[Abhik Sarkar <sarkar.abhik@xxxxxxxxx>]

How about registering a third common protocol PROTO, putting the common fields in that and then calling dissect methods in the common dissector from the variant dissectors? Would that work?

On Tue, Apr 7, 2009 at 8:06 PM, Tamazov, Artem <artem.tamazov@xxxxxxxxxxx> wrote:

Hello,

I would like to implement two dissectors which are very similar.
How can I re-use definition of hf[]?

See sample code below (question is in comments):

==================
...
static int proto_PROTOABBREV_VARIATION_A = -1;
static int proto_PROTOABBREV_VARIATION_B = -1;
static int hf_PROTOABBREV_FIELDABBREV = -1;
static gint ett_PROTOABBREV = -1;

static int dissect_PROTOABBREV_VARIATION_A(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
...
}

static int dissect_PROTOABBREV_VARIATION_B(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
...
}

void proto_register_PROTOABBREV(void)
{
       static hf_register_info hf[] = {
               { &hf_PROTOABBREV_FIELDABBREV,
                       { "FIELDNAME",           "PROTOABBREV.FIELDABBREV",
                       FIELDTYPE, FIELDBASE, FIELDCONVERT, BITMASK,
                       "FIELDDESCR", HFILL }
               }
       };

       static gint *ett[] = {
               &ett_PROTOABBREV
       };

       proto_PROTOABBREV_VARIATION_A = proto_register_protocol("PROTONAME VARIATION A",
           "PROTOSHORTNAME A", "PROTOABBREVA");
       proto_PROTOABBREV_VARIATION_B = proto_register_protocol("PROTONAME VARIATION B",
           "PROTOSHORTNAME B", "PROTOABBREVB");

       proto_register_field_array(proto_PROTOABBREV_VARIATION_A, hf, array_length(hf));
       /*
        * *QUESTION*:
        *      AFAIK double registration of hf[] is wrong, although currently Wireshark
        *      tolerates this. How to _properly_ re-use hf[] in variation B?
      */
       proto_register_field_array(proto_PROTOABBREV_VARIATION_B, hf, array_length(hf));
       proto_register_subtree_array(ett, array_length(ett));
}

void
proto_reg_handoff_PROTOABBREV(void)
{
       dissector_handle_t PROTOABBREV_handle;
       PROTOABBREV_handle = new_create_dissector_handle(dissect_PROTOABBREV_VARIATION_A, proto_PROTOABBREV_VARIATION_A);
       dissector_add("PARENT_SUBFIELD", ID_VALUE, PROTOABBREV_handle);
       PROTOABBREV_handle = new_create_dissector_handle(dissect_PROTOABBREV_VARIATION_B, proto_PROTOABBREV_VARIATION_B);
       dissector_add("PARENT_SUBFIELD", ID_VALUE, PROTOABBREV_handle);
}
==================

I see one possible way -- using of C preprocessor capabilities:

==================
...
static int hf_PROTOABBREV_FIELDABBREV_for_A = -1;
static int hf_PROTOABBREV_FIELDABBREV_for_B = -1;
...
#define HF_INITIALIZER_FIELDABBREV(hf_handle)\
               { &(hf_handle),\
                       { "FIELDNAME",           "PROTOABBREV.FIELDABBREV",\
                       FIELDTYPE, FIELDBASE, FIELDCONVERT, BITMASK,\
                       "FIELDDESCR", HFILL }\
               }\
       }
...
       static hf_register_info hf_a[] = HF_INITIALIZER_FIELDABBREV(hf_PROTOABBREV_FIELDABBREV_for_A);
       static hf_register_info hf_b[] = HF_INITIALIZER_FIELDABBREV(hf_PROTOABBREV_FIELDABBREV_for_B);
...
       proto_register_field_array(proto_PROTOABBREV_VARIATION_A, hf_a, array_length(hf_a));
       proto_register_field_array(proto_PROTOABBREV_VARIATION_B, hf_b, array_length(hf_b));
...
==================

But this solution is not elegant, I guess.
Any ideas?

Thank you in advance,
artem//
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