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

[Beyers Cronje]

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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