1719 lines
62 KiB
Plaintext
1719 lines
62 KiB
Plaintext
$Id: README.developer,v 1.32 2001/07/20 23:38:30 guy Exp $
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This file is a HOWTO for Ethereal developers. It describes how to start coding
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a Ethereal protocol dissector and the use some of the important functions and
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variables.
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The file is target at creating dissectors based upon tvbuffers. All
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new dissector should be written with tvbuffers not with the old style, pd packet
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data pointer, dissectors. The tvbuffer dissectors improve the handling of short
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packets. See the README.tvbuff for more details on tvbuffers.
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1. Setting up your protocol dissector code.
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This section provides skeleton code for a protocol dissector. It also explains
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the basic functions needed to enter values in the traffic summary columns,
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add to the protocol tree, and work with registered header fields.
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1.1 Code style.
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1.1.1 Portability.
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Ethereal runs on many platforms, and can be compiled with a number of
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different compilers; here are some rules for writing code that will work
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on multiple platforms.
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Don't use C++-style comments (comments beginning with "//" and running
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to the end of the line); Ethereal's dissectors are written in C, and
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thus run through C rather than C++ compilers, and not all C compilers
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support C++-style comments (GCC does, but IBM's C compiler for AIX, for
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example, doesn't do so by default).
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Don't use zero-length arrays; not all compilers support them. If an
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array would have no members, just leave it out.
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Don't use "inline"; not all compilers support it. If you want to have a
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function be an inline function if the compiler supports it, use
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G_INLINE_FUNC, which is declared by <glib.h>. This may not work with
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functions declared in header files; if it doesn't work, don't declare
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the function in a header file, even if this requires that you not make
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it inline on any platform.
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Don't use "long long"; use "gint64" or "guint64", and only do so if
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G_HAVE_GINT64 is defined. Make sure your code works even if
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G_HAVE_GINT64 isn't defined, even if that means treating 64-bit integral
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data types as opaque arrays of bytes on platforms where it's not
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defined. Also, don't assume you can use "%lld", "%llu", "%llx", or
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"%llo" to print 64-bit integral data types - not all platforms support
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"%ll" for printing them.
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1.1.2 Name convention.
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Ethereal uses the underscore_convention rather than the InterCapConvention for
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function names, so new code should probably use underscores rather than
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intercaps for functions and variable names. This is especially important if you
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are writing code that will be called from outside your code. We are just
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trying to keep thing consistent for other users.
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1.2 Skeleton code.
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Ethereal requires certain things when setting up a protocol dissector.
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Below is skeleton code for a dissector that you can copy to a file and
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fill in. Your dissector should follow the naming convention of packet-
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followed by the abbreviated name for the protocol. It is recommended
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that where possible you keep to the IANA abbreviated name for the
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protocol, if there is one, or a commonly-used abbreviation for the
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protocol, if any.
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Dissectors that use the dissector registration to tell a lower level
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dissector don't need to define a prototype in the .h file. For other
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dissectors the main dissector routine should have a prototype in a header
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file whose name is "packet-", followed by the abbreviated name for the
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protocol, followed by ".h"; any dissector file that calls your dissector
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should be changed to include that file.
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You may not need to include all the headers listed in the skeleton
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below, and you may need to include additional headers. For example, the
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code inside
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#ifdef NEED_SNPRINTF_H
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...
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#endif
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is needed only if you are using the "snprintf()" function.
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The "$Id: README.developer,v 1.32 2001/07/20 23:38:30 guy Exp $"
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in the comment will be updated by CVS when the file is
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checked in; it will allow the RCS "ident" command to report which
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version of the file is currently checked out.
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------------------------------------Cut here------------------------------------
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/* packet-PROTOABBREV.c
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* Routines for PROTONAME dissection
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* Copyright 2000, YOUR_NAME <YOUR_EMAIL_ADDRESS>
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*
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* $Id: README.developer,v 1.32 2001/07/20 23:38:30 guy Exp $
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*
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* Ethereal - Network traffic analyzer
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* By Gerald Combs <gerald@ethereal.com>
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* Copyright 1998 Gerald Combs
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*
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* Copied from WHATEVER_FILE_YOU_USED (where "WHATEVER_FILE_YOU_USED"
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* is a dissector file; if you just copied this from README.developer,
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* don't bother with the "Copied from" - you don't even need to put
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* in a "Copied from" if you copied an existing dissector, especially
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* if the bulk of the code in the new dissector is your code)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*/
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#ifdef HAVE_CONFIG_H
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# include "config.h"
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#endif
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#ifdef HAVE_SYS_TYPES_H
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# include <sys/types.h>
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#endif
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#ifdef HAVE_NETINET_IN_H
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# include <netinet/in.h>
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#endif
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#include <glib.h>
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#ifdef NEED_SNPRINTF_H
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# include "snprintf.h"
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#endif
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#include "packet.h"
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#include "packet-PROTOABBREV.h"
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/* Initialize the protocol and registered fields */
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static int proto_PROTOABBREV = -1;
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static int hf_PROTOABBREV_FIELDABBREV = -1;
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/* Initialize the subtree pointers */
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static gint ett_PROTOABBREV = -1;
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/* Code to actually dissect the packets */
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static void
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dissect_PROTOABBREV(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
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{
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/* Set up structures needed to add the protocol subtree and manage it */
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proto_item *ti;
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proto_tree *PROTOABBREV_tree;
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/* Make entries in Protocol column and Info column on summary display */
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if (check_col(pinfo->fd, COL_PROTOCOL))
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col_set_str(pinfo->fd, COL_PROTOCOL, "PROTOABBREV");
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/* This field shows up as the "Info" column in the display; you should make
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it, if possible, summarize what's in the packet, so that a user looking
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at the list of packets can tell what type of packet it is. See section 1.5
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for more information.
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If you are setting it to a constant string, use "col_set_str()", as
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it's more efficient than the other "col_set_XXX()" calls.
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If you're setting it to a string you've constructed, or will be
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appending to the column later, use "col_add_str()".
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"col_add_fstr()" can be used instead of "col_add_str()"; it takes
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"printf()"-like arguments. Don't use "col_add_fstr()" with a format
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string of "%s" - just use "col_add_str()" or "col_set_str()", as it's
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more efficient than "col_add_fstr()".
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If you will be fetching any data from the packet before filling in
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the Info column, clear that column first, in case the calls to fetch
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data from the packet throw an exception because they're fetching data
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past the end of the packet, so that the Info column doesn't have data
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left over from the previous dissector; do
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if (check_col(pinfo->fd, COL_INFO))
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col_clear(pinfo->fd, COL_INFO);
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*/
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if (check_col(pinfo->fd, COL_INFO))
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col_set_str(pinfo->fd, COL_INFO, "XXX Request");
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/* In the interest of speed, if "tree" is NULL, don't do any work not
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necessary to generate protocol tree items. */
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if (tree) {
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/* NOTE: The offset and length values in the call to
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"proto_tree_add_item()" define what data bytes to highlight in the hex
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display window when the line in the protocol tree display
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corresponding to that item is selected.
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tvb_length(tvb) is a handy way to highlight all data from the offset to
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the end of the packet. */
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/* create display subtree for the protocol */
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ti = proto_tree_add_item(tree, proto_PROTOABBREV, tvb, 0, tvb_length(tvb), FALSE);
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PROTOABBREV_tree = proto_item_add_subtree(ti, ett_PROTOABBREV);
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/* add an item to the subtree, see section 1.6 for more information */
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proto_tree_add_uint(tree, hf_PROTOABBREV_FIELDABBREV, tvb, offset, len, value)
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/* Continue adding tree items to process the packet here */
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}
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/* If this protocol has a sub-dissector call it here, see section 1.8 */
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}
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/* Register the protocol with Ethereal */
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/* this format is require because a script is used to build the C function
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that calls all the protocol registration.
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*/
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void
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proto_register_PROTOABBREV(void)
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{
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/* Setup list of header fields See Section 1.6.1 for details*/
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static hf_register_info hf[] = {
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{ &hf_PROTOABBREV_FIELDABBREV,
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{ "FIELDNAME", "PROTOABBREV.FIELDABBREV",
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FIELDTYPE, FIELDBASE, FIELDCONVERT, BITMASK,
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"FIELDDESCR" }
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},
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};
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/* Setup protocol subtree array */
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static gint *ett[] = {
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&ett_PROTOABBREV,
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};
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/* Register the protocol name and description */
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proto_PROTOABBREV = proto_register_protocol("PROTONAME",
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"PROTOSHORTNAME", "PROTOABBREV");
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/* Required function calls to register the header fields and subtrees used */
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proto_register_field_array(proto_PROTOABBREV, hf, array_length(hf));
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proto_register_subtree_array(ett, array_length(ett));
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}
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/* If this dissector uses sub-dissector registration add a registration routine.
