Version: v1.3.14 Latest Latest

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Published: Nov 2, 2020 License: ISC Imports: 14 Imported by: 4


What are the performance impacts of this library?

Not a lot for a Discord bot:


# Cold functions, or functions that are called once in runtime:
BenchmarkConstructor-8               	  150537	      7617 ns/op
BenchmarkSubcommandConstructor-8     	  155068	      7721 ns/op

# Hot functions, or functions that can be called multiple times:
BenchmarkCall-8                      	 1000000	      1194 ns/op
BenchmarkHelp-8                      	 1751619	       680 ns/op

# Hot functions, but called implicitly on non-message-create events:
BenchmarkReflectChannelID_1Level-8   	10111023	       113 ns/op
BenchmarkReflectChannelID_5Level-8   	 1872080	       686 ns/op




This section is empty.


View Source
var (
	ErrTooManyArgs   = errors.New("too many arguments given")
	ErrNotEnoughArgs = errors.New("not enough arguments given")
View Source
var Break = errors.New("break middleware chain, non-fatal")

Break is a non-fatal error that could be returned from middlewares to stop the chain of execution.

View Source
var HelpUnderline = true

HelpUnderline formats command arguments with an underline, similar to manpages.

View Source
var InvalidUsageString = func(err *ErrInvalidUsage) string {
	if err.Index == 0 && err.Wrap != nil {
		return "invalid usage, error: " + err.Wrap.Error() + "."

	if err.Index == 0 || len(err.Args) == 0 {
		return "missing arguments. Refer to help."

	body := "Invalid usage at " +

		err.Prefix +

		strings.Join(err.Args[:err.Index], " ") +

		" __" + err.Args[err.Index] + "__ " +

		strings.Join(err.Args[err.Index+1:], " ")

	if err.Wrap != nil {
		body += "\nError: " + err.Wrap.Error() + "."

	return body
View Source
var ShellwordsEscaper = strings.NewReplacer(
	"\\", "\\\\",
View Source
var UnknownCommandString = func(err *ErrUnknownCommand) string {
	return "unknown command: " + strings.Join(err.Parts, " ")


func IndentLines added in v0.8.0

func IndentLines(input string) string

IndentLine prefixes every line from input with a single-level indentation.

func Start

func Start(
	token string, cmd interface{},
	opts func(*Context) error) (wait func() error, err error)

Start quickly starts a bot with the given command. It will prepend "Bot" into the token automatically. Refer to example/ for usage.

func Wait

func Wait()

Wait blocks until SIGINT.


type ArgsParser added in v0.6.2

type ArgsParser func(content string) ([]string, error)

ArgsParser is the function type for parsing message content into fields, usually delimited by spaces.

func DefaultArgsParser added in v0.6.2

func DefaultArgsParser() ArgsParser

DefaultArgsParser implements a parser similar to that of shell's, implementing quotes as well as escapes.

type Argument added in v0.0.10

type Argument struct {
	String string
	// contains filtered or unexported fields

Argument is each argument in a method.

func (*Argument) Type added in v0.0.10

func (a *Argument) Type() reflect.Type

type ArgumentParts added in v0.6.0

type ArgumentParts []string

ArgumentParts implements ManualParser, in case you want to parse arguments manually. It borrows the library's argument parser.

func (ArgumentParts) After added in v0.6.0

func (r ArgumentParts) After(n int) string

func (ArgumentParts) Arg added in v0.6.0

func (r ArgumentParts) Arg(n int) string

func (ArgumentParts) Length added in v0.6.0

func (r ArgumentParts) Length() int

func (*ArgumentParts) ParseContent added in v0.6.0

func (r *ArgumentParts) ParseContent(args []string) error

ParseContent implements ManualParser.

func (ArgumentParts) String added in v0.6.0

func (r ArgumentParts) String() string

func (ArgumentParts) Usage added in v0.8.0

func (r ArgumentParts) Usage() string

Usage implements Usager.

type CanHelp added in v0.8.0

type CanHelp interface {
	Help() string

CanHelp is an interface that subcommands can implement to return its own help message. Those messages will automatically be indented into suitable sections by the default Help() implementation. Unlike Usager or CanSetup, the Help() method will be called every time it's needed.

type CanSetup added in v0.0.10

type CanSetup interface {
	// Setup should panic when it has an error.

