3 This file is a HOWTO for Ethereal developers. It describes how to start coding
4 a Ethereal protocol dissector and the use some of the important functions and
7 1. Setting up your protocol dissector code.
9 This section provides skeleton code for a protocol dissector. It also explains
10 the basic functions needed to enter values in the traffic summary columns,
11 add to the protocol tree, and work with registered header fields.
17 Ethereal runs on many platforms, and can be compiled with a number of
18 different compilers; here are some rules for writing code that will work
19 on multiple platforms.
21 Don't use C++-style comments (comments beginning with "//" and running
22 to the end of the line); Ethereal's dissectors are written in C, and
23 thus run through C rather than C++ compilers, and not all C compilers
24 support C++-style comments (GCC does, but IBM's C compiler for AIX, for
25 example, doesn't do so by default).
27 Don't initialize variables in their declaration with non-constant
28 values. Not all compilers support this. E.g. don't use
29 guint32 i = somearray[2];
35 Don't use zero-length arrays; not all compilers support them. If an
36 array would have no members, just leave it out.
38 Don't declare variables in the middle of executable code; not all C
39 compilers support that. Variables should be declared outside a
40 function, or at the beginning of a function or compound statement.
42 Don't use "inline"; not all compilers support it. If you want to have a
43 function be an inline function if the compiler supports it, use
44 G_INLINE_FUNC, which is declared by <glib.h>. This may not work with
45 functions declared in header files; if it doesn't work, don't declare
46 the function in a header file, even if this requires that you not make
47 it inline on any platform.
49 Don't use "uchar", "u_char", "ushort", "u_short", "uint", "u_int",
50 "ulong", "u_long" or "boolean"; they aren't defined on all platforms.
51 If you want an 8-bit unsigned quantity, use "guint8"; if you want an
52 8-bit character value with the 8th bit not interpreted as a sign bit,
53 use "guchar"; if you want a 16-bit unsigned quantity, use "guint16";
54 if you want a 32-bit unsigned quantity, use "guint32"; and if you want
55 an "int-sized" unsigned quantity, use "guint"; if you want a boolean,
56 use "gboolean". Use "%d", "%u", "%x", and "%o" to print those types;
57 don't use "%ld", "%lu", "%lx", or "%lo", as longs are 64 bits long on
58 many platforms, but "guint32" is 32 bits long.
60 Don't use "long" to mean "signed 32-bit integer", and don't use
61 "unsigned long" to mean "unsigned 32-bit integer"; "long"s are 64 bits
62 long on many platforms. Use "gint32" for signed 32-bit integers and use
63 "guint32" for unsigned 32-bit integers.
65 Don't use "long" to mean "signed 64-bit integer" and don't use "unsigned
66 long" to mean "unsigned 64-bit integer"; "long"s are 32 bits long on
67 other many platforms. Don't use "long long" or "unsigned long long",
68 either, as not all platforms support them; use "gint64" or "guint64",
69 which will be defined as the appropriate types for 64-bit signed and
72 When printing or displaying the values of 64-bit integral data types,
73 don't assume use "%lld", "%llu", "%llx", or "%llo" - not all platforms
74 support "%ll" for printing 64-bit integral data types. Instead, use
75 PRId64, PRIu64, PRIx64, and PRIo64, for example
77 proto_tree_add_text(tree, tvb, offset, 8,
78 "Sequence Number: %" PRIu64, sequence_number);
80 When specifying an integral constant that doesn't fit in 32 bits, don't
81 use "LL" at the end of the constant - not all compilers use "LL" for
82 that. Instead, put the constant in a call to the "G_GINT64_CONSTANT()"
85 G_GINT64_CONSTANT(11644473600U)
91 Don't use a label without a statement following it. For example,
101 will not work with all compilers - you have to do
111 with some statement, even if it's a null statement, after the label.
113 Don't use "bzero()", "bcopy()", or "bcmp()"; instead, use the ANSI C
116 "memset()" (with zero as the second argument, so that it sets
117 all the bytes to zero);
119 "memcpy()" or "memmove()" (note that the first and second
120 arguments to "memcpy()" are in the reverse order to the
121 arguments to "bcopy()"; note also that "bcopy()" is typically
122 guaranteed to work on overlapping memory regions, while
123 "memcpy()" isn't, so if you may be copying from one region to a
124 region that overlaps it, use "memmove()", not "memcpy()" - but
125 "memcpy()" might be faster as a result of not guaranteeing
126 correct operation on overlapping memory regions);
128 and "memcmp()" (note that "memcmp()" returns 0, 1, or -1, doing
129 an ordered comparison, rather than just returning 0 for "equal"
130 and 1 for "not equal", as "bcmp()" does).
132 Not all platforms necessarily have "bzero()"/"bcopy()"/"bcmp()", and
133 those that do might not declare them in the header file on which they're
134 declared on your platform.
136 Don't use "index()" or "rindex()"; instead, use the ANSI C equivalents,
137 "strchr()" and "strrchr()". Not all platforms necessarily have
138 "index()" or "rindex()", and those that do might not declare them in the
139 header file on which they're declared on your platform.
141 Don't fetch data from packets by getting a pointer to data in the packet
142 with "tvb_get_ptr()", casting that pointer to a pointer to a structure,
143 and dereferencing that pointer. That point won't necessarily be aligned
144 on the proper boundary, which can cause crashes on some platforms (even
145 if it doesn't crash on an x86-based PC); furthermore, the data in a
146 packet is not necessarily in the byte order of the machine on which
147 Ethereal is running. Use the tvbuff routines to extract individual
148 items from the packet, or use "proto_tree_add_item()" and let it extract
151 Don't use "ntohs()", "ntohl()", "htons()", or "htonl()"; the header
152 files required to define or declare them differ between platforms, and
153 you might be able to get away with not including the appropriate header
154 file on your platform but that might not work on other platforms.
155 Instead, use "g_ntohs()", "g_ntohl()", "g_htons()", and "g_htonl()";
156 those are declared by <glib.h>, and you'll need to include that anyway,
157 as Ethereal header files that all dissectors must include use stuff from
160 Don't fetch a little-endian value using "tvb_get_ntohs() or
161 "tvb_get_ntohl()" and then using "g_ntohs()", "g_htons()", "g_ntohl()",
162 or "g_htonl()" on the resulting value - the g_ routines in question
163 convert between network byte order (big-endian) and *host* byte order,
164 not *little-endian* byte order; not all machines on which Ethereal runs
165 are little-endian, even though PC's are. Fetch those values using
166 "tvb_get_letohs()" and "tvb_get_letohl()".
168 Don't put a comma after the last element of an enum - some compilers may
169 either warn about it (producing extra noise) or refuse to accept it.
171 Don't include <unistd.h> without protecting it with
179 and, if you're including it to get routines such as "open()", "close()",
180 "read()", and "write()" declared, also include <io.h> if present:
186 in order to declare the Windows C library routines "_open()",
187 "_close()", "_read()", and "_write()". Your file must include <glib.h>
188 - which many of the Ethereal header files include, so you might not have
189 to include it explicitly - in order to get "open()", "close()",
190 "read()", "write()", etc. mapped to "_open()", "_close()", "_read()",
193 When opening a file with "fopen()", "freopen()", or "fdopen()", if the
194 file contains ASCII text, use "r", "w", "a", and so on as the open mode
195 - but if it contains binary data, use "rb", "wb", and so on. On
196 Windows, if a file is opened in a text mode, writing a byte with the
197 value of octal 12 (newline) to the file causes two bytes, one with the
198 value octal 15 (carriage return) and one with the value octal 12, to be
199 written to the file, and causes bytes with the value octal 15 to be
200 discarded when reading the file (to translate between C's UNIX-style
201 lines that end with newline and Windows' DEC-style lines that end with
202 carriage return/line feed).
204 In addition, that also means that when opening or creating a binary
205 file, you must use "open()" (with O_CREAT and possibly O_TRUNC if the
206 file is to be created if it doesn't exist), and OR in the O_BINARY flag.
207 That flag is not present on most, if not all, UNIX systems, so you must
214 to properly define it for UNIX (it's not necessary on UNIX).
216 Don't use forward declarations of static arrays without a specified size
217 in a fashion such as this:
219 static const value_string foo_vals[];
223 static const value_string foo_vals[] = {
230 as some compilers will reject the first of those statements. Instead,
231 initialize the array at the point at which it's first declared, so that
234 Don't put declarations in the middle of a block; put them before all
235 code. Not all compilers support declarations in the middle of code,
244 For #define names and enum member names, prefix the names with a tag so
245 as to avoid collisions with other names - this might be more of an issue
246 on Windows, as it appears to #define names such as DELETE and
249 Don't use the "numbered argument" feature that many UNIX printf's
252 sprintf(add_string, " - (%1$d) (0x%1$04x)", value);
254 as not all UNIX printf's implement it, and Windows printf doesn't appear
255 to implement it. Use something like
257 sprintf(add_string, " - (%d) (0x%04x)", value, value);
261 Don't use "variadic macros", such as
263 #define DBG(format, args...) fprintf(stderr, format, ## args)
265 as not all C compilers support them. Use macros that take a fixed
266 number of arguments, such as
268 #define DBG0(format) fprintf(stderr, format)
269 #define DBG1(format, arg1) fprintf(stderr, format, arg1)
270 #define DBG2(format, arg1, arg2) fprintf(stderr, format, arg1, arg2)
276 #define DBG(args) printf args
278 snprintf() -> g_snprintf()
279 snprintf() is not available on all platforms, so it's a good idea to use the
280 g_snprintf() function declared by <glib.h> instead.
282 tmpnam() -> mkstemp()
283 tmpnam is insecure and should not be used any more. Ethereal brings its
284 own mkstemp implementation for use on platforms that lack mkstemp.
285 Note: mkstemp does not accept NULL as a parameter.
287 The pointer retured by a call to "tvb_get_ptr()" is not guaranteed to be
288 aligned on any particular byte boundary; this means that you cannot
289 safely cast it to any data type other than a pointer to "char",
290 "unsigned char", "guint8", or other one-byte data types. You cannot,
291 for example, safely cast it to a pointer to a structure, and then access
292 the structure members directly; on some systems, unaligned accesses to
293 integral data types larger than 1 byte, and floating-point data types,
294 cause a trap, which will, at best, result in the OS slowly performing an
295 unaligned access for you, and will, on at least some platforms, cause
296 the program to be terminated.
298 Ethereal supports both platforms with GLib 1.2[.x]/GTK+ 1.2[.x] and GLib
299 2.x/GTK+ 1.3[.x] and 2.x. If at all possible, either use only
300 mechanisms that are present in GLib 1.2[.x] and GTK+ 1.2[.x], use #if's
301 to conditionally use older or newer mechanisms depending on the platform
302 on which Ethereal is being built, or, if the code in GLib or GTK+ that
303 implements that mechanism will build with GLib 1.2[.x]/GTK+ 1.2[.x],
304 conditionally include that code as part of the Ethereal source and use
305 the included version with GLib 1.2[.x] or GTK+ 1.2[.x]. In particular,
306 if the GLib 2.x or GTK+ 2.x mechanism indicates that a routine is
307 deprecated and shouldn't be used in new code, and that it was renamed in
308 GLib 2.x or GTK+ 2.x and the new name should be used, disregard that and
309 use the old name - it'll still work with GLib 2.x or GTK+ 2.x, but will
310 also work with GLib 1.2[.x] and GTK+ 1.2[.x].
312 When different code must be used on UN*X and Win32, use a #if or #ifdef
313 that tests _WIN32, not WIN32. Try to write code portably whenever
314 possible, however; note that there are some routines in Ethereal with
315 platform-dependent implementations and platform-independent APIs, such
316 as the routines in epan/filesystem.c, allowing the code that calls it to
317 be written portably without #ifdefs.
319 1.1.2 String handling
321 Do not use functions such as strcat() or strcpy().
322 A lot of work has been done to remove the existing calls to these functions and
323 we do not want any new callers of these functions.
325 Instead use g_snprintf() since that function will if used correctly prevent
326 buffer overflows for large strings.
328 When using a buffer to create a string, do not use a buffer stored on the stack.
329 I.e. do not use a buffer declared as
331 instead allocate a buffer dynamically using the emem routines (see README.malloc) such as
334 #define MAX_BUFFER 1024
335 buffer=ep_alloc(MAX_BUFFER);
338 g_snprintf(buffer, MAX_BUFFER, ...
340 This avoid the stack to be corrupted in case there is a bug in your code that
341 accidentally writes beyond the end of the buffer.
344 If you write a routine that will create and return a pointer to a filled in
345 string and if that buffer will not be further processed or appended to after
346 the routine returns (except being added to the proto tree),
347 do not preallocate the buffer to fill in and pass as a parameter instead
348 pass a pointer to a pointer to the function and return a pointer to an
349 emem allocated buffer that will be automatically freed. (see README.malloc)
351 I.e. do not write code such as
353 foo_to_str(char *string, ... ){
359 foo_to_str(buffer, ...
360 proto_tree_add_text(... buffer ...
362 instead write the code as
364 foo_to_str(char **buffer, ...
372 foo_to_str(&buffer, ...
373 proto_tree_add_text(... *buffer ...
375 Use ep_ allocated buffers. They are very fast and nice. These buffers are all
376 automatically free()d when the dissection of the current packet ends so you
377 dont have to worry about free()ing them explicitely in order to not leak memory.
378 Please read README.malloc .
383 Ethereal is not guaranteed to read only network traces that contain correctly-
384 formed packets. Ethereal is commonly used is to track down networking problems,
385 and the problems might be due to a buggy protocol implementation sending out
388 Therefore, protocol dissectors not only have to be able to handle
389 correctly-formed packets without, for example, crashing or looping
390 infinitely, they also have to be able to handle *incorrectly*-formed
391 packets without crashing or looping infinitely.
393 Here are some suggestions for making dissectors more robust in the face
394 of incorrectly-formed packets:
396 Do *NOT* use "g_assert()" or "g_assert_not_reached()" in dissectors.
397 *NO* value in a packet's data should be considered "wrong" in the sense
398 that it's a problem with the dissector if found; if it cannot do
399 anything else with a particular value from a packet's data, the
400 dissector should put into the protocol tree an indication that the
401 value is invalid, and should return.
403 If you are allocating a chunk of memory to contain data from a packet,
404 or to contain information derived from data in a packet, and the size of
405 the chunk of memory is derived from a size field in the packet, make
406 sure all the data is present in the packet before allocating the buffer.
409 1) Ethereal won't leak that chunk of memory if an attempt to
410 fetch data not present in the packet throws an exception
414 2) it won't crash trying to allocate an absurdly-large chunk of
415 memory if the size field has a bogus large value.
417 If you're fetching into such a chunk of memory a string from the buffer,
418 and the string has a specified size, you can use "tvb_get_*_string()",
419 which will check whether the entire string is present before allocating
420 a buffer for the string, and will also put a trailing '\0' at the end of
423 If you're fetching into such a chunk of memory a 2-byte Unicode string
424 from the buffer, and the string has a specified size, you can use
425 "tvb_get_ephemeral_faked_unicode()", which will check whether the entire
426 string is present before allocating a buffer for the string, and will also
427 put a trailing '\0' at the end of the buffer. The resulting string will be
428 a sequence of single-byte characters; the only Unicode characters that
429 will be handled correctly are those in the ASCII range. (Ethereal's
430 ability to handle non-ASCII strings is limited; it needs to be
433 If you're fetching into such a chunk of memory a sequence of bytes from
434 the buffer, and the sequence has a specified size, you can use
435 "tvb_memdup()", which will check whether the entire sequence is present
436 before allocating a buffer for it.
