Upgrade requests exceptions to AnymailRequestsAPIError

Catch and re-raise requests.RequestException in
AnymailRequestsBackend.post_to_esp.

* AnymailRequestsAPIError is needed for proper
  fail_silently handling.
* Retain original requests exception type, to avoid
  breaking existing code that might look for specific
  requests exceptions.

Closes #16

anymail/backends/base_requests.py

@@ -65,7 +65,15 @@ def post_to_esp(self, payload, message):
         Can raise AnymailRequestsAPIError for HTTP errors in the post
         """
         params = payload.get_request_params(self.api_url)
-        response = self.session.request(**params)
+        try:
+            response = self.session.request(**params)
+        except requests.RequestException as err:
+            # raise an exception that is both AnymailRequestsAPIError
+            # and the original requests exception type
+            exc_class = type('AnymailRequestsAPIError', (AnymailRequestsAPIError, type(err)), {})
+            raise exc_class(
+                "Error posting to %s:" % params.get('url', '<missing url>'),
+                raised_from=err, email_message=message, payload=payload)
         self.raise_for_status(response, payload, message)
         return response
 

anymail/exceptions.py

@@ -1,4 +1,5 @@
 import json
+from traceback import format_exception_only
 
 from django.core.exceptions import ImproperlyConfigured, SuspiciousOperation
 from requests import HTTPError
@@ -18,11 +19,13 @@ def __init__(self, *args, **kwargs):
           status_code: HTTP status code of response to ESP send call
           payload: data arg (*not* json-stringified) for the ESP send call
           response: requests.Response from the send call
+          raised_from: original/wrapped Exception
         """
         self.backend = kwargs.pop('backend', None)
         self.email_message = kwargs.pop('email_message', None)
         self.payload = kwargs.pop('payload', None)
         self.status_code = kwargs.pop('status_code', None)
+        self.raised_from = kwargs.pop('raised_from', None)
         if isinstance(self, HTTPError):
             # must leave response in kwargs for HTTPError
             self.response = kwargs.get('response', None)
@@ -33,6 +36,7 @@ def __init__(self, *args, **kwargs):
     def __str__(self):
         parts = [
             " ".join([str(arg) for arg in self.args]),
+            self.describe_raised_from(),
             self.describe_send(),
             self.describe_response(),
         ]
@@ -68,6 +72,12 @@ def describe_response(self):
                 pass
         return description
 
+    def describe_raised_from(self):
+        """Return the original exception"""
+        if self.raised_from is None:
+            return None
+        return ''.join(format_exception_only(type(self.raised_from), self.raised_from)).strip()
+
 
 class AnymailAPIError(AnymailError):
     """Exception for unsuccessful response from ESP's API."""

tests/test_mailgun_backend.py

@@ -12,7 +12,7 @@
 from django.test.utils import override_settings
 from django.utils.timezone import get_fixed_timezone, override as override_current_timezone
 
-from anymail.exceptions import AnymailAPIError, AnymailUnsupportedFeature
+from anymail.exceptions import AnymailAPIError, AnymailRequestsAPIError, AnymailUnsupportedFeature
 from anymail.message import attach_inline_image_file
 
 from .mock_requests_backend import RequestsBackendMockAPITestCase, SessionSharingTestCasesMixin
@@ -258,6 +258,20 @@ def test_api_error_includes_details(self):
         with self.assertRaises(AnymailAPIError):
             self.message.send()
 
+    def test_requests_exception(self):
+        """Exception during API call should be AnymailAPIError"""
+        # (The post itself raises an error -- different from returning a failure response)
+        from requests.exceptions import SSLError  # a low-level requests exception
+        self.mock_request.side_effect = SSLError("Something bad")
+        with self.assertRaisesMessage(AnymailRequestsAPIError, "Something bad") as cm:
+            self.message.send()
+        self.assertIsInstance(cm.exception, SSLError)  # also retains specific requests exception class
+
+        # Make sure fail_silently is respected
+        self.mock_request.side_effect = SSLError("Something bad")
+        sent = mail.send_mail('Subject', 'Body', 'from@example.com', ['to@example.com'], fail_silently=True)
+        self.assertEqual(sent, 0)
+
 
 class MailgunBackendAnymailFeatureTests(MailgunBackendMockAPITestCase):
     """Test backend support for Anymail added features"""