trace Django Rest Framework (#389)

* Patch rest_framework
* Add a test app for rest_framework
* Add unit tests for rest_framework integration
* Use the existing django tox env to test rest_framework
* Modify the docs

Author: Gabin Marignier

.circleci/config.yml

@@ -298,11 +298,13 @@ jobs:
               - tox-cache-django-{{ checksum "tox.ini" }}
       - run: tox -e '{py27,py34,py35,py36}-django{18,19,110,111}-djangopylibmc06-djangoredis45-pylibmc-redis{210}-memcached' --result-json /tmp/django.1.results
       - run: tox -e '{py27,py34,py35,py36}-django-autopatch{18,19,110,111}-djangopylibmc06-djangoredis45-pylibmc-redis{210}-memcached' --result-json /tmp/django.2.results
+      - run: tox -e '{py27,py34,py35,py36}-django-drf{110,111}-djangorestframework{34,35,36,37}' --result-json /tmp/django.3.results
       - persist_to_workspace:
           root: /tmp
           paths:
             - django.1.results
             - django.2.results
+            - django.3.results
       - save_cache:
           key: tox-cache-django-{{ checksum "tox.ini" }}
           paths:

ddtrace/contrib/django/apps.py

@@ -1,7 +1,7 @@
 import logging
 
 # 3rd party
-from django.apps import AppConfig
+from django.apps import AppConfig, apps
 
 # project
 from .db import patch_db
@@ -68,3 +68,11 @@ def ready(self):
                     patch_cache(tracer)
                 except Exception:
                     log.exception('error patching Django cache')
+
+            # Instrument rest_framework app to trace custom exception handling.
+            if apps.is_installed('rest_framework'):
+                try:
+                    from .restframework import patch_restframework
+                    patch_restframework(tracer)
+                except Exception:
+                    log.exception('error patching rest_framework app')

ddtrace/contrib/django/restframework.py

@@ -0,0 +1,42 @@
+from wrapt import wrap_function_wrapper as wrap
+
+from rest_framework.views import APIView
+
+from ddtrace.util import unwrap
+
+
+def patch_restframework(tracer):
+    """ Patches rest_framework app.
+
+    To trace exceptions occuring during view processing we currently use a TraceExceptionMiddleware.
+    However the rest_framework handles exceptions before they come to our middleware.
+    So we need to manually patch the rest_framework exception handler
+    to set the exception stack trace in the current span.
+
+    """
+
+    def _traced_handle_exception(wrapped, instance, args, kwargs):
+        """ Sets the error message, error type and exception stack trace to the current span
+            before calling the original exception handler.
+        """
+        span = tracer.current_span()
+        if span is not None:
+            span.set_traceback()
+
+        return wrapped(*args, **kwargs)
+
+    # do not patch if already patched
+    if getattr(APIView, '_datadog_patch', False):
+        return
+    else:
+        setattr(APIView, '_datadog_patch', True)
+
+    # trace the handle_exception method
+    wrap('rest_framework.views', 'APIView.handle_exception', _traced_handle_exception)
+
+
+def unpatch_restframework():
+    """ Unpatches rest_framework app."""
+    if getattr(APIView, '_datadog_patch', False):
+        setattr(APIView, '_datadog_patch', False)
+        unwrap(APIView, 'handle_exception')

docs/index.rst

@@ -538,7 +538,9 @@ We officially support Python 2.7, 3.4 and above.
 | celery          | >= 3.1             |
 +-----------------+--------------------+
 | cassandra       | >= 3.5             |
-+-----------------+--------------------+
++---------------------+----------------+
+| djangorestframework | >= 3.4         |
++---------------------+----------------+
 | django          | >= 1.8             |
 +-----------------+--------------------+
 | elasticsearch   | >= 1.6             |

tests/contrib/django/test_tracing_disabled.py

@@ -1,6 +1,6 @@
 # 3rd party
 from django.apps import apps
-from django.test import TestCase, override_settings
+from django.test import TestCase
 
 # project
 from ddtrace.tracer import Tracer
@@ -12,23 +12,25 @@
 
 class DjangoTracingDisabledTest(TestCase):
     def setUp(self):
-        tracer = Tracer()
-        tracer.writer = DummyWriter()
-        self.tracer = tracer
-        # Backup the old conf
-        self.backupTracer = settings.TRACER
+        # backup previous conf
         self.backupEnabled = settings.ENABLED
-        # Disable tracing
+        self.backupTracer = settings.TRACER
+
+        # Use a new tracer to be sure that a new service
+        # would be sent to the the writer
+        self.tracer = Tracer()
+        self.tracer.writer = DummyWriter()
+
+        # Restart app with tracing disabled
         settings.ENABLED = False
-        settings.TRACER = tracer
-        # Restart the app
-        app = apps.get_app_config('datadog_django')
-        app.ready()
+        self.app = apps.get_app_config('datadog_django')
+        self.app.ready()
 
     def tearDown(self):
         # Reset the original settings
         settings.ENABLED = self.backupEnabled
         settings.TRACER = self.backupTracer
+        self.app.ready()
 
     def test_no_service_info_is_written(self):
         services = self.tracer.writer.pop_services()