438 Otherwise, you can check whether the data is present by using
439 "tvb_ensure_bytes_exist()" or by getting a pointer to the data by using
440 "tvb_get_ptr()", although note that there might be problems with using
441 the pointer from "tvb_get_ptr()" (see the item on this in the
442 Portability section above, and the next item below).
444 Note also that you should only fetch string data into a fixed-length
445 buffer if the code ensures that no more bytes than will fit into the
446 buffer are fetched ("the protocol ensures" isn't good enough, as
447 protocol specifications can't ensure only packets that conform to the
448 specification will be transmitted or that only packets for the protocol
449 in question will be interpreted as packets for that protocol by
450 Ethereal). If there's no maximum length of string data to be fetched,
451 routines such as "tvb_get_*_string()" are safer, as they allocate a buffer
452 large enough to hold the string. (Note that some variants of this call
453 require you to free the string once you're finished with it.)
455 If you have gotten a pointer using "tvb_get_ptr()", you must make sure
456 that you do not refer to any data past the length passed as the last
457 argument to "tvb_get_ptr()"; while the various "tvb_get" routines
458 perform bounds checking and throw an exception if you refer to data not
459 available in the tvbuff, direct references through a pointer gotten from
460 "tvb_get_ptr()" do not do any bounds checking.
462 If you have a loop that dissects a sequence of items, each of which has
463 a length field, with the offset in the tvbuff advanced by the length of
464 the item, then, if the length field is the total length of the item, and
465 thus can be zero, you *MUST* check for a zero-length item and abort the
466 loop if you see one. Otherwise, a zero-length item could cause the
467 dissector to loop infinitely. You should also check that the offset,
468 after having the length added to it, is greater than the offset before
469 the length was added to it, if the length field is greater than 24 bits
470 long, so that, if the length value is *very* large and adding it to the
471 offset causes an overflow, that overflow is detected.
473 If you are fetching a length field from the buffer, corresponding to the
474 length of a portion of the packet, and subtracting from that length a
475 value corresponding to the length of, for example, a header in the
476 packet portion in question, *ALWAYS* check that the value of the length
477 field is greater than or equal to the length you're subtracting from it,
478 and report an error in the packet and stop dissecting the packet if it's
479 less than the length you're subtracting from it. Otherwise, the
480 resulting length value will be negative, which will either cause errors
481 in the dissector or routines called by the dissector, or, if the value
482 is interpreted as an unsigned integer, will cause the value to be
483 interpreted as a very large positive value.
485 Any tvbuff offset that is added to as processing is done on a packet
486 should be stored in a 32-bit variable, such as an "int"; if you store it
487 in an 8-bit or 16-bit variable, you run the risk of the variable
490 sprintf() -> g_snprintf()
491 Prevent yourself from using the sprintf() function, as it does not test the
492 length of the given output buffer and might be writing into memory areas not
493 intended for. This function is one of the main causes of security problems
494 like buffer exploits and many other bugs that are very hard to find. It's
495 much better to use the g_snprintf() function declared by <glib.h> instead.
497 You should test your dissector against incorrectly-formed packets. This
498 can be done using the randpkt and editcap utilities that come with the
499 Ethereal distribution. Testing using randpkt can be done by generating
500 output at the same layer as your protocol, and forcing Ethereal/Tethereal
501 to decode it as your protocol, e.g. if your protocol sits on top of UDP:
503 randpkt -c 50000 -t dns randpkt.pcap
504 tethereal -nVr randpkt.pcap -d udp.port==53,<myproto>
506 Testing using editcap can be done using preexisting capture files and the
507 "-E" flag, which introduces errors in a capture file. E.g.:
509 editcap -E 0.03 infile.pcap outfile.pcap
510 tethereal -nVr outfile.pcap
512 1.1.4 Name convention.
514 Ethereal uses the underscore_convention rather than the InterCapConvention for
515 function names, so new code should probably use underscores rather than
516 intercaps for functions and variable names. This is especially important if you
517 are writing code that will be called from outside your code. We are just
518 trying to keep things consistent for other users.
520 1.1.5 White space convention.
522 Avoid using tab expansions different from 8 spaces, as not all text editors in
523 use by the developers support this.
525 When creating a new file, you are free to choose an indentation logic. Most of
526 the files in Ethereal tend to use 2-space or 4-space indentation. You are
527 encouraged to write a short comment on the indentation logic at the beginning
530 When editing an existing file, try following the existing indentation logic and
531 even if it very tempting, never ever use a restyler/reindenter utility on an
536 Ethereal requires certain things when setting up a protocol dissector.
537 Below is skeleton code for a dissector that you can copy to a file and
538 fill in. Your dissector should follow the naming convention of packet-
539 followed by the abbreviated name for the protocol. It is recommended
540 that where possible you keep to the IANA abbreviated name for the
541 protocol, if there is one, or a commonly-used abbreviation for the
544 Usually, you will put your newly created dissector file into the directory
545 epan/dissectors, just like all the other packet-....c files already in there.
547 Also, please add your dissector file to the corresponding makefile,
548 described in section "1.9 Editing Makefile.common to add your dissector" below.
550 Dissectors that use the dissector registration to register with a lower level
551 dissector don't need to define a prototype in the .h file. For other
552 dissectors the main dissector routine should have a prototype in a header
553 file whose name is "packet-", followed by the abbreviated name for the
554 protocol, followed by ".h"; any dissector file that calls your dissector
555 should be changed to include that file.
557 You may not need to include all the headers listed in the skeleton
558 below, and you may need to include additional headers. For example, the
567 is needed only if you are using a function from libpcre, e.g. the
568 "pcre_compile()" function.
571 in the comment will be updated by CVS when the file is
572 checked in; it will allow the RCS "ident" command to report which
573 version of the file is currently checked out.
575 When creating a new file, it is fine to just write "$Id$" as RCS will
576 automatically fill in the identifier at the time the file will be added to the
577 SVN repository (checked in).
579 ------------------------------------Cut here------------------------------------
580 /* packet-PROTOABBREV.c
581 * Routines for PROTONAME dissection
582 * Copyright 2000, YOUR_NAME <YOUR_EMAIL_ADDRESS>
586 * Wireshark - Network traffic analyzer
587 * By Gerald Combs <gerald@wireshark.org>
588 * Copyright 1998 Gerald Combs
590 * Copied from WHATEVER_FILE_YOU_USED (where "WHATEVER_FILE_YOU_USED"
591 * is a dissector file; if you just copied this from README.developer,
592 * don't bother with the "Copied from" - you don't even need to put
593 * in a "Copied from" if you copied an existing dissector, especially
594 * if the bulk of the code in the new dissector is your code)
596 * This program is free software; you can redistribute it and/or
597 * modify it under the terms of the GNU General Public License
598 * as published by the Free Software Foundation; either version 2
599 * of the License, or (at your option) any later version.
601 * This program is distributed in the hope that it will be useful,
602 * but WITHOUT ANY WARRANTY; without even the implied warranty of
603 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
604 * GNU General Public License for more details.
606 * You should have received a copy of the GNU General Public License
607 * along with this program; if not, write to the Free Software
608 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
621 #include <epan/packet.h>
622 #include <epan/prefs.h>
624 /* IF PROTO exposes code to other dissectors, then it must be exported
625 in a header file. If not, a header file is not needed at all. */
626 #include "packet-PROTOABBREV.h"
628 /* Forward declaration we need below */
629 void proto_reg_handoff_PROTOABBREV(void);
631 /* Initialize the protocol and registered fields */
632 static int proto_PROTOABBREV = -1;
633 static int hf_PROTOABBREV_FIELDABBREV = -1;
635 /* Global sample preference ("controls" display of numbers) */
636 static gboolean gPREF_HEX = FALSE;
638 /* Initialize the subtree pointers */
639 static gint ett_PROTOABBREV = -1;
641 /* Code to actually dissect the packets */
643 dissect_PROTOABBREV(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
646 /* Set up structures needed to add the protocol subtree and manage it */
648 proto_tree *PROTOABBREV_tree;
650 /* Make entries in Protocol column and Info column on summary display */
651 if (check_col(pinfo->cinfo, COL_PROTOCOL))
652 col_set_str(pinfo->cinfo, COL_PROTOCOL, "PROTOABBREV");
654 /* This field shows up as the "Info" column in the display; you should use
655 it, if possible, to summarize what's in the packet, so that a user looking
656 at the list of packets can tell what type of packet it is. See section 1.5
657 for more information.
659 Before changing the contents of a column you should make sure the column is
660 active by calling "check_col(pinfo->cinfo, COL_*)". If it is not active
661 don't bother setting it.
663 If you are setting the column to a constant string, use "col_set_str()",
664 as it's more efficient than the other "col_set_XXX()" calls.
666 If you're setting it to a string you've constructed, or will be
667 appending to the column later, use "col_add_str()".
669 "col_add_fstr()" can be used instead of "col_add_str()"; it takes
670 "printf()"-like arguments. Don't use "col_add_fstr()" with a format
671 string of "%s" - just use "col_add_str()" or "col_set_str()", as it's
672 more efficient than "col_add_fstr()".
674 If you will be fetching any data from the packet before filling in
675 the Info column, clear that column first, in case the calls to fetch
676 data from the packet throw an exception because they're fetching data
677 past the end of the packet, so that the Info column doesn't have data
678 left over from the previous dissector; do
680 if (check_col(pinfo->cinfo, COL_INFO))
681 col_clear(pinfo->cinfo, COL_INFO);
685 if (check_col(pinfo->cinfo, COL_INFO))
686 col_set_str(pinfo->cinfo, COL_INFO, "XXX Request");
688 /* A protocol dissector can be called in 2 different ways:
690 (a) Operational dissection
692 In this mode, Ethereal is only interested in the way protocols
693 interact, protocol conversations are created, packets are reassembled
694 and handed over to higher-level protocol dissectors.
695 In this mode Ethereal does not build a so-called "protocol tree".
697 (b) Detailed dissection
699 In this mode, Ethereal is also interested in all details of a given
700 protocol, so a "protocol tree" is created.
702 Ethereal distinguishes between the 2 modes with the proto_tree pointer:
706 In the interest of speed, if "tree" is NULL, avoid building a
707 protocol tree and adding stuff to it, or even looking at any packet
708 data needed only if you're building the protocol tree, if possible.
710 Note, however, that you must fill in column information, create
711 conversations, reassemble packets, build any other persistent state
712 needed for dissection, and call subdissectors regardless of whether
713 "tree" is NULL or not. This might be inconvenient to do without
714 doing most of the dissection work; the routines for adding items to
715 the protocol tree can be passed a null protocol tree pointer, in
716 which case they'll return a null item pointer, and
717 "proto_item_add_subtree()" returns a null tree pointer if passed a
718 null item pointer, so, if you're careful not to dereference any null
719 tree or item pointers, you can accomplish this by doing all the
720 dissection work. This might not be as efficient as skipping that
721 work if you're not building a protocol tree, but if the code would
722 have a lot of tests whether "tree" is null if you skipped that work,
723 you might still be better off just doing all that work regardless of
724 whether "tree" is null or not. */
727 /* NOTE: The offset and length values in the call to
728 "proto_tree_add_item()" define what data bytes to highlight in the hex
729 display window when the line in the protocol tree display
730 corresponding to that item is selected.
732 Supplying a length of -1 is the way to highlight all data from the
733 offset to the end of the packet. */
735 /* create display subtree for the protocol */
736 ti = proto_tree_add_item(tree, proto_PROTOABBREV, tvb, 0, -1, FALSE);
738 PROTOABBREV_tree = proto_item_add_subtree(ti, ett_PROTOABBREV);
740 /* add an item to the subtree, see section 1.6 for more information */
741 proto_tree_add_item(PROTOABBREV_tree,
742 hf_PROTOABBREV_FIELDABBREV, tvb, offset, len, FALSE)
745 /* Continue adding tree items to process the packet here */
750 /* If this protocol has a sub-dissector call it here, see section 1.8 */
754 /* Register the protocol with Ethereal */
756 /* this format is require because a script is used to build the C function
757 that calls all the protocol registration.
761 proto_register_PROTOABBREV(void)
763 module_t *PROTOABBREV_module;
765 /* Setup list of header fields See Section 1.6.1 for details*/
766 static hf_register_info hf[] = {
767 { &hf_PROTOABBREV_FIELDABBREV,
768 { "FIELDNAME", "PROTOABBREV.FIELDABBREV",
769 FIELDTYPE, FIELDBASE, FIELDCONVERT, BITMASK,
770 "FIELDDESCR", HFILL }
774 /* Setup protocol subtree array */
775 static gint *ett[] = {
779 /* Register the protocol name and description */
780 proto_PROTOABBREV = proto_register_protocol("PROTONAME",
781 "PROTOSHORTNAME", "PROTOABBREV");
783 /* Required function calls to register the header fields and subtrees used */
784 proto_register_field_array(proto_PROTOABBREV, hf, array_length(hf));
785 proto_register_subtree_array(ett, array_length(ett));
787 /* Register preferences module (See Section 2.6 for more on preferences) */
788 PROTOABBREV_module = prefs_register_protocol(proto_PROTOABBREV, proto_reg_handoff_PROTOABBREV);
790 /* Register a sample preference */
791 prefs_register_bool_preference(PROTOABBREV_module, "showHex",
792 "Display numbers in Hex",
793 "Enable to display numerical values in hexidecimal.",
798 /* If this dissector uses sub-dissector registration add a registration routine.
799 This exact format is required because a script is used to find these routines
800 and create the code that calls these routines.
802 This function is also called by preferences whenever "Apply" is pressed
803 (see prefs_register_protocol above) so it should accommodate being called
807 proto_reg_handoff_PROTOABBREV(void)
809 static gboolean inited = FALSE;
813 dissector_handle_t PROTOABBREV_handle;
815 PROTOABBREV_handle = create_dissector_handle(dissect_PROTOABBREV,
817 dissector_add("PARENT_SUBFIELD", ID_VALUE, PROTOABBREV_handle);
823 If you perform registration functions which are dependant upon
824 prefs the you should de-register everything which was associated
825 with the previous settings and re-register using the new prefs settings
826 here. In general this means you need to keep track of what value the
827 preference had at the time you registered using a local static in this
830 static int currentPort = -1;
832 if( -1 != currentPort ) {
833 dissector_delete( "tcp.port", currentPort, PROTOABBREV_handle);
836 currentPort = gPortPref;
838 dissector_add("tcp.port", currentPort, PROTOABBREV_handle);
843 ------------------------------------Cut here------------------------------------
845 1.3 Explanation of needed substitutions in code skeleton.
847 In the above code block the following strings should be substituted with
850 YOUR_NAME Your name, of course. You do want credit, don't you?
851 It's the only payment you will receive....
852 YOUR_EMAIL_ADDRESS Keep those cards and letters coming.
853 WHATEVER_FILE_YOU_USED Add this line if you are using another file as a
855 PROTONAME The name of the protocol; this is displayed in the
856 top-level protocol tree item for that protocol.
