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Diffstat (limited to 'src/leap/mx/bounce.py')
| -rw-r--r-- | src/leap/mx/bounce.py | 526 |
1 files changed, 526 insertions, 0 deletions
diff --git a/src/leap/mx/bounce.py b/src/leap/mx/bounce.py new file mode 100644 index 0000000..2ece6df --- /dev/null +++ b/src/leap/mx/bounce.py @@ -0,0 +1,526 @@ +#!/usr/bin/env python +# -*- encoding: utf-8 -*- +# bounce.py +# Copyright (C) 2015 LEAP +# +# This program is free software: you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation, either version 3 of the License, or +# (at your option) any later version. +# +# This program is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU General Public License for more details. +# +# You should have received a copy of the GNU General Public License +# along with this program. If not, see <http://www.gnu.org/licenses/>. + + +""" +Everything you need to correctly bounce a message! + +This is built from the following RFCs: + + * The Multipart/Report Media Type for the Reporting of Mail System + Administrative Messages + https://tools.ietf.org/html/rfc6522 + + * Recommendations for Automatic Responses to Electronic Mail + https://tools.ietf.org/html/rfc3834 + + * An Extensible Message Format for Delivery Status Notifications + https://tools.ietf.org/html/rfc3464 +""" + + +import re +import socket + +from StringIO import StringIO +from textwrap import wrap + +from email.errors import MessageError +from email.message import Message +from email.utils import formatdate +from email.utils import parseaddr +from email.mime.base import MIMEBase +from email.mime.multipart import MIMEMultipart +from email.mime.text import MIMEText +from email.generator import Generator +from email.generator import NL + +from twisted.internet import defer +from twisted.internet import protocol +from twisted.internet import reactor +from twisted.internet.error import ProcessDone +from twisted.python import log + + +EMAIL_ADDRESS_REGEXP = re.compile("[^@]+@[^@]+\.[^@]+") +HOSTNAME = socket.gethostbyaddr(socket.gethostname())[0] + + +def _valid_address(address): + """ + Return whether address is a valid email address. + + :param address: An email address candidate. + :type address: str + + :return: Whether address is valid. + :rtype: bool + """ + return bool(EMAIL_ADDRESS_REGEXP.match(address)) + + +def bounce_message(bounce_from, bounce_subject, orig_msg, reason): + """ + Bounce a message. + + :param bounce_from: The sender of the bounce message. + :type bounce_from: str + :param bounce_subject: The subject of the bounce message. + :type bounce_subject: str + :param orig_msg: The original message that will be bounced. + :type orig_msg: email.message.Message + :param reason: The reason for bouncing the message. + :type reason: str + + :return: A deferred that will fire with the output of the sendmail process + if it was successful or with a failure containing the reason for + the end of the process if it failed. + :rtype: Deferred + """ + orig_rpath = orig_msg.get("Return-Path") + + # do not bounce if sender address is invalid + _, addr = parseaddr(orig_rpath) + if not _valid_address(addr): + log.msg( + "Will not send a bounce message to an invalid address: %s" + % orig_rpath) + return + + msg = _build_bounce_message( + bounce_from, bounce_subject, orig_msg, reason) + return _async_check_output(["/usr/sbin/sendmail", "-t"], msg.as_string()) + + +def _check_valid_return_path(return_path): + """ + Check if a certain return path is valid. + + From RFC 3834: + + Responders MUST NOT generate any response for which the + destination of that response would be a null address (e.g., an + address for which SMTP MAIL FROM or Return-Path is <>), since the + response would not be delivered to a useful destination. + Responders MAY refuse to generate responses for addresses commonly + used as return addresses by responders - e.g., those with local- + parts matching "owner-*", "*-request", "MAILER-DAEMON", etc. + Responders are encouraged to check the destination address for + validity before generating the response, to avoid generating + responses that cannot be delivered or are unlikely to be useful. + + :return: Whether the return_path is valid. + :rtype: bool + """ + _, addr = parseaddr(return_path) + + # check null address + if not addr: + return False + + # check addresses commonly used as return addresses by responders + local, _ = addr.split("@", 1) + if local.startswith("owner-") \ + or local.endswith("-request") \ + or local.startswith("MAILER-DAEMON"): + return False + + return True + + +class DeliveryStatusNotificationMessage(MIMEBase): + """ + A delivery status message, as per RFC 3464. + """ + + def __init__(self, orig_msg): + """ + Initialize the DSN. + """ + MIMEBase.__init__(self, "message", "delivery-status") + self.