tests/contrib/djangorestframework/__init__.py

@@ -0,0 +1,14 @@
+from rest_framework.views import exception_handler
+from rest_framework.response import Response
+from rest_framework.exceptions import APIException
+from rest_framework import status
+
+
+def custom_exception_handler(exc, context):
+    response = exception_handler(exc, context)
+
+    # We overwrite the response status code to 500
+    if response is not None:
+        return Response({'detail': str(exc)}, status=status.HTTP_500_INTERNAL_SERVER_ERROR)
+
+    return response

tests/contrib/djangorestframework/app/__init__.py

@@ -0,0 +1,101 @@
+"""
+Settings configuration for the Django web framework. Update this
+configuration if you need to change the default behavior of
+Django during tests
+"""
+import os
+import django
+
+
+BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+
+DATABASES = {
+    'default': {
+        'ENGINE': 'django.db.backends.sqlite3',
+        'NAME': ':memory:'
+    }
+}
+
+SITE_ID = 1
+SECRET_KEY = 'not_very_secret_in_tests'
+USE_I18N = True
+USE_L10N = True
+STATIC_URL = '/static/'
+ROOT_URLCONF = 'app.views'
+
+TEMPLATES = [
+    {
+        'BACKEND': 'django.template.backends.django.DjangoTemplates',
+        'DIRS': [
+            os.path.join(BASE_DIR, 'app', 'templates'),
+        ],
+        'APP_DIRS': True,
+        'OPTIONS': {
+            'context_processors': [
+                'django.template.context_processors.debug',
+                'django.template.context_processors.request',
+                'django.contrib.auth.context_processors.auth',
+                'django.contrib.messages.context_processors.messages',
+            ],
+        },
+    },
+]
+
+if django.VERSION >= (1, 10):
+    MIDDLEWARE = [
+        'django.contrib.sessions.middleware.SessionMiddleware',
+        'django.middleware.common.CommonMiddleware',
+        'django.middleware.csrf.CsrfViewMiddleware',
+        'django.contrib.auth.middleware.AuthenticationMiddleware',
+        'django.contrib.auth.middleware.SessionAuthenticationMiddleware',
+        'django.contrib.messages.middleware.MessageMiddleware',
+        'django.middleware.clickjacking.XFrameOptionsMiddleware',
+        'django.middleware.security.SecurityMiddleware',
+
+        'tests.contrib.django.app.middlewares.CatchExceptionMiddleware',
+    ]
+
+# Always add the legacy conf to make sure we handle it properly
+# Pre 1.10 style
+MIDDLEWARE_CLASSES = [
+    'django.contrib.sessions.middleware.SessionMiddleware',
+    'django.middleware.common.CommonMiddleware',
+    'django.middleware.csrf.CsrfViewMiddleware',
+    'django.contrib.auth.middleware.AuthenticationMiddleware',
+    'django.contrib.auth.middleware.SessionAuthenticationMiddleware',
+    'django.contrib.messages.middleware.MessageMiddleware',
+    'django.middleware.clickjacking.XFrameOptionsMiddleware',
+    'django.middleware.security.SecurityMiddleware',
+
+    'tests.contrib.django.app.middlewares.CatchExceptionMiddleware',
+]
+
+INSTALLED_APPS = [
+    'django.contrib.admin',
+    'django.contrib.auth',
+    'django.contrib.contenttypes',
+    'django.contrib.sessions',
+
+    # tracer app
+    'ddtrace.contrib.django',
+
+    # djangorestframework
+    'rest_framework'
+]
+
+DATADOG_TRACE = {
+    # tracer with a DummyWriter
+    'TRACER': 'tests.contrib.django.utils.tracer',
+    'ENABLED': True,
+    'TAGS': {
+        'env': 'test',
+    },
+}
+
+REST_FRAMEWORK = {
+    'DEFAULT_PERMISSION_CLASSES': [
+        'rest_framework.permissions.IsAdminUser',
+    ],
+
+    'EXCEPTION_HANDLER': 'app.exceptions.custom_exception_handler'
+}

tests/contrib/djangorestframework/app/exceptions.py

@@ -0,0 +1,31 @@
+from django.conf.urls import url, include
+from django.contrib.auth.models import User, Group
+from django.http import HttpResponse
+
+from rest_framework import viewsets, routers, serializers
+from rest_framework.exceptions import APIException
+
+
+class UserSerializer(serializers.HyperlinkedModelSerializer):
+    class Meta:
+        model = User
+        fields = ('url', 'username', 'email', 'groups')
+
+
+class UserViewSet(viewsets.ModelViewSet):
+    """
+    API endpoint that allows users to be viewed or edited.
+    """
+    queryset = User.objects.all().order_by('-date_joined')
+    serializer_class = UserSerializer
+
+
+router = routers.DefaultRouter()
+router.register(r'users', UserViewSet)
+
+# Wire up our API using automatic URL routing.
+# Additionally, we include login URLs for the browsable API.
+urlpatterns = [
+    url(r'^', include(router.urls)),
+    url(r'^api-auth/', include('rest_framework.urls', namespace='rest_framework')),
+]