From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <41b9f1bf163c2d3c41e182407477eb28@quanstro.net>
To: 9fans@9fans.net
From: erik quanstrom <quanstro@quanstro.net>
Date: Thu, 17 Apr 2008 15:29:42 -0400
In-Reply-To: <20080417184152.369735B52@mail.bitblocks.com>
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Subject: Re: [9fans] telnet vs. godaddy whois
Topicbox-Message-UUID: 90f3c2dc-ead3-11e9-9d60-3106f5b1d025

> On Thu, 17 Apr 2008 09:18:31 BST Charles Forsyth <forsyth@terzarima.net>  wrote:
>> > having said that, i now suspect that sending one byte into a zero-window is
>>  not the problem.
>>
>> because the one-byte probe can only be done if there is data to send, and i
>> already knew that a plain connection (dial only) to that port also failed:
>
> Not setting the PSH bit on a pure ACK (== no data is being
> sent) seems to fix this (see ip/tcp.c around line 2530).  May
> be it tickles a bug on the receiver (0 byte read?).

this does work for me.  is there some subtile reason *to* set the psh bit
on a pure ack?  in certain circumstances?

good call. from rfc793, p 42:

      [...]  If the the user signals a push function then the
      data must be sent even if it is a small segment.

minooka; 9diff ip/tcp.c
/n/sources/plan9//sys/src/9/ip/tcp.c:2529,2535 - ip/tcp.c:2529,2535
  			}
  		}

- 		if(sent+dsize == sndcnt)
+ 		if(sent+dsize == sndcnt && dsize)
  			seg.flags |= PSH;

  		/* keep track of balance of resent data */

- erik