Wireshark-dev: [Wireshark-dev] controlling the display of the leading bit string when bitmask !

From: "John Dill" <John.Dill@xxxxxxxxxxxxxxxxx>
Date: Thu, 24 Apr 2014 14:48:25 -0400
Title: controlling the display of the leading bit string when bitmask != 0

Is there a mechanism to control whether I want the bit string
displayed when the bitmask field is non-zero?  Granted, in most
circumstances, it looks good for data elements that consist of
consecutive bits, but in others it just looks jarring.

For example, I have a character attribute that has three data
elements, where two of the data elements are stored in a nibble,
followed by one that is in a byte.

0000 .... Field 1 - Char 1 (4 bit)
.... 0000 Field 2 - Char 1 (4 bit)
Field 3 - Char 1           (8 bit)
0000 .... Field 1 - Char 2
.... 0000 Field 2 - Char 2
Field 3 - Char 2
etc. for 24 characters

I need to display an array of this data, and it would be nice
to just remove the leading bit string altogether.  I can see
something in 'proto_tree_set_representation_value' (1.10.6) that
triggers off of 'bitmask != 0', but I don't see anything that
would hide that string using the normal api.

I hacked something crudely together to do it manually.

\code snippet
  header_field_info *hf;
  guint32 value;
  guint32 tmpval;

  ...

  /* Emit the code to display a data element without the leading
     bitmask display. */
#define EMIT_HF_NO_BITMASK(hf_index, tvb_offset)                             \
  hf = proto_registrar_get_nth(hf_index);                                    \
  value = tvb_get_guint8(tvb, (tvb_offset));                                 \
  tmpval = (value & hf->bitmask) >> hf->bitshift;                            \
  if (hf->strings) {                                                         \
    proto_tree_add_uint_format(tree, hf_index, tvb, (tvb_offset), 1, tmpval, \
      "%s: %s (%u)",                                                         \
      hf->name, val_to_str_const(tmpval, cVALS(hf->strings), "Unknown"), tmpval); \
  }                                                                          \
  else {                                                                     \
    proto_tree_add_uint_format(tree, hf_index, tvb, (tvb_offset), 1, tmpval, \
      "%s: %u",                                                              \
      hf->name, tmpval);                                                     \
  }
\endif

I'm tempted to add another bit next to BASE_RANGE_STRING
and BASE_EXT_STRING to flip the bit string display off in
'proto_tree_set_representation_value' so that I can just use
'proto_tree_add_item' and be done with it.

Or perhaps I missed something completely obvious.  Any
suggestions?

Thanks,
John Dill