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This format is required because a script is used to find these routines and
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create the code that calls these routines.
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*/
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void
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proto_reg_handoff_PROTOABBREV(void)
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{
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dissector_add("PARENT_SUBFIELD", ID_VALUE, dissect_PROTOABBREV,
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proto_PROTOABBREV);
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}
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------------------------------------Cut here------------------------------------
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1.3 Explanation of needed substitutions in code skeleton.
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In the above code block the following strings should be substituted with
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your information.
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YOUR_NAME Your name, of course. You do want credit, don't you?
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It's the only payment you will receive....
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YOUR_EMAIL_ADDRESS Keep those cards and letters coming.
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WHATEVER_FILE_YOU_USED Add this line if you are using another file as a
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starting point.
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PROTONAME The name of the protocol.
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PROTOABBREV An abbreviated name for the protocol. (NO SPACES) (rec.
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a-z, 0-9 only and try to conform with IANA names)
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FIELDNAME The displayed name for the header field.
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FIELDABBREV The abbreviated name for the header field. (NO SPACES)
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FIELDTYPE FT_NONE, FT_BOOLEAN, FT_UINT8, FT_UINT16, FT_UINT24,
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FT_UINT32, FT_INT8, FT_INT16, FT_INT24, FT_INT32,
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FT_DOUBLE, FT_ABSOLUTE_TIME, FT_RELATIVE_TIME, FT_STRING,
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FT_STRINGZ, FT_UINT_STRING, FT_ETHER, FT_BYTES, FT_IPv4,
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FT_IPv6, FT_IPXNET
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FIELDBASE BASE_NONE, BASE_DEC, BASE_HEX, BASE_OCT, BASE_BIN
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FIELDCONVERT VALS(x), TFS(x), NULL
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BITMASK Usually 0x0 unless using the TFS(x) field conversion.
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FIELDDESCR A brief description of the field.
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PARENT_SUBFIELD Lower level protocol field used for lookup, i.e. "tcp.port"
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ID_VALUE Lower level protocol field value that identifies this protocol
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For example the TCP or UDP port number
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1.4 The dissector and the data it receives.
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1.4.1 Header file.
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This is only needed if the dissector doesn't use self-registration to
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register itself with the lower level dissector.
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The dissector has the following header that must be placed into
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packet-PROTOABBREV.h.
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void
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dissect_PROTOABBREV(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree);
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1.4.2 Extracting data from packets.
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NOTE: See the README.tvbuff for more details
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The "tvb" argument to a dissector points to a buffer containing the raw
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data for the frame. A tvbuffer is a opaque data structure, the internal
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data structures are hidden and the data must be access via the tvbuffer
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accessors.
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The accessors are:
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Single-byte accessor:
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guint8 tvb_get_guint8(tvbuff_t*, gint offset);
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Network-to-host-order access for shorts (guint16), longs (guint24), and
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24-bit ints:
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guint16 tvb_get_ntohs(tvbuff_t*, gint offset);
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guint32 tvb_get_ntohl(tvbuff_t*, gint offset);
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guint32 tvb_get_ntoh24(tvbuff_t*, gint offset);
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Little-Endian-to-host-order access for shorts (guint16), longs (guint24), and
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24-bit ints:
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guint16 tvb_get_letohs(tvbuff_t*, gint offset);
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guint32 tvb_get_letohl(tvbuff_t*, gint offset);
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guint32 tvb_get_letoh24(tvbuff_t*, gint offset);
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Copying memory:
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guint8* tvb_memcpy(tvbuff_t*, guint8* target, gint offset, gint length);
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guint8* tvb_memdup(tvbuff_t*, gint offset, gint length);
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Pointer-retrieval:
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/* WARNING! This function is possibly expensive, temporarily allocating
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* another copy of the packet data. Furthermore, it's dangerous because once
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* this pointer is given to the user, there's no guarantee that the user will
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* honor the 'length' and not overstep the boundaries of the buffer.
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*/
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guint8* tvb_get_ptr(tvbuff_t*, gint offset, gint length);
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The reason that tvb_get_ptr() have to allocate a copy of its data only
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occurs with TVBUFF_COMPOSITES, data that spans multiple tvbuffers. If the
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user request a pointer to a range of bytes that spans the member tvbuffs that
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make up the TVBUFF_COMPOSITE, the data will have to be copied to another
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memory region to assure that all the bytes are contiguous.
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1.5 Functions to handle columns in the traffic summary window.
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The topmost pane of the main window is a list of the packets in the
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capture, possibly filtered by a display filter.
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Each line corresponds to a packet, and has one or more columns, as
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configured by the user.
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Many of the columns are handled by code outside individual dissectors;
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most dissectors need only specify the value to put in the "Protocol" and
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"Info" columns.
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Columns are specified by COL_ values; the COL_ value for the "Protocol"
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field, typically giving an abbreviated name for the protocol (but not
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the all-lower-case abbreviation used elsewhere) is COL_PROTOCOL, and the
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COL_ value for the "Info" field, giving a summary of the contents of the
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packet for that protocol, is COL_INFO.
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A value for a column should only be added if the user specified that it
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be displayed; to check whether a given column is to be displayed, call
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'col_info' with the COL_ value for that field as an argument - it will
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return TRUE if the column is to be displayed and FALSE if it is not to
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be displayed.
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The value for a column can be specified with one of several functions,
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all of which take the 'fd' argument to the dissector as their first
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argument, and the COL_ value for the column as their second argument.
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1.5.1 The col_set_str function.
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'col_set_str' takes a string as its third argument, and sets the value
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for the column to that value. It assumes that the pointer passed to it
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points to a string constant or a static "const" array, not to a
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variable, as it doesn't copy the string, it merely saves the pointer
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value; the argument can itself be a variable, as long as it always
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points to a string constant or a static "const" array.
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It is more efficient than 'col_add_str' or 'col_add_fstr'; however, if
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the dissector will be using 'col_append_str' or 'col_append_fstr" to
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append more information to the column, the string will have to be copied
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anyway, so it's best to use 'col_add_str' rather than 'col_set_str' in
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that case.
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For example, to set the "Protocol" column
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to "PROTOABBREV":
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if (check_col(pinfo->fd, COL_PROTOCOL))
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col_set_str(pinfo->fd, COL_PROTOCOL, "PROTOABBREV");
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1.5.2 The col_add_str function.
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'col_add_str' takes a string as its third argument, and sets the value
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for the column to that value. It takes the same arguments as
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'col_set_str', but copies the string, so that if the string is, for
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example, an automatic variable that won't remain in scope when the
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dissector returns, it's safe to use.
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1.5.3 The col_add_fstr function.
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'col_add_fstr' takes a 'printf'-style format string as its third
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argument, and 'printf'-style arguments corresponding to '%' format
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items in that string as its subsequent arguments. For example, to set
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the "Info" field to "<XXX> request, <N> bytes", where "reqtype" is a
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string containing the type of the request in the packet and "n" is an
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unsigned integer containing the number of bytes in the request:
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if (check_col(pinfo->fd, COL_INFO))
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col_add_fstr(pinfo->fd, COL_INFO, "%s request, %u bytes",
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reqtype, n);
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Don't use 'col_add_fstr' with a format argument of just "%s" -
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'col_add_str', or possibly even 'col_set_str' if the string that matches
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the "%s" is a static constant string, will do the same job more
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efficiently.
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1.5.4 The col_clear function.
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If the Info column will be filled with information from the packet, that
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means that some data will be fetched from the packet before the Info
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column is filled in. If the packet is so small that the data in
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question cannot be fetched, the routines to fetch the data will throw an
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exception (see the comment at the beginning about tvbuffers improving
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the handling of short packets - the tvbuffers keep track of how much
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data is in the packet, and throw an exception on an attempt to fetch
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data past the end of the packet, so that the dissector won't process
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bogus data), causing the Info column not to be filled in.
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This means that the Info column will have data for the previous
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protocol, which would be confusing if, for example, the Protocol column
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had data for this protocol.