__delitem__("MIME-Version") + self._build_dsn(orig_msg) + + def _build_dsn(self, orig_msg): + """ + Build an RFC 3464 compliant delivery status message. + + :param orig_msg: The original bouncing message. + :type orig_msg: email.message.Message + """ + content = [] + + # Per-Message DSN fields + # ====================== + + # Original-Envelope-Id (optional) + envelope_id = orig_msg.get("Envelope-Id") + if envelope_id: + content.append("Original-Envelope-Id: %s" % envelope_id) + + # Reporting-MTA (required) + content.append("Reporting-MTA: dns; %s" % HOSTNAME) + + # XXX add Arrival-Date DSN field? (optional). + + content.append("") + + # Per-Recipient DSN fields + # ======================== + + # Original-Recipient (optional) + orig_to = orig_msg.get("X-Original-To") # added by postfix + _, orig_addr = parseaddr(orig_to) + if orig_addr: + content.append("Original-Recipient: rfc822; %s" % orig_addr) + + # Final-Recipient (required) + delivered_to = orig_msg.get("Delivered-To") + content.append("Final-Recipient: rfc822; %s" % delivered_to) + + # Action (required) + content.append("Action: failed") + + # Status (required) + content.append("Status: 5.0.0") # permanent failure + + # XXX add other optional fields? (Remote-MTA, Diagnostic-Code, + # Last-Attempt-Date, Final-Log-ID, Will-Retry-Until) + + # return a "message/delivery-status" message + msg = Message() + msg.set_payload("\n".join(content)) + self.attach(msg) + + +class RFC822Headers(MIMEText): + """ + A text/rfc822-headers mime message as defined in RFC 6522. + """ + + def __init__(self, _text, **kwargs): + """ + Initialize the message. + + :param _text: The contents of the message. + :type _text: str + """ + MIMEText.__init__( + self, _text, + # set "text/rfc822-headers" mime type + _subtype='rfc822-headers', + **kwargs) + + +BOUNCE_TEMPLATE = """ +This is the mail system at {0}. + +I'm sorry to have to inform you that your message could not +be delivered to one or more recipients. It's attached below. + +For further assistance, please send mail to postmaster. + +If you do so, please include this problem report. You can +delete your own text from the attached returned message. + + The mail system + +{1} +""".strip() + + +class InvalidReturnPathError(MessageError): + """ + Exception raised when the return path is invalid. + """ + + +def _build_bounce_message(bounce_from, bounce_subject, orig_msg, reason): + """ + Build a bounce message. + + :param bounce_from: The sender address of the bounce message. + :type bounce_from: str + :param bounce_subject: The subject of the bounce message. + :type bounce_subject: str + :param orig_msg: The original bouncing message. + :type orig_msg: email.message.Message + :param reason: The reason for the bounce. + :type reason: str + + :return: The bounce message. + :rtype: MIMEMultipartReport + + :raise InvalidReturnPathError: Raised when the "Return-Path" header of the + original message is invalid for creating a + bounce message. + """ + # abort creation if "Return-Path" header is invalid + orig_rpath = orig_msg.get("Return-Path") + if not _check_valid_return_path(orig_rpath): + raise InvalidReturnPathError + + msg = MIMEMultipartReport() + msg['From'] = bounce_from + msg['To'] = orig_rpath + msg['Date'] = formatdate(localtime=True) + msg['Subject'] = bounce_subject + msg['Return-Path'] = "<>" # prevent bounce message loop, see RFC 3834 + + # create and attach first required part + orig_to = orig_msg.get("X-Original-To") # added by postfix + wrapped_reason = wrap(("<%s>: " % orig_to) + reason, 74) + for i in xrange(1, len(wrapped_reason)): + wrapped_reason[i] = " " + wrapped_reason[i] + wrapped_reason = "\n".join(wrapped_reason) + text = BOUNCE_TEMPLATE.format(HOSTNAME, wrapped_reason) + msg.attach(MIMEText(text)) + + # create and attach second required part + msg.attach(DeliveryStatusNotificationMessage(orig_msg)) + + # attach third (optional) part. + # + # XXX From RFC 6522: + # + # When 8-bit or binary data not encoded in a 7-bit form is to be + # returned, and the return path is not guaranteed to be 8-bit or + # binary capable, two options are available. The original message + # MAY be re-encoded into a legal 7-bit MIME message or the + # text/rfc822-headers media type MAY be used to return only the + # original message headers. + # + # This is not implemented yet, we should detect if content is 7bit and + # use the class RFC822Headers if it is not. +# try: +# payload = orig_msg.get_payload() +# payload.encode("ascii") +# except UnicodeError: +# headers = [] +# for k in orig_msg.keys(): +# headers.append("%s: %s" % (k, orig_msg[k])) +# orig_msg = RFC822Headers("\n".join(headers)) + msg.attach(orig_msg) + + return msg + + +class BouncerSubprocessProtocol(protocol.ProcessProtocol): + """ + Bouncer subprocess protocol that will feed the msg contents to be + bounced through stdin + """ + + def __init__(self, msg): + """ + Constructor for the BouncerSubprocessProtocol + + :param msg: Message to send to stdin when the process has + launched + :type msg: str + """ + self._msg = msg + self._outBuffer = "" + self._errBuffer = "" + self._d = defer.Deferred() + + @property + def deferred(self): + return self._d + + def connectionMade(self): + self.transport.write(self._msg) + self.transport.closeStdin() + + def outReceived(self, data): + self._outBuffer += data + + def errReceived(self, data): + self._errBuffer += data + + def