118 lines
3.6 KiB
Rust
118 lines
3.6 KiB
Rust
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use crate::{
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error::Error,
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future::ResponseFuture,
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message::Message,
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worker::{Handle, Worker, WorkerExecutor},
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};
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use futures::Poll;
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use tokio_executor::DefaultExecutor;
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use tokio_sync::{mpsc, oneshot};
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use tower_service::Service;
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/// Adds a buffer in front of an inner service.
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///
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/// See crate level documentation for more details.
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pub struct Buffer<T, Request>
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where
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T: Service<Request>,
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{
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tx: mpsc::Sender<Message<Request, T::Future>>,
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worker: Handle,
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}
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impl<T, Request> Buffer<T, Request>
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where
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T: Service<Request>,
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T::Error: Into<Error>,
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{
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/// Creates a new `Buffer` wrapping `service`.
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///
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/// `bound` gives the maximal number of requests that can be queued for the service before
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/// backpressure is applied to callers.
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///
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/// The default Tokio executor is used to run the given service, which means that this method
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/// must be called while on the Tokio runtime.
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pub fn new(service: T, bound: usize) -> Result<Self, Error>
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where
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T: Send + 'static,
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T::Future: Send,
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T::Error: Send + Sync,
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Request: Send + 'static,
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{
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Self::with_executor(service, bound, &mut DefaultExecutor::current())
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}
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/// Creates a new `Buffer` wrapping `service`.
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///
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/// `executor` is used to spawn a new `Worker` task that is dedicated to
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/// draining the buffer and dispatching the requests to the internal
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/// service.
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///
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/// `bound` gives the maximal number of requests that can be queued for the service before
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/// backpressure is applied to callers.
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pub fn with_executor<E>(service: T, bound: usize, executor: &mut E) -> Result<Self, Error>
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where
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E: WorkerExecutor<T, Request>,
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{
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let (tx, rx) = mpsc::channel(bound);
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Worker::spawn(service, rx, executor).map(|worker| Buffer { tx, worker })
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}
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}
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impl<T, Request> Service<Request> for Buffer<T, Request>
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where
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T: Service<Request>,
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T::Error: Into<Error>,
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{
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type Response = T::Response;
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type Error = Error;
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type Future = ResponseFuture<T::Future>;
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fn poll_ready(&mut self) -> Poll<(), Self::Error> {
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// If the inner service has errored, then we error here.
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self.tx
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.poll_ready()
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.map_err(|_| self.worker.get_error_on_closed())
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}
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fn call(&mut self, request: Request) -> Self::Future {
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// TODO:
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// ideally we'd poll_ready again here so we don't allocate the oneshot
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// if the try_send is about to fail, but sadly we can't call poll_ready
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// outside of task context.
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let (tx, rx) = oneshot::channel();
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match self.tx.try_send(Message { request, tx }) {
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Err(e) => {
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if e.is_closed() {
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ResponseFuture::failed(self.worker.get_error_on_closed())
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} else {
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// When `mpsc::Sender::poll_ready` returns `Ready`, a slot
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// in the channel is reserved for the handle. Other `Sender`
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// handles may not send a message using that slot. This
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// guarantees capacity for `request`.
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//
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// Given this, the only way to hit this code path is if
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// `poll_ready` has not been called & `Ready` returned.
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panic!("buffer full; poll_ready must be called first");
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}
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}
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Ok(_) => ResponseFuture::new(rx),
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}
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}
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}
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impl<T, Request> Clone for Buffer<T, Request>
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where
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T: Service<Request>,
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{
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fn clone(&self) -> Self {
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Self {
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tx: self.tx.clone(),
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worker: self.worker.clone(),
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}
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}
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}
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