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Therefore, before a dissector fetches any data whatsoever from the
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packet (unless it's a heuristic dissector fetching data to determine
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whether the packet is one that it should dissect, in which case it
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should check, before fetching the data, whether there's any data to
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fetch; if there isn't, it should return FALSE), it should set the
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Protocol column and the Info column.
|
|
|
|
If the Protocol column will ultimately be set to, for example, a value
|
|
containing a protocol version number, with the version number being a
|
|
field in the packet, the dissector should, before fetching the version
|
|
number field or any other field from the packet, set it to a value
|
|
without a version number, using 'col_set_str', and should later set it
|
|
to a value with the version number after it's fetched the version
|
|
number.
|
|
|
|
If the Info column will ultimately be set to a value containing
|
|
information from the packet, the dissector should, before fetching any
|
|
fields from the packet, clear the column using 'col_clear' (which is
|
|
more efficient than clearing it by calling 'col_set_str' or
|
|
'col_add_str' with a null string), and should later set it to the real
|
|
string after it's fetched the data to use when doing that.
|
|
|
|
|
|
1.5.5 The col_append_str function.
|
|
|
|
Sometimes the value of a column, especially the "Info" column, can't be
|
|
conveniently constructed at a single point in the dissection process;
|
|
for example, it might contain small bits of information from many of the
|
|
fields in the packet. 'col_append_str' takes, as arguments, the same
|
|
arguments as 'col_add_str', but the string is appended to the end of the
|
|
current value for the column, rather than replacing the value for that
|
|
column. (Note that no blank separates the appended string from the
|
|
string to which it is appended; if you want a blank there, you must add
|
|
it yourself as part of the string being appended.)
|
|
|
|
|
|
1.5.6 The col_append_fstr function.
|
|
|
|
'col_append_fstr' is to 'col_add_fstr' as 'col_append_str' is to
|
|
'col_add_str' - it takes, as arguments, the same arguments as
|
|
'col_add_fstr', but the formatted string is appended to the end of the
|
|
current value for the column, rather than replacing the value for that
|
|
column.
|
|
|
|
|
|
1.6 Constructing the protocol tree.
|
|
|
|
The middle pane of the main window, and the topmost pane of a packet
|
|
popup window, are constructed from the "protocol tree" for a packet.
|
|
|
|
The protocol tree, or proto_tree, is a GNode, the N-way tree structure
|
|
available within GLIB. Of course the protocol dissectors don't care
|
|
what a proto_tree really is; they just pass the proto_tree pointer as an
|
|
argument to the routines which allow them to add items and new branches
|
|
to the tree.
|
|
|
|
When a packet is selected in the packet-list pane, or a packet popup
|
|
window is created, a new logical protocol tree (proto_tree) is created.
|
|
The pointer to the proto_tree (in this case, 'protocol tree'), is passed
|
|
to the top-level protocol dissector, and then to all subsequent protocol
|
|
dissectors for that packet, and then the GUI tree is drawn via
|
|
proto_tree_draw().
|
|
|
|
The logical proto_tree needs to know detailed information about the
|
|
protocols and fields about which information will be collected from the
|
|
dissection routines. By strictly defining (or "typing") the data that can
|
|
be attached to a proto tree, searching and filtering becomes possible.
|
|
This means that the for every protocol and field (which I also call
|
|
"header fields", since they are fields in the protocol headers) which
|
|
might be attached to a tree, some information is needed.
|
|
|
|
Every dissector routine will need to register its protocols and fields
|
|
with the central protocol routines (in proto.c). At first I thought I
|
|
might keep all the protocol and field information about all the
|
|
dissectors in one file, but decentralization seemed like a better idea.
|
|
That one file would have gotten very large; one small change would have
|
|
required a re-compilation of the entire file. Also, by allowing
|
|
registration of protocols and fields at run-time, loadable modules of
|
|
protocol dissectors (perhaps even user-supplied) is feasible.
|
|
|
|
To do this, each protocol should have a register routine, which will be
|
|
called when Ethereal starts. The code to call the register routines is
|
|
generated automatically; to arrange that a protocol's register routine
|
|
be called at startup:
|
|
|
|
the file containing a dissector's "register" routine must be
|
|
added to "DISSECTOR_SOURCES" in "Makefile.am";
|
|
|
|
the "register" routine must have a name of the form
|
|
"proto_register_XXX";
|
|
|
|
the "register" routine must take no argument, and return no
|
|
value;
|
|
|
|
the "register" routine's name must appear in the source file
|
|
either at the beginning of the line, or preceded only by "void "
|
|
at the beginning of the line (that'd typically be the
|
|
definition) - other white space shouldn't cause a problem, e.g.:
|
|
|
|
void proto_register_XXX(void) {
|
|
|
|
...
|
|
|
|
}
|
|
|
|
and
|
|
|
|
void
|
|
proto_register_XXX( void )
|
|
{
|
|
|
|
...
|
|
|
|
}
|
|
|
|
and so on should work.
|
|
|
|
For every protocol or field that a dissector wants to register, a variable of
|
|
type int needs to be used to keep track of the protocol. The IDs are
|
|
needed for establishing parent/child relationships between protocols and
|
|
fields, as well as associating data with a particular field so that it
|
|
can be stored in the logical tree and displayed in the GUI protocol
|
|
tree.
|
|
|
|
Some dissectors will need to create branches within their tree to help
|
|
organize header fields. These branches should be registered as header
|
|
fields. Only true protocols should be registered as protocols. This is
|
|
so that a display filter user interface knows how to distinguish
|
|
protocols from fields.
|
|
|
|
A protocol is registered with the name of the protocol and its
|
|
abbreviation.
|
|
|
|
Here is how the frame "protocol" is registered.
|
|
|
|
int proto_frame;
|
|
|
|
proto_frame = proto_register_protocol (
|
|
/* name */ "Frame",
|
|
/* short name */ "Frame",
|
|
/* abbrev */ "frame" );
|
|
|
|
A header field is also registered with its name and abbreviation, but
|
|
information about the its data type is needed. It helps to look at
|
|
the header_field_info struct to see what information is expected:
|
|
|
|
struct header_field_info {
|
|
char *name;
|
|
char *abbrev;
|
|
enum ftenum type;
|
|
int display;
|
|
void *strings;
|
|
guint bitmask;
|
|
char *blurb;
|
|
|
|
int id; /* calculated */
|
|
int parent;
|
|
int bitshift; /* calculated */
|
|
};
|
|
|
|
name
|
|
----
|
|
A string representing the name of the field. This is the name
|
|
that will appear in the graphical protocol tree.
|
|
|
|
abbrev
|
|
------
|
|
A string with an abbreviation of the field. We concatenate the
|
|
abbreviation of the parent protocol with an abbreviation for the field,
|
|
using a period as a separator. For example, the "src" field in an IP packet
|
|
would have "ip.addr" as an abbreviation. It is acceptable to have
|
|
multiple levels of periods if, for example, you have fields in your
|
|
protocol that are then subdivided into subfields. For example, TRMAC
|
|
has multiple error fields, so the abbreviations follow this pattern:
|
|
"trmac.errors.iso", "trmac.errors.noniso", etc.
|
|
|
|
The abbreviation is the identifier used in a display filter.
|
|
|
|
type
|
|
----
|
|
The type of value this field holds. The current field types are:
|
|
|
|
FT_NONE No field type. Used for fields that
|
|
aren't given a value, and that can only
|
|
be tested for presence or absence; a
|
|
field that represents a data structure,
|
|
with a subtree below it containing
|
|
fields for the members of the structure,
|
|
or that represents an array with a
|
|
subtree below it containing fields for
|
|
the members of the array, might be an
|
|
FT_NONE field.
|
|
FT_BOOLEAN 0 means "false", any other value means
|
|
"true".
|
|
FT_UINT8 An 8-bit unsigned integer.
|
|
FT_UINT16 A 16-bit unsigned integer.
|
|
FT_UINT24 A 24-bit unsigned integer.
|
|
FT_UINT32 A 32-bit unsigned integer.
|
|
FT_INT8 An 8-bit signed integer.
|
|
FT_INT16 A 16-bit signed integer.
|
|
FT_INT24 A 24-bit signed integer.
|
|
FT_INT32 A 32-bit signed integer.
|
|
FT_DOUBLE A floating point number.
|
|
FT_ABSOLUTE_TIME Seconds (4 bytes) and microseconds (4 bytes)
|
|
of time displayed as month name, month day,
|
|
year, hours, minutes, and seconds with 4
|
|
digits after the decimal point.
|
|
FT_RELATIVE_TIME Seconds (4 bytes) and microseconds (4 bytes)
|
|
of time displayed as seconds and 6 digits
|
|
after the decimal point.
|
|
FT_STRING A string of characters, not necessarily
|
|
NUL-terminated, but possibly NUL-padded.
|
|
This, and the other string-of-characters
|
|
types, are to be used for text strings,
|
|
not raw binary data.
|
|
FT_STRINGZ A NUL-terminated string of characters.
|
|
FT_UINT_STRING A counted string of characters, consisting
|
|
of a count (represented as an integral
|
|
value) followed immediately by the
|
|
specified number of characters.
