6 This file is a HOWTO for Wireshark developers. It describes how to start coding
7 a Wireshark protocol dissector and the use of some of the important functions
10 This file is compiled to give in depth information on Wireshark.
11 It is by no means all inclusive and complete. Please feel free to send
12 remarks and patches to the developer mailing list.
16 Before starting to develop a new dissector, a "running" Wireshark build
17 environment is required - there's no such thing as a standalone "dissector
20 How to setup such an environment is platform dependent; detailed information
21 about these steps can be found in the "Developer's Guide" (available from:
22 http://www.wireshark.org) and in the INSTALL and README files of the sources
25 0.1. General README files.
27 You'll find additional information in the following README files:
29 - README.capture - the capture engine internals
30 - README.design - Wireshark software design - incomplete
31 - README.developer - this file
32 - README.display_filter - Display Filter Engine
33 - README.idl2wrs - CORBA IDL converter
34 - README.packaging - how to distribute a software package containing WS
35 - README.regression - regression testing of WS and TS
36 - README.stats_tree - a tree statistics counting specific packets
37 - README.tapping - "tap" a dissector to get protocol specific events
38 - README.xml-output - how to work with the PDML exported output
39 - wiretap/README.developer - how to add additional capture file types to
42 0.2. Dissector related README files.
44 You'll find additional dissector related information in the following README
47 - README.binarytrees - fast access to large data collections
48 - README.heuristic - what are heuristic dissectors and how to write them
49 - README.malloc - how to obtain "memory leak free" memory
50 - README.plugins - how to "pluginize" a dissector
51 - README.request_response_tracking - how to track req./resp. times and such
55 James Coe <jammer[AT]cin.net>
56 Gilbert Ramirez <gram[AT]alumni.rice.edu>
57 Jeff Foster <jfoste[AT]woodward.com>
58 Olivier Abad <oabad[AT]cybercable.fr>
59 Laurent Deniel <laurent.deniel[AT]free.fr>
60 Gerald Combs <gerald[AT]wireshark.org>
61 Guy Harris <guy[AT]alum.mit.edu>
62 Ulf Lamping <ulf.lamping[AT]web.de>
64 1. Setting up your protocol dissector code.
66 This section provides skeleton code for a protocol dissector. It also explains
67 the basic functions needed to enter values in the traffic summary columns,
68 add to the protocol tree, and work with registered header fields.
74 Wireshark runs on many platforms, and can be compiled with a number of
75 different compilers; here are some rules for writing code that will work
76 on multiple platforms.
78 Don't use C++-style comments (comments beginning with "//" and running
79 to the end of the line); Wireshark's dissectors are written in C, and
80 thus run through C rather than C++ compilers, and not all C compilers
81 support C++-style comments (GCC does, but IBM's C compiler for AIX, for
82 example, doesn't do so by default).
84 Don't initialize variables in their declaration with non-constant
85 values. Not all compilers support this. E.g. don't use
86 guint32 i = somearray[2];
92 Don't use zero-length arrays; not all compilers support them. If an
93 array would have no members, just leave it out.
95 Don't declare variables in the middle of executable code; not all C
96 compilers support that. Variables should be declared outside a
97 function, or at the beginning of a function or compound statement.
99 Don't use anonymous unions; not all compilers support it.
106 } u; /* have a name here */
109 Don't use "uchar", "u_char", "ushort", "u_short", "uint", "u_int",
110 "ulong", "u_long" or "boolean"; they aren't defined on all platforms.
111 If you want an 8-bit unsigned quantity, use "guint8"; if you want an
112 8-bit character value with the 8th bit not interpreted as a sign bit,
113 use "guchar"; if you want a 16-bit unsigned quantity, use "guint16";
114 if you want a 32-bit unsigned quantity, use "guint32"; and if you want
115 an "int-sized" unsigned quantity, use "guint"; if you want a boolean,
116 use "gboolean". Use "%d", "%u", "%x", and "%o" to print those types;
117 don't use "%ld", "%lu", "%lx", or "%lo", as longs are 64 bits long on
118 many platforms, but "guint32" is 32 bits long.
120 Don't use "long" to mean "signed 32-bit integer", and don't use
121 "unsigned long" to mean "unsigned 32-bit integer"; "long"s are 64 bits
122 long on many platforms. Use "gint32" for signed 32-bit integers and use
123 "guint32" for unsigned 32-bit integers.
125 Don't use "long" to mean "signed 64-bit integer" and don't use "unsigned
126 long" to mean "unsigned 64-bit integer"; "long"s are 32 bits long on
127 many other platforms. Don't use "long long" or "unsigned long long",
128 either, as not all platforms support them; use "gint64" or "guint64",
129 which will be defined as the appropriate types for 64-bit signed and
132 When printing or displaying the values of 64-bit integral data types,
133 don't use "%lld", "%llu", "%llx", or "%llo" - not all platforms
134 support "%ll" for printing 64-bit integral data types. Instead, for
135 GLib routines, and routines that use them, such as all the routines in
136 Wireshark that take format arguments, use G_GINT64_MODIFIER, for example:
138 proto_tree_add_text(tree, tvb, offset, 8,
139 "Sequence Number: %" G_GINT64_MODIFIER "u",
142 When using standard C routines, such as printf and scanf, use
143 PRId64, PRIu64, PRIx64, PRIX64, and PRIo64; for example:
145 printf("Sequence Number: %" PRIu64 "\n", sequence_number);
147 When specifying an integral constant that doesn't fit in 32 bits, don't
148 use "LL" at the end of the constant - not all compilers use "LL" for
149 that. Instead, put the constant in a call to the "G_GINT64_CONSTANT()"
152 G_GINT64_CONSTANT(11644473600U)
158 Don't use a label without a statement following it. For example,
168 will not work with all compilers - you have to do
178 with some statement, even if it's a null statement, after the label.
180 Don't use "bzero()", "bcopy()", or "bcmp()"; instead, use the ANSI C
183 "memset()" (with zero as the second argument, so that it sets
184 all the bytes to zero);
186 "memcpy()" or "memmove()" (note that the first and second
187 arguments to "memcpy()" are in the reverse order to the
188 arguments to "bcopy()"; note also that "bcopy()" is typically
189 guaranteed to work on overlapping memory regions, while
190 "memcpy()" isn't, so if you may be copying from one region to a
191 region that overlaps it, use "memmove()", not "memcpy()" - but
192 "memcpy()" might be faster as a result of not guaranteeing
193 correct operation on overlapping memory regions);
195 and "memcmp()" (note that "memcmp()" returns 0, 1, or -1, doing
196 an ordered comparison, rather than just returning 0 for "equal"
197 and 1 for "not equal", as "bcmp()" does).
199 Not all platforms necessarily have "bzero()"/"bcopy()"/"bcmp()", and
200 those that do might not declare them in the header file on which they're
201 declared on your platform.
203 Don't use "index()" or "rindex()"; instead, use the ANSI C equivalents,
204 "strchr()" and "strrchr()". Not all platforms necessarily have
205 "index()" or "rindex()", and those that do might not declare them in the
206 header file on which they're declared on your platform.
208 Don't fetch data from packets by getting a pointer to data in the packet
209 with "tvb_get_ptr()", casting that pointer to a pointer to a structure,
210 and dereferencing that pointer. That pointer won't necessarily be aligned
211 on the proper boundary, which can cause crashes on some platforms (even
212 if it doesn't crash on an x86-based PC); furthermore, the data in a
213 packet is not necessarily in the byte order of the machine on which
214 Wireshark is running. Use the tvbuff routines to extract individual
215 items from the packet, or use "proto_tree_add_item()" and let it extract
218 Don't use structures that overlay packet data, or into which you copy
219 packet data; the C programming language does not guarantee any
220 particular alignment of fields within a structure, and even the
221 extensions that try to guarantee that are compiler-specific and not
222 necessarily supported by all compilers used to build Wireshark. Using
223 bitfields in those structures is even worse; the order of bitfields
226 Don't use "ntohs()", "ntohl()", "htons()", or "htonl()"; the header
227 files required to define or declare them differ between platforms, and
228 you might be able to get away with not including the appropriate header
229 file on your platform but that might not work on other platforms.
230 Instead, use "g_ntohs()", "g_ntohl()", "g_htons()", and "g_htonl()";
231 those are declared by <glib.h>, and you'll need to include that anyway,
232 as Wireshark header files that all dissectors must include use stuff from
235 Don't fetch a little-endian value using "tvb_get_ntohs() or
236 "tvb_get_ntohl()" and then using "g_ntohs()", "g_htons()", "g_ntohl()",
237 or "g_htonl()" on the resulting value - the g_ routines in question
238 convert between network byte order (big-endian) and *host* byte order,
239 not *little-endian* byte order; not all machines on which Wireshark runs
240 are little-endian, even though PCs are. Fetch those values using
241 "tvb_get_letohs()" and "tvb_get_letohl()".
243 Don't put a comma after the last element of an enum - some compilers may
244 either warn about it (producing extra noise) or refuse to accept it.
246 Don't include <unistd.h> without protecting it with
254 and, if you're including it to get routines such as "open()", "close()",
255 "read()", and "write()" declared, also include <io.h> if present:
261 in order to declare the Windows C library routines "_open()",
262 "_close()", "_read()", and "_write()". Your file must include <glib.h>
263 - which many of the Wireshark header files include, so you might not have
264 to include it explicitly - in order to get "open()", "close()",
265 "read()", "write()", etc. mapped to "_open()", "_close()", "_read()",
268 Do not use "open()", "rename()", "mkdir()", "stat()", "unlink()", "remove()",
269 "fopen()", "freopen()" directly. Instead use "ws_open()", "ws_rename()",
270 "ws_mkdir()", "ws_stat()", "ws_unlink()", "ws_remove()", "ws_fopen()",
271 "ws_freopen()": these wrapper functions change the path and file name from
272 UTF8 to UTF16 on Windows allowing the functions to work correctly when the
273 path or file name contain non-ASCII characters.
275 When opening a file with "ws_fopen()", "ws_freopen()", or "ws_fdopen()", if
276 the file contains ASCII text, use "r", "w", "a", and so on as the open mode
277 - but if it contains binary data, use "rb", "wb", and so on. On
278 Windows, if a file is opened in a text mode, writing a byte with the
279 value of octal 12 (newline) to the file causes two bytes, one with the
280 value octal 15 (carriage return) and one with the value octal 12, to be
281 written to the file, and causes bytes with the value octal 15 to be
282 discarded when reading the file (to translate between C's UNIX-style
283 lines that end with newline and Windows' DEC-style lines that end with
284 carriage return/line feed).
286 In addition, that also means that when opening or creating a binary
287 file, you must use "ws_open()" (with O_CREAT and possibly O_TRUNC if the
288 file is to be created if it doesn't exist), and OR in the O_BINARY flag.
289 That flag is not present on most, if not all, UNIX systems, so you must
296 to properly define it for UNIX (it's not necessary on UNIX).
298 Don't use forward declarations of static arrays without a specified size
299 in a fashion such as this:
301 static const value_string foo_vals[];
305 static const value_string foo_vals[] = {
312 as some compilers will reject the first of those statements. Instead,
313 initialize the array at the point at which it's first declared, so that
316 Don't put a comma after the last tuple of an initializer of an array.
318 For #define names and enum member names, prefix the names with a tag so
319 as to avoid collisions with other names - this might be more of an issue
320 on Windows, as it appears to #define names such as DELETE and
323 Don't use the "numbered argument" feature that many UNIX printf's
326 g_snprintf(add_string, 30, " - (%1$d) (0x%1$04x)", value);
328 as not all UNIX printf's implement it, and Windows printf doesn't appear
329 to implement it. Use something like
331 g_snprintf(add_string, 30, " - (%d) (0x%04x)", value, value);
335 Don't use "variadic macros", such as
337 #define DBG(format, args...) fprintf(stderr, format, ## args)
339 as not all C compilers support them. Use macros that take a fixed
340 number of arguments, such as
342 #define DBG0(format) fprintf(stderr, format)
343 #define DBG1(format, arg1) fprintf(stderr, format, arg1)
344 #define DBG2(format, arg1, arg2) fprintf(stderr, format, arg1, arg2)
350 #define DBG(args) printf args
356 as that's not supported by all compilers.
358 snprintf() -> g_snprintf()
359 snprintf() is not available on all platforms, so it's a good idea to use the
360 g_snprintf() function declared by <glib.h> instead.
362 tmpnam() -> mkstemp()
363 tmpnam is insecure and should not be used any more. Wireshark brings its
364 own mkstemp implementation for use on platforms that lack mkstemp.
365 Note: mkstemp does not accept NULL as a parameter.
367 The pointer returned by a call to "tvb_get_ptr()" is not guaranteed to be
368 aligned on any particular byte boundary; this means that you cannot
369 safely cast it to any data type other than a pointer to "char",
370 "unsigned char", "guint8", or other one-byte data types. You cannot,
371 for example, safely cast it to a pointer to a structure, and then access
372 the structure members directly; on some systems, unaligned accesses to
373 integral data types larger than 1 byte, and floating-point data types,
374 cause a trap, which will, at best, result in the OS slowly performing an
375 unaligned access for you, and will, on at least some platforms, cause
376 the program to be terminated.
378 Wireshark supports platforms with GLib 2.4[.x]/GTK+ 2.4[.x] or newer.
379 If a Glib/GTK+ mechanism is available only in Glib/GTK+ versions
380 newer than 2.4/2.4 then use "#if GTK_CHECK_VERSION(...)" to conditionally
381 compile code using that mechanism.
383 When different code must be used on UN*X and Win32, use a #if or #ifdef
384 that tests _WIN32, not WIN32. Try to write code portably whenever
385 possible, however; note that there are some routines in Wireshark with
386 platform-dependent implementations and platform-independent APIs, such
387 as the routines in epan/filesystem.c, allowing the code that calls it to
388 be written portably without #ifdefs.
390 1.1.2 String handling
392 Do not use functions such as strcat() or strcpy().
393 A lot of work has been done to remove the existing calls to these functions and
394 we do not want any new callers of these functions.
396 Instead use g_snprintf() since that function will if used correctly prevent
397 buffer overflows for large strings.
399 When using a buffer to create a string, do not use a buffer stored on the stack.
400 I.e. do not use a buffer declared as
402 instead allocate a buffer dynamically using the emem routines (see
403 README.malloc) such as
406 #define MAX_BUFFER 1024
407 buffer=ep_alloc(MAX_BUFFER);
410 g_snprintf(buffer, MAX_BUFFER, ...
412 This avoids the stack from being corrupted in case there is a bug in your code
413 that accidentally writes beyond the end of the buffer.
416 If you write a routine that will create and return a pointer to a filled in
417 string and if that buffer will not be further processed or appended to after
418 the routine returns (except being added to the proto tree),
419 do not preallocate the buffer to fill in and pass as a parameter instead
420 pass a pointer to a pointer to the function and return a pointer to an
421 emem allocated buffer that will be automatically freed. (see README.malloc)
423 I.e. do not write code such as
425 foo_to_str(char *string, ... ){
431 foo_to_str(buffer, ...
432 proto_tree_add_text(... buffer ...
434 instead write the code as
436 foo_to_str(char **buffer, ...
438 *buffer=ep_alloc(MAX_BUFFER);
444 foo_to_str(&buffer, ...
445 proto_tree_add_text(... *buffer ...
447 Use ep_ allocated buffers. They are very fast and nice. These buffers are all
448 automatically free()d when the dissection of the current packet ends so you
449 don't have to worry about free()ing them explicitly in order to not leak memory.
450 Please read README.malloc.
454 Wireshark is not guaranteed to read only network traces that contain correctly-
455 formed packets. Wireshark is commonly used to track down networking
456 problems, and the problems might be due to a buggy protocol implementation
457 sending out bad packets.
459 Therefore, protocol dissectors not only have to be able to handle
460 correctly-formed packets without, for example, crashing or looping
461 infinitely, they also have to be able to handle *incorrectly*-formed
462 packets without crashing or looping infinitely.
464 Here are some suggestions for making dissectors more robust in the face
465 of incorrectly-formed packets:
467 Do *NOT* use "g_assert()" or "g_assert_not_reached()" in dissectors.
468 *NO* value in a packet's data should be considered "wrong" in the sense
469 that it's a problem with the dissector if found; if it cannot do
470 anything else with a particular value from a packet's data, the
471 dissector should put into the protocol tree an indication that the
472 value is invalid, and should return. You can use the DISSECTOR_ASSERT
473 macro for that purpose.
475 If you are allocating a chunk of memory to contain data from a packet,
476 or to contain information derived from data in a packet, and the size of
477 the chunk of memory is derived from a size field in the packet, make
478 sure all the data is present in the packet before allocating the buffer.
481 1) Wireshark won't leak that chunk of memory if an attempt to
482 fetch data not present in the packet throws an exception.
486 2) it won't crash trying to allocate an absurdly-large chunk of
487 memory if the size field has a bogus large value.
