[utils] Implement DRF custom exception handler

This will allow to log the exceptions comming from
DRF in case they cannot be properly propagated back
to the user.

beat/web/utils/drf.py

+# vim: set fileencoding=utf-8 :
+
+###############################################################################
+#                                                                             #
+# Copyright (c) 2020 Idiap Research Institute, http://www.idiap.ch/           #
+# Contact: beat.support@idiap.ch                                              #
+#                                                                             #
+# This file is part of the beat.web module of the BEAT platform.              #
+#                                                                             #
+# Commercial License Usage                                                    #
+# Licensees holding valid commercial BEAT licenses may use this file in       #
+# accordance with the terms contained in a written agreement between you      #
+# and Idiap. For further information contact tto@idiap.ch                     #
+#                                                                             #
+# Alternatively, this file may be used under the terms of the GNU Affero      #
+# Public License version 3 as published by the Free Software and appearing    #
+# in the file LICENSE.AGPL included in the packaging of this file.            #
+# The BEAT platform is distributed in the hope that it will be useful, but    #
+# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY  #
+# or FITNESS FOR A PARTICULAR PURPOSE.                                        #
+#                                                                             #
+# You should have received a copy of the GNU Affero Public License along      #
+# with the BEAT platform. If not, see http://www.gnu.org/licenses/.           #
+#                                                                             #
+###############################################################################
+
+"""
+Django REST framework helpers
+"""
+
+import logging
+
+from rest_framework.views import exception_handler
+from rest_framework.exceptions import APIException
+from rest_framework.status import is_client_error
+
+logger = logging.getLogger("beat.drf_exceptions")
+
+
+def custom_exception_handler(exc, context):
+    # Call REST framework's default exception handler first,
+    # to get the standard error response.
+    response = exception_handler(exc, context)
+
+    # check that a ValidationError exception is raised
+    if isinstance(exc, APIException):
+        # Log all client errors
+        if is_client_error(exc.status_code):
+            view = context["view"]
+            request = context["request"]
+            detail = {
+                "user": request.user.username,
+                "view": view.__class__.__name__,
+                "kwargs": view.kwargs,
+                "error": exc.detail,
+            }
+            logger.warning("Error occured: {}".format(detail))
+
+    return response