857 PROTOSHORTNAME An abbreviated name for the protocol; this is displayed
858 in the "Preferences" dialog box if your dissector has
859 any preferences, and in the dialog box for filter fields
860 when constructing a filter expression.
861 PROTOABBREV A name for the protocol for use in filter expressions;
862 it should contain only lower-case letters, digits, and
864 FIELDNAME The displayed name for the header field.
865 FIELDABBREV The abbreviated name for the header field. (NO SPACES)
866 FIELDTYPE FT_NONE, FT_BOOLEAN, FT_UINT8, FT_UINT16, FT_UINT24,
867 FT_UINT32, FT_UINT64, FT_INT8, FT_INT16, FT_INT24, FT_INT32,
868 FT_INT64, FT_FLOAT, FT_DOUBLE, FT_ABSOLUTE_TIME,
869 FT_RELATIVE_TIME, FT_STRING, FT_STRINGZ, FT_UINT_STRING,
870 FT_ETHER, FT_BYTES, FT_IPv4, FT_IPv6, FT_IPXNET,
871 FT_FRAMENUM, FT_PROTOCOL, FT_GUID, FT_OID
872 FIELDBASE BASE_NONE, BASE_DEC, BASE_HEX, BASE_OCT, BASE_DEC_HEX, BASE_HEX_DEC
873 FIELDCONVERT VALS(x), TFS(x), NULL
874 BITMASK Usually 0x0 unless using the TFS(x) field conversion.
875 FIELDDESCR A brief description of the field.
876 PARENT_SUBFIELD Lower level protocol field used for lookup, i.e. "tcp.port"
877 ID_VALUE Lower level protocol field value that identifies this protocol
878 For example the TCP or UDP port number
880 If, for example, PROTONAME is "Internet Bogosity Discovery Protocol",
881 PROTOSHORTNAME would be "IBDP", and PROTOABBREV would be "ibdp". Try to
882 conform with IANA names.
884 1.4 The dissector and the data it receives.
889 This is only needed if the dissector doesn't use self-registration to
890 register itself with the lower level dissector, or if the protocol dissector
891 wants/needs to expose code to other subdissectors.
893 The dissector must declared as exactly as follows in the file
894 packet-PROTOABBREV.h:
897 dissect_PROTOABBREV(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree);
900 1.4.2 Extracting data from packets.
902 NOTE: See the tvbuff.h file for more details
904 The "tvb" argument to a dissector points to a buffer containing the raw
905 data to be analyzed by the dissector; for example, for a protocol
906 running atop UDP, it contains the UDP payload (but not the UDP header,
907 or any protocol headers above it). A tvbuffer is a opaque data
908 structure, the internal data structures are hidden and the data must be
909 access via the tvbuffer accessors.
913 Single-byte accessor:
915 guint8 tvb_get_guint8(tvbuff_t*, gint offset);
917 Network-to-host-order accessors for 16-bit integers (guint16), 32-bit
918 integers (guint32), and 24-bit integers:
920 guint16 tvb_get_ntohs(tvbuff_t*, gint offset);
921 guint32 tvb_get_ntohl(tvbuff_t*, gint offset);
922 guint32 tvb_get_ntoh24(tvbuff_t*, gint offset);
924 Network-to-host-order accessors for single-precision and
925 double-precision IEEE floating-point numbers:
927 gfloat tvb_get_ntohieee_float(tvbuff_t*, gint offset);
928 gdouble tvb_get_ntohieee_double(tvbuff_t*, gint offset);
930 Little-Endian-to-host-order accessors for 16-bit integers (guint16),
931 32-bit integers (guint32), and 24-bit integers:
933 guint16 tvb_get_letohs(tvbuff_t*, gint offset);
934 guint32 tvb_get_letohl(tvbuff_t*, gint offset);
935 guint32 tvb_get_letoh24(tvbuff_t*, gint offset);
937 Little-Endian-to-host-order accessors for single-precision and
938 double-precision IEEE floating-point numbers:
940 gfloat tvb_get_letohieee_float(tvbuff_t*, gint offset);
941 gdouble tvb_get_letohieee_double(tvbuff_t*, gint offset);
943 Accessors for IPv4 and IPv6 addresses:
945 guint32 tvb_get_ipv4(tvbuff_t*, gint offset);
946 void tvb_get_ipv6(tvbuff_t*, gint offset, struct e_in6_addr *addr);
948 NOTE: IPv4 addresses are not to be converted to host byte order before
949 being passed to "proto_tree_add_ipv4()". You should use "tvb_get_ipv4()"
950 to fetch them, not "tvb_get_ntohl()" *OR* "tvb_get_letohl()" - don't,
951 for example, try to use "tvb_get_ntohl()", find that it gives you the
952 wrong answer on the PC on which you're doing development, and try
953 "tvb_get_letohl()" instead, as "tvb_get_letohl()" will give the wrong
954 answer on big-endian machines.
958 void tvb_get_ntohguid(tvbuff_t *, gint offset, e_guid_t *guid);
959 void tvb_get_letohguid(tvbuff_t *, gint offset, e_guid_t *guid);
963 guint8 *tvb_get_string(tvbuff_t*, gint offset, gint length);
964 guint8 *tvb_get_ephemeral_string(tvbuff_t*, gint offset, gint length);
966 Returns a null-terminated buffer containing data from the specified
967 tvbuff, starting at the specified offset, and containing the specified
968 length worth of characters (the length of the buffer will be length+1,
969 as it includes a null character to terminate the string).
971 tvb_get_string() returns a buffer allocated by g_malloc() so you must
972 g_free() it when you are finished with the string. Failure to g_free() this
973 buffer will lead to memory leaks.
974 tvb_get_ephemeral_string() returns a buffer allocated from a special heap
975 with a lifetime until the next packet is dissected. You do not need to
976 free() this buffer, it will happen automatically once the next packet is
980 guint8 *tvb_get_stringz(tvbuff_t *tvb, gint offset, gint *lengthp);
981 guint8 *tvb_get_ephemeral_stringz(tvbuff_t *tvb, gint offset, gint *lengthp);
983 Returns a null-terminated buffer, allocated with "g_malloc()",
984 containing data from the specified tvbuff, starting with at the
985 specified offset, and containing all characters from the tvbuff up to
986 and including a terminating null character in the tvbuff. "*lengthp"
987 will be set to the length of the string, including the terminating null.
989 tvb_get_stringz() returns a buffer allocated by g_malloc() so you must
990 g_free() it when you are finished with the string. Failure to g_free() this
991 buffer will lead to memory leaks.
992 tvb_get_ephemeral_stringz() returns a buffer allocated from a special heap
993 with a lifetime until the next packet is dissected. You do not need to
994 free() this buffer, it will happen automatically once the next packet is
998 guint8 *tvb_fake_unicode(tvbuff_t*, gint offset, gint length);
999 guint8 *tvb_get_ephemeral_faked_unicode(tvbuff_t*, gint offset, gint length);
1001 Converts a 2-byte unicode string to an ASCII string.
1002 Returns a null-terminated buffer containing data from the specified
1003 tvbuff, starting at the specified offset, and containing the specified
1004 length worth of characters (the length of the buffer will be length+1,
1005 as it includes a null character to terminate the string).
1007 tvb_fake_unicode() returns a buffer allocated by g_malloc() so you must
1008 g_free() it when you are finished with the string. Failure to g_free() this
1009 buffer will lead to memory leaks.
1010 tvb_get_ephemeral_faked_unicode() returns a buffer allocated from a special
1011 heap with a lifetime until the next packet is dissected. You do not need to
1012 free() this buffer, it will happen automatically once the next packet is
1017 guint8* tvb_memcpy(tvbuff_t*, guint8* target, gint offset, gint length);
1019 Copies into the specified target the specified length's worth of data
1020 from the specified tvbuff, starting at the specified offset.
1022 guint8* tvb_memdup(tvbuff_t*, gint offset, gint length);
1023 guint8* ep_tvb_memdup(tvbuff_t*, gint offset, gint length);
1025 Returns a buffer, allocated with "g_malloc()", containing the specified
1026 length's worth of data from the specified tvbuff, starting at the
1027 specified offset. The ephemeral variant is freed automatically after the
1028 packet is dissected.
1031 /* WARNING! This function is possibly expensive, temporarily allocating
1032 * another copy of the packet data. Furthermore, it's dangerous because once
1033 * this pointer is given to the user, there's no guarantee that the user will
1034 * honor the 'length' and not overstep the boundaries of the buffer.
1036 guint8* tvb_get_ptr(tvbuff_t*, gint offset, gint length);
1038 The reason that tvb_get_ptr() might have to allocate a copy of its data
1039 only occurs with TVBUFF_COMPOSITES, data that spans multiple tvbuffers.
1040 If the user request a pointer to a range of bytes that spans the member
1041 tvbuffs that make up the TVBUFF_COMPOSITE, the data will have to be
1042 copied to another memory region to assure that all the bytes are
1047 1.5 Functions to handle columns in the traffic summary window.
1049 The topmost pane of the main window is a list of the packets in the
1050 capture, possibly filtered by a display filter.
1052 Each line corresponds to a packet, and has one or more columns, as
1053 configured by the user.
1055 Many of the columns are handled by code outside individual dissectors;
1056 most dissectors need only specify the value to put in the "Protocol" and
1059 Columns are specified by COL_ values; the COL_ value for the "Protocol"
1060 field, typically giving an abbreviated name for the protocol (but not
1061 the all-lower-case abbreviation used elsewhere) is COL_PROTOCOL, and the
1062 COL_ value for the "Info" field, giving a summary of the contents of the
1063 packet for that protocol, is COL_INFO.
1065 A value for a column should only be added if the user specified that it
1066 be displayed; to check whether a given column is to be displayed, call
1067 'check_col' with the COL_ value for that field as an argument - it will
1068 return TRUE if the column is to be displayed and FALSE if it is not to
1071 The value for a column can be specified with one of several functions,
1072 all of which take the 'fd' argument to the dissector as their first
1073 argument, and the COL_ value for the column as their second argument.
1075 1.5.1 The col_set_str function.
1077 'col_set_str' takes a string as its third argument, and sets the value
1078 for the column to that value. It assumes that the pointer passed to it
1079 points to a string constant or a static "const" array, not to a
1080 variable, as it doesn't copy the string, it merely saves the pointer
1081 value; the argument can itself be a variable, as long as it always
1082 points to a string constant or a static "const" array.
1084 It is more efficient than 'col_add_str' or 'col_add_fstr'; however, if
1085 the dissector will be using 'col_append_str' or 'col_append_fstr" to
1086 append more information to the column, the string will have to be copied
1087 anyway, so it's best to use 'col_add_str' rather than 'col_set_str' in
1090 For example, to set the "Protocol" column
1093 if (check_col(pinfo->cinfo, COL_PROTOCOL))
1094 col_set_str(pinfo->cinfo, COL_PROTOCOL, "PROTOABBREV");
1097 1.5.2 The col_add_str function.
1099 'col_add_str' takes a string as its third argument, and sets the value
1100 for the column to that value. It takes the same arguments as
1101 'col_set_str', but copies the string, so that if the string is, for
1102 example, an automatic variable that won't remain in scope when the
1103 dissector returns, it's safe to use.
1106 1.5.3 The col_add_fstr function.
1108 'col_add_fstr' takes a 'printf'-style format string as its third
1109 argument, and 'printf'-style arguments corresponding to '%' format
1110 items in that string as its subsequent arguments. For example, to set
1111 the "Info" field to "<XXX> request, <N> bytes", where "reqtype" is a
1112 string containing the type of the request in the packet and "n" is an
1113 unsigned integer containing the number of bytes in the request:
1115 if (check_col(pinfo->cinfo, COL_INFO))
1116 col_add_fstr(pinfo->cinfo, COL_INFO, "%s request, %u bytes",
1119 Don't use 'col_add_fstr' with a format argument of just "%s" -
1120 'col_add_str', or possibly even 'col_set_str' if the string that matches
1121 the "%s" is a static constant string, will do the same job more
1125 1.5.4 The col_clear function.
1127 If the Info column will be filled with information from the packet, that
1128 means that some data will be fetched from the packet before the Info
1129 column is filled in. If the packet is so small that the data in
1130 question cannot be fetched, the routines to fetch the data will throw an
1131 exception (see the comment at the beginning about tvbuffers improving
1132 the handling of short packets - the tvbuffers keep track of how much
1133 data is in the packet, and throw an exception on an attempt to fetch
1134 data past the end of the packet, so that the dissector won't process
1135 bogus data), causing the Info column not to be filled in.
1137 This means that the Info column will have data for the previous
1138 protocol, which would be confusing if, for example, the Protocol column
1139 had data for this protocol.
1141 Therefore, before a dissector fetches any data whatsoever from the
1142 packet (unless it's a heuristic dissector fetching data to determine
1143 whether the packet is one that it should dissect, in which case it
1144 should check, before fetching the data, whether there's any data to
1145 fetch; if there isn't, it should return FALSE), it should set the
1146 Protocol column and the Info column.
1148 If the Protocol column will ultimately be set to, for example, a value
1149 containing a protocol version number, with the version number being a
1150 field in the packet, the dissector should, before fetching the version
1151 number field or any other field from the packet, set it to a value
1152 without a version number, using 'col_set_str', and should later set it
1153 to a value with the version number after it's fetched the version
1156 If the Info column will ultimately be set to a value containing
1157 information from the packet, the dissector should, before fetching any
1158 fields from the packet, clear the column using 'col_clear' (which is
1159 more efficient than clearing it by calling 'col_set_str' or
1160 'col_add_str' with a null string), and should later set it to the real
1161 string after it's fetched the data to use when doing that.
1164 1.5.5 The col_append_str function.
1166 Sometimes the value of a column, especially the "Info" column, can't be
1167 conveniently constructed at a single point in the dissection process;
1168 for example, it might contain small bits of information from many of the
1169 fields in the packet. 'col_append_str' takes, as arguments, the same
1170 arguments as 'col_add_str', but the string is appended to the end of the
1171 current value for the column, rather than replacing the value for that
1172 column. (Note that no blank separates the appended string from the
1173 string to which it is appended; if you want a blank there, you must add
1174 it yourself as part of the string being appended.)
1177 1.5.6 The col_append_fstr function.
1179 'col_append_fstr' is to 'col_add_fstr' as 'col_append_str' is to
1180 'col_add_str' - it takes, as arguments, the same arguments as
1181 'col_add_fstr', but the formatted string is appended to the end of the
1182 current value for the column, rather than replacing the value for that
1185 1.5.7 The col_append_sep_str and col_append_sep_fstr functions.
1187 In specific situations the developer knows that a column's value will be
1188 created in a stepwise manner, where the appended values are listed. Both
1189 'col_append_sep_str' and 'col_append_sep_fstr' functions will add an item
1190 separator between two consecutive items, and will not add the separator at the
1191 beginning of the column. The remainder of the work both functions do is
1192 identical to what 'col_append_str' and 'col_append_fstr' do.
1194 1.6 Constructing the protocol tree.
1196 The middle pane of the main window, and the topmost pane of a packet
1197 popup window, are constructed from the "protocol tree" for a packet.
1199 The protocol tree, or proto_tree, is a GNode, the N-way tree structure
1200 available within GLIB. Of course the protocol dissectors don't care
1201 what a proto_tree really is; they just pass the proto_tree pointer as an
1202 argument to the routines which allow them to add items and new branches
1205 When a packet is selected in the packet-list pane, or a packet popup
1206 window is created, a new logical protocol tree (proto_tree) is created.