|
|
FT_ETHER A six octet string displayed in
|
|
Ethernet-address format.
|
|
FT_BYTES A string of bytes with arbitrary values;
|
|
used for raw binary data.
|
|
FT_IPv4 A version 4 IP address (4 bytes) displayed
|
|
in dotted-quad IP address format (4
|
|
decimal numbers separated by dots).
|
|
FT_IPv6 A version 6 IP address (16 bytes) displayed
|
|
in standard IPv6 address format.
|
|
FT_IPXNET An IPX address displayed in hex as a 6-byte
|
|
network number followed by a 6-byte station
|
|
address.
|
|
|
|
Some of these field types are still not handled in the display filter
|
|
routines, but the most common ones are. The FT_UINT* variables all
|
|
represent unsigned integers, and the FT_INT* variables all represent
|
|
signed integers; the number on the end represent how many bits are used
|
|
to represent the number.
|
|
|
|
display
|
|
-------
|
|
The display field has a couple of overloaded uses. This is unfortunate,
|
|
but since we're C as an application programming language, this sometimes
|
|
makes for cleaner programs. Right now I still think that overloading
|
|
this variable was okay.
|
|
|
|
For integer fields (FT_UINT* and FT_INT*), this variable represents the
|
|
base in which you would like the value displayed. The acceptable bases
|
|
are:
|
|
|
|
BASE_DEC,
|
|
BASE_HEX,
|
|
BASE_OCT,
|
|
BASE_BIN
|
|
|
|
BASE_DEC, BASE_HEX, and BASE_OCT are decimal, hexadecimal, and octal,
|
|
respectively. BASE_BIN is reserved for binary, although it's currently
|
|
treated as decimal - if you want decimal, use BASE_DEC, not BASE_BIN.
|
|
|
|
For FT_BOOLEAN fields that are also bitfields, 'display' is used to tell
|
|
the proto_tree how wide the parent bitfield is. With integers this is
|
|
not needed since the type of integer itself (FT_UINT8, FT_UINT16,
|
|
FT_UINT24, FT_UINT32, etc.) tells the proto_tree how wide the parent
|
|
bitfield is.
|
|
|
|
Additionally, BASE_NONE is used for 'display' as a NULL-value. That is,
|
|
for non-integers and non-bitfield FT_BOOLEANs, you'll want to use BASE_NONE
|
|
in the 'display' field. You may not use BASE_NONE for integers.
|
|
|
|
It is possible that in the future we will record the endianness of
|
|
integers. If so, it is likely that we'll use a bitmask on the display field
|
|
so that integers would be represented as BEND|BASE_DEC or LEND|BASE_HEX.
|
|
But that has not happened yet.
|
|
|
|
strings
|
|
-------
|
|
Some integer fields, of type FT_UINT*, need labels to represent the true
|
|
value of a field. You could think of those fields as having an
|
|
enumerated data type, rather than an integral data type.
|
|
|
|
A 'value_string' structure is a way to map values to strings.
|
|
|
|
typedef struct _value_string {
|
|
guint32 value;
|
|
gchar *strptr;
|
|
} value_string;
|
|
|
|
For fields of that type, you would declare an array of "value_string"s:
|
|
|
|
static const value_string valstringname[] = {
|
|
{ INTVAL1, "Descriptive String 1" },
|
|
{ INTVAL2, "Descriptive String 2" },
|
|
{ 0, NULL },
|
|
};
|
|
|
|
(the last entry in the array must have a NULL 'strptr' value, to
|
|
indicate the end of the array). The 'strings' field would be set to
|
|
'VALS(valstringname)'.
|
|
|
|
(Note: before Ethereal 0.7.6, we had separate field types like
|
|
FT_VALS_UINT8 which denoted the use of value_strings. Now, the
|
|
non-NULLness of the pointer lets the proto_tree know that a value_string
|
|
is meant for this field).
|
|
|
|
If the field has a numeric rather than an enumerated type, the 'strings'
|
|
field would be set to NULL.
|
|
|
|
FT_BOOLEANS have a default map of 0 = "False", 1 (or anything else) = "True".
|
|
Sometimes it is useful to change the labels for boolean values (e.g.,
|
|
to "Yes"/"No", "Fast"/"Slow", etc.). For these mappings, a struct called
|
|
true_false_string is used. (This struct is new as of Ethereal 0.7.6).
|
|
|
|
typedef struct true_false_string {
|
|
char *true_string;
|
|
char *false_string;
|
|
} true_false_string;
|
|
|
|
For Boolean fields for which "False" and "True" aren't the desired
|
|
labels, you would declare a "true_false_string"s:
|
|
|
|
static const true_false_string boolstringname = {
|
|
"String for True",
|
|
"String for False"
|
|
};
|
|
|
|
Its two fields are pointers to the string representing truth, and the
|
|
string representing falsehood. For FT_BOOLEAN fields that need a
|
|
'true_false_string' struct, the 'strings' field would be set to
|
|
'TFS(&boolstringname)'.
|
|
|
|
If the Boolean field is to be displayed as "False" or "True", the
|
|
'strings' field would be set to NULL.
|
|
|
|
bitmask
|
|
-------
|
|
If the field is a bitfield, then the bitmask is the mask which will
|
|
leave only the bits needed to make the field when ANDed with a value.
|
|
The proto_tree routines will calculate 'bitshift' automatically
|
|
from 'bitmask', by finding the rightmost set bit in the bitmask.
|
|
If the field is not a bitfield, then bitmask should be set to 0.
|
|
|
|
blurb
|
|
-----
|
|
This is a string giving a proper description of the field.
|
|
It should be at least one grammatically complete sentence.
|
|
It is meant to provide a more detailed description of the field than the
|
|
name alone provides. This information will be used in the man page, and
|
|
in a future GUI display-filter creation tool. We might also add tooltips
|
|
to the labels in the GUI protocol tree, in which case the blurb would
|
|
be used as the tooltip text.
|
|
|
|
|
|
1.6.1 Field Registration.
|
|
|
|
Protocol registration is handled by creating an instance of the
|
|
header_field_info struct (or an array of such structs), and
|
|
calling the registration function along with the registration ID of
|
|
the protocol that is the parent of the fields. Here is a complete example:
|
|
|
|
static int proto_eg = -1;
|
|
static int hf_field_a = -1;
|
|
static int hf_field_b = -1;
|
|
|
|
static hf_register_info hf[] = {
|
|
|
|
{ &hf_field_a,
|
|
{ "Field A", "proto.field_a", FT_UINT8, BASE_HEX, NULL,
|
|
0xf0, "Field A represents Apples" }},
|
|
|
|
{ &hf_field_b,
|
|
{ "Field B", "proto.field_b", FT_UINT16, BASE_DEC, VALS(vs),
|
|
0x0, "Field B represents Bananas" }}
|
|
};
|
|
|
|
proto_eg = proto_register_protocol("Example Protocol",
|
|
"PROTO", "proto");
|
|
proto_register_field_array(proto_eg, hf, array_length(hf));
|
|
|
|
Be sure that your array of hf_register_info structs is declared 'static',
|
|
since the proto_register_field_array() function does not create a copy
|
|
of the information in the array... it uses that static copy of the
|
|
information that the compiler created inside your array. Here's the
|
|
layout of the hf_register_info struct:
|
|
|
|
typedef struct hf_register_info {
|
|
int *p_id; /* pointer to parent variable */
|
|
header_field_info hfinfo;
|
|
} hf_register_info;
|
|
|
|
Also be sure to use the handy array_length() macro found in packet.h
|
|
to have the compiler compute the array length for you at compile time.
|
|
|
|
If you don't have any fields to register, do *NOT* create a zero-length
|
|
"hf" array; not all compilers used to compile Ethereal support them.
|
|
Just omit the "hf" array, and the "proto_register_field_array()" call,
|
|
entirely.
|
|
|
|
1.6.2 Adding Items and Values to the Protocol Tree.
|
|
|
|
A protocol item is added to an existing protocol tree with one of a
|
|
handful of proto_tree_add_XXX() functions.
|
|
|
|
Subtrees can be made with the proto_item_add_subtree() function:
|
|
|
|
item = proto_tree_add_item(....);
|
|
new_tree = proto_item_add_subtree(item, tree_type);
|
|
|
|
This will add a subtree under the item in question; a subtree can be
|
|
created under an item made by any of the "proto_tree_add_XXX" functions,
|
|
so that the tree can be given an arbitrary depth.
