add basic implementation for a mq-sendmail script

This script is intended as an alternative to `/usr/bin/sendmail`
and `/usr/bin/msmtp` (albeit with less functionality).

The idea is to provide local queueing in a robust manner using
the code from mailqueue-runner. "msmtp" queueing is implemented
by some community-contributed bash scripts which I do not find
particularly trust inspiring. Other implementations like "ssmtp"
do not support queueing at all or require a full-blown mail server
(Exim, postfix).

schwarz/mailqueue/cli/__init__.py

@@ -1,3 +1,4 @@
 
+from .mq_sendmail import *
 from .one_shot_queue_run import *
 from .send_test_message import *

schwarz/mailqueue/cli/mq_sendmail.py

@@ -0,0 +1,109 @@
+"""
+mq-sendmail
+
+Usage:
+    mq-sendmail [options] <recipients>...
+
+Options:
+  -C, --config=<CFG>  Path to the config file (default: /etc/mailqueue-runner.ini)
+  --set-date-header   Add a "Date" header to the message (if not present)
+  --set-from-header   Set the "From:" header in the outgoing mail based on the unix user
+  --set-msgid-header  Add a "Message-ID" header to the message (if not present)
+  --verbose, -v       more verbose program output
+"""
+
+import os
+import platform
+import sys
+from datetime import datetime as DateTime, timezone
+from email.message import EmailMessage
+from email.parser import BytesHeaderParser
+from email.utils import format_datetime, make_msgid
+from io import BytesIO
+
+from docopt import docopt
+
+from schwarz.mailqueue.app_helpers import init_app, init_smtp_mailer
+from schwarz.mailqueue.message_handler import InMemoryMsg, MessageHandler
+
+
+__all__ = ['mq_sendmail_main']
+
+def mq_sendmail_main(argv=sys.argv, return_rc_code=False):
+    arguments = docopt(__doc__, argv=argv[1:])
+    config_path = arguments['--config']
+    recipients = arguments['<recipients>']
+    verbose = arguments['--verbose']
+
+    set_date_header = arguments['--set-date-header']
+    set_from_header = arguments['--set-from-header']
+    set_msgid_header = arguments['--set-msgid-header']
+
+    msg_bytes = sys.stdin.buffer.read()
+    smtp_sender_domain = platform.uname().node
+    msg_sender = os.getlogin() + '@' + smtp_sender_domain
+
+    cli_options = {
+        'verbose': verbose,
+        'quiet'  : not verbose,
+    }
+    settings = init_app(config_path, options=cli_options)
+    mailer = init_smtp_mailer(settings)
+
+    extra_header_lines = autogenerated_headers(
+        set_date_header,
+        set_from_header,
+        set_msgid_header,
+        msg_bytes,
+        msg_sender,
+    )
+    msg = InMemoryMsg(msg_sender, recipients, extra_header_lines + msg_bytes)
+
+    mh = MessageHandler(transports=(mailer,))
+    send_result = mh.send_message(msg)
+
+    if verbose:
+        cli_output = build_cli_output(send_result)
+        print(cli_output)
+    was_sent = bool(send_result)
+    exit_code = 0 if was_sent else 100
+    if return_rc_code:
+        return exit_code
+    sys.exit(exit_code)
+
+
+def autogenerated_headers(set_date_header, set_from_header, set_msgid_header, msg_bytes, msg_sender):  # noqa: E501 (line-too-long)
+    input_headers = BytesHeaderParser().parse(BytesIO(msg_bytes))
+    extra_headers = EmailMessage()
+    input_msg_date = input_headers.get('Date')
+    if set_date_header and not input_msg_date:
+        extra_headers['Date'] = format_datetime(DateTime.now(timezone.utc))
+    input_msg_from = input_headers.get('From')
+    if set_from_header and not input_msg_from:
+        extra_headers['From'] = msg_sender
+    input_msg_id = input_headers.get('Message-ID')
+    if set_msgid_header and not input_msg_id:
+        _, smtp_sender_domain = msg_sender.split('@', 1)
+        extra_headers['Message-ID'] = make_msgid(domain=smtp_sender_domain)
+
+    prepended_header_lines = b''
+    if extra_headers:
+        fake_msg_bytes = extra_headers.as_bytes()
+        prepended_header_lines = fake_msg_bytes.split(b'\n\n', 1)[0] + b'\n'
+    return prepended_header_lines
+
+
+def build_cli_output(send_result) -> str:
+    was_sent = bool(send_result)
+    if was_sent:
+        if send_result.queued:
+            verb = 'queued'
+            via = f' via {send_result.transport}'
+        elif send_result.discarded:
+            verb = 'discarded'
+            via = ''
+        else:
+            verb = 'sent'
+            via = f' via {send_result.transport}'
+        return f'Message was {verb}{via}.'
+    return ''

