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//! Convert panics into responses.
//!
//! Note that using panics for error handling is _not_ recommended. Prefer instead to use `Result`
//! whenever possible.
//!
//! # Example
//!
//! ```rust
//! use http::{Request, Response, header::HeaderName};
//! use std::convert::Infallible;
//! use tower_async::{Service, ServiceExt, ServiceBuilder, service_fn};
//! use tower_async_http::catch_panic::CatchPanicLayer;
//! use hyper::Body;
//!
//! # #[tokio::main]
//! # async fn main() -> Result<(), Box<dyn std::error::Error>> {
//! async fn handle(req: Request<Body>) -> Result<Response<Body>, Infallible> {
//! panic!("something went wrong...")
//! }
//!
//! let mut svc = ServiceBuilder::new()
//! // Catch panics and convert them into responses.
//! .layer(CatchPanicLayer::new())
//! .service_fn(handle);
//!
//! // Call the service.
//! let request = Request::new(Body::empty());
//!
//! let response = svc.call(request).await?;
//!
//! assert_eq!(response.status(), 500);
//! #
//! # Ok(())
//! # }
//! ```
//!
//! Using a custom panic handler:
//!
//! ```rust
//! use http::{Request, StatusCode, Response, header::{self, HeaderName}};
//! use std::{any::Any, convert::Infallible};
//! use tower_async::{Service, ServiceExt, ServiceBuilder, service_fn};
//! use tower_async_http::catch_panic::CatchPanicLayer;
//! use hyper::Body;
//!
//! # #[tokio::main]
//! # async fn main() -> Result<(), Box<dyn std::error::Error>> {
//! async fn handle(req: Request<Body>) -> Result<Response<Body>, Infallible> {
//! panic!("something went wrong...")
//! }
//!
//! fn handle_panic(err: Box<dyn Any + Send + 'static>) -> Response<Body> {
//! let details = if let Some(s) = err.downcast_ref::<String>() {
//! s.clone()
//! } else if let Some(s) = err.downcast_ref::<&str>() {
//! s.to_string()
//! } else {
//! "Unknown panic message".to_string()
//! };
//!
//! let body = serde_json::json!({
//! "error": {
//! "kind": "panic",
//! "details": details,
//! }
//! });
//! let body = serde_json::to_string(&body).unwrap();
//!
//! Response::builder()
//! .status(StatusCode::INTERNAL_SERVER_ERROR)
//! .header(header::CONTENT_TYPE, "application/json")
//! .body(Body::from(body))
//! .unwrap()
//! }
//!
//! let svc = ServiceBuilder::new()
//! // Use `handle_panic` to create the response.
//! .layer(CatchPanicLayer::custom(handle_panic))
//! .service_fn(handle);
//! #
//! # Ok(())
//! # }
//! ```
use bytes::Bytes;
use futures_util::future::FutureExt;
use http::{HeaderValue, Request, Response, StatusCode};
use http_body::{combinators::UnsyncBoxBody, Body, Full};
use std::{any::Any, panic::AssertUnwindSafe};
use tower_async_layer::Layer;
use tower_async_service::Service;
use crate::BoxError;
/// Layer that applies the [`CatchPanic`] middleware that catches panics and converts them into
/// `500 Internal Server` responses.
///
/// See the [module docs](self) for an example.
#[derive(Debug, Clone, Copy, Default)]
pub struct CatchPanicLayer<T> {
panic_handler: T,
}
impl CatchPanicLayer<DefaultResponseForPanic> {
/// Create a new `CatchPanicLayer` with the default panic handler.
pub fn new() -> Self {
CatchPanicLayer {
panic_handler: DefaultResponseForPanic,
}
}
}
impl<T> CatchPanicLayer<T> {
/// Create a new `CatchPanicLayer` with a custom panic handler.
pub fn custom(panic_handler: T) -> Self
where
T: ResponseForPanic,
{
Self { panic_handler }
}
}
impl<T, S> Layer<S> for CatchPanicLayer<T>
where
T: Clone,
{
type Service = CatchPanic<S, T>;
fn layer(&self, inner: S) -> Self::Service {
CatchPanic {
inner,
panic_handler: self.panic_handler.clone(),
}
}
}
/// Middleware that catches panics and converts them into `500 Internal Server` responses.
///
/// See the [module docs](self) for an example.