|
|
|
|
Subtree types are integers, assigned by
|
|
"proto_register_subtree_array()". To register subtree types, pass an
|
|
array of pointers to "gint" variables to hold the subtree type values to
|
|
"proto_register_subtree_array()":
|
|
|
|
static gint ett_eg = -1;
|
|
static gint ett_field_a = -1;
|
|
|
|
static gint *ett[] = {
|
|
&ett_eg,
|
|
&ett_field_a,
|
|
};
|
|
|
|
proto_register_subtree_array(ett, array_length(ett));
|
|
|
|
in your "register" routine, just as you register the protocol and the
|
|
fields for that protocol.
|
|
|
|
There are several functions that the programmer can use to add either
|
|
protocol or field labels to the proto_tree:
|
|
|
|
proto_item*
|
|
proto_tree_add_item(tree, id, start, length, value);
|
|
|
|
proto_item*
|
|
proto_tree_add_item_hidden(tree, id, start, length, value);
|
|
|
|
proto_item*
|
|
proto_tree_add_protocol_format(tree, id, start, length, format, ...);
|
|
|
|
proto_item *
|
|
proto_tree_add_bytes_format(tree, id, start, length, start_ptr,
|
|
format, ...);
|
|
|
|
proto_item *
|
|
proto_tree_add_time_format(tree, id, start, length, value_ptr,
|
|
format, ...);
|
|
|
|
proto_item *
|
|
proto_tree_add_ipxnet_format(tree, id, start, length, value,
|
|
format, ...);
|
|
|
|
proto_item *
|
|
proto_tree_add_ipv4_format(tree, id, start, length, value,
|
|
format, ...);
|
|
|
|
proto_item *
|
|
proto_tree_add_ipv6_format(tree, id, start, length, value_ptr,
|
|
format, ...);
|
|
|
|
proto_item *
|
|
proto_tree_add_ether_format(tree, id, start, length, value_ptr,
|
|
format, ...);
|
|
|
|
proto_item *
|
|
proto_tree_add_string_format(tree, id, start, length, value_ptr,
|
|
format, ...);
|
|
|
|
proto_item *
|
|
proto_tree_add_boolean_format(tree, id, start, length, value,
|
|
format, ...);
|
|
|
|
proto_item *
|
|
proto_tree_add_uint_format(tree, id, start, length, value,
|
|
format, ...);
|
|
|
|
proto_item*
|
|
proto_tree_add_text(tree, start, length, format, ...);
|
|
|
|
proto_item*
|
|
proto_tree_add_notext(tree, start, length);
|
|
|
|
The 'tree' argument is the tree to which the item is to be added. The
|
|
'start' argument is the offset from the beginning of the frame (not the
|
|
offset from the beginning of the part of the packet belonging to this
|
|
protocol, but the offset from the beginning of the frame as a whole) of
|
|
the item being added, and the 'length' argument is the length, in bytes,
|
|
of the item.
|
|
|
|
The length of some items cannot be determined until the item has been
|
|
dissected; to add such an item, add it with a length of 0, and, when the
|
|
dissection is complete (or fails because the packet is too short), set
|
|
the length with 'proto_item_set_len()':
|
|
|
|
void
|
|
proto_item_set_len(ti, length);
|
|
|
|
The "ti" argument is the value returned by the call that added the item
|
|
to the tree, and the "length" argument is the length of the item.
|
|
|
|
proto_tree_add_item()
|
|
---------------------
|
|
proto_tree_add_item is used when you wish to do no special formatting.
|
|
The item added to the GUI tree will contain the name (as passed in the
|
|
proto_register_*() function) and any value. If your field does have a
|
|
value, it is passed after the length variable (notice the ellipsis in
|
|
the function prototype).
|
|
|
|
Now that the proto_tree has detailed information about bitfield fields,
|
|
you can use proto_tree_add_item() with no extra processing to add bitfield
|
|
values to your tree. Here's an example. Take the Format Identifer (FID)
|
|
field in the Transmission Header (TH) portion of the SNA protocol. The
|
|
FID is the high nibble of the first byte of the TH. The FID would be
|
|
registered like this:
|
|
|
|
name = "Format Identifer"
|
|
abbrev = "sna.th.fid"
|
|
type = FT_UINT8
|
|
display = BASE_HEX
|
|
strings = sna_th_fid_vals
|
|
bitmask = 0xf0
|
|
|
|
The bitmask contains the value which would leave only the FID if bitwise-ANDed
|
|
against the parent field, the first byte of the TH.
|
|
|
|
The code to add the FID to the tree would be;
|
|
|
|
guint8 th_0 = pd[offset];
|
|
proto_tree_add_item(bf_tree, hf_sna_th_fid, offset, 1, th_0);
|
|
|
|
Note: we do not do *any* manipulation of th_0 in order to get the FID value.
|
|
We just pass it to proto_tree_add_item(). The proto_tree already has
|
|
the information about bitmasking and bitshifting, so it does the work
|
|
of masking and shifting for us! This also means that you no longer
|
|
have to crate value_string structs with the values bitshifted. The
|
|
value_string for FID looks like this, even though the FID value is
|
|
actually contained in the high nibble. (You'd expect the values to be
|
|
0x0, 0x10, 0x20, etc.)
|
|
|
|
/* Format Identifier */
|
|
static const value_string sna_th_fid_vals[] = {
|
|
{ 0x0, "SNA device <--> Non-SNA Device" },
|
|
{ 0x1, "Subarea Node <--> Subarea Node" },
|
|
{ 0x2, "Subarea Node <--> PU2" },
|
|
{ 0x3, "Subarea Node or SNA host <--> Subarea Node" },
|
|
{ 0x4, "?" },
|
|
{ 0x5, "?" },
|
|
{ 0xf, "Adjaced Subarea Nodes" },
|
|
{ 0, NULL }
|
|
};
|
|
|
|
The final implication of this is that display filters work the way you'd
|
|
naturally expect them to. You'd type "sna.th.fid == 0xf" to find Adjacent
|
|
Subarea Nodes. The user does not have to shift the value of the FID to
|
|
the high nibble of the byte ("sna.th.fid == 0xf0") as was necessary
|
|
before Ethereal 0.7.6.
|
|
|
|
proto_tree_add_item_hidden()
|
|
----------------------------
|
|
proto_tree_add_item_hidden is used to add fields and values to a tree,
|
|
but not show them on a GUI tree. The caller may want a value to be
|
|
included in a tree so that the packet can be filtered on this field, but
|
|
the representation of that field in the tree is not appropriate. An
|
|
example is the token-ring routing information field (RIF). The best way
|
|
to show the RIF in a GUI is by a sequence of ring and bridge numbers.
|
|
Rings are 3-digit hex numbers, and bridges are single hex digits:
|
|
|
|
RIF: 001-A-013-9-C0F-B-555
|
|
|
|
In the case of RIF, the programmer should use a field with no value and
|
|
use proto_tree_add_item_format() to build the above representation. The
|
|
programmer can then add the ring and bridge values, one-by-one, with
|
|
proto_tree_add_item_hidden() so that the user can then filter on or
|
|
search for a particular ring or bridge. Here's a skeleton of how the
|
|
programmer might code this.
|
|
|
|
char *rif;
|
|
rif = create_rif_string(...);
|
|
|
|
proto_tree_add_item_format(tree, hf_tr_rif_label,..., "RIF: %s", rif);
|
|
|
|
for(i = 0; i < num_rings; i++) {
|
|
proto_tree_add_item_hidden(tree, hf_tr_rif_ring, ..., ring[i]);
|
|
}
|
|
for(i = 0; i < num_rings - 1; i++) {
|
|
proto_tree_add_item_hidden(tree, hf_tr_rif_ring, ..., bridge[i]);
|
|
}
|
|
|
|
The logical tree has these items:
|
|
|
|
hf_tr_rif_label, text="RIF: 001-A-013-9-C0F-B-555", value = NONE
|
|
hf_tr_rif_ring, hidden, value=0x001
|
|
hf_tr_rif_bridge, hidden, value=0xA
|
|
hf_tr_rif_ring, hidden, value=0x013
|
|
hf_tr_rif_bridge, hidden, value=0x9
|
|
hf_tr_rif_ring, hidden, value=0xC0F
|
|
hf_tr_rif_bridge, hidden, value=0xB
|
|
hf_tr_rif_ring, hidden, value=0x555
|
|
|
|
GUI or print code will not display the hidden fields, but a display
|
|
filter or "packet grep" routine will still see the values. The possible
|
|
filter is then possible:
|
|
|
|
tr.rif_ring eq 0x013
|
|
|
|
proto_tree_add_protocol_format()
|
|
----------------------------
|
|
proto_tree_add_protocol_format is used to add the top-level item for the
|
|
protocol when the dissector routines wants complete control over how the
|
|
field and value will be represented on the GUI tree. The ID value for
|
|
the protocol is passed in as the "id" argument; the rest of the
|
|
arguments are a "printf"-style format and any arguments for that format.