CanSetup is used for subcommands to change variables, such as Description. This method will be triggered when InitCommands is called, which is during New for Context and during RegisterSubcommand for subcommands.

type Context

type Context struct {

	// Descriptive (but optional) bot name
	Name string

	// Descriptive help body
	Description string

	// Called to parse message content, default to DefaultArgsParser().
	ParseArgs ArgsParser

	// Called to check a message's prefix. The default prefix is "!". Refer to
	// NewPrefix().
	HasPrefix Prefixer

	// AllowBot makes the router also process MessageCreate events from bots.
	// This is false by default and only applies to MessageCreate.
	AllowBot bool

	// QuietUnknownCommand, if true, will not make the bot reply with an unknown
	// command error into the chat. This will apply to all other subcommands.
	// SilentUnknown controls whether or not an ErrUnknownCommand should be
	// returned (instead of a silent error).
	SilentUnknown struct {
		// Command when true will silent only unknown commands. Known
		// subcommands with unknown commands will still error out.
		Command bool
		// Subcommand when true will suppress unknown subcommands.
		Subcommand bool

	// FormatError formats any errors returned by anything, including the method
	// commands or the reflect functions. This also includes invalid usage
	// errors or unknown command errors. Returning an empty string means
	// ignoring the error.
	// By default, this field replaces all @ with @\u200b, which prevents an
	// @everyone mention.
	FormatError func(error) string

	// ErrorLogger logs any error that anything makes and the library can't
	// reply to the client. This includes any event callback errors that aren't
	// Message Create.
	ErrorLogger func(error)

	// ReplyError when true replies to the user the error. This only applies to
	// MessageCreate events.
	ReplyError bool

	// EditableCommands when true will also listen for MessageUpdateEvent and
	// treat them as newly created messages. This is convenient if you want
	// to quickly edit a message and re-execute the command.
	EditableCommands bool
	// contains filtered or unexported fields

Context is the bot state for commands and subcommands.


A command can be created by making it a method of Commands, or whatever struct was given to the constructor. This following example creates a command with a single integer argument (which can be ran with "~example 123"):

func (c *Commands) Example(
    m *gateway.MessageCreateEvent, i int) (string, error) {

    return fmt.Sprintf("You sent: %d", i)

Commands' exported methods will all be used as commands. Messages are parsed with its first argument (the command) mapped accordingly to c.MapName, which capitalizes the first letter automatically to reflect the exported method name.

A command can either return either an error, or data and error. The only data types allowed are string, *discord.Embed, and *api.SendMessageData. Any other return types will invalidate the method.


An event can only have one argument, which is the pointer to the event struct. It can also only return error.

func (c *Commands) Example(o *gateway.TypingStartEvent) error {
    log.Println("Someone's typing!")
    return nil

func New

func New(s *state.State, cmd interface{}) (*Context, error)

New makes a new context with a "~" as the prefix. cmds must be a pointer to a struct with a *Context field. Example:

type Commands struct {
    Ctx *Context

cmds := &Commands{}
c, err := bot.New(session, cmds)

The default prefix is "~", which means commands must start with "~" followed by the command name in the first argument, else it will be ignored.

c.Start() should be called afterwards to actually handle incoming events.

func (*Context) AddIntent added in v0.10.0

func (ctx *Context) AddIntent(i gateway.Intents)

AddIntent adds the given Gateway Intent into the Gateway. This is a convenient function that calls Gateway's AddIntent.

func (*Context) Call

func (ctx *Context) Call(event interface{}) error

Call should only be used if you know what you're doing.

func (*Context) FindCommand added in v0.0.10

func (ctx *Context) FindCommand(structName, methodName string) *MethodContext

FindMethod finds a method based on the struct and method name. The queried names will have their flags stripped.

// Find a command from the main context:
cmd := ctx.FindMethod("", "Method")
// Find a command from a subcommand:
cmd  = ctx.FindMethod("Starboard", "Reset")

func (*Context) Help

func (ctx *Context) Help() string

Help generates a full Help message. It serves mainly as a reference for people to reimplement and change. It doesn't show hidden commands.

func (*Context) HelpGenerate added in v0.10.4

func (ctx *Context) HelpGenerate(showHidden bool) string

HelpGenerate generates a full Help message. It serves mainly as a reference for people to reimplement and change. If showHidden is true, then hidden subcommands and commands will be shown.

func (*Context) MustRegisterSubcommand added in v0.0.9

func (ctx *Context) MustRegisterSubcommand(cmd interface{}) *Subcommand

MustRegisterSubcommand tries to register a subcommand, and will panic if it fails. This is recommended, as subcommands won't change after initializing once in runtime, thus fairly harmless after development.

func (*Context) MustRegisterSubcommandCustom added in v0.8.0

func (ctx *Context) MustRegisterSubcommandCustom(cmd interface{}, name string) *Subcommand

