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Re: Why Postfix always complain "unexpected EOF" with my own tcp_table program?

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  • Wietse Venema
    ... Caution: it is not a good idea to close a connection immediately after writing data to it. Some TCP/IP implementations may discard unsent data when a
    Message 1 of 7 , Jul 28, 2013
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      Zhang Huangbin:
      > On Sunday, July 28, 2013 at 8:24 PM, Wietse Venema wrote:
      >
      > > 1) Use a network sniffer to see what Python actually sends. You may
      > > assume that your program sends \n, but Postfix does not receive \n.
      >
      > Thanks Wietse, and John.
      > I think this is the root cause, will try a network sniffer later.
      > > 2) Unrelated to this bug: closing the connection after one request
      > > is inefficient.
      >
      > My program closes the connection immediately.

      Caution: it is not a good idea to close a connection immediately
      after writing data to it. Some TCP/IP implementations may discard
      unsent data when a connection is closed.

      In Postfix, I avoid "write-close" bugs by keeping a connection open
      until the receiver closes it (with of course a time limit that
      forces the connection to be closed when things take too long).

      Wietse
    • King Cao
      You can enable the debug mode of postfix smtp daemon ( http://www.postfix.org/DEBUG_README.html). Then you can see the request and response which postfix
      Message 2 of 7 , Jul 28, 2013
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        You can enable the debug mode of postfix smtp daemon (http://www.postfix.org/DEBUG_README.html). Then you can see the request and response which postfix talked with your tcp_table script.

        PS:
          From the postfix source code, it seems postfix has not received any response from your tcp_table.  However postfix will retry 10 times for such scenario (sleep 1 sec before each retry).


        2013/7/28 Wietse Venema <wietse@...>
        Zhang Huangbin:
        > On Sunday, July 28, 2013 at 8:24 PM, Wietse Venema wrote:
        >
        > > 1) Use a network sniffer to see what Python actually sends. You may
        > > assume that your program sends \n, but Postfix does not receive \n.
        >
        > Thanks Wietse, and John.
        > I think this is the root cause, will try a network sniffer later.
        > > 2) Unrelated to this bug: closing the connection after one request
        > > is inefficient.
        >
        > My program closes the connection immediately.

        Caution: it is not a good idea to close a connection immediately
        after writing data to it.  Some TCP/IP implementations may discard
        unsent data when a connection is closed.

        In Postfix, I avoid "write-close" bugs by keeping a connection open
        until the receiver closes it (with of course a time limit that
        forces the connection to be closed when things take too long).

                Wietse

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