forking smtpd

Discussion in 'Python' started by Eric S. Johansson, Aug 20, 2004.

  1. I was working on a filter for postfix and instead of using the "fork a
    new python process on every message" route, I decided to use the SMTP
    interface instead and try forking after having started the Python process.

    obviously, I needed some way to receive and processed SMTP.
    works OK if you are willing to use single threaded one at a time
    filtering. Because filtering takes significant amounts of time, I
    decided to expand smtpd to support a forking server.

    I make no claims to the correctness or suitability of these
    modifications or even that I understood wtf was going on with
    asyncore/chat. it will also be interesting to see what improvements
    others have to suggest. But here's what I found:

    it was relatively easy to create a subclass (forkSMTPServer) and inside
    of the accept handler, I was able to fork off the child process and
    release the connection. I suspect that I haven't released the listen
    socket properly but I will look into that.

    I also copied the asyncore polling loop into SMTPServer and modified it
    to support forking and exit on the same signal as the rest of asyncore.

    the last change I added was a close method to SMTPChannel and
    process_close method SMTPServer. This is so one can detect when a
    channel has closed and do something about it such as ending a child process.

    so, in the end a forking smtp receiver looks like:

    class filter(smtpd.forkSMTPServer):

    def process_message(self, peer, mailfrom, rcpttos, data):

    log("postfix peer %s %s"%(peer))
    log("postfix mail from %s"%(mailfrom))
    log("postfix rcpt to %s"%(rcpttos))
    #<do something with message here>
    print "processing",self.parent_ID

    f = filter2(("localhost",40025))

    print "exit from loop"
    except KeyboardInterrupt:
    except SystemExit:

    except Exception, error:
    print str(error)
    etype, value, tb = sys.exc_info()
    exception_strings = traceback.format_exception(etype, value, tb)
    for i in exception_strings:
    print(i, 1)

    line wrapped patches below:
    < def close(self):
    < print "outside close"
    < asynchat.async_chat.close(self)
    < self.__server.process_close()
    < def process_close (self):
    < """override this abstract method to handle the close of SMTP
    channel. """
    < pass
    < def loop (self, timeout=30.0, use_poll=0, map=None):
    < global f
    < if map is None:
    < map=asyncore.socket_map
    < if use_poll:
    < if hasattr (select, 'poll'):
    < poll_fun = asyncore.poll3
    < else:
    < poll_fun = asyncore.poll2
    < else:
    < poll_fun = asyncore.poll
    < while map:
    < try:
    < status = os.waitpid(-1,os.WNOHANG)
    < print "timeout loop %s %s"% (self.parent_ID, str(status))
    < except OSError, error:
    < if error[0] == 10:
    < status = (0,0)
    < else:
    < print self.parent_ID, error
    < if status[0] == 0:
    < try:
    < poll_fun (timeout, map)
    < except asyncore.ExitNow:
    < return
    < class forkSMTPServer(SMTPServer):
    < def __init__(self, address):
    < self.parent_ID = None
    < SMTPServer.__init__(self, address,(0,0))
    < self.mychannel = None
    < def handle_accept(self):
    < conn, addr = self.accept()
    < self.parent_ID = os.fork()
    < if not self.parent_ID:
    < print >> DEBUGSTREAM, 'Incoming connection from %s' %
    < self.mychannel = SMTPChannel(self, conn, addr)
    < else:
    < # close off socket in parent and fake lack of connection
    < conn.close()
    < self.connected = 0
    < print "child fork ID", self.parent_ID
    < def process_close(self):
    < print "process my very own close "
    < # if we are a child process, we are done so exit
    < if not self.parent_ID:
    < print "exit stage left %s"% (self.parent_ID)
    < raise asyncore.ExitNow

    Speech recognition in use. It makes mistakes, I correct most
    Eric S. Johansson, Aug 20, 2004
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