Using the SMTP test framework

The SMTP test framework provides a real SMTP server listening on a port and speaking the SMTP protocol. It runs the server in a separate thread so that the main thread can send it messages, and verify that it received the messages.

To use, start by defining a subclass of the Server class.

>>> from lazr.smtptest.server import Server

Override the handle_message() method to do whatever you want to do with the message. For example, you might want to pass the message between the threads via a Queue.

>>> try:
...     from queue import Queue
... except ImportError:
...     # Python 2
...     from Queue import Queue
>>> queue = Queue()

>>> class MyServer(Server):
...     def handle_message(self, message):
...         queue.put(message)

Start a controller, with our new server.

>>> from lazr.smtptest.controller import Controller
>>> controller = Controller(MyServer('localhost', 9025))
>>> controller.start()

Connect to the server…

>>> from smtplib import SMTP
>>> smtpd = SMTP()
>>> code, helo = smtpd.connect('localhost', 9025)
>>> print(code, str(helo))
220 ... Python SMTP proxy version ...

…and send it a message.

>>> smtpd.sendmail('aperson@example.com', ['bperson@example.com'], """\
... From: Abby Person <aperson@example.com>
... To: Bart Person <bperson@example.com>
... Subject: A test
... Message-ID: <aardvark>
...
... Hi Bart, this is a test.
... """)
{}

Now print the message that the server has just received.

>>> message = queue.get()
>>> print(message.as_string())
From: Abby Person <aperson@example.com>
To: Bart Person <bperson@example.com>
Subject: A test
Message-ID: <aardvark>
X-Peer: 127.0.0.1:...
X-MailFrom: aperson@example.com
X-RcptTo: bperson@example.com
<BLANKLINE>
Hi Bart, this is a test.

When you’re done with the server, stop it via the controller.

>>> controller.stop()

The server is guaranteed to be stopped.

>>> # The traceback text is different between Python 2.5 and 2.6.
>>> import socket
>>> try:
...     smtpd.connect('localhost', 9025)
... except socket.error as error:
...     errno, message = error.args
...     print(message)
Connection refused

Resetting

The SMTP server can be reset, which defines application specific behavior. For example, a server which stores messages in an mbox can be sent the RSET command to clear the mbox.

This server stores messages in Maildir.

>>> import os
>>> import mailbox
>>> import tempfile
>>> tempdir = tempfile.mkdtemp()
>>> mailbox_dir = os.path.join(tempdir, 'maildir')

>>> class MyServer(Server):
...     def __init__(self, host, port):
...         Server.__init__(self, host, port)
...         self._maildir = mailbox.Maildir(mailbox_dir)
...
...     def handle_message(self, message):
...         self._maildir.add(message)
...
...     def reset(self):
...         self._maildir.clear()

>>> controller = Controller(MyServer('localhost', 9025))
>>> controller.start()

Now we can send a couple of messages to the server.

>>> smtpd = SMTP()
>>> code, helo = smtpd.connect('localhost', 9025)
>>> print(code, str(helo))
220 ... Python SMTP proxy version ...

>>> smtpd.sendmail('cperson@example.com', ['dperson@example.com'], """\
... From: Cris Person <cperson@example.com>
... To: Dave Person <dperson@example.com>
... Subject: A test
... Message-ID: <badger>
...
... Hi Dave, this is a test.
... """)
{}

>>> smtpd.sendmail('eperson@example.com', ['fperson@example.com'], """\
... From: Elly Person <eperson@example.com>
... To: Fred Person <fperson@example.com>
... Subject: A test
... Message-ID: <cougar>
...
... Hi Fred, this is a test.
... """)
{}

>>> smtpd.sendmail('gperson@example.com', ['hperson@example.com'], """\
... From: Gwen Person <gperson@example.com>
... To: Herb Person <hperson@example.com>
... Subject: A test
... Message-ID: <dingo>
...
... Hi Herb, this is a test.
... """)
{}

All of these messages are in the mailbox.

>>> for message_id in sorted(message['message-id']
...                          for message in mailbox.Maildir(mailbox_dir)):
...     print(message_id)
<badger>
<cougar>
<dingo>

Reading the messages does not affect their appearance in the mailbox.

>>> for message_id in sorted(message['message-id']
...                          for message in mailbox.Maildir(mailbox_dir)):
...     print(message_id)
<badger>
<cougar>
<dingo>

But if we reset the server, the messages disappear.

>>> controller.reset()
>>> sum(1 for message in mailbox.Maildir(mailbox_dir))
0

Clean up

>>> # In Python 2.6, this returns a 221, but not in Python 2.5.
>>> status = smtpd.quit()
>>> controller.stop()
>>> import shutil
>>> shutil.rmtree(tempdir)