Normalize send_at date/datetime/timestamp in BasePayload.

Interpret dates and naive datetimes as Django's
current_timezone (rather than UTC like Djrill did).
This should be more likely to behave as expected
when running with a non-UTC TIME_ZONE setting.

anymail/backends/base.py

@@ -1,5 +1,8 @@
+from datetime import date, datetime
+
 from django.conf import settings
 from django.core.mail.backends.base import BaseEmailBackend
+from django.utils.timezone import is_naive, get_current_timezone, make_aware, utc
 
 from ..exceptions import AnymailError, AnymailUnsupportedFeature
 from ..utils import Attachment, ParsedEmail, UNSET, combine, last, get_anymail_setting
@@ -191,7 +194,7 @@ class BasePayload(object):
     anymail_message_attrs = (
         # Anymail expando-props
         ('metadata', combine, None),
-        ('send_at', last, None),  # normalize to datetime?
+        ('send_at', last, 'aware_datetime'),
         ('tags', combine, None),
         ('track_clicks', last, None),
         ('track_opens', last, None),
@@ -219,6 +222,7 @@ class BasePayload(object):
                     if not callable(converter):
                         converter = getattr(self, converter)
                     value = converter(value)
+            if value is not UNSET:
                 if attr == 'body':
                     setter = self.set_html_body if message.content_subtype == 'html' else self.set_text_body
                 else:
@@ -246,6 +250,29 @@ class BasePayload(object):
         str_encoding = self.message.encoding or settings.DEFAULT_CHARSET
         return [Attachment(attachment, str_encoding) for attachment in attachments]
 
+    def aware_datetime(self, value):
+        """Converts a date or datetime or timestamp to an aware datetime.
+
+        Naive datetimes are assumed to be in Django's current_timezone.
+        Dates are interpreted as midnight that date, in Django's current_timezone.
+        Integers are interpreted as POSIX timestamps (which are inherently UTC).
+
+        Anything else (e.g., str) is returned unchanged, which won't be portable.
+        """
+        if isinstance(value, datetime):
+            dt = value
+        else:
+            if isinstance(value, date):
+                dt = datetime(value.year, value.month, value.day)  # naive, midnight
+            else:
+                try:
+                    dt = datetime.utcfromtimestamp(value).replace(tzinfo=utc)
+                except (TypeError, ValueError):
+                    return value
+        if is_naive(dt):
+            dt = make_aware(dt, get_current_timezone())
+        return dt
+
     #
     # Abstract implementation
     #

anymail/backends/mandrill.py

@@ -57,21 +57,15 @@ def _expand_merge_vars(vardict):
 
 
 def encode_date_for_mandrill(dt):
-    """Format a date or datetime for use as a Mandrill API date field
+    """Format a datetime for use as a Mandrill API date field
 
-    datetime becomes "YYYY-MM-DD HH:MM:SS"
+    Mandrill expects "YYYY-MM-DD HH:MM:SS" in UTC
-             converted to UTC, if timezone-aware
-             microseconds removed
-    date     becomes "YYYY-MM-DD 00:00:00"
-    anything else gets returned intact
     """
     if isinstance(dt, datetime):
         dt = dt.replace(microsecond=0)
         if dt.utcoffset() is not None:
             dt = (dt - dt.utcoffset()).replace(tzinfo=None)
         return dt.isoformat(' ')
-    elif isinstance(dt, date):
-        return dt.isoformat() + ' 00:00:00'
     else:
         return dt
 
@@ -128,9 +122,10 @@ class MandrillPayload(RequestsPayload):
     def add_alternative(self, content, mimetype):
         if mimetype != 'text/html':
             self.unsupported_feature("alternative part with mimetype '%s'" % mimetype)
-        if "html" in self.data["message"]:
+        elif "html" in self.data["message"]:
             self.unsupported_feature("multiple html parts")
-        self.data["message"]["html"] = content
+        else:
+            self.set_html_body(content)
 
     def add_attachment(self, attachment):
         key = "images" if attachment.inline else "attachments"

anymail/tests/test_mandrill_send.py

@@ -8,7 +8,7 @@ import re
 import six
 import unittest
 from base64 import b64decode
-from datetime import date, datetime, timedelta, tzinfo
+from datetime import date, datetime
 from decimal import Decimal
 from email.mime.base import MIMEBase
 from email.mime.image import MIMEImage
@@ -18,6 +18,7 @@ from django.core.exceptions import ImproperlyConfigured
 from django.core.mail import make_msgid
 from django.test import TestCase
 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, AnymailRecipientsRefused,
                                 AnymailSerializationError, AnymailUnsupportedFeature)
@@ -451,34 +452,40 @@ class DjrillMandrillFeatureTests(DjrillBackendMockAPITestCase):
             ])
 
     def test_send_at(self):
-        # String passed unchanged
+        utc_plus_6 = get_fixed_timezone(6 * 60)
+        utc_minus_8 = get_fixed_timezone(-8 * 60)
+
+        with override_current_timezone(utc_plus_6):
+            # Timezone-naive datetime assumed to be Django current_timezone
+            self.message.send_at = datetime(2022, 10, 11, 12, 13, 14, 567)
+            self.message.send()
+            data = self.get_api_call_data()
+            self.assertEqual(data['send_at'], "2022-10-11 06:13:14")  # 12:13 UTC+6 == 06:13 UTC
+
+            # Timezone-aware datetime converted to UTC:
+            self.message.send_at = datetime(2016, 3, 4, 5, 6, 7, tzinfo=utc_minus_8)
+            self.message.send()
+            data = self.get_api_call_data()
+            self.assertEqual(data['send_at'], "2016-03-04 13:06:07")  # 05:06 UTC-8 == 13:06 UTC
+
+            # Date-only treated as midnight in current timezone
+            self.message.send_at = date(2022, 10, 22)
+            self.message.send()
+            data = self.get_api_call_data()
+            self.assertEqual(data['send_at'], "2022-10-21 18:00:00")  # 00:00 UTC+6 == 18:00-1d UTC
+
+            # POSIX timestamp
+            self.message.send_at = 1651820889  # 2022-05-06 07:08:09 UTC
+            self.message.send()
+            data = self.get_api_call_data()
+            self.assertEqual(data['send_at'], "2022-05-06 07:08:09")
+
+            # String passed unchanged (this is *not* portable between ESPs)
             self.message.send_at = "2013-11-12 01:02:03"
             self.message.send()
             data = self.get_api_call_data()
             self.assertEqual(data['send_at'], "2013-11-12 01:02:03")
 
-        # Timezone-naive datetime assumed to be UTC
-        self.message.send_at = datetime(2022, 10, 11, 12, 13, 14, 567)
-        self.message.send()
-        data = self.get_api_call_data()
-        self.assertEqual(data['send_at'], "2022-10-11 12:13:14")
-
-        # Timezone-aware datetime converted to UTC:
-        class GMTminus8(tzinfo):
-            def utcoffset(self, dt): return timedelta(hours=-8)
-            def dst(self, dt): return timedelta(0)
-
-        self.message.send_at = datetime(2016, 3, 4, 5, 6, 7, tzinfo=GMTminus8())
-        self.message.send()
-        data = self.get_api_call_data()
-        self.assertEqual(data['send_at'], "2016-03-04 13:06:07")
-
-        # Date-only treated as midnight UTC
-        self.message.send_at = date(2022, 10, 22)
-        self.message.send()
-        data = self.get_api_call_data()
-        self.assertEqual(data['send_at'], "2022-10-22 00:00:00")
-
     def test_default_omits_options(self):
         """Make sure by default we don't send any Mandrill-specific options.