#Request pipeline

Boot gives HTTP, WebSocket, and message transports consistent execution concepts while preserving protocol-specific contexts and reply types.

#HTTP execution order

request
  |
middleware
  |
guards
  |
interceptors before
  |
pipes
  |
validation
  |
handler
  |
interceptors after
  |
response

unrecovered error -> exception filters

Components of the same category are composed from application, module, controller, and route topology. Explicit order is part of the API contract. A component should not rely on an undeclared global side effect.

#Responsibility by stage

#Register global components

let app = BootApplication::builder()
    .import(AppModule)
    .use_global_middleware(RequestIdMiddleware)
    .use_global_guard(AuthGuard::new())
    .use_global_interceptor(TracingInterceptor)
    .use_global_pipe(NormalizeInputPipe)
    .use_global_validation()
    .use_global_filter(ApiErrorFilter)
    .build()?;

Controllers and routes add local components through #[use_guard], #[use_interceptor], #[use_pipe], and #[use_filter]. #[apply_decorators(...)] composes a reusable group of attributes.

Declare application-wide enhancers as HTTP, WebSocket, or transport enhancer providers when they must be resolved from the DI container. Provider-backed enhancers support scope bubbling and resolve in the invocation context. Values passed directly to the builder do not receive module injection.

#Around interceptors

An Interceptor receives a CallHandler, so it can:

• Run work before and after downstream execution
• Short circuit without calling next
• Transform a successful response
• Recover a selected failure
• Call next.handle() more than once for a sequential retry or timeout wrapper

Retries have at-least-once semantics. Provider state, logs, database writes, and external side effects do not roll back automatically. Retry only explicitly replayable work and use idempotency keys for side effects.

Filters only receive failures an interceptor did not recover. A local filter is closer to the handler than a global filter. Use catch_errors(...) or #[catch] to restrict handling by BootErrorKind.

#Protocol-neutral and protocol-specific components

ExecutionContext exposes a protocol kind and shared metadata for guards or interceptors that genuinely span HTTP, WebSocket, and transports. Protocol-specific components use:

Use a protocol-neutral enhancer only for a shared policy. WebSocket rooms, message acknowledgements, and HTTP headers belong in protocol-specific layers.

#Middleware consumer

A module's configure method can use MiddlewareConsumer to include and exclude routes. This is useful for applying logging, compatibility handling, or request labels to selected controllers without repeating branches in handlers.

#Error boundaries

• Adapter validation finishes before middleware and handler execution.
• A guard rejection does not enter the handler.
• Pipe and validation errors use the same filter chain.
• A result recovered by an interceptor does not reach a filter.
• Boot returns a stable default error response when no filter handles the failure.

Continue to validation and serialization to configure the DTO boundary.