chore: checkpoint before Python removal

vendor/tower/src/buffer/error.rs

@@ -0,0 +1,68 @@
+//! Error types for the `Buffer` middleware.
+
+use crate::BoxError;
+use std::{fmt, sync::Arc};
+
+/// An error produced by a [`Service`] wrapped by a [`Buffer`]
+///
+/// [`Service`]: crate::Service
+/// [`Buffer`]: crate::buffer::Buffer
+#[derive(Debug)]
+pub struct ServiceError {
+    inner: Arc<BoxError>,
+}
+
+/// An error produced when the a buffer's worker closes unexpectedly.
+pub struct Closed {
+    _p: (),
+}
+
+// ===== impl ServiceError =====
+
+impl ServiceError {
+    pub(crate) fn new(inner: BoxError) -> ServiceError {
+        let inner = Arc::new(inner);
+        ServiceError { inner }
+    }
+
+    // Private to avoid exposing `Clone` trait as part of the public API
+    pub(crate) fn clone(&self) -> ServiceError {
+        ServiceError {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+impl fmt::Display for ServiceError {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        write!(fmt, "buffered service failed: {}", self.inner)
+    }
+}
+
+impl std::error::Error for ServiceError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        Some(&**self.inner)
+    }
+}
+
+// ===== impl Closed =====
+
+impl Closed {
+    pub(crate) fn new() -> Self {
+        Closed { _p: () }
+    }
+}
+
+impl fmt::Debug for Closed {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        fmt.debug_tuple("Closed").finish()
+    }
+}
+
+impl fmt::Display for Closed {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        fmt.write_str("buffer's worker closed unexpectedly")
+    }
+}
+
+impl std::error::Error for Closed {}

vendor/tower/src/buffer/future.rs

@@ -0,0 +1,78 @@
+//! Future types for the [`Buffer`] middleware.
+//!
+//! [`Buffer`]: crate::buffer::Buffer
+
+use super::{error::Closed, message};
+use pin_project_lite::pin_project;
+use std::{
+    future::Future,
+    pin::Pin,
+    task::{ready, Context, Poll},
+};
+
+pin_project! {
+    /// Future that completes when the buffered service eventually services the submitted request.
+    #[derive(Debug)]
+    pub struct ResponseFuture<T> {
+        #[pin]
+        state: ResponseState<T>,
+    }
+}
+
+pin_project! {
+    #[project = ResponseStateProj]
+    #[derive(Debug)]
+    enum ResponseState<T> {
+        Failed {
+            error: Option<crate::BoxError>,
+        },
+        Rx {
+            #[pin]
+            rx: message::Rx<T>,
+        },
+        Poll {
+            #[pin]
+            fut: T,
+        },
+    }
+}
+
+impl<T> ResponseFuture<T> {
+    pub(crate) fn new(rx: message::Rx<T>) -> Self {
+        ResponseFuture {
+            state: ResponseState::Rx { rx },
+        }
+    }
+
+    pub(crate) fn failed(err: crate::BoxError) -> Self {
+        ResponseFuture {
+            state: ResponseState::Failed { error: Some(err) },
+        }
+    }
+}
+
+impl<F, T, E> Future for ResponseFuture<F>
+where
+    F: Future<Output = Result<T, E>>,
+    E: Into<crate::BoxError>,
+{
+    type Output = Result<T, crate::BoxError>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut this = self.project();
+
+        loop {
+            match this.state.as_mut().project() {
+                ResponseStateProj::Failed { error } => {
+                    return Poll::Ready(Err(error.take().expect("polled after error")));
+                }
+                ResponseStateProj::Rx { rx } => match ready!(rx.poll(cx)) {
+                    Ok(Ok(fut)) => this.state.set(ResponseState::Poll { fut }),
+                    Ok(Err(e)) => return Poll::Ready(Err(e.into())),
+                    Err(_) => return Poll::Ready(Err(Closed::new().into())),
+                },
+                ResponseStateProj::Poll { fut } => return fut.poll(cx).map_err(Into::into),
+            }
+        }
+    }
+}