|
|
The caller must include the name of the protocol in the format; it is
|
|
not added automatically as in proto_tree_add_item().
|
|
|
|
proto_tree_add_bytes_format()
|
|
proto_tree_add_time_format()
|
|
proto_tree_add_ipxnet_format()
|
|
proto_tree_add_ipv4_format()
|
|
proto_tree_add_ipv6_format()
|
|
proto_tree_add_ether_format()
|
|
proto_tree_add_string_format()
|
|
proto_tree_add_boolean_format()
|
|
proto_tree_add_uint_format()
|
|
----------------------------
|
|
|
|
The other "proto_tree_add_XXX_format" routines are used to add items to
|
|
the protocol tree when the dissector routines wants complete control
|
|
over how the field and value will be represented on the GUI tree.
|
|
|
|
For "proto_tree_add_time_format", the "value_ptr" argument is a pointer
|
|
to a "struct timeval" containing the time to be added; for those other
|
|
functions that take a "value_ptr" argument, that argument is a pointer
|
|
to the first byte of the value to be added.
|
|
|
|
For the other functions, the "value" argument is a 32-bit integral value
|
|
to be added.
|
|
|
|
The rest of the arguments are a "printf"-style format and any arguments
|
|
for that format. The caller must include the name of the field in the
|
|
format; it is not added automatically as in proto_tree_add_item().
|
|
|
|
proto_tree_add_text()
|
|
---------------------
|
|
The fourth function, proto_tree_add_text(), is used to add a label to
|
|
the GUI tree. It will contain no value, so it is not searchable in the
|
|
display filter process. This function was needed in the transition from
|
|
the old-style proto_tree to this new-style proto_tree so that Ethereal
|
|
would still decode all protocols w/o being able to filter on all
|
|
protocols and fields. Otherwise we would have had to cripple Ethereal's
|
|
functionality while we converted all the old-style proto_tree calls to
|
|
the new-style proto_tree calls.
|
|
|
|
This can also be used for items with subtrees, which may not have values
|
|
themselves - the items in the subtree are the ones with values.
|
|
|
|
proto_tree_add_notext()
|
|
-----------------------
|
|
The fifth function, proto_tree_add_notext(), is used to add an item to
|
|
the logical tree that will have only a label, and no value (so it is not
|
|
searchable in the display filter process), but that doesn't yet have a
|
|
label, either. This is for items where the value is to be filled in
|
|
later. This is typically used for an item with a subtree, where the
|
|
label is to contain a summary of the subtree, with the values of some of
|
|
the fields in the subtree shown in the label of the item for the subtree
|
|
as a whole; the item can be created as a placeholder, with the label
|
|
added when the dissection is complete - and, if the dissection doesn't
|
|
complete because the packet is too short and not all the required fields
|
|
are present, the label could be set to something indicating this.
|
|
|
|
The text is set by 'proto_item_set_text()':
|
|
|
|
void
|
|
proto_tree_set_text(proto_item *ti, ...);
|
|
|
|
which takes as an argument the value returned by
|
|
'proto_tree_add_notext()', a 'printf'-style format string, and a set of
|
|
arguments corresponding to '%' format items in that string. For
|
|
example, early in the dissection, one might do:
|
|
|
|
ti = proto_tree_add_notext(tree, offset, length);
|
|
|
|
and later do
|
|
|
|
proto_item_set_text(ti, "%s: %s", type, value);
|
|
|
|
after the "type" and "value" fields have been extracted and dissected.
|
|
|
|
1.7 Utility routines
|
|
|
|
1.7.1 match_strval and val_to_str
|
|
|
|
A dissector may need to convert a value to a string, using a
|
|
'value_string' structure, by hand, rather than by declaring a field with
|
|
an associated 'value_string' structure; this might be used, for example,
|
|
to generate a COL_INFO line for a frame.
|
|
|
|
'match_strval()' will do that:
|
|
|
|
gchar*
|
|
match_strval(guint32 val, const value_string *vs)
|
|
|
|
It will look up the value 'val' in the 'value_string' table pointed to
|
|
by 'vs', and return either the corresponding string, or NULL if the
|
|
value could not be found in the table.
|
|
|
|
'val_to_str()' can be used to generate a string for values not found in
|
|
the table:
|
|
|
|
gchar*
|
|
val_to_str(guint32 val, const value_string *vs, const char *fmt)
|
|
|
|
If the value 'val' is found in the 'value_string' table pointed to by
|
|
'vs', 'val_to_str' will return the corresponding string; otherwise, it
|
|
will use 'fmt' as an 'sprintf'-style format, with 'val' as an argument,
|
|
to generate a string, and will return a pointer to that string.
|
|
(Currently, it has three 64-byte static buffers, and cycles through
|
|
them; this permits the results of up to three calls to 'val_to_str' to
|
|
be passed as arguments to a routine using those strings.)
|
|
|
|
|
|
1.8 Calling Other Dissector
|
|
|
|
|
|
1.8.1 TVBuffer Calling Old Style Dissector
|
|
|
|
When a TVBuffer based dissector is calling a old style dissector it must
|
|
create the data structures need to make the call. The tvb_compat function
|
|
is used to set the pd value and the offset value.
|
|
|
|
|
|
void
|
|
dissect_my(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
|
|
{
|
|
|
|
tvbuff_t *next_tvb;
|
|
const guint8 *next_pd;
|
|
int next_offset;
|
|
|
|
/* create new tv_buffer that starts at the current offset */
|
|
next_tvb = tvb_new_subset(tvb, offset, -1, -1);
|
|
|
|
/* set the pd and offset values need to call next dissector */
|
|
tvb_compat(next_tvb, &next_pd, &next_offset);
|
|
|
|
/* call next dissector */
|
|
dissect_next( next_pd, next_offset, pinfo->fd, tree,
|
|
END_OF_FRAME - next_offset);
|
|
|
|
|
|
1.8.2 TVBuffer Calling TVBuffer Dissector
|
|
|
|
NOTE: This is discussed in the README.tvbuff file. For more
|
|
information on tvbuffers consult that file.
|
|
|
|
As each dissector completes its portion of the protocol analysis, it
|
|
is expected to create a new tvbuff of type TVBUFF_SUBSET which
|
|
contains the payload portion of the protocol (that is, the bytes
|
|
that are relevant to the next dissector).
|
|
|
|
The syntax for creating a new TVBUFF_SUBSET is:
|
|
|
|
next_tvb = tvb_new_subset(tvb, offset, length, reported_length)
|
|
|
|
Where:
|
|
tvb is the tvbuff that the dissector has been working on. It
|
|
can be a tvbuff of any type.
|
|
|
|
next_tvb is the new TVBUFF_SUBSET.
|
|
|
|
offset is the byte offset of 'tvb' at which the new tvbuff
|
|
should start. The first byte is the 0th byte.
|
|
|
|
length is the number of bytes in the new TVBUFF_SUBSET. A length
|
|
argument of -1 says to use as many bytes as are available in
|
|
'tvb'.
|
|
|
|
reported_length is the number of bytes that the current protocol
|
|
says should be in the payload. A reported_length of -1 says that
|
|
the protocol doesn't say anything about the size of its payload.
|
|
|
|
|
|
An example from packet-ipx.c -
|
|
|
|
void
|
|
dissect_ipx(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
|
|
{
|
|
tvbuff_t *next_tvb;
|
|
int reported_length, available_length;
|
|
|
|
|
|
/* Make the next tvbuff */
|
|
|
|
/* IPX does have a length value in the header, so calculate report_length */
|
|
Set this to -1 if there isn't any length information in the protocol
|
|
*/
|
|
reported_length = ipx_length - IPX_HEADER_LEN;
|
|
|
|
/* Calculate the available data in the packet,
|
|
set this to -1 to use all the data in the tv_buffer
|
|
*/
|
|
available_length = tvb_length(tvb) - IPX_HEADER_LEN;
|
|
|
|
/* Create the tvbuffer for the next dissector */
|
|
next_tvb = tvb_new_subset(tvb, IPX_HEADER_LEN,
|
|
MIN(available_length, reported_length),
|
|
reported_length);
|
|
|
|
/* call the next dissector */
|
|
dissector_next( next_tvb, pinfo, tree);
|
|
|
|
|
|
|
|
1.8.3 Old Style Dissector calling TVBuffer Dissector
|
|
|
|
When an old style dissector calls a tvbuffer type dissector it must
|
|
create the tvbuffer to pass to the tvbuffer dissector. This is done
|
|
with the tvb_create_from_top call. The functions requires one
|
|
parameter, the offset to the start of the data for the next dissector.
