Unhandled exceptions in a RESTful API are not getting jsonify'ed

Question

I have the following code - It has a http handler function (func1) and a RESTful API (func2) and they are reachable through URLs /test1 and /test2. I have a exception handler function (exception_handler) which is decorated by app.errorhandler() to ensure that all unhandled exceptions are jsonify'ed and sent back as response.

from flask import Flask, jsonify
from flask.ext.restful import Resource, Api

app = Flask(__name__)
api = Api(app)

@app.errorhandler(Exception)
def exception_handler(e):
  return jsonify(reason=e.message), 500

@app.route("/test1", methods=["GET"])
def func1():
    raise Exception('Exception - test1')

class func2(Resource):
  def get(self):
    raise Exception('Exception - test2')

api.add_resource(func2, '/test2')

if __name__ == "__main__":
    app.run(debug=True)

Now converting an unhandled exception to a HTTP response with a JSON containing exception message works fine for a normal http handler function i.e. func1 but the same does not work for a RESTful API (created using Resource) i.e func2.

The following works fine as expected with func1:

$ curl http://127.0.0.1:5000/test1 -X GET
{
  "reason": "Exception - test1"
}

With func2 we are getting a {"message": "Internal Server Error", "status": 500} instead of {"reason": "Exception - test2"}

$ curl http://127.0.0.1:5000/test2 -X GET
{
    "message": "Internal Server Error",
    "status": 500
}

So the question is why the unhandled exceptions in RESTful API is not converted to JSON using app.errorhandler? or is there any other way of doing this?

Answer 1

This because Flask-Restful monkeypatch default Flask.handle_user_exception which will have specific logic for Flask-Restful endpoints and default behaviour for other endpoints.