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 On LLP64 data model systems (notably 64-bit Windows), "int" and "long"
133 are 32 bits while "size_t" and "ptrdiff_t" are 64 bits. This means that
134 the following will generate a compiler warning:
137 i = strlen("hello, sailor"); /* Compiler warning */
139 Normally, you'd just make "i" a size_t. However, many GLib and Wireshark
140 functions won't accept a size_t on LLP64:
143 char greeting[] = "hello, sailor";
144 guint byte_after_greet;
146 i = strlen(greeting);
147 byte_after_greet = tvb_get_guint8(tvb, i); /* Compiler warning */
149 Try to use the appropriate data type when you can. When you can't, you
150 will have to cast to a compatible data type, e.g.
153 char greeting[] = "hello, sailor";
154 guint byte_after_greet;
156 i = strlen(greeting);
157 byte_after_greet = tvb_get_guint8(tvb, (gint) i); /* OK */
162 char greeting[] = "hello, sailor";
163 guint byte_after_greet;
165 i = (gint) strlen(greeting);
166 byte_after_greet = tvb_get_guint8(tvb, i); /* Compiler warning */
168 See http://www.unix.org/version2/whatsnew/lp64_wp.html for more
169 information on the sizes of common types in different data models.
171 When printing or displaying the values of 64-bit integral data types,
172 don't use "%lld", "%llu", "%llx", or "%llo" - not all platforms
173 support "%ll" for printing 64-bit integral data types. Instead, for
174 GLib routines, and routines that use them, such as all the routines in
175 Wireshark that take format arguments, use G_GINT64_MODIFIER, for example:
177 proto_tree_add_text(tree, tvb, offset, 8,
178 "Sequence Number: %" G_GINT64_MODIFIER "u",
181 When using standard C routines, such as printf and scanf, use
182 PRId64, PRIu64, PRIx64, PRIX64, and PRIo64; for example:
184 printf("Sequence Number: %" PRIu64 "\n", sequence_number);
186 When specifying an integral constant that doesn't fit in 32 bits, don't
187 use "LL" at the end of the constant - not all compilers use "LL" for
188 that. Instead, put the constant in a call to the "G_GINT64_CONSTANT()"
191 G_GINT64_CONSTANT(11644473600U)
197 Don't use a label without a statement following it. For example,
207 will not work with all compilers - you have to do
217 with some statement, even if it's a null statement, after the label.
219 Don't use "bzero()", "bcopy()", or "bcmp()"; instead, use the ANSI C
222 "memset()" (with zero as the second argument, so that it sets
223 all the bytes to zero);
225 "memcpy()" or "memmove()" (note that the first and second
226 arguments to "memcpy()" are in the reverse order to the
227 arguments to "bcopy()"; note also that "bcopy()" is typically
228 guaranteed to work on overlapping memory regions, while
229 "memcpy()" isn't, so if you may be copying from one region to a
230 region that overlaps it, use "memmove()", not "memcpy()" - but
231 "memcpy()" might be faster as a result of not guaranteeing
232 correct operation on overlapping memory regions);
234 and "memcmp()" (note that "memcmp()" returns 0, 1, or -1, doing
235 an ordered comparison, rather than just returning 0 for "equal"
236 and 1 for "not equal", as "bcmp()" does).
238 Not all platforms necessarily have "bzero()"/"bcopy()"/"bcmp()", and
239 those that do might not declare them in the header file on which they're
240 declared on your platform.
242 Don't use "index()" or "rindex()"; instead, use the ANSI C equivalents,
243 "strchr()" and "strrchr()". Not all platforms necessarily have
244 "index()" or "rindex()", and those that do might not declare them in the
245 header file on which they're declared on your platform.
247 Don't fetch data from packets by getting a pointer to data in the packet
248 with "tvb_get_ptr()", casting that pointer to a pointer to a structure,
249 and dereferencing that pointer. That pointer won't necessarily be aligned
250 on the proper boundary, which can cause crashes on some platforms (even
251 if it doesn't crash on an x86-based PC); furthermore, the data in a
252 packet is not necessarily in the byte order of the machine on which
253 Wireshark is running. Use the tvbuff routines to extract individual
254 items from the packet, or use "proto_tree_add_item()" and let it extract
257 Don't use structures that overlay packet data, or into which you copy
258 packet data; the C programming language does not guarantee any
259 particular alignment of fields within a structure, and even the
260 extensions that try to guarantee that are compiler-specific and not
261 necessarily supported by all compilers used to build Wireshark. Using
262 bitfields in those structures is even worse; the order of bitfields
265 Don't use "ntohs()", "ntohl()", "htons()", or "htonl()"; the header
266 files required to define or declare them differ between platforms, and
267 you might be able to get away with not including the appropriate header
268 file on your platform but that might not work on other platforms.