|
|
|
|
An example -
|
|
|
|
static void
|
|
dissect_my(const u_char *pd, int offset, frame_data *fd, proto_tree *tree) {
|
|
|
|
tvbuff_t *tvb;
|
|
int offset = 0;
|
|
|
|
/* create the tvbuffer for the next dissector */
|
|
tvb = tvb_create_from_top(offset);
|
|
|
|
dissector_next(tvb, &pi, tree);
|
|
|
|
|
|
1.9 Editing Makefile.am and Makefile.nmake to add your dissector.
|
|
|
|
To arrange that your dissector will be built as part of Ethereal, you
|
|
must add the name of the source file for your dissector, and the header
|
|
file that declares your main dissector routine, to the
|
|
'DISSECTOR_SOURCES' macro in the 'Makefile.am' file in the top-level
|
|
directory, and must add the name the object file for the dissector will
|
|
have when built on Windows - if your dissector source file is
|
|
'packet-PROTOABBREV.c', the object file for it will be
|
|
'packet-PROTOABBREV.obj' - to the 'DISSECTOR_OBJECTS' macro in the
|
|
'Makefile.nmake' file in the top-level directory. (Note that this is
|
|
for modern versions of UNIX, so there is no 14-character limitation on
|
|
file names, and for modern versions of Windows, so there is no
|
|
8.3-character limitation on file names.)
|
|
|
|
Please remember to update both files; it may not be necessary to do so
|
|
in order for you to build Ethereal on your machine, but both changes
|
|
will need to be checked in to the Ethereal source code, to allow it to
|
|
build on all platforms.
|
|
|
|
1.10 Using the CVS source code tree.
|
|
|
|
1.11 Submitting code for your new dissector.
|
|
|
|
2. Advanced dissector topics.
|
|
|
|
2.1 ??
|
|
|
|
2.2 Following "conversations."
|
|
|
|
In ethereal a conversation is defined as a series of data packet between two
|
|
address:port combinations. A conversation is not sensitive to the direction of
|
|
the packet. The same conversation will be returned for a packet bound from
|
|
ServerA:1000 to ClientA:2000 and the packet from ClientA:2000 to ServerA:1000.
|
|
|
|
There are two routine that you will use to work with a conversation:
|
|
conversation_new and find_conversation.
|
|
|
|
|
|
2.2.1 The conversation_init function.
|
|
|
|
This is an internal routine for the conversation code. As such the you will not
|
|
have to call this routine. Just be aware that this routine is called at the
|
|
start of each capture and before the packets are filtered with a display filter.
|
|
The routine will destroy all stored conversations. This routine does NOT clean
|
|
up any data pointers that is passed in the conversation_new 'data' variable.
|
|
You are responsible for this clean up if you pass a malloc'ed pointer in this
|
|
variable.
|
|
|
|
See item 2.2.4 for more information about the 'data' pointer.
|
|
|
|
|
|
2.2.2 The conversation_new function.
|
|
|
|
This routine will create a new conversation based upon the source address:port
|
|
and destination address:port. If you want store a pointer to memory structure it
|
|
should be passed in the conversation_new 'data' variable. The ptype variable is
|
|
used to differentiate between conversations over different protocols, ie. TCP
|
|
and UDP. The options variable is used to define a conversation that will accept
|
|
any destination address and/or port. Set options = 0 if the destination port and
|
|
address are know when conversation_new is called. See section 2.4 for more
|
|
information on usage of the options parameter.
|
|
|
|
The conversation_new prototype:
|
|
conversation_t *conversation_new(address *src, address *dst, port_type ptype,
|
|
guint32 src_port, guint32 dst_port, void *data, guint options);
|
|
|
|
Where:
|
|
address* src = data packet source address
|
|
address* src = data packet destination address
|
|
port_type ptype = port type, this is defined in packet.h
|
|
guint32 src_port = data packet source port
|
|
guint32 dst_port = data packet destination port
|
|
void *data = dissector data structure
|
|
guint options = conversation options, NO_DST_ADDR and/or NO_DST_PORT
|
|
|
|
|
|
|
|
2.2.3 The find_conversation function.
|
|
|
|
Call this routine to lookup a conversation. If no conversation is found the
|
|
routine will return a NULL value. You don't have to worry about interchanging
|
|
the source and destination values. The conversation routine will automatically
|
|
return the same conversation for packets traveling in both directions. The
|
|
options value is used to define is the destination address and/or port should
|
|
be use to match the lookup. The matching conversation must have the same options
|
|
as the value of the find call.
|
|
|
|
|
|
2.2.4 The example conversation code with GMemChunk's
|
|
|
|
For a conversation between two IP addresses and ports you can use this as an
|
|
example. This example uses the GMemChunk to allocate memory and stores the data
|
|
pointer in the conversation 'data' variable.
|
|
|
|
NOTE: Remember to register the init routine (my_dissector_init) in the
|
|
protocol_register routine.
|
|
|
|
|
|
/************************ Globals values ************************/
|
|
|
|
/* the number of entries in the memory chunk array */
|
|
#define my_init_count 10
|
|
|
|
/* define your structure here */
|
|
typedef struct {
|
|
|
|
}my_entry_t;
|
|
|
|
/* the GMemChunk base structure */
|
|
static GMemChunk *my_vals = NULL;
|
|
|
|
|
|
/********************* in the dissector routine *********************/
|
|
|
|
/* the local variables in the dissector */
|
|
|
|
conversation_t *conversation;
|
|
my_entry_t *data_ptr
|
|
|
|
|
|
/* look up the conversation */
|
|
/* pi is a global variable of type packet_info, see packet.h */
|
|
|
|
conversation = find_conversation( &pi.src, &pi.dst, pi.ptype,
|
|
pi.srcport, pi.destport, 0);
|
|
|
|
/* if conversation found get the data pointer that you stored */
|
|
if ( conversation)
|
|
data_ptr = (my_entry_t*)conversation->data;
|
|
else {
|
|
|
|
/* new conversation create local data structure */
|
|
|
|
data_ptr = g_mem_chunk_alloc(my_protocol_vals);
|
|
|
|
/*** add your code here to setup the new data structure ***/
|
|
|
|
/* create the conversation with your data pointer */
|
|
|
|
conversation_new( &pi.src, &pi.dst, pi.ptype,
|
|
pi.srcport, pi.destport, (void*)data_ptr, 0);
|
|
}
|
|
|
|
/* at this point the conversation data is ready */
|
|
|
|
|
|
/******************* in the dissector init routine *******************/
|
|
|
|
#define proto_hash_init_count 20
|
|
|
|
static void
|
|
my_dissector_init( void){
|
|
|
|
/* destroy memory chunks if needed */
|
|
|
|
if ( my_vals)
|
|
g_mem_chunk_destroy(my_vals);
|
|
|
|
/* now create memory chunks */
|
|
|
|
my_vals = g_mem_chunk_new( "my_proto_vals",
|
|
sizeof( _entry_t),
|
|
my_init_count * sizeof( my_entry_t),
|
|
G_ALLOC_AND_FREE);
|
|
}
|
|
|
|
/***************** in the protocol register routine *****************/
|
|
|
|
/* register re-init routine */
|
|
|
|
register_init_routine( &my_dissector_init);
|
|
|
|
|
|
2.2.4 The example conversation code using conversation index field
|
|
|
|
Sometimes the conversation isn't enough to define a unique data storage value
|
|
for the network traffic. For example if you are storing information about requests
|
|
carried in a conversation, the request may have an identifier that is used to
|
|
define the request. In this case the conversation and the identifier are required
|
|
to find the data storage pointer. You can use the conversation data structure
|
|
index value to uniquely define the conversation.
|
|
|
|
See packet-afs.c for an example of how to use the conversation index. In
|
|
this dissector multiple requests are sent in the same conversation. To store
|
|
information for each request the dissector has an internal hash table based
|
|
upon the conversation index and values inside the request packets.
