feat: add reusable SMTP batch sessions

tests/test_smtp_helpers.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import smtplib
 import unittest
 from unittest.mock import patch
 
@@ -7,6 +8,9 @@ from govoplan_core.security.outbound_http import OutboundHttpBlocked
 from govoplan_mail.backend.config import SmtpConfig
 from govoplan_mail.backend.sending.smtp import (
     SmtpConfigurationError,
+    SmtpBatchPolicy,
+    SmtpBatchSession,
+    SmtpSendError,
     _open_smtp,
     _prepare_smtp_send,
     _smtp_send_result,
@@ -70,6 +74,109 @@ class SmtpSendHelperTests(unittest.TestCase):
         self.assertEqual(result.accepted_count, 1)
         self.assertEqual(result.refused_recipients["blocked@example.org"], (550, "blocked"))
 
+    def test_batch_preflight_reuses_one_authenticated_connection(self):
+        config = SmtpConfig(host="smtp.example.org", port=587, security="starttls")
+        smtp = _FakeSmtp()
+        with patch("govoplan_mail.backend.sending.smtp._open_smtp", return_value=smtp) as opener:
+            with SmtpBatchSession(config) as batch:
+                first = batch.send(b"first", envelope_from="sender@example.org", envelope_recipients=["one@example.org"])
+                second = batch.send(b"second", envelope_from="sender@example.org", envelope_recipients=["two@example.org"])
+
+        opener.assert_called_once_with(config)
+        self.assertFalse(first.session_reused)
+        self.assertTrue(second.session_reused)
+        self.assertEqual(1, second.connection_sequence)
+        self.assertEqual([b"first", b"second"], smtp.messages)
+        self.assertTrue(smtp.quit_called)
+
+    def test_batch_reconnects_before_next_message_when_health_check_fails(self):
+        config = SmtpConfig(host="smtp.example.org", port=587, security="starttls")
+        first_smtp = _FakeSmtp(noop_error_on_call=1)
+        second_smtp = _FakeSmtp()
+        policy = SmtpBatchPolicy(reconnect_attempts=1)
+        with patch(
+            "govoplan_mail.backend.sending.smtp._open_smtp",
+            side_effect=[first_smtp, second_smtp],
+        ) as opener:
+            with SmtpBatchSession(config, policy=policy) as batch:
+                batch.send(b"first", envelope_from="sender@example.org", envelope_recipients=["one@example.org"])
+                result = batch.send(b"second", envelope_from="sender@example.org", envelope_recipients=["two@example.org"])
+
+        self.assertEqual(2, opener.call_count)
+        self.assertEqual(2, result.connection_sequence)
+        self.assertEqual(1, result.reconnect_count)
+        self.assertEqual([b"first"], first_smtp.messages)
+        self.assertEqual([b"second"], second_smtp.messages)
+
+    def test_preflight_retries_a_transient_connection_failure(self):
+        config = SmtpConfig(host="smtp.example.org", port=587, security="starttls")
+        smtp = _FakeSmtp()
+        with patch(
+            "govoplan_mail.backend.sending.smtp._open_smtp",
+            side_effect=[OSError("temporary DNS failure"), smtp],
+        ) as opener:
+            with SmtpBatchSession(config, policy=SmtpBatchPolicy(reconnect_attempts=1)) as batch:
+                result = batch.send(b"message", envelope_from="sender@example.org", envelope_recipients=["one@example.org"])
+
+        self.assertEqual(2, opener.call_count)
+        self.assertEqual(1, result.reconnect_count)
+
+    def test_connection_loss_after_send_starts_is_unknown_and_never_replayed(self):
+        config = SmtpConfig(host="smtp.example.org", port=587, security="starttls")
+        smtp = _FakeSmtp(send_error=smtplib.SMTPServerDisconnected("lost"))
+        with patch("govoplan_mail.backend.sending.smtp._open_smtp", return_value=smtp), self.assertRaises(SmtpSendError) as raised:
+            with SmtpBatchSession(config) as batch:
+                batch.send(b"one", envelope_from="sender@example.org", envelope_recipients=["one@example.org"])
+
+        self.assertTrue(raised.exception.outcome_unknown)
+        self.assertTrue(raised.exception.systemic)
+        self.assertEqual("smtp_connection_lost_after_transmission", raised.exception.reason_code)
+        self.assertEqual(1, smtp.send_calls)
+
+    def test_authentication_preflight_is_systemic_and_blocks_batch(self):
+        config = SmtpConfig(host="smtp.example.org", port=587, security="starttls")
+        error = smtplib.SMTPAuthenticationError(535, b"bad credentials")
+        with patch("govoplan_mail.backend.sending.smtp._open_smtp", side_effect=error), self.assertRaises(SmtpSendError) as raised:
+            SmtpBatchSession(config).preflight()
+
+        self.assertTrue(raised.exception.systemic)
+        self.assertFalse(raised.exception.temporary)
+        self.assertEqual("preflight", raised.exception.phase)
+        self.assertEqual("smtp_authentication_failed", raised.exception.reason_code)
+
+
+class _FakeSmtp:
+    def __init__(self, *, noop_error_on_call: int | None = None, send_error: BaseException | None = None):
+        self.noop_error_on_call = noop_error_on_call
+        self.send_error = send_error
+        self.noop_calls = 0
+        self.send_calls = 0
+        self.messages: list[bytes] = []
+        self.quit_called = False
+
+    def noop(self):
+        self.noop_calls += 1
+        if self.noop_error_on_call == self.noop_calls:
+            raise smtplib.SMTPServerDisconnected("stale")
+        return 250, b"ok"
+
+    def sendmail(self, _sender, _recipients, message):
+        self.send_calls += 1
+        if self.send_error is not None:
+            raise self.send_error
+        self.messages.append(message)
+        return {}
+
+    def send_message(self, message, **_kwargs):
+        return self.sendmail(None, None, message.as_bytes())
+
+    def quit(self):
+        self.quit_called = True
+        return 221, b"bye"
+
+    def close(self):
+        return None
+
 
 if __name__ == "__main__":
     unittest.main()