Crate composure 

Composure is a framework for Discord bots that only answer Interactions over HTTP: no gateway connection, so a bot runs on the edge (Cloudflare Workers, compiled to WASM) or on any hosted server (tokio), and scales to zero between requests.

use composure::{app, command};

/// Repeat some text
#[command]
fn echo(
    #[option("What to say", max_len = 200)] text: &str,
    #[option("How many times", min = 1, max = 5)] times: Option<u8>,
) -> String {
    text.repeat(times.unwrap_or(1).into())
}

/// Everything the bot serves
#[app(handlers(echo))]
pub struct Bot;

Each Command is written once, as a function: its parameters become the Command’s Options, its doc comment the description, its return value the answer. Bot is then handed to an Adapter to serve Interactions, and to composure_sync at deploy time to register the Commands with Discord.

Where to start

The guide walks through everything a bot does, chapter by chapter:

Chapter
Getting started	Crates, features, a first bot, serving it, syncing it
Commands	#[command], Options, Choices, Groups, context menus, autocomplete, Scopes
Responses	What a handler can return; ephemeral messages, embeds, files, errors
Components and modals	Buttons, selects and forms with #[component], #[modal], #[derive(Modal)]
Views	rsx! markup and #[view]: every tag and attribute
Themes	Consistent colors and branding on embeds and containers
REST and deferring	ctx.bot(), follow-ups, Deferred Responses, Background Work
Webhook Events	App installs, entitlements, lobby messages
Platforms	Adapters, State, platform-specific Commands, logging
Testing	Running handlers without Discord

Crates

Crate
composure (this one)	Types, request validation, the handler runtime, the REST client, and (with macros) the attribute macros
composure_adapter_cloudflare	Serves a bot on Cloudflare Workers
composure_adapter_tokio	Serves a bot from a hosted server on tokio
composure_sync	Registers an App’s Commands with Discord at deploy time
composure_macros	The macros; use them through composure’s macros feature
composure_commands	A builder for Command Definitions, for bots not using #[command]

Modules

• command: the handler runtime: Ctx, responses (Ephemeral, Update, …), Theme, View, errors, and the traits the macros implement
• types: Discord’s objects (Interactions, messages, embeds, components, users, …), shared by Interactions, responses and REST
• definition: Command Definitions, as Discord stores them
• rest: the REST client over an Adapter’s Transport
• adapter: the request pipeline every Adapter shares (validate, parse, dispatch)
• auth: Ed25519 request signature validation
• credentials: Credentials, what identifies the application, however the bot loads them

Feature flags

No feature is on by default: the core stays small for WASM bundles.

Feature
macros	#[app], #[command], #[group], #[component], #[modal], #[autocomplete], #[view], rsx!, #[derive(Choice)], #[derive(Modal)]
rest	The REST client (rest) with the Interaction Endpoints, Platform, ctx.defer(..), and the adapter pipeline
rest-commands, rest-messages, rest-users, rest-channels, rest-guilds, rest-members, rest-roles	One group of Endpoints each on BotClient
rest-bans, rest-threads, rest-invites, rest-emojis, rest-stickers, rest-scheduled-events, rest-automod, rest-audit-log, rest-webhooks, rest-monetization, rest-polls, rest-soundboard, rest-application	The rest of Discord’s Endpoints, one group each
tier1	rest and the Endpoints most bots need (commands, messages, users, channels, guilds, members, roles)
full	Every Endpoint
tracing	Spans and events through tracing; see Platforms
web-crypto	Validate signatures with the host’s Web Crypto on wasm32-unknown-unknown instead of compiling ed25519-dalek in
reqwest	A blocking ReqwestTransport for deploy-time tools (not for WASM)

Re-exports

pub use command::Ctx;

pub use credentials::Credentials;

pub use credentials::CredentialsError;