489 If you're fetching into such a chunk of memory a string from the buffer,
490 and the string has a specified size, you can use "tvb_get_*_string()",
491 which will check whether the entire string is present before allocating
492 a buffer for the string, and will also put a trailing '\0' at the end of
495 If you're fetching into such a chunk of memory a 2-byte Unicode string
496 from the buffer, and the string has a specified size, you can use
497 "tvb_get_ephemeral_faked_unicode()", which will check whether the entire
498 string is present before allocating a buffer for the string, and will also
499 put a trailing '\0' at the end of the buffer. The resulting string will be
500 a sequence of single-byte characters; the only Unicode characters that
501 will be handled correctly are those in the ASCII range. (Wireshark's
502 ability to handle non-ASCII strings is limited; it needs to be
505 If you're fetching into such a chunk of memory a sequence of bytes from
506 the buffer, and the sequence has a specified size, you can use
507 "tvb_memdup()", which will check whether the entire sequence is present
508 before allocating a buffer for it.
510 Otherwise, you can check whether the data is present by using
511 "tvb_ensure_bytes_exist()" or by getting a pointer to the data by using
512 "tvb_get_ptr()", although note that there might be problems with using
513 the pointer from "tvb_get_ptr()" (see the item on this in the
514 Portability section above, and the next item below).
516 Note also that you should only fetch string data into a fixed-length
517 buffer if the code ensures that no more bytes than will fit into the
518 buffer are fetched ("the protocol ensures" isn't good enough, as
519 protocol specifications can't ensure only packets that conform to the
520 specification will be transmitted or that only packets for the protocol
521 in question will be interpreted as packets for that protocol by
522 Wireshark). If there's no maximum length of string data to be fetched,
523 routines such as "tvb_get_*_string()" are safer, as they allocate a buffer
524 large enough to hold the string. (Note that some variants of this call
525 require you to free the string once you're finished with it.)
527 If you have gotten a pointer using "tvb_get_ptr()", you must make sure
528 that you do not refer to any data past the length passed as the last
529 argument to "tvb_get_ptr()"; while the various "tvb_get" routines
530 perform bounds checking and throw an exception if you refer to data not
531 available in the tvbuff, direct references through a pointer gotten from
532 "tvb_get_ptr()" do not do any bounds checking.
534 If you have a loop that dissects a sequence of items, each of which has
535 a length field, with the offset in the tvbuff advanced by the length of
536 the item, then, if the length field is the total length of the item, and
537 thus can be zero, you *MUST* check for a zero-length item and abort the
538 loop if you see one. Otherwise, a zero-length item could cause the
539 dissector to loop infinitely. You should also check that the offset,
540 after having the length added to it, is greater than the offset before
541 the length was added to it, if the length field is greater than 24 bits
542 long, so that, if the length value is *very* large and adding it to the
543 offset causes an overflow, that overflow is detected.
545 If you are fetching a length field from the buffer, corresponding to the
546 length of a portion of the packet, and subtracting from that length a
547 value corresponding to the length of, for example, a header in the
548 packet portion in question, *ALWAYS* check that the value of the length
549 field is greater than or equal to the length you're subtracting from it,
550 and report an error in the packet and stop dissecting the packet if it's
551 less than the length you're subtracting from it. Otherwise, the
552 resulting length value will be negative, which will either cause errors
553 in the dissector or routines called by the dissector, or, if the value
554 is interpreted as an unsigned integer, will cause the value to be
555 interpreted as a very large positive value.
557 Any tvbuff offset that is added to as processing is done on a packet
558 should be stored in a 32-bit variable, such as an "int"; if you store it
559 in an 8-bit or 16-bit variable, you run the risk of the variable
562 sprintf() -> g_snprintf()
563 Prevent yourself from using the sprintf() function, as it does not test the
564 length of the given output buffer and might be writing into unintended memory
565 areas. This function is one of the main causes of security problems like buffer
566 exploits and many other bugs that are very hard to find. It's much better to
567 use the g_snprintf() function declared by <glib.h> instead.
569 You should test your dissector against incorrectly-formed packets. This
570 can be done using the randpkt and editcap utilities that come with the
571 Wireshark distribution. Testing using randpkt can be done by generating
572 output at the same layer as your protocol, and forcing Wireshark/TShark
573 to decode it as your protocol, e.g. if your protocol sits on top of UDP:
575 randpkt -c 50000 -t dns randpkt.pcap
576 tshark -nVr randpkt.pcap -d udp.port==53,<myproto>
578 Testing using editcap can be done using preexisting capture files and the
579 "-E" flag, which introduces errors in a capture file. E.g.:
581 editcap -E 0.03 infile.pcap outfile.pcap
582 tshark -nVr outfile.pcap
584 The script fuzz-test.sh is available to help automate these tests.
586 1.1.4 Name convention.
588 Wireshark uses the underscore_convention rather than the InterCapConvention for
589 function names, so new code should probably use underscores rather than
590 intercaps for functions and variable names. This is especially important if you
591 are writing code that will be called from outside your code. We are just
592 trying to keep things consistent for other developers.
594 1.1.5 White space convention.
596 Avoid using tab expansions different from 8 column widths, as not all
597 text editors in use by the developers support this. For a detailed
598 discussion of tabs, spaces, and indentation, see
600 http://www.jwz.org/doc/tabs-vs-spaces.html
602 When creating a new file, you are free to choose an indentation logic.
603 Most of the files in Wireshark tend to use 2-space or 4-space
604 indentation. You are encouraged to write a short comment on the
605 indentation logic at the beginning of this new file, especially if
606 you're using non-mod-8 tabs. The tabs-vs-spaces document above provides
607 examples of Emacs and vi modelines for this purpose.
609 When editing an existing file, try following the existing indentation
610 logic and even if it very tempting, never ever use a restyler/reindenter
611 utility on an existing file. If you run across wildly varying
612 indentation styles within the same file, it might be helpful to send a
613 note to wireshark-dev for guidance.
615 1.1.6 Compiler warnings
617 You should write code that is free of compiler warnings. Such warnings will
618 often indicate questionable code and sometimes even real bugs, so it's best
619 to avoid warnings at all.
621 The compiler flags in the Makefiles are set to "treat warnings as errors",
622 so your code won't even compile when warnings occur.
626 Wireshark requires certain things when setting up a protocol dissector.
627 Below is skeleton code for a dissector that you can copy to a file and
628 fill in. Your dissector should follow the naming convention of packet-
629 followed by the abbreviated name for the protocol. It is recommended
630 that where possible you keep to the IANA abbreviated name for the
631 protocol, if there is one, or a commonly-used abbreviation for the
634 Usually, you will put your newly created dissector file into the directory
635 epan/dissectors, just like all the other packet-....c files already in there.
637 Also, please add your dissector file to the corresponding makefile,
638 described in section "1.9 Editing Makefile.common to add your dissector" below.
640 Dissectors that use the dissector registration to register with a lower level
641 dissector don't need to define a prototype in the .h file. For other
642 dissectors the main dissector routine should have a prototype in a header
643 file whose name is "packet-", followed by the abbreviated name for the
644 protocol, followed by ".h"; any dissector file that calls your dissector
645 should be changed to include that file.
647 You may not need to include all the headers listed in the skeleton
648 below, and you may need to include additional headers. For example, the
657 is needed only if you are using a function from libpcre, e.g. the
658 "pcre_compile()" function.
660 The "$Id$" in the comment will be updated by Subversion when the file is
663 When creating a new file, it is fine to just write "$Id$" as Subversion will
664 automatically fill in the identifier at the time the file will be added to the
665 SVN repository (committed).
667 ------------------------------------Cut here------------------------------------
668 /* packet-PROTOABBREV.c
669 * Routines for PROTONAME dissection
670 * Copyright 200x, YOUR_NAME <YOUR_EMAIL_ADDRESS>
674 * Wireshark - Network traffic analyzer
675 * By Gerald Combs <gerald@wireshark.org>
676 * Copyright 1998 Gerald Combs
678 * Copied from WHATEVER_FILE_YOU_USED (where "WHATEVER_FILE_YOU_USED"
679 * is a dissector file; if you just copied this from README.developer,
680 * don't bother with the "Copied from" - you don't even need to put
681 * in a "Copied from" if you copied an existing dissector, especially
682 * if the bulk of the code in the new dissector is your code)
684 * This program is free software; you can redistribute it and/or
685 * modify it under the terms of the GNU General Public License
686 * as published by the Free Software Foundation; either version 2
687 * of the License, or (at your option) any later version.
689 * This program is distributed in the hope that it will be useful,
690 * but WITHOUT ANY WARRANTY; without even the implied warranty of
691 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
692 * GNU General Public License for more details.
694 * You should have received a copy of the GNU General Public License
695 * along with this program; if not, write to the Free Software
696 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
710 #include <epan/packet.h>
711 #include <epan/prefs.h>
713 /* IF PROTO exposes code to other dissectors, then it must be exported
714 in a header file. If not, a header file is not needed at all. */
715 #include "packet-PROTOABBREV.h"
717 /* Forward declaration we need below (if using proto_reg_handoff...
718 as a prefs callback) */
719 void proto_reg_handoff_PROTOABBREV(void);
721 /* Initialize the protocol and registered fields */
722 static int proto_PROTOABBREV = -1;
723 static int hf_PROTOABBREV_FIELDABBREV = -1;
725 /* Global sample preference ("controls" display of numbers) */
726 static gboolean gPREF_HEX = FALSE;
727 /* Global sample port pref */
728 static guint gPORT_PREF = 1234;
730 /* Initialize the subtree pointers */
731 static gint ett_PROTOABBREV = -1;
733 /* Code to actually dissect the packets */
735 dissect_PROTOABBREV(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
738 /* Set up structures needed to add the protocol subtree and manage it */
740 proto_tree *PROTOABBREV_tree;
742 /* First, if at all possible, do some heuristics to check if the packet cannot
743 * possibly belong to your protocol. This is especially important for
744 * protocols directly on top of TCP or UDP where port collisions are
745 * common place (e.g., even though your protocol uses a well known port,
746 * someone else may set up, for example, a web server on that port which,
747 * if someone analyzed that web server's traffic in Wireshark, would result
748 * in Wireshark handing an HTTP packet to your dissector). For example:
750 /* Check that there's enough data */
751 if (tvb_length(tvb) < /* your protocol's smallest packet size */)
754 /* Get some values from the packet header, probably using tvb_get_*() */
755 if ( /* these values are not possible in PROTONAME */ )
756 /* This packet does not appear to belong to PROTONAME.
757 * Return 0 to give another dissector a chance to dissect it.
761 /* Make entries in Protocol column and Info column on summary display */
762 if (check_col(pinfo->cinfo, COL_PROTOCOL))
763 col_set_str(pinfo->cinfo, COL_PROTOCOL, "PROTOABBREV");
765 /* This field shows up as the "Info" column in the display; you should use
766 it, if possible, to summarize what's in the packet, so that a user looking
767 at the list of packets can tell what type of packet it is. See section 1.5
768 for more information.
770 Before changing the contents of a column you should make sure the column is
771 active by calling "check_col(pinfo->cinfo, COL_*)". If it is not active
772 don't bother setting it.
774 If you are setting the column to a constant string, use "col_set_str()",
775 as it's more efficient than the other "col_set_XXX()" calls.
777 If you're setting it to a string you've constructed, or will be
778 appending to the column later, use "col_add_str()".
780 "col_add_fstr()" can be used instead of "col_add_str()"; it takes
781 "printf()"-like arguments. Don't use "col_add_fstr()" with a format
782 string of "%s" - just use "col_add_str()" or "col_set_str()", as it's
783 more efficient than "col_add_fstr()".
785 If you will be fetching any data from the packet before filling in
786 the Info column, clear that column first, in case the calls to fetch
787 data from the packet throw an exception because they're fetching data
788 past the end of the packet, so that the Info column doesn't have data
789 left over from the previous dissector; do
791 if (check_col(pinfo->cinfo, COL_INFO))
792 col_clear(pinfo->cinfo, COL_INFO);
796 if (check_col(pinfo->cinfo, COL_INFO))
797 col_set_str(pinfo->cinfo, COL_INFO, "XXX Request");
799 /* A protocol dissector can be called in 2 different ways:
801 (a) Operational dissection
803 In this mode, Wireshark is only interested in the way protocols
804 interact, protocol conversations are created, packets are
805 reassembled and handed over to higher-level protocol dissectors.
806 In this mode Wireshark does not build a so-called "protocol
809 (b) Detailed dissection
811 In this mode, Wireshark is also interested in all details of
812 a given protocol, so a "protocol tree" is created.
814 Wireshark distinguishes between the 2 modes with the proto_tree pointer:
818 In the interest of speed, if "tree" is NULL, avoid building a
819 protocol tree and adding stuff to it, or even looking at any packet
820 data needed only if you're building the protocol tree, if possible.
822 Note, however, that you must fill in column information, create
823 conversations, reassemble packets, build any other persistent state
824 needed for dissection, and call subdissectors regardless of whether
825 "tree" is NULL or not. This might be inconvenient to do without
826 doing most of the dissection work; the routines for adding items to
827 the protocol tree can be passed a null protocol tree pointer, in
828 which case they'll return a null item pointer, and
829 "proto_item_add_subtree()" returns a null tree pointer if passed a
830 null item pointer, so, if you're careful not to dereference any null
831 tree or item pointers, you can accomplish this by doing all the
832 dissection work. This might not be as efficient as skipping that
833 work if you're not building a protocol tree, but if the code would
834 have a lot of tests whether "tree" is null if you skipped that work,
835 you might still be better off just doing all that work regardless of
836 whether "tree" is null or not. */
839 /* NOTE: The offset and length values in the call to
840 "proto_tree_add_item()" define what data bytes to highlight in the hex
841 display window when the line in the protocol tree display
842 corresponding to that item is selected.
844 Supplying a length of -1 is the way to highlight all data from the
845 offset to the end of the packet. */
847 /* create display subtree for the protocol */
848 ti = proto_tree_add_item(tree, proto_PROTOABBREV, tvb, 0, -1, FALSE);
850 PROTOABBREV_tree = proto_item_add_subtree(ti, ett_PROTOABBREV);
852 /* add an item to the subtree, see section 1.6 for more information */
853 proto_tree_add_item(PROTOABBREV_tree,
854 hf_PROTOABBREV_FIELDABBREV, tvb, offset, len, FALSE);
857 /* Continue adding tree items to process the packet here */
862 /* If this protocol has a sub-dissector call it here, see section 1.8 */
864 /* Return the amount of data this dissector was able to dissect */
865 return tvb_length(tvb);
869 /* Register the protocol with Wireshark */
871 /* this format is require because a script is used to build the C function
872 that calls all the protocol registration.
876 proto_register_PROTOABBREV(void)
878 module_t *PROTOABBREV_module;
880 /* Setup list of header fields See Section 1.6.1 for details*/
881 static hf_register_info hf[] = {
882 { &hf_PROTOABBREV_FIELDABBREV,
883 { "FIELDNAME", "PROTOABBREV.FIELDABBREV",
884 FIELDTYPE, FIELDBASE, FIELDCONVERT, BITMASK,
885 "FIELDDESCR", HFILL }
889 /* Setup protocol subtree array */
890 static gint *ett[] = {
894 /* Register the protocol name and description */
895 proto_PROTOABBREV = proto_register_protocol("PROTONAME",
896 "PROTOSHORTNAME", "PROTOABBREV");
898 /* Required function calls to register the header fields and subtrees used */
899 proto_register_field_array(proto_PROTOABBREV, hf, array_length(hf));
900 proto_register_subtree_array(ett, array_length(ett));
902 /* Register preferences module (See Section 2.6 for more on preferences) */
903 /* (Registration of a prefs callback is not required if there are no */
904 /* prefs-dependent registration functions (eg: a port pref). */
905 /* See proto_reg_handoff below. */
906 /* If a prefs callback is not needed, use NULL instead of */
907 /* proto_reg_handoff_PROTOABBREV in the following). */
908 PROTOABBREV_module = prefs_register_protocol(proto_PROTOABBREV,
909 proto_reg_handoff_PROTOABBREV);
911 /* Register a sample preference */
912 prefs_register_bool_preference(PROTOABBREV_module, "show_hex",
913 "Display numbers in Hex",
914 "Enable to display numerical values in hexadecimal.",
917 /* Register a sample port preference */
918 prefs_register_uint_preference(PROTOABBREV_module, "tcp.port", "PROTOABBREV TCP Port",
919 " PROTOABBREV TCP port if other than the default",
922 /* If this dissector uses sub-dissector registration add a registration routine.
923 This exact format is required because a script is used to find these
924 routines and create the code that calls these routines.
926 If this function is registered as a prefs callback (see prefs_register_protocol
927 above) this function is also called by preferences whenever "Apply" is pressed;
928 In that case, it should accommodate being called more than once.
930 This form of the reg_handoff function is used if if you perform
931 registration functions which are dependent upon prefs. See below
932 for a simpler form which can be used if there are no
933 prefs-dependent registration functions.
936 proto_reg_handoff_PROTOABBREV(void)
938 static gboolean initialized = FALSE;
939 static dissector_handle_t PROTOABBREV_handle;
940 static int currentPort;
944 /* Use new_create_dissector_handle() to indicate that dissect_PROTOABBREV()
945 * returns the number of bytes it dissected (or 0 if it thinks the packet
946 * does not belong to PROTONAME).
948 PROTOABBREV_handle = new_create_dissector_handle(dissect_PROTOABBREV,
950 dissector_add("PARENT_SUBFIELD", ID_VALUE, PROTOABBREV_handle);
956 If you perform registration functions which are dependent upon
957 prefs the you should de-register everything which was associated
958 with the previous settings and re-register using the new prefs
959 settings here. In general this means you need to keep track of
960 the PROTOABBREV_handle and the value the preference had at the time
961 you registered. The PROTOABBREV_handle value and the value of the
962 preference can be saved using local statics in this
963 function (proto_reg_handoff).
