Email-based exception handler

dmarcreceiver/commands.py

@@ -8,7 +8,7 @@ from lxml.etree import parse as parse_xml
 from dmarcreceiver.model import DBSession, Report, ReportError, ReportRecord, OverrideReason, DKIMResult, SPFResult, metadata, init_model
 import transaction
 
-from .util import sendmail
+from .util import sendmail, install_exception_handler
 from .config import config
 
 def parse_metadata(tree):
@@ -89,6 +89,10 @@ def receive_report(args):
     # read email message from stdin
     msg = message_from_file(sys.stdin)
 
+    # if not running on a tty, install email-based exception handler
+    if not sys.stderr.isatty():
+        install_exception_handler(msg)
+
     # check for zip file
     content_type = msg['content-type']
     if content_type.find(';') != -1:

dmarcreceiver/util.py

@@ -1,5 +1,11 @@
-import os
+import sys, os
 import subprocess
+from email.mime.text import MIMEText
+from email.mime.multipart import MIMEMultipart
+from email.mime.message import MIMEMessage
+from traceback import format_exception, format_exception_only
+
+from .config import config
 
 def sendmail(msg):
     sendmail_executable = None
@@ -11,6 +17,30 @@ def sendmail(msg):
         raise FileNotFoundError('Could not find sendmail executable')
 
     pipe = subprocess.Popen([ sendmail_executable, '-t' ], stdin=subprocess.PIPE)
-    stdout, stderr = pipe.communicate(msg.as_bytes)
+    stdout, stderr = pipe.communicate(msg.as_bytes())
     return pipe.wait()
 
+def install_exception_handler(incoming_msg):
+    bounce_address = config.get('bounce_address')
+    if bounce_address is None:
+        return
+
+    def exception_handler(exctype, value, traceback):
+        exc_text = ''.join(format_exception(exctype, value, traceback))
+        msg = MIMEMultipart()
+        txt_msg = MIMEText('''There was a problem processing an incoming DMARC report:
+
+{}'''.format(exc_text))
+        txt_msg['Content-Disposition'] = 'inline'
+        msg.attach(txt_msg)
+        att = MIMEMessage(incoming_msg)
+        att['Content-Disposition'] = 'attachment'
+        att['Content-Description'] = 'Original DMARC report message'
+        msg.attach(att)
+        msg['To'] = bounce_address
+        msg['From'] = bounce_address
+        msg['Subject'] = 'Exception: ' + format_exception_only(exctype, value)[-1][:70]
+        sendmail(msg)
+
+    sys.excepthook = exception_handler
+