brigodier

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Brigodier is a command parser & dispatcher, designed and developed to provide a simple and flexible command framework.

It can be used in many command-line environments such as for chat commands in the Minecraft Java Edition.

It is completely ported to Go from Mojang’s Brigadier (written in Java), including all features and tests.

Installation

For use in your projects go get it with:

go get -u go.minekube.com/brigodier

Usage

At the heart of Brigodier, you need a Dispatcher.

A command dispatcher holds a “command tree”, which is a series of CommandNodes that represent the various possible syntax options that form a valid command.

Registering a new command

Before we can start parsing and dispatching commands, we need to build up our command tree. Every registration is an append operation, so you can freely extend existing commands in a project without needing access to the source code that created them.

Command registration also encourages the use of a builder pattern to keep code cruft to a minimum.

A “command” is a fairly loose term, but typically it means an exit point of the command tree. Every node can have an Executes function attached to it, which signifies that if the input stops here then this function will be called with the context so far.

Consider the following example:

var d Dispatcher

d.Register(
	Literal("foo").Then(
		Argument("bar", Int).
			Executes(CommandFunc(func(c *CommandContext) error {
				fmt.Println("Bar is", c.Int("bar"))
				return nil
			})),
	).Executes(CommandFunc(func(c *CommandContext) error {
		fmt.Println("Called foo with no arguments")
		return nil
	})),
)

This snippet registers two “commands”: foo and foo <bar>. It is also common to refer to the <bar> as a “subcommand” of foo, as it’s a child node.

At the start of the tree is a “root node”, and it must have LiteralCommandNodes as children. Here, we register one command under the root: Literal("foo"), which means “the user must type the literal string ‘foo'”.

Under that is two extra definitions: a child node for possible further evaluation, or an executes block if the user input stops here.

The child node works exactly the same way, but is no longer limited to literals. The other type of node that is now allowed is an ArgumentCommandNode, which takes in a name, and an argument type.

Arguments can be anything, and you are encouraged to build your own for seamless integration into your own product. There are some builtin ArgumentTypes included, such as Int or String.

Argument types will be asked to parse input as much as they can, and then store the “result” of that argument however they see fit or throw a relevant error if they can’t parse.

For example, an integer argument would parse “123” and store it as 123 (int), but throw an error if the input were onetwothree.

When a command function runs, it can access these arguments in the context provided to the registered function.

Parsing user input

So, we’ve registered some commands, and now we’re ready to take in user input. If you’re in a rush, you can just call dispatcher.Execute(ctx, "foo 123") and call it a day.

Go’s context.Context can be used to track users/players/etc and will be provided to the command to give context on what’s happening (e.g., who has run the command).

If the command failed or could not parse, some form of CommandSyntaxError will be returned, or the error that the Command returned.

If you wish to have more control over the parsing & executing of commands, or wish to cache the parse results, so you can execute it multiple times, you can split it up into two steps:

parse := dispatcher.Parse(ctx, "foo 123")
err := dispatcher.Execute(parse)

This is highly recommended as the parse step is the most expensive, and may be easily cached depending on your application.

You can also use this to do further introspection on a command, before (or without) actually running it.

The convenient method to parse and execute a command is:

err := dispatcher.Do(ctx, "foo 123")

Inspecting a command

If you Parse some input, you can find out what it will perform (if anything) and provide hints to the user safely and immediately.

The parse will never fail, and the ParseResults it returns will contain a possible context that a command may be called with (and from that, you can inspect which nodes the user entered, complete with start/end positions in the input string). It also contains a map of parse exceptions for each command node it encountered. If it couldn’t build a valid context, then the reason is inside this exception map.

Displaying usage info

There are two forms of “usage strings” provided by this library, both require a target node.

  • dispatcher.AllUsage(ctx, node, restricted) will return a list of all possible commands (executable end-points) under the target node and their human-readable path. If restricted, it will ignore commands that ctx does not have access to. This will look like [foo, foo <bar>].

  • dispatcher.SmartUsage(ctx, node) will return a map of the child nodes to their “smart usage” human-readable path. This tries to squash future-nodes together and show optional & typed information, and can look like foo (<bar>).

GitHub

https://github.com/minekube/brigodier