Module middleware 

Middleware implementations. Middleware: the core Middleware trait + ClientWithMiddleware chain runner, plus the bundled feature-gated implementations.

Ordering semantics

Middleware wrap the transport in an onion; the middleware registered first is the outermost layer — it observes the request first and the response last:

ClientBuilder::new(client)
    .with(AuthMiddleware)       // 1st registered → outermost
    .with(RetryMiddleware::new(config))
    .build();

request  →  Auth  →  Retry  →  transport
response ←  Auth  ←  Retry  ←  ╹

Inner middleware therefore see every attempt a retry-style outer middleware issues, and outer middleware see only the final outcome. The built-in default client composes [retry, breaker]: the breaker sits inside the retry loop and records each HTTP attempt individually.

Built-ins vs middleware (the composition story)

The bundled middleware are the composition points; the crate::ClientBuilder knobs are the defaults:

Knob (default)	Middleware equivalent (composable)
retries / retry_bounds	RetryMiddleware (feature retry, default-on)
with_breaker	CircuitBreakerMiddleware (feature circuit-breaker)
—	ThrottleMiddleware (feature throttle)
—	TimeoutMiddleware (feature timeout)
base_url (eager)	BaseUrlMiddleware (feature base-url)

crate::ClientBuilder::with_middleware registers custom middleware outermost — wrapping the built-ins — so user middleware observe the final outcome of the whole default stack.

Structs

ClientBuilder

Builder for ClientWithMiddleware: wrap a reqwest::Client with middleware, first-registered = outermost.

ClientWithMiddleware

A reqwest::Client wrapped in a middleware chain.

Next

The continuation passed to Middleware::handle.

RequestBuilder

A request builder bound to a ClientWithMiddleware.

RetryConfig

Configuration for retry behavior.

RetryMiddleware

Retry middleware wrapping the remainder of the chain in the estate’s loop-retry backoff loop.

Enums

Error

Error type produced by the middleware stack.

Traits

Middleware

Async middleware that wraps a ClientWithMiddleware.

Functions

is_retryable_error

Whether err is retried by RetryMiddleware: transport-level timeouts and connection failures. Middleware errors are permanent by design — a short-circuit (e.g. an open circuit breaker) must not be masked by retries.

is_retryable_status

Whether status is retried by RetryMiddleware: 408 Request Timeout, 429 Too Many Requests, and 5xx except 501 Not Implemented.

Type Aliases

Result

Result alias used throughout the middleware stack.