ping-mee-self-service-platform/portal/tests/test_smtp_mailer.py

"""The SMTP adapter against a stand-in for `smtplib`; no network."""

import smtplib
import ssl

import pytest

from portal.adapters.mail import MailMessage, MailRejected, MailUnavailable, SmtpMailer
from portal.config.env import SmtpConfig

MESSAGE = MailMessage(
    sender="Portal <portal@example.test>",
    recipient="lena@example.test",
    subject="Hallo Lena",
    body_text="Guten Tag, schöne Grüße\n",
)


def config(security="starttls", port=587):
    return SmtpConfig("mail.example.test", port, security, "box@example.test", "pw", "a@b.test")


class FakeSmtpModule:
    """Looks like the `smtplib` module and records what the adapter does."""

    SMTPException = smtplib.SMTPException
    SMTPAuthenticationError = smtplib.SMTPAuthenticationError
    SMTPRecipientsRefused = smtplib.SMTPRecipientsRefused
    SMTPResponseException = smtplib.SMTPResponseException

    def __init__(self):
        self.calls = []
        self.fail_at = {}  # step name -> exception to raise
        self.sent = []
        self.connect_error = None

    def _connection(self, kind, args, kwargs):
        if self.connect_error:
            raise self.connect_error
        module = self
        module.calls.append((kind, args, kwargs))

        class Connection:
            def _step(self, name, *a, **k):
                module.calls.append((name, a, k))
                if name in module.fail_at:
                    raise module.fail_at[name]

            def ehlo(self):
                self._step("ehlo")

            def starttls(self, context=None):
                self._step("starttls", context=context)

            def login(self, user, password):
                self._step("login", user, password)

            def send_message(self, message):
                self._step("send_message")
                module.sent.append(message)

            def quit(self):
                self._step("quit")

            def close(self):
                module.calls.append(("close", (), {}))

        return Connection()

    def SMTP(self, *args, **kwargs):  # noqa: N802
        return self._connection("SMTP", args, kwargs)

    def SMTP_SSL(self, *args, **kwargs):  # noqa: N802
        return self._connection("SMTP_SSL", args, kwargs)

    def names(self):
        return [c[0] for c in self.calls]


@pytest.fixture
def smtp():
    return FakeSmtpModule()


def test_starttls_encrypts_before_the_login(smtp):
    SmtpMailer(config("starttls"), smtp).send(MESSAGE)
    assert smtp.names() == ["SMTP", "ehlo", "starttls", "ehlo", "login", "send_message", "quit"]
    context = [c for c in smtp.calls if c[0] == "starttls"][0][2]["context"]
    assert context.verify_mode == ssl.CERT_REQUIRED and context.check_hostname


def test_ssl_mode_uses_an_encrypted_connection_from_the_start(smtp):
    SmtpMailer(config("ssl", 465), smtp).send(MESSAGE)
    assert smtp.names() == ["SMTP_SSL", "ehlo", "login", "send_message", "quit"]
    kind, args, kwargs = smtp.calls[0]
    assert args == ("mail.example.test", 465) and kwargs["timeout"] > 0
    assert kwargs["context"].verify_mode == ssl.CERT_REQUIRED


def test_the_login_uses_the_configured_mailbox(smtp):
    SmtpMailer(config(), smtp).send(MESSAGE)
    assert ("login", ("box@example.test", "pw"), {}) in smtp.calls


def test_the_message_is_a_utf8_plain_text_mail_with_the_usual_headers(smtp):
    SmtpMailer(config(), smtp).send(MESSAGE)
    email = smtp.sent[0]
    assert email["From"] == "Portal <portal@example.test>"
    assert email["To"] == "lena@example.test"
    assert email["Subject"] == "Hallo Lena"
    assert email["Date"] and email["Message-ID"].endswith("@mail.example.test>")
    assert email.get_content_type() == "text/plain"
    assert "schöne Grüße" in email.get_content()


@pytest.mark.parametrize(
    "bad",
    [
        {"subject": "Hi\r\nBcc: x@evil.test"},
        {"recipient": "a@example.test\r\nBcc: x@evil.test"},
        {"recipient": "a@example.test\nBcc: x@evil.test"},
    ],
)
def test_a_line_break_in_a_header_cannot_add_headers(smtp, bad):
    message = MailMessage(**{**MESSAGE.__dict__, **bad})
    with pytest.raises(MailRejected):
        SmtpMailer(config(), smtp).send(message)
    assert smtp.sent == []


@pytest.mark.parametrize(
    ("error", "expected"),
    [
        (smtplib.SMTPResponseException(421, b"busy"), MailUnavailable),
        (smtplib.SMTPResponseException(450, b"try later"), MailUnavailable),
        (smtplib.SMTPResponseException(550, b"no such user"), MailRejected),
        (smtplib.SMTPResponseException(554, b"refused"), MailRejected),
        (smtplib.SMTPServerDisconnected("gone"), MailUnavailable),
        (TimeoutError("slow"), MailUnavailable),
        (ssl.SSLError("bad certificate"), MailUnavailable),
        (
            smtplib.SMTPRecipientsRefused({"lena@example.test": (550, b"unknown")}),
            MailRejected,
        ),
        (
            smtplib.SMTPRecipientsRefused({"lena@example.test": (452, b"mailbox full")}),
            MailUnavailable,
        ),
    ],
)
def test_server_answers_are_mapped_to_temporary_or_permanent(smtp, error, expected):
    smtp.fail_at["send_message"] = error
    with pytest.raises(expected):
        SmtpMailer(config(), smtp).send(MESSAGE)


def test_a_refused_login_is_temporary_so_a_fixed_password_works_on_the_retry(smtp):
    smtp.fail_at["login"] = smtplib.SMTPAuthenticationError(535, b"bad credentials")
    with pytest.raises(MailUnavailable):
        SmtpMailer(config(), smtp).send(MESSAGE)
    assert "close" in smtp.names() and "send_message" not in smtp.names()


def test_an_unreachable_server_is_temporary(smtp):
    smtp.connect_error = ConnectionRefusedError("no")
    with pytest.raises(MailUnavailable):
        SmtpMailer(config(), smtp).send(MESSAGE)


def test_a_failing_quit_does_not_hide_a_successful_send(smtp):
    smtp.fail_at["quit"] = smtplib.SMTPServerDisconnected("closed")
    SmtpMailer(config(), smtp).send(MESSAGE)
    assert len(smtp.sent) == 1


def test_errors_never_contain_the_recipient_or_the_server_text(smtp):
    smtp.fail_at["send_message"] = smtplib.SMTPResponseException(550, b"lena@example.test unknown")
    with pytest.raises(MailRejected) as caught:
        SmtpMailer(config(), smtp).send(MESSAGE)
    assert "lena" not in str(caught.value) and "unknown" not in str(caught.value)