1207 The pointer to the proto_tree (in this case, 'protocol tree'), is passed
1208 to the top-level protocol dissector, and then to all subsequent protocol
1209 dissectors for that packet, and then the GUI tree is drawn via
1212 The logical proto_tree needs to know detailed information about the
1213 protocols and fields about which information will be collected from the
1214 dissection routines. By strictly defining (or "typing") the data that can
1215 be attached to a proto tree, searching and filtering becomes possible.
1216 This means that the for every protocol and field (which I also call
1217 "header fields", since they are fields in the protocol headers) which
1218 might be attached to a tree, some information is needed.
1220 Every dissector routine will need to register its protocols and fields
1221 with the central protocol routines (in proto.c). At first I thought I
1222 might keep all the protocol and field information about all the
1223 dissectors in one file, but decentralization seemed like a better idea.
1224 That one file would have gotten very large; one small change would have
1225 required a re-compilation of the entire file. Also, by allowing
1226 registration of protocols and fields at run-time, loadable modules of
1227 protocol dissectors (perhaps even user-supplied) is feasible.
1229 To do this, each protocol should have a register routine, which will be
1230 called when Ethereal starts. The code to call the register routines is
1231 generated automatically; to arrange that a protocol's register routine
1232 be called at startup:
1234 the file containing a dissector's "register" routine must be
1235 added to "DISSECTOR_SRC" in "epan/dissectors/Makefile.common";
1237 the "register" routine must have a name of the form
1238 "proto_register_XXX";
1240 the "register" routine must take no argument, and return no
1243 the "register" routine's name must appear in the source file
1244 either at the beginning of the line, or preceded only by "void "
1245 at the beginning of the line (that'd typically be the
1246 definition) - other white space shouldn't cause a problem, e.g.:
1248 void proto_register_XXX(void) {
1257 proto_register_XXX( void )
1264 and so on should work.
1266 For every protocol or field that a dissector wants to register, a variable of
1267 type int needs to be used to keep track of the protocol. The IDs are
1268 needed for establishing parent/child relationships between protocols and
1269 fields, as well as associating data with a particular field so that it
1270 can be stored in the logical tree and displayed in the GUI protocol
1273 Some dissectors will need to create branches within their tree to help
1274 organize header fields. These branches should be registered as header
1275 fields. Only true protocols should be registered as protocols. This is
1276 so that a display filter user interface knows how to distinguish
1277 protocols from fields.
1279 A protocol is registered with the name of the protocol and its
1282 Here is how the frame "protocol" is registered.
1286 proto_frame = proto_register_protocol (
1288 /* short name */ "Frame",
1289 /* abbrev */ "frame" );
1291 A header field is also registered with its name and abbreviation, but
1292 information about the its data type is needed. It helps to look at
1293 the header_field_info struct to see what information is expected:
1295 struct header_field_info {
1304 int id; /* calculated */
1306 int bitshift; /* calculated */
1311 A string representing the name of the field. This is the name
1312 that will appear in the graphical protocol tree.
1316 A string with an abbreviation of the field. We concatenate the
1317 abbreviation of the parent protocol with an abbreviation for the field,
1318 using a period as a separator. For example, the "src" field in an IP packet
1319 would have "ip.src" as an abbreviation. It is acceptable to have
1320 multiple levels of periods if, for example, you have fields in your
1321 protocol that are then subdivided into subfields. For example, TRMAC
1322 has multiple error fields, so the abbreviations follow this pattern:
1323 "trmac.errors.iso", "trmac.errors.noniso", etc.
1325 The abbreviation is the identifier used in a display filter.
1329 The type of value this field holds. The current field types are:
1331 FT_NONE No field type. Used for fields that
1332 aren't given a value, and that can only
1333 be tested for presence or absence; a
1334 field that represents a data structure,
1335 with a subtree below it containing
1336 fields for the members of the structure,
1337 or that represents an array with a
1338 subtree below it containing fields for
1339 the members of the array, might be an
1341 FT_PROTOCOL Used for protocols which will be placing
1342 themselves as top-level items in the
1343 "Packet Details" pane of the UI.
1344 FT_BOOLEAN 0 means "false", any other value means
1346 FT_FRAMENUM A frame number; if this is used, the "Go
1347 To Corresponding Frame" menu item can
1349 FT_UINT8 An 8-bit unsigned integer.
1350 FT_UINT16 A 16-bit unsigned integer.
1351 FT_UINT24 A 24-bit unsigned integer.
1352 FT_UINT32 A 32-bit unsigned integer.
1353 FT_UINT64 A 64-bit unsigned integer.
1354 FT_INT8 An 8-bit signed integer.
1355 FT_INT16 A 16-bit signed integer.
1356 FT_INT24 A 24-bit signed integer.
1357 FT_INT32 A 32-bit signed integer.
1358 FT_INT64 A 64-bit signed integer.
1359 FT_FLOAT A single-precision floating point number.
1360 FT_DOUBLE A double-precision floating point number.
1361 FT_ABSOLUTE_TIME Seconds (4 bytes) and nanoseconds (4 bytes)
1362 of time displayed as month name, month day,
1363 year, hours, minutes, and seconds with 9
1364 digits after the decimal point.
1365 FT_RELATIVE_TIME Seconds (4 bytes) and nanoseconds (4 bytes)
1366 of time displayed as seconds and 9 digits
1367 after the decimal point.
1368 FT_STRING A string of characters, not necessarily
1369 NUL-terminated, but possibly NUL-padded.
1370 This, and the other string-of-characters
1371 types, are to be used for text strings,
1372 not raw binary data.
1373 FT_STRINGZ A NUL-terminated string of characters.
1374 FT_UINT_STRING A counted string of characters, consisting
1375 of a count (represented as an integral
1376 value) followed immediately by the
1377 specified number of characters.
1378 FT_ETHER A six octet string displayed in
1379 Ethernet-address format.
1380 FT_BYTES A string of bytes with arbitrary values;
1381 used for raw binary data.
1382 FT_IPv4 A version 4 IP address (4 bytes) displayed
1383 in dotted-quad IP address format (4
1384 decimal numbers separated by dots).
1385 FT_IPv6 A version 6 IP address (16 bytes) displayed
1386 in standard IPv6 address format.
1387 FT_IPXNET An IPX address displayed in hex as a 6-byte
1388 network number followed by a 6-byte station
1390 FT_GUID A Globally Unique Identifier
1391 FT_OID An ASN.1 Object Identifier
1393 Some of these field types are still not handled in the display filter
1394 routines, but the most common ones are. The FT_UINT* variables all
1395 represent unsigned integers, and the FT_INT* variables all represent
1396 signed integers; the number on the end represent how many bits are used
1397 to represent the number.
1401 The display field has a couple of overloaded uses. This is unfortunate,
1402 but since we're C as an application programming language, this sometimes
1403 makes for cleaner programs. Right now I still think that overloading
1404 this variable was okay.
1406 For integer fields (FT_UINT* and FT_INT*), this variable represents the
1407 base in which you would like the value displayed. The acceptable bases
1416 BASE_DEC, BASE_HEX, and BASE_OCT are decimal, hexadecimal, and octal,
1417 respectively. BASE_DEC_HEX and BASE_HEX_DEC display value in two bases
1418 (the 1st representation folowed by the 2nd in parenthes)
1420 For FT_BOOLEAN fields that are also bitfields, 'display' is used to tell
1421 the proto_tree how wide the parent bitfield is. With integers this is
1422 not needed since the type of integer itself (FT_UINT8, FT_UINT16,
1423 FT_UINT24, FT_UINT32, etc.) tells the proto_tree how wide the parent
1426 Additionally, BASE_NONE is used for 'display' as a NULL-value. That is,
1427 for non-integers and non-bitfield FT_BOOLEANs, you'll want to use BASE_NONE
1428 in the 'display' field. You may not use BASE_NONE for integers.
1430 It is possible that in the future we will record the endianness of
1431 integers. If so, it is likely that we'll use a bitmask on the display field
1432 so that integers would be represented as BEND|BASE_DEC or LEND|BASE_HEX.
1433 But that has not happened yet.
1437 Some integer fields, of type FT_UINT*, need labels to represent the true
1438 value of a field. You could think of those fields as having an
1439 enumerated data type, rather than an integral data type.
1441 A 'value_string' structure is a way to map values to strings.
1443 typedef struct _value_string {
1448 For fields of that type, you would declare an array of "value_string"s:
1450 static const value_string valstringname[] = {
1451 { INTVAL1, "Descriptive String 1" },
1452 { INTVAL2, "Descriptive String 2" },
1456 (the last entry in the array must have a NULL 'strptr' value, to
1457 indicate the end of the array). The 'strings' field would be set to
1458 'VALS(valstringname)'.
1460 If the field has a numeric rather than an enumerated type, the 'strings'
1461 field would be set to NULL.
1463 FT_BOOLEANS have a default map of 0 = "False", 1 (or anything else) = "True".
1464 Sometimes it is useful to change the labels for boolean values (e.g.,
1465 to "Yes"/"No", "Fast"/"Slow", etc.). For these mappings, a struct called
1466 true_false_string is used. (This struct is new as of Ethereal 0.7.6).
1468 typedef struct true_false_string {
1471 } true_false_string;
1473 For Boolean fields for which "False" and "True" aren't the desired
1474 labels, you would declare a "true_false_string"s:
1476 static const true_false_string boolstringname = {
1481 Its two fields are pointers to the string representing truth, and the
1482 string representing falsehood. For FT_BOOLEAN fields that need a
1483 'true_false_string' struct, the 'strings' field would be set to
1484 'TFS(&boolstringname)'.
1486 If the Boolean field is to be displayed as "False" or "True", the
1487 'strings' field would be set to NULL.
1491 If the field is a bitfield, then the bitmask is the mask which will
1492 leave only the bits needed to make the field when ANDed with a value.
1493 The proto_tree routines will calculate 'bitshift' automatically
1494 from 'bitmask', by finding the rightmost set bit in the bitmask.
1495 If the field is not a bitfield, then bitmask should be set to 0.
1499 This is a string giving a proper description of the field.
1500 It should be at least one grammatically complete sentence.
1501 It is meant to provide a more detailed description of the field than the
1502 name alone provides. This information will be used in the man page, and
1503 in a future GUI display-filter creation tool. We might also add tooltips
1504 to the labels in the GUI protocol tree, in which case the blurb would
1505 be used as the tooltip text.
1508 1.6.1 Field Registration.
1510 Protocol registration is handled by creating an instance of the
1511 header_field_info struct (or an array of such structs), and
1512 calling the registration function along with the registration ID of
1513 the protocol that is the parent of the fields. Here is a complete example:
1515 static int proto_eg = -1;
1516 static int hf_field_a = -1;
1517 static int hf_field_b = -1;
1519 static hf_register_info hf[] = {
1522 { "Field A", "proto.field_a", FT_UINT8, BASE_HEX, NULL,
1523 0xf0, "Field A represents Apples", HFILL }},
1526 { "Field B", "proto.field_b", FT_UINT16, BASE_DEC, VALS(vs),
1527 0x0, "Field B represents Bananas", HFILL }}
1530 proto_eg = proto_register_protocol("Example Protocol",
1532 proto_register_field_array(proto_eg, hf, array_length(hf));
1534 Be sure that your array of hf_register_info structs is declared 'static',
1535 since the proto_register_field_array() function does not create a copy
1536 of the information in the array... it uses that static copy of the
1537 information that the compiler created inside your array. Here's the
1538 layout of the hf_register_info struct:
1540 typedef struct hf_register_info {
1541 int *p_id; /* pointer to parent variable */
1542 header_field_info hfinfo;
1545 Also be sure to use the handy array_length() macro found in packet.h
1546 to have the compiler compute the array length for you at compile time.
1548 If you don't have any fields to register, do *NOT* create a zero-length
1549 "hf" array; not all compilers used to compile Ethereal support them.
1550 Just omit the "hf" array, and the "proto_register_field_array()" call,
1553 It is OK to have header fields with a different format be registered with
1554 the same abbreviation. For instance, the following is valid:
1556 static hf_register_info hf[] = {
1558 { &hf_field_8bit, /* 8-bit version of proto.field */
1559 { "Field (8 bit)", "proto.field", FT_UINT8, BASE_DEC, NULL,
1560 0x00, "Field represents FOO", HFILL }},
1562 { &hf_field_32bit, /* 32-bit version of proto.field */
1563 { "Field (32 bit)", "proto.field", FT_UINT32, BASE_DEC, NULL,
1564 0x00, "Field represents FOO", HFILL }}
1567 This way a filter expression can match a header field, irrespective of the
1568 representation of it in the specific protocol context. This is interesting
1569 for protocols with variable-width header fields.
1571 The HFILL macro at the end of the struct will set resonable default values
1572 for internally used fields.
1574 1.6.2 Adding Items and Values to the Protocol Tree.
1576 A protocol item is added to an existing protocol tree with one of a
1577 handful of proto_XXX_DO_YYY() functions.
1579 Remember that it only makes sense to add items to a protocol tree if its
1580 proto_tree pointer is not null. Should you add an item to a NULL tree, then
1581 the proto_XXX_DO_YYY() function will immediately return. The cost of this
1582 function call can be avoided by checking for the tree pointer.
1584 Subtrees can be made with the proto_item_add_subtree() function:
1586 item = proto_tree_add_item(....);
1587 new_tree = proto_item_add_subtree(item, tree_type);
1589 This will add a subtree under the item in question; a subtree can be
1590 created under an item made by any of the "proto_tree_add_XXX" functions,
1591 so that the tree can be given an arbitrary depth.
1593 Subtree types are integers, assigned by
1594 "proto_register_subtree_array()". To register subtree types, pass an
1595 array of pointers to "gint" variables to hold the subtree type values to
1596 "proto_register_subtree_array()":
1598 static gint ett_eg = -1;
1599 static gint ett_field_a = -1;
1601 static gint *ett[] = {
1606 proto_register_subtree_array(ett, array_length(ett));
1608 in your "register" routine, just as you register the protocol and the
1609 fields for that protocol.
