feat(dx): add @app.exception_handler decorator syntax

oxyroute/app.py

@@ -383,6 +383,23 @@ def add_exception_handler(
         """
         self._app.add_exception_handler(exc_type, handler)
 
+    def exception_handler(self, exc_type: type[BaseException]) -> Callable[[F], F]:
+        """
+        Decorator to register a global exception handler for a specific exception type.
+
+        Example::
+
+            @app.exception_handler(ValueError)
+            def handle_value_error(scope, exc: ValueError):
+                return Response(status=400, body=str(exc).encode())
+        """
+
+        def decorator(handler: F) -> F:
+            self.add_exception_handler(exc_type, handler)
+            return handler
+
+        return decorator
+
     def set_middleware(self, handler: Callable[..., Any] | None) -> None:
         """
         One optional pre-route callback ``(scope, protocol)`` — return ``None`` to pass through.

tests/test_exception_handlers.py

@@ -15,11 +15,6 @@ class SubCustomError(CustomError):
 
     app = App()
 
-    # Note: the `add_exception_handler` method might be used as a decorator or a regular method.
-    # We didn't implement it as a decorator returning the function, but in our `app.py` it's just:
-    # def add_exception_handler(self, exc_type: type[BaseException], handler: Callable[..., Any]) -> None:
-    # So we call it directly.
-
     def handle_custom_error(scope, exc):
         return Response(status=400, body=exc.msg.encode())
 
@@ -56,3 +51,30 @@ async def _run() -> None:
             assert r3.status_code == 500
 
     asyncio.run(_run())
+
+
+def test_exception_handler_decorator():
+    """@app.exception_handler(exc_type) decorator syntax (issue #274)."""
+
+    class DecoratorError(Exception):
+        def __init__(self, msg: str):
+            self.msg = msg
+
+    app = App()
+
+    @app.exception_handler(DecoratorError)
+    def handle_decorator_error(scope, exc: DecoratorError):
+        return Response(status=422, body=f"decorated:{exc.msg}".encode())
+
+    @app.get("/decorated-error")
+    def raise_decorated() -> str:
+        raise DecoratorError("via-decorator")
+
+    async def _run() -> None:
+        transport = httpx.ASGITransport(app=asgi_test_app(app))
+        async with httpx.AsyncClient(transport=transport, base_url="http://test") as c:
+            r = await c.get("/decorated-error")
+            assert r.status_code == 422
+            assert r.text == "decorated:via-decorator"
+
+    asyncio.run(_run())