how to get access to error message from abort command when using custom error handler

Question

Using a python flask server, I want to be able to throw an http error response with the abort command and use a custom response string and a custom message in the body

@app.errorhandler(400)
def custom400(error):
    response = jsonify({'message': error.message})
    response.status_code = 404
    response.status = 'error.Bad Request'
    return response

abort(400,'{"message":"custom error message to appear in body"}')

But the error.message variable comes up as an empty string. I can't seem to find documentation on how to get access to the second variable of the abort function with a custom error handler

Sexpot

Is error.description what you're looking for? – Saturant

Answer 1

If you look at flask/__init__.py you will see that abort is actually imported from werkzeug.exceptions. Looking at the Aborter class, we can see that when called with a numeric code, the particular HTTPException subclass is looked up and called with all of the arguments provided to the Aborter instance. Looking at HTTPException, paying particular attention to lines 85-89 we can see that the second argument passed to HTTPException.__init__ is stored in the description property, as @dirn pointed out.

You can either access the message from the description property:

@app.errorhandler(400)
def custom400(error):
    response = jsonify({'message': error.description['message']})
    # etc.

abort(400, {'message': 'custom error message to appear in body'})

or just pass the description in by itself:

@app.errorhandler(400)
def custom400(error):
    response = jsonify({'message': error.description})
    # etc.

abort(400, 'custom error message to appear in body')

Focalize

This is a great way to extend abort's functionality with custom error messages. Thank you for this – Devoir

Is there a way to do this with every status code instead of having to write a custom error handler for each code? Ex: abort(409, 'There was a time conflict'), abort(400, 'custom error message to appear in body') – Enthusiasm

Duplicate answer - https://mcmap.net/q/64822/-sending-json-and-status-code-with-a-flask-response-duplicate – Singlecross

Answer 2

People rely on abort() too much. The truth is that there are much better ways to handle errors.

For example, you can write this helper function:

def bad_request(message):
    response = jsonify({'message': message})
    response.status_code = 400
    return response

Then from your view function you can return an error with:

@app.route('/')
def index():
    if error_condition:
        return bad_request('message that appears in body')

If the error occurs deeper in your call stack in a place where returning a response isn't possible then you can use a custom exception. For example:

class BadRequestError(ValueError):
    pass

@app.errorhandler(BadRequestError)
def bad_request_handler(error):
    return bad_request(str(error))

Then in the function that needs to issue the error you just raise the exception:

def some_function():
    if error_condition:
        raise BadRequestError('message that appears in the body')

I hope this helps.

Damick

is it preferable (faster) to return bad_request(...) directly when you can rather than just raise BadRequestError(...) ? – Hussy

You can raise abort anywhere when you want, no need to return. – Refraction

How is this any better? When not done from a view (and you need to register the error handler), the only difference is that you call raise BadRequestError instead of abort, with the added complication of having to register a custom exception. – Faint

Answer 3

I simply do it like this:

    abort(400, description="Required parameter is missing")

Ashleyashli

The best answer in my opinion. – Empale

When you want to return a json type response. You need make_response. – Refraction

To clarify Minh's comment from Jul 7, in Werkzeug>=1.0.1 the code in this answer will generate a proper JSON response. I was even able to pass a dict as description and Werkzeug correctly generated a nested JSON response. – Nievelt

Unfortunately this returns HTML I do not want. I just want the message to print ONLY. Here is what curl output looks like: <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> <title>403 Forbidden</title> <h1>Forbidden</h1> <p>Required parameter is missing</p> – Evocative

Answer 4

flask.abort also accepts flask.Response

abort(make_response(jsonify(message="Error message"), 400))

Barbarous

You even not need to using jsonify: abort(make_response({'message': 'Error message'}, 400)) – Refraction