1611 There are several functions that the programmer can use to add either
1612 protocol or field labels to the proto_tree:
1615 proto_tree_add_item(tree, id, tvb, start, length, little_endian);
1618 proto_tree_add_item_hidden(tree, id, tvb, start, length, little_endian);
1621 proto_tree_add_none_format(tree, id, tvb, start, length, format, ...);
1624 proto_tree_add_protocol_format(tree, id, tvb, start, length,
1628 proto_tree_add_bytes(tree, id, tvb, start, length, start_ptr);
1631 proto_tree_add_bytes_hidden(tree, id, tvb, start, length, start_ptr);
1634 proto_tree_add_bytes_format(tree, id, tvb, start, length, start_ptr,
1638 proto_tree_add_bytes_format_value(tree, id, tvb, start, length,
1639 start_ptr, format, ...);
1642 proto_tree_add_time(tree, id, tvb, start, length, value_ptr);
1645 proto_tree_add_time_hidden(tree, id, tvb, start, length, value_ptr);
1648 proto_tree_add_time_format(tree, id, tvb, start, length, value_ptr,
1652 proto_tree_add_time_format_value(tree, id, tvb, start, length,
1653 value_ptr, format, ...);
1656 proto_tree_add_ipxnet(tree, id, tvb, start, length, value);
1659 proto_tree_add_ipxnet_hidden(tree, id, tvb, start, length, value);
1662 proto_tree_add_ipxnet_format(tree, id, tvb, start, length, value,
1666 proto_tree_add_ipxnet_format_value(tree, id, tvb, start, length,
1667 value, format, ...);
1670 proto_tree_add_ipv4(tree, id, tvb, start, length, value);
1673 proto_tree_add_ipv4_hidden(tree, id, tvb, start, length, value);
1676 proto_tree_add_ipv4_format(tree, id, tvb, start, length, value,
1680 proto_tree_add_ipv4_format_value(tree, id, tvb, start, length,
1681 value, format, ...);
1684 proto_tree_add_ipv6(tree, id, tvb, start, length, value_ptr);
1687 proto_tree_add_ipv6_hidden(tree, id, tvb, start, length, value_ptr);
1690 proto_tree_add_ipv6_format(tree, id, tvb, start, length, value_ptr,
1694 proto_tree_add_ipv6_format_value(tree, id, tvb, start, length,
1695 value_ptr, format, ...);
1698 proto_tree_add_ether(tree, id, tvb, start, length, value_ptr);
1701 proto_tree_add_ether_hidden(tree, id, tvb, start, length, value_ptr);
1704 proto_tree_add_ether_format(tree, id, tvb, start, length, value_ptr,
1708 proto_tree_add_ether_format_value(tree, id, tvb, start, length,
1709 value_ptr, format, ...);
1712 proto_tree_add_string(tree, id, tvb, start, length, value_ptr);
1715 proto_tree_add_string_hidden(tree, id, tvb, start, length, value_ptr);
1718 proto_tree_add_string_format(tree, id, tvb, start, length, value_ptr,
1722 proto_tree_add_string_format_value(tree, id, tvb, start, length,
1723 value_ptr, format, ...);
1726 proto_tree_add_boolean(tree, id, tvb, start, length, value);
1729 proto_tree_add_boolean_hidden(tree, id, tvb, start, length, value);
1732 proto_tree_add_boolean_format(tree, id, tvb, start, length, value,
1736 proto_tree_add_boolean_format_value(tree, id, tvb, start, length,
1737 value, format, ...);
1740 proto_tree_add_float(tree, id, tvb, start, length, value);
1743 proto_tree_add_float_hidden(tree, id, tvb, start, length, value);
1746 proto_tree_add_float_format(tree, id, tvb, start, length, value,
1750 proto_tree_add_float_format_value(tree, id, tvb, start, length,
1751 value, format, ...);
1754 proto_tree_add_double(tree, id, tvb, start, length, value);
1757 proto_tree_add_double_hidden(tree, id, tvb, start, length, value);
1760 proto_tree_add_double_format(tree, id, tvb, start, length, value,
1764 proto_tree_add_double_format_value(tree, id, tvb, start, length,
1765 value, format, ...);
1768 proto_tree_add_uint(tree, id, tvb, start, length, value);
1771 proto_tree_add_uint_hidden(tree, id, tvb, start, length, value);
1774 proto_tree_add_uint_format(tree, id, tvb, start, length, value,
1778 proto_tree_add_uint_format_value(tree, id, tvb, start, length,
1779 value, format, ...);
1782 proto_tree_add_uint64(tree, id, tvb, start, length, value);
1785 proto_tree_add_uint64_format(tree, id, tvb, start, length, value,
1789 proto_tree_add_uint64_format_value(tree, id, tvb, start, length,
1790 value, format, ...);
1793 proto_tree_add_int(tree, id, tvb, start, length, value);
1796 proto_tree_add_int_hidden(tree, id, tvb, start, length, value);
1799 proto_tree_add_int_format(tree, id, tvb, start, length, value,
1803 proto_tree_add_int_format_value(tree, id, tvb, start, length,
1804 value, format, ...);
1807 proto_tree_add_int64(tree, id, tvb, start, length, value);
1810 proto_tree_add_int64_format(tree, id, tvb, start, length, value,
1814 proto_tree_add_int64_format_value(tree, id, tvb, start, length,
1815 value, format, ...);
1818 proto_tree_add_text(tree, tvb, start, length, format, ...);
1821 proto_tree_add_text_valist(tree, tvb, start, length, format, ap);
1824 proto_tree_add_guid(tree, id, tvb, start, length, value_ptr);
1827 proto_tree_add_guid_hidden(tree, id, tvb, start, length, value_ptr);
1830 proto_tree_add_guid_format(tree, id, tvb, start, length, value_ptr,
1834 proto_tree_add_guid_format_value(tree, id, tvb, start, length,
1835 value_ptr, format, ...);
1838 proto_tree_add_oid(tree, id, tvb, start, length, value_ptr);
1841 proto_tree_add_oid_hidden(tree, id, tvb, start, length, value_ptr);
1844 proto_tree_add_oid_format(tree, id, tvb, start, length, value_ptr,
1848 proto_tree_add_oid_format_value(tree, id, tvb, start, length,
1849 value_ptr, format, ...);
1851 The 'tree' argument is the tree to which the item is to be added. The
1852 'tvb' argument is the tvbuff from which the item's value is being
1853 extracted; the 'start' argument is the offset from the beginning of that
1854 tvbuff of the item being added, and the 'length' argument is the length,
1855 in bytes, of the item.
1857 The length of some items cannot be determined until the item has been
1858 dissected; to add such an item, add it with a length of -1, and, when the
1859 dissection is complete, set the length with 'proto_item_set_len()':
1862 proto_item_set_len(ti, length);
1864 The "ti" argument is the value returned by the call that added the item
1865 to the tree, and the "length" argument is the length of the item.
1867 proto_tree_add_item()
1868 ---------------------
1869 proto_tree_add_item is used when you wish to do no special formatting.
1870 The item added to the GUI tree will contain the name (as passed in the
1871 proto_register_*() function) and a value. The value will be fetched
1872 from the tvbuff by proto_tree_add_item(), based on the type of the field
1873 and, for integral and Boolean fields, the byte order of the value; the
1874 byte order is specified by the 'little_endian' argument, which is TRUE
1875 if the value is little-endian and FALSE if it is big-endian.
1877 Now that definitions of fields have detailed information about bitfield
1878 fields, you can use proto_tree_add_item() with no extra processing to
1879 add bitfield values to your tree. Here's an example. Take the Format
1880 Identifer (FID) field in the Transmission Header (TH) portion of the SNA
1881 protocol. The FID is the high nibble of the first byte of the TH. The
1882 FID would be registered like this:
1884 name = "Format Identifer"
1885 abbrev = "sna.th.fid"
1888 strings = sna_th_fid_vals
1891 The bitmask contains the value which would leave only the FID if bitwise-ANDed
1892 against the parent field, the first byte of the TH.
1894 The code to add the FID to the tree would be;
1896 proto_tree_add_item(bf_tree, hf_sna_th_fid, tvb, offset, 1, TRUE);
1898 The definition of the field already has the information about bitmasking
1899 and bitshifting, so it does the work of masking and shifting for us!
1900 This also means that you no longer have to create value_string structs
1901 with the values bitshifted. The value_string for FID looks like this,
1902 even though the FID value is actually contained in the high nibble.
1903 (You'd expect the values to be 0x0, 0x10, 0x20, etc.)
1905 /* Format Identifier */
1906 static const value_string sna_th_fid_vals[] = {
1907 { 0x0, "SNA device <--> Non-SNA Device" },
1908 { 0x1, "Subarea Node <--> Subarea Node" },
1909 { 0x2, "Subarea Node <--> PU2" },
1910 { 0x3, "Subarea Node or SNA host <--> Subarea Node" },
1913 { 0xf, "Adjaced Subarea Nodes" },
1917 The final implication of this is that display filters work the way you'd
1918 naturally expect them to. You'd type "sna.th.fid == 0xf" to find Adjacent
1919 Subarea Nodes. The user does not have to shift the value of the FID to
1920 the high nibble of the byte ("sna.th.fid == 0xf0") as was necessary
1921 before Ethereal 0.7.6.
1923 proto_tree_add_item_hidden()
1924 ----------------------------
1925 proto_tree_add_item_hidden is used to add fields and values to a tree,
1926 but not show them on a GUI tree. The caller may want a value to be
1927 included in a tree so that the packet can be filtered on this field, but
1928 the representation of that field in the tree is not appropriate. An
1929 example is the token-ring routing information field (RIF). The best way
1930 to show the RIF in a GUI is by a sequence of ring and bridge numbers.
1931 Rings are 3-digit hex numbers, and bridges are single hex digits:
1933 RIF: 001-A-013-9-C0F-B-555
1935 In the case of RIF, the programmer should use a field with no value and
1936 use proto_tree_add_none_format() to build the above representation. The
1937 programmer can then add the ring and bridge values, one-by-one, with
1938 proto_tree_add_item_hidden() so that the user can then filter on or
1939 search for a particular ring or bridge. Here's a skeleton of how the
1940 programmer might code this.
1943 rif = create_rif_string(...);
1945 proto_tree_add_none_format(tree, hf_tr_rif_label, ..., "RIF: %s", rif);
1947 for(i = 0; i < num_rings; i++) {
1948 proto_tree_add_item_hidden(tree, hf_tr_rif_ring, ..., FALSE);
1950 for(i = 0; i < num_rings - 1; i++) {
1951 proto_tree_add_item_hidden(tree, hf_tr_rif_bridge, ..., FALSE);
1954 The logical tree has these items:
1956 hf_tr_rif_label, text="RIF: 001-A-013-9-C0F-B-555", value = NONE
1957 hf_tr_rif_ring, hidden, value=0x001
1958 hf_tr_rif_bridge, hidden, value=0xA
1959 hf_tr_rif_ring, hidden, value=0x013
1960 hf_tr_rif_bridge, hidden, value=0x9
1961 hf_tr_rif_ring, hidden, value=0xC0F
1962 hf_tr_rif_bridge, hidden, value=0xB
1963 hf_tr_rif_ring, hidden, value=0x555
1965 GUI or print code will not display the hidden fields, but a display
1966 filter or "packet grep" routine will still see the values. The possible
1967 filter is then possible:
1969 tr.rif_ring eq 0x013
1971 proto_tree_add_protocol_format()
1972 ----------------------------
1973 proto_tree_add_protocol_format is used to add the top-level item for the
1974 protocol when the dissector routines wants complete control over how the
1975 field and value will be represented on the GUI tree. The ID value for
1976 the protocol is passed in as the "id" argument; the rest of the
1977 arguments are a "printf"-style format and any arguments for that format.
1978 The caller must include the name of the protocol in the format; it is
1979 not added automatically as in proto_tree_add_item().
1981 proto_tree_add_none_format()
1982 ----------------------------
1983 proto_tree_add_none_format is used to add an item of type FT_NONE.
1984 The caller must include the name of the field in the format; it is
1985 not added automatically as in proto_tree_add_item().
1987 proto_tree_add_bytes()
1988 proto_tree_add_time()
1989 proto_tree_add_ipxnet()
1990 proto_tree_add_ipv4()
1991 proto_tree_add_ipv6()
1992 proto_tree_add_ether()
1993 proto_tree_add_string()
1994 proto_tree_add_boolean()
1995 proto_tree_add_float()
1996 proto_tree_add_double()
1997 proto_tree_add_uint()
1998 proto_tree_add_uint64()
1999 proto_tree_add_int()
2000 proto_tree_add_int64()
2001 proto_tree_add_guid()
2002 proto_tree_add_oid()
2003 ----------------------------
2004 These routines are used to add items to the protocol tree if either:
2006 the value of the item to be added isn't just extracted from the
2007 packet data, but is computed from data in the packet;
2009 the value was fetched into a variable.
2011 The 'value' argument has the value to be added to the tree.
2013 NOTE: in all cases where the 'value' argument is a pointer, a copy is
2014 made of the object pointed to; if you have dynamically allocated a
2015 buffer for the object, that buffer will not be freed when the protocol
2016 tree is freed - you must free the buffer yourself when you don't need it
2019 For proto_tree_add_bytes(), the 'value_ptr' argument is a pointer to a
2022 For proto_tree_add_time(), the 'value_ptr' argument is a pointer to an
2023 "nstime_t", which is a structure containing the time to be added; it has
2024 'secs' and 'nsecs' members, giving the integral part and the fractional
2025 part of a time in units of seconds, with 'nsecs' being the number of
2026 nanoseconds. For absolute times, "secs" is a UNIX-style seconds since
2027 January 1, 1970, 00:00:00 GMT value.
2029 For proto_tree_add_ipxnet(), the 'value' argument is a 32-bit IPX
2032 For proto_tree_add_ipv4(), the 'value' argument is a 32-bit IPv4
2033 address, in network byte order.
2035 For proto_tree_add_ipv6(), the 'value_ptr' argument is a pointer to a
2036 128-bit IPv6 address.
2038 For proto_tree_add_ether(), the 'value_ptr' argument is a pointer to a
2041 For proto_tree_add_string(), the 'value_ptr' argument is a pointer to a
2044 For proto_tree_add_boolean(), the 'value' argument is a 32-bit integer;
2045 zero means "false", and non-zero means "true".
2047 For proto_tree_add_float(), the 'value' argument is a 'float' in the
2048 host's floating-point format.
2050 For proto_tree_add_double(), the 'value' argument is a 'double' in the
2051 host's floating-point format.
2053 For proto_tree_add_uint(), the 'value' argument is a 32-bit unsigned
2054 integer value, in host byte order. (This routine cannot be used to add
2057 For proto_tree_add_uint64(), the 'value' argument is a 64-bit unsigned
2058 integer value, in host byte order.
2060 For proto_tree_add_int(), the 'value' argument is a 32-bit signed
2061 integer value, in host byte order. (This routine cannot be used to add
2064 For proto_tree_add_int64(), the 'value' argument is a 64-bit signed
2065 integer value, in host byte order.
2067 For proto_tree_add_guid(), the 'value_ptr' argument is a pointer to an
2070 For proto_tree_add_oid(), the 'value_ptr' argument is a pointer to an
2071 ASN.1 Object Identifier.
2073 proto_tree_add_bytes_hidden()
2074 proto_tree_add_time_hidden()
2075 proto_tree_add_ipxnet_hidden()
2076 proto_tree_add_ipv4_hidden()
2077 proto_tree_add_ipv6_hidden()
2078 proto_tree_add_ether_hidden()
2079 proto_tree_add_string_hidden()
2080 proto_tree_add_boolean_hidden()
2081 proto_tree_add_float_hidden()
2082 proto_tree_add_double_hidden()
2083 proto_tree_add_uint_hidden()
2084 proto_tree_add_int_hidden()
2085 proto_tree_add_guid_hidden()
2086 proto_tree_add_oid_hidden()
2087 ----------------------------
2088 These routines add fields and values to a tree, but don't show them in
2089 the GUI tree. They are used for the same reason that
2090 proto_tree_add_item() is used.
