pub trait Layer<S> {
    type Service;

    fn layer(&self, inner: S) -> Self::Service;
Expand description

Decorates a Service, transforming either the request or the response.

Often, many of the pieces needed for writing network applications can be reused across multiple services. The Layer trait can be used to write reusable components that can be applied to very different kinds of services; for example, it can be applied to services operating on different protocols, and to both the client and server side of a network transaction.


Take request logging as an example:

pub struct LogLayer {
    target: &'static str,

impl<S> Layer<S> for LogLayer {
    type Service = LogService<S>;

    fn layer(&self, service: S) -> Self::Service {
        LogService {

// This service implements the Log behavior
pub struct LogService<S> {
    target: &'static str,
    service: S,

impl<S, Request> Service<Request> for LogService<S>
    S: Service<Request>,
    Request: fmt::Debug,
    type Response = S::Response;
    type Error = S::Error;
    type Future = S::Future;

    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {

    fn call(&mut self, request: Request) -> Self::Future {
        // Insert log statement here or other functionality
        println!("request = {:?}, target = {:?}", request,;

The above log implementation is decoupled from the underlying protocol and is also decoupled from client or server concerns. In other words, the same log middleware could be used in either a client or a server.

Required Associated Types

The wrapped service

Required Methods

Wrap the given service with the middleware, returning a new service that has been decorated with the middleware.

Implementations on Foreign Types


Decorates a Service, transforming either the request or the response.