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#![allow(async_fn_in_trait)]
#![deny(missing_docs, missing_debug_implementations)]
//! An experimental service framework.
//!
//! The [`Service`] trait is the central abstraction. It is an
//! [asynchronous function](Service::call), accepting a request and returning a response, which
//! can only be executed _after_ a [permit](Service::Permit) is [acquired](Service::acquire).
//!
//! The root exports [`Service`] constructors, and an extension trait, [`ServiceExt`] containing
//! combinators to modify a [`Service`]. Both the combinators and constructors each have an
//! associated module containing related documentation, traits, and types.
//!
//! # Example
//!
//! ```rust
//! use burger::*;
//! # use tokio::time::sleep;
//! # use std::time::Duration;
//!
//! # #[tokio::main]
//! # async fn main() {
//! let svc = service_fn(|x| async move {
//! sleep(Duration::from_secs(1)).await;
//! 2 * x
//! })
//! .map(|x| x + 3)
//! .concurrency_limit(1)
//! .buffer(3)
//! .load_shed();
//! let response = svc.oneshot(30).await;
//! assert_eq!(Ok(63), response);
//! # }
//! ```
//!
//! # Usage
//!
//! A typical [`Service`] will consist of distinct layers, each providing specific dynamics. The
//! following flowchart attempts to categorize the exports of this crate:
//!
//! <pre class="mermaid" style="text-align:center">
#![doc = include_str!("flowchart.mmd")]
//! </pre>
//! <script type="module">
//! import mermaid from 'https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.esm.min.mjs';
//! let config = { theme: "dark", startOnLoad: true, flowchart: { useMaxWidth: true, htmlLabels: true } };
//! mermaid.initialize(config);
//! </script>
pub mod balance;
pub mod buffer;
#[cfg(feature = "compat")]
pub mod compat;
pub mod concurrency_limit;
pub mod depressurize;
pub mod either;
pub mod leak;
pub mod load;
pub mod load_shed;
pub mod map;
pub mod rate_limit;
pub mod retry;
pub mod select;
pub mod service_fn;
pub mod steer;
pub mod then;
use std::{convert::Infallible, sync::Arc, time::Duration};
use buffer::Buffer;
use concurrency_limit::ConcurrencyLimit;
use depressurize::Depressurize;
use either::Either;
use leak::Leak;
use load::{Load, PendingRequests};
use load_shed::LoadShed;
use map::Map;
use rate_limit::RateLimit;
use retry::Retry;
use then::Then;
use tokio::sync::{Mutex, RwLock};
#[cfg(feature = "compat")]
#[doc(inline)]
pub use compat::compat;
#[doc(inline)]
pub use select::select;
#[doc(inline)]
pub use service_fn::service_fn;
#[doc(inline)]
pub use steer::steer;
/// An asynchronous function call, which can only be executed _after_ obtaining a permit.
///
/// # Example
///
/// ```rust
/// use burger::{service_fn::ServiceFn, *};
///
/// # #[tokio::main]
/// # async fn main() {
/// let svc = service_fn(|x: usize| async move { x.to_string() });
/// let permit = svc.acquire().await;
/// let response = ServiceFn::call(permit, 32).await;
/// # }
/// ```
pub trait Service<Request> {
/// The type produced by the service call.
type Response;
/// The type of the permit required to call the service.
type Permit<'a>
where
Self: 'a;
/// Obtains a permit.
async fn acquire(&self) -> Self::Permit<'_>;
/// Consumes a permit to call the service.
async fn call<'a>(permit: Self::Permit<'a>, request: Request) -> Self::Response
where
Self: 'a;
}
/// An extension trait for [`Service`].
pub trait ServiceExt<Request>: Service<Request> {
/// Acquires the [`Service::Permit`] and then immediately uses it to [call](Service::call) the
/// [`Service`].
///
/// # Example
///
/// ```rust
/// use burger::*;
///
/// # #[tokio::main]
/// # async fn main() {
/// let svc = service_fn(|x: usize| async move { x.to_string() });
/// let response = svc.oneshot(32).await;
/// # }
/// ```
async fn oneshot(&self, request: Request) -> Self::Response
where
Self: Sized,
{
let permit = self.acquire().await;
Self::call(permit, request).await
}
/// Extends the service using a closure accepting [`Self::Response`](Service::Response) and
/// returning a [`Future`](std::future::Future).
///
/// See the [module](then) for more information.
fn then<F>(self, closure: F) -> Then<Self, F>
where
Self: Sized,
{
Then::new(self, closure)
}
/// Extends the service using a closure accepting [Self::Response](Service::Response) and returning a
/// [`Future`](std::future::Future).
///
/// See the [module](map) for more information.
fn map<F>(self, closure: F) -> Map<Self, F>
where
Self: Sized,
{
Map::new(self, closure)
}
/// Applies a concurrency limit to the service with a specified number of permits.
///
/// See [concurrency limit](concurrency_limit) module for more information.
fn concurrency_limit(self, n_permits: usize) -> ConcurrencyLimit<Self>
where
Self: Sized,
{
ConcurrencyLimit::new(self, n_permits)
}
/// Applies load shedding to the service.
///
/// See [module](load_shed) for more information.
fn load_shed(self) -> LoadShed<Self>
where
Self: Sized,
{
LoadShed::new(self)
}
/// Applies buffering to the service with a specified capacity.
///
/// See the [module](buffer) for more information.
fn buffer(self, capacity: usize) -> Buffer<Self>
where
Self: Sized,
{
Buffer::new(self, capacity)
}
/// Applies rate limiting to the service with a specified interval and number of permits.
