Fix fail_silently when session/client creation fails

Make sure backends actually fail silently when asked
(rather than raising inaccurate errors suggesting
coding problems).

Fixes #308

Author: medmunds

Diff for: CHANGELOG.rst

@@ -33,6 +33,10 @@ vNext
 Fixes
 ~~~~~
 
+* Fix misleading error messages when sending with ``fail_silently=True``
+  and session creation fails (e.g., with Amazon SES backend and missing
+  credentials). (Thanks to `@technolingo`_.)
+
 * **Postmark:** Fix spurious AnymailInvalidAddress in ``message.cc`` when
   inbound message has no Cc recipients. (Thanks to `@Ecno92`_.)
 
@@ -1455,6 +1459,7 @@ Features
 .. _@slinkymanbyday: https://github.com/slinkymanbyday
 .. _@swrobel: https://github.com/swrobel
 .. _@tcourtqtm: https://github.com/tcourtqtm
+.. _@technolingo: https://github.com/technolingo
 .. _@Thorbenl: https://github.com/Thorbenl
 .. _@tiltec:  https://github.com/tiltec
 .. _@tim-schilling: https://github.com/tim-schilling

Diff for: anymail/backends/amazon_ses.py

@@ -59,7 +59,7 @@ def open(self):
             self.client = boto3.session.Session(**self.session_params).client(
                 "ses", **self.client_params
             )
-        except BOTO_BASE_ERRORS:
+        except Exception:
             if not self.fail_silently:
                 raise
         else:
@@ -71,6 +71,22 @@ def close(self):
         # self.client.close()  # boto3 doesn't support (or require) client shutdown
         self.client = None
 
+    def _send(self, message):
+        if self.client:
+            return super()._send(message)
+        elif self.fail_silently:
+            # (Probably missing boto3 credentials in open().)
+            return False
+        else:
+            class_name = self.__class__.__name__
+            raise RuntimeError(
+                "boto3 Session has not been opened in {class_name}._send. "
+                "(This is either an implementation error in {class_name}, "
+                "or you are incorrectly calling _send directly.)".format(
+                    class_name=class_name
+                )
+            )
+
     def build_message_payload(self, message, defaults):
         # The SES SendRawEmail and SendBulkTemplatedEmail calls have
         # very different signatures, so use a custom payload for each

Diff for: anymail/backends/amazon_sesv2.py

@@ -63,7 +63,7 @@ def open(self):
             self.client = boto3.session.Session(**self.session_params).client(
                 "sesv2", **self.client_params
             )
-        except BOTO_BASE_ERRORS:
+        except Exception:
             if not self.fail_silently:
                 raise
         else:
@@ -75,6 +75,22 @@ def close(self):
         self.client.close()
         self.client = None
 
+    def _send(self, message):
+        if self.client:
+            return super()._send(message)
+        elif self.fail_silently:
+            # (Probably missing boto3 credentials in open().)
+            return False
+        else:
+            class_name = self.__class__.__name__
+            raise RuntimeError(
+                "boto3 Session has not been opened in {class_name}._send. "
+                "(This is either an implementation error in {class_name}, "
+                "or you are incorrectly calling _send directly.)".format(
+                    class_name=class_name
+                )
+            )
+
     def build_message_payload(self, message, defaults):
         if getattr(message, "template_id", UNSET) is not UNSET:
             # For simplicity, use SESv2 SendBulkEmail for all templated messages

Diff for: anymail/backends/base_requests.py

@@ -47,7 +47,12 @@ def close(self):
             self.session = None
 
     def _send(self, message):
-        if self.session is None:
+        if self.session:
+            return super()._send(message)
+        elif self.fail_silently:
+            # create_session failed
+            return False
+        else:
             class_name = self.__class__.__name__
             raise RuntimeError(
                 "Session has not been opened in {class_name}._send. "
@@ -56,7 +61,6 @@ def _send(self, message):
                     class_name=class_name
                 )
             )
-        return super()._send(message)
 
     def create_session(self):
         """Create the requests.Session object used by this instance of the backend.

Diff for: tests/test_amazon_ses_backend.py

@@ -393,6 +393,16 @@ def test_api_failure_fail_silently(self):
         sent = self.message.send(fail_silently=True)
         self.assertEqual(sent, 0)
 
+    def test_session_failure_fail_silently(self):
+        # Make sure fail_silently is respected if boto3.Session creation fails
+        # (e.g., due to invalid or missing credentials)
+        from botocore.exceptions import NoCredentialsError
+
+        self.mock_session.side_effect = NoCredentialsError()
+
+        sent = self.message.send(fail_silently=True)
+        self.assertEqual(sent, 0)
+
     def test_prevents_header_injection(self):
         # Since we build the raw MIME message, we're responsible for preventing header
         # injection. django.core.mail.EmailMessage.message() implements most of that

Diff for: tests/test_amazon_sesv2_backend.py

@@ -403,6 +403,16 @@ def test_api_failure_fail_silently(self):
         sent = self.message.send(fail_silently=True)
         self.assertEqual(sent, 0)
 
+    def test_session_failure_fail_silently(self):
+        # Make sure fail_silently is respected if boto3.Session creation fails
+        # (e.g., due to invalid or missing credentials)
+        from botocore.exceptions import NoCredentialsError
+
+        self.mock_session.side_effect = NoCredentialsError()
+
+        sent = self.message.send(fail_silently=True)
+        self.assertEqual(sent, 0)
+
     def test_prevents_header_injection(self):
         # Since we build the raw MIME message, we're responsible for preventing header
         # injection. django.core.mail.EmailMessage.message() implements most of that

Diff for: tests/test_base_backends.py

@@ -1,3 +1,5 @@
+from unittest import mock
+
 from django.test import SimpleTestCase, override_settings, tag
 
 from anymail.backends.base_requests import AnymailRequestsBackend, RequestsPayload
@@ -69,6 +71,14 @@ def test_timeout_setting(self):
         timeout = self.get_api_call_arg("timeout")
         self.assertEqual(timeout, 5)
 
+    @mock.patch(f"{__name__}.MinimalRequestsBackend.create_session")
+    def test_create_session_error_fail_silently(self, mock_create_session):
+        # If create_session fails and fail_silently is True,
+        # make sure _send doesn't raise a misleading error.
+        mock_create_session.side_effect = ValueError("couldn't create session")
+        sent = self.message.send(fail_silently=True)
+        self.assertEqual(sent, 0)
+
 
 @tag("live")
 @override_settings(EMAIL_BACKEND="tests.test_base_backends.MinimalRequestsBackend")