Wireshark · Ethereal-dev: [Ethereal-dev] Precisions needed on how to integrate the call to the sub-dissector into the parent

["Yann Samama" <ysamama@xxxxxxxxxxxxxxxxxx>]

Title: [Ethereal-dev] Precisions needed on how to integrate the call to the sub-dissector into the parent dissector

Hi List,

I'm currently writing a dissector for a proprietary protocol (let's call it myproto) that runs on top of TCP and use a field value to discriminate between two sub-dissectors to call : either TCAP or MAP.

The integration to TCP is OK.
My problem is that I don't know how to integrate those calls to the sub-dissectors in my code.
I know that a similar question has been asked beginning of november, but I read the answers and I am still confused about the way to implement it.

Could somebody complete those code snippets below ?

Thanks in advance,

Yann.

static void
dissect_myproto_common(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
  guint offset             = 0;
  guint packet_length      = 0;
  guint msgtype            = 0;
  proto_tree *myproto_tree = NULL;
  proto_tree *header_tree  = NULL;
  proto_item *ti           = NULL;
  tvbuff_t *next_tvb       = NULL;;
  int reported_length      = 0;
  int available_length     = 0;
  int data_offset          = 0;
  int field                = 0;
 
  if (check_col(pinfo->cinfo, COL_INFO))
    col_clear(pinfo->cinfo, COL_INFO);
   
  packet_length = tvb_get_letohs(tvb, 1);
  if (tree) {
    /* Tree building code snipped */
  }
  if (data_offset > 0) { /* offset to the first byte of the sub-protocol ; should be non-zero */
    available_length = tvb_length(tvb) - data_offset;
    reported_length = tvb_get_letohs(tvb, data_offset - 2); /* the length of the data is given just before the start */
    next_tvb = tvb_new_subset(tvb, offset, MIN(available_length, reported_length), reported_length);
    switch (field) {
      case TCAP:
      /* What should I do here ??? */
        break;
      case MAP:
      /* What should I do here ??? */
        break;
      default:
        break;
    }
  }
}

void
proto_register_myproto(void)
{
  static hf_register_info hf[] = {
    { &hf_myproto_header, {"Header", "myproto.header", FT_UINT8, BASE_DEC, NULL, 0x0, "Sub-dissector Field", HFILL }},
  };

  static gint *ett[] = {
    &ett_myproto,
  };
 
  module_t *myproto_module;
 
  /* Registering the MYPROTO protocol */
  proto_myproto = proto_register_protocol("MYPROTO Protocol", "MYPROTO", "myproto");
  proto_register_field_array(proto_myproto, hf, array_length(hf));
  proto_register_subtree_array(ett, array_length(ett));

  /* Registering the MYPROTO protocol preferences */
  myproto_module = prefs_register_protocol(proto_myproto, NULL);

  /* Registering the default ports to use over TCP */
  prefs_register_uint_preference(myproto_module, "tcp_port", "MYPROTO port", "MYPROTO port (default 3000)", 10, &tcp_port_myproto);

  /* Registering the desegmentation preference*/
  prefs_register_bool_preference(myproto_module, "desegment_myproto_messages", "Desegment all MYPROTO messages spanning multiple TCP segments", "Whether the MYPROTO dissector should desegment all messages spanning multiple TCP segments", &myproto_desegment);

  /* What should I do here ??? */
}

void
proto_reg_handoff_myproto(void)
{
  dissector_handle_t myproto_tcp_handle;

  myproto_tcp_handle = create_dissector_handle(dissect_myproto_tcp, proto_myproto);
  dissector_add("tcp.port", tcp_port_myproto, myproto_tcp_handle);
 
  /* What should I do here ??? */
}