MustRegisterSubcommandCustom works similarly to MustRegisterSubcommand, but takes an extra argument for a command name override.

func (*Context) RegisterSubcommand

func (ctx *Context) RegisterSubcommand(cmd interface{}) (*Subcommand, error)

RegisterSubcommand registers and adds cmd to the list of subcommands. It will also return the resulting Subcommand.

func (*Context) RegisterSubcommandCustom added in v0.8.0

func (ctx *Context) RegisterSubcommandCustom(cmd interface{}, name string) (*Subcommand, error)

RegisterSubcommand registers and adds cmd to the list of subcommands with a custom command name (optional).

func (*Context) Start

func (ctx *Context) Start() func()

Start adds itself into the session handlers. This needs to be run. The returned function is a delete function, which removes itself from the Session handlers.

func (*Context) Subcommands

func (ctx *Context) Subcommands() []*Subcommand

Subcommands returns the slice of subcommands. To add subcommands, use RegisterSubcommand().

type CustomParser added in v0.0.12

type CustomParser interface {
	CustomParse(arguments string) error

CustomParser has a CustomParse method, which would be passed in the full message content with the prefix and command trimmed. This is used for commands that require more advanced parsing than the default parser.

Keep in mind that this does not trim arguments before it.

type ErrInvalidUsage

type ErrInvalidUsage struct {
	Prefix string
	Args   []string
	Index  int
	Wrap   error

	// TODO: usage generator?
	// Here, as a reminder
	Ctx *MethodContext

func (*ErrInvalidUsage) Error

func (err *ErrInvalidUsage) Error() string

func (*ErrInvalidUsage) Unwrap added in v0.6.0

func (err *ErrInvalidUsage) Unwrap() error

type ErrUnknownCommand

type ErrUnknownCommand struct {
	Parts  []string // max len 2
	Subcmd *Subcommand

func (*ErrUnknownCommand) Error

func (err *ErrUnknownCommand) Error() string

type ManualParser added in v0.0.12

type ManualParser interface {
	// $0 will have its prefix trimmed.
	ParseContent([]string) error

ManualParser has a ParseContent(string) method. If the library sees this for an argument, it will send all of the arguments into the method. If used, this should be the only argument followed after the Message Create event. Any more and the router will ignore.

type MethodContext added in v0.8.0

type MethodContext struct {
	Description string

	// MethodName is the name of the method. This field should NOT be changed.
	MethodName string

	// Command is the Discord command used to call the method.
	Command string // plumb if empty

	// Aliases is alternative way to call command in Discord.
	Aliases []string

	// Hidden if true will not be shown by (*Subcommand).HelpGenerate().
	Hidden bool

	// Variadic is true if the function is a variadic one or if the last
	// argument accepts multiple strings.
	Variadic bool

	Arguments []Argument
	// contains filtered or unexported fields

MethodContext is an internal struct containing fields to make this library work. As such, they're all unexported. Description, however, is exported for editing, and may be used to generate more informative help messages.

func (*MethodContext) SetName added in v0.8.0

func (cctx *MethodContext) SetName(name string)

SetName sets the command name.

func (*MethodContext) Usage added in v0.8.0

func (cctx *MethodContext) Usage() []string

type MiddlewareContext added in v0.8.0

type MiddlewareContext struct {
	// contains filtered or unexported fields

func ParseMiddleware added in v0.8.0

func ParseMiddleware(mw interface{}) *MiddlewareContext

ParseMiddleware parses a middleware function. This function panics.

type Parser added in v0.0.12

type Parser interface {
	Parse(string) error

Parser implements a Parse(string) method for data structures that can be used as arguments.

type Prefixer added in v0.2.0

type Prefixer func(*gateway.MessageCreateEvent) (prefix string, ok bool)

Prefixer checks a message if it starts with the desired prefix. By default, NewPrefix() is used.

func NewPrefix added in v0.2.0

func NewPrefix(prefixes ...string) Prefixer

NewPrefix creates a simple prefix checker using strings. As the default prefix is "!", the function is called as NewPrefix("!").

type RawArguments

type RawArguments string

RawArguments implements the CustomParser interface, which sets all the arguments into it as raw as it could.

func (*RawArguments) CustomParse added in v0.6.0

func (a *RawArguments) CustomParse(arguments string) error

type Subcommand

type Subcommand struct {
	// Description is a string that's appended after the subcommand name in
	// (*Context).Help().
	Description string

	// Hidden if true will not be shown by (*Context).Help(). It will
	// also cause unknown command errors to be suppressed.
	Hidden bool

	// Raw struct name, including the flag (only filled for actual subcommands,
	// will be empty for Context):
	StructName string
	// Parsed command name:
	Command string

	// SanitizeMessage is executed on the message content if the method returns
	// a string content or a SendMessageData.
	SanitizeMessage func(content string) string

	// All registered method contexts:
	Events   []*MethodContext
	Commands []*MethodContext
	// contains filtered or unexported fields

Subcommand is any form of command, which could be a top-level command or a subcommand.