966 dissector_delete("tcp.port", currentPort, PROTOABBREV_handle);
969 currentPort = gPORT_PREF;
971 dissector_add("tcp.port", currentPort, PROTOABBREV_handle);
976 /* Simple form of proto_reg_handoff_PROTOABBREV which can be used if there are
977 no prefs-dependent registration function calls.
981 proto_reg_handoff_PROTOABBREV(void)
983 dissector_handle_t PROTOABBREV_handle;
985 /* Use new_create_dissector_handle() to indicate that dissect_PROTOABBREV()
986 * returns the number of bytes it dissected (or 0 if it thinks the packet
987 * does not belong to PROTONAME).
989 PROTOABBREV_handle = new_create_dissector_handle(dissect_PROTOABBREV,
991 dissector_add("PARENT_SUBFIELD", ID_VALUE, PROTOABBREV_handle);
996 ------------------------------------Cut here------------------------------------
998 1.3 Explanation of needed substitutions in code skeleton.
1000 In the above code block the following strings should be substituted with
1003 YOUR_NAME Your name, of course. You do want credit, don't you?
1004 It's the only payment you will receive....
1005 YOUR_EMAIL_ADDRESS Keep those cards and letters coming.
1006 WHATEVER_FILE_YOU_USED Add this line if you are using another file as a
1008 PROTONAME The name of the protocol; this is displayed in the
1009 top-level protocol tree item for that protocol.
1010 PROTOSHORTNAME An abbreviated name for the protocol; this is displayed
1011 in the "Preferences" dialog box if your dissector has
1012 any preferences, in the dialog box of enabled protocols,
1013 and in the dialog box for filter fields when constructing
1014 a filter expression.
1015 PROTOABBREV A name for the protocol for use in filter expressions;
1016 it shall contain only lower-case letters, digits, and
1018 FIELDNAME The displayed name for the header field.
1019 FIELDABBREV The abbreviated name for the header field. (NO SPACES)
1020 FIELDTYPE FT_NONE, FT_BOOLEAN, FT_UINT8, FT_UINT16, FT_UINT24,
1021 FT_UINT32, FT_UINT64, FT_INT8, FT_INT16, FT_INT24, FT_INT32,
1022 FT_INT64, FT_FLOAT, FT_DOUBLE, FT_ABSOLUTE_TIME,
1023 FT_RELATIVE_TIME, FT_STRING, FT_STRINGZ, FT_EBCDIC,
1024 FT_UINT_STRING, FT_ETHER, FT_BYTES, FT_UINT_BYTES, FT_IPv4,
1025 FT_IPv6, FT_IPXNET, FT_FRAMENUM, FT_PROTOCOL, FT_GUID, FT_OID
1026 FIELDBASE BASE_NONE, BASE_DEC, BASE_HEX, BASE_OCT, BASE_DEC_HEX,
1027 BASE_HEX_DEC, BASE_RANGE_STRING, BASE_CUSTOM
1028 FIELDCONVERT VALS(x), RVALS(x), TFS(x), NULL
1029 BITMASK Usually 0x0 unless using the TFS(x) field conversion.
1030 FIELDDESCR A brief description of the field, or NULL.
1031 PARENT_SUBFIELD Lower level protocol field used for lookup, i.e. "tcp.port"
1032 ID_VALUE Lower level protocol field value that identifies this protocol
1033 For example the TCP or UDP port number
1035 If, for example, PROTONAME is "Internet Bogosity Discovery Protocol",
1036 PROTOSHORTNAME would be "IBDP", and PROTOABBREV would be "ibdp". Try to
1037 conform with IANA names.
1039 1.4 The dissector and the data it receives.
1044 This is only needed if the dissector doesn't use self-registration to
1045 register itself with the lower level dissector, or if the protocol dissector
1046 wants/needs to expose code to other subdissectors.
1048 The dissector must be declared exactly as follows in the file
1049 packet-PROTOABBREV.h:
1052 dissect_PROTOABBREV(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree);
1055 1.4.2 Extracting data from packets.
1057 NOTE: See the file /epan/tvbuff.h for more details.
1059 The "tvb" argument to a dissector points to a buffer containing the raw
1060 data to be analyzed by the dissector; for example, for a protocol
1061 running atop UDP, it contains the UDP payload (but not the UDP header,
1062 or any protocol headers above it). A tvbuffer is an opaque data
1063 structure, the internal data structures are hidden and the data must be
1064 accessed via the tvbuffer accessors.
1068 Bit accessors for a maximum of 8-bits, 16-bits 32-bits and 64-bits:
1070 guint8 tvb_get_bits8(tvbuff_t *tvb, gint bit_offset, gint no_of_bits);
1071 guint16 tvb_get_bits16(tvbuff_t *tvb, gint bit_offset, gint no_of_bits,gboolean little_endian);
1072 guint32 tvb_get_bits32(tvbuff_t *tvb, gint bit_offset, gint no_of_bits,gboolean little_endian);
1073 guint64 tvb_get_bits64(tvbuff_t *tvb, gint bit_offset, gint no_of_bits,gboolean little_endian);
1075 Single-byte accessor:
1077 guint8 tvb_get_guint8(tvbuff_t*, gint offset);
1079 Network-to-host-order accessors for 16-bit integers (guint16), 24-bit
1080 integers, 32-bit integers (guint32), and 64-bit integers (guint64):
1082 guint16 tvb_get_ntohs(tvbuff_t*, gint offset);
1083 guint32 tvb_get_ntoh24(tvbuff_t*, gint offset);
1084 guint32 tvb_get_ntohl(tvbuff_t*, gint offset);
1085 guint64 tvb_get_ntoh64(tvbuff_t*, gint offset);
1087 Network-to-host-order accessors for single-precision and
1088 double-precision IEEE floating-point numbers:
1090 gfloat tvb_get_ntohieee_float(tvbuff_t*, gint offset);
1091 gdouble tvb_get_ntohieee_double(tvbuff_t*, gint offset);
1093 Little-Endian-to-host-order accessors for 16-bit integers (guint16),
1094 24-bit integers, 32-bit integers (guint32), and 64-bit integers
1097 guint16 tvb_get_letohs(tvbuff_t*, gint offset);
1098 guint32 tvb_get_letoh24(tvbuff_t*, gint offset);
1099 guint32 tvb_get_letohl(tvbuff_t*, gint offset);
1100 guint64 tvb_get_letoh64(tvbuff_t*, gint offset);
1102 Little-Endian-to-host-order accessors for single-precision and
1103 double-precision IEEE floating-point numbers:
1105 gfloat tvb_get_letohieee_float(tvbuff_t*, gint offset);
1106 gdouble tvb_get_letohieee_double(tvbuff_t*, gint offset);
1108 Accessors for IPv4 and IPv6 addresses:
1110 guint32 tvb_get_ipv4(tvbuff_t*, gint offset);
1111 void tvb_get_ipv6(tvbuff_t*, gint offset, struct e_in6_addr *addr);
1113 NOTE: IPv4 addresses are not to be converted to host byte order before
1114 being passed to "proto_tree_add_ipv4()". You should use "tvb_get_ipv4()"
1115 to fetch them, not "tvb_get_ntohl()" *OR* "tvb_get_letohl()" - don't,
1116 for example, try to use "tvb_get_ntohl()", find that it gives you the
1117 wrong answer on the PC on which you're doing development, and try
1118 "tvb_get_letohl()" instead, as "tvb_get_letohl()" will give the wrong
1119 answer on big-endian machines.
1123 void tvb_get_ntohguid(tvbuff_t *, gint offset, e_guid_t *guid);
1124 void tvb_get_letohguid(tvbuff_t *, gint offset, e_guid_t *guid);
1128 guint8 *tvb_get_string(tvbuff_t*, gint offset, gint length);
1129 guint8 *tvb_get_ephemeral_string(tvbuff_t*, gint offset, gint length);
1131 Returns a null-terminated buffer containing data from the specified
1132 tvbuff, starting at the specified offset, and containing the specified
1133 length worth of characters (the length of the buffer will be length+1,
1134 as it includes a null character to terminate the string).
1136 tvb_get_string() returns a buffer allocated by g_malloc() so you must
1137 g_free() it when you are finished with the string. Failure to g_free() this
1138 buffer will lead to memory leaks.
1139 tvb_get_ephemeral_string() returns a buffer allocated from a special heap
1140 with a lifetime until the next packet is dissected. You do not need to
1141 free() this buffer, it will happen automatically once the next packet is
1145 guint8 *tvb_get_stringz(tvbuff_t *tvb, gint offset, gint *lengthp);
1146 guint8 *tvb_get_ephemeral_stringz(tvbuff_t *tvb, gint offset, gint *lengthp);
1148 Returns a null-terminated buffer, allocated with "g_malloc()",
1149 containing data from the specified tvbuff, starting at the
1150 specified offset, and containing all characters from the tvbuff up to
1151 and including a terminating null character in the tvbuff. "*lengthp"
1152 will be set to the length of the string, including the terminating null.
1154 tvb_get_stringz() returns a buffer allocated by g_malloc() so you must
1155 g_free() it when you are finished with the string. Failure to g_free() this
1156 buffer will lead to memory leaks.
1157 tvb_get_ephemeral_stringz() returns a buffer allocated from a special heap
1158 with a lifetime until the next packet is dissected. You do not need to
1159 free() this buffer, it will happen automatically once the next packet is
1163 guint8 *tvb_fake_unicode(tvbuff_t*, gint offset, gint length, gboolean little_endian);
1164 guint8 *tvb_get_ephemeral_faked_unicode(tvbuff_t*, gint offset, gint length, gboolean little_endian);
1166 Converts a 2-byte unicode string to an ASCII string.
1167 Returns a null-terminated buffer containing data from the specified
1168 tvbuff, starting at the specified offset, and containing the specified
1169 length worth of characters (the length of the buffer will be length+1,
1170 as it includes a null character to terminate the string).
1172 tvb_fake_unicode() returns a buffer allocated by g_malloc() so you must
1173 g_free() it when you are finished with the string. Failure to g_free() this
1174 buffer will lead to memory leaks.
1175 tvb_get_ephemeral_faked_unicode() returns a buffer allocated from a special
1176 heap with a lifetime until the next packet is dissected. You do not need to
1177 free() this buffer, it will happen automatically once the next packet is
1180 Byte Array Accessors:
1182 gchar *tvb_bytes_to_str(tvbuff_t *tvb, gint offset, gint len);
1184 Formats a bunch of data from a tvbuff as bytes, returning a pointer
1185 to the string with the data formatted as two hex digits for each byte.
1186 The string pointed to is stored in an "ep_alloc'd" buffer which will be freed
1187 before the next frame is dissected. The formatted string will contain the hex digits
1188 for at most the first 16 bytes of the data. If len is greater than 16 bytes, a
1189 trailing "..." will be added to the string.
1191 gchar *tvb_bytes_to_str_punct(tvbuff_t *tvb, gint offset, gint len, gchar punct);
1193 This function is similar to tvb_bytes_to_str(...) except that 'punct' is inserted
1194 between the hex representation of each byte.
1198 guint8* tvb_memcpy(tvbuff_t*, guint8* target, gint offset, gint length);
1200 Copies into the specified target the specified length's worth of data
1201 from the specified tvbuff, starting at the specified offset.
1203 guint8* tvb_memdup(tvbuff_t*, gint offset, gint length);
1204 guint8* ep_tvb_memdup(tvbuff_t*, gint offset, gint length);
1206 Returns a buffer, allocated with "g_malloc()", containing the specified
1207 length's worth of data from the specified tvbuff, starting at the
1208 specified offset. The ephemeral variant is freed automatically after the
1209 packet is dissected.
1212 /* WARNING! This function is possibly expensive, temporarily allocating
1213 * another copy of the packet data. Furthermore, it's dangerous because once
1214 * this pointer is given to the user, there's no guarantee that the user will
1215 * honor the 'length' and not overstep the boundaries of the buffer.
1217 guint8* tvb_get_ptr(tvbuff_t*, gint offset, gint length);
1219 The reason that tvb_get_ptr() might have to allocate a copy of its data
1220 only occurs with TVBUFF_COMPOSITES, data that spans multiple tvbuffers.
1221 If the user requests a pointer to a range of bytes that span the member
1222 tvbuffs that make up the TVBUFF_COMPOSITE, the data will have to be
1223 copied to another memory region to assure that all the bytes are
1228 1.5 Functions to handle columns in the traffic summary window.
1230 The topmost pane of the main window is a list of the packets in the
1231 capture, possibly filtered by a display filter.
1233 Each line corresponds to a packet, and has one or more columns, as
1234 configured by the user.
1236 Many of the columns are handled by code outside individual dissectors;
1237 most dissectors need only specify the value to put in the "Protocol" and
1240 Columns are specified by COL_ values; the COL_ value for the "Protocol"
1241 field, typically giving an abbreviated name for the protocol (but not
1242 the all-lower-case abbreviation used elsewhere) is COL_PROTOCOL, and the
1243 COL_ value for the "Info" field, giving a summary of the contents of the
1244 packet for that protocol, is COL_INFO.
1246 A value for a column should only be added if the user specified that it
1247 be displayed; to check whether a given column is to be displayed, call
1248 'check_col' with the COL_ value for that field as an argument - it will
1249 return TRUE if the column is to be displayed and FALSE if it is not to
1252 The value for a column can be specified with one of several functions,
1253 all of which take the 'fd' argument to the dissector as their first
1254 argument, and the COL_ value for the column as their second argument.
1256 1.5.1 The col_set_str function.
1258 'col_set_str' takes a string as its third argument, and sets the value
1259 for the column to that value. It assumes that the pointer passed to it
1260 points to a string constant or a static "const" array, not to a
1261 variable, as it doesn't copy the string, it merely saves the pointer
1262 value; the argument can itself be a variable, as long as it always
1263 points to a string constant or a static "const" array.
1265 It is more efficient than 'col_add_str' or 'col_add_fstr'; however, if
1266 the dissector will be using 'col_append_str' or 'col_append_fstr" to
1267 append more information to the column, the string will have to be copied
1268 anyway, so it's best to use 'col_add_str' rather than 'col_set_str' in
1271 For example, to set the "Protocol" column
1274 if (check_col(pinfo->cinfo, COL_PROTOCOL))
1275 col_set_str(pinfo->cinfo, COL_PROTOCOL, "PROTOABBREV");
1278 1.5.2 The col_add_str function.
1280 'col_add_str' takes a string as its third argument, and sets the value
1281 for the column to that value. It takes the same arguments as
1282 'col_set_str', but copies the string, so that if the string is, for
1283 example, an automatic variable that won't remain in scope when the
1284 dissector returns, it's safe to use.
1287 1.5.3 The col_add_fstr function.
1289 'col_add_fstr' takes a 'printf'-style format string as its third
1290 argument, and 'printf'-style arguments corresponding to '%' format
1291 items in that string as its subsequent arguments. For example, to set
1292 the "Info" field to "<XXX> request, <N> bytes", where "reqtype" is a
1293 string containing the type of the request in the packet and "n" is an
1294 unsigned integer containing the number of bytes in the request:
1296 if (check_col(pinfo->cinfo, COL_INFO))
1297 col_add_fstr(pinfo->cinfo, COL_INFO, "%s request, %u bytes",
1300 Don't use 'col_add_fstr' with a format argument of just "%s" -
1301 'col_add_str', or possibly even 'col_set_str' if the string that matches
1302 the "%s" is a static constant string, will do the same job more
1306 1.5.4 The col_clear function.
1308 If the Info column will be filled with information from the packet, that
1309 means that some data will be fetched from the packet before the Info
1310 column is filled in. If the packet is so small that the data in
1311 question cannot be fetched, the routines to fetch the data will throw an
1312 exception (see the comment at the beginning about tvbuffers improving
1313 the handling of short packets - the tvbuffers keep track of how much
1314 data is in the packet, and throw an exception on an attempt to fetch
1315 data past the end of the packet, so that the dissector won't process
1316 bogus data), causing the Info column not to be filled in.
1318 This means that the Info column will have data for the previous
1319 protocol, which would be confusing if, for example, the Protocol column
1320 had data for this protocol.
1322 Therefore, before a dissector fetches any data whatsoever from the
1323 packet (unless it's a heuristic dissector fetching data to determine
1324 whether the packet is one that it should dissect, in which case it
1325 should check, before fetching the data, whether there's any data to
1326 fetch; if there isn't, it should return FALSE), it should set the
1327 Protocol column and the Info column.
1329 If the Protocol column will ultimately be set to, for example, a value
1330 containing a protocol version number, with the version number being a
1331 field in the packet, the dissector should, before fetching the version
1332 number field or any other field from the packet, set it to a value
1333 without a version number, using 'col_set_str', and should later set it
1334 to a value with the version number after it's fetched the version
1337 If the Info column will ultimately be set to a value containing
1338 information from the packet, the dissector should, before fetching any
1339 fields from the packet, clear the column using 'col_clear' (which is
1340 more efficient than clearing it by calling 'col_set_str' or
1341 'col_add_str' with a null string), and should later set it to the real
1342 string after it's fetched the data to use when doing that.
1345 1.5.5 The col_append_str function.