processEnded(self, reason): + if reason.check(ProcessDone): + self._d.callback(self._outBuffer) + else: + self._d.errback(reason) + + +def _async_check_output(args, msg): + """ + Async spawn a process and return a defer to be able to check the + output with a callback/errback + + :param args: the command to execute along with the params for it + :type args: list of str + :param msg: string that will be send to stdin of the process once + it's spawned + :type msg: str + + :rtype: defer.Deferred + """ + pprotocol = BouncerSubprocessProtocol(msg) + reactor.spawnProcess(pprotocol, args[0], args) + return pprotocol.deferred + + +class DSNGenerator(Generator): + """ + A slightly modified generator to correctly parse delivery status + notifications. + """ + + def _handle_message_delivery_status(self, msg): + """ + Handle a message of type "message/delivery-status". + + This is modified from upstream version in that it also removes empty + lines in the beginning of each part. + + :param msg: The message to be handled. + :type msg: Message + """ + # We can't just write the headers directly to self's file object + # because this will leave an extra newline between the last header + # block and the boundary. Sigh. + blocks = [] + for part in msg.get_payload(): + s = StringIO() + g = self.clone(s) + g.flatten(part, unixfrom=False) + text = s.getvalue() + lines = text.split('\n') + # Strip off the unnecessary trailing empty line + if lines: + if lines[0] == '': + lines.pop(0) + if lines[-1] == '': + lines.pop() + blocks.append(NL.join(lines)) + else: + blocks.append(text) + # Now join all the blocks with an empty line. This has the lovely + # effect of separating each block with an empty line, but not adding + # an extra one after the last one. + self._fp.write(NL.join(blocks)) + + +class MIMEMultipartReport(MIMEMultipart): + """ + Implement multipart/report MIME type as defined in RFC 6522. + + The syntax of multipart/report is identical to the multipart/mixed + content type defined in https://tools.ietf.org/html/rfc2045. + + The multipart/report media type contains either two or three sub- + parts, in the following order: + + 1. (REQUIRED) A human-readable message. + 2. (REQUIRED) A machine-parsable body part containing an account of + the reported message handling event. + 3. (OPTIONAL) A body part containing the returned message or a + portion thereof. + """ + + def __init__( + self, report_type="message/delivery-status", boundary=None, + _subparts=None): + """ + Initialize the message. + + As per RFC 6522, boundary and report_type are required parameters. + + :param report_type: The type of report. This is set as a + "Content-Type" parameter, and should match the + MIME subtype of the second body part. + :type report_type: str + + """ + MIMEMultipart.__init__( + self, + # set mime type to "multipart/report" + _subtype="report", + boundary=boundary, + _subparts=_subparts, + # add "report-type" as a "Content-Type" parameter + report_type=report_type) + self._report_type = report_type + + def attach(self, payload): + """ + Add the given payload to the current payload, but first verify if it's + valid according to RFC6522. + + :param payload: The payload to be attached. + :type payload: Message + + :raise MessageError: Raised if the payload is invalid. + """ + idx = len(self.get_payload()) + 1 + self._check_valid_payload(idx, payload) + MIMEMultipart.attach(self, payload) + + def _check_valid_payload(self, idx, payload): + """ + Check that an attachment is valid according to RFC6522. + + :param payload: The payload to be attached. + :type payload: Message + + :raise MessageError: Raised if the payload is invalid. + """ + if idx == 1: + # The text in the first section can use any IANA-registered MIME + # media type, charset, or language. + cond = lambda payload: isinstance(payload, MIMEBase) + error_msg = "The first attachment must be a MIME message." + elif idx == 2: + # RFC 6522 requires that the report-type parameter is equal to the + # MIME subtype of the second body type of the multipart/report. + cond = lambda payload: \ + payload.get_content_type() == self._report_type + error_msg = "The second attachment's subtype must be %s." \ + % self._report_type + elif idx == 3: + # A body part containing the returned message or a portion thereof. + cond = lambda payload: isinstance(payload, Message) + error_msg = "The third attachment must be a message." + else: + # The multipart/report media type contains either two or three sub- + # parts. + cond = lambda _: False + error_msg = "The multipart/report media type contains either " \ + "two or three sub-parts." + if not cond(payload): + raise MessageError("Invalid attachment: %s" % error_msg) + + def as_string(self, unixfrom=False): + """ + Return the entire formatted message as string. + + This is modified from upstream to use our own generator. + + :param as_string: Whether to include the Unix From envelope heder. + :type as_string: bool + + :return: The entire formatted message. + :rtype: str + """ + fp = StringIO() + g = DSNGenerator(fp) + g.flatten(self, unixfrom=unixfrom) + return fp.getvalue() |