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# A simple milter.
# Author: Stuart D. Gathman <stuart@bmsi.com>
# Copyright 2001 Business Management Systems, Inc.
# This code is under GPL. See COPYING for details.
import sys
import os
import StringIO
import rfc822
import mime
import Milter
import tempfile
from time import strftime
#import syslog
#syslog.openlog('milter')
class sampleMilter(Milter.Milter):
"Milter to replace attachments poisonous to Windows with a WARNING message."
def log(self,*msg):
print "%s [%d]" % (strftime('%Y%b%d %H:%M:%S'),self.id),
for i in msg: print i,
print
def __init__(self):
self.tempname = None
self.mailfrom = None
self.fp = None
self.bodysize = 0
self.id = Milter.uniqueID()
# multiple messages can be received on a single connection
# envfrom (MAIL FROM in the SMTP protocol) seems to mark the start
# of each message.
def envfrom(self,f,*str):
self.log("mail from",f,str)
self.fp = StringIO.StringIO()
self.tempname = None
self.mailfrom = f
self.bodysize = 0
return Milter.CONTINUE
def envrcpt(self,to,*str):
# mail to MAILER-DAEMON is generally spam that bounced
if to.startswith('<MAILER-DAEMON@'):
self.log('DISCARD: RCPT TO:',to,str)
return Milter.DISCARD
self.log("rcpt to",to,str)
return Milter.CONTINUE
def header(self,name,val):
lname = name.lower()
if lname == 'subject':
# even if we wanted the Taiwanese spam, we can't read Chinese
# (delete if you read chinese mail)
if val.startswith('=?big5') or val.startswith('=?ISO-2022-JP'):
self.log('REJECT: %s: %s' % (name,val))
#self.setreply('550','','Go away spammer')
return Milter.REJECT
# check for common spam keywords
if val.find("$$$") >= 0 or val.find("XXX") >= 0 \
or val.find("!!!") >= 0 or val.find("FREE") >= 0:
self.log('REJECT: %s: %s' % (name,val))
#self.setreply('550','','Go away spammer')
return Milter.REJECT
# check for spam that pretends to be legal
lval = val.lower()
if lval.startswith("adv:") or lval.startswith("adv.") \
or lval.find('viagra') >= 0:
self.log('REJECT: %s: %s' % (name,val))
return Milter.REJECT
# check for invalid message id
if lname == 'message-id' and len(val) < 4:
self.log('REJECT: %s: %s' % (name,val))
#self.setreply('550','','Go away spammer')
return Milter.REJECT
# check for common bulk mailers
if lname == 'x-mailer' and \
val.lower() in ('direct email','calypso','mail bomber'):
self.log('REJECT: %s: %s' % (name,val))
#self.setreply('550','','Go away spammer')
return Milter.REJECT
# log selected headers
if lname in ('subject','x-mailer'):
self.log('%s: %s' % (name,val))
if self.fp:
self.fp.write("%s: %s\n" % (name,val)) # add header to buffer
return Milter.CONTINUE
def eoh(self):
if not self.fp: return Milter.TEMPFAIL # not seen by envfrom
self.fp.write("\n")
self.fp.seek(0)
# copy headers to a temp file for scanning the body
headers = self.fp.getvalue()
self.fp.close()
self.tempname = fname = tempfile.mktemp(".defang")
self.fp = open(fname,"w+b")
self.fp.write(headers) # IOError (e.g. disk full) causes TEMPFAIL
return Milter.CONTINUE
def body(self,chunk): # copy body to temp file
if self.fp:
self.fp.write(chunk) # IOError causes TEMPFAIL in milter
self.bodysize += len(chunk)
return Milter.CONTINUE
def _headerChange(self,msg,name,value):
if value: # add header
self.addheader(name,value)
else: # delete all headers with name
h = msg.getheaders(name)
cnt = len(h)
for i in range(cnt,0,-1):
self.chgheader(name,i-1,'')
def eom(self):
if not self.fp: return Milter.ACCEPT
self.fp.seek(0)
msg = mime.message_from_file(self.fp)
msg.headerchange = self._headerChange
if not mime.defang(msg,self.tempname):
os.remove(self.tempname)
self.tempname = None # prevent re-removal
self.log("eom")
return Milter.ACCEPT # no suspicious attachments
self.log("Temp file:",self.tempname)
self.tempname = None # prevent removal of original message copy
# copy defanged message to a temp file
out = tempfile.TemporaryFile()
try:
msg.dump(out)
out.seek(0)
msg = rfc822.Message(out)
msg.rewindbody()
while 1:
buf = out.read(8192)
if len(buf) == 0: break
self.replacebody(buf) # feed modified message to sendmail
return Milter.ACCEPT # ACCEPT modified message
finally:
out.close()
return Milter.TEMPFAIL
def close(self):
sys.stdout.flush() # make log messages visible
if self.tempname:
os.remove(self.tempname) # remove in case session aborted
if self.fp:
self.fp.close()
return Milter.CONTINUE
def abort(self):
self.log("abort after %d body chars" % self.bodysize)
return Milter.CONTINUE
if __name__ == "__main__":
#tempfile.tempdir = "/var/log/milter"
#socketname = "/var/log/milter/pythonsock"
socketname = os.getenv("HOME") + "/pythonsock"
Milter.factory = sampleMilter
Milter.set_flags(Milter.CHGBODY + Milter.CHGHDRS + Milter.ADDHDRS)
print """To use this with sendmail, add the following to sendmail.cf:
O InputMailFilters=pythonfilter
Xpythonfilter, S=local:%s
See the sendmail README for libmilter.
sample milter startup""" % socketname
sys.stdout.flush()
Milter.runmilter("pythonfilter",socketname,240)
print "sample milter shutdown"
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