Allowed method signatures

These are the acceptable function signatures that would be parsed as commands or events. A return type <T> implies that return value will be ignored.

func(*gateway.MessageCreateEvent, ...) (string, error)
func(*gateway.MessageCreateEvent, ...) (*discord.Embed, error)
func(*gateway.MessageCreateEvent, ...) (*api.SendMessageData, error)
func(*gateway.MessageCreateEvent, ...) (T, error)
func(*gateway.MessageCreateEvent, ...) error
func(*gateway.MessageCreateEvent, ...)
func(<AnyEvent>) (T, error)
func(<AnyEvent>) error

func NewSubcommand

func NewSubcommand(cmd interface{}) (*Subcommand, error)

NewSubcommand is used to make a new subcommand. You usually wouldn't call this function, but instead use (*Context).RegisterSubcommand().

func (*Subcommand) AddAliases added in v0.9.3

func (sub *Subcommand) AddAliases(commandName string, aliases ...string)

AddAliases add alias(es) to specific command (defined with commandName).

func (*Subcommand) AddMiddleware added in v0.8.0

func (sub *Subcommand) AddMiddleware(methodName string, middleware interface{})

AddMiddleware adds a middleware into multiple or all methods, including commands and events. Multiple method names can be comma-delimited. For all methods, use a star (*). The given middleware argument can either be a function with one of the allowed methods or a *MiddlewareContext.

Allowed function signatures

Below are the acceptable function signatures that would be parsed as a proper middleware. A return value of type T will be ignored. If the given function is invalid, then this method will panic.

func(<AnyEvent>) (T, error)
func(<AnyEvent>) error

Note that although technically all of the above function signatures are acceptable, one should almost always return only an error.

func (*Subcommand) ChangeCommandInfo added in v0.0.10

func (sub *Subcommand) ChangeCommandInfo(methodName, cmd, desc string)

ChangeCommandInfo changes the matched methodName's Command and Description. Empty means unchanged. This function panics if methodName is not found.

func (*Subcommand) FindCommand added in v0.3.0

func (sub *Subcommand) FindCommand(methodName string) *MethodContext

FindCommand finds the MethodContext. It panics if methodName is not found.

func (*Subcommand) Help added in v0.0.11

func (sub *Subcommand) Help() string

Help calls the subcommand's Help() or auto-generates one with HelpGenerate() if the subcommand doesn't implement CanHelp. It doesn't show hidden commands by default.

func (*Subcommand) HelpGenerate added in v0.8.0

func (sub *Subcommand) HelpGenerate(showHidden bool) string

HelpGenerate auto-generates a help message. Use this only if you want to override the Subcommand's help, else use Help(). This function will show hidden commands if showHidden is true.

func (*Subcommand) HelpShowHidden added in v0.10.4

func (sub *Subcommand) HelpShowHidden(showHidden bool) string

HelpShowHidden does the same as Help(), except it will render hidden commands if the subcommand doesn't implement CanHelp and showHiddeen is true.

func (*Subcommand) Hide added in v0.8.0

func (sub *Subcommand) Hide(methodName string)

Hide marks a command as hidden, meaning it won't be shown in help and its UnknownCommand errors will be suppressed.

func (*Subcommand) InitCommands

func (sub *Subcommand) InitCommands(ctx *Context) error

InitCommands fills a Subcommand with a context. This shouldn't be called at all, rather you should use the RegisterSubcommand method of a Context.

func (*Subcommand) NeedsName

func (sub *Subcommand) NeedsName()

NeedsName sets the name for this subcommand. Like InitCommands, this shouldn't be called at all, rather you should use RegisterSubcommand.

func (*Subcommand) SetPlumb added in v0.8.0

func (sub *Subcommand) SetPlumb(methodName string)

SetPlumb sets the method as the plumbed command.

type Usager

type Usager interface {
	Usage() string

Usager is used in place of the automatically parsed struct name for Parser and other interfaces.


Path Synopsis
Package infer implements reflect functions that package bot uses.
Package infer implements reflect functions that package bot uses.

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