1347 Sometimes the value of a column, especially the "Info" column, can't be
1348 conveniently constructed at a single point in the dissection process;
1349 for example, it might contain small bits of information from many of the
1350 fields in the packet. 'col_append_str' takes, as arguments, the same
1351 arguments as 'col_add_str', but the string is appended to the end of the
1352 current value for the column, rather than replacing the value for that
1353 column. (Note that no blank separates the appended string from the
1354 string to which it is appended; if you want a blank there, you must add
1355 it yourself as part of the string being appended.)
1358 1.5.6 The col_append_fstr function.
1360 'col_append_fstr' is to 'col_add_fstr' as 'col_append_str' is to
1361 'col_add_str' - it takes, as arguments, the same arguments as
1362 'col_add_fstr', but the formatted string is appended to the end of the
1363 current value for the column, rather than replacing the value for that
1366 1.5.7 The col_append_sep_str and col_append_sep_fstr functions.
1368 In specific situations the developer knows that a column's value will be
1369 created in a stepwise manner, where the appended values are listed. Both
1370 'col_append_sep_str' and 'col_append_sep_fstr' functions will add an item
1371 separator between two consecutive items, and will not add the separator at the
1372 beginning of the column. The remainder of the work both functions do is
1373 identical to what 'col_append_str' and 'col_append_fstr' do.
1375 1.5.8 The col_set_fence and col_prepend_fence_fstr functions.
1377 Sometimes a dissector may be called multiple times for different PDUs in the
1378 same frame (for example in the case of SCTP chunk bundling: several upper
1379 layer data packets may be contained in one SCTP packet). If the upper layer
1380 dissector calls 'col_set_str()' or 'col_clear()' on the Info column when it
1381 begins dissecting each of those PDUs then when the frame is fully dissected
1382 the Info column would contain only the string from the last PDU in the frame.
1383 The 'col_set_fence' function erects a "fence" in the column that prevents
1384 subsequent 'col_...' calls from clearing the data currently in that column.
1385 For example, the SCTP dissector calls 'col_set_fence' on the Info column
1386 after it has called any subdissectors for that chunk so that subdissectors
1387 of any subsequent chunks may only append to the Info column.
1388 'col_prepend_fence_fstr' prepends data before a fence (moving it if
1389 necessary). It will create a fence at the end of the prended data if the
1390 fence does not already exist.
1393 1.5.9 The col_set_time function.
1395 The 'col_set_time' function takes an nstime value as its third argument.
1396 This nstime value is a relative value and will be added as such to the
1397 column. The fourth argument is the filtername holding this value. This
1398 way, rightclicking on the column makes it possible to build a filter
1399 based on the time-value.
1403 if (check_col(pinfo->cinfo, COL_REL_CONV_TIME)) {
1404 nstime_delta(&ts, &pinfo->fd->abs_ts, &tcpd->ts_first);
1405 col_set_time(pinfo->cinfo, COL_REL_CONV_TIME, &ts, "tcp.time_relative");
1409 1.6 Constructing the protocol tree.
1411 The middle pane of the main window, and the topmost pane of a packet
1412 popup window, are constructed from the "protocol tree" for a packet.
1414 The protocol tree, or proto_tree, is a GNode, the N-way tree structure
1415 available within GLIB. Of course the protocol dissectors don't care
1416 what a proto_tree really is; they just pass the proto_tree pointer as an
1417 argument to the routines which allow them to add items and new branches
1420 When a packet is selected in the packet-list pane, or a packet popup
1421 window is created, a new logical protocol tree (proto_tree) is created.
1422 The pointer to the proto_tree (in this case, 'protocol tree'), is passed
1423 to the top-level protocol dissector, and then to all subsequent protocol
1424 dissectors for that packet, and then the GUI tree is drawn via
1427 The logical proto_tree needs to know detailed information about the protocols
1428 and fields about which information will be collected from the dissection
1429 routines. By strictly defining (or "typing") the data that can be attached to a
1430 proto tree, searching and filtering becomes possible. This means that for
1431 every protocol and field (which I also call "header fields", since they are
1432 fields in the protocol headers) which might be attached to a tree, some
1433 information is needed.
1435 Every dissector routine will need to register its protocols and fields
1436 with the central protocol routines (in proto.c). At first I thought I
1437 might keep all the protocol and field information about all the
1438 dissectors in one file, but decentralization seemed like a better idea.
1439 That one file would have gotten very large; one small change would have
1440 required a re-compilation of the entire file. Also, by allowing
1441 registration of protocols and fields at run-time, loadable modules of
1442 protocol dissectors (perhaps even user-supplied) is feasible.
1444 To do this, each protocol should have a register routine, which will be
1445 called when Wireshark starts. The code to call the register routines is
1446 generated automatically; to arrange that a protocol's register routine
1447 be called at startup:
1449 the file containing a dissector's "register" routine must be
1450 added to "DISSECTOR_SRC" in "epan/dissectors/Makefile.common";
1452 the "register" routine must have a name of the form
1453 "proto_register_XXX";
1455 the "register" routine must take no argument, and return no
1458 the "register" routine's name must appear in the source file
1459 either at the beginning of the line, or preceded only by "void "
1460 at the beginning of the line (that would typically be the
1461 definition) - other white space shouldn't cause a problem, e.g.:
1463 void proto_register_XXX(void) {
1472 proto_register_XXX( void )
1479 and so on should work.
1481 For every protocol or field that a dissector wants to register, a variable of
1482 type int needs to be used to keep track of the protocol. The IDs are
1483 needed for establishing parent/child relationships between protocols and
1484 fields, as well as associating data with a particular field so that it
1485 can be stored in the logical tree and displayed in the GUI protocol
1488 Some dissectors will need to create branches within their tree to help
1489 organize header fields. These branches should be registered as header
1490 fields. Only true protocols should be registered as protocols. This is
1491 so that a display filter user interface knows how to distinguish
1492 protocols from fields.
1494 A protocol is registered with the name of the protocol and its
1497 Here is how the frame "protocol" is registered.
1501 proto_frame = proto_register_protocol (
1503 /* short name */ "Frame",
1504 /* abbrev */ "frame" );
1506 A header field is also registered with its name and abbreviation, but
1507 information about its data type is needed. It helps to look at
1508 the header_field_info struct to see what information is expected:
1510 struct header_field_info {
1515 const void *strings;
1523 A string representing the name of the field. This is the name
1524 that will appear in the graphical protocol tree. It must be a non-empty
1529 A string with an abbreviation of the field. We concatenate the
1530 abbreviation of the parent protocol with an abbreviation for the field,
1531 using a period as a separator. For example, the "src" field in an IP packet
1532 would have "ip.src" as an abbreviation. It is acceptable to have
1533 multiple levels of periods if, for example, you have fields in your
1534 protocol that are then subdivided into subfields. For example, TRMAC
1535 has multiple error fields, so the abbreviations follow this pattern:
1536 "trmac.errors.iso", "trmac.errors.noniso", etc.
1538 The abbreviation is the identifier used in a display filter. If it is
1539 an empty string then the field will not be filterable.
1543 The type of value this field holds. The current field types are:
1545 FT_NONE No field type. Used for fields that
1546 aren't given a value, and that can only
1547 be tested for presence or absence; a
1548 field that represents a data structure,
1549 with a subtree below it containing
1550 fields for the members of the structure,
1551 or that represents an array with a
1552 subtree below it containing fields for
1553 the members of the array, might be an
1555 FT_PROTOCOL Used for protocols which will be placing
1556 themselves as top-level items in the
1557 "Packet Details" pane of the UI.
1558 FT_BOOLEAN 0 means "false", any other value means
1560 FT_FRAMENUM A frame number; if this is used, the "Go
1561 To Corresponding Frame" menu item can
1563 FT_UINT8 An 8-bit unsigned integer.
1564 FT_UINT16 A 16-bit unsigned integer.
1565 FT_UINT24 A 24-bit unsigned integer.
1566 FT_UINT32 A 32-bit unsigned integer.
1567 FT_UINT64 A 64-bit unsigned integer.
1568 FT_INT8 An 8-bit signed integer.
1569 FT_INT16 A 16-bit signed integer.
1570 FT_INT24 A 24-bit signed integer.
1571 FT_INT32 A 32-bit signed integer.
1572 FT_INT64 A 64-bit signed integer.
1573 FT_FLOAT A single-precision floating point number.
1574 FT_DOUBLE A double-precision floating point number.
1575 FT_ABSOLUTE_TIME Seconds (4 bytes) and nanoseconds (4 bytes)
1576 of time displayed as month name, month day,
1577 year, hours, minutes, and seconds with 9
1578 digits after the decimal point.
1579 FT_RELATIVE_TIME Seconds (4 bytes) and nanoseconds (4 bytes)
1580 of time displayed as seconds and 9 digits
1581 after the decimal point.
1582 FT_STRING A string of characters, not necessarily
1583 NUL-terminated, but possibly NUL-padded.
1584 This, and the other string-of-characters
1585 types, are to be used for text strings,
1586 not raw binary data.
1587 FT_STRINGZ A NUL-terminated string of characters.
1588 FT_EBCDIC A string of characters, not necessarily
1589 NUL-terminated, but possibly NUL-padded.
1590 The data from the packet is converted from
1591 EBCDIC to ASCII before displaying to the user.
1592 FT_UINT_STRING A counted string of characters, consisting
1593 of a count (represented as an integral value,
1594 of width given in the proto_tree_add_item()
1595 call) followed immediately by that number of
1597 FT_ETHER A six octet string displayed in
1598 Ethernet-address format.
1599 FT_BYTES A string of bytes with arbitrary values;
1600 used for raw binary data.
1601 FT_UINT_BYTES A counted string of bytes, consisting
1602 of a count (represented as an integral value,
1603 of width given in the proto_tree_add_item()
1604 call) followed immediately by that number of
1605 arbitrary values; used for raw binary data.
1606 FT_IPv4 A version 4 IP address (4 bytes) displayed
1607 in dotted-quad IP address format (4
1608 decimal numbers separated by dots).
1609 FT_IPv6 A version 6 IP address (16 bytes) displayed
1610 in standard IPv6 address format.
1611 FT_IPXNET An IPX address displayed in hex as a 6-byte
1612 network number followed by a 6-byte station
1614 FT_GUID A Globally Unique Identifier
1615 FT_OID An ASN.1 Object Identifier
1617 Some of these field types are still not handled in the display filter
1618 routines, but the most common ones are. The FT_UINT* variables all
1619 represent unsigned integers, and the FT_INT* variables all represent
1620 signed integers; the number on the end represent how many bits are used
1621 to represent the number.
1625 The display field has a couple of overloaded uses. This is unfortunate,
1626 but since we're using C as an application programming language, this sometimes
1627 makes for cleaner programs. Right now I still think that overloading
1628 this variable was okay.
1630 For integer fields (FT_UINT* and FT_INT*), this variable represents the
1631 base in which you would like the value displayed. The acceptable bases
1641 BASE_DEC, BASE_HEX, and BASE_OCT are decimal, hexadecimal, and octal,
1642 respectively. BASE_DEC_HEX and BASE_HEX_DEC display value in two bases
1643 (the 1st representation followed by the 2nd in parenthesis).
1645 BASE_CUSTOM allows one to specify a callback function pointer that will
1646 format the value. The function pointer of the same type as defined by
1647 custom_fmt_func_t in epan/proto.h, specifically:
1649 void func(gchar *, guint32);
1651 The first argument is a pointer to a buffer of the ITEM_LABEL_LENGTH size
1652 and the second argument is the value to be formatted.
1654 For FT_BOOLEAN fields that are also bitfields, 'display' is used to tell
1655 the proto_tree how wide the parent bitfield is. With integers this is
1656 not needed since the type of integer itself (FT_UINT8, FT_UINT16,
1657 FT_UINT24, FT_UINT32, etc.) tells the proto_tree how wide the parent
1660 Additionally, BASE_NONE is used for 'display' as a NULL-value. That is,
1661 for non-integers and non-bitfield FT_BOOLEANs, you'll want to use BASE_NONE
1662 in the 'display' field. You may not use BASE_NONE for integers.
1664 It is possible that in the future we will record the endianness of
1665 integers. If so, it is likely that we'll use a bitmask on the display field
1666 so that integers would be represented as BEND|BASE_DEC or LEND|BASE_HEX.
1667 But that has not happened yet.
1671 Some integer fields, of type FT_UINT*, need labels to represent the true
1672 value of a field. You could think of those fields as having an
1673 enumerated data type, rather than an integral data type.
1675 A 'value_string' structure is a way to map values to strings.
1677 typedef struct _value_string {
1682 For fields of that type, you would declare an array of "value_string"s:
1684 static const value_string valstringname[] = {
1685 { INTVAL1, "Descriptive String 1" },
1686 { INTVAL2, "Descriptive String 2" },
1690 (the last entry in the array must have a NULL 'strptr' value, to
1691 indicate the end of the array). The 'strings' field would be set to
1692 'VALS(valstringname)'.
1694 If the field has a numeric rather than an enumerated type, the 'strings'
1695 field would be set to NULL.
1697 If the field has a numeric type that might logically fit in ranges of values
1698 one can use a range_string struct.
1700 Thus a 'range_string' structure is a way to map ranges to strings.
1702 typedef struct _range_string {
1705 const gchar *strptr;
1708 For fields of that type, you would declare an array of "range_string"s:
1710 static const range_string rvalstringname[] = {
1711 { INTVAL_MIN1, INTVALMAX1, "Descriptive String 1" },
1712 { INTVAL_MIN2, INTVALMAX2, "Descriptive String 2" },
1716 If INTVAL_MIN equals INTVAL_MAX for a given entry the range_string
1717 behavior collapses to the one of value_string.
1718 For FT_(U)INT* fields that need a 'range_string' struct, the 'strings' field
1719 would be set to 'RVALS(rvalstringname)'. Furthermore, 'display' field must be
1720 ORed with 'BASE_RANGE_STRING' (e.g. BASE_DEC|BASE_RANGE_STRING).
1722 FT_BOOLEANs have a default map of 0 = "False", 1 (or anything else) = "True".
1723 Sometimes it is useful to change the labels for boolean values (e.g.,
1724 to "Yes"/"No", "Fast"/"Slow", etc.). For these mappings, a struct called
1725 true_false_string is used.
1727 typedef struct true_false_string {
1730 } true_false_string;
1732 For Boolean fields for which "False" and "True" aren't the desired
1733 labels, you would declare a "true_false_string"s:
1735 static const true_false_string boolstringname = {
1740 Its two fields are pointers to the string representing truth, and the
1741 string representing falsehood. For FT_BOOLEAN fields that need a
1742 'true_false_string' struct, the 'strings' field would be set to
1743 'TFS(&boolstringname)'.
1745 If the Boolean field is to be displayed as "False" or "True", the
1746 'strings' field would be set to NULL.
1748 Wireshark predefines a whole range of ready made "true_false_string"s
1749 in tfs.h, included via packet.h.
1753 If the field is a bitfield, then the bitmask is the mask which will
1754 leave only the bits needed to make the field when ANDed with a value.
1755 The proto_tree routines will calculate 'bitshift' automatically
1756 from 'bitmask', by finding the rightmost set bit in the bitmask.
1757 This shift is applied before applying string mapping functions or
1759 If the field is not a bitfield, then bitmask should be set to 0.
1763 This is a string giving a proper description of the field. It should be
1764 at least one grammatically complete sentence, or NULL in which case the
1766 It is meant to provide a more detailed description of the field than the
1767 name alone provides. This information will be used in the man page, and
1768 in a future GUI display-filter creation tool. We might also add tooltips
1769 to the labels in the GUI protocol tree, in which case the blurb would
1770 be used as the tooltip text.
1773 1.6.1 Field Registration.
1775 Protocol registration is handled by creating an instance of the
1776 header_field_info struct (or an array of such structs), and
1777 calling the registration function along with the registration ID of
1778 the protocol that is the parent of the fields. Here is a complete example:
1780 static int proto_eg = -1;
1781 static int hf_field_a = -1;
1782 static int hf_field_b = -1;
1784 static hf_register_info hf[] = {
1787 { "Field A", "proto.field_a", FT_UINT8, BASE_HEX, NULL,
1788 0xf0, "Field A represents Apples", HFILL }},
1791 { "Field B", "proto.field_b", FT_UINT16, BASE_DEC, VALS(vs),
1792 0x0, "Field B represents Bananas", HFILL }}
1795 proto_eg = proto_register_protocol("Example Protocol",
1797 proto_register_field_array(proto_eg, hf, array_length(hf));
1799 Be sure that your array of hf_register_info structs is declared 'static',
1800 since the proto_register_field_array() function does not create a copy
1801 of the information in the array... it uses that static copy of the
1802 information that the compiler created inside your array. Here's the
1803 layout of the hf_register_info struct:
1805 typedef struct hf_register_info {
1806 int *p_id; /* pointer to parent variable */
1807 header_field_info hfinfo;
1810 Also be sure to use the handy array_length() macro found in packet.h
1811 to have the compiler compute the array length for you at compile time.
1813 If you don't have any fields to register, do *NOT* create a zero-length
1814 "hf" array; not all compilers used to compile Wireshark support them.