///
/// See the [module](rate_limit) for more information.
fn rate_limit(self, interval: Duration, permits: usize) -> RateLimit<Self>
where
Self: Sized,
{
RateLimit::new(self, interval, permits)
}
/// Applies retries to tbe service with a specified [Policy](crate::retry::Policy).
///
/// See the [module](retry) for more information.
fn retry<P>(self, policy: P) -> Retry<Self, P>
where
Self: Sized,
{
Retry::new(self, policy)
}
/// Depressurizes the service.
///
/// See the [module](depressurize) for more information,
fn depressurize(self) -> Depressurize<Self>
where
Self: Sized,
{
Depressurize::new(self)
}
/// Records [`Load`] on the service, measured by number of pending requests.
///
/// See the [load] module for more information.
fn pending_requests(self) -> PendingRequests<Self>
where
Self: Sized,
{
PendingRequests::new(self)
}
/// Extends the lifetime of the permit.
///
/// See the [module](leak) for more information.
fn leak<'t>(self: Arc<Self>) -> Leak<'t, Self>
where
Self: Sized,
{
Leak::new(self)
}
/// Wraps as [Either::Left]. For the other variant see [ServiceExt::right].
///
/// See the [module](either) for more information.
fn left<T>(self) -> Either<Self, T>
where
Self: Sized,
{
Either::Left(self)
}
/// Wraps as [Either::Right]. For the other variant see [ServiceExt::right].
///
/// See the [module](either) for more information.
fn right<T>(self) -> Either<T, Self>
where
Self: Sized,
{
Either::Right(self)
}
}
impl<Request, S> ServiceExt<Request> for S where S: Service<Request> {}
/// A fallible [`Service`].
pub trait TryService<Request>: Service<Request, Response = Result<Self::Ok, Self::Error>> {
/// The [`Result::Ok`] variant of the [`Service::Response`].
type Ok;
/// The [`Result::Err`] variant of the [`Service::Response`].
type Error;
}
impl<Request, Ok, Error, S> TryService<Request> for S
where
S: Service<Request, Response = Result<Ok, Error>>,
{
type Ok = Ok;
type Error = Error;
}
impl<Request, S> Service<Request> for Arc<S>
where
S: Service<Request>,
{
type Response = S::Response;
type Permit<'a> = S::Permit<'a>
where
S: 'a;
async fn acquire(&self) -> Self::Permit<'_> {
S::acquire(self).await
}
async fn call(permit: Self::Permit<'_>, request: Request) -> Self::Response {
S::call(permit, request).await
}
}
impl<S> Load for Arc<S>
where
S: Load,
{
type Metric = S::Metric;
fn load(&self) -> Self::Metric {
S::load(self)
}
}
impl<'t, Request, S> Service<Request> for &'t S
where
S: Service<Request>,
{
type Response = S::Response;
type Permit<'a> = S::Permit<'a>
where
S:'a, 't: 'a;
async fn acquire(&self) -> Self::Permit<'_> {
S::acquire(self).await
}
async fn call<'a>(permit: Self::Permit<'a>, request: Request) -> Self::Response
where
Self: 'a,
{
S::call(permit, request).await
}
}
impl<'t, S> Load for &'t S
where
S: Load,
{
type Metric = S::Metric;
fn load(&self) -> Self::Metric {
S::load(self)
}
}
impl<Request, Permit, S> Service<Request> for Mutex<S>
where
// NOTE: These bounds seem too tight
for<'a> S: Service<Request, Permit<'a> = Permit>,
S: 'static,
{
type Response = S::Response;
type Permit<'a> = Permit
where
S: 'a;
async fn acquire(&self) -> Self::Permit<'_> {
let guard = self.lock().await;
guard.acquire().await
}
async fn call(permit: Self::Permit<'_>, request: Request) -> Self::Response {
S::call(permit, request).await
}
}
impl<Request, S, Permit> Service<Request> for RwLock<S>
where
// NOTE: These bounds seem too tight
for<'a> S: Service<Request, Permit<'a> = Permit>,
S: 'static,
{
type Response = S::Response;
type Permit<'a> = S::Permit<'a>
where
Self: 'a;
async fn acquire(&self) -> Self::Permit<'_> {
self.read().await.acquire().await
}
async fn call(permit: Self::Permit<'_>, request: Request) -> Self::Response {
S::call(permit, request).await
}
}
/// A middleware, used to incrementally add behaviour to a [`Service`].
pub trait Middleware<S> {
/// The resultant service.
type Service;
/// Applies this middleware to an existing service.
fn apply(self, svc: S) -> Self::Service;
}
/// The root of a chain of [`Middleware`]s.
///
/// The [`ServiceExt`] combinators can be used to extend with additional middleware.
///
/// # Example
///
/// ```
/// use burger::*;
///
/// let middleware = MiddlewareBuilder.concurrency_limit(3).buffer(2).load_shed();
/// let svc = service_fn(|x: u32| async move { x.to_string() });
/// let svc = middleware.apply(svc);
/// ```
#[derive(Debug, Clone)]
pub struct MiddlewareBuilder;
impl Service<Infallible> for MiddlewareBuilder {
type Permit<'a> = ();
type Response = Infallible;
async fn acquire(&self) -> Self::Permit<'_> {}
async fn call<'a>(_permit: Self::Permit<'a>, request: Infallible) -> Self::Response
where
Self: 'a,
{
request
}
}
impl<S> Middleware<S> for MiddlewareBuilder {
type Service = S;
fn apply(self, svc: S) -> Self::Service {
svc
}
}