269 Instead, use "g_ntohs()", "g_ntohl()", "g_htons()", and "g_htonl()";
270 those are declared by <glib.h>, and you'll need to include that anyway,
271 as Wireshark header files that all dissectors must include use stuff from
274 Don't fetch a little-endian value using "tvb_get_ntohs() or
275 "tvb_get_ntohl()" and then using "g_ntohs()", "g_htons()", "g_ntohl()",
276 or "g_htonl()" on the resulting value - the g_ routines in question
277 convert between network byte order (big-endian) and *host* byte order,
278 not *little-endian* byte order; not all machines on which Wireshark runs
279 are little-endian, even though PCs are. Fetch those values using
280 "tvb_get_letohs()" and "tvb_get_letohl()".
282 Don't put a comma after the last element of an enum - some compilers may
283 either warn about it (producing extra noise) or refuse to accept it.
285 Don't include <unistd.h> without protecting it with
293 and, if you're including it to get routines such as "open()", "close()",
294 "read()", and "write()" declared, also include <io.h> if present:
300 in order to declare the Windows C library routines "_open()",
301 "_close()", "_read()", and "_write()". Your file must include <glib.h>
302 - which many of the Wireshark header files include, so you might not have
303 to include it explicitly - in order to get "open()", "close()",
304 "read()", "write()", etc. mapped to "_open()", "_close()", "_read()",
307 Do not use "open()", "rename()", "mkdir()", "stat()", "unlink()", "remove()",
308 "fopen()", "freopen()" directly. Instead use "ws_open()", "ws_rename()",
309 "ws_mkdir()", "ws_stat()", "ws_unlink()", "ws_remove()", "ws_fopen()",
310 "ws_freopen()": these wrapper functions change the path and file name from
311 UTF8 to UTF16 on Windows allowing the functions to work correctly when the
312 path or file name contain non-ASCII characters.
314 When opening a file with "ws_fopen()", "ws_freopen()", or "ws_fdopen()", if
315 the file contains ASCII text, use "r", "w", "a", and so on as the open mode
316 - but if it contains binary data, use "rb", "wb", and so on. On
317 Windows, if a file is opened in a text mode, writing a byte with the
318 value of octal 12 (newline) to the file causes two bytes, one with the
319 value octal 15 (carriage return) and one with the value octal 12, to be
320 written to the file, and causes bytes with the value octal 15 to be
321 discarded when reading the file (to translate between C's UNIX-style
322 lines that end with newline and Windows' DEC-style lines that end with
323 carriage return/line feed).
325 In addition, that also means that when opening or creating a binary
326 file, you must use "ws_open()" (with O_CREAT and possibly O_TRUNC if the
327 file is to be created if it doesn't exist), and OR in the O_BINARY flag.
328 That flag is not present on most, if not all, UNIX systems, so you must
335 to properly define it for UNIX (it's not necessary on UNIX).
337 Don't use forward declarations of static arrays without a specified size
338 in a fashion such as this:
340 static const value_string foo_vals[];
344 static const value_string foo_vals[] = {
351 as some compilers will reject the first of those statements. Instead,
352 initialize the array at the point at which it's first declared, so that
355 Don't put a comma after the last tuple of an initializer of an array.
357 For #define names and enum member names, prefix the names with a tag so
358 as to avoid collisions with other names - this might be more of an issue
359 on Windows, as it appears to #define names such as DELETE and
362 Don't use the "numbered argument" feature that many UNIX printf's
365 g_snprintf(add_string, 30, " - (%1$d) (0x%1$04x)", value);
367 as not all UNIX printf's implement it, and Windows printf doesn't appear
368 to implement it. Use something like
370 g_snprintf(add_string, 30, " - (%d) (0x%04x)", value, value);
374 Don't use