Resend: workaround display-name bug

anymail/backends/resend.py

@@ -1,9 +1,16 @@
 import mimetypes
+from email.charset import QP, Charset
+from email.utils import formataddr
 
 from ..message import AnymailRecipientStatus
 from ..utils import CaseInsensitiveCasePreservingDict, get_anymail_setting
 from .base_requests import AnymailRequestsBackend, RequestsPayload
 
+# Used to force RFC-2047 encoded word
+# in address formatting workaround
+QP_CHARSET = Charset("utf-8")
+QP_CHARSET.header_encoding = QP
+
 
 class EmailBackend(AnymailRequestsBackend):
     """
@@ -69,22 +76,41 @@ def serialize_data(self):
     def init_payload(self):
         self.data = {}  # becomes json
 
+    @staticmethod
+    def _resend_email_address(address):
+        """
+        Return EmailAddress address formatted for use with Resend.
+
+        Works around a Resend bug that rejects properly formatted RFC 5822
+        addresses that have the display-name enclosed in double quotes (e.g.,
+        any display-name containing a comma).
+        """
+        formatted = address.address
+        if formatted.startswith('"'):
+            # Workaround: force RFC-2047 encoded word
+            formatted = formataddr(
+                (QP_CHARSET.header_encode(address.display_name), address.addr_spec)
+            )
+        return formatted
+
     def set_from_email(self, email):
-        self.data["from"] = email.address
+        self.data["from"] = self._resend_email_address(email)
 
     def set_recipients(self, recipient_type, emails):
         assert recipient_type in ["to", "cc", "bcc"]
         if emails:
             field = recipient_type
-            self.data[field] = [email.address for email in emails]
+            self.data[field] = [self._resend_email_address(email) for email in emails]
             self.recipients += emails
 
     def set_subject(self, subject):
         self.data["subject"] = subject
 
     def set_reply_to(self, emails):
         if emails:
-            self.data["reply_to"] = [email.address for email in emails]
+            self.data["reply_to"] = [
+                self._resend_email_address(email) for email in emails
+            ]
 
     def set_extra_headers(self, headers):
         self.data.setdefault("headers", {}).update(headers)

tests/test_resend_backend.py

@@ -94,6 +94,37 @@ def test_name_addr(self):
             data["bcc"], ["Blind Copy <[email protected]>", "[email protected]"]
         )
 
+    def test_quoted_display_names(self):
+        # Resend's API has a bug that rejects a display-name that is quoted
+        # (per RFC 5822 section 3.4). Attempting to omit the quotes works, unless
+        # the display-name also contains a comma. Try to avoid the whole problem
+        # by using RFC 2047 encoded words for addresses Resend will parse incorrectly.
+        msg = mail.EmailMessage(
+            "Subject",
+            "Message",
+            '"From, comma" <[email protected]>',
+            [
+                '"To, comma" <[email protected]>',
+                "non–ascii <[email protected]>",
+                "=?utf-8?q?pre_encoded?= <[email protected]>",
+            ],
+            reply_to=['"Reply, comma" <[email protected]>'],
+        )
+        msg.send()
+        data = self.get_api_call_json()
+        self.assertEqual(data["from"], "=?utf-8?q?From=2C_comma?= <[email protected]>")
+        self.assertEqual(
+            data["to"],
+            [
+                "=?utf-8?q?To=2C_comma?= <[email protected]>",
+                "=?utf-8?b?bm9u4oCTYXNjaWk=?= <[email protected]>",
+                "=?utf-8?q?pre_encoded?= <[email protected]>",
+            ],
+        )
+        self.assertEqual(
+            data["reply_to"], ["=?utf-8?q?Reply=2C_comma?= <[email protected]>"]
+        )
+
     def test_email_message(self):
         email = mail.EmailMessage(
             "Subject",