Add middleware for catching panics (#265)

Cargo.toml

@@ -60,6 +60,7 @@ members = [
     "tide-log",
     "tide-querystring",
     "tide-slog",
+    "tide-panic",
 ]
 
 [patch.crates-io]

tide-panic/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "tide-panic"
+version = "0.1.0"
+edition = "2018"
+authors = ["Tide Developers"]
+description = "Advanced panic support for Tide"
+documentation = "https://docs.rs/tide-panic"
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/rustasync/tide"
+
+[dependencies]
+futures-preview = "0.3.0-alpha.16"
+http = "0.1"
+http-service = "0.2.0"
+tide-core = { path = "../tide-core" }

tide-panic/LICENSE-APACHE

@@ -0,0 +1 @@
+../LICENSE-APACHE

tide-panic/LICENSE-MIT

@@ -0,0 +1 @@
+../LICENSE-MIT

tide-panic/src/catch_unwind.rs

@@ -0,0 +1,65 @@
+use futures::future::{BoxFuture, FutureExt, TryFutureExt};
+use http::status::StatusCode;
+use std::{
+    any::Any,
+    panic::{AssertUnwindSafe, RefUnwindSafe},
+};
+use tide_core::{
+    middleware::{Middleware, Next},
+    response::IntoResponse,
+    Context, Response,
+};
+
+/// A [`Middleware`] that will catch any panics from later middleware or handlers and return a
+/// response to the client.
+///
+/// It is **not** recommended to use this middleware for a general try/catch mechanism. The
+/// [`Result`] type is more appropriate to use for middleware/handlers that can fail on a regular
+/// basis.  Additionally, this middleware is not guaranteed to catch all panics, see the "Notes"
+/// section in the [`std::panic::catch_unwind`] docs.
+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: RefUnwindSafe + 'static> Middleware<State> for CatchUnwind {
+    fn handle<'a>(&'a self, cx: Context<State>, next: Next<'a, State>) -> BoxFuture<'a, Response> {
+        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()
+    }
+}

tide-panic/src/lib.rs

@@ -0,0 +1,18 @@
+#![feature(async_await, doc_cfg)]
+#![warn(
+    nonstandard_style,
+    rust_2018_idioms,
+    future_incompatible,
+    missing_debug_implementations,
+    missing_docs
+)]
+
+//! Advanced panic support for Tide applications.
+//!
+//! These middleware should not generally be necessary, they are provided for situations in which
+//! Tide's default panic handling is not usable by your application. Before using these you should
+//! have a good understanding of how the different components involved in [`std::panic`] works.
+
+mod catch_unwind;
+
+pub use crate::catch_unwind::CatchUnwind;