pub trait Middleware<S> {
type Request;
type Response;
type Error;
type Service: Service<Request = Self::Request, Response = Self::Response, Error = Self::Error>;
// Required method
fn wrap(&self, inner: S) -> Self::Service;
// Provided method
fn chain<T>(self, middleware: T) -> Chain<Self, T>
where T: Middleware<Self::Service>,
Self: Sized { ... }
}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 Middleware 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.
§Log
Take request logging as an example:
use tower_service::Service;
use tower_web::middleware::Middleware;
use futures::{Future, Poll};
use std::fmt;
pub struct LogMiddleware {
target: &'static str,
}
impl<S> Middleware<S> for LogMiddleware
where
S: Service,
S::Request: fmt::Debug,
{
type Request = S::Request;
type Response = S::Response;
type Error = S::Error;
type Service = LogService<S>;
fn wrap(&self, service: S) -> LogService<S> {
LogService {
target: self.target,
service
}
}
}
// This service implements the Log behavior
pub struct LogService<S> {
target: &'static str,
service: S,
}
impl<S> Service for LogService<S>
where
S: Service,
S::Request: fmt::Debug,
{
type Request = S::Request;
type Response = S::Response;
type Error = S::Error;
type Future = S::Future;
fn poll_ready(&mut self) -> Poll<(), Self::Error> {
self.service.poll_ready()
}
fn call(&mut self, request: Self::Request) -> Self::Future {
info!(target: self.target, "request = {:?}", request);
self.service.call(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.