vendor/tower/src/buffer/layer.rs

@@ -0,0 +1,72 @@
+use super::service::Buffer;
+use std::{fmt, marker::PhantomData};
+use tower_layer::Layer;
+use tower_service::Service;
+
+/// Adds an mpsc buffer in front of an inner service.
+///
+/// The default Tokio executor is used to run the given service,
+/// which means that this layer can only be used on the Tokio runtime.
+///
+/// See the module documentation for more details.
+pub struct BufferLayer<Request> {
+    bound: usize,
+    _p: PhantomData<fn(Request)>,
+}
+
+impl<Request> BufferLayer<Request> {
+    /// Creates a new [`BufferLayer`] with the provided `bound`.
+    ///
+    /// `bound` gives the maximal number of requests that can be queued for the service before
+    /// backpressure is applied to callers.
+    ///
+    /// # A note on choosing a `bound`
+    ///
+    /// When [`Buffer`]'s implementation of [`poll_ready`] returns [`Poll::Ready`], it reserves a
+    /// slot in the channel for the forthcoming [`call`]. However, if this call doesn't arrive,
+    /// this reserved slot may be held up for a long time. As a result, it's advisable to set
+    /// `bound` to be at least the maximum number of concurrent requests the [`Buffer`] will see.
+    /// If you do not, all the slots in the buffer may be held up by futures that have just called
+    /// [`poll_ready`] but will not issue a [`call`], which prevents other senders from issuing new
+    /// requests.
+    ///
+    /// [`Poll::Ready`]: std::task::Poll::Ready
+    /// [`call`]: crate::Service::call
+    /// [`poll_ready`]: crate::Service::poll_ready
+    pub const fn new(bound: usize) -> Self {
+        BufferLayer {
+            bound,
+            _p: PhantomData,
+        }
+    }
+}
+
+impl<S, Request> Layer<S> for BufferLayer<Request>
+where
+    S: Service<Request> + Send + 'static,
+    S::Future: Send,
+    S::Error: Into<crate::BoxError> + Send + Sync,
+    Request: Send + 'static,
+{
+    type Service = Buffer<Request, S::Future>;
+
+    fn layer(&self, service: S) -> Self::Service {
+        Buffer::new(service, self.bound)
+    }
+}
+
+impl<Request> fmt::Debug for BufferLayer<Request> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("BufferLayer")
+            .field("bound", &self.bound)
+            .finish()
+    }
+}
+
+impl<Request> Clone for BufferLayer<Request> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl<Request> Copy for BufferLayer<Request> {}

vendor/tower/src/buffer/message.rs

@@ -0,0 +1,16 @@
+use super::error::ServiceError;
+use tokio::sync::oneshot;
+
+/// Message sent over buffer
+#[derive(Debug)]
+pub(crate) struct Message<Request, Fut> {
+    pub(crate) request: Request,
+    pub(crate) tx: Tx<Fut>,
+    pub(crate) span: tracing::Span,
+}
+
+/// Response sender
+pub(crate) type Tx<Fut> = oneshot::Sender<Result<Fut, ServiceError>>;
+
+/// Response receiver
+pub(crate) type Rx<Fut> = oneshot::Receiver<Result<Fut, ServiceError>>;

vendor/tower/src/buffer/mod.rs

@@ -0,0 +1,47 @@
+//! Middleware that provides a buffered mpsc channel to a service.
+//!
+//! Sometimes you want to give out multiple handles to a single service, and allow each handle to
+//! enqueue requests. That is, you want a [`Service`] to be [`Clone`]. This module allows you to do
+//! that by placing the service behind a multi-producer, single-consumer buffering channel. Clients
+//! enqueue requests by sending on the channel from any of the handles ([`Buffer`]), and the single
+//! service running elsewhere (usually spawned) receives and services the requests one by one. Each
+//! request is enqueued alongside a response channel that allows the service to report the result
+//! of the request back to the caller.
+//!
+//! # Examples
+//!
+//! ```rust
+//! # #[cfg(feature = "util")]
+//! use tower::buffer::Buffer;
+//! # #[cfg(feature = "util")]
+//! use tower::{Service, ServiceExt};
+//! # #[cfg(feature = "util")]
+//! async fn mass_produce<S: Service<usize>>(svc: S)
+//! where
+//!   S: 'static + Send,
+//!   S::Error: Send + Sync + std::error::Error,
+//!   S::Future: Send
+//! {
+//!     let svc = Buffer::new(svc, 10 /* buffer length */);
+//!     for _ in 0..10 {
+//!         let mut svc = svc.clone();
+//!         tokio::spawn(async move {
+//!             for i in 0usize.. {
+//!                 svc.ready().await.expect("service crashed").call(i).await;
+//!             }
+//!         });
+//!     }
+//! }
+//! ```
+//!
+//! [`Service`]: crate::Service
+
+pub mod error;
+pub mod future;
+mod layer;
+mod message;
+mod service;
+mod worker;
+
+pub use self::layer::BufferLayer;
+pub use self::service::Buffer;

