1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78

//! A constant `Load` implementation. Primarily useful for testing.

use futures_core::ready;
use pin_project::pin_project;
use std::{
    pin::Pin,
    task::{Context, Poll},
};
use tower_discover::{Change, Discover};
use tower_service::Service;

use crate::Load;

/// Wraps a type so that `Load::load` returns a constant value.
#[pin_project]
#[derive(Debug)]
pub struct Constant<T, M> {
    inner: T,
    load: M,
}

// ===== impl Constant =====

impl<T, M: Copy> Constant<T, M> {
    /// Wraps a `T`-typed service with a constant `M`-typed load metric.
    pub fn new(inner: T, load: M) -> Self {
        Self { inner, load }
    }
}

impl<T, M: Copy + PartialOrd> Load for Constant<T, M> {
    type Metric = M;

    fn load(&self) -> M {
        self.load
    }
}

impl<S, M, Request> Service<Request> for Constant<S, M>
where
    S: Service<Request>,
    M: Copy,
{
    type Response = S::Response;
    type Error = S::Error;
    type Future = S::Future;

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

    fn call(&mut self, req: Request) -> Self::Future {
        self.inner.call(req)
    }
}

/// Proxies `Discover` such that all changes are wrapped with a constant load.
impl<D: Discover + Unpin, M: Copy> Discover for Constant<D, M> {
    type Key = D::Key;
    type Service = Constant<D::Service, M>;
    type Error = D::Error;

    /// Yields the next discovery change set.
    fn poll_discover(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<Result<Change<D::Key, Self::Service>, D::Error>> {
        use self::Change::*;

        let this = self.project();
        let change = match ready!(Pin::new(this.inner).poll_discover(cx))? {
            Insert(k, svc) => Insert(k, Constant::new(svc, *this.load)),
            Remove(k) => Remove(k),
        };

        Poll::Ready(Ok(change))
    }
}