Hi David,
2016-07-20 9:56 GMT+02:00 David Arnold <[email protected]>:
> I’m writing a dissector for a protocol that includes a 96 bit (12 byte)
> big-endian integer value.
>
> I’d like to display it as a decimal number. I’m happy to write a
> BASE_CUSTOM renderer for it, but how should it be described in the
> hf_register_info array?
>
> In my dissect() function, I have
>
> proto_tree_add_item(ouch_asx_tree,
> hf_ouch_asx_match_id,
> tvb, offset, 12,
> ENC_BIG_ENDIAN);
> offset += 12;
>
> In the hf_register_info array, I’d have something like
>
> { &hf_ouch_asx_match_id,
> { "Match ID", "ouch_asx.match_id",
> FT_BYTES, BASE_CUSTOM, CF_FUNC(format_match_id), 0x0, NULL,
> HFILL }},
>
> except that generates a runtime error:
>
> Err Field 'Match ID' (ouch-asx.match_id) has a 'strings' value
> but is of type FT_BYTES (which is not allowed to have strings)
>
> Quick hint, someone?
>
You cannot use BASE_CUSTOM for this use case, as explained in
doc/README.dissector:
"BASE_CUSTOM allows one to specify a callback function pointer that will
format the value.
For 32-bit and smaller values, custom_fmt_func_t can be used to declare
the callback function pointer. Specifically, this is defined as:
void func(gchar *, guint32);
For values larger than 32-bits, custom_fmt_func_64_t can be used to declare
the callback function pointer. Specifically, this is defined as:
void func(gchar *, guint64);
The first argument is a pointer to a buffer of the ITEM_LABEL_LENGTH size
and the second argument is the value to be formatted.
Both custom_fmt_func_t and custom_fmt_func_64_t are defined in
epan/proto.h."
So it can only work with FT_(U_)INTX types.
Instead you probably want to use proto_tree_add_bytes_format_value() taht
gives you a full control on what is displayed in the tree.
Regards,
Pascal.
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