Switch error messages to have content type JSON

Fixes #893

endpoints/decorated.py

@@ -1,7 +1,7 @@
 import logging
 import json
 
-from flask import make_response
+from flask import make_response, jsonify
 from app import app
 from util.useremails import CannotSendEmailException
 from util.config.provider.baseprovider import CannotWriteConfigException
@@ -13,20 +13,25 @@ logger = logging.getLogger(__name__)
 @app.errorhandler(model.DataModelException)
 def handle_dme(ex):
   logger.exception(ex)
-  return make_response(json.dumps({'message': ex.message}), 400)
+  response = jsonify({'message': ex.message})
+  response.status_code = 400
+  return response
 
 @app.errorhandler(CannotSendEmailException)
 def handle_emailexception(ex):
   message = 'Could not send email. Please contact an administrator and report this problem.'
-  return make_response(json.dumps({'message': message}), 400)
+  response = jsonify({'message': message})
+  response.status_code = 400
+  return response
 
 @app.errorhandler(CannotWriteConfigException)
 def handle_configexception(ex):
   message = ('Configuration could not be written to the mounted volume. \n' +
              'Please make sure the mounted volume is not read-only and restart ' +
              'the setup process. \n\nIssue: %s' % ex)
-
-  return make_response(json.dumps({'message': message}), 400)
+  response = jsonify({'message': message})
+  response.status_code = 400
+  return response
 
 @app.errorhandler(model.TooManyLoginAttemptsException)
 @crossdomain(origin='*', headers=['Authorization', 'Content-Type'])