Postmark: workaround invalid "test inbound" data

Postmark's "test" button in their inbound settings
posts data with attachments that don't match their docs or
actual inbound behavior. Accept that and issue a warning.

Closes #304

CHANGELOG.rst

@@ -30,6 +30,12 @@ vNext
 
 *Unreleased changes*
 
+Fixes
+~~~~~
+
+* **Postmark:** Workaround for handling inbound test webhooks.
+  (`More info <https://github.com/anymail/django-anymail/issues/304>`__)
+
 Other
 ~~~~~
 

anymail/webhooks/postmark.py

@@ -1,8 +1,9 @@
 import json
+import warnings
 
 from django.utils.dateparse import parse_datetime
 
-from ..exceptions import AnymailConfigurationError
+from ..exceptions import AnymailConfigurationError, AnymailWarning
 from ..inbound import AnymailInboundMessage
 from ..signals import (
     AnymailInboundEvent,
@@ -169,7 +170,13 @@ class PostmarkInboundWebhookView(PostmarkBaseWebhookView):
         attachments = [
             AnymailInboundMessage.construct_attachment(
                 content_type=attachment["ContentType"],
-                content=attachment["Content"],
+                content=(
+                    attachment.get("Content")
+                    # WORKAROUND:
+                    # The test webhooks are not like their real webhooks
+                    # This allows the test webhooks to be parsed.
+                    or attachment["Data"]
+                ),
                 base64=True,
                 filename=attachment.get("Name", "") or None,
                 content_id=attachment.get("ContentID", "") or None,
@@ -177,6 +184,18 @@ class PostmarkInboundWebhookView(PostmarkBaseWebhookView):
             for attachment in esp_event.get("Attachments", [])
         ]
 
+        # Warning to the user regarding the workaround of above.
+        for attachment in esp_event.get("Attachments", []):
+            if "Data" in attachment:
+                warnings.warn(
+                    "Received a test webhook attachment. "
+                    "It is recommended to test with real inbound events. "
+                    "See https://github.com/anymail/django-anymail/issues/304 "
+                    "for more information.",
+                    AnymailWarning,
+                )
+                break
+
         message = AnymailInboundMessage.construct(
             from_email=self._address(esp_event.get("FromFull")),
             to=", ".join([self._address(to) for to in esp_event.get("ToFull", [])]),

tests/test_postmark_inbound.py

@@ -4,7 +4,7 @@ from unittest.mock import ANY
 
 from django.test import tag
 
-from anymail.exceptions import AnymailConfigurationError
+from anymail.exceptions import AnymailConfigurationError, AnymailWarning
 from anymail.inbound import AnymailInboundMessage
 from anymail.signals import AnymailInboundEvent
 from anymail.webhooks.postmark import PostmarkInboundWebhookView
@@ -165,14 +165,27 @@ class PostmarkInboundTestCase(WebhookTestCase):
                     "ContentType": 'message/rfc822; charset="us-ascii"',
                     "ContentLength": len(email_content),
                 },
+                # This is an attachement like send by the test webhook
+                # A workaround is implemented to handle it.
+                # Once Postmark solves the bug on their side this workaround
+                # can be reverted.
+                {
+                    "Name": "test.txt",
+                    "ContentType": "text/plain",
+                    "Data": "VGhpcyBpcyBhdHRhY2htZW50IGNvbnRlbnRzLCBiYXNlLTY0IGVuY29kZWQu",
+                    "ContentLength": 45,
+                },
             ]
         }
 
-        response = self.client.post(
-            "/anymail/postmark/inbound/",
-            content_type="application/json",
-            data=json.dumps(raw_event),
-        )
+        with self.assertWarnsRegex(
+            AnymailWarning, r"Received a test webhook attachment. "
+        ):
+            response = self.client.post(
+                "/anymail/postmark/inbound/",
+                content_type="application/json",
+                data=json.dumps(raw_event),
+            )
         self.assertEqual(response.status_code, 200)
         kwargs = self.assert_handler_called_once_with(
             self.inbound_handler,
@@ -183,7 +196,7 @@ class PostmarkInboundTestCase(WebhookTestCase):
         event = kwargs["event"]
         message = event.message
         attachments = message.attachments  # AnymailInboundMessage convenience accessor
-        self.assertEqual(len(attachments), 2)
+        self.assertEqual(len(attachments), 3)
         self.assertEqual(attachments[0].get_filename(), "test.txt")
         self.assertEqual(attachments[0].get_content_type(), "text/plain")
         self.assertEqual(attachments[0].get_content_text(), "test attachment")
@@ -192,6 +205,14 @@ class PostmarkInboundTestCase(WebhookTestCase):
             attachments[1].get_content_bytes(), email_content
         )
 
+        # Attachment of test webhook
+        self.assertEqual(attachments[2].get_filename(), "test.txt")
+        self.assertEqual(attachments[2].get_content_type(), "text/plain")
+        self.assertEqual(
+            attachments[2].get_content_text(),
+            "This is attachment contents, base-64 encoded.",
+        )
+
         inlines = message.inline_attachments
         self.assertEqual(len(inlines), 1)
         inline = inlines["abc123"]