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//! Async functions that can be used to handle requests.
//!
#![doc = include_str!("../docs/handlers_intro.md")]
//!
//! Some examples of handlers:
//!
//! ```rust
//! use bytes::Bytes;
//! use http::StatusCode;
//!
//! // Handler that immediately returns an empty `200 OK` response.
//! async fn unit_handler() {}
//!
//! // Handler that immediately returns an empty `200 OK` response with a plain
//! // text body.
//! async fn string_handler() -> String {
//! "Hello, World!".to_string()
//! }
//!
//! // Handler that buffers the request body and returns it.
//! //
//! // This works because `Bytes` implements `FromRequest`
//! // and therefore can be used as an extractor.
//! //
//! // `String` and `StatusCode` both implement `IntoResponse` and
//! // therefore `Result<String, StatusCode>` also implements `IntoResponse`
//! async fn echo(body: Bytes) -> Result<String, StatusCode> {
//! if let Ok(string) = String::from_utf8(body.to_vec()) {
//! Ok(string)
//! } else {
//! Err(StatusCode::BAD_REQUEST)
//! }
//! }
//! ```
//!
//! ## Debugging handler type errors
//!
//! For a function to used as a handler it must implement the [`Handler`] trait.
//! axum provides blanket implementations for functions that:
//!
//! - Are `async fn`s.
//! - Take no more than 16 arguments that all implement [`FromRequest`].
//! - Returns something that implements [`IntoResponse`].
//! - If a closure is used it must implement `Clone + Send + Sync` and be
//! `'static`.
//! - Returns a future that is `Send`. The most common way to accidentally make a
//! future `!Send` is to hold a `!Send` type across an await.
//!
//! Unfortunately Rust gives poor error messages if you try to use a function
//! that doesn't quite match what's required by [`Handler`].
//!
//! You might get an error like this:
//!
//! ```not_rust
//! error[E0277]: the trait bound `fn(bool) -> impl Future {handler}: Handler<_, _>` is not satisfied
//! --> src/main.rs:13:44
//! |
//! 13 | let app = Router::new().route("/", get(handler));
//! | ^^^^^^^ the trait `Handler<_, _>` is not implemented for `fn(bool) -> impl Future {handler}`
//! |
//! ::: axum/src/handler/mod.rs:116:8
//! |
//! 116 | H: Handler<B, T>,
//! | ------------- required by this bound in `axum::routing::get`
//! ```
//!
//! This error doesn't tell you _why_ your function doesn't implement
//! [`Handler`]. It's possible to improve the error with the [`debug_handler`]
//! proc-macro from the [axum-debug] crate.
use crate::{
body::{box_body, BoxBody},
extract::{
connect_info::{Connected, IntoMakeServiceWithConnectInfo},
FromRequest, RequestParts,
},
response::IntoResponse,
routing::IntoMakeService,
BoxError,
};
use async_trait::async_trait;
use bytes::Bytes;
use http::{Request, Response};
use std::{fmt, future::Future, marker::PhantomData};
use tower::ServiceExt;
use tower_layer::Layer;
use tower_service::Service;
pub mod future;
mod into_service;
pub use self::into_service::IntoService;
pub(crate) mod sealed {
#![allow(unreachable_pub, missing_docs, missing_debug_implementations)]
pub trait HiddenTrait {}
pub struct Hidden;
impl HiddenTrait for Hidden {}
}
/// Trait for async functions that can be used to handle requests.
///
/// You shouldn't need to depend on this trait directly. It is automatically
/// implemented to closures of the right types.
///
/// See the [module docs](crate::handler) for more details.
#[async_trait]
pub trait Handler<B, T>: Clone + Send + Sized + 'static {
// This seals the trait. We cannot use the regular "sealed super trait"
// approach due to coherence.
#[doc(hidden)]
type Sealed: sealed::HiddenTrait;
/// Call the handler with the given request.
async fn call(self, req: Request<B>) -> Response<BoxBody>;
/// Apply a [`tower::Layer`] to the handler.
///
/// All requests to the handler will be processed by the layer's
/// corresponding middleware.
///
/// This can be used to add additional processing to a request for a single
/// handler.
///
/// Note this differs from [`routing::Router::layer`](crate::routing::Router::layer)
/// which adds a middleware to a group of routes.
