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Flask JSON required decorator
Demo of json_required decorator for API input validation/error handling
import inspect
import functools
import json
from traceback import format_exception
from flask import jsonify, request
import sys
from flask.exceptions import JSONBadRequest
from flask import Flask
import re
app = Flask(__name__)
def api_error_response(code=404, message="Requested resource was not found", errors=list()):
Convenience function for returning a JSON response that includes
appropriate error messages and code.
response = jsonify(dict(code=code, message=message, errors=errors, success=False))
response.status_code = code
return response
def bad_json_error_response():
Convenience function for returning an error message related to
malformed/missing JSON data.
return api_error_response(code=400,
message="There was a problem parsing the supplied JSON data. Please send valid JSON.")
def json_required(func=None, required_fields={}, validations=[]):
Decorator used to validate JSON input to an API request
if func is None:
return functools.partial(json_required, required_fields=required_fields, validations=validations)
def decorated_function(*args, **kwargs):
#If no JSON was supplied (or it didn't parse correctly)
if request.json is None:
return bad_json_error_response()
except JSONBadRequest:
return bad_json_error_response()
#Check for specific fields
errors = []
def check_required_fields(data, fields):
for field, requirements in fields.iteritems():
nested_fields = type(requirements) == dict
if data.get(field) in (None, ''):
if nested_fields:
error_msg = requirements.get('message')
error_msg = requirements
errors.append({'field': field, 'message': error_msg})
elif nested_fields:
check_required_fields(data[field], requirements.get('fields', {}))
check_required_fields(request.json, required_fields)
for validation_field, validation_message, validation_func in validations:
func_args = inspect.getargspec(validation_func).args
func_params = []
for arg in func_args:
if not validation_func(*func_params):
errors.append({'field': validation_field, 'message': validation_message})
if errors:
return api_error_response(code=422, message="JSON Validation Failed", errors=errors)
except Exception:
#For internal use, nice to have the traceback in the API response for debugging
#Probably don't want to include for public APIs
etype, value, tb = sys.exc_info()
error_info = ''.join(format_exception(etype, value, tb))
return api_error_response(code=500, message="Internal Error validating API input", errors=[{'message':error_info}])
return func(*args, **kwargs)
return decorated_function
EMAIL_REGEX = re.compile(r"[A-Za-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[A-Za-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[A-Za-z0-9](?:[A-Za-z0-9-]*[A-Za-z0-9])?\.)+[A-Za-z0-9](?:[A-Za-z0-9-]*[A-Za-z0-9])?")
def verify_account_available(email):
Check to see if this email is already registered
#Run a query, use an ORM, use Twilio to call someone and ask them :-)
return True
def valid_date_of_birth(date_of_birth):
Does the supplied date string meet our criteria for a date of birth
#Do whatever you need to do...
return True
@app.route("/do/something", methods=['POST'])
'first_name':"Please provide your first name.",
'last_name':"Please provide your last name.",
'email':'Please specify a valid email address',
'date_of_birth':'Please provide your date of birth'
('email', 'Please provide a valid email address', lambda email: email is not None and EMAIL_REGEX.match(email)),
('email', "This email is already in use. Please try a different email address.", verify_account_available),
('date_of_birth', 'Please provide a valid date of birth', valid_date_of_birth)
def do_something_useful():
#Confidently use the data in request.json...
return jsonify(dict(status='OK'))
if __name__ == "__main__":
with app.test_client() as client:
response =
data=json.dumps({ "first_name": "Brian",
"last_name": "Corbin",
"email": "",
"date_of_birth": "01/01/1970" }),
response_dict = json.loads(
assert response_dict['status'] == 'OK'
response =
data=json.dumps({ "last_name": "Corbin",
"email": "",
"date_of_birth": "01/01/1970" }),
response_dict = json.loads(
assert response.status_code == 422
assert response_dict['code'] == 422
assert response_dict['message'] == "JSON Validation Failed"
assert len(response_dict['errors']) == 1
assert response_dict['errors'][0]['field'] == 'first_name'
assert response_dict['errors'][0]['message'] == 'Please provide your first name.'
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