101 lines
2.7 KiB
Rust
101 lines
2.7 KiB
Rust
use std::marker::PhantomData;
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/// A `Layer` wraps `M`-typed `Stack<U>` to produce a `Stack<T>`
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///
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/// Some `Stack` types are dependendent on and generic over an inner `Stack`. For
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/// example, a load balancer may implement `Stack<Authority>` and be
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/// configured with a `Stack<SocketAddr>` that is used to build a service for
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/// each enpdoint. Such a load balancer would provide a signature like:
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///
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/// ```ignore
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/// impl<M: Stack<SocketAddr>> Layer<Authority, SocketAddr, M> for BalanceLayer<M> { ... }
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/// ```
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pub trait Layer<T, U, S: super::Stack<U>> {
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type Value;
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type Error;
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type Stack: super::Stack<T, Value = Self::Value, Error = Self::Error>;
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/// Produces a `Stack` value from a `M` value.
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fn bind(&self, next: S) -> Self::Stack;
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/// Produces a new Layer with this layer wrapping the provided inner layer.
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fn and_then<V, N, L>(self, inner: L)
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-> AndThen<U, Self, L>
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where
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N: super::Stack<V>,
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L: Layer<U, V, N>,
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Self: Layer<T, U, L::Stack> + Sized,
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{
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AndThen {
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outer: self,
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inner,
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_p: PhantomData,
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}
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}
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/// Produces a new Layer with another layer wrapping this one.
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fn push<R, L>(self, outer: L)
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-> AndThen<T, L, Self>
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where
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L: Layer<R, T, Self::Stack>,
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Self: Sized,
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{
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AndThen {
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outer,
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inner: self,
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_p: PhantomData,
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}
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}
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/// Wraps this layer such that stack errors are modified by `map_err`.
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fn map_err<M>(self, map_err: M)
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-> AndThen<T, super::map_err::Layer<M>, Self>
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where
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Self: Sized,
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M: super::map_err::MapErr<Self::Error>,
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super::map_err::Layer<M>: Layer<T, T, Self::Stack>,
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{
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super::map_err::layer(map_err).and_then(self)
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}
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}
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/// The identity layer.
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impl<T, M: super::Stack<T>> Layer<T, T, M> for () {
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type Value = M::Value;
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type Error = M::Error;
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type Stack = M;
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fn bind(&self, inner: M) -> M {
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inner
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}
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}
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/// Combines two `Layers` as one.
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///
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/// Given an `Outer: Layer<T, U, _>` and an `Inner: Layer<U, V, _>`, producesa
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/// `Layer<T, C, _>`, encapsulating the logic of the Outer and Inner layers.
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#[derive(Debug, Clone)]
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pub struct AndThen<U, Outer, Inner>
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{
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outer: Outer,
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inner: Inner,
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// `AndThen` should be Send/Sync independently of U`.
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_p: PhantomData<fn() -> U>,
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}
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impl<T, U, V, M, Outer, Inner> Layer<T, V, M>
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for AndThen<U, Outer, Inner>
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where
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Outer: Layer<T, U, Inner::Stack>,
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Inner: Layer<U, V, M>,
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M: super::Stack<V>,
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{
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type Value = Outer::Value;
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type Error = Outer::Error;
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type Stack = Outer::Stack;
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fn bind(&self, next: M) -> Self::Stack {
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self.outer.bind(self.inner.bind(next))
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}
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}
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