Set customizable default errors handler for flask app and blueprints.

You can register error handler for:

• api that returns JSON, default response is as API problem specification like (see https://tools.ietf.org/html/rfc7807). Instead you can use your own response implementation passed as argument to ErrorHandler class: it must be a decorator and must take 3 args, a dict response, status code and dict headers.
• web that returns html page or api response if request is XHR (for compatibility with old clients)
• you can register custom handlers for blueprint or the entire app

This module provide also an abstract ErrorDispatcher class in order to dispatch 404 or 405 error to the correct blueprint because flask Blueprint does not own url_prefix (see pallets/flask#1498).

There are 2 concrete implementation:

• SubdomainDispatcher: dispatch the error to the handler associate with blueprint with certain subdomain (if 2 or more Blueprint has the same subdomain the first blueprint handler matched is used)
• URLPrefixDispatcher: dispatch the error to the handler associate with blueprint with certain url prefix. This will not work if 2 Blueprint are registered under the same url prefix, for example: Blueprint A registered under /prefix/blueprint, Blueprint B registered under /prefix, this dispatcher executes the handler of B in both case if B is registered after A.

Moreover you can create you own dispatcher by extending ErrorDispatcher class and implementing dispatch method. Only the last ErrorDispatcher registered is executed. This is the best solution I have found, suggestions are welcome.

Notices:

1. In order to use correctly dispatcher you must set prefix or subdomain in Blueprints constructor, see example below.
2. If you use dispatcher do not register an handler to app object because it overwrites dispatcher.
3. When using a dispatcher you should use failure handler on app to catch unhandled exceptions.

Install flask_errors_handler using pip:

$ pip install Flask-ErrorsHandler

import flask

from flask_errors_handler import ErrorHandler

app = flask.Flask(__name__)
error = ErrorHandler(app, dispatcher='urlprefix')

api = flask.Blueprint('api', __name__, url_prefix='/api')
web = flask.Blueprint('web', __name__, url_prefix='/web')
custom = flask.Blueprint('custom', __name__, url_prefix='/custom')

error.web_register(web)
error.api_register(api)
error.failure_register(app)


@error.register(custom)
def error_handler(exc):
    return str(exc), 500, {'Content-Type': 'text/plain'}


@api.route('/')
def index():
    flask.abort(500, 'Error from api blueprint')


@web.route('/')
def index():
    flask.abort(500, 'Error from web blueprint')


@custom.route('/')
def index():
    flask.abort(500, 'Error from custom blueprint')


@app.route('/')
def index():
    raise NameError("test custom")


app.register_blueprint(web)
app.register_blueprint(api)
app.register_blueprint(custom)
app.run()

• Go to http://127.0.0.1:5000/api and see error message response as a JSON
• Go to http://127.0.0.1:5000/web and see error message response as an HTML page
• Go to http://127.0.0.1:5000/custom and see error message response as a plain text

1. ERROR_PAGE: (default: error.html) path of html template to use for show error message
2. ERROR_DEFAULT_MSG: (default: Unhandled Exception) default message for unhandled exceptions
3. ERROR_XHR_ENABLED: (default: True) enable or disable api response where request is XHR
4. ERROR_FORCE_CONTENT_TYPE: (True) force response content type to be api problem compliant
5. ERROR_CONTENT_TYPES: ('json', 'xml')) list of format types to force api problem content type
6. ERROR_DISPATCHER: dispatcher to use, one of: default, urlprefix, subdomain
7. ERROR_HANDLER: global error handler, one of: api, web

License MIT