also consider Content-ID when marking attachment as inline (#126)

Handle MIME attachments with Content-ID as inline by default.

Treat MIME attachments that have a *Content-ID* but no explicit *Content-Disposition*
header as inline, matching the behavior of many email clients.

CHANGELOG.rst

@@ -33,6 +33,10 @@ v4.3
 Features
 ~~~~~~~~
 
+*  Treat MIME attachments that have a *Content-ID* but no explicit *Content-Disposition*
+   header as inline, matching the behavior of many email clients. For maximum
+   compatibility, you should always set both (or use Anymail's inline helper functions).
+   (Thanks `@costela`_.)
 *  Add (undocumented) DEBUG_API_REQUESTS Anymail setting. When enabled, prints raw
    API request and response during send. Currently implemented only for Requests-based
    backends (all but Amazon SES and SparkPost). Because this can expose API keys and

anymail/utils.py

@@ -291,7 +291,8 @@ class Attachment(object):
                     self.content = attachment.as_string().encode(self.encoding)
             self.mimetype = attachment.get_content_type()
 
-            if get_content_disposition(attachment) == 'inline':
+            content_disposition = get_content_disposition(attachment)
+            if content_disposition == 'inline' or (not content_disposition and 'Content-ID' in attachment):
                 self.inline = True
                 self.content_id = attachment["Content-ID"]  # probably including the <...>
                 if self.content_id is not None:

docs/sending/django_email.rst

@@ -88,6 +88,15 @@ and :meth:`~email.message.Message.add_header` should be helpful.)
 Even if you mark an attachment as inline, some email clients may decide to also
 display it as an attachment. This is largely outside your control.
 
+.. versionchanged:: 4.3
+
+    For convenience, Anymail will treat an attachment with a :mailheader:`Content-ID`
+    but no :mailheader:`Content-Disposition` as inline. (Many---though not all---email
+    clients make the same assumption. But to ensure consistent behavior with non-Anymail
+    email backends, you should always set *both* :mailheader:`Content-ID` and
+    :mailheader:`Content-Disposition: inline` headers for inline images. Or just use
+    Anymail's :ref:`inline image helpers <inline-images>`, which handle this for you.)
+
 
 .. _message-headers:
 

tests/test_utils.py

@@ -1,6 +1,7 @@
 # Tests for the anymail/utils.py module
 # (not to be confused with utilities for testing found in in tests/utils.py)
 import base64
+from email.mime.image import MIMEImage
 from unittest import skipIf
 
 import six
@@ -21,6 +22,7 @@ except ImportError:
 from anymail.exceptions import AnymailInvalidAddress, _LazyError
 from anymail.utils import (
     parse_address_list, parse_single_address, EmailAddress,
+    Attachment,
     is_lazy, force_non_lazy, force_non_lazy_dict, force_non_lazy_list,
     update_deep,
     get_request_uri, get_request_basic_auth, parse_rfc2822date, querydict_getfirst)
@@ -161,6 +163,51 @@ class ParseAddressListTests(SimpleTestCase):
             parse_single_address(" ")
 
 
+class NormalizedAttachmentTests(SimpleTestCase):
+    """Test utils.Attachment"""
+
+    # (Several basic tests could be added here)
+
+    def test_content_disposition_attachment(self):
+        image = MIMEImage(b";-)", "x-emoticon")
+        image["Content-Disposition"] = 'attachment; filename="emoticon.txt"'
+        att = Attachment(image, "ascii")
+        self.assertEqual(att.name, "emoticon.txt")
+        self.assertEqual(att.content, b";-)")
+        self.assertFalse(att.inline)
+        self.assertIsNone(att.content_id)
+        self.assertEqual(att.cid, "")
+
+    def test_content_disposition_inline(self):
+        image = MIMEImage(b";-)", "x-emoticon")
+        image["Content-Disposition"] = 'inline'
+        att = Attachment(image, "ascii")
+        self.assertIsNone(att.name)
+        self.assertEqual(att.content, b";-)")
+        self.assertTrue(att.inline)  # even without the Content-ID
+        self.assertIsNone(att.content_id)
+        self.assertEqual(att.cid, "")
+
+        image["Content-ID"] = "<abc123@example.net>"
+        att = Attachment(image, "ascii")
+        self.assertEqual(att.content_id, "<abc123@example.net>")
+        self.assertEqual(att.cid, "abc123@example.net")
+
+    def test_content_id_implies_inline(self):
+        """A MIME object with a Content-ID should be assumed to be inline"""
+        image = MIMEImage(b";-)", "x-emoticon")
+        image["Content-ID"] = "<abc123@example.net>"
+        att = Attachment(image, "ascii")
+        self.assertTrue(att.inline)
+        self.assertEqual(att.content_id, "<abc123@example.net>")
+
+        # ... but not if explicit Content-Disposition says otherwise
+        image["Content-Disposition"] = "attachment"
+        att = Attachment(image, "ascii")
+        self.assertFalse(att.inline)
+        self.assertIsNone(att.content_id)  # ignored for non-inline Attachment
+
+
 class LazyCoercionTests(SimpleTestCase):
     """Test utils.is_lazy and force_non_lazy*"""