Improve support for single-character fields and filter expressions.

Add an FT_CHAR type, which is like FT_UINT8 except that the value is
displayed as a C-style character constant.

Allow use of C-style character constants in filter expressions; they can
be used in comparisons with all integral types, and in "contains"
operators.

Use that type for some fields that appear (based on the way they're
displayed, or on the use of C-style character constants in their
value_string tables) to be 1-byte characters rather than 8-bit numbers.

Change-Id: I39a9f0dda0bd7f4fa02a9ca8373216206f4d7135
Reviewed-on: https://code.wireshark.org/review/17787
Reviewed-by: Guy Harris <guy@alum.mit.edu>

1 files changed, 17 insertions, 5 deletions

diff --git a/doc/README.dissector b/doc/README.dissector
index bd34d416fb..e15ca6e26c 100644
--- a/doc/README.dissector
+++ b/doc/README.dissector
@@ -103,7 +103,7 @@ PROTOABBREV     A name for the protocol for use in filter expressions;
 FIELDNAME       The displayed name for the header field.
 FIELDABBREV     The abbreviated name for the header field; it may contain
                 only letters, digits, hyphens, underscores, and periods.
-FIELDTYPE       FT_NONE, FT_BOOLEAN, FT_UINT8, FT_UINT16, FT_UINT24,
+FIELDTYPE       FT_NONE, FT_BOOLEAN, FT_CHAR, FT_UINT8, FT_UINT16, FT_UINT24,
                 FT_UINT32, FT_UINT40, FT_UINT48, FT_UINT56, FT_UINT64,
                 FT_INT8, FT_INT16, FT_INT24, FT_INT32, FT_INT40, FT_INT48,
                 FT_INT56, FT_INT64, FT_FLOAT, FT_DOUBLE, FT_ABSOLUTE_TIME,
@@ -129,6 +129,13 @@ FIELDDISPLAY    --For FT_UINT{8,16,24,32,40,48,56,64} and
 
                   BASE_PT_UDP, BASE_PT_TCP, BASE_PT_DCCP or BASE_PT_SCTP
 
+                --For FT_CHAR:
+                  BASE_HEX, BASE_OCT, BASE_CUSTOM, or BASE_NONE, possibly
+                  ORed with BASE_RANGE_STRING, BASE_EXT_STRING or
+                  BASE_VAL64_STRING.
+
+                  BASE_NONE can be used in the same way as with FT_UINT8.
+
                 --For FT_ABSOLUTE_TIME:
 
                   ABSOLUTE_TIME_LOCAL, ABSOLUTE_TIME_UTC, or
@@ -747,6 +754,9 @@ The type of value this field holds. The current field types are:
     FT_FRAMENUM A frame number; if this is used, the "Go
                 To Corresponding Frame" menu item can
                 work on that field.
+    FT_CHAR     An 8-bit ASCII character.  It's treated similarly to an
+                FT_UINT8, but is displayed as a C-style character
+                constant.
     FT_UINT8    An 8-bit unsigned integer.
     FT_UINT16   A 16-bit unsigned integer.
     FT_UINT24   A 24-bit unsigned integer.
@@ -880,9 +890,11 @@ For FT_BOOLEAN fields that are also bitfields (i.e., 'bitmask' is non-zero),
 wide the parent bitfield is). (If the FT_BOOLEAN 'bitmask' is zero, then
 'display' must be BASE_NONE).
 
-For integer fields a "field-width" is not needed since the type of integer itself
-(FT_UINT8, FT_UINT16, FT_UINT24, FT_UINT32, FT_UINT40, FT_UINT48, FT_UINT56,
-FT_UINT64, etc) tells the proto_tree how wide the parent bitfield is.
+For integer fields a "field-width" is not needed since the type of
+integer itself (FT_UINT8, FT_UINT16, FT_UINT24, FT_UINT32, FT_UINT40,
+FT_UINT48, FT_UINT56, FT_UINT64, etc) tells the proto_tree how wide the
+parent bitfield is.  The same is true of FT_CHAR, as it's an 8-bit
+character.
 
 For FT_ABSOLUTE_TIME fields, 'display' is used to indicate whether the
 time is to be displayed as a time in the time zone for the machine on
@@ -1125,7 +1137,7 @@ for protocols with variable-width header fields.
 
 Note that the formats used must all belong to the same group as defined below:
 - FT_INT8, FT_INT16, FT_INT24 and FT_INT32
-- FT_UINT8, FT_UINT16, FT_UINT24, FT_UINT32, FT_IPXNET and FT_FRAMENUM
+- FT_CHAR, FT_UINT8, FT_UINT16, FT_UINT24, FT_UINT32, FT_IPXNET and FT_FRAMENUM
 - FT_INT40, FT_INT48, FT_INT56 and FT_INT64
 - FT_UINT40, FT_UINT48, FT_UINT56, FT_UINT64 and FT_EUI64
 - FT_ABSOLUTE_TIME and FT_RELATIVE_TIME