1815 Just omit the "hf" array, and the "proto_register_field_array()" call,
1818 It is OK to have header fields with a different format be registered with
1819 the same abbreviation. For instance, the following is valid:
1821 static hf_register_info hf[] = {
1823 { &hf_field_8bit, /* 8-bit version of proto.field */
1824 { "Field (8 bit)", "proto.field", FT_UINT8, BASE_DEC, NULL,
1825 0x00, "Field represents FOO", HFILL }},
1827 { &hf_field_32bit, /* 32-bit version of proto.field */
1828 { "Field (32 bit)", "proto.field", FT_UINT32, BASE_DEC, NULL,
1829 0x00, "Field represents FOO", HFILL }}
1832 This way a filter expression can match a header field, irrespective of the
1833 representation of it in the specific protocol context. This is interesting
1834 for protocols with variable-width header fields.
1836 The HFILL macro at the end of the struct will set reasonable default values
1837 for internally used fields.
1839 1.6.2 Adding Items and Values to the Protocol Tree.
1841 A protocol item is added to an existing protocol tree with one of a
1842 handful of proto_XXX_DO_YYY() functions.
1844 Remember that it only makes sense to add items to a protocol tree if its
1845 proto_tree pointer is not null. Should you add an item to a NULL tree, then
1846 the proto_XXX_DO_YYY() function will immediately return. The cost of this
1847 function call can be avoided by checking for the tree pointer.
1849 Subtrees can be made with the proto_item_add_subtree() function:
1851 item = proto_tree_add_item(....);
1852 new_tree = proto_item_add_subtree(item, tree_type);
1854 This will add a subtree under the item in question; a subtree can be
1855 created under an item made by any of the "proto_tree_add_XXX" functions,
1856 so that the tree can be given an arbitrary depth.
1858 Subtree types are integers, assigned by
1859 "proto_register_subtree_array()". To register subtree types, pass an
1860 array of pointers to "gint" variables to hold the subtree type values to
1861 "proto_register_subtree_array()":
1863 static gint ett_eg = -1;
1864 static gint ett_field_a = -1;
1866 static gint *ett[] = {
1871 proto_register_subtree_array(ett, array_length(ett));
1873 in your "register" routine, just as you register the protocol and the
1874 fields for that protocol.
1876 There are several functions that the programmer can use to add either
1877 protocol or field labels to the proto_tree:
1880 proto_tree_add_item(tree, id, tvb, start, length, little_endian);
1883 proto_tree_add_none_format(tree, id, tvb, start, length, format, ...);
1886 proto_tree_add_protocol_format(tree, id, tvb, start, length,
1890 proto_tree_add_bytes(tree, id, tvb, start, length, start_ptr);
1893 proto_tree_add_bytes_format(tree, id, tvb, start, length, start_ptr,
1897 proto_tree_add_bytes_format_value(tree, id, tvb, start, length,
1898 start_ptr, format, ...);
1901 proto_tree_add_time(tree, id, tvb, start, length, value_ptr);
1904 proto_tree_add_time_format(tree, id, tvb, start, length, value_ptr,
1908 proto_tree_add_time_format_value(tree, id, tvb, start, length,
1909 value_ptr, format, ...);
1912 proto_tree_add_ipxnet(tree, id, tvb, start, length, value);
1915 proto_tree_add_ipxnet_format(tree, id, tvb, start, length, value,
1919 proto_tree_add_ipxnet_format_value(tree, id, tvb, start, length,
1920 value, format, ...);
1923 proto_tree_add_ipv4(tree, id, tvb, start, length, value);
1926 proto_tree_add_ipv4_format(tree, id, tvb, start, length, value,
1930 proto_tree_add_ipv4_format_value(tree, id, tvb, start, length,
1931 value, format, ...);
1934 proto_tree_add_ipv6(tree, id, tvb, start, length, value_ptr);
1937 proto_tree_add_ipv6_format(tree, id, tvb, start, length, value_ptr,
1941 proto_tree_add_ipv6_format_value(tree, id, tvb, start, length,
1942 value_ptr, format, ...);
1945 proto_tree_add_ether(tree, id, tvb, start, length, value_ptr);
1948 proto_tree_add_ether_format(tree, id, tvb, start, length, value_ptr,
1952 proto_tree_add_ether_format_value(tree, id, tvb, start, length,
1953 value_ptr, format, ...);
1956 proto_tree_add_string(tree, id, tvb, start, length, value_ptr);
1959 proto_tree_add_string_format(tree, id, tvb, start, length, value_ptr,
1963 proto_tree_add_string_format_value(tree, id, tvb, start, length,
1964 value_ptr, format, ...);
1967 proto_tree_add_boolean(tree, id, tvb, start, length, value);
1970 proto_tree_add_boolean_format(tree, id, tvb, start, length, value,
1974 proto_tree_add_boolean_format_value(tree, id, tvb, start, length,
1975 value, format, ...);
1978 proto_tree_add_float(tree, id, tvb, start, length, value);
1981 proto_tree_add_float_format(tree, id, tvb, start, length, value,
1985 proto_tree_add_float_format_value(tree, id, tvb, start, length,
1986 value, format, ...);
1989 proto_tree_add_double(tree, id, tvb, start, length, value);
1992 proto_tree_add_double_format(tree, id, tvb, start, length, value,
1996 proto_tree_add_double_format_value(tree, id, tvb, start, length,
1997 value, format, ...);
2000 proto_tree_add_uint(tree, id, tvb, start, length, value);
2003 proto_tree_add_uint_format(tree, id, tvb, start, length, value,
2007 proto_tree_add_uint_format_value(tree, id, tvb, start, length,
2008 value, format, ...);
2011 proto_tree_add_uint64(tree, id, tvb, start, length, value);
2014 proto_tree_add_uint64_format(tree, id, tvb, start, length, value,
2018 proto_tree_add_uint64_format_value(tree, id, tvb, start, length,
2019 value, format, ...);
2022 proto_tree_add_int(tree, id, tvb, start, length, value);
2025 proto_tree_add_int_format(tree, id, tvb, start, length, value,
2029 proto_tree_add_int_format_value(tree, id, tvb, start, length,
2030 value, format, ...);
2033 proto_tree_add_int64(tree, id, tvb, start, length, value);
2036 proto_tree_add_int64_format(tree, id, tvb, start, length, value,
2040 proto_tree_add_int64_format_value(tree, id, tvb, start, length,
2041 value, format, ...);
2044 proto_tree_add_text(tree, tvb, start, length, format, ...);
2047 proto_tree_add_text_valist(tree, tvb, start, length, format, ap);
2050 proto_tree_add_guid(tree, id, tvb, start, length, value_ptr);
2053 proto_tree_add_guid_format(tree, id, tvb, start, length, value_ptr,
2057 proto_tree_add_guid_format_value(tree, id, tvb, start, length,
2058 value_ptr, format, ...);
2061 proto_tree_add_oid(tree, id, tvb, start, length, value_ptr);
2064 proto_tree_add_oid_format(tree, id, tvb, start, length, value_ptr,
2068 proto_tree_add_oid_format_value(tree, id, tvb, start, length,
2069 value_ptr, format, ...);
2072 proto_tree_add_bits_item(tree, id, tvb, bit_offset, no_of_bits,
2076 proto_tree_add_bits_ret_val(tree, id, tvb, bit_offset, no_of_bits,
2077 return_value, little_endian);
2080 proto_tree_add_bitmask(tree, tvb, start, header, ett, fields,
2084 proto_tree_add_bitmask_text(tree, tvb, offset, len, name, fallback,
2085 ett, fields, little_endian, flags);
2087 The 'tree' argument is the tree to which the item is to be added. The
2088 'tvb' argument is the tvbuff from which the item's value is being
2089 extracted; the 'start' argument is the offset from the beginning of that
2090 tvbuff of the item being added, and the 'length' argument is the length,
2091 in bytes, of the item, bit_offset is the offset in bits and no_of_bits
2092 is the lenght in bits.
2094 The length of some items cannot be determined until the item has been
2095 dissected; to add such an item, add it with a length of -1, and, when the
2096 dissection is complete, set the length with 'proto_item_set_len()':
2099 proto_item_set_len(ti, length);
2101 The "ti" argument is the value returned by the call that added the item
2102 to the tree, and the "length" argument is the length of the item.
2104 proto_tree_add_item()
2105 ---------------------
2106 proto_tree_add_item is used when you wish to do no special formatting.
2107 The item added to the GUI tree will contain the name (as passed in the
2108 proto_register_*() function) and a value. The value will be fetched
2109 from the tvbuff by proto_tree_add_item(), based on the type of the field
2110 and, for integral and Boolean fields, the byte order of the value; the
2111 byte order is specified by the 'little_endian' argument, which is TRUE
2112 if the value is little-endian and FALSE if it is big-endian.
2114 Now that definitions of fields have detailed information about bitfield
2115 fields, you can use proto_tree_add_item() with no extra processing to
2116 add bitfield values to your tree. Here's an example. Take the Format
2117 Identifier (FID) field in the Transmission Header (TH) portion of the SNA
2118 protocol. The FID is the high nibble of the first byte of the TH. The
2119 FID would be registered like this:
2121 name = "Format Identifier"
2122 abbrev = "sna.th.fid"
2125 strings = sna_th_fid_vals
2128 The bitmask contains the value which would leave only the FID if bitwise-ANDed
2129 against the parent field, the first byte of the TH.
2131 The code to add the FID to the tree would be;
2133 proto_tree_add_item(bf_tree, hf_sna_th_fid, tvb, offset, 1, TRUE);
2135 The definition of the field already has the information about bitmasking
2136 and bitshifting, so it does the work of masking and shifting for us!
2137 This also means that you no longer have to create value_string structs
2138 with the values bitshifted. The value_string for FID looks like this,
2139 even though the FID value is actually contained in the high nibble.
2140 (You'd expect the values to be 0x0, 0x10, 0x20, etc.)
2142 /* Format Identifier */
2143 static const value_string sna_th_fid_vals[] = {
2144 { 0x0, "SNA device <--> Non-SNA Device" },
2145 { 0x1, "Subarea Node <--> Subarea Node" },
2146 { 0x2, "Subarea Node <--> PU2" },
2147 { 0x3, "Subarea Node or SNA host <--> Subarea Node" },
2150 { 0xf, "Adjaced Subarea Nodes" },
2154 The final implication of this is that display filters work the way you'd
2155 naturally expect them to. You'd type "sna.th.fid == 0xf" to find Adjacent
2156 Subarea Nodes. The user does not have to shift the value of the FID to
2157 the high nibble of the byte ("sna.th.fid == 0xf0") as was necessary
2160 proto_tree_add_protocol_format()
2161 --------------------------------
2162 proto_tree_add_protocol_format is used to add the top-level item for the
2163 protocol when the dissector routine wants complete control over how the
2164 field and value will be represented on the GUI tree. The ID value for
2165 the protocol is passed in as the "id" argument; the rest of the
2166 arguments are a "printf"-style format and any arguments for that format.
2167 The caller must include the name of the protocol in the format; it is
2168 not added automatically as in proto_tree_add_item().
2170 proto_tree_add_none_format()
2171 ----------------------------
2172 proto_tree_add_none_format is used to add an item of type FT_NONE.
2173 The caller must include the name of the field in the format; it is
2174 not added automatically as in proto_tree_add_item().
2176 proto_tree_add_bytes()
2177 proto_tree_add_time()
2178 proto_tree_add_ipxnet()
2179 proto_tree_add_ipv4()
2180 proto_tree_add_ipv6()
2181 proto_tree_add_ether()
2182 proto_tree_add_string()
2183 proto_tree_add_boolean()
2184 proto_tree_add_float()
2185 proto_tree_add_double()
2186 proto_tree_add_uint()
2187 proto_tree_add_uint64()
2188 proto_tree_add_int()
2189 proto_tree_add_int64()
2190 proto_tree_add_guid()
2191 proto_tree_add_oid()
2192 ------------------------
2193 These routines are used to add items to the protocol tree if either:
2195 the value of the item to be added isn't just extracted from the
2196 packet data, but is computed from data in the packet;
2198 the value was fetched into a variable.
2200 The 'value' argument has the value to be added to the tree.
2202 NOTE: in all cases where the 'value' argument is a pointer, a copy is
2203 made of the object pointed to; if you have dynamically allocated a
2204 buffer for the object, that buffer will not be freed when the protocol
2205 tree is freed - you must free the buffer yourself when you don't need it
2208 For proto_tree_add_bytes(), the 'value_ptr' argument is a pointer to a
2211 For proto_tree_add_time(), the 'value_ptr' argument is a pointer to an
2212 "nstime_t", which is a structure containing the time to be added; it has
2213 'secs' and 'nsecs' members, giving the integral part and the fractional
2214 part of a time in units of seconds, with 'nsecs' being the number of
2215 nanoseconds. For absolute times, "secs" is a UNIX-style seconds since
2216 January 1, 1970, 00:00:00 GMT value.
2218 For proto_tree_add_ipxnet(), the 'value' argument is a 32-bit IPX
2221 For proto_tree_add_ipv4(), the 'value' argument is a 32-bit IPv4
2222 address, in network byte order.
2224 For proto_tree_add_ipv6(), the 'value_ptr' argument is a pointer to a
2225 128-bit IPv6 address.
2227 For proto_tree_add_ether(), the 'value_ptr' argument is a pointer to a
2230 For proto_tree_add_string(), the 'value_ptr' argument is a pointer to a
2233 For proto_tree_add_boolean(), the 'value' argument is a 32-bit integer.
2234 It is masked and shifted as defined by the field info after which zero
2235 means "false", and non-zero means "true".
2237 For proto_tree_add_float(), the 'value' argument is a 'float' in the
2238 host's floating-point format.
2240 For proto_tree_add_double(), the 'value' argument is a 'double' in the
2241 host's floating-point format.
2243 For proto_tree_add_uint(), the 'value' argument is a 32-bit unsigned
2244 integer value, in host byte order. (This routine cannot be used to add
2247 For proto_tree_add_uint64(), the 'value' argument is a 64-bit unsigned
2248 integer value, in host byte order.
2250 For proto_tree_add_int(), the 'value' argument is a 32-bit signed
2251 integer value, in host byte order. (This routine cannot be used to add
2254 For proto_tree_add_int64(), the 'value' argument is a 64-bit signed
2255 integer value, in host byte order.
2257 For proto_tree_add_guid(), the 'value_ptr' argument is a pointer to an
2260 For proto_tree_add_oid(), the 'value_ptr' argument is a pointer to an
2261 ASN.1 Object Identifier.
2263 proto_tree_add_bytes_format()
2264 proto_tree_add_time_format()
2265 proto_tree_add_ipxnet_format()
2266 proto_tree_add_ipv4_format()
2267 proto_tree_add_ipv6_format()
2268 proto_tree_add_ether_format()
2269 proto_tree_add_string_format()
2270 proto_tree_add_boolean_format()
2271 proto_tree_add_float_format()
2272 proto_tree_add_double_format()
2273 proto_tree_add_uint_format()
2274 proto_tree_add_uint64_format()
2275 proto_tree_add_int_format()
2276 proto_tree_add_int64_format()
2277 proto_tree_add_guid_format()
2278 proto_tree_add_oid_format()
2279 ----------------------------
2280 These routines are used to add items to the protocol tree when the
2281 dissector routine wants complete control over how the field and value
2282 will be represented on the GUI tree. The argument giving the value is
2283 the same as the corresponding proto_tree_add_XXX() function; the rest of
2284 the arguments are a "printf"-style format and any arguments for that
2285 format. The caller must include the name of the field in the format; it
2286 is not added automatically as in the proto_tree_add_XXX() functions.
2288 proto_tree_add_bytes_format_value()
2289 proto_tree_add_time_format_value()
2290 proto_tree_add_ipxnet_format_value()
2291 proto_tree_add_ipv4_format_value()
2292 proto_tree_add_ipv6_format_value()
2293 proto_tree_add_ether_format_value()
2294 proto_tree_add_string_format_value()
2295 proto_tree_add_boolean_format_value()
2296 proto_tree_add_float_format_value()
2297 proto_tree_add_double_format_value()
2298 proto_tree_add_uint_format_value()
2299 proto_tree_add_uint64_format_value()
2300 proto_tree_add_int_format_value()
2301 proto_tree_add_int64_format_value()
2302 proto_tree_add_guid_format_value()
2303 proto_tree_add_oid_format_value()
2304 ------------------------------------
2306 These routines are used to add items to the protocol tree when the
2307 dissector routine wants complete control over how the value will be
2308 represented on the GUI tree. The argument giving the value is the same
2309 as the corresponding proto_tree_add_XXX() function; the rest of the
2310 arguments are a "printf"-style format and any arguments for that format.
2311 With these routines, unlike the proto_tree_add_XXX_format() routines,
2312 the name of the field is added automatically as in the
2313 proto_tree_add_XXX() functions; only the value is added with the format.
2315 proto_tree_add_text()
2316 ---------------------
2317 proto_tree_add_text() is used to add a label to the GUI tree. It will
2318 contain no value, so it is not searchable in the display filter process.
2319 This function was needed in the transition from the old-style proto_tree
2320 to this new-style proto_tree so that Wireshark would still decode all
2321 protocols w/o being able to filter on all protocols and fields.
2322 Otherwise we would have had to cripple Wireshark's functionality while we
2323 converted all the old-style proto_tree calls to the new-style proto_tree
2324 calls. In other words, you should not use this in new code unless you've got
2325 a specific reason (see below).
2327 This can also be used for items with subtrees, which may not have values
2328 themselves - the items in the subtree are the ones with values.
