerPlugin,
}
```

For the instance plugin it's exactly the same except "Controller" is replaced with "Instance", and for the clusterioctl plugin "Control" is used.
The available hooks that you can override are documented in the base class [in lib/plugin.js](/packages/lib/plugin.js).

It's best to avoid defining a constructor, but if you insist on defining one, forward all arguments to the base class.
E.g.:

```js
constructor(...args) {
    super(...args);

    // Code here
}
```

The arguments passed may change, and attempting to modify them will result in unpredicatable behaviour.
The async init method is always called immediatly after the constructor, so there's little reason to do this.


## Logging Messages

The base plugin classes provide a winston logger for logging messages to the shared cluster log.
For instances a copy of the log is also stored on the host the instance is on.
To use it, pass a string to one of the log levels functions, for example:

```js
async init() {
    this.logger.info("Initializing frobbing");
}
```

Metadata covering which plugin and instance (for instance plugin classes) the log event happened on will automatically be attached to the log message.

The available levels are fatal, error, warn, audit, info, and verbose.
These levels have roughly the following meanings:

- fatal: Unrecoverable error that prevents continuing execution of the Node.js process.
  Note that Plugins shouldn't have fatal errors.
- error: An unexpected error condition occured, usually an exception thrown when it wasn't expected.
  Should be investigated and fixed.
- warn: An potential error was detected, but operation continued gracefully.
  These may indicate that something is running sub-optimally, or is not working as intedend.
- audit: Record of actions performed by users of the cluster.
  This is usually emitted in response to management requests by a control link.
- info: A general log message.
  May indicae a status or operation completed.
  This should not be emitted by periodic tasks that run often.
- verbose: A verbose log message which might be useful when investigating issues, does not show by default.
  Note that logging messages is not a cheap operation even when the messages do not show up and spammy logging should be avoided for the verbose level.
  If the logs are still valuable in certain cases consider putting them behind a config option.

For guarding unexpected errors the best option is to log a short description along with the`stack` property of the Error:

```js
try {
    // Operation that should not throw but may end up throwing
} catch (err) {
    this.logger.error(`Operation failed:\n${err.stack}`);
)
```

For plugin hooks expections thrown are automatically catched and logged, but for event handlers registered on EventEmitters it's critical that exceptions are catched and handled appropriately.


## Plugin Configuration

Clusterio provides a configuration system that handles storing, distributing, editing and validating config fields for you.
You can take advantage of it by subclassing `PluginConfigGroup`, setting `defaultAccess` to where config entries can be accessed from, setting the `groupName` to your plugin name, defining fields on it, finalizing it, and passing it as either `ControllerConfigGroup` or `InstanceConfigGroup` in the `info.js` export.
For example in info.js:

```js
const libConfig = require("@clusterio/lib/config");

class ControllerConfigGroup extends libConfig.PluginConfigGroup { }
ControllerConfigGroup.defaultAccess = ["controller", "host", "control"];
ControllerConfigGroup.groupName = "foo_frobber";
ControllerConfigGroup.define({
    name: "level",
    description: "Level of frobnication done",
    type: "number",
    initial_value: 2,
});
ControllerConfigGroup.finalize();

module.exports = {
    ...
    ControllerConfigGroup: ControllerConfigGroup,
};
```

Code inside the `ControllerPlugin` class will then be able to access the level config field through the `Config` object at `this.controller.config`, for example in the ControllerPluginClass:

```js
async init() {
    let level = this.controller.config.get("foo_frobber.level");
    this.logger.info(`I got a frobnication level of ${level}`);
}
```

The same applies for instance configs, replace "controller" with "instance" where appropriate.
See [Configuration System](config-system.md) for more details on how this system works.


### Handling Invalid Configuration

If the plugin requires a certain feature to be enabled to function it should throw an error during init if this is not the case.
The most common such feature is the save patching, which can be disabled to run vanilla or scenarios not compatible with Clusterio.
For example:

```js
async init() {
    if (!this.instance.config.get("factorio.enable_save_patching")) {
        throw new Error("foo_frobber plugin requires save patching.");
    }
}
```


## Communicating with Factorio

For pushing data into Factorio there's RCON, which lets you send arbitrary Lua commands to invoke whatever code you want in the game.
This is done by calling the `sendRcon` method on the plugin object.
For example:

```js
async onStart() {
    let response = await this.sendRcon(
        "/sc rcon.print('data')"
    );

    // Do stuff with response.
}
```

Because data into Factorio is streamed at a rate of 3-6 kB/s by default, it is recommended to avoid sending large commands as much as possible, and to strip down the data on the ones you send to only what's strictly necessary.
You can have lua code injected into the game via the module system and call that from RCON to avoid having to send code through the commands.

For getting data out from Factorio there's both RCON and the `send_json` API of the Clusterio module.
Returning data via RCON is prefered if the action is initiated from the Node.js side.
The `send_json` API allows sending JSON payloads on channels that plugins can listen to.
From a plugin you listen for an event named `ipc-channel_name` in order to get data sent by `send_json`.
For example in the plugin code:

```js
async init() {
    this.instance.server.on("ipc-my_plugin_foo", content =>
        this.handleFoo(content).catch(err => this.logger.error(
            `Error handling foo:\n${err.stack}`
        ))
    );
}

async handleFoo(content) {
    // Do stuff with content
}
```

And then in the module for the plugin:

```lua
local clusterio_api = require("modules/clusterio/api")

-- inside some event handler
clusterio_api.send_json("my_plugin_foo", { data = 123 })
```

It's recommended to either use the plugin name as the channel name or to prefix the channel name with the name of the plugin if you need multiple channels.
It's also important to catch any errors that might occur as they will otherwise be propogated to the instance code and kill the server.

Data out from Factorio does not have the same limits as data into Factorio, RCON responses can be in 100kB range without causing issues, and payloads to the `send_json` API can be in the 4MB range provided the server has a fast enough storage system.

**Note:** both `send_json` and RCON can operate out of order.
For `send_json` it's possible that payloads greater than 4kB are received after payloads that were sent at a later point in time.
For RCON, commands longer than 50 characters may end up being executed after shorter commands sent after it.


## Defining Link Messages

You will most likely have to communicate with the controller or other instances in your plugin for it to do anything useful.
For this there's a WebSocket communication channel established between the hosts and the controller that plugins can define their own messages to send over it.
This channel is bi-directional and all messages sent over it are validated with a JSON schema (see [this guide][guide] for an introduction to writing JSON schema).

[guide]: https://json-schema.org/learn/getting-started-step-by-step.html

There are currently two kinds of messages that can be defined: events and requests.
Events are simple one-way notifications that invoke a handler on the target it's sent to.
Requests are pairs of request and response messages where the request is sent to the target and the response is the reply back from the target.
The requests are similar to HTTP requests, except both parties of a link may initiate one.


### Defining Events

Events are defined as properties of the messages object exported by `info.js` that map to instances of the `Event` class from `lib/link`.
The name of the property correspond to the handler invoked on the plugin class.
The Event constructor takes an object of properties that define the event, for example the following could be defined in `info.js`:

```js
messages: {
    startFrobnication: new libLink.Event({
        type: "foo_frobber:start_frobnication",
        links: ["controller-host", "host-instance"],
        forwardTo: "instance",
        eventRequired: ["frobnication_type"],
        eventProperties: {
            "frobnication_type": { type: "string" },
            "urgent": { type: "boolean" },
        },
    }),
},
```

This specifies an event that can be sent from the controller to a host, and from a host to an instance.
It also specifies that the event must contain the property `frobnication_type`, with a string value in the data payload and that it may optionally contain a boolean `urgent` property.
It will also be forwarded by hosts to a specific instance.

The following properties are recognized by the Event constructor:

#### type

The message type sent over the wire.
This must start with the name of the plugin followed by colon and and be unique for the plugin.
The type of the message sent over the socket will have the suffix `_event` appended to it.

#### links

An array of strings describing which links this event can be sent over.
Direction matters, `"controller-host"` means the event can be sent from the controller to the host, but can't be sent back the other way, unless `"host-controller"` is also present in the links array.

The available endpoints are `controller`, `host`, `instance`, and `control`.
Controller talks with host and control, and host talks to instance.
The full chain must be specified as the individual links in order for a message to travers multiple hops, (i.e., for a message to go from controller to instance it must have both `"controller-host"` and `"host-instance"` in the links array).
See `forwardTo` and `broadcastTo` for ways to forward an event to the next link in a chain.

#### forwardTo

Target to forward an event to.
Can either be `"controller"`, to indicate a host should forward it to the controller, or `"instance"`, to indicate it should be forwarded to the instances specified by the `instance_id` event property.
This works by using a default handler for the event at the links that forward it.

#### broadcastTo

Target to broadcast this message towards.
A value of "instance" means the event will be broadcast to all instances downstream of the target it's sent to, but not back from where it came from.
Currently, only "instance" is supported.
This means that sending the event to a host from an instance will cause it to be broadcast to all instances of that host except for the instance it came from.

#### eventRequired

By default all properties defined in `eventProperties` are required to be present in the payload for the event.
This can be overriden by specifying an array of properties which are required here.
This is equivalent to using the `required` keyword in JSON schema.

#### eventProperties

Object with properties mapping to a JSON schema of that property that specifies what's valid to send in the event.
This is equivalent to using the `properties` keyword in JSON schema, except that the properties specified are by default required and additional properties are not allowed.
See [this guide][guide] for an introduction to writing JSON schemas.

The forwardTo and broadcastTo can be combined such that specifying `"controller"` as the forwardTo value and `"instance"` as the broadcastTo value will cause the event to be broadcast to all instances in the cluster.
For this to work, you will need to specify `instance-host`, `host-controller`, `controller-host`, and `host-instance` as the links.

Keep in mind when forwarding events that if the target an event is being forwarded to is not online, the event will be dropped.
Use a request if you need a confirmation that the message was received.

### Definining Requests

Requests are defined as properties of the messages object exported by `info.js` that map to instances of the `Request` class from `lib/link`.
The name of the property corresponds to the handler invoked on the plugin class.
The Request constructor takes an object of properties that define the event.
For example, the following could be defined in `info.js`:

```js
messages: {
    reportFrobnication: new libLink.Request({
        type: "foo_frobber:report_frobnication",
        links: ["controller-host", "host-instance"],
        forwardTo: "instance",
        requestRequired: ["verbosity"],
        requestProperties: {
            "verbosity": { type: "integer" },
            "special": { type: "boolean" },
        },
        responseProperties: {
            "report": {
                type: "array",
                items: { type: "string" },
            },
        },
    }),
},
```

This specifies a request that can be sent from the controller to a host, and from a host to an instance.
The request data must contain the property `verbosity` with an integer number as the value, as well as the `instance_id` property (implied by `forwardTo: "instance"`) and it may also contain a boolean `special` property.
It also defines that the response sent must contain a `report` property mapping to an array of strings.
When received by a host, it will also be forwarded to the instance specified by `instance_id`.

The following properties are recognized by the Request constructor:

#### type

The message type sent over the wire.
This must start with the name of the plugin followed by colon and and be unique for the plugin.
The type of the message sent over the socket will have the suffix `_request` appended to it for the request and `_response` appended to it for the response.

#### links

An array of strings describing which links this request can be sent over.
Direction matters; `"controller-host"` means the request can be sent from the controller to the host and the host can reply to the controller, but the host can't send a request to the controller unless `"host-controller"` is also present in the links array.

The available endpoints are `controller`, `host`, `instance`, and `control`.
Controller talks with host and control, and host talks to instance.
The full chain must be specified as the individual links in order for a message to travers multiple hops, (i.e., for a message to go from controller to instance it must have both `"controller-host"` and `"host-instance"` in the links array).
See `forwardTo` for ways to forward a request to the next link in a chain.

#### forwardTo

Target to forward the request to.
Can either be `"controller"` to indicate a host should forward it to the controller when receiving it from an instance, or `"instance"` to indicate it should be forwarded to the instances specified by the `instance_id` request property.
This works by using a default handler for the request by the links that forward it.

#### requestRequired

By default all properties defined in `requestProperties` are required to be present in the payload for the request.
This can be overriden by specifying an array of properties which are required here.
This is equivalent to using the `required` keyword in JSON schema.

#### requestProperties

Object with properties mapping to a JSON schema of that property that specifies what's valid to send in the request.
This is equivalent to using the `properties` keyword in JSON schema, except that the properties specified are by default required and additional properties are not allowed.
See [this guide][guide] for an introduction to writing JSON schemas

#### responseRequired

Same as the requestRequired only for the response sent back by the target.

#### responseProperties

Same as the requestProperties only for the response sent back by the target.


## Sending Link Messages

Link messages are sent by calling the `.send()` method on the Event/Request instance with the link you want to send it over and the data to send.
For `InstancePlugin` code the link to the host is the `instance` itself, which is accessible through the `.instance` property of the `InstancePlugin`.
The `.info` property of the plugin class exposes the data exported from the plugin's `info.js` module.
In other words:

```js
// In an InstancePlugin class
async frobnicate() {
    this.info.messages.exampleEvent.send(this.instance, { foo: "bar" });
}
```

For the Request class the send method is async and returns the response data received from the target it was sent to, or throws an error if the request failed.


### Handling connection events

There are a few connection related events that plugins neeed to repsond to in order to avoid data loss and connection problems.
The most important is the prepare disconnect for the link between controller and host.
This is signaled to `ControllerPlugin` classes via the `onPrepareHostDisconnect` hook and to `InstancePlugin` classes via the `onPrepareControllerDisconnect` hook.

After the prepare disconnect the connection will be closed, which will result in pending requests and events being dropped.
Plugins must respond to the prepare disconnect by stopping any processess it does that send events or requests over the link in question.
This can be accomplished either through listening for the prepare disconnect hook, or by checking the `connected` property of the `HostConnection` class and `Host` class on the controller and host respectively.
For example the sending of an event from an `InstancePlugin` class can be stopped while the connection is not connected, not in the dropped state, and not in the process of discunnecting by using the following code:

```js
if (this.host.connected) {
    this.info.messages.frobnicate.send(this.instance, { foo: "bar" });
}
```

If the event or request needs to be sent to the controller it can be put into a queue stored on the plugin instance and sent out when the connection is established again.
The re-establishement of the connection is  notified to plugins via the `connect` event to the `onControllerConnectionEvent` and `onHostConnectionEvent` hooks.

The second connection event which is of lesser importance to respond to is the `drop` connection event served through `onControllerConnectionEvent` for `InstancePlugin` classes and through `onHostConnectionEvent` for `ControllerPlugin` classes.
This is raised when the connection between the controller and host in question is lost, most likely due to networking issues.
When in the dropped state the host will keep trying to reconnect to the controller in order to re-establish it, and if successful no events or requests will be lost.
However while in the dropped state any requests and events sent gets queued up in memory until the connection is either re-established or the session times out.
This means that if your plugin sends a lot of events or requests, they can end up being queued up in a buffer and sent out all at once the connection is re-estabished.
To avoid this you should be throtteling and/or stopping your requests/events after `drop` has been raised, and continue back as normal when `resume` is raised.


## Collecting Statistics

Clusterio comes with its own Prometheus client implementation, one part due to Not Invented Here and another part due to collectors in prom-client being difficult to get to work nicely with collecting data from plugins optionally loaded at runtime on different computers.

In its simplest form collecting data from plugins consists of defining the metric and updating it somewhere in the plugin code.
For example:

```js
const { Counter } = require("@clusterio/lib/prometheus");

const fooMetric = new Counter(
    "clusterio_foo_frobber_foo_metric", "Measures the level of foo",
);

// Somewhere in the controller plugin code
fooMetric.inc();
```

This works for controller plugins, and the metric will be automatically available through the /metric HTTP endpoint.
It's recommended that plugin metrics follow `clusterio_<plugin_name>_<metric_name>` as the naming scheme.

For metrics that are per-instance, you must define an `instance_id` label and set it accordingly, for example:

```js
const { Counter } = require("@clusterio/lib/prometheus");

const barMetric = new Gauge(
    "clusterio_foo_frobber_bar_metric", "Bar instance level",
    { labels: ["instance_id"] }
);

// Somewhere in the instance plugin code
barMetric.labels(String(this.instance.id)).set(someValue);
```

Metrics are automatically registered to the default registry, and this default registry is automatically polled by the controller on hosts.
This means that it's important that you place the definition of the metric at module level so that it's not created more than once over the lifetime of a host.
Since the metrics remember their values and would continue to be exported after an instance is shutdown, there's code at instance shutdown that removes all the values where the `instance_id` label matches the id of the instance shut down.

For statistics you need to update on collection there's an `onMetrics` hook on both controller and instance plugins that is run before the metrics in the default registry are collected.


## Adding Custom Commands to clusterioctl

The control entrypoint for plugins allows you to extend clustectl with your own commands.
The creation of custom commands typically starts with defining a command tree for the plugin:

```js
const { Command, CommandTree } = require("@clusterio/lib/command");
const fooFrobberCommands = new CommandTree({
    name: "foo-frobber", description: "Foo Frobber Plugin commands"
});
```

Then commands are added to the the plugin's command tree:

```js
const info = require("./info");

fooFrobberCommands.add(new Command({
    definition: ["frobnicate <type>", "Do frobnications", (yargs) => {
        yargs.positional("level", {
            describe: "type of frobnication", type: "string"
        });
    }],
    handler: async function(args, control) {
        await info.messages.frobnicate.send(control, {
            instance_name: "Console",
            content: args.message,
        });
    },
}));
```

For a command the `definition` is the arguments to pass to [yargs.command](http://yargs.js.org/docs/#api-reference-commandcmd-desc-builder-handler) (see also [yargs.positional](http://yargs.js.org/docs/#api-reference-positionalkey-opt) and [yargs.options](http://yargs.js.org/docs/#api-reference-optionskey-opt) for setting up positional and optional arguments to commands).
The `handler` is an async function that's invoked when the command is executed and it's passed the parsed command line arguments and a reference to the `Control` class of clusterioctl.
It's possible to optain a reference to the plugin class with `control.plugins.get(info.name)`.

Note that messages sent from clusterioctl needs to have `"control-controller"` as a part of the links array for it to be accepted by the controller, see [Defining Link Messages](#defining-link-messages) for how to define the messages that can be sent to the controller.

To have the command tree become part of clusterioctl it needs to be added to the rootCommand tree in `addCommands` callback of the Control plugin:

```js
const libPlugin = require("@clusterio/lib/plugin");

class ControlPlugin extends libPlugin.BaseControlPlugin {
    async addCommands(rootCommand) {
        rootCommand.add(fooFrobberCommands);
    }
}

module.exports = {
    ControlPlugin,
}
```