Adding upstream version 115.7.0esr.upstream/115.7.0esr

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 389 insertions, 0 deletions

diff --git a/third_party/rust/tower-service/src/lib.rs b/third_party/rust/tower-service/src/lib.rs
new file mode 100644
index 0000000000..a6ef0ecec8
--- /dev/null
+++ b/third_party/rust/tower-service/src/lib.rs
@@ -0,0 +1,389 @@
+#![warn(
+    missing_debug_implementations,
+    missing_docs,
+    rust_2018_idioms,
+    unreachable_pub
+)]
+#![forbid(unsafe_code)]
+// `rustdoc::broken_intra_doc_links` is checked on CI
+
+//! Definition of the core `Service` trait to Tower
+//!
+//! The [`Service`] trait provides the necessary abstractions for defining
+//! request / response clients and servers. It is simple but powerful and is
+//! used as the foundation for the rest of Tower.
+
+use std::future::Future;
+use std::task::{Context, Poll};
+
+/// An asynchronous function from a `Request` to a `Response`.
+///
+/// The `Service` trait is a simplified interface making it easy to write
+/// network applications in a modular and reusable way, decoupled from the
+/// underlying protocol. It is one of Tower's fundamental abstractions.
+///
+/// # Functional
+///
+/// A `Service` is a function of a `Request`. It immediately returns a
+/// `Future` representing the eventual completion of processing the
+/// request. The actual request processing may happen at any time in the
+/// future, on any thread or executor. The processing may depend on calling
+/// other services. At some point in the future, the processing will complete,
+/// and the `Future` will resolve to a response or error.
+///
+/// At a high level, the `Service::call` function represents an RPC request. The
+/// `Service` value can be a server or a client.
+///
+/// # Server
+///
+/// An RPC server *implements* the `Service` trait. Requests received by the
+/// server over the network are deserialized and then passed as an argument to the
+/// server value. The returned response is sent back over the network.
+///
+/// As an example, here is how an HTTP request is processed by a server:
+///
+/// ```rust
+/// # use std::pin::Pin;
+/// # use std::task::{Poll, Context};
+/// # use std::future::Future;
+/// # use tower_service::Service;
+/// use http::{Request, Response, StatusCode};
+///
+/// struct HelloWorld;
+///
+/// impl Service<Request<Vec<u8>>> for HelloWorld {
+///     type Response = Response<Vec<u8>>;
+///     type Error = http::Error;
+///     type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>>>>;
+///
+///     fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+///         Poll::Ready(Ok(()))
+///     }
+///
+///     fn call(&mut self, req: Request<Vec<u8>>) -> Self::Future {
+///         // create the body
+///         let body: Vec<u8> = "hello, world!\n"
+///             .as_bytes()
+///             .to_owned();
+///         // Create the HTTP response
+///         let resp = Response::builder()
+///             .status(StatusCode::OK)
+///             .body(body)
+///             .expect("Unable to create `http::Response`");
+///
+///         // create a response in a future.
+///         let fut = async {
+///             Ok(resp)
+///         };
+///
+///         // Return the response as an immediate future
+///         Box::pin(fut)
+///     }
+/// }
+/// ```
+///
+/// # Client
+///
+/// A client consumes a service by using a `Service` value. The client may
+/// issue requests by invoking `call` and passing the request as an argument.
+/// It then receives the response by waiting for the returned future.
+///
+/// As an example, here is how a Redis request would be issued:
+///
+/// ```rust,ignore
+/// let client = redis::Client::new()
+///     .connect("127.0.0.1:6379".parse().unwrap())
+///     .unwrap();
+///
+/// let resp = client.call(Cmd::set("foo", "this is the value of foo")).await?;
+///
+/// // Wait for the future to resolve
+/// println!("Redis response: {:?}", resp);
+/// ```
+///
+/// # Middleware / Layer
+///
+/// More often than not, all the pieces needed for writing robust, scalable
+/// network applications are the same no matter the underlying protocol. By
+/// unifying the API for both clients and servers in a protocol agnostic way,
+/// it is possible to write middleware that provide these pieces in a
+/// reusable way.
+///
+/// Take timeouts as an example:
+///
+/// ```rust
+/// use tower_service::Service;
+/// use tower_layer::Layer;
+/// use futures::FutureExt;
+/// use std::future::Future;
+/// use std::task::{Context, Poll};
+/// use std::time::Duration;
+/// use std::pin::Pin;
+/// use std::fmt;
+/// use std::error::Error;
+///
+/// // Our timeout service, which wraps another service and
+/// // adds a timeout to its response future.