2092 proto_tree_add_bytes_format()
2093 proto_tree_add_time_format()
2094 proto_tree_add_ipxnet_format()
2095 proto_tree_add_ipv4_format()
2096 proto_tree_add_ipv6_format()
2097 proto_tree_add_ether_format()
2098 proto_tree_add_string_format()
2099 proto_tree_add_boolean_format()
2100 proto_tree_add_float_format()
2101 proto_tree_add_double_format()
2102 proto_tree_add_uint_format()
2103 proto_tree_add_uint64_format()
2104 proto_tree_add_int_format()
2105 proto_tree_add_int64_format()
2106 proto_tree_add_guid_format()
2107 proto_tree_add_oid_format()
2108 ----------------------------
2109 These routines are used to add items to the protocol tree when the
2110 dissector routines wants complete control over how the field and value
2111 will be represented on the GUI tree. The argument giving the value is
2112 the same as the corresponding proto_tree_add_XXX() function; the rest of
2113 the arguments are a "printf"-style format and any arguments for that
2114 format. The caller must include the name of the field in the format; it
2115 is not added automatically as in the proto_tree_add_XXX() functions.
2117 proto_tree_add_bytes_format_value()
2118 proto_tree_add_time_format_value()
2119 proto_tree_add_ipxnet_format_value()
2120 proto_tree_add_ipv4_format_value()
2121 proto_tree_add_ipv6_format_value()
2122 proto_tree_add_ether_format_value()
2123 proto_tree_add_string_format_value()
2124 proto_tree_add_boolean_format_value()
2125 proto_tree_add_float_format_value()
2126 proto_tree_add_double_format_value()
2127 proto_tree_add_uint_format_value()
2128 proto_tree_add_uint64_format_value()
2129 proto_tree_add_int_format_value()
2130 proto_tree_add_int64_format_value()
2131 proto_tree_add_guid_format_value()
2132 proto_tree_add_oid_format_value()
2133 ----------------------------
2135 These routines are used to add items to the protocol tree when the
2136 dissector routines wants complete control over how the value will be
2137 represented on the GUI tree. The argument giving the value is the same
2138 as the corresponding proto_tree_add_XXX() function; the rest of the
2139 arguments are a "printf"-style format and any arguments for that format.
2140 With these routines, unlike the proto_tree_add_XXX_format() routines,
2141 the name of the field is added automatically as in the
2142 proto_tree_add_XXX() functions; only the value is added with the format.
2144 proto_tree_add_text()
2145 ---------------------
2146 proto_tree_add_text() is used to add a label to the GUI tree. It will
2147 contain no value, so it is not searchable in the display filter process.
2148 This function was needed in the transition from the old-style proto_tree
2149 to this new-style proto_tree so that Ethereal would still decode all
2150 protocols w/o being able to filter on all protocols and fields.
2151 Otherwise we would have had to cripple Ethereal's functionality while we
2152 converted all the old-style proto_tree calls to the new-style proto_tree
2155 This can also be used for items with subtrees, which may not have values
2156 themselves - the items in the subtree are the ones with values.
2158 For a subtree, the label on the subtree might reflect some of the items
2159 in the subtree. This means the label can't be set until at least some
2160 of the items in the subtree have been dissected. To do this, use
2161 'proto_item_set_text()' or 'proto_item_append_text()':
2164 proto_item_set_text(proto_item *ti, ...);
2167 proto_item_append_text(proto_item *ti, ...);
2169 'proto_item_set_text()' takes as an argument the value returned by
2170 'proto_tree_add_text()', a 'printf'-style format string, and a set of
2171 arguments corresponding to '%' format items in that string, and replaces
2172 the text for the item created by 'proto_tree_add_text()' with the result
2173 of applying the arguments to the format string.
2175 'proto_item_append_text()' is similar, but it appends to the text for
2176 the item the result of applying the arguments to the format string.
2178 For example, early in the dissection, one might do:
2180 ti = proto_tree_add_text(tree, tvb, offset, length, <label>);
2184 proto_item_set_text(ti, "%s: %s", type, value);
2186 after the "type" and "value" fields have been extracted and dissected.
2187 <label> would be a label giving what information about the subtree is
2188 available without dissecting any of the data in the subtree.
2190 Note that an exception might thrown when trying to extract the values of
2191 the items used to set the label, if not all the bytes of the item are
2192 available. Thus, one should create the item with text that is as
2193 meaningful as possible, and set it or append additional information to
2194 it as the values needed to supply that information is extracted.
2196 proto_tree_add_text_valist()
2197 ---------------------
2198 This is like proto_tree_add_text(), but takes, as the last argument, a
2199 'va_list'; it is used to allow routines that take a printf-like
2200 variable-length list of arguments to add a text item to the protocol
2203 1.7 Utility routines
2205 1.7.1 match_strval and val_to_str
2207 A dissector may need to convert a value to a string, using a
2208 'value_string' structure, by hand, rather than by declaring a field with
2209 an associated 'value_string' structure; this might be used, for example,
2210 to generate a COL_INFO line for a frame.
2212 'match_strval()' will do that:
2215 match_strval(guint32 val, const value_string *vs)
2217 It will look up the value 'val' in the 'value_string' table pointed to
2218 by 'vs', and return either the corresponding string, or NULL if the
2219 value could not be found in the table. Note that, unless 'val' is
2220 guaranteed to be a value in the 'value_string' table ("guaranteed" as in
2221 "the code has already checked that it's one of those values" or "the
2222 table handles all possible values of the size of 'val'", not "the
2223 protocol spec says it has to be" - protocol specs do not prevent invalid
2224 packets from being put onto a network or into a purported packet capture
2225 file), you must check whether 'match_strval()' returns NULL, and arrange
2226 that its return value not be dereferenced if it's NULL. In particular,
2227 don't use it in a call to generate a COL_INFO line for a frame such as
2229 col_add_fstr(COL_INFO, ", %s", match_strval(val, table));
2231 unless is it certain that 'val' is in 'table'.
2233 'val_to_str()' can be used to generate a string for values not found in
2237 val_to_str(guint32 val, const value_string *vs, const char *fmt)
2239 If the value 'val' is found in the 'value_string' table pointed to by
2240 'vs', 'val_to_str' will return the corresponding string; otherwise, it
2241 will use 'fmt' as an 'sprintf'-style format, with 'val' as an argument,
2242 to generate a string, and will return a pointer to that string.
2243 (Currently, it has three 64-byte static buffers, and cycles through
2244 them; this permits the results of up to three calls to 'val_to_str' to
2245 be passed as arguments to a routine using those strings.)
2248 1.8 Calling Other Dissectors
2250 As each dissector completes its portion of the protocol analysis, it
2251 is expected to create a new tvbuff of type TVBUFF_SUBSET which
2252 contains the payload portion of the protocol (that is, the bytes
2253 that are relevant to the next dissector).
2255 The syntax for creating a new TVBUFF_SUBSET is:
2257 next_tvb = tvb_new_subset(tvb, offset, length, reported_length)
2260 tvb is the tvbuff that the dissector has been working on. It
2261 can be a tvbuff of any type.
2263 next_tvb is the new TVBUFF_SUBSET.
2265 offset is the byte offset of 'tvb' at which the new tvbuff
2266 should start. The first byte is the 0th byte.
2268 length is the number of bytes in the new TVBUFF_SUBSET. A length
2269 argument of -1 says to use as many bytes as are available in
2272 reported_length is the number of bytes that the current protocol
2273 says should be in the payload. A reported_length of -1 says that
2274 the protocol doesn't say anything about the size of its payload.
2277 An example from packet-ipx.c -
2280 dissect_ipx(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
2283 int reported_length, available_length;
2286 /* Make the next tvbuff */
2288 /* IPX does have a length value in the header, so calculate report_length */
2289 Set this to -1 if there isn't any length information in the protocol
2291 reported_length = ipx_length - IPX_HEADER_LEN;
2293 /* Calculate the available data in the packet,
2294 set this to -1 to use all the data in the tv_buffer
2296 available_length = tvb_length(tvb) - IPX_HEADER_LEN;
2298 /* Create the tvbuffer for the next dissector */
2299 next_tvb = tvb_new_subset(tvb, IPX_HEADER_LEN,
2300 MIN(available_length, reported_length),
2303 /* call the next dissector */
2304 dissector_next( next_tvb, pinfo, tree);
2307 1.9 Editing Makefile.common to add your dissector.
2309 To arrange that your dissector will be built as part of Ethereal, you
2310 must add the name of the source file for your dissector to the
2311 'DISSECTOR_SRC' macro in the 'Makefile.common' file in the 'epan/dissectors'
2312 directory. (Note that this is for modern versions of UNIX, so there
2313 is no 14-character limitation on file names, and for modern versions of
2314 Windows, so there is no 8.3-character limitation on file names.)
2316 If your dissector also has its own header file or files, you must add
2317 them to the 'DISSECTOR_INCLUDES' macro in the 'Makefile.common' file in
2318 the 'epan/dissectors' directory, so that it's included when release source
2319 tarballs are built (otherwise, the source in the release tarballs won't
2322 1.10 Using the SVN source code tree.
2324 See <http://www.ethereal.com/development.html#source>
2326 1.11 Submitting code for your new dissector.
2328 - TEST YOUR DISSECTOR BEFORE SUBMITTING IT.
2329 Use fuzz-test.sh and/or randpkt against your dissector. These are
2330 described at <http://wiki.ethereal.com/FuzzTesting>.
2332 - Subscribe to <mailto:ethereal-dev@ethereal.com> by sending an email to
2333 <mailto:ethereal-dev-request@ethereal.com?body="help"> or visiting
2334 <http://www.ethereal.com/lists/>.
2336 - 'svn add' all the files of your new dissector.
2338 - 'svn diff' the workspace and save the result to a file.
2340 - Send the diff file along with a note requesting it's inclusion to
2341 <mailto:ethereal-dev@ethereal.com>. You can also use this procedure for
2342 providing patches to your dissector or any other part of ethereal.
2344 - If possible, add sample capture files to the sample captures page at
2345 <http://wiki.ethereal.com/SampleCaptures>. These files are used by
2346 the automated build system for fuzz testing.
2348 - If you find that you are contributing a lot to ethereal on an ongoing
2349 basis you can request to become a committer which will allow you to
2350 commit files to subversion directly.
2352 2. Advanced dissector topics.
2356 2.2 Following "conversations".
2358 In ethereal a conversation is defined as a series of data packet between two
2359 address:port combinations. A conversation is not sensitive to the direction of
2360 the packet. The same conversation will be returned for a packet bound from
2361 ServerA:1000 to ClientA:2000 and the packet from ClientA:2000 to ServerA:1000.
2363 There are five routines that you will use to work with a conversation:
2364 conversation_new, find_conversation, conversation_add_proto_data,
2365 conversation_get_proto_data, and conversation_delete_proto_data.
2368 2.2.1 The conversation_init function.
2370 This is an internal routine for the conversation code. As such the you
2371 will not have to call this routine. Just be aware that this routine is
2372 called at the start of each capture and before the packets are filtered
2373 with a display filter. The routine will destroy all stored
2374 conversations. This routine does NOT clean up any data pointers that are
2375 passed in the conversation_new 'data' variable. You are responsible for
2376 this clean up if you pass a malloc'ed pointer in this variable.
2378 See item 2.2.7 for more information about the 'data' pointer.
2381 2.2.2 The conversation_new function.
2383 This routine will create a new conversation based upon two address/port
2384 pairs. If you want to associate with the conversation a pointer to a
2385 private data structure you must use the conversation_add_proto_data
2386 function. The ptype variable is used to differentiate between
2387 conversations over different protocols, i.e. TCP and UDP. The options
2388 variable is used to define a conversation that will accept any destination
2389 address and/or port. Set options = 0 if the destination port and address
2390 are know when conversation_new is called. See section 2.4 for more
2391 information on usage of the options parameter.
2393 The conversation_new prototype:
2394 conversation_t *conversation_new(guint32 setup_frame, address *addr1,
2395 address *addr2, port_type ptype, guint32 port1, guint32 port2,
2399 guint32 setup_frame = The lowest numbered frame for this conversation
2400 address* addr1 = first data packet address
2401 address* addr2 = second data packet address
2402 port_type ptype = port type, this is defined in packet.h
2403 guint32 port1 = first data packet port
2404 guint32 port2 = second data packet port
2405 guint options = conversation options, NO_ADDR2 and/or NO_PORT2
2407 setup_frame indicates the first frame for this conversation, and is used to
2408 distinguish multiple conversations with the same addr1/port1 and addr2/port2
2409 pair that occur within the same capture session.
2411 "addr1" and "port1" are the first address/port pair; "addr2" and "port2"
2412 are the second address/port pair. A conversation doesn't have source
2413 and destination address/port pairs - packets in a conversation go in
2414 both directions - so "addr1"/"port1" may be the source or destination
2415 address/port pair; "addr2"/"port2" would be the other pair.
2417 If NO_ADDR2 is specified, the conversation is set up so that a
2418 conversation lookup will match only the "addr1" address; if NO_PORT2 is
2419 specified, the conversation is set up so that a conversation lookup will
2420 match only the "port1" port; if both are specified, i.e.
2421 NO_ADDR2|NO_PORT2, the conversation is set up so that the lookup will
2422 match only the "addr1"/"port1" address/port pair. This can be used if a
2423 packet indicates that, later in the capture, a conversation will be
2424 created using certain addresses and ports, in the case where the packet
2425 doesn't specify the addresses and ports of both sides.
2427 2.2.3 The find_conversation function.
2429 Call this routine to look up a conversation. If no conversation is found,
2430 the routine will return a NULL value.
2432 The find_conversation prototype:
2434 conversation_t *find_conversation(guint32 frame_num, address *addr_a,
2435 address *addr_b, port_type ptype, guint32 port_a, guint32 port_b,
2439 guint32 frame_num = a frame number to match
2440 address* addr_a = first address
2441 address* addr_b = second address
2442 port_type ptype = port type
2443 guint32 port_a = first data packet port
2444 guint32 port_b = second data packet port
2445 guint options = conversation options, NO_ADDR_B and/or NO_PORT_B
2447 frame_num is a frame number to match. The conversation returned is where
2448 (frame_num >= conversation->setup_frame
2449 && frame_num < conversation->next->setup_frame)
2450 Suppose there are a total of 3 conversations (A, B, and C) that match
2451 addr_a/port_a and addr_b/port_b, where the setup_frame used in
2452 conversation_new() for A, B and C are 10, 50, and 100 respectively. The
2453 frame_num passed in find_conversation is compared to the setup_frame of each
2454 conversation. So if (frame_num >= 10 && frame_num < 50), conversation A is
2455 returned. If (frame_num >= 50 && frame_num < 100), conversation B is returned.
2456 If (frame_num >= 100) conversation C is returned.
2458 "addr_a" and "port_a" are the first address/port pair; "addr_b" and
2459 "port_b" are the second address/port pair. Again, as a conversation
2460 doesn't have source and destination address/port pairs, so
2461 "addr_a"/"port_a" may be the source or destination address/port pair;
2462 "addr_b"/"port_b" would be the other pair. The search will match the
2463 "a" address/port pair against both the "1" and "2" address/port pairs,
2464 and match the "b" address/port pair against both the "2" and "1"
2465 address/port pairs; you don't have to worry about which side the "a" or
2466 "b" pairs correspond to.
2468 If the NO_ADDR_B flag was specified to "find_conversation()", the
2469 "addr_b" address will be treated as matching any "wildcarded" address;
2470 if the NO_PORT_B flag was specified, the "port_b" port will be treated
2471 as matching any "wildcarded" port. If both flags are specified, i.e.
2472 NO_ADDR_B|NO_PORT_B, the "addr_b" address will be treated as matching
2473 any "wildcarded" address and the "port_b" port will be treated as
2474 matching any "wildcarded" port.
