Implement mail dispatcher app.

reviewbot/mail_dispatcher.py

+# Copyright (c) 2013 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Main app that handles incoming mail and dispatches it to handlers."""
+
+import logging
+import re
+
+import webapp2
+import webob.exc
+
+from google.appengine.api import app_identity
+from google.appengine.api import mail
+
+import third_party  # pylint: disable=W0611
+
+import handlers.policy_checklist
+from review import Review
+from rietveld import Rietveld
+import util
+
+
+# Lists the handlers served by the review bot app. The local part of email
+# addresses the app receives email on is used as a key into the handler map.
+# Each handler is just a function that gets called with the email address, the
+# email message, a Review object and a Rietveld interface.
+#
+# New handlers can be added by adding the code in handlers/<handler_name>.py,
+# importing the module and adding an entry to the HANDLERS map.
+HANDLERS = {
+    'policy_checklist': handlers.policy_checklist.process
+}
+
+
+# Regular expression that matches email addresses belonging to the review bot
+# app and extracts the handler name.
+REVIEW_BOT_RECIPIENT_RE = re.compile('^([^@]+)@%s.appspotmail.com$' %
+                                     app_identity.get_application_id())
+
+
+# This is the regular expression that rietveld uses to extract the issue number
+# from the mail subject at the time of writing this. This code needs to be kept
+# up-to-date with the mechanism rietveld uses so the tools don't confuse issues.
+RIETVELD_ISSUE_NUMBER_RE = re.compile(r'\(issue *(?P<id>\d+)\)$')
+
+
+class MailDispatcher(webapp2.RequestHandler):
+  """Dispatches mail to handlers as indicated by email addresses."""
+
+  def post(self):
+    """Handles POST requests.
+
+    Parses the incoming mail message. Dispatches to interested handlers based on
+    the list of mail recipients.
+    """
+
+    # Singleton Rietveld interface for this request.
+    rietveld = Rietveld()
+
+    # Parse the message and instantiate the review interface.
+    message = mail.InboundEmailMessage(self.request.body)
+    match = RIETVELD_ISSUE_NUMBER_RE.search(message.subject)
+    if match is None:
+      raise webob.exc.HTTPBadRequest('Failed to parse issue id: %s' %
+                                     message.subject)
+    review = Review(rietveld, match.groupdict()['id'])
+
+    # Determine recipients and run the handlers one by one.
+    recipients = set(util.get_emails(getattr(message, 'to', '')) +
+                     util.get_emails(getattr(message, 'cc', '')))
+    for addr in recipients:
+      match = REVIEW_BOT_RECIPIENT_RE.match(addr)
+      if not match:
+        continue
+
+      try:
+        handler = HANDLERS[match.group(1)]
+      except KeyError:
+        continue
+
+      try:
+        handler(addr, message, review, rietveld)
+      except:  # pylint: disable=W0702
+        logging.exception('Handler %s failed!', match.group(1))
+
+  def handle_exception(self, exception, debug):
+    """Handles exceptions to print HTTP error details.
+
+    Args:
+      exception: The exception.
+      debug: Whether we're in debug mode.
+    """
+    if isinstance(exception, webob.exc.HTTPException):
+      logging.warning('Request %s failed: %d - %s',
+                      self.request.url, exception.code, exception.detail)
+
+    webapp2.RequestHandler.handle_exception(self, exception, debug)
+
+
+app = webapp2.WSGIApplication([('/_ah/mail/.*', MailDispatcher)])