[Click] Modification(handling) of an ip packet data field ?

[yacine.djemaiel]

Hi Beyers,

Thank you very much for informations that you provide, i think
that this is what i look for. To insert data in this field, i
think that i need to use memcpy to insert data because put
method allocate only free space.

Thanks again  
 


> Hi Yacine,
> 
> On TCP packets I use the following to access data:
> 
> unsigned data_offset = (iph->ip_hl << 2) + (tcph->th_off <<
2);  // IP Header length + TCP Header length
> unsigned char *data = p->data() + data_offset;
> 
> The above non-const data pointer should only work on a
writeable packet gained via uniqueify or make as Eddie pointed
out.
> 
> Cheer
> 
> Beyers
> 
> -----Original Message-----
> From: click-bounces at amsterdam.lcs.mit.edu
> [mailto:click-bounces at amsterdam.lcs.mit.edu]On Behalf Of
ystar master
> Sent: Wednesday, October 20, 2004 9:07 AM
> To: Eddie Kohler
> Cc: click at amsterdam.lcs.mit.edu
> Subject: Re: [Click] Modification(handling) of an ip packet
data field ?
> 
> 
> Hi Eddie,
> 
> Thank you for informations that you have provided. I
> think that i have found the solution to access the
> data  field by using th_off defined in the
> include/clicknet/tcp.h. If there are another mean to
> access data field, please inform me.
> 
> Thanks again
> YacineI
> 
> 
>  --- Eddie Kohler <kohler at cs.ucla.edu> a écrit : 
> 
> > Hi Yacine,
> > 
> > The general pattern is to "uniqueify" the packet,
> > making sure that it is not 
> > shared.  Then the "ip_header()" and "tcp_header()"
> > return values will become 
> > writable.  See IPMirror (elements/ip/ipmirror.cc)
> > for an example.
> > 
> > Eddie
> 
> 
> 
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> 
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