2477 2.2.4 The conversation_add_proto_data function.
2479 Once you have created a conversation with conversation_new, you can
2480 associate data with it using this function.
2482 The conversation_add_proto_data prototype:
2484 void conversation_add_proto_data(conversation_t *conv, int proto,
2488 conversation_t *conv = the conversation in question
2489 int proto = registered protocol number
2490 void *data = dissector data structure
2492 "conversation" is the value returned by conversation_new. "proto" is a
2493 unique protocol number created with proto_register_protocol. Protocols
2494 are typically registered in the proto_register_XXXX section of your
2495 dissector. "data" is a pointer to the data you wish to associate with the
2496 conversation. Using the protocol number allows several dissectors to
2497 associate data with a given conversation.
2500 2.2.5 The conversation_get_proto_data function.
2502 After you have located a conversation with find_conversation, you can use
2503 this function to retrieve any data associated with it.
2505 The conversation_get_proto_data prototype:
2507 void *conversation_get_proto_data(conversation_t *conv, int proto);
2510 conversation_t *conv = the conversation in question
2511 int proto = registered protocol number
2513 "conversation" is the conversation created with conversation_new. "proto"
2514 is a unique protocol number acreated with proto_register_protocol,
2515 typically in the proto_register_XXXX portion of a dissector. The function
2516 returns a pointer to the data requested, or NULL if no data was found.
2519 2.2.6 The conversation_delete_proto_data function.
2521 After you are finished with a conversation, you can remove your assocation
2522 with this function. Please note that ONLY the conversation entry is
2523 removed. If you have allocated any memory for your data, you must free it
2526 The conversation_delete_proto_data prototype:
2528 void conversation_delete_proto_data(conversation_t *conv, int proto);
2531 conversation_t *conv = the conversation in question
2532 int proto = registered protocol number
2534 "conversation" is the conversation created with conversation_new. "proto"
2535 is a unique protocol number acreated with proto_register_protocol,
2536 typically in the proto_register_XXXX portion of a dissector.
2538 2.2.7 The example conversation code with GMemChunk's
2540 For a conversation between two IP addresses and ports you can use this as an
2541 example. This example uses the GMemChunk to allocate memory and stores the data
2542 pointer in the conversation 'data' variable.
2544 NOTE: Remember to register the init routine (my_dissector_init) in the
2545 protocol_register routine.
2548 /************************ Globals values ************************/
2550 /* the number of entries in the memory chunk array */
2551 #define my_init_count 10
2553 /* define your structure here */
2558 /* the GMemChunk base structure */
2559 static GMemChunk *my_vals = NULL;
2561 /* Registered protocol number
2562 static int my_proto = -1;
2565 /********************* in the dissector routine *********************/
2567 /* the local variables in the dissector */
2569 conversation_t *conversation;
2570 my_entry_t *data_ptr
2573 /* look up the conversation */
2575 conversation = find_conversation(pinfo->fd->num, &pinfo->src, &pinfo->dst,
2576 pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
2578 /* if conversation found get the data pointer that you stored */
2580 data_ptr = (my_entry_t*)conversation_get_proto_data(conversation,
2584 /* new conversation create local data structure */
2586 data_ptr = g_mem_chunk_alloc(my_vals);
2588 /*** add your code here to setup the new data structure ***/
2590 /* create the conversation with your data pointer */
2592 conversation_new(pinfo->fd->num, &pinfo->src, &pinfo->dst, pinfo->ptype,
2593 pinfo->srcport, pinfo->destport, 0);
2594 conversation_add_proto_data(conversation, my_proto, (void *) data_ptr);
2597 /* at this point the conversation data is ready */
2600 /******************* in the dissector init routine *******************/
2602 #define my_init_count 20
2605 my_dissector_init( void){
2607 /* destroy memory chunks if needed */
2610 g_mem_chunk_destroy(my_vals);
2612 /* now create memory chunks */
2614 my_vals = g_mem_chunk_new( "my_proto_vals",
2616 my_init_count * sizeof( my_entry_t),
2620 /***************** in the protocol register routine *****************/
2622 /* register re-init routine */
2624 register_init_routine( &my_dissector_init);
2626 my_proto = proto_register_protocol("My Protocol", "My Protocol", "my_proto");
2629 2.2.8 An example conversation code that starts at a specific frame number
2631 Sometimes a disector has determined that a new conversation is needed that
2632 starts at a specific frame number, when a capture session encompasses multiple
2633 conversation that reuse the same src/dest ip/port pairs. You can use the
2634 compare the conversation->setup_frame returned by find_conversation with
2635 pinfo->fd->num to determine whether or not there already exists a conversation
2636 that starts at the specific frame number.
2638 /* in the dissector routine */
2640 conversation = find_conversation(pinfo->fd->num, &pinfo->src, &pinfo->dst,
2641 pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
2642 if (conversation == NULL || (conversation->setup_frame != pinfo->fd->num)) {
2643 /* It's not part of any conversation or the returned
2644 * conversation->setup_frame doesn't match the current frame
2647 conversation = conversation_new(pinfo->fd->num, &pinfo->src,
2648 &pinfo->dst, pinfo->ptype, pinfo->srcport, pinfo->destport,
2653 2.2.9 The example conversation code using conversation index field
2655 Sometimes the conversation isn't enough to define a unique data storage
2656 value for the network traffic. For example if you are storing information
2657 about requests carried in a conversation, the request may have an
2658 identifier that is used to define the request. In this case the
2659 conversation and the identifier are required to find the data storage
2660 pointer. You can use the conversation data structure index value to
2661 uniquely define the conversation.
2663 See packet-afs.c for an example of how to use the conversation index. In
2664 this dissector multiple requests are sent in the same conversation. To store
2665 information for each request the dissector has an internal hash table based
2666 upon the conversation index and values inside the request packets.
2669 /* in the dissector routine */
2671 /* to find a request value, first lookup conversation to get index */
2672 /* then used the conversation index, and request data to find data */
2673 /* in the local hash table */
2675 conversation = find_conversation(pinfo->fd->num, &pinfo->src, &pinfo->dst,
2676 pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
2677 if (conversation == NULL) {
2678 /* It's not part of any conversation - create a new one. */
2679 conversation = conversation_new(pinfo->fd->num, &pinfo->src,
2680 &pinfo->dst, pinfo->ptype, pinfo->srcport, pinfo->destport,
2684 request_key.conversation = conversation->index;
2685 request_key.service = pntohs(&rxh->serviceId);
2686 request_key.callnumber = pntohl(&rxh->callNumber);
2688 request_val = (struct afs_request_val *) g_hash_table_lookup(
2689 afs_request_hash, &request_key);
2691 /* only allocate a new hash element when it's a request */
2693 if ( !request_val && !reply)
2695 new_request_key = g_mem_chunk_alloc(afs_request_keys);
2696 *new_request_key = request_key;
2698 request_val = g_mem_chunk_alloc(afs_request_vals);
2699 request_val -> opcode = pntohl(&afsh->opcode);
2700 opcode = request_val->opcode;
2702 g_hash_table_insert(afs_request_hash, new_request_key,
2708 2.3 Dynamic conversation dissector registration
2711 NOTE: This sections assumes that all information is available to
2712 create a complete conversation, source port/address and
2713 destination port/address. If either the destination port or
2714 address is know, see section 2.4 Dynamic server port dissector
2717 For protocols that negotiate a secondary port connection, for example
2718 packet-msproxy.c, a conversation can install a dissector to handle
2719 the secondary protocol dissection. After the conversation is created
2720 for the negotiated ports use the conversation_set_dissector to define
2721 the dissection routine.
2722 Before we create these conversations or assign a dissector to them we should
2723 first check that the conversation does not already exist and if it exists
2724 whether it is registered to our protocol or not.
2725 We should do this because is uncommon but it does happen that multiple
2726 different protocols can use the same socketpair during different stages of
2727 an application cycle. By keeping track of the frame number a conversation
2728 was started in ethereal can still tell these different protocols apart.
2730 The second argument to conversation_set_dissector is a dissector handle,
2731 which is created with a call to create_dissector_handle or
2734 create_dissector_handle takes as arguments a pointer to the dissector
2735 function and a protocol ID as returned by proto_register_protocol;
2736 register_dissector takes as arguments a string giving a name for the
2737 dissector, a pointer to the dissector function, and a protocol ID.
2739 The protocol ID is the ID for the protocol dissected by the function.
2740 The function will not be called if the protocol has been disabled by the
2741 user; instead, the data for the protocol will be dissected as raw data.
2745 /* the handle for the dynamic dissector *
2746 static dissector_handle_t sub_dissector_handle;
2748 /* prototype for the dynamic dissector */
2749 static void sub_dissector( tvbuff_t *tvb, packet_info *pinfo,
2752 /* in the main protocol dissector, where the next dissector is setup */
2754 /* if conversation has a data field, create it and load structure */
2756 /* First check if a conversation already exists for this
2759 conversation = find_conversation(pinfo->fd->num,
2760 &pinfo->src, &pinfo->dst, protocol,
2761 src_port, dst_port, new_conv_info, 0);
2763 /* If there is no such conversation, or if there is one but for
2764 someone elses protocol then we just create a new conversation
2765 and assign our protocol to it.
2767 if( (conversation==NULL)
2768 || (conversation->dissector_handle!=sub_dissector_handle) ){
2769 new_conv_info = g_mem_chunk_alloc( new_conv_vals);
2770 new_conv_info->data1 = value1;
2772 /* create the conversation for the dynamic port */
2773 conversation = conversation_new(pinfo->fd->num,
2774 &pinfo->src, &pinfo->dst, protocol,
2775 src_port, dst_port, new_conv_info, 0);
2777 /* set the dissector for the new conversation */
2778 conversation_set_dissector(conversation, sub_dissector_handle);
2783 proto_register_PROTOABBREV(void)
2787 sub_dissector_handle = create_dissector_handle(sub_dissector,
2793 2.4 Dynamic server port dissector registration
2795 NOTE: While this example used both NO_ADDR2 and NO_PORT2 to create a
2796 conversation with only one port and address set, this isn't a
2797 requirement. Either the second port or the second address can be set
2798 when the conversation is created.
2800 For protocols that define a server address and port for a secondary
2801 protocol, a conversation can be used to link a protocol dissector to
2802 the server port and address. The key is to create the new
2803 conversation with the second address and port set to the "accept
2806 Some server applications can use the same port for different protocols during
2807 different stages of a transaction. For example it might initially use SNMP
2808 to perform some discovery and later switch to use TFTP using the same port.
2809 In order to handle this properly we must first check whether such a
2810 conversation already exists or not and if it exists we also check whether the
2811 registered dissector_handle for that conversation is "our" dissector or not.
2812 If not we create a new conversation ontop of the previous one and set this new
2813 conversation to use our protocol.
2814 Since ethereal keeps track of the frame number where a conversation started
2815 ethereal will still be able to keep the packets apart eventhough they do use
2816 the same socketpair.
2817 (See packet-tftp.c and packet-snmp.c for examples of this)
2819 There are two support routines that will allow the second port and/or
2820 address to be set latter.
2822 conversation_set_port2( conversation_t *conv, guint32 port);
2823 conversation_set_addr2( conversation_t *conv, address addr);
2825 These routines will change the second address or port for the
2826 conversation. So, the server port conversation will be converted into a
2827 more complete conversation definition. Don't use these routines if you
2828 want create a conversation between the server and client and retain the
2829 server port definition, you must create a new conversation.
2834 /* the handle for the dynamic dissector *
2835 static dissector_handle_t sub_dissector_handle;
2839 /* in the main protocol dissector, where the next dissector is setup */
2841 /* if conversation has a data field, create it and load structure */
2843 new_conv_info = g_mem_chunk_alloc( new_conv_vals);
2844 new_conv_info->data1 = value1;
2846 /* create the conversation for the dynamic server address and port */
2847 /* NOTE: The second address and port values don't matter because the */
2848 /* NO_ADDR2 and NO_PORT2 options are set. */
2850 /* First check if a conversation already exists for this
2853 conversation = find_conversation(pinfo->fd->num,
2854 &server_src_addr, 0, protocol,
2855 server_src_port, 0, NO_ADDR2 | NO_PORT_B);
2856 /* If there is no such conversation, or if there is one but for
2857 someone elses protocol then we just create a new conversation
2858 and assign our protocol to it.
2860 if( (conversation==NULL)
2861 || (conversation->dissector_handle!=sub_dissector_handle) ){
2862 conversation = conversation_new(pinfo->fd->num,
2863 &server_src_addr, 0, protocol,
2864 server_src_port, 0, new_conv_info, NO_ADDR2 | NO_PORT2);
2866 /* set the dissector for the new conversation */
2867 conversation_set_dissector(conversation, sub_dissector_handle);
2870 2.5 Per packet information
2872 Information can be stored for each data packet that is processed by the dissector.
2873 The information is added with the p_add_proto_data function and retreived with the
2874 p_get_proto_data function. The data pointers passed into the p_add_proto_data are
2875 not managed by the proto_data routines. If you use malloc or any other dynamic
2876 memory allocation scheme, you must release the data when it isn't required.
2879 p_add_proto_data(frame_data *fd, int proto, void *proto_data)
2881 p_get_proto_data(frame_data *fd, int proto)
2884 fd - The fd pointer in the pinfo structure, pinfo->fd
2885 proto - Protocol id returned by the proto_register_protocol call during initialization
2886 proto_data - pointer to the dissector data.
2889 2.6 User Preferences
2891 If the dissector has user options, there is support for adding these preferences
2892 to a configuration dialog.
2894 You must register the module with the preferences routine with -
2896 module_t *prefs_register_protocol(proto_id, void (*apply_cb)(void))
2898 Where: proto_id - the value returned by "proto_register_protocol()" when
2899 the protocol was registered
2900 apply_cb - Callback routine that is call when preferences are applied
2903 Then you can register the fields that can be configured by the user with these routines -
2905 /* Register a preference with an unsigned integral value. */
2906 void prefs_register_uint_preference(module_t *module, const char *name,
2907 const char *title, const char *description, guint base, guint *var);
2909 /* Register a preference with an Boolean value. */
2910 void prefs_register_bool_preference(module_t *module, const char *name,
2911 const char *title, const char *description, gboolean *var);
2913 /* Register a preference with an enumerated value. */
2914 void prefs_register_enum_preference(module_t *module, const char *name,
2915 const char *title, const char *description, gint *var,
2916 const enum_val_t *enumvals, gboolean radio_buttons)
2918 /* Register a preference with a character-string value. */
2919 void prefs_register_string_preference(module_t *module, const char *name,
2920 const char *title, const char *description, char **var)
2922 /* Register a preference with a range of unsigned integers (e.g.,
2925 void prefs_register_range_preference(module_t *module, const char *name,
2926 const char *title, const char *description, range_t *var,
2929 Where: module - Returned by the prefs_register_protocol routine
2930 name - This is appended to the name of the protocol, with a
2931 "." between them, to construct a name that identifies
2932 the field in the preference file; the name itself
2933 should not include the protocol name, as the name in
2934 the preference file will already have it
2935 title - Field title in the preferences dialog
2936 description - Comments added to the preference file above the
2938 var - pointer to the storage location that is updated when the
2939 field is changed in the preference dialog box
2940 enumvals - an array of enum_val_t structures. This must be
2941 NULL-terminated; the members of that structure are:
2943 a short name, to be used with the "-o" flag - it
2944 should not contain spaces or upper-case letters,
2945 so that it's easier to put in a command line;
2947 a description, which is used in the GUI (and
2948 which, for compatibility reasons, is currently
2949 what's written to the preferences file) - it can
2950 contain spaces, capital letters, punctuation,
2953 the numerical value corresponding to that name
2955 radio_buttons - TRUE if the field is to be displayed in the
2956 preferences dialog as a set of radio buttons,
2957 FALSE if it is to be displayed as an option
2959 max_value - The maximum allowed value for a range (0 is the minimum).
