Wireshark · Ethereal-dev: Re: RE: [Ethereal-dev] problem in new dissector added

["bunty " <bunty123_4@xxxxxxxxxxxxxx>]

Hello,
        Thanks for reply. Sorry for not stating problem in detail. Following are 4 changes i made to ethereal-0.10.10 sourcecode. Sorry i dont know how to create patch.
My packet structure is ETHER + MYIP + IP + TCP/UDP/ICMP headers
        Please kindly check my implementation for why its producing segmentation fault.

1) add new type ETHERTYPE_MYIP to etypes.h
2)Changes to packet-ethertype.c => Added new ether protocol ID and written case to handle no. of that packets.
*****************************************************
  {ETHERTYPE_MYIP,          "MYIP"               },

  case ETHERTYPE_MYIP:
      ld->myip++;
      capture_myip(pd, offset, len, ld);
      break;


3)New header packet-myip.h
*******************************************************************
#ifndef __PACKET_MYIP_H__
#define __PACKET_MYIP_H__

typedef struct _e_mymyip
    {
    guchar  *myip_text;
    guint32  myip_num;

} e_myip;

void capture_myip(const guchar *, int, int, packet_counts *);

/* Export the DSCP value-string table for other protocols */
extern const value_string dscp_vals[];

#endif


4)New header packet-myip.c
*****************************************************************
#ifdef HAVE_CONFIG_H
# include "config.h"
#endif
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <glib.h>
#include <epan/packet.h>
#include <epan/prefs.h>
#include <epan/ipproto.h>
#include "etypes.h"
#include "packet-myip.h"
#include "packet-ip.h"

void proto_reg_handoff_myip(void);
static int proto_myip = -1;
static gint ett_myip = -1;
static int hf_myip_num = -1;
static unsigned char* hf_myip_text = -1;
static void dissect_myip(tvbuff_t *, packet_info *, proto_tree *);
static dissector_table_t myip_dissector_table;
static dissector_handle_t data_handle;


void capture_myip(const guchar *pd, int offset, int len, packet_counts *ld) {
capture_ip(pd,offset+8,len,ld);
}


static void dissect_myip(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
proto_tree      *myh_tree;
proto_item      *volatile myti = NULL;
e_myip *myh;
guint8    nxt;
guint16 num;
guchar *str;
tvbuff_t  *next_tvb;
int        offset = 0;

     if (check_col(pinfo->cinfo, COL_PROTOCOL))
          col_set_str(pinfo->cinfo, COL_PROTOCOL, "MYIP");
if (check_col(pinfo->cinfo, COL_INFO))
          col_clear(pinfo->cinfo, COL_INFO);

myh->myip_num = tvb_get_ntohl(tvb, 0);
num=myh->myip_num;

if(tree)
{
myti = proto_tree_add_item(tree, proto_myip, tvb, 0, num, FALSE);
myh_tree = proto_item_add_subtree(myti, ett_myip);

proto_tree_add_uint_format(myh_tree, hf_myip_num, tvb, offset, 1,num,
        "Sequence no: %u", num);
}

myh->myip_text = tvb_get_string(tvb, 4,4);
str=myh->myip_text;

if(tree)
{
myti = proto_tree_add_string(myh_tree, hf_myip_text, tvb,0, 0, "");

}
  next_tvb = tvb_new_subset(tvb, 8, -1, -1);

  if (!dissector_try_port(myip_dissector_table, 8 , next_tvb, pinfo, tree)) {
  call_dissector(data_handle,next_tvb, pinfo, tree);
  }

}




void proto_register_myip(void)
{
  module_t *myip_module;

     static hf_register_info hf[] = {
          { &hf_myip_text,
          { "myip_text",          "myip.text", FT_STRING, BASE_HEX, NULL, 0x0,"", HFILL }},
          { &hf_myip_num,
          { "myip_num",          "myip.num", FT_UINT32, BASE_DEC, NULL, 0x0,"", HFILL }}
};
     static gint *ett[] = {
          &ett_myip,
     };

     proto_myip = proto_register_protocol("My Internet Protocol","MYIP", "myip");
     proto_register_field_array(proto_myip, hf, array_length(hf));
     proto_register_subtree_array(ett, array_length(ett));
           myip_dissector_table = register_dissector_table("myip.proto",
         "MYIP protocol", FT_UINT8, BASE_DEC);   

        myip_module = prefs_register_protocol(proto_myip, proto_reg_handoff_myip);

register_dissector("myip", dissect_myip, proto_myip);
}
void proto_reg_handoff_myip(void)
{
     dissector_handle_t myip_handle;
     data_handle = find_dissector("data");
        myip_handle = find_dissector("myip");
     dissector_add("ethertype", ETHERTYPE_MYIP, myip_handle);
}


regards,
bunty.
On Tue, 05 Apr 2005 Francisco Alcoba(TS/EEM) wrote :
>Hi,
>
>Unless you have checked the option "update packet list in real time" the packets are dissected
>only when the capture stops, so any problem the dissector has will show up then. The best way
>to find out what is happening is, in my experience, to start ethereal in debug mode. You might
>be using uninitialized pointers, incorrectly called functions, whatever; the fact that is shows in
>the protocol list does not mean the dissector is 100% bug free.
>
>I can only speak for myself, but I find it very difficult to understand code without knowing what it
>is trying to do -in this case, without knowing what packet it is trying to dissect-. And, of course,
>the more defined a problem is the easiest to offer suggestions -i.e. it is easier to suggest an
>answer to "why in this line of code I use this function with this arguments and the result is not
>what I expected" than to "why is my code not working?"-.
>
>Regards,
>
>  Francisco
>
>-----Original Message-----
> From: ethereal-dev-bounces@xxxxxxxxxxxx [mailto:ethereal-dev-bounces@xxxxxxxxxxxx]
>Sent: martes, 05 de abril de 2005 18:22
>To: ethereal-dev@xxxxxxxxxxxx
>Subject: [Ethereal-dev] problem in new dissector added
>
>
>
>
>Hello,
>      I added new dissector. I already mailed that on forum but unable to get reply for that from anyone. I tried then to implement on my own and get successfully added to list of protocols(dont know whether its correct  implemented or not?).
>      Curretly i am facing problem that when i try to capture packets, capture windows shows packet captured but when i stop it then accidently ethereal stops working giving segmentation fault. What is the reason i am getting segmentation fault?
>        Hope this time i will get response from list.
>Thanks in advance.
>regards,
>bunty.
>
>
>
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>
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