|
|
|
|
|
|
/* in the dissector routine */
|
|
|
|
/* to find a request value, first lookup conversation to get index */
|
|
/* then used the conversation index, and request data to find data */
|
|
/* in the local hash table */
|
|
|
|
conversation = find_conversation(&pi.src, &pi.dst, pi.ptype,
|
|
pi.srcport, pi.destport, 0);
|
|
if (conversation == NULL) {
|
|
/* It's not part of any conversation - create a new one. */
|
|
conversation = conversation_new(&pi.src, &pi.dst, pi.ptype,
|
|
pi.srcport, pi.destport, NULL, 0);
|
|
}
|
|
|
|
request_key.conversation = conversation->index;
|
|
request_key.service = pntohs(&rxh->serviceId);
|
|
request_key.callnumber = pntohl(&rxh->callNumber);
|
|
|
|
request_val = (struct afs_request_val *) g_hash_table_lookup(
|
|
afs_request_hash, &request_key);
|
|
|
|
/* only allocate a new hash element when it's a request */
|
|
opcode = 0;
|
|
if ( !request_val && !reply)
|
|
{
|
|
new_request_key = g_mem_chunk_alloc(afs_request_keys);
|
|
*new_request_key = request_key;
|
|
|
|
request_val = g_mem_chunk_alloc(afs_request_vals);
|
|
request_val -> opcode = pntohl(&afsh->opcode);
|
|
opcode = request_val->opcode;
|
|
|
|
g_hash_table_insert(afs_request_hash, new_request_key,
|
|
request_val);
|
|
}
|
|
|
|
|
|
|
|
2.3 Dynamic conversation dissector registration
|
|
|
|
|
|
NOTE: This sections assumes that all information is available to
|
|
create a complete conversation, source port/address and
|
|
destination port/address. If either the destination port or
|
|
address is know, see section 2.4 Dynamic server port dissector
|
|
registration.
|
|
|
|
For protocols that negotiate a secondary port connection, for example
|
|
packet-msproxy.c, a conversation can install a dissector to handle
|
|
the secondary protocol dissection. After the conversation is created
|
|
for the negotiated ports use the conversation_set_dissector to define
|
|
the dissection routine.
|
|
|
|
An example -
|
|
|
|
|
|
/* prototype for the dynamic dissector */
|
|
static void sub_dissector( tvbuff_t *tvb, packet_info *pinfo,
|
|
proto_tree *tree);
|
|
|
|
|
|
/* in the main protocol dissector, where the next dissector is setup */
|
|
|
|
/* if conversation has a data field, create it and load structure */
|
|
|
|
new_conv_info = g_mem_chunk_alloc( new_conv_vals);
|
|
new_conv_info->data1 = value1;
|
|
|
|
/* create the conversation for the dynamic port */
|
|
conversation = conversation_new( &pi.src, &pi.dst, protocol,
|
|
src_port, dst_port, new_conv_info, 0);
|
|
|
|
/* set the dissector for the new conversation */
|
|
conversation_set_dissector(conversation, sub_dissector);
|
|
|
|
|
|
|
|
2.4 Dynamic server port dissector registration
|
|
|
|
NOTE: While this example used both NO_DST_ADDR and NO_DST_PORT to
|
|
create a conversation with only the source port and address set, this
|
|
isn't a requirement. Either the destination port or address can be
|
|
set when the conversation is create.
|
|
|
|
For protocols that define a server address and port for a secondary
|
|
protocol, a conversation can be use to link a protocol dissector to
|
|
the server port and address. The key is to create the new
|
|
conversation with the destination address and port set to the accept
|
|
any values.
|
|
|
|
There are two support routines that will allow the destination port and/or
|
|
address to be set latter.
|
|
|
|
conversation_set_port( conversation_t *conv, guint32 port);
|
|
conversation_set_addr( conversation_t *conv, address addr);
|
|
|
|
These routines will change the destination information for the conversation.
|
|
So, the server port conversation will be converted into a more complete
|
|
conversation definition. Don't use these routines if you want create a
|
|
conversation between the server and client and retain the server port
|
|
definition, you must create a new conversation.
|
|
|
|
|
|
An example -
|
|
|
|
/* prototype for the dynamic dissector */
|
|
static void sub_dissector( tvbuff_t *tvb, packet_info *pinfo,
|
|
proto_tree *tree);
|
|
|
|
|
|
/* in the main protocol dissector, where the next dissector is setup */
|
|
|
|
/* if conversation has a data field, create it and load structure */
|
|
|
|
new_conv_info = g_mem_chunk_alloc( new_conv_vals);
|
|
new_conv_info->data1 = value1;
|
|
|
|
/* create the conversation for the dynamic server address and port */
|
|
/* NOTE: The destination values don't matter because the NO_DST_ADDR */
|
|
/* NO_DST_PORT options are set. */
|
|
|
|
conversation = conversation_new( &server_src_addr, 0, protocol,
|
|
server_src_port, 0, new_conv_info, NO_DST_ADDR | NO_DST_PORT);
|
|
|
|
/* set the dissector for the new conversation */
|
|
conversation_set_dissector(conversation, sub_dissector);
|
|
|
|
|
|
2.5 Per packet information
|
|
|
|
Information can be stored for each data packet that is process by the dissector.
|
|
The information is added with the p_add_proto_data function and retreived with the
|
|
p_get_proto_data function. The data pointers passed into the p_add_proto_data are
|
|
not managed by the proto_data routines. If you use malloc or any other dynamic
|
|
memory allocation scheme, you must release the data when it isn't required.
|
|
|
|
void
|
|
p_add_proto_data(frame_data *fd, int proto, void *proto_data)
|
|
void *
|
|
p_get_proto_data(frame_data *fd, int proto)
|
|
|
|
Where:
|
|
fd - The fd pointer in the pinfo structure, usually pinfo->fd
|
|
proto - Protocol id returned by the proto_register_protocol call during initialization
|
|
proto_data - pointer to the dissector data.
|
|
|
|
|
|
2.5 User Preferences
|
|
|
|
If the dissector has user options, there is support for adding these preferences
|
|
to a configuration dialog.
|
|
|
|
You must register the module with the preferences routine with -
|
|
|
|
module_t *prefs_register_protocol(proto_id, void (*apply_cb)(void))
|
|
|
|
Where: proto_id - the value returned by "proto_register_protocol()" when
|
|
the protocol was registered
|
|
apply_cb - Callback routine that is call when preferences are applied
|
|
|
|
|
|
Then you can register the fields that can be configured by the user with these routines -
|
|
|
|
/* Register a preference with an unsigned integral value. */
|
|
void prefs_register_uint_preference(module_t *module, const char *name,
|
|
const char *title, const char *description, guint base, guint *var);
|
|
|
|
/* Register a preference with an Boolean value. */
|
|
void prefs_register_bool_preference(module_t *module, const char *name,
|
|
const char *title, const char *description, gboolean *var);
|
|
|
|
/* Register a preference with an enumerated value. */
|
|
void prefs_register_enum_preference(module_t *module, const char *name,
|
|
const char *title, const char *description, gint *var,
|
|
const enum_val *enumvals, gboolean radio_buttons)
|
|
|
|
/* Register a preference with a character-string value. */
|
|
void prefs_register_string_preference(module_t *module, const char *name,
|
|
const char *title, const char *description, char **var)
|
|
|
|
Where: module - Returned by the prefs_register_protocol routine
|
|
name - Appended to the module name to identify the field in the preference file
|
|
title - Field title in the preferences dialog
|
|
description - Comments added to the preference file above the
|
|
preference value
|
|
var - pointer to the storage location that is updated when the
|
|
field is changed in the preference dialog box
|
|
enumvals - an array of enum_val structures. This must be NULL terminated
|
|
radio_buttons - Is the enumvals a list of radio buttons?
|
|
|
|
|
|
An example from packet-bxxp.c -
|
|
|
|
proto_bxxp = proto_register_protocol("Blocks eXtensible eXchange Protocol",
|
|
"BXXP", "bxxp");
|
|
|
|
/* Register our configuration options for BXXP, particularly our port */
|
|
|
|
bxxp_module = prefs_register_protocol(proto_bxxp, proto_reg_handoff_bxxp);
|
|
|
|
prefs_register_uint_preference(bxxp_module, "tcp.port", "BXXP TCP Port",
|
|
"Set the port for BXXP messages (if other"
|
|
" than the default of 10288)",
|
|
10, &global_bxxp_tcp_port);
|
|
|
|
prefs_register_bool_preference(bxxp_module, "strict_header_terminator",
|
|
"BXXP Header Requires CRLF",
|
|
"Specifies that BXXP requires CRLF as a "
|
|
"terminator, and not just CR or LF",
|
|
&global_bxxp_strict_term);
|
|
|
|
|
|
3. Plugins
|
|
|
|
See the README.plugins for more information on how to "pluginize"
|
|
a dissector.
|
|
|
|
4.0 Extending Wiretap.
|
|
|
|
5.0 Adding new capabilities.
|
|
|
|
|
|
|
|
|
|
James Coe <jammer@cin.net>
|
|
Gilbert Ramirez <gram@xiexie.org>
|
|
Jeff Foster <jfoste@woodward.com>
|
|
Olivier Abad <oabad@cybercable.fr>
|
|
Laurent Deniel <deniel@worldnet.fr>
|
|
|