2961 An example from packet-beep.c -
2963 proto_beep = proto_register_protocol("Blocks Extensible Exchange Protocol",
2968 /* Register our configuration options for BEEP, particularly our port */
2970 beep_module = prefs_register_protocol(proto_beep, proto_reg_handoff_beep);
2972 prefs_register_uint_preference(beep_module, "tcp.port", "BEEP TCP Port",
2973 "Set the port for BEEP messages (if other"
2974 " than the default of 10288)",
2975 10, &global_beep_tcp_port);
2977 prefs_register_bool_preference(beep_module, "strict_header_terminator",
2978 "BEEP Header Requires CRLF",
2979 "Specifies that BEEP requires CRLF as a "
2980 "terminator, and not just CR or LF",
2981 &global_beep_strict_term);
2983 This will create preferences "beep.tcp.port" and
2984 "beep.strict_header_terminator", the first of which is an unsigned
2985 integer and the second of which is a Boolean.
2987 2.7 Reassembly/desegmentation for protocols running atop TCP
2989 There are two main ways of reassembling a Protocol Data Unit (PDU) which
2990 spans across multiple TCP segments. The first approach is simpler, but
2991 assumes you are running atop of TCP when this occurs (but your dissector
2992 might run atop of UDP, too, for example), and that your PDUs consist of a
2993 fixed amount of data that includes enough information to determine the PDU
2994 length, possibly followed by additional data. The second method is more
2995 generic but requires more code and is less efficient.
2997 2.7.1 Using tcp_dissect_pdus()
2999 For the first method, you register two different dissection methods, one
3000 for the TCP case, and one for the other cases. It is a good idea to
3001 also have a dissect_PROTO_common function which will parse the generic
3002 content that you can find in all PDUs which is called from
3003 dissect_PROTO_tcp when the reassembly is complete and from
3004 dissect_PROTO_udp (or dissect_PROTO_other).
3006 To register the distinct dissector functions, consider the following
3007 example, stolen from packet-dns.c:
3009 dissector_handle_t dns_udp_handle;
3010 dissector_handle_t dns_tcp_handle;
3011 dissector_handle_t mdns_udp_handle;
3013 dns_udp_handle = create_dissector_handle(dissect_dns_udp,
3015 dns_tcp_handle = create_dissector_handle(dissect_dns_tcp,
3017 mdns_udp_handle = create_dissector_handle(dissect_mdns_udp,
3020 dissector_add("udp.port", UDP_PORT_DNS, dns_udp_handle);
3021 dissector_add("tcp.port", TCP_PORT_DNS, dns_tcp_handle);
3022 dissector_add("udp.port", UDP_PORT_MDNS, mdns_udp_handle);
3023 dissector_add("tcp.port", TCP_PORT_MDNS, dns_tcp_handle);
3025 The dissect_dns_udp function does very little work and calls
3026 dissect_dns_common, while dissect_dns_tcp calls tcp_dissect_pdus with a
3027 reference to a callback which will be called with reassembled data:
3030 dissect_dns_tcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
3032 tcp_dissect_pdus(tvb, pinfo, tree, dns_desegment, 2,
3033 get_dns_pdu_len, dissect_dns_tcp_pdu);
3036 (The dissect_dns_tcp_pdu function acts similarly to dissect_dns_udp.)
3037 The arguments to tcp_dissect_pdus are:
3039 the tvbuff pointer, packet_info pointer, and proto_tree pointer
3040 passed to the dissector;
3042 a gboolean flag indicating whether desegmentation is enabled for
3045 the number of bytes of PDU data required to determine the length
3048 a routine that takes as arguments a tvbuff pointer and an offset
3049 value representing the offset into the tvbuff at which a PDU
3050 begins and should return - *without* throwing an exception (it
3051 is guaranteed that the number of bytes specified by the previous
3052 argument to tcp_dissect_pdus is available, but more data might
3053 not be available, so don't refer to any data past that) - the
3054 total length of the PDU, in bytes;
3056 a routine that's passed a tvbuff pointer, packet_info pointer,
3057 and proto_tree pointer, with the tvbuff containing a
3058 possibly-reassembled PDU, and that should dissect that PDU.
3060 2.7.2 Modifying the pinfo struct
3062 The second reassembly mode is prefered when the dissector cannot determine
3063 how many bytes it will need to read in order to determine the size of a PDU.
3064 For this mode it is reccommended that your dissector be the newer dissector
3065 type which returns "int" rather than the older type which returned "void".
3067 This reassembly mode relies on Ethereal's mechanism for processing multiple PDUs
3068 per frame. When a dissector processes a PDU from a tvbuff the PDU may not be
3069 aligned to a frame of the underlying protocol. Ethereal allows dissectors to
3070 process PDUs in an idempotent way--dissectors only need to consider one PDU at a
3071 time. If your dissector discovers that it can not process a complete PDU from
3072 the current tvbuff the dissector should halt processing and request additional
3073 bytes from the lower level dissector.
3075 Your dissect_PROTO will be called by the lower level dissector whenever
3076 sufficient new bytes become available. Each time your dissector is called it is
3077 provided a different tvbuff, though the tvbuffs may contain data that your
3078 dissector declined to process during a previous call. When called a dissector
3079 should examine the tvbuff provided and determine if an entire PDU is available.
3080 If sufficient bytes are available the dissector processes the PDU and returns
3081 the length of the PDU from your dissect_PROTO.
3083 Completion of a PDU is signified by dissect_PROTO returning a positive value.
3084 The value is the number of bytes which were processed from the tvbuff. If there
3085 were insufficient bytes in the tvbuff to complete a PDU then the dissect_PROTO
3086 returns a negative value requesting additional bytes. The negative return value
3087 indicates how many additional bytes are required. Additionally dissect_PROTO
3088 must update the pinfo structure to indicate that more bytes are required. The
3089 desegment_offset field is the offset in the tvbuff at which the dissector will
3090 continue processing when next called. The desegment_len field should contain the
3091 estimated number of additional bytes required for completing the PDU. The
3092 dissect_PROTO will not be called again until the specified number of bytes are
3093 available. pinfo->desegment_len may be set to -1 if dissect_PROTO cannot
3094 determine how many additional bytes are required. Dissectors should set the
3095 desegment_len to a reasonable value when possible rather than always setting
3096 -1 as it will generally be more efficient.
3098 static hf_register_info hf[] = {
3100 {"C String", "c.string", FT_STRING, BASE_NONE, NULL, 0x0,
3106 * Dissect a buffer containing a C string.
3108 * @param tvb The buffer to dissect.
3109 * @param pinfo Packet Info.
3110 * @param tree The protocol tree.
3111 * @return Number of bytes from the tvbuff_t which were processed or a negative
3112 * value indicating more bytes are needed.
3114 static int dissect_cstr(tvbuff_t * tvb, packet_info * pinfo, proto_tree * tree)
3117 gint available = tvb_reported_length_remaining(tvb, offset);
3118 gint len = tvb_strnlen( tvb, offset, available );
3121 /* No '\0' found, ask for another byte. */
3122 pinfo->desegment_offset = offset;
3123 pinfo->desegment_len = 1;
3127 if (check_col(pinfo->cinfo, COL_INFO)) {
3128 col_set_str(pinfo->cinfo, COL_INFO, "C String");
3131 len += 1; /* Add one for the '\0' */
3134 proto_tree_add_item(tree, hf_cstring, tvb, offset, len, FALSE);
3140 This simple dissector will repeatedly return -1 requesting one more byte until
3141 the tvbuff contains a complete C string. The C string will then be added to the
3142 protocol tree. Unfortunately since there is no way to guess the size of C String
3143 without seeing the entire string this dissector can never request more than one
3148 The ptvcursor API allows a simpler approach to writing dissectors for
3149 simple protocols. The ptvcursor API works best for protocols whose fields
3150 are static and whose format does not depend on the value of other fields.
3151 However, even if only a portion of your protocol is statically defined,
3152 then that portion could make use of ptvcursors.
3154 The ptvcursor API lets you extract data from a tvbuff, and add it to a
3155 protocol tree in one step. It also keeps track of the position in the
3156 tvbuff so that you can extract data again without having to compute any
3157 offsets --- hence the "cursor" name of the API.
3159 The three steps for a simple protocol are:
3160 1. Create a new ptvcursor with ptvcursor_new()
3161 2. Add fields with multiple calls of ptvcursor_add()
3162 3. Delete the ptvcursor with ptvcursor_free()
3164 To use the ptvcursor API, include the "ptvcursor.h" file. The NCP dissector
3165 is an overly-complicated example of how to use it. I don't recommend
3166 looking at it as a guide; instead, the API description here should be good
3172 ptvcursor_new(proto_tree*, tvbuff_t*, gint offset)
3173 This creates a new ptvcursor_t object for iterating over a tvbuff.
3174 You must call this and use this ptvbcursor_t object so you can use the
3178 ptvcursor_add(ptvcursor_t*, int hf, gint length, gboolean endianness)
3179 This will extract 'length' bytes from the tvbuff and place it in
3180 the proto_tree as field 'hf', which is a registered header_field. The
3181 pointer to the proto_item that is created is passed back to you. Internally,
3182 the ptvcursor advances its cursor so the next call to ptvcursor_add
3183 starts where this call finished. The 'endianness' parameter matters for
3184 FT_UINT* and FT_INT* fields.
3187 ptvcursor_add_no_advance(ptvcursor_t*, int hf, gint length, gboolean endianness)
3188 Like ptvcursor_add, but does not advance the internal cursor.
3191 ptvcursor_advance(ptvcursor_t*, gint length)
3192 Advances the internal cursor without adding anything to the proto_tree.
3195 ptvcursor_free(ptvcursor_t*)
3196 Frees the memory associated with the ptvcursor. You must call this
3197 after your dissection with the ptvcursor API is completed.
3199 2.8.2 Miscellaneous functions
3200 ptvcursor_tvbuff - returns the tvbuff associated with the ptvcursor
3201 ptvcursor_current_offset - returns the current offset
3202 ptvcursor_tree - returns the proto_tree associated with the ptvcursor
3203 ptvcursor_set_tree - sets a new proto_tree for the ptvcursor
3208 See the README.plugins for more information on how to "pluginize"
3211 4.0 Extending Wiretap.
3213 5.0 How the Display Filter Engine works
3216 epan/dfilter/* - the display filter engine, including
3217 scanner, parser, syntax-tree semantics checker, DFVM bytecode
3218 generator, and DFVM engine.
3219 epan/ftypes/* - the definitions of the various FT_* field types.
3220 epan/proto.c - proto_tree-related routines
3224 The scanner/parser pair read the string representing the display filter
3225 and convert it into a very simple syntax tree. The syntax tree is very
3226 simple in that it is possible that many of the nodes contain unparsed
3227 chunks of text from the display filter.
3229 5.1 Enhancing the syntax tree.
3231 The semantics of the simple syntax tree are checked to make sure that
3232 the fields that are being compared are being compared to appropriate
3233 values. For example, if a field is an integer, it can't be compared to
3234 a string, unless a value_string has been defined for that field.
3236 During the process of checking the semantics, the simple syntax tree is
3237 fleshed out and no longer contains nodes with unparsed information. The
3238 syntax tree is no longer in its simple form, but in its complete form.
3240 5.2 Converting to DFVM bytecode
3242 The syntax tree is analyzed to create a sequence of bytecodes in the
3243 "DFVM" language. "DFVM" stands for Display Filter Virtual Machine. The
3244 DFVM is similar in spirit, but not in definition, to the BPF VM that
3245 libpcap uses to analyze packets.
3247 A virtual bytecode is created and used so that the actual process of
3248 filtering packets will be fast. That is, it should be faster to process
3249 a list of VM bytecodes than to attempt to filter packets directly from
3250 the syntax tree. (heh... no measurement has been made to support this
3255 Once the DFVM bytecode has been produced, it's a simple matter of
3256 running the DFVM engine against the proto_tree from the packet
3257 dissection, using the DFVM bytecodes as instructions. If the DFVM
3258 bytecode is known before packet dissection occurs, the
3259 proto_tree-related code can be "primed" to store away pointers to
3260 field_info structures that are interesting to the display filter. This
3261 makes lookup of those field_info structures during the filtering process
3264 5.4 Display Filter Functions
3266 You define a desplay filte function by adding an entry to
3267 the df_functions table in epan/dfilter/dfunctions.c. The record struct
3268 is defined in defunctions.h, and shown here:
3272 DFFuncType function;
3273 ftenum_t retval_ftype;
3276 DFSemCheckType semcheck_param_function;
3279 name - the name of the function; this is how the user will call your
3280 function in the display filter language
3282 function - this is the run-time processing of your function.
3284 retval_ftype - what type of FT_* type does your function return?
3286 min_nargs - minimum number of arguments your function accepts
3287 max_nargs - maximum number of arguments your function accepts
3289 semcheck_param_function - called during the semantic check of the
3290 display filter string.
3294 typedef gboolean (*DFFuncType)(GList *arg1list, GList *arg2list, GList **retval);
3296 The return value of your function is a gboolean; TRUE if processing went fine,
3297 or FALSE if there was some sort of exception.
3299 For now, display filter functions can accept a maximum of 2 arguments.
3300 The "arg1list" parameter is the GList for the first argument. The
3301 'arg2list" parameter is the GList for the second argument. All arguments
3302 to display filter functions are lists. This is because in the display
3303 filter language a protocol field may have multiple instances. For example,
3304 a field like "ip.addr" will exist more than once in a single frame. So
3305 when the user invokes this display filter:
3307 somefunc(ip.addr) == TRUE
3309 even though "ip.addr" is a single argument, the "somefunc" function will
3310 receive a GList of *all* the values of "ip.addr" in the frame.
3312 Similarly, the return value of the function needs to be a GList, since all
3313 values in the display filter language are lists. The GList** retval argument
3314 is passed to your function so you can set the pointer to your return value.
3318 typedef void (*DFSemCheckType)(int param_num, stnode_t *st_node);
3320 For each parameter in the syntax tree, this function will be called.
3321 "param_num" will indicate the number of the parameter, starting with 0.
3322 The "stnode_t" is the syntax-tree node representing that parameter.
3323 If everything is okay with the value of that stnode_t, your function
3324 does nothing --- it merely returns. If something is wrong, however,
3325 it should THROW a TypeError exception.
3329 6.0 Adding new capabilities.
3334 James Coe <jammer@cin.net>
3335 Gilbert Ramirez <gram@alumni.rice.edu>
3336 Jeff Foster <jfoste@woodward.com>
3337 Olivier Abad <oabad@cybercable.fr>
3338 Laurent Deniel <laurent.deniel@free.fr>
3339 Gerald Combs <gerald@wireshark.org>
3340 Guy Harris <guy@alum.mit.edu>