From 4ce18167e70d3becb6f24cc1b8fc5929e02294bf Mon Sep 17 00:00:00 2001
From: Yurii Karabas <1998uriyyo@gmail.com>
Date: Thu, 5 Nov 2020 23:21:40 +0200
Subject: [PATCH] =?UTF-8?q?=F0=9F=90=9B=20Fix=20bug=20overriding=20custom?=
 =?UTF-8?q?=20HTTPException=20and=20RequestValidationError=20from=20except?=
 =?UTF-8?q?ion=5Fhandlers=20(#1924)?=
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---
 fastapi/applications.py          |  8 +++---
 tests/test_exception_handlers.py | 44 ++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 4 deletions(-)
 create mode 100644 tests/test_exception_handlers.py

diff --git a/fastapi/applications.py b/fastapi/applications.py
index f3ce08e9f..24a242a4e 100644
--- a/fastapi/applications.py
+++ b/fastapi/applications.py
@@ -66,6 +66,10 @@ class FastAPI(Starlette):
         self.exception_handlers = (
             {} if exception_handlers is None else dict(exception_handlers)
         )
+        self.exception_handlers.setdefault(HTTPException, http_exception_handler)
+        self.exception_handlers.setdefault(
+            RequestValidationError, request_validation_exception_handler
+        )
 
         self.user_middleware = [] if middleware is None else list(middleware)
         self.middleware_stack = self.build_middleware_stack()
@@ -165,10 +169,6 @@ class FastAPI(Starlette):
                 )
 
             self.add_route(self.redoc_url, redoc_html, include_in_schema=False)
-        self.add_exception_handler(HTTPException, http_exception_handler)
-        self.add_exception_handler(
-            RequestValidationError, request_validation_exception_handler
-        )
 
     async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
         if self.root_path:
diff --git a/tests/test_exception_handlers.py b/tests/test_exception_handlers.py
new file mode 100644
index 000000000..6153f7ab9
--- /dev/null
+++ b/tests/test_exception_handlers.py
@@ -0,0 +1,44 @@
+from fastapi import FastAPI, HTTPException
+from fastapi.exceptions import RequestValidationError
+from fastapi.testclient import TestClient
+from starlette.responses import JSONResponse
+
+
+def http_exception_handler(request, exception):
+    return JSONResponse({"exception": "http-exception"})
+
+
+def request_validation_exception_handler(request, exception):
+    return JSONResponse({"exception": "request-validation"})
+
+
+app = FastAPI(
+    exception_handlers={
+        HTTPException: http_exception_handler,
+        RequestValidationError: request_validation_exception_handler,
+    }
+)
+
+client = TestClient(app)
+
+
+@app.get("/http-exception")
+def route_with_http_exception():
+    raise HTTPException(status_code=400)
+
+
+@app.get("/request-validation/{param}/")
+def route_with_request_validation_exception(param: int):
+    pass  # pragma: no cover
+
+
+def test_override_http_exception():
+    response = client.get("/http-exception")
+    assert response.status_code == 200
+    assert response.json() == {"exception": "http-exception"}
+
+
+def test_override_request_validation_exception():
+    response = client.get("/request-validation/invalid")
+    assert response.status_code == 200
+    assert response.json() == {"exception": "request-validation"}