feat: handle errors in async middlewares

errors thrown in async middlewares would usually lead to
unhandled promise rejections and wouldn't trigger the express
error handler.

this change catches exceptions in async middlewares and forwards
them to the express error handler by calling `next`

Co-authored-by: Björn Brauer <[email protected]>
Co-authored-by: Jonas Holland <[email protected]>

packages/express/lib/serve.js

@@ -11,6 +11,25 @@ const isPlainObject = require('is-plain-obj');
 
 const { Router } = express;
 
+function wrapMiddleware(middleware, domain) {
+  return Object.defineProperty(
+    domain.bind((...args) => {
+      try {
+        const maybePromise = middleware(...args);
+        if (maybePromise && typeof maybePromise.catch === 'function') {
+          maybePromise.catch(args[args.length - 1]);
+        }
+      } catch (e) {
+        args[args.length - 1](e);
+      }
+    }),
+    'length',
+    {
+      value: middleware.length,
+    }
+  );
+}
+
 module.exports = (mode, { configureServer, handleError }) => {
   const phases = ['initial', 'files', 'parse', 'routes', 'final'].reduce(
     (result, key) => [...result, `pre${key}`, key, `post${key}`],
@@ -36,16 +55,12 @@ module.exports = (mode, { configureServer, handleError }) => {
         const handlers = [].concat(handler);
         container[method](
           path,
-          ...handlers.map((handler) => domain.bind(handler))
+          ...handlers.map((handler) => wrapMiddleware(handler, domain))
         );
       } else {
         const middlewares = [].concat(middleware);
         container.use(
-          ...middlewares.map((middleware) =>
-            Object.defineProperty(domain.bind(middleware), 'length', {
-              value: middleware.length,
-            })
-          )
+          ...middlewares.map((middleware) => wrapMiddleware(middleware, domain))
         );
       }
     });