+/// pub struct Timeout<T> {
+///     inner: T,
+///     timeout: Duration,
+/// }
+///
+/// impl<T> Timeout<T> {
+///     pub fn new(inner: T, timeout: Duration) -> Timeout<T> {
+///         Timeout {
+///             inner,
+///             timeout
+///         }
+///     }
+/// }
+///
+/// // The error returned if processing a request timed out
+/// #[derive(Debug)]
+/// pub struct Expired;
+///
+/// impl fmt::Display for Expired {
+///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+///         write!(f, "expired")
+///     }
+/// }
+///
+/// impl Error for Expired {}
+///
+/// // We can implement `Service` for `Timeout<T>` if `T` is a `Service`
+/// impl<T, Request> Service<Request> for Timeout<T>
+/// where
+///     T: Service<Request>,
+///     T::Future: 'static,
+///     T::Error: Into<Box<dyn Error + Send + Sync>> + 'static,
+///     T::Response: 'static,
+/// {
+///     // `Timeout` doesn't modify the response type, so we use `T`'s response type
+///     type Response = T::Response;
+///     // Errors may be either `Expired` if the timeout expired, or the inner service's
+///     // `Error` type. Therefore, we return a boxed `dyn Error + Send + Sync` trait object to erase
+///     // the error's type.
+///     type Error = Box<dyn Error + Send + Sync>;
+///     type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>>>>;
+///
+///     fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+///         // Our timeout service is ready if the inner service is ready.
+///         // This is how backpressure can be propagated through a tree of nested services.
+///        self.inner.poll_ready(cx).map_err(Into::into)
+///     }
+///
+///     fn call(&mut self, req: Request) -> Self::Future {
+///         // Create a future that completes after `self.timeout`
+///         let timeout = tokio::time::sleep(self.timeout);
+///
+///         // Call the inner service and get a future that resolves to the response
+///         let fut = self.inner.call(req);
+///
+///         // Wrap those two futures in another future that completes when either one completes
+///         //
+///         // If the inner service is too slow the `sleep` future will complete first
+///         // And an error will be returned and `fut` will be dropped and not polled again
+///         //
+///         // We have to box the errors so the types match
+///         let f = async move {
+///             tokio::select! {
+///                 res = fut => {
+///                     res.map_err(|err| err.into())
+///                 },
+///                 _ = timeout => {
+///                     Err(Box::new(Expired) as Box<dyn Error + Send + Sync>)
+///                 },
+///             }
+///         };
+///
+///         Box::pin(f)
+///     }
+/// }
+///
+/// // A layer for wrapping services in `Timeout`
+/// pub struct TimeoutLayer(Duration);
+///
+/// impl TimeoutLayer {
+///     pub fn new(delay: Duration) -> Self {
+///         TimeoutLayer(delay)
+///     }
+/// }
+///
+/// impl<S> Layer<S> for TimeoutLayer {
+///     type Service = Timeout<S>;
+///
+///     fn layer(&self, service: S) -> Timeout<S> {
+///         Timeout::new(service, self.0)
+///     }
+/// }
+/// ```
+///
+/// The above timeout implementation is decoupled from the underlying protocol
+/// and is also decoupled from client or server concerns. In other words, the
+/// same timeout middleware could be used in either a client or a server.
+///
+/// # Backpressure
+///
+/// Calling a `Service` which is at capacity (i.e., it is temporarily unable to process a
+/// request) should result in an error. The caller is responsible for ensuring
+/// that the service is ready to receive the request before calling it.
+///
+/// `Service` provides a mechanism by which the caller is able to coordinate
+/// readiness. `Service::poll_ready` returns `Ready` if the service expects that
+/// it is able to process a request.
+///
+/// # Be careful when cloning inner services
+///
+/// Services are permitted to panic if `call` is invoked without obtaining `Poll::Ready(Ok(()))`
+/// from `poll_ready`. You should therefore be careful when cloning services for example to move
+/// them into boxed futures. Even though the original service is ready, the clone might not be.
+///
+/// Therefore this kind of code is wrong and might panic:
+///
+/// ```rust
+/// # use std::pin::Pin;
+/// # use std::task::{Poll, Context};
+/// # use std::future::Future;
+/// # use tower_service::Service;
+/// #
+/// struct Wrapper<S> {
+///     inner: S,
+/// }
+///
+/// impl<R, S> Service<R> for Wrapper<S>
+/// where
+///     S: Service<R> + Clone + 'static,
+///     R: 'static,
+/// {
+///     type Response = S::Response;
+///     type Error = S::Error;
+///     type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>>>>;
+///
+///     fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+///         Poll::Ready(Ok(()))
+///     }
+///
+///     fn call(&mut self, req: R) -> Self::Future {
+///         let mut inner = self.inner.clone();
+///         Box::pin(async move {
+///             // `inner` might not be ready since its a clone
+///             inner.call(req).await
+///         })
+///     }
+/// }
+/// ```
+///
+/// You should instead use [`std::mem::replace`] to take the service that was ready:
+///
+/// ```rust
+/// # use std::pin::Pin;
+/// # use std::task::{Poll, Context};
+/// # use std::future::Future;
+/// # use tower_service::Service;
+/// #
+/// struct Wrapper<S> {
+///     inner: S,
+/// }
+///
+/// impl<R, S> Service<R> for Wrapper<S>
+/// where
+///     S: Service<R> + Clone + 'static,
+///     R: 'static,
+/// {
+///     type Response = S::Response;
+///     type Error = S::Error;
+///     type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>>>>;
+///
+///     fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+///         Poll::Ready(Ok(()))
+///     }
+///
+///     fn call(&mut self, req: R) -> Self::Future {
+///         let clone = self.inner.clone();
+///         // take the service that was ready
+///         let mut inner = std::mem::replace(&mut self.inner, clone);
+///         Box::pin(async move {
+///             inner.call(req).await
+///         })
+///     }
+/// }
+/// ```
+pub trait Service<Request> {
+    /// Responses given by the service.
+    type Response;
+
+    /// Errors produced by the service.
+    type Error;
+
+    /// The future response value.
+    type Future: Future<Output = Result<Self::Response, Self::Error>>;
+
+    /// Returns `Poll::Ready(Ok(()))` when the service is able to process requests.
+    ///
+    /// If the service is at capacity, then `Poll::Pending` is returned and the task
+    /// is notified when the service becomes ready again. This function is
+    /// expected to be called while on a task. Generally, this can be done with
+    /// a simple `futures::future::poll_fn` call.
+    ///
+    /// If `Poll::Ready(Err(_))` is returned, the service is no longer able to service requests
+    /// and the caller should discard the service instance.
+    ///
+    /// Once `poll_ready` returns `Poll::Ready(Ok(()))`, a request may be dispatched to the
+    /// service using `call`. Until a request is dispatched, repeated calls to
+    /// `poll_ready` must return either `Poll::Ready(Ok(()))` or `Poll::Ready(Err(_))`.
+    ///
+    /// Note that `poll_ready` may reserve shared resources that are consumed in a subsequent
+    /// invocation of `call`. Thus, it is critical for implementations to not assume that `call`
+    /// will always be invoked and to ensure that such resources are released if the service is
+    /// dropped before `call` is invoked or the future returned by `call` is dropped before it
+    /// is polled.
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>;
+
+    /// Process the request and return the response asynchronously.
+    ///
+    /// This function is expected to be callable off task. As such,
+    /// implementations should take care to not call `poll_ready`.
+    ///
+    /// Before dispatching a request, `poll_ready` must be called and return
+    /// `Poll::Ready(Ok(()))`.
+    ///
+    /// # Panics
+    ///
+    /// Implementations are permitted to panic if `call` is invoked without
+    /// obtaining `Poll::Ready(Ok(()))` from `poll_ready`.
+    fn call(&mut self, req: Request) -> Self::Future;
+}
+
+impl<'a, S, Request> Service<Request> for &'a mut S
+where
+    S: Service<Request> + 'a,
+{
+    type Response = S::Response;
+    type Error = S::Error;
+    type Future = S::Future;
+
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), S::Error>> {
+        (**self).poll_ready(cx)
+    }
+
+    fn call(&mut self, request: Request) -> S::Future {
+        (**self).call(request)
+    }
+}
+
+impl<S, Request> Service<Request> for Box<S>
+where
+    S: Service<Request> + ?Sized,
+{
+    type Response = S::Response;
+    type Error = S::Error;
+    type Future = S::Future;
+
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), S::Error>> {
+        (**self).poll_ready(cx)
+    }
+
+    fn call(&mut self, request: Request) -> S::Future {
+        (**self).call(request)
+    }
+}