Modules

adapterrest

What every Adapter does with a request, whatever the platform: verify the signature, parse, dispatch to the InteractionHandler (or hand a Webhook Event to the EventHandler as Background Work), and send responses with files through the callback endpoint. Adapters map the outcomes to their platform’s HTTP response, so every Adapter answers alike.

auth

Verifying that requests come from Discord: every Interaction and Webhook Event is signed with Ed25519 over timestamp || body, checked against the application’s public key. Adapters do this for you (adapter::verify, with the rest feature); use PublicKey directly when writing one.

command

Commands defined once with #[command], from which both their handler and their Command Definition derive, collected with the handlers for components, modals and Views into an App with #[app].

credentials

What identifies and authorizes the Discord application (ADR 0014). Composure never loads configuration itself: an Adapter (or the bot) builds Credentials from wherever it keeps them, by the conventional names with Credentials::from_lookup, or through serde with any loader (config, figment, envy, …).

definition

Application command definitions: what Discord stores for each command. Used when syncing commands, not when handling interactions.

restrest

Async Discord REST client over an Adapter-provided Transport (ADR 0004, 0005).

types

Discord’s data model, shared by Interactions, Responses and REST. Organized by resource; everything is re-exported flat as composure::types::X.

Macros

rsxmacros

Markup for message and modal layouts. Every tag and attribute is listed in Views. Markup for a message or modal layout, as JSX: built-in tags are Discord’s components (<Container>, <Section>, <Text>, <Thumbnail>, <Gallery>/<Item>, <File>, <Separator>, <Row>, <Button>, <StringSelect>/<Option>, <UserSelect>, …; in a <Modal>: <Label>, <TextInput>, <RadioGroup>, <CheckboxGroup>, <Checkbox>, <FileUpload>), PascalCase tags are #[view]s. Evaluates to a View, or a ModalView for a <Modal> root.

Traits

Mentionable

Something Discord renders as a mention in message content: <@id> for users, <#id> for channels, <@&id> for roles.

Attribute Macros

appmacros

Collects Routes into an App, the handler an Adapter serves. See Getting started and Platforms. Makes a unit struct an App: the Interaction Handler routing to the Commands, Groups, Component and Modal Handlers, Views and other Apps listed in handlers(..), in any mix and order.

autocompletemacros

Suggests values for an Option while the user types. See Commands. Defines an Autocomplete Handler from a function taking an optional leading ctx: Ctx and what the user has typed so far as input: &str. Attach it to a string, integer, or number Option with #[option("...", autocomplete = name)].

commandmacros

Defines a Command from a function. See Commands. Defines a Command from a function. Parameters after an optional leading ctx: Ctx become Options; the doc comment becomes the description.

componentmacros

Answers a component by custom_id prefix. See Components and modals. Defines a Component Handler from a function: it answers components whose custom_id starts with the prefix. Parameters after an optional leading ctx: ComponentCtx are state carried in the custom_id (owned, serde-serializable), built with the generated name::custom_id(..).

groupmacros

Groups Commands as subcommands. See Commands. Makes a unit struct a Group that routes to its subcommands. Groups can contain Groups one level deep.

modalmacros

Answers a modal submit by custom_id prefix. See Components and modals. Defines a Modal Handler from a function: it answers submits of modals whose custom_id starts with the prefix. After an optional leading ctx: ModalCtx comes the form (a #[derive(Modal)] type), then state carried in the custom_id. name::show(..) is the modal response that opens the form.

viewmacros

A layout rendered from Props, with inline handlers. See Views. Defines a View: a layout rendered from its Props (the parameters, owned values), whose rsx!s may hold inline handlers.

Derive Macros

Choicemacros

An enum of fixed Choices, for Options, selects and radio groups. See Commands. Makes a fieldless enum (1-25 variants) usable as an Option restricted to its variants, and as the options of selects, radio groups and checkbox groups.

Modalmacros

A form shown as a modal. See Components and modals. A form shown as a modal: each named field is one input inside a Label.