107 lines
2.9 KiB
Rust
107 lines
2.9 KiB
Rust
use futures_util::ready;
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use pin_project::{pin_project, project};
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use std::time::Duration;
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use std::{
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future::Future,
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pin::Pin,
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task::{Context, Poll},
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};
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use tower_service::Service;
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/// A policy which specifies how long each request should be delayed for.
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pub trait Policy<Request> {
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fn delay(&self, req: &Request) -> Duration;
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}
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/// A middleware which delays sending the request to the underlying service
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/// for an amount of time specified by the policy.
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#[derive(Debug)]
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pub struct Delay<P, S> {
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policy: P,
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service: S,
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}
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#[pin_project]
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#[derive(Debug)]
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pub struct ResponseFuture<Request, S, F> {
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service: S,
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#[pin]
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state: State<Request, F>,
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}
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#[pin_project]
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#[derive(Debug)]
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enum State<Request, F> {
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Delaying(#[pin] tokio::time::Delay, Option<Request>),
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Called(#[pin] F),
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}
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impl<P, S> Delay<P, S> {
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pub fn new<Request>(policy: P, service: S) -> Self
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where
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P: Policy<Request>,
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S: Service<Request> + Clone,
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S::Error: Into<super::Error>,
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{
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Delay { policy, service }
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}
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}
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impl<Request, P, S> Service<Request> for Delay<P, S>
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where
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P: Policy<Request>,
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S: Service<Request> + Clone,
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S::Error: Into<super::Error>,
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{
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type Response = S::Response;
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type Error = super::Error;
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type Future = ResponseFuture<Request, S, S::Future>;
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fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
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self.service.poll_ready(cx).map_err(|e| e.into())
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}
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fn call(&mut self, request: Request) -> Self::Future {
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let deadline = tokio::time::Instant::now() + self.policy.delay(&request);
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let mut cloned = self.service.clone();
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// Pass the original service to the ResponseFuture and keep the cloned service on self.
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let orig = {
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std::mem::swap(&mut cloned, &mut self.service);
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cloned
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};
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ResponseFuture {
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service: orig,
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state: State::Delaying(tokio::time::delay_until(deadline), Some(request)),
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}
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}
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}
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impl<Request, S, F, T, E> Future for ResponseFuture<Request, S, F>
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where
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F: Future<Output = Result<T, E>>,
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E: Into<super::Error>,
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S: Service<Request, Future = F, Response = T, Error = E>,
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{
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type Output = Result<T, super::Error>;
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#[project]
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fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
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let mut this = self.project();
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loop {
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#[project]
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match this.state.as_mut().project() {
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State::Delaying(delay, req) => {
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ready!(delay.poll(cx));
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let req = req.take().expect("Missing request in delay");
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let fut = this.service.call(req);
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this.state.set(State::Called(fut));
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}
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State::Called(fut) => {
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return fut.poll(cx).map_err(Into::into);
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}
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};
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}
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}
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}
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