SIP conntrack helper

[sougol gheissi]

Hello all,
I have read that helpers in conntrack would give us the opportunity to pars
the packets up to application layer. I want to pars the SIP packet, so I
decided to use the SIP conntrack helper;which is nf_conntrack_sip. Unlike
the functionality the helper itself gives, I want to find the SIP messages
of type MESSAGE and read the request line of the packet. SO I add  the
following code into the line 256.

char sub[mlen+1];
      memcpy(sub,&limit[0], mlen))
      sub[mlen]='\0';
      printk(KERN_ALERT "method is:[%s]", sub);


But the problem is, nothing is being printed. My question is, Can I use
nf_conntrack_sip for my purpose? and if yes, what is wrong with my code?

Thanks in advance.
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