[Gajim-devel] Gajim-svn and problem with SOCKS5 proxy

Marcin Zajączkowski mszpak at wp.pl
Sun Jun 29 00:41:09 CEST 2008

On 2008-06-15 09:12, Yann Leboulanger wrote:
> Marcin Zajączkowski wrote:
>> Thank you for your answer Yann.
>> I checked my Gajim with ssh -D (I didn't even know about that option to
>> get SOCKS5 proxy) and it was fine. I have also checked it with pure Tor
>> and it worked either. It seems to be an issue with privoxy itself.
>> I'm a little bit astonish, because a few other apps work with privoxy
>> without any problem. I will try to debug it on the privoxy side.
> Ok, thanks for trying to make it work ! Please keep us informed of your
> progress.

Hello again,

Today I was debugging the problem at the privoxy side and it seems that 
gajim hangs at the beginning of the conversation, before sending any 
"real" data.

At gajim side it looks like (gajim.py -v):
DEBUG: CONNECTproxy start Plugging 
<common.xmpp.transports_nb.NBSOCKS5PROXYsocket instance at 0x98015cc> 
into <common.xmpp.client_nb.NonBlockingClient instance at 0x904e08c>
DEBUG: CONNECTproxy start Proxy server contacted, performing 
DEBUG: CONNECTproxy sent

tcpdump shows following traffic on lo (szpak is a hostname):
23:55:35.994463 IP szpak.45365 > szpak.privoxy: S 580179035:580179035(0) 
win 32792 <mss 16396,sackOK,timestamp 12080872 0,nop,wscale 6>
23:55:35.994519 IP szpak.privoxy > szpak.45365: S 580266575:580266575(0) 
ack 580179036 win 32768 <mss 16396,sackOK,timestamp 12080872 
12080872,nop,wscale 6>
23:55:35.994553 IP szpak.45365 > szpak.privoxy: . ack 1 win 513 
<nop,nop,timestamp 12080872 12080872>
23:55:35.996639 IP szpak.45365 > szpak.privoxy: P 1:5(4) ack 1 win 513 
<nop,nop,timestamp 12080874 12080872>
23:55:35.996714 IP szpak.privoxy > szpak.45365: . ack 5 win 512 
<nop,nop,timestamp 12080874 12080874>

In the communication with pure Tor there is one more packet PSH,ACK from 
Tor, which is confirmed by Gajim and next Gajim sends its request.
I'm not a TCP expert, but do you thing the lack of that one PSH packet 
can cause that ACK is not push to Gajim and it waits for ACK forever (or 
at least until a timeout)?

I have more detailed dump from Wireshark if someone is interested.


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