2330 For a subtree, the label on the subtree might reflect some of the items
2331 in the subtree. This means the label can't be set until at least some
2332 of the items in the subtree have been dissected. To do this, use
2333 'proto_item_set_text()' or 'proto_item_append_text()':
2336 proto_item_set_text(proto_item *ti, ...);
2339 proto_item_append_text(proto_item *ti, ...);
2341 'proto_item_set_text()' takes as an argument the value returned by
2342 'proto_tree_add_text()', a 'printf'-style format string, and a set of
2343 arguments corresponding to '%' format items in that string, and replaces
2344 the text for the item created by 'proto_tree_add_text()' with the result
2345 of applying the arguments to the format string.
2347 'proto_item_append_text()' is similar, but it appends to the text for
2348 the item the result of applying the arguments to the format string.
2350 For example, early in the dissection, one might do:
2352 ti = proto_tree_add_text(tree, tvb, offset, length, <label>);
2356 proto_item_set_text(ti, "%s: %s", type, value);
2358 after the "type" and "value" fields have been extracted and dissected.
2359 <label> would be a label giving what information about the subtree is
2360 available without dissecting any of the data in the subtree.
2362 Note that an exception might be thrown when trying to extract the values of
2363 the items used to set the label, if not all the bytes of the item are
2364 available. Thus, one should create the item with text that is as
2365 meaningful as possible, and set it or append additional information to
2366 it as the values needed to supply that information are extracted.
2368 proto_tree_add_text_valist()
2369 ----------------------------
2370 This is like proto_tree_add_text(), but takes, as the last argument, a
2371 'va_list'; it is used to allow routines that take a printf-like
2372 variable-length list of arguments to add a text item to the protocol
2375 proto_tree_add_bits_item()
2376 --------------------------
2377 Adds a number of bits to the protocol tree which does not have to be byte
2378 aligned. The offset and length is in bits.
2381 ..10 1010 10.. .... "value" (formated as FT_ indicates).
2383 proto_tree_add_bits_ret_val()
2384 -----------------------------
2385 Works in the same way but also returns the value of the read bits.
2387 proto_tree_add_bitmask() and proto_tree_add_bitmask_text()
2388 ----------------------------------------------------------
2389 This function provides an easy to use and convenient helper function
2390 to manage many types of common bitmasks that occur in protocols.
2392 This function will dissect a 1/2/3/4 byte large bitmask into its individual
2394 header is an integer type and must be of type FT_[U]INT{8|16|24|32} and
2395 represents the entire width of the bitmask.
2397 'header' and 'ett' are the hf fields and ett field respectively to create an
2398 expansion that covers the 1-4 bytes of the bitmask.
2400 'fields' is a NULL terminated array of pointers to hf fields representing
2401 the individual subfields of the bitmask. These fields must either be integers
2402 of the same byte width as 'header' or of the type FT_BOOLEAN.
2403 Each of the entries in 'fields' will be dissected as an item under the
2404 'header' expansion and also IF the field is a boolean and IF it is set to 1,
2405 then the name of that boolean field will be printed on the 'header' expansion
2406 line. For integer type subfields that have a value_string defined, the
2407 matched string from that value_string will be printed on the expansion line
2410 Example: (from the SCSI dissector)
2411 static int hf_scsi_inq_peripheral = -1;
2412 static int hf_scsi_inq_qualifier = -1;
2413 static int hf_scsi_inq_devtype = -1;
2415 static gint ett_scsi_inq_peripheral = -1;
2417 static const int *peripheal_fields[] = {
2418 &hf_scsi_inq_qualifier,
2419 &hf_scsi_inq_devtype,
2423 /* Qualifier and DeviceType */
2424 proto_tree_add_bitmask(tree, tvb, offset, hf_scsi_inq_peripheral,
2425 ett_scsi_inq_peripheral, peripheal_fields, FALSE);
2428 { &hf_scsi_inq_peripheral,
2429 {"Peripheral", "scsi.inquiry.preipheral", FT_UINT8, BASE_HEX,
2430 NULL, 0, NULL, HFILL}},
2431 { &hf_scsi_inq_qualifier,
2432 {"Qualifier", "scsi.inquiry.qualifier", FT_UINT8, BASE_HEX,
2433 VALS (scsi_qualifier_val), 0xE0, NULL, HFILL}},
2434 { &hf_scsi_inq_devtype,
2435 {"Device Type", "scsi.inquiry.devtype", FT_UINT8, BASE_HEX,
2436 VALS (scsi_devtype_val), SCSI_DEV_BITS, "", HFILL}},
2439 Which provides very pretty dissection of this one byte bitmask.
2441 Peripheral: 0x05, Qualifier: Device type is connected to logical unit, Device Type: CD-ROM
2442 000. .... = Qualifier: Device type is connected to logical unit (0x00)
2443 ...0 0101 = Device Type: CD-ROM (0x05)
2445 The proto_tree_add_bitmask_text() function is an extended version of
2446 the proto_tree_add_bitmask() function. In addition, it allows to:
2447 - Provide a leading text (e.g. "Flags: ") that will appear before
2448 the comma-separated list of field values
2449 - Provide a fallback text (e.g. "None") that will be appended if
2450 no fields warranted a change to the top-level title.
2451 - Using flags, specify which fields will affect the top-level title.
2453 There are the following flags defined:
2455 BMT_NO_APPEND - the title is taken "as-is" from the 'name' argument.
2456 BMT_NO_INT - only boolean flags are added to the title.
2457 BMT_NO_FALSE - boolean flags are only added to the title if they are set.
2458 BMT_NO_TFS - only add flag name to the title, do not use true_false_string
2460 The proto_tree_add_bitmask() behavior can be obtained by providing
2461 both 'name' and 'fallback' arguments as NULL, and a flags of
2462 (BMT_NO_FALSE|BMT_NO_TFS).
2464 PROTO_ITEM_SET_GENERATED()
2465 --------------------------
2466 PROTO_ITEM_SET_GENERATED is used to mark fields as not being read from the
2467 captured data directly, but infered from one or more values.
2469 One of the primary uses of this is the presentation of verification of
2470 checksums. Every IP packet has a checksum line, which can present the result
2471 of the checksum verification, if enabled in the preferences. The result is
2472 presented as a subtree, where the result is enclosed in square brackets
2473 indicating a generated field.
2475 Header checksum: 0x3d42 [correct]
2479 PROTO_ITEM_SET_HIDDEN()
2480 -----------------------
2481 PROTO_ITEM_SET_HIDDEN is used to hide fields, which have already been added
2482 to the tree, from being visible in the displayed tree.
2484 NOTE that creating hidden fields is actually quite a bad idea from a UI design
2485 perspective because the user (someone who did not write nor has ever seen the
2486 code) has no way of knowing that hidden fields are there to be filtered on
2487 thus defeating the whole purpose of putting them there. A Better Way might
2488 be to add the fields (that might otherwise be hidden) to a subtree where they
2489 won't be seen unless the user opens the subtree--but they can be found if the
2492 One use for hidden fields (which would be better implemented using visible
2493 fields in a subtree) follows: The caller may want a value to be
2494 included in a tree so that the packet can be filtered on this field, but
2495 the representation of that field in the tree is not appropriate. An
2496 example is the token-ring routing information field (RIF). The best way
2497 to show the RIF in a GUI is by a sequence of ring and bridge numbers.
2498 Rings are 3-digit hex numbers, and bridges are single hex digits:
2500 RIF: 001-A-013-9-C0F-B-555
2502 In the case of RIF, the programmer should use a field with no value and
2503 use proto_tree_add_none_format() to build the above representation. The
2504 programmer can then add the ring and bridge values, one-by-one, with
2505 proto_tree_add_item() and hide them with PROTO_ITEM_SET_HIDDEN() so that the
2506 user can then filter on or search for a particular ring or bridge. Here's a
2507 skeleton of how the programmer might code this.
2510 rif = create_rif_string(...);
2512 proto_tree_add_none_format(tree, hf_tr_rif_label, ..., "RIF: %s", rif);
2514 for(i = 0; i < num_rings; i++) {
2517 pi = proto_tree_add_item(tree, hf_tr_rif_ring, ..., FALSE);
2518 PROTO_ITEM_SET_HIDDEN(pi);
2520 for(i = 0; i < num_rings - 1; i++) {
2523 pi = proto_tree_add_item(tree, hf_tr_rif_bridge, ..., FALSE);
2524 PROTO_ITEM_SET_HIDDEN(pi);
2527 The logical tree has these items:
2529 hf_tr_rif_label, text="RIF: 001-A-013-9-C0F-B-555", value = NONE
2530 hf_tr_rif_ring, hidden, value=0x001
2531 hf_tr_rif_bridge, hidden, value=0xA
2532 hf_tr_rif_ring, hidden, value=0x013
2533 hf_tr_rif_bridge, hidden, value=0x9
2534 hf_tr_rif_ring, hidden, value=0xC0F
2535 hf_tr_rif_bridge, hidden, value=0xB
2536 hf_tr_rif_ring, hidden, value=0x555
2538 GUI or print code will not display the hidden fields, but a display
2539 filter or "packet grep" routine will still see the values. The possible
2540 filter is then possible:
2542 tr.rif_ring eq 0x013
2546 PROTO_ITEM_SET_URL is used to mark fields as containing a URL. This can only
2547 be done with fields of type FT_STRING(Z). If these fields are presented they
2548 are underlined, as could be done in a browser. These fields are sensitive to
2549 clicks as well, launching the configured browser with this URL as parameter.
2551 1.7 Utility routines.
2553 1.7.1 match_strval and val_to_str.
2555 A dissector may need to convert a value to a string, using a
2556 'value_string' structure, by hand, rather than by declaring a field with
2557 an associated 'value_string' structure; this might be used, for example,
2558 to generate a COL_INFO line for a frame.
2560 'match_strval()' will do that:
2563 match_strval(guint32 val, const value_string *vs)
2565 It will look up the value 'val' in the 'value_string' table pointed to
2566 by 'vs', and return either the corresponding string, or NULL if the
2567 value could not be found in the table. Note that, unless 'val' is
2568 guaranteed to be a value in the 'value_string' table ("guaranteed" as in
2569 "the code has already checked that it's one of those values" or "the
2570 table handles all possible values of the size of 'val'", not "the
2571 protocol spec says it has to be" - protocol specs do not prevent invalid
2572 packets from being put onto a network or into a purported packet capture
2573 file), you must check whether 'match_strval()' returns NULL, and arrange
2574 that its return value not be dereferenced if it's NULL. 'val_to_str()'
2575 can be used to generate a string for values not found in the table:
2578 val_to_str(guint32 val, const value_string *vs, const char *fmt)
2580 If the value 'val' is found in the 'value_string' table pointed to by
2581 'vs', 'val_to_str' will return the corresponding string; otherwise, it
2582 will use 'fmt' as an 'sprintf'-style format, with 'val' as an argument,
2583 to generate a string, and will return a pointer to that string.
2584 You can use it in a call to generate a COL_INFO line for a frame such as
2586 col_add_fstr(COL_INFO, ", %s", val_to_str(val, table, "Unknown %d"));
2588 1.7.2 match_strrval and rval_to_str.
2590 A dissector may need to convert a range of values to a string, using a
2591 'range_string' structure.
2593 'match_strrval()' will do that:
2596 match_strrval(guint32 val, const range_string *rs)
2598 It will look up the value 'val' in the 'range_string' table pointed to
2599 by 'rs', and return either the corresponding string, or NULL if the
2600 value could not be found in the table. Please note that its base
2601 behavior is inherited from match_strval().
2603 'rval_to_str()' can be used to generate a string for values not found in
2607 rval_to_str(guint32 val, const range_string *rs, const char *fmt)
2609 If the value 'val' is found in the 'range_string' table pointed to by
2610 'rs', 'rval_to_str' will return the corresponding string; otherwise, it
2611 will use 'fmt' as an 'sprintf'-style format, with 'val' as an argument,
2612 to generate a string, and will return a pointer to that string. Please
2613 note that its base behavior is inherited from match_strval().
2615 1.8 Calling Other Dissectors.
2617 As each dissector completes its portion of the protocol analysis, it
2618 is expected to create a new tvbuff of type TVBUFF_SUBSET which
2619 contains the payload portion of the protocol (that is, the bytes
2620 that are relevant to the next dissector).
2622 The syntax for creating a new TVBUFF_SUBSET is:
2624 next_tvb = tvb_new_subset(tvb, offset, length, reported_length)
2627 tvb is the tvbuff that the dissector has been working on. It
2628 can be a tvbuff of any type.
2630 next_tvb is the new TVBUFF_SUBSET.
2632 offset is the byte offset of 'tvb' at which the new tvbuff
2633 should start. The first byte is the 0th byte.
2635 length is the number of bytes in the new TVBUFF_SUBSET. A length
2636 argument of -1 says to use as many bytes as are available in
2639 reported_length is the number of bytes that the current protocol
2640 says should be in the payload. A reported_length of -1 says that
2641 the protocol doesn't say anything about the size of its payload.
2644 An example from packet-ipx.c -
2647 dissect_ipx(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
2650 int reported_length, available_length;
2653 /* Make the next tvbuff */
2655 /* IPX does have a length value in the header, so calculate report_length */
2656 Set this to -1 if there isn't any length information in the protocol
2658 reported_length = ipx_length - IPX_HEADER_LEN;
2660 /* Calculate the available data in the packet,
2661 set this to -1 to use all the data in the tv_buffer
2663 available_length = tvb_length(tvb) - IPX_HEADER_LEN;
2665 /* Create the tvbuffer for the next dissector */
2666 next_tvb = tvb_new_subset(tvb, IPX_HEADER_LEN,
2667 MIN(available_length, reported_length),
2670 /* call the next dissector */
2671 dissector_next( next_tvb, pinfo, tree);
2674 1.9 Editing Makefile.common to add your dissector.
2676 To arrange that your dissector will be built as part of Wireshark, you
2677 must add the name of the source file for your dissector to the
2678 'DISSECTOR_SRC' macro in the 'Makefile.common' file in the 'epan/dissectors'
2679 directory. (Note that this is for modern versions of UNIX, so there
2680 is no 14-character limitation on file names, and for modern versions of
2681 Windows, so there is no 8.3-character limitation on file names.)
2683 If your dissector also has its own header file or files, you must add
2684 them to the 'DISSECTOR_INCLUDES' macro in the 'Makefile.common' file in
2685 the 'epan/dissectors' directory, so that it's included when release source
2686 tarballs are built (otherwise, the source in the release tarballs won't
2689 1.10 Using the SVN source code tree.
2691 See <http://www.wireshark.org/develop.html>
2693 1.11 Submitting code for your new dissector.
2695 - VERIFY that your dissector code does not use prohibited or deprecated APIs
2697 perl <wireshark_root>/tools/checkAPIs.pl <source-filename(s)>
2699 - TEST YOUR DISSECTOR BEFORE SUBMITTING IT.
2700 Use fuzz-test.sh and/or randpkt against your dissector. These are
2701 described at <http://wiki.wireshark.org/FuzzTesting>.
2703 - Subscribe to <mailto:wireshark-dev[AT]wireshark.org> by sending an email to
2704 <mailto:wireshark-dev-request[AT]wireshark.org?body="help"> or visiting
2705 <http://www.wireshark.org/lists/>.
2707 - 'svn add' all the files of your new dissector.
2709 - 'svn diff' the workspace and save the result to a file.
2711 - Edit the diff file - remove any changes unrelated to your new dissector,
2712 e.g. changes in config.nmake
2714 - Submit a bug report to the Wireshark bug database, found at
2715 <http://bugs.wireshark.org>, qualified as an enhancement and attach your
2716 diff file there. Set the review request flag to '?' so it will pop up in
2717 the patch review list.
2719 - Create a Wiki page on the protocol at <http://wiki.wireshark.org>.
2720 A template is provided so it is easy to setup in a consistent style.
2722 - If possible, add sample capture files to the sample captures page at
2723 <http://wiki.wireshark.org/SampleCaptures>. These files are used by
2724 the automated build system for fuzz testing.
2726 - If you find that you are contributing a lot to wireshark on an ongoing
2727 basis you can request to become a committer which will allow you to
2728 commit files to subversion directly.
2730 2. Advanced dissector topics.
2734 Some of the advanced features are being worked on constantly. When using them
2735 it is wise to check the relevant header and source files for additional details.
2737 2.2 Following "conversations".
2739 In wireshark a conversation is defined as a series of data packets between two
2740 address:port combinations. A conversation is not sensitive to the direction of
2741 the packet. The same conversation will be returned for a packet bound from
2742 ServerA:1000 to ClientA:2000 and the packet from ClientA:2000 to ServerA:1000.
2744 There are five routines that you will use to work with a conversation:
2745 conversation_new, find_conversation, conversation_add_proto_data,
2746 conversation_get_proto_data, and conversation_delete_proto_data.
2749 2.2.1 The conversation_init function.
2751 This is an internal routine for the conversation code. As such you
2752 will not have to call this routine. Just be aware that this routine is
2753 called at the start of each capture and before the packets are filtered
2754 with a display filter. The routine will destroy all stored
2755 conversations. This routine does NOT clean up any data pointers that are
2756 passed in the conversation_new 'data' variable. You are responsible for
2757 this clean up if you pass a malloc'ed pointer in this variable.
2759 See item 2.2.8 for more information about the 'data' pointer.
2762 2.2.2 The conversation_new function.