schwarz/mailqueue/mq_sendmail.py

@@ -0,0 +1,6 @@
+
+from .cli import mq_sendmail_main
+
+
+if __name__ == '__main__':
+    mq_sendmail_main()

tests/mq_sendmail_test.py

@@ -0,0 +1,99 @@
+# SPDX-License-Identifier: MIT
+
+import email
+import re
+import subprocess
+import sys
+import textwrap
+from datetime import datetime as DateTime, timedelta as TimeDelta, timezone
+from email.utils import parsedate_to_datetime
+
+import pytest
+from dotmap import DotMap
+from pymta.test_util import SMTPTestHelper
+
+from schwarz.mailqueue.testutils import create_ini
+
+
+@pytest.fixture
+def ctx(tmp_path):
+    mta_helper = SMTPTestHelper()
+    (hostname, listen_port) = mta_helper.start_mta()
+    ctx = {
+        'hostname': hostname,
+        'listen_port': listen_port,
+        'mta': mta_helper,
+        'tmp_path': tmp_path,
+    }
+    try:
+        yield DotMap(_dynamic=False, **ctx)
+    finally:
+        mta_helper.stop_mta()
+
+
+def _example_message() -> str:
+    return textwrap.dedent('''
+        To: baz@site.example
+        Subject: Test message
+
+        Mail body
+    ''').strip()
+
+
+def test_mq_sendmail(ctx):
+    rfc_msg = _example_message()
+    _mq_sendmail(['foo@site.example'], msg=rfc_msg, ctx=ctx)
+
+    smtp_msg = _retrieve_sent_message(ctx.mta)
+    # smtp from is auto-generated from current user+host, so not easy to test
+    assert tuple(smtp_msg.smtp_to) == ('foo@site.example',)
+    assert smtp_msg.username is None  # no smtp user name set in config
+    assert smtp_msg.msg_data == rfc_msg
+
+
+def _retrieve_sent_message(mta):
+    received_queue = mta.get_received_messages()
+    assert received_queue.qsize() == 1
+    smtp_msg = received_queue.get(block=False)
+    return smtp_msg
+
+
+def test_mq_sendmail_can_add_headers(ctx):
+    sent_msg = _example_message()
+    cli_params = [
+        '--set-from-header',
+        '--set-date-header',
+        '--set-msgid-header',
+        'foo@site.example',
+    ]
+    _mq_sendmail(cli_params, msg=sent_msg, ctx=ctx)
+
+    smtp_msg = _retrieve_sent_message(ctx.mta)
+    msg = email.message_from_string(smtp_msg.msg_data)
+    assert msg['To'] == 'baz@site.example'
+    assert _is_email_address(msg['From'])
+    msg_date = parsedate_to_datetime(msg['Date'])
+    assert _almost_now(msg_date)
+    assert msg['Message-ID']
+
+def _almost_now(dt):
+    return dt - DateTime.now(timezone.utc) < TimeDelta(seconds=1)
+
+def _is_email_address(s):
+    pattern = r'^\w+@[\w.]+$'
+    return re.match(pattern, s) is not None
+
+def _mq_sendmail(cli_params, msg, *, ctx):
+    cfg_dir = str(ctx.tmp_path)
+    config_path = create_ini(ctx.hostname, ctx.listen_port, dir_path=cfg_dir)
+
+    cli_params = [f'--config={config_path}'] + cli_params
+    cmd = [sys.executable, '-m', 'schwarz.mailqueue.mq_sendmail'] + cli_params
+    msg_bytes = msg.encode('utf-8')
+    proc = subprocess.run(cmd, input=msg_bytes, capture_output=True)
+
+    if proc.stderr:
+        # sys.stderr.buffer.write(proc.stderr)
+        raise AssertionError(proc.stderr)
+    assert not proc.stdout
+    assert proc.returncode == 0