Compatibility with earlier Python 2.7 versions

Compatibility with Python 2.7 versions older than 2.7.7

* Use Django's constant_time_compare method
* Include sparkpost in test requirements
* Don't use non-public `EnvironmentVarGuard` in tests

Fixes #41

anymail/webhooks/mailgun.py

@@ -3,6 +3,7 @@ from datetime import datetime
 
 import hashlib
 import hmac
+from django.utils.crypto import constant_time_compare
 from django.utils.timezone import utc
 
 from .base import AnymailBaseWebhookView
@@ -34,7 +35,7 @@ class MailgunBaseWebhookView(AnymailBaseWebhookView):
             raise AnymailWebhookValidationFailure("Mailgun webhook called without required security fields")
         expected_signature = hmac.new(key=self.api_key, msg='{}{}'.format(timestamp, token).encode('ascii'),
                                       digestmod=hashlib.sha256).hexdigest()
-        if not hmac.compare_digest(signature, expected_signature):
+        if not constant_time_compare(signature, expected_signature):
             raise AnymailWebhookValidationFailure("Mailgun webhook called with incorrect signature")
 
     def parse_events(self, request):

anymail/webhooks/mandrill.py

@@ -4,6 +4,7 @@ from datetime import datetime
 import hashlib
 import hmac
 from base64 import b64encode
+from django.utils.crypto import constant_time_compare
 from django.utils.timezone import utc
 
 from .base import AnymailBaseWebhookView
@@ -44,7 +45,7 @@ class MandrillSignatureMixin(object):
 
         expected_signature = b64encode(hmac.new(key=self.webhook_key, msg=signed_data.encode('utf-8'),
                                                 digestmod=hashlib.sha1).digest())
-        if not hmac.compare_digest(signature, expected_signature):
+        if not constant_time_compare(signature, expected_signature):
             raise AnymailWebhookValidationFailure("Mandrill webhook called with incorrect signature")
 
 

setup.py

@@ -47,7 +47,7 @@ setup(
     },
     include_package_data=True,
     test_suite="runtests.runtests",
-    tests_require=["mock"],
+    tests_require=["mock", "sparkpost"],
     classifiers=[
         "Development Status :: 2 - Pre-Alpha",
         "Programming Language :: Python",

tests/test_sparkpost_backend.py

@@ -3,6 +3,7 @@
 from datetime import datetime, date
 from email.mime.base import MIMEBase
 from email.mime.image import MIMEImage
+import os
 
 import requests
 import six
@@ -17,13 +18,6 @@ from anymail.exceptions import (AnymailAPIError, AnymailUnsupportedFeature, Anym
                                 AnymailConfigurationError)
 from anymail.message import attach_inline_image_file
 
-try:
-    # noinspection PyUnresolvedReferences
-    from test.support import EnvironmentVarGuard  # python3
-except ImportError:
-    # noinspection PyUnresolvedReferences
-    from test.test_support import EnvironmentVarGuard  # python2
-
 from .utils import AnymailTestMixin, decode_att, SAMPLE_IMAGE_FILENAME, sample_image_path, sample_image_content
 
 
@@ -579,8 +573,9 @@ class SparkPostBackendImproperlyConfiguredTests(SimpleTestCase, AnymailTestMixin
 
     def test_api_key_in_env(self):
         """SparkPost package allows API key in env var; make sure Anymail works with that"""
-        with EnvironmentVarGuard() as env:
+        with patch.dict(
-            env['SPARKPOST_API_KEY'] = 'key_from_environment'
+                os.environ,
+                {'SPARKPOST_API_KEY': 'key_from_environment'}):
             conn = mail.get_connection()
             # Poke into implementation details to verify:
             self.assertIsNone(conn.api_key)  # Anymail prop