///
/// If you're applying middleware that produces errors you have to handle the errors
/// so they're converted into responses. You can learn more about doing that
/// [here](crate::error_handling).
///
/// # Example
///
/// Adding the [`tower::limit::ConcurrencyLimit`] middleware to a handler
/// can be done like so:
///
/// ```rust
/// use axum::{
/// routing::get,
/// handler::Handler,
/// Router,
/// };
/// use tower::limit::{ConcurrencyLimitLayer, ConcurrencyLimit};
///
/// async fn handler() { /* ... */ }
///
/// let layered_handler = handler.layer(ConcurrencyLimitLayer::new(64));
/// let app = Router::new().route("/", get(layered_handler));
/// # async {
/// # axum::Server::bind(&"".parse().unwrap()).serve(app.into_make_service()).await.unwrap();
/// # };
/// ```
fn layer<L>(self, layer: L) -> Layered<L::Service, T>
where
L: Layer<IntoService<Self, B, T>>,
{
Layered::new(layer.layer(self.into_service()))
}
/// Convert the handler into a [`Service`].
///
/// This is commonly used together with [`Router::fallback`]:
///
/// ```rust
/// use axum::{
/// Server,
/// handler::Handler,
/// http::{Uri, Method, StatusCode},
/// response::IntoResponse,
/// routing::{get, Router},
/// };
/// use tower::make::Shared;
/// use std::net::SocketAddr;
///
/// async fn handler(method: Method, uri: Uri) -> impl IntoResponse {
/// (StatusCode::NOT_FOUND, format!("Nothing to see at {} {}", method, uri))
/// }
///
/// let app = Router::new()
/// .route("/", get(|| async {}))
/// .fallback(handler.into_service());
///
/// # async {
/// Server::bind(&SocketAddr::from(([127, 0, 0, 1], 3000)))
/// .serve(app.into_make_service())
/// .await?;
/// # Ok::<_, hyper::Error>(())
/// # };
/// ```
///
/// [`Router::fallback`]: crate::routing::Router::fallback
fn into_service(self) -> IntoService<Self, B, T> {
IntoService::new(self)
}
/// Convert the handler into a [`MakeService`].
///
/// This allows you to serve a single handler if you don't need any routing:
///
/// ```rust
/// use axum::{
/// Server, handler::Handler, http::{Uri, Method}, response::IntoResponse,
/// };
/// use std::net::SocketAddr;
///
/// async fn handler(method: Method, uri: Uri, body: String) -> impl IntoResponse {
/// format!("received `{} {}` with body `{:?}`", method, uri, body)
/// }
///
/// # async {
/// Server::bind(&SocketAddr::from(([127, 0, 0, 1], 3000)))
/// .serve(handler.into_make_service())
/// .await?;
/// # Ok::<_, hyper::Error>(())
/// # };
/// ```
///
/// [`MakeService`]: tower::make::MakeService
fn into_make_service(self) -> IntoMakeService<IntoService<Self, B, T>> {
IntoMakeService::new(self.into_service())
}
/// Convert the handler into a [`MakeService`] which stores information
/// about the incoming connection.
///
/// See [`Router::into_make_service_with_connect_info`] for more details.
