PROBLEM: all bytes of extracted payload from a dump file appears to be zero

[Irfan Ahmed]

I am using TCPTRACE in Fedora Linux Kernel version 2.6.18.1 to extract and 
process packets from a packet dump file. To process each packet, the md_read() 
function is called . The code of which is as follows.
I am trying to extract payload from these packets. but when I display the bytes 
of the payload or infact the packet using *payload or *pip pointer 
...........all bytes appear to be zero.........
I could not figure out why this is happening............

any suggestions or help ..............

void
md_read(
    struct ip *pip,        /* the packet */
    tcp_pair *ptp,        /* info I have about this connection */
    void *plast,        /* past byte in the packet */
    void *mod_data)        /* connection info for this one */
{
        unsigned int j;
    unsigned char *payload,*packet;
    long  bytes,payload_length,size_iphdr,size_tcphdr;

    if (pip->ip_p != IPPROTO_TCP) return; //only process tcp packets

    packet =  pip;

    size_iphdr = 4*IP_HL(pip);
    if(size_iphdr<20){printf("Invalid IP header:%u bytes\n",size_iphdr); 
return;}
    struct tcphdr *ptcp = (struct tcphdr *) (packet + size_iphdr);  

    size_tcphdr = 4*TH_OFF(ptcp);
    if(size_tcphdr<20){printf("Invalid TCP header:%u bytes\n",size_tcphdr); 
return;}

       //contains the pointer to the payload
     payload =  (packet + size_iphdr + size_tcphdr );  

        bytes = ntohs(pip->ip_len);    //total length of the packet
    payload_length = bytes - size_iphdr  -size_tcphdr  ;  //payload length    

}



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