Add middleware for catching panics

Author: Nemo157

src/catch_unwind.rs

@@ -0,0 +1,57 @@
+use crate::{
+    middleware::{Middleware, Next},
+    response::IntoResponse,
+    Context, Response,
+};
+use futures::future::{BoxFuture, FutureExt, TryFutureExt};
+use http::status::StatusCode;
+use std::any::Any;
+
+/// A [`Middleware`] that will catch any panics from later middleware or handlers and return a
+/// response to the client.
+pub struct CatchUnwind {
+    f: Box<dyn Fn(Box<dyn Any + Send + 'static>) -> Response + Send + Sync>,
+}
+
+impl CatchUnwind {
+    /// Create a [`CatchUnwind`] which will respond with [`StatusCode::INTERNAL_SERVER_ERROR`] when
+    /// any panic is caught.
+    pub fn new() -> Self {
+        Self::with_response(|_| {
+            "Internal server error"
+                .with_status(StatusCode::INTERNAL_SERVER_ERROR)
+                .into_response()
+        })
+    }
+
+    /// Create a [`CatchUnwind`] with a custom function to generate the response, the function will
+    /// be passed the caught panic.
+    pub fn with_response(
+        response: impl Fn(Box<dyn Any + Send + 'static>) -> Response + Send + Sync + 'static,
+    ) -> Self {
+        Self {
+            f: Box::new(response),
+        }
+    }
+}
+
+impl<State: 'static> Middleware<State> for CatchUnwind {
+    fn handle<'a>(&'a self, cx: Context<State>, next: Next<'a, State>) -> BoxFuture<'a, Response> {
+        std::panic::AssertUnwindSafe(next.run(cx))
+            .catch_unwind()
+            .unwrap_or_else(move |err| (self.f)(err))
+            .boxed()
+    }
+}
+
+impl Default for CatchUnwind {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl std::fmt::Debug for CatchUnwind {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("CatchUnwind").finish()
+    }
+}

src/lib.rs

@@ -20,6 +20,8 @@
 #[doc(include = "../README.md")]
 const _README: () = ();
 
+mod catch_unwind;
+
 pub use http;
 
 #[cfg(feature = "cookies")]
@@ -58,6 +60,9 @@ pub mod middleware {
     // Core
     pub use tide_core::middleware::{Middleware, Next};
 
+    // Trivial middleware defined here
+    pub use crate::catch_unwind::CatchUnwind;
+
     // Exports from tide repo.
     pub use tide_headers::DefaultHeaders;
     pub use tide_log::RequestLogger;