///
/// ```rust
/// use axum::{
/// Server,
/// handler::Handler,
/// response::IntoResponse,
/// extract::ConnectInfo,
/// };
/// use std::net::SocketAddr;
///
/// async fn handler(ConnectInfo(addr): ConnectInfo<SocketAddr>) -> impl IntoResponse {
/// format!("Hello {}", addr)
/// }
///
/// # async {
/// Server::bind(&SocketAddr::from(([127, 0, 0, 1], 3000)))
/// .serve(handler.into_make_service_with_connect_info::<SocketAddr, _>())
/// .await?;
/// # Ok::<_, hyper::Error>(())
/// # };
/// ```
///
/// [`MakeService`]: tower::make::MakeService
/// [`Router::into_make_service_with_connect_info`]: crate::routing::Router::into_make_service_with_connect_info
fn into_make_service_with_connect_info<C, Target>(
self,
) -> IntoMakeServiceWithConnectInfo<IntoService<Self, B, T>, C>
where
C: Connected<Target>,
{
IntoMakeServiceWithConnectInfo::new(self.into_service())
}
}
#[async_trait]
impl<F, Fut, Res, B> Handler<B, ()> for F
where
F: FnOnce() -> Fut + Clone + Send + Sync + 'static,
Fut: Future<Output = Res> + Send,
Res: IntoResponse,
B: Send + 'static,
{
type Sealed = sealed::Hidden;
async fn call(self, _req: Request<B>) -> Response<BoxBody> {
self().await.into_response().map(box_body)
}
}
macro_rules! impl_handler {
( $($ty:ident),* $(,)? ) => {
#[async_trait]
#[allow(non_snake_case)]
impl<F, Fut, B, Res, $($ty,)*> Handler<B, ($($ty,)*)> for F
where
F: FnOnce($($ty,)*) -> Fut + Clone + Send + Sync + 'static,
Fut: Future<Output = Res> + Send,
B: Send + 'static,
Res: IntoResponse,
$( $ty: FromRequest<B> + Send,)*
{
type Sealed = sealed::Hidden;
async fn call(self, req: Request<B>) -> Response<BoxBody> {
let mut req = RequestParts::new(req);
$(
let $ty = match $ty::from_request(&mut req).await {
Ok(value) => value,
Err(rejection) => return rejection.into_response().map(box_body),
};
)*
let res = self($($ty,)*).await;
res.into_response().map(box_body)
}
}
};
}
impl_handler!(T1);
impl_handler!(T1, T2);
impl_handler!(T1, T2, T3);
impl_handler!(T1, T2, T3, T4);
impl_handler!(T1, T2, T3, T4, T5);
impl_handler!(T1, T2, T3, T4, T5, T6);
impl_handler!(T1, T2, T3, T4, T5, T6, T7);
impl_handler!(T1, T2, T3, T4, T5, T6, T7, T8);
impl_handler!(T1, T2, T3, T4, T5, T6, T7, T8, T9);
impl_handler!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10);
impl_handler!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11);
impl_handler!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12);
impl_handler!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13);
impl_handler!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14);
impl_handler!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15);
impl_handler!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16);
/// A [`Service`] created from a [`Handler`] by applying a Tower middleware.
///
/// Created with [`Handler::layer`]. See that method for more details.
pub struct Layered<S, T> {
svc: S,
_input: PhantomData<fn() -> T>,
}
impl<S, T> fmt::Debug for Layered<S, T>
where
S: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Layered").field("svc", &self.svc).finish()
}
}
impl<S, T> Clone for Layered<S, T>
where
S: Clone,
{
fn clone(&self) -> Self {
Self::new(self.svc.clone())
}
}
#[async_trait]
impl<S, T, ReqBody, ResBody> Handler<ReqBody, T> for Layered<S, T>
where
S: Service<Request<ReqBody>, Response = Response<ResBody>> + Clone + Send + 'static,
S::Error: IntoResponse,
S::Future: Send,
T: 'static,
ReqBody: Send + 'static,
ResBody: http_body::Body<Data = Bytes> + Send + 'static,
ResBody::Error: Into<BoxError>,
{
type Sealed = sealed::Hidden;
async fn call(self, req: Request<ReqBody>) -> Response<BoxBody> {
match self
.svc
.oneshot(req)
.await
.map_err(IntoResponse::into_response)
{
Ok(res) => res.map(box_body),
Err(res) => res.map(box_body),
}
}
}
impl<S, T> Layered<S, T> {
pub(crate) fn new(svc: S) -> Self {
Self {
svc,
_input: PhantomData,
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::test_helpers::*;
use http::StatusCode;
#[tokio::test]
async fn handler_into_service() {
async fn handle(body: String) -> impl IntoResponse {
format!("you said: {}", body)
}
let client = TestClient::new(handle.into_service());
let res = client.post("/").body("hi there!").send().await;
assert_eq!(res.status(), StatusCode::OK);
assert_eq!(res.text().await, "you said: hi there!");
}
#[test]
fn traits() {
use crate::routing::MethodRouter;
use crate::test_helpers::*;
assert_send::<MethodRouter<(), NotSendSync, NotSendSync, ()>>();
assert_sync::<MethodRouter<(), NotSendSync, NotSendSync, ()>>();
}
}