2764 This routine will create a new conversation based upon two address/port
2765 pairs. If you want to associate with the conversation a pointer to a
2766 private data structure you must use the conversation_add_proto_data
2767 function. The ptype variable is used to differentiate between
2768 conversations over different protocols, i.e. TCP and UDP. The options
2769 variable is used to define a conversation that will accept any destination
2770 address and/or port. Set options = 0 if the destination port and address
2771 are know when conversation_new is called. See section 2.4 for more
2772 information on usage of the options parameter.
2774 The conversation_new prototype:
2775 conversation_t *conversation_new(guint32 setup_frame, address *addr1,
2776 address *addr2, port_type ptype, guint32 port1, guint32 port2,
2780 guint32 setup_frame = The lowest numbered frame for this conversation
2781 address* addr1 = first data packet address
2782 address* addr2 = second data packet address
2783 port_type ptype = port type, this is defined in packet.h
2784 guint32 port1 = first data packet port
2785 guint32 port2 = second data packet port
2786 guint options = conversation options, NO_ADDR2 and/or NO_PORT2
2788 setup_frame indicates the first frame for this conversation, and is used to
2789 distinguish multiple conversations with the same addr1/port1 and addr2/port2
2790 pair that occur within the same capture session.
2792 "addr1" and "port1" are the first address/port pair; "addr2" and "port2"
2793 are the second address/port pair. A conversation doesn't have source
2794 and destination address/port pairs - packets in a conversation go in
2795 both directions - so "addr1"/"port1" may be the source or destination
2796 address/port pair; "addr2"/"port2" would be the other pair.
2798 If NO_ADDR2 is specified, the conversation is set up so that a
2799 conversation lookup will match only the "addr1" address; if NO_PORT2 is
2800 specified, the conversation is set up so that a conversation lookup will
2801 match only the "port1" port; if both are specified, i.e.
2802 NO_ADDR2|NO_PORT2, the conversation is set up so that the lookup will
2803 match only the "addr1"/"port1" address/port pair. This can be used if a
2804 packet indicates that, later in the capture, a conversation will be
2805 created using certain addresses and ports, in the case where the packet
2806 doesn't specify the addresses and ports of both sides.
2808 2.2.3 The find_conversation function.
2810 Call this routine to look up a conversation. If no conversation is found,
2811 the routine will return a NULL value.
2813 The find_conversation prototype:
2815 conversation_t *find_conversation(guint32 frame_num, address *addr_a,
2816 address *addr_b, port_type ptype, guint32 port_a, guint32 port_b,
2820 guint32 frame_num = a frame number to match
2821 address* addr_a = first address
2822 address* addr_b = second address
2823 port_type ptype = port type
2824 guint32 port_a = first data packet port
2825 guint32 port_b = second data packet port
2826 guint options = conversation options, NO_ADDR_B and/or NO_PORT_B
2828 frame_num is a frame number to match. The conversation returned is where
2829 (frame_num >= conversation->setup_frame
2830 && frame_num < conversation->next->setup_frame)
2831 Suppose there are a total of 3 conversations (A, B, and C) that match
2832 addr_a/port_a and addr_b/port_b, where the setup_frame used in
2833 conversation_new() for A, B and C are 10, 50, and 100 respectively. The
2834 frame_num passed in find_conversation is compared to the setup_frame of each
2835 conversation. So if (frame_num >= 10 && frame_num < 50), conversation A is
2836 returned. If (frame_num >= 50 && frame_num < 100), conversation B is returned.
2837 If (frame_num >= 100) conversation C is returned.
2839 "addr_a" and "port_a" are the first address/port pair; "addr_b" and
2840 "port_b" are the second address/port pair. Again, as a conversation
2841 doesn't have source and destination address/port pairs, so
2842 "addr_a"/"port_a" may be the source or destination address/port pair;
2843 "addr_b"/"port_b" would be the other pair. The search will match the
2844 "a" address/port pair against both the "1" and "2" address/port pairs,
2845 and match the "b" address/port pair against both the "2" and "1"
2846 address/port pairs; you don't have to worry about which side the "a" or
2847 "b" pairs correspond to.
2849 If the NO_ADDR_B flag was specified to "find_conversation()", the
2850 "addr_b" address will be treated as matching any "wildcarded" address;
2851 if the NO_PORT_B flag was specified, the "port_b" port will be treated
2852 as matching any "wildcarded" port. If both flags are specified, i.e.
2853 NO_ADDR_B|NO_PORT_B, the "addr_b" address will be treated as matching
2854 any "wildcarded" address and the "port_b" port will be treated as
2855 matching any "wildcarded" port.
2858 2.2.4 The conversation_add_proto_data function.
2860 Once you have created a conversation with conversation_new, you can
2861 associate data with it using this function.
2863 The conversation_add_proto_data prototype:
2865 void conversation_add_proto_data(conversation_t *conv, int proto,
2869 conversation_t *conv = the conversation in question
2870 int proto = registered protocol number
2871 void *data = dissector data structure
2873 "conversation" is the value returned by conversation_new. "proto" is a
2874 unique protocol number created with proto_register_protocol. Protocols
2875 are typically registered in the proto_register_XXXX section of your
2876 dissector. "data" is a pointer to the data you wish to associate with the
2877 conversation. Using the protocol number allows several dissectors to
2878 associate data with a given conversation.
2881 2.2.5 The conversation_get_proto_data function.
2883 After you have located a conversation with find_conversation, you can use
2884 this function to retrieve any data associated with it.
2886 The conversation_get_proto_data prototype:
2888 void *conversation_get_proto_data(conversation_t *conv, int proto);
2891 conversation_t *conv = the conversation in question
2892 int proto = registered protocol number
2894 "conversation" is the conversation created with conversation_new. "proto"
2895 is a unique protocol number created with proto_register_protocol,
2896 typically in the proto_register_XXXX portion of a dissector. The function
2897 returns a pointer to the data requested, or NULL if no data was found.
2900 2.2.6 The conversation_delete_proto_data function.
2902 After you are finished with a conversation, you can remove your association
2903 with this function. Please note that ONLY the conversation entry is
2904 removed. If you have allocated any memory for your data, you must free it
2907 The conversation_delete_proto_data prototype:
2909 void conversation_delete_proto_data(conversation_t *conv, int proto);
2912 conversation_t *conv = the conversation in question
2913 int proto = registered protocol number
2915 "conversation" is the conversation created with conversation_new. "proto"
2916 is a unique protocol number created with proto_register_protocol,
2917 typically in the proto_register_XXXX portion of a dissector.
2920 2.2.7 Using timestamps relative to the conversation
2922 There is a framework to calculate timestamps relative to the start of the
2923 conversation. First of all the timestamp of the first packet that has been
2924 seen in the conversation must be kept in the protocol data to be able
2925 to calculate the timestamp of the current packet relative to the start
2926 of the conversation. The timestamp of the last packet that was seen in the
2927 conversation should also be kept in the protocol data. This way the
2928 delta time between the current packet and the previous packet in the
2929 conversation can be calculated.
2931 So add the following items to the struct that is used for the protocol data:
2936 The ts_prev value should only be set during the first run through the
2937 packets (ie pinfo->fd->flags.visited is false).
2939 Next step is to use the per-packet information (described in section 2.5)
2940 to keep the calculated delta timestamp, as it can only be calculated
2941 on the first run through the packets. This is because a packet can be
2942 selected in random order once the whole file has been read.
2944 After calculating the conversation timestamps, it is time to put them in
2945 the appropriate columns with the function 'col_set_time' (described in
2946 section 1.5.9). There are two columns for conversation timestamps:
2948 COL_REL_CONV_TIME, /* Relative time to beginning of conversation */
2949 COL_DELTA_CONV_TIME,/* Delta time to last frame in conversation */
2951 Last but not least, there MUST be a preference in each dissector that
2952 uses conversation timestamps that makes it possible to enable and
2953 disable the calculation of conversation timestamps. The main argument
2954 for this is that a higher level conversation is able to overwrite
2955 the values of lowel level conversations in these two columns. Being
2956 able to actively select which protocols may overwrite the conversation
2957 timestamp columns gives the user the power to control these columns.
2958 (A second reason is that conversation timestamps use the per-packet
2959 data structure which uses additional memory, which should be avoided
2960 if these timestamps are not needed)
2962 Have a look at the differences to packet-tcp.[ch] in SVN 22966 and
2963 SVN 23058 to see the implementation of conversation timestamps for
2967 2.2.8 The example conversation code with GMemChunk's.
2969 For a conversation between two IP addresses and ports you can use this as an
2970 example. This example uses the GMemChunk to allocate memory and stores the data
2971 pointer in the conversation 'data' variable.
2973 NOTE: Remember to register the init routine (my_dissector_init) in the
2974 protocol_register routine.
2977 /************************ Global values ************************/
2979 /* the number of entries in the memory chunk array */
2980 #define my_init_count 10
2982 /* define your structure here */
2987 /* the GMemChunk base structure */
2988 static GMemChunk *my_vals = NULL;
2990 /* Registered protocol number */
2991 static int my_proto = -1;
2994 /********************* in the dissector routine *********************/
2996 /* the local variables in the dissector */
2998 conversation_t *conversation;
2999 my_entry_t *data_ptr;
3002 /* look up the conversation */
3004 conversation = find_conversation(pinfo->fd->num, &pinfo->src, &pinfo->dst,
3005 pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
3007 /* if conversation found get the data pointer that you stored */
3009 data_ptr = (my_entry_t*)conversation_get_proto_data(conversation, my_proto);
3012 /* new conversation create local data structure */
3014 data_ptr = g_mem_chunk_alloc(my_vals);
3016 /*** add your code here to setup the new data structure ***/
3018 /* create the conversation with your data pointer */
3020 conversation = conversation_new(pinfo->fd->num, &pinfo->src, &pinfo->dst, pinfo->ptype,
3021 pinfo->srcport, pinfo->destport, 0);
3022 conversation_add_proto_data(conversation, my_proto, (void *)data_ptr);
3025 /* at this point the conversation data is ready */
3028 /******************* in the dissector init routine *******************/
3030 #define my_init_count 20
3033 my_dissector_init(void)
3036 /* destroy memory chunks if needed */
3039 g_mem_chunk_destroy(my_vals);
3041 /* now create memory chunks */
3043 my_vals = g_mem_chunk_new("my_proto_vals",
3045 my_init_count * sizeof(my_entry_t),
3049 /***************** in the protocol register routine *****************/
3051 /* register re-init routine */
3053 register_init_routine(&my_dissector_init);
3055 my_proto = proto_register_protocol("My Protocol", "My Protocol", "my_proto");
3058 2.2.9 An example conversation code that starts at a specific frame number.
3060 Sometimes a dissector has determined that a new conversation is needed that
3061 starts at a specific frame number, when a capture session encompasses multiple
3062 conversation that reuse the same src/dest ip/port pairs. You can use the
3063 conversation->setup_frame returned by find_conversation with
3064 pinfo->fd->num to determine whether or not there already exists a conversation
3065 that starts at the specific frame number.
3067 /* in the dissector routine */
3069 conversation = find_conversation(pinfo->fd->num, &pinfo->src, &pinfo->dst,
3070 pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
3071 if (conversation == NULL || (conversation->setup_frame != pinfo->fd->num)) {
3072 /* It's not part of any conversation or the returned
3073 * conversation->setup_frame doesn't match the current frame
3076 conversation = conversation_new(pinfo->fd->num, &pinfo->src,
3077 &pinfo->dst, pinfo->ptype, pinfo->srcport, pinfo->destport,
3082 2.2.10 The example conversation code using conversation index field.
3084 Sometimes the conversation isn't enough to define a unique data storage
3085 value for the network traffic. For example if you are storing information
3086 about requests carried in a conversation, the request may have an
3087 identifier that is used to define the request. In this case the
3088 conversation and the identifier are required to find the data storage
3089 pointer. You can use the conversation data structure index value to
3090 uniquely define the conversation.
3092 See packet-afs.c for an example of how to use the conversation index. In
3093 this dissector multiple requests are sent in the same conversation. To store
3094 information for each request the dissector has an internal hash table based
3095 upon the conversation index and values inside the request packets.
3098 /* in the dissector routine */
3100 /* to find a request value, first lookup conversation to get index */
3101 /* then used the conversation index, and request data to find data */
3102 /* in the local hash table */
3104 conversation = find_conversation(pinfo->fd->num, &pinfo->src, &pinfo->dst,
3105 pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
3106 if (conversation == NULL) {
3107 /* It's not part of any conversation - create a new one. */
3108 conversation = conversation_new(pinfo->fd->num, &pinfo->src,
3109 &pinfo->dst, pinfo->ptype, pinfo->srcport, pinfo->destport,
3113 request_key.conversation = conversation->index;
3114 request_key.service = pntohs(&rxh->serviceId);
3115 request_key.callnumber = pntohl(&rxh->callNumber);
3117 request_val = (struct afs_request_val *)g_hash_table_lookup(
3118 afs_request_hash, &request_key);
3120 /* only allocate a new hash element when it's a request */
3122 if (!request_val && !reply)
3124 new_request_key = g_mem_chunk_alloc(afs_request_keys);
3125 *new_request_key = request_key;
3127 request_val = g_mem_chunk_alloc(afs_request_vals);
3128 request_val -> opcode = pntohl(&afsh->opcode);
3129 opcode = request_val->opcode;
3131 g_hash_table_insert(afs_request_hash, new_request_key,
3137 2.3 Dynamic conversation dissector registration.
3140 NOTE: This sections assumes that all information is available to
3141 create a complete conversation, source port/address and
3142 destination port/address. If either the destination port or
3143 address is know, see section 2.4 Dynamic server port dissector
3146 For protocols that negotiate a secondary port connection, for example
3147 packet-msproxy.c, a conversation can install a dissector to handle
3148 the secondary protocol dissection. After the conversation is created
3149 for the negotiated ports use the conversation_set_dissector to define
3150 the dissection routine.
3151 Before we create these conversations or assign a dissector to them we should
3152 first check that the conversation does not already exist and if it exists
3153 whether it is registered to our protocol or not.
3154 We should do this because it is uncommon but it does happen that multiple
3155 different protocols can use the same socketpair during different stages of
3156 an application cycle. By keeping track of the frame number a conversation
3157 was started in wireshark can still tell these different protocols apart.
3159 The second argument to conversation_set_dissector is a dissector handle,
3160 which is created with a call to create_dissector_handle or
3163 create_dissector_handle takes as arguments a pointer to the dissector
3164 function and a protocol ID as returned by proto_register_protocol;
3165 register_dissector takes as arguments a string giving a name for the
3166 dissector, a pointer to the dissector function, and a protocol ID.
3168 The protocol ID is the ID for the protocol dissected by the function.
3169 The function will not be called if the protocol has been disabled by the
3170 user; instead, the data for the protocol will be dissected as raw data.
3174 /* the handle for the dynamic dissector *
3175 static dissector_handle_t sub_dissector_handle;
3177 /* prototype for the dynamic dissector */
3178 static void sub_dissector(tvbuff_t *tvb, packet_info *pinfo,
3181 /* in the main protocol dissector, where the next dissector is setup */
3183 /* if conversation has a data field, create it and load structure */
3185 /* First check if a conversation already exists for this
3188 conversation = find_conversation(pinfo->fd->num,
3189 &pinfo->src, &pinfo->dst, protocol,
3190 src_port, dst_port, new_conv_info, 0);
3192 /* If there is no such conversation, or if there is one but for
3193 someone else's protocol then we just create a new conversation
3194 and assign our protocol to it.
3196 if ( (conversation == NULL) ||
3197 (conversation->dissector_handle != sub_dissector_handle) ) {
3198 new_conv_info = g_mem_chunk_alloc(new_conv_vals);
3199 new_conv_info->data1 = value1;
3201 /* create the conversation for the dynamic port */
3202 conversation = conversation_new(pinfo->fd->num,
3203 &pinfo->src, &pinfo->dst, protocol,
3204 src_port, dst_port, new_conv_info, 0);
3206 /* set the dissector for the new conversation */
3207 conversation_set_dissector(conversation, sub_dissector_handle);
3212 proto_register_PROTOABBREV(void)
3216 sub_dissector_handle = create_dissector_handle(sub_dissector,
3222 2.4 Dynamic server port dissector registration.
3224 NOTE: While this example used both NO_ADDR2 and NO_PORT2 to create a
3225 conversation with only one port and address set, this isn't a
3226 requirement. Either the second port or the second address can be set
3227 when the conversation is created.
3229 For protocols that define a server address and port for a secondary
3230 protocol, a conversation can be used to link a protocol dissector to
3231 the server port and address. The key is to create the new
3232 conversation with the second address and port set to the "accept
3235 Some server applications can use the same port for different protocols during
3236 different stages of a transaction. For example it might initially use SNMP
3237 to perform some discovery and later switch to use TFTP using the same port.
3238 In order to handle this properly we must first check whether such a
3239 conversation already exists or not and if it exists we also check whether the
3240 registered dissector_handle for that conversation is "our" dissector or not.
3241 If not we create a new conversation on top of the previous one and set this new
3242 conversation to use our protocol.
3243 Since wireshark keeps track of the frame number where a conversation started
3244 wireshark will still be able to keep the packets apart even though they do use
3245 the same socketpair.
3246 (See packet-tftp.c and packet-snmp.c for examples of this)
3248 There are two support routines that will allow the second port and/or
3249 address to be set later.