#[derive(Debug, Clone, Copy)]
pub struct CatchPanic<S, T> {
inner: S,
panic_handler: T,
}
impl<S> CatchPanic<S, DefaultResponseForPanic> {
/// Create a new `CatchPanic` with the default panic handler.
pub fn new(inner: S) -> Self {
Self {
inner,
panic_handler: DefaultResponseForPanic,
}
}
}
impl<S, T> CatchPanic<S, T> {
define_inner_service_accessors!();
/// Create a new `CatchPanic` with a custom panic handler.
pub fn custom(inner: S, panic_handler: T) -> Self
where
T: ResponseForPanic,
{
Self {
inner,
panic_handler,
}
}
}
impl<S, T, ReqBody, ResBody> Service<Request<ReqBody>> for CatchPanic<S, T>
where
S: Service<Request<ReqBody>, Response = Response<ResBody>>,
ResBody: Body<Data = Bytes> + Send + 'static,
ResBody::Error: Into<BoxError>,
T: ResponseForPanic + Clone,
T::ResponseBody: Body<Data = Bytes> + Send + 'static,
<T::ResponseBody as Body>::Error: Into<BoxError>,
{
type Response = Response<UnsyncBoxBody<Bytes, BoxError>>;
type Error = S::Error;
async fn call(&mut self, req: Request<ReqBody>) -> Result<Self::Response, Self::Error> {
let future = match std::panic::catch_unwind(AssertUnwindSafe(|| self.inner.call(req))) {
Ok(future) => future,
Err(panic_err) => {
return Ok(self
.panic_handler
.response_for_panic(panic_err)
.map(|body| body.map_err(Into::into).boxed_unsync()))
}
};
match AssertUnwindSafe(future).catch_unwind().await {
Ok(res) => match res {
Ok(res) => Ok(res.map(|body| body.map_err(Into::into).boxed_unsync())),
Err(err) => Err(err),
},
Err(panic_err) => Ok(self
.panic_handler
.response_for_panic(panic_err)
.map(|body| body.map_err(Into::into).boxed_unsync())),
}
}
}
/// Trait for creating responses from panics.
pub trait ResponseForPanic: Clone {
/// The body type used for responses to panics.
type ResponseBody;
/// Create a response from the panic error.
fn response_for_panic(
&mut self,
err: Box<dyn Any + Send + 'static>,
) -> Response<Self::ResponseBody>;
}
impl<F, B> ResponseForPanic for F
where
F: FnMut(Box<dyn Any + Send + 'static>) -> Response<B> + Clone,
{
type ResponseBody = B;
fn response_for_panic(
&mut self,
err: Box<dyn Any + Send + 'static>,
) -> Response<Self::ResponseBody> {
self(err)
}
}
/// The default `ResponseForPanic` used by `CatchPanic`.
///
/// It will log the panic message and return a `500 Internal Server` error response with an empty
/// body.
#[derive(Debug, Default, Clone, Copy)]
#[non_exhaustive]
pub struct DefaultResponseForPanic;
impl ResponseForPanic for DefaultResponseForPanic {
type ResponseBody = Full<Bytes>;
fn response_for_panic(
&mut self,
err: Box<dyn Any + Send + 'static>,
) -> Response<Self::ResponseBody> {
if let Some(s) = err.downcast_ref::<String>() {
tracing::error!("Service panicked: {}", s);
} else if let Some(s) = err.downcast_ref::<&str>() {
tracing::error!("Service panicked: {}", s);
} else {
tracing::error!(
"Service panicked but `CatchPanic` was unable to downcast the panic info"
);
};
let mut res = Response::new(Full::from("Service panicked"));
*res.status_mut() = StatusCode::INTERNAL_SERVER_ERROR;
#[allow(clippy::declare_interior_mutable_const)]
const TEXT_PLAIN: HeaderValue = HeaderValue::from_static("text/plain; charset=utf-8");
res.headers_mut()
.insert(http::header::CONTENT_TYPE, TEXT_PLAIN);
res
}
}
#[cfg(test)]
mod tests {
#![allow(unreachable_code)]
use super::*;
use hyper::{Body, Response};
use std::convert::Infallible;
use tower_async::{ServiceBuilder, ServiceExt};
#[tokio::test]
async fn panic_before_returning_future() {
let svc = ServiceBuilder::new()
.layer(CatchPanicLayer::new())
.service_fn(|_: Request<Body>| {
panic!("service panic");
async { Ok::<_, Infallible>(Response::new(Body::empty())) }
});
let req = Request::new(Body::empty());
let res = svc.oneshot(req).await.unwrap();
assert_eq!(res.status(), StatusCode::INTERNAL_SERVER_ERROR);
let body = hyper::body::to_bytes(res).await.unwrap();
assert_eq!(&body[..], b"Service panicked");
}
#[tokio::test]
async fn panic_in_future() {
let svc = ServiceBuilder::new()
.layer(CatchPanicLayer::new())
.service_fn(|_: Request<Body>| async {
panic!("future panic");
Ok::<_, Infallible>(Response::new(Body::empty()))
});
let req = Request::new(Body::empty());
let res = svc.oneshot(req).await.unwrap();
assert_eq!(res.status(), StatusCode::INTERNAL_SERVER_ERROR);
let body = hyper::body::to_bytes(res).await.unwrap();
assert_eq!(&body[..], b"Service panicked");
}
}