vendor/tower/src/buffer/service.rs

@@ -0,0 +1,144 @@
+use super::{
+    future::ResponseFuture,
+    message::Message,
+    worker::{Handle, Worker},
+};
+
+use std::{
+    future::Future,
+    task::{Context, Poll},
+};
+use tokio::sync::{mpsc, oneshot};
+use tokio_util::sync::PollSender;
+use tower_service::Service;
+
+/// Adds an mpsc buffer in front of an inner service.
+///
+/// See the module documentation for more details.
+#[derive(Debug)]
+pub struct Buffer<Req, F> {
+    tx: PollSender<Message<Req, F>>,
+    handle: Handle,
+}
+
+impl<Req, F> Buffer<Req, F>
+where
+    F: 'static,
+{
+    /// Creates a new [`Buffer`] wrapping `service`.
+    ///
+    /// `bound` gives the maximal number of requests that can be queued for the service before
+    /// backpressure is applied to callers.
+    ///
+    /// The default Tokio executor is used to run the given service, which means that this method
+    /// must be called while on the Tokio runtime.
+    ///
+    /// # A note on choosing a `bound`
+    ///
+    /// When [`Buffer`]'s implementation of [`poll_ready`] returns [`Poll::Ready`], it reserves a
+    /// slot in the channel for the forthcoming [`call`]. However, if this call doesn't arrive,
+    /// this reserved slot may be held up for a long time. As a result, it's advisable to set
+    /// `bound` to be at least the maximum number of concurrent requests the [`Buffer`] will see.
+    /// If you do not, all the slots in the buffer may be held up by futures that have just called
+    /// [`poll_ready`] but will not issue a [`call`], which prevents other senders from issuing new
+    /// requests.
+    ///
+    /// [`Poll::Ready`]: std::task::Poll::Ready
+    /// [`call`]: crate::Service::call
+    /// [`poll_ready`]: crate::Service::poll_ready
+    pub fn new<S>(service: S, bound: usize) -> Self
+    where
+        S: Service<Req, Future = F> + Send + 'static,
+        F: Send,
+        S::Error: Into<crate::BoxError> + Send + Sync,
+        Req: Send + 'static,
+    {
+        let (service, worker) = Self::pair(service, bound);
+        tokio::spawn(worker);
+        service
+    }
+
+    /// Creates a new [`Buffer`] wrapping `service`, but returns the background worker.
+    ///
+    /// This is useful if you do not want to spawn directly onto the tokio runtime
+    /// but instead want to use your own executor. This will return the [`Buffer`] and
+    /// the background `Worker` that you can then spawn.
+    pub fn pair<S>(service: S, bound: usize) -> (Self, Worker<S, Req>)
+    where
+        S: Service<Req, Future = F> + Send + 'static,
+        F: Send,
+        S::Error: Into<crate::BoxError> + Send + Sync,
+        Req: Send + 'static,
+    {
+        let (tx, rx) = mpsc::channel(bound);
+        let (handle, worker) = Worker::new(service, rx);
+        let buffer = Self {
+            tx: PollSender::new(tx),
+            handle,
+        };
+        (buffer, worker)
+    }
+
+    fn get_worker_error(&self) -> crate::BoxError {
+        self.handle.get_error_on_closed()
+    }
+}
+
+impl<Req, Rsp, F, E> Service<Req> for Buffer<Req, F>
+where
+    F: Future<Output = Result<Rsp, E>> + Send + 'static,
+    E: Into<crate::BoxError>,
+    Req: Send + 'static,
+{
+    type Response = Rsp;
+    type Error = crate::BoxError;
+    type Future = ResponseFuture<F>;
+
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        // First, check if the worker is still alive.
+        if self.tx.is_closed() {
+            // If the inner service has errored, then we error here.
+            return Poll::Ready(Err(self.get_worker_error()));
+        }
+
+        // Poll the sender to acquire a permit.
+        self.tx
+            .poll_reserve(cx)
+            .map_err(|_| self.get_worker_error())
+    }
+
+    fn call(&mut self, request: Req) -> Self::Future {
+        tracing::trace!("sending request to buffer worker");
+
+        // get the current Span so that we can explicitly propagate it to the worker
+        // if we didn't do this, events on the worker related to this span wouldn't be counted
+        // towards that span since the worker would have no way of entering it.
+        let span = tracing::Span::current();
+
+        // If we've made it here, then a channel permit has already been
+        // acquired, so we can freely allocate a oneshot.
+        let (tx, rx) = oneshot::channel();
+
+        match self.tx.send_item(Message { request, span, tx }) {
+            Ok(_) => ResponseFuture::new(rx),
+            // If the channel is closed, propagate the error from the worker.
+            Err(_) => {
+                tracing::trace!("buffer channel closed");
+                ResponseFuture::failed(self.get_worker_error())
+            }
+        }
+    }
+}
+
+impl<Req, F> Clone for Buffer<Req, F>
+where
+    Req: Send + 'static,
+    F: Send + 'static,
+{
+    fn clone(&self) -> Self {
+        Self {
+            handle: self.handle.clone(),
+            tx: self.tx.clone(),
+        }
+    }
+}

vendor/tower/src/buffer/worker.rs

@@ -0,0 +1,226 @@
+use super::{
+    error::{Closed, ServiceError},
+    message::Message,
+};
+use std::sync::{Arc, Mutex};
+use std::{
+    future::Future,
+    pin::Pin,
+    task::{ready, Context, Poll},
+};
+use tokio::sync::mpsc;
+use tower_service::Service;
+
+pin_project_lite::pin_project! {
+    /// Task that handles processing the buffer. This type should not be used
+    /// directly, instead `Buffer` requires an `Executor` that can accept this task.
+    ///
+    /// The struct is `pub` in the private module and the type is *not* re-exported
+    /// as part of the public API. This is the "sealed" pattern to include "private"
+    /// types in public traits that are not meant for consumers of the library to
+    /// implement (only call).
+    #[derive(Debug)]
+    pub struct Worker<T, Request>
+    where
+        T: Service<Request>,
+    {
+        current_message: Option<Message<Request, T::Future>>,
+        rx: mpsc::Receiver<Message<Request, T::Future>>,
+        service: T,
+        finish: bool,
+        failed: Option<ServiceError>,
+        handle: Handle,
+    }
+}
+
+/// Get the error out
+#[derive(Debug)]
+pub(crate) struct Handle {
+    inner: Arc<Mutex<Option<ServiceError>>>,
+}
+
+impl<T, Request> Worker<T, Request>
+where
+    T: Service<Request>,
+    T::Error: Into<crate::BoxError>,
+{
+    pub(crate) fn new(
+        service: T,
+        rx: mpsc::Receiver<Message<Request, T::Future>>,
+    ) -> (Handle, Worker<T, Request>) {
+        let handle = Handle {
+            inner: Arc::new(Mutex::new(None)),
+        };
+
+        let worker = Worker {
+            current_message: None,
+            finish: false,
+            failed: None,
+            rx,
+            service,
+            handle: handle.clone(),
+        };
+
+        (handle, worker)
+    }
+
+    /// Return the next queued Message that hasn't been canceled.
+    ///
+    /// If a `Message` is returned, the `bool` is true if this is the first time we received this
+    /// message, and false otherwise (i.e., we tried to forward it to the backing service before).
+    fn poll_next_msg(
+        &mut self,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<(Message<Request, T::Future>, bool)>> {
+        if self.finish {
+            // We've already received None and are shutting down
+            return Poll::Ready(None);
+        }
+
+        tracing::trace!("worker polling for next message");
+        if let Some(msg) = self.current_message.take() {
+            // If the oneshot sender is closed, then the receiver is dropped,
+            // and nobody cares about the response. If this is the case, we
+            // should continue to the next request.
+            if !msg.tx.is_closed() {
+                tracing::trace!("resuming buffered request");
+                return Poll::Ready(Some((msg, false)));
+            }
+
+            tracing::trace!("dropping cancelled buffered request");
+        }
+
+        // Get the next request
+        while let Some(msg) = ready!(Pin::new(&mut self.rx).poll_recv(cx)) {
+            if !msg.tx.is_closed() {
+                tracing::trace!("processing new request");
+                return Poll::Ready(Some((msg, true)));
+            }
+            // Otherwise, request is canceled, so pop the next one.
+            tracing::trace!("dropping cancelled request");
+        }
+
+        Poll::Ready(None)
+    }
+
+    fn failed(&mut self, error: crate::BoxError) {
+        // The underlying service failed when we called `poll_ready` on it with the given `error`. We
+        // need to communicate this to all the `Buffer` handles. To do so, we wrap up the error in
+        // an `Arc`, send that `Arc<E>` to all pending requests, and store it so that subsequent
+        // requests will also fail with the same error.
+
+        // Note that we need to handle the case where some handle is concurrently trying to send us
+        // a request. We need to make sure that *either* the send of the request fails *or* it
+        // receives an error on the `oneshot` it constructed. Specifically, we want to avoid the
+        // case where we send errors to all outstanding requests, and *then* the caller sends its
+        // request. We do this by *first* exposing the error, *then* closing the channel used to
+        // send more requests (so the client will see the error when the send fails), and *then*
+        // sending the error to all outstanding requests.
+        let error = ServiceError::new(error);
+
+        let mut inner = self.handle.inner.lock().unwrap();
+
+        if inner.is_some() {
+            // Future::poll was called after we've already errored out!
+            return;
+        }
+
+        *inner = Some(error.clone());
+        drop(inner);
+
+        self.rx.close();
+
+        // By closing the mpsc::Receiver, we know that poll_next_msg will soon return Ready(None),
+        // which will trigger the `self.finish == true` phase. We just need to make sure that any
+        // requests that we receive before we've exhausted the receiver receive the error:
+        self.failed = Some(error);
+    }
+}
+
+impl<T, Request> Future for Worker<T, Request>
+where
+    T: Service<Request>,
+    T::Error: Into<crate::BoxError>,
+{
+    type Output = ();
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        if self.finish {
+            return Poll::Ready(());
+        }
+
+        loop {
+            match ready!(self.poll_next_msg(cx)) {
+                Some((msg, first)) => {
+                    let _guard = msg.span.enter();
+                    if let Some(ref failed) = self.failed {
+                        tracing::trace!("notifying caller about worker failure");
+                        let _ = msg.tx.send(Err(failed.clone()));
+                        continue;
+                    }
+
+                    // Wait for the service to be ready
+                    tracing::trace!(
+                        resumed = !first,
+                        message = "worker received request; waiting for service readiness"
+                    );
+                    match self.service.poll_ready(cx) {
+                        Poll::Ready(Ok(())) => {
+                            tracing::debug!(service.ready = true, message = "processing request");
+                            let response = self.service.call(msg.request);
+
+                            // Send the response future back to the sender.
+                            //
+                            // An error means the request had been canceled in-between
+                            // our calls, the response future will just be dropped.
+                            tracing::trace!("returning response future");
+                            let _ = msg.tx.send(Ok(response));
+                        }
+                        Poll::Pending => {
+                            tracing::trace!(service.ready = false, message = "delay");
+                            // Put out current message back in its slot.
+                            drop(_guard);
+                            self.current_message = Some(msg);
+                            return Poll::Pending;
+                        }
+                        Poll::Ready(Err(e)) => {
+                            let error = e.into();
+                            tracing::debug!({ %error }, "service failed");
+                            drop(_guard);
+                            self.failed(error);
+                            let _ = msg.tx.send(Err(self
+                                .failed
+                                .as_ref()
+                                .expect("Worker::failed did not set self.failed?")
+                                .clone()));
+                        }
+                    }
+                }
+                None => {
+                    // No more more requests _ever_.
+                    self.finish = true;
+                    return Poll::Ready(());
+                }
+            }
+        }
+    }
+}
+
+impl Handle {
+    pub(crate) fn get_error_on_closed(&self) -> crate::BoxError {
+        self.inner
+            .lock()
+            .unwrap()
+            .as_ref()
+            .map(|svc_err| svc_err.clone().into())
+            .unwrap_or_else(|| Closed::new().into())
+    }
+}
+
+impl Clone for Handle {
+    fn clone(&self) -> Handle {
+        Handle {
+            inner: self.inner.clone(),
+        }
+    }
+}