3251 conversation_set_port2( conversation_t *conv, guint32 port);
3252 conversation_set_addr2( conversation_t *conv, address addr);
3254 These routines will change the second address or port for the
3255 conversation. So, the server port conversation will be converted into a
3256 more complete conversation definition. Don't use these routines if you
3257 want to create a conversation between the server and client and retain the
3258 server port definition, you must create a new conversation.
3263 /* the handle for the dynamic dissector *
3264 static dissector_handle_t sub_dissector_handle;
3268 /* in the main protocol dissector, where the next dissector is setup */
3270 /* if conversation has a data field, create it and load structure */
3272 new_conv_info = g_mem_chunk_alloc(new_conv_vals);
3273 new_conv_info->data1 = value1;
3275 /* create the conversation for the dynamic server address and port */
3276 /* NOTE: The second address and port values don't matter because the */
3277 /* NO_ADDR2 and NO_PORT2 options are set. */
3279 /* First check if a conversation already exists for this
3282 conversation = find_conversation(pinfo->fd->num,
3283 &server_src_addr, 0, protocol,
3284 server_src_port, 0, NO_ADDR2 | NO_PORT_B);
3285 /* If there is no such conversation, or if there is one but for
3286 someone else's protocol then we just create a new conversation
3287 and assign our protocol to it.
3289 if ( (conversation == NULL) ||
3290 (conversation->dissector_handle != sub_dissector_handle) ) {
3291 conversation = conversation_new(pinfo->fd->num,
3292 &server_src_addr, 0, protocol,
3293 server_src_port, 0, new_conv_info, NO_ADDR2 | NO_PORT2);
3295 /* set the dissector for the new conversation */
3296 conversation_set_dissector(conversation, sub_dissector_handle);
3299 2.5 Per-packet information.
3301 Information can be stored for each data packet that is processed by the
3302 dissector. The information is added with the p_add_proto_data function and
3303 retrieved with the p_get_proto_data function. The data pointers passed into
3304 the p_add_proto_data are not managed by the proto_data routines. If you use
3305 malloc or any other dynamic memory allocation scheme, you must release the
3306 data when it isn't required.
3309 p_add_proto_data(frame_data *fd, int proto, void *proto_data)
3311 p_get_proto_data(frame_data *fd, int proto)
3314 fd - The fd pointer in the pinfo structure, pinfo->fd
3315 proto - Protocol id returned by the proto_register_protocol call
3316 during initialization
3317 proto_data - pointer to the dissector data.
3320 2.6 User Preferences.
3322 If the dissector has user options, there is support for adding these preferences
3323 to a configuration dialog.
3325 You must register the module with the preferences routine with -
3327 module_t *prefs_register_protocol(proto_id, void (*apply_cb)(void))
3329 Where: proto_id - the value returned by "proto_register_protocol()" when
3330 the protocol was registered.
3331 apply_cb - Callback routine that is called when preferences are
3332 applied. It may be NULL, which inhibits the callback.
3334 Then you can register the fields that can be configured by the user with these
3337 /* Register a preference with an unsigned integral value. */
3338 void prefs_register_uint_preference(module_t *module, const char *name,
3339 const char *title, const char *description, guint base, guint *var);
3341 /* Register a preference with an Boolean value. */
3342 void prefs_register_bool_preference(module_t *module, const char *name,
3343 const char *title, const char *description, gboolean *var);
3345 /* Register a preference with an enumerated value. */
3346 void prefs_register_enum_preference(module_t *module, const char *name,
3347 const char *title, const char *description, gint *var,
3348 const enum_val_t *enumvals, gboolean radio_buttons)
3350 /* Register a preference with a character-string value. */
3351 void prefs_register_string_preference(module_t *module, const char *name,
3352 const char *title, const char *description, char **var)
3354 /* Register a preference with a range of unsigned integers (e.g.,
3357 void prefs_register_range_preference(module_t *module, const char *name,
3358 const char *title, const char *description, range_t *var,
3361 Where: module - Returned by the prefs_register_protocol routine
3362 name - This is appended to the name of the protocol, with a
3363 "." between them, to construct a name that identifies
3364 the field in the preference file; the name itself
3365 should not include the protocol name, as the name in
3366 the preference file will already have it
3367 title - Field title in the preferences dialog
3368 description - Comments added to the preference file above the
3370 var - pointer to the storage location that is updated when the
3371 field is changed in the preference dialog box
3372 base - Base that the unsigned integer is expected to be in,
3374 enumvals - an array of enum_val_t structures. This must be
3375 NULL-terminated; the members of that structure are:
3377 a short name, to be used with the "-o" flag - it
3378 should not contain spaces or upper-case letters,
3379 so that it's easier to put in a command line;
3381 a description, which is used in the GUI (and
3382 which, for compatibility reasons, is currently
3383 what's written to the preferences file) - it can
3384 contain spaces, capital letters, punctuation,
3387 the numerical value corresponding to that name
3389 radio_buttons - TRUE if the field is to be displayed in the
3390 preferences dialog as a set of radio buttons,
3391 FALSE if it is to be displayed as an option
3393 max_value - The maximum allowed value for a range (0 is the minimum).
3395 An example from packet-beep.c -
3397 proto_beep = proto_register_protocol("Blocks Extensible Exchange Protocol",
3402 /* Register our configuration options for BEEP, particularly our port */
3404 beep_module = prefs_register_protocol(proto_beep, proto_reg_handoff_beep);
3406 prefs_register_uint_preference(beep_module, "tcp.port", "BEEP TCP Port",
3407 "Set the port for BEEP messages (if other"
3408 " than the default of 10288)",
3409 10, &global_beep_tcp_port);
3411 prefs_register_bool_preference(beep_module, "strict_header_terminator",
3412 "BEEP Header Requires CRLF",
3413 "Specifies that BEEP requires CRLF as a "
3414 "terminator, and not just CR or LF",
3415 &global_beep_strict_term);
3417 This will create preferences "beep.tcp.port" and
3418 "beep.strict_header_terminator", the first of which is an unsigned
3419 integer and the second of which is a Boolean.
3421 Note that a warning will pop up if you've saved such preference to the
3422 preference file and you subsequently take the code out. The way to make
3423 a preference obsolete is to register it as such:
3425 /* Register a preference that used to be supported but no longer is. */
3426 void prefs_register_obsolete_preference(module_t *module,
3429 2.7 Reassembly/desegmentation for protocols running atop TCP.
3431 There are two main ways of reassembling a Protocol Data Unit (PDU) which
3432 spans across multiple TCP segments. The first approach is simpler, but
3433 assumes you are running atop of TCP when this occurs (but your dissector
3434 might run atop of UDP, too, for example), and that your PDUs consist of a
3435 fixed amount of data that includes enough information to determine the PDU
3436 length, possibly followed by additional data. The second method is more
3437 generic but requires more code and is less efficient.
3439 2.7.1 Using tcp_dissect_pdus().
3441 For the first method, you register two different dissection methods, one
3442 for the TCP case, and one for the other cases. It is a good idea to
3443 also have a dissect_PROTO_common function which will parse the generic
3444 content that you can find in all PDUs which is called from
3445 dissect_PROTO_tcp when the reassembly is complete and from
3446 dissect_PROTO_udp (or dissect_PROTO_other).
3448 To register the distinct dissector functions, consider the following
3449 example, stolen from packet-dns.c:
3451 dissector_handle_t dns_udp_handle;
3452 dissector_handle_t dns_tcp_handle;
3453 dissector_handle_t mdns_udp_handle;
3455 dns_udp_handle = create_dissector_handle(dissect_dns_udp,
3457 dns_tcp_handle = create_dissector_handle(dissect_dns_tcp,
3459 mdns_udp_handle = create_dissector_handle(dissect_mdns_udp,
3462 dissector_add("udp.port", UDP_PORT_DNS, dns_udp_handle);
3463 dissector_add("tcp.port", TCP_PORT_DNS, dns_tcp_handle);
3464 dissector_add("udp.port", UDP_PORT_MDNS, mdns_udp_handle);
3465 dissector_add("tcp.port", TCP_PORT_MDNS, dns_tcp_handle);
3467 The dissect_dns_udp function does very little work and calls
3468 dissect_dns_common, while dissect_dns_tcp calls tcp_dissect_pdus with a
3469 reference to a callback which will be called with reassembled data:
3472 dissect_dns_tcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
3474 tcp_dissect_pdus(tvb, pinfo, tree, dns_desegment, 2,
3475 get_dns_pdu_len, dissect_dns_tcp_pdu);
3478 (The dissect_dns_tcp_pdu function acts similarly to dissect_dns_udp.)
3479 The arguments to tcp_dissect_pdus are:
3481 the tvbuff pointer, packet_info pointer, and proto_tree pointer
3482 passed to the dissector;
3484 a gboolean flag indicating whether desegmentation is enabled for
3487 the number of bytes of PDU data required to determine the length
3490 a routine that takes as arguments a packet_info pointer, a tvbuff
3491 pointer and an offset value representing the offset into the tvbuff
3492 at which a PDU begins and should return - *without* throwing an
3493 exception (it is guaranteed that the number of bytes specified by the
3494 previous argument to tcp_dissect_pdus is available, but more data
3495 might not be available, so don't refer to any data past that) - the
3496 total length of the PDU, in bytes;
3498 a routine that's passed a tvbuff pointer, packet_info pointer,
3499 and proto_tree pointer, with the tvbuff containing a
3500 possibly-reassembled PDU, and that should dissect that PDU.
3502 2.7.2 Modifying the pinfo struct.
3504 The second reassembly mode is preferred when the dissector cannot determine
3505 how many bytes it will need to read in order to determine the size of a PDU.
3506 It may also be useful if your dissector needs to support reassembly from
3507 protocols other than TCP.
3509 Your dissect_PROTO will initially be passed a tvbuff containing the payload of
3510 the first packet. It should dissect as much data as it can, noting that it may
3511 contain more than one complete PDU. If the end of the provided tvbuff coincides
3512 with the end of a PDU then all is well and your dissector can just return as
3513 normal. (If it is a new-style dissector, it should return the number of bytes
3514 successfully processed.)
3516 If the dissector discovers that the end of the tvbuff does /not/ coincide with
3517 the end of a PDU, (ie, there is half of a PDU at the end of the tvbuff), it can
3518 indicate this to the parent dissector, by updating the pinfo struct. The
3519 desegment_offset field is the offset in the tvbuff at which the dissector will
3520 continue processing when next called. The desegment_len field should contain
3521 the estimated number of additional bytes required for completing the PDU. Next
3522 time your dissect_PROTO is called, it will be passed a tvbuff composed of the
3523 end of the data from the previous tvbuff together with desegment_len more bytes.
3525 If the dissector cannot tell how many more bytes it will need, it should set
3526 desegment_len=DESEGMENT_ONE_MORE_SEGMENT; it will then be called again as soon
3527 as any more data becomes available. Dissectors should set the desegment_len to a
3528 reasonable value when possible rather than always setting
3529 DESEGMENT_ONE_MORE_SEGMENT as it will generally be more efficient. Also, you
3530 *must not* set desegment_len=1 in this case, in the hope that you can change
3531 your mind later: once you return a positive value from desegment_len, your PDU
3532 boundary is set in stone.
3534 static hf_register_info hf[] = {
3536 {"C String", "c.string", FT_STRING, BASE_NONE, NULL, 0x0,
3542 * Dissect a buffer containing C strings.
3544 * @param tvb The buffer to dissect.
3545 * @param pinfo Packet Info.
3546 * @param tree The protocol tree.
3548 static void dissect_cstr(tvbuff_t * tvb, packet_info * pinfo, proto_tree * tree)
3551 while(offset < tvb_reported_length(tvb)) {
3552 gint available = tvb_reported_length_remaining(tvb, offset);
3553 gint len = tvb_strnlen(tvb, offset, available);
3556 /* we ran out of data: ask for more */
3557 pinfo->desegment_offset = offset;
3558 pinfo->desegment_len = DESEGMENT_ONE_MORE_SEGMENT;
3562 if (check_col(pinfo->cinfo, COL_INFO)) {
3563 col_set_str(pinfo->cinfo, COL_INFO, "C String");
3566 len += 1; /* Add one for the '\0' */
3569 proto_tree_add_item(tree, hf_cstring, tvb, offset, len, FALSE);
3571 offset += (guint)len;
3574 /* if we get here, then the end of the tvb coincided with the end of a
3575 string. Happy days. */
3578 This simple dissector will repeatedly return DESEGMENT_ONE_MORE_SEGMENT
3579 requesting more data until the tvbuff contains a complete C string. The C string
3580 will then be added to the protocol tree. Note that there may be more
3581 than one complete C string in the tvbuff, so the dissection is done in a
3586 The ptvcursor API allows a simpler approach to writing dissectors for
3587 simple protocols. The ptvcursor API works best for protocols whose fields
3588 are static and whose format does not depend on the value of other fields.
3589 However, even if only a portion of your protocol is statically defined,
3590 then that portion could make use of ptvcursors.
3592 The ptvcursor API lets you extract data from a tvbuff, and add it to a
3593 protocol tree in one step. It also keeps track of the position in the
3594 tvbuff so that you can extract data again without having to compute any
3595 offsets --- hence the "cursor" name of the API.
3597 The three steps for a simple protocol are:
3598 1. Create a new ptvcursor with ptvcursor_new()
3599 2. Add fields with multiple calls of ptvcursor_add()
3600 3. Delete the ptvcursor with ptvcursor_free()
3602 ptvcursor offers the possibility to add subtrees in the tree as well. It can be
3603 done in very simple steps :
3604 1. Create a new subtree with ptvcursor_push_subtree(). The old subtree is
3605 pushed in a stack and the new subtree will be used by ptvcursor.
3606 2. Add fields with multiple calls of ptvcursor_add(). The fields will be
3607 added in the new subtree created at the previous step.
3608 3. Pop the previous subtree with ptvcursor_pop_subtree(). The previous
3609 subtree is again used by ptvcursor.
3610 Note that at the end of the parsing of a packet you must have popped each
3611 subtree you pushed. If it's not the case, the dissector will generate an error.
3613 To use the ptvcursor API, include the "ptvcursor.h" file. The PGM dissector
3614 is an example of how to use it. You don't need to look at it as a guide;
3615 instead, the API description here should be good enough.
3617 2.8.1 ptvcursor API.
3620 ptvcursor_new(proto_tree* tree, tvbuff_t* tvb, gint offset)
3621 This creates a new ptvcursor_t object for iterating over a tvbuff.
3622 You must call this and use this ptvcursor_t object so you can use the
3626 ptvcursor_add(ptvcursor_t* ptvc, int hf, gint length, gboolean endianness)
3627 This will extract 'length' bytes from the tvbuff and place it in
3628 the proto_tree as field 'hf', which is a registered header_field. The
3629 pointer to the proto_item that is created is passed back to you. Internally,
3630 the ptvcursor advances its cursor so the next call to ptvcursor_add
3631 starts where this call finished. The 'endianness' parameter matters for
3632 FT_UINT* and FT_INT* fields.
3635 ptvcursor_add_no_advance(ptvcursor_t* ptvc, int hf, gint length, gboolean endianness)
3636 Like ptvcursor_add, but does not advance the internal cursor.
3639 ptvcursor_advance(ptvcursor_t* ptvc, gint length)
3640 Advances the internal cursor without adding anything to the proto_tree.
3643 ptvcursor_free(ptvcursor_t* ptvc)
3644 Frees the memory associated with the ptvcursor. You must call this
3645 after your dissection with the ptvcursor API is completed.
3649 ptvcursor_push_subtree(ptvcursor_t* ptvc, proto_item* it, gint ett_subtree)
3650 Pushes the current subtree in the tree stack of the cursor, creates a new
3651 one and sets this one as the working tree.
3654 ptvcursor_pop_subtree(ptvcursor_t* ptvc);
3655 Pops a subtree in the tree stack of the cursor
3658 ptvcursor_add_with_subtree(ptvcursor_t* ptvc, int hfindex, gint length,
3659 gboolean little_endian, gint ett_subtree);
3660 Adds an item to the tree and creates a subtree.
3661 If the length is unknown, length may be defined as SUBTREE_UNDEFINED_LENGTH.
3662 In this case, at the next pop, the item length will be equal to the advancement
3663 of the cursor since the creation of the subtree.
3666 ptvcursor_add_text_with_subtree(ptvcursor_t* ptvc, gint length,
3667 gint ett_subtree, const char* format, ...);
3668 Add a text node to the tree and create a subtree.
3669 If the length is unknown, length may be defined as SUBTREE_UNDEFINED_LENGTH.
3670 In this case, at the next pop, the item length will be equal to the advancement
3671 of the cursor since the creation of the subtree.
3673 2.8.2 Miscellaneous functions.
3676 ptvcursor_tvbuff(ptvcursor_t* ptvc)
3677 Returns the tvbuff associated with the ptvcursor.
3680 ptvcursor_current_offset(ptvcursor_t* ptvc)
3681 Returns the current offset.
3684 ptvcursor_tree(ptvcursor_t* ptvc)
3685 Returns the proto_tree associated with the ptvcursor.
3688 ptvcursor_set_tree(ptvcursor_t* ptvc, proto_tree *tree)
3689 Sets a new proto_tree for the ptvcursor.
3692 ptvcursor_set_subtree(ptvcursor_t* ptvc, proto_item* it, gint ett_subtree);
3693 Creates a subtree and adds it to the cursor as the working tree but does
3694 not save the old working tree.