Add global errorhandler

README.md

@@ -102,6 +102,29 @@ curl localhost:8080
 # Output: Hello world!
 ```
 
+### Quickstart: Error handling
+
+The framework includes an error handler that is similar to the
+[`flask.Flask.errorhandler`](https://flask.palletsprojects.com/en/1.1.x/api/#flask.Flask.errorhandler)
+function, which allows you to handle specific error types with a decorator:
+
+```python
+import functions_framework
+
+
+@functions_framework.errorhandler(ZeroDivisionError)
+def handle_zero_division(e):
+    return "I'm a teapot", 418
+
+
+def function(request):
+    1 / 0
+    return "Success", 200
+```
+
+This function will catch the `ZeroDivisionError` and return a different
+response instead.
+
 ### Quickstart: Build a Deployable Container
 
 1. Install [Docker](https://store.docker.com/search?type=edition&offering=community) and the [`pack` tool](https://buildpacks.io/docs/install-pack/).

src/functions_framework/__init__.py

@@ -228,6 +228,8 @@ def create_app(target=None, source=None, signature_type=None):
     # 5. Create the application
     app = flask.Flask(target, template_folder=template_folder)
     app.config["MAX_CONTENT_LENGTH"] = MAX_CONTENT_LENGTH
+    global errorhandler
+    errorhandler = app.errorhandler
 
     # 6. Execute the module, within the application context
     with app.app_context():

tests/test_functions.py

@@ -359,3 +359,16 @@ def test_legacy_function_returns_none(monkeypatch):
 
     assert resp.status_code == 200
     assert resp.data == b"OK"
+
+
+def test_errorhandler(monkeypatch):
+    source = TEST_FUNCTIONS_DIR / "errorhandler" / "main.py"
+    target = "function"
+
+    monkeypatch.setenv("ENTRY_POINT", target)
+
+    client = create_app(target, source).test_client()
+    resp = client.get("/")
+
+    assert resp.status_code == 418
+    assert resp.data == b"I'm a teapot"

tests/test_functions/errorhandler/main.py

@@ -0,0 +1,25 @@
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import functions_framework
+
+
+@functions_framework.errorhandler(ZeroDivisionError)
+def handle_zero_division(e):
+    return "I'm a teapot", 418
+
+
+def function(request):
+    1 / 0
+    return "Success", 200