[IMP] mail: log a warning when having invalid headers on mail.mail

In this commit we add some logs when we fail to evaluate the 'headers' field
on a 'mail.mail' record, used to populate the headers of outgoing emails.

Some tests are added to ensure we do not crash if headers is malformed, and
to cover the feature itself as it was still not really done.

Task-2710804 (Mail: Clean MailThread Posting API)
Task-3093268 (Mail: Stop spamming CCs)
Prepares Task-2684479 (Mail: Better report errors when sending emails)

Part-of: odoo/odoo#99482

addons/mail/models/mail_mail.py

@@ -352,8 +352,18 @@ class MailMail(models.Model):
         if self.headers:
             try:
                 headers.update(ast.literal_eval(self.headers))
-            except Exception:
-                pass
+            except (ValueError, TypeError) as e:
+                _logger.warning(
+                    'Evaluation error when evaluating mail headers (received %r): %s',
+                    self.headers, e,
+                )
+            # global except as we don't want to crash the queue just due to a malformed
+            # headers value
+            except Exception as e:
+                _logger.warning(
+                    'Unknown error when evaluating mail headers (received %r): %s',
+                    self.headers, e,
+                )
 
         # prepare recipients: use email_to if defined then check recipient_ids
         # that receive a specific email, notably due to link shortening / redirect

addons/test_mail/tests/test_mail_mail.py

@@ -11,7 +11,7 @@ from OpenSSL.SSL import Error as SSLError
 from socket import gaierror, timeout
 from unittest.mock import call, patch
 
-from odoo import api, Command, tools
+from odoo import api, Command
 from odoo.addons.base.models.ir_mail_server import MailDeliveryException
 from odoo.addons.test_mail.tests.common import TestMailCommon
 from odoo.exceptions import AccessError
@@ -126,6 +126,35 @@ class TestMailMail(TestMailCommon):
             self.assertEqual(mail.sudo().restricted_attachment_count, 2)
             self.assertEqual(len(mail.sudo().unrestricted_attachment_ids), 0)
 
+    @mute_logger('odoo.addons.mail.models.mail_mail')
+    def test_mail_mail_headers(self):
+        """ Test headers management when set on outgoing mail. """
+        # mail without thread-enabled record
+        base_values = {
+            'body_html': '<p>Test</p>',
+            'email_to': 'test@example.com',
+            'headers': {'foo': 'bar'},
+        }
+
+        for headers, expected in [
+            ({'foo': 'bar'}, {'foo': 'bar'}),
+            ("{'foo': 'bar'}", {'foo': 'bar'}),
+            ("{'foo': 'bar', 'baz': '3+2'}", {'foo': 'bar', 'baz': '3+2'}),
+            (['not_a_dict'], {}),
+            ('alsonotadict', {}),
+            ("['not_a_dict']", {}),
+            ("{'invaliddict'}", {}),
+        ]:
+            with self.subTest(headers=headers, expected=expected):
+                mail = self.env['mail.mail'].create([
+                    dict(base_values, headers=headers)
+                ])
+                with self.mock_mail_gateway():
+                    mail.send()
+                for key, value in expected.items():
+                    self.assertIn(key, self._mails[0]['headers'])
+                    self.assertEqual(self._mails[0]['headers'][key], value)
+
     @mute_logger('odoo.addons.mail.models.mail_mail')
     def test_mail_mail_recipients(self):
         """ Partner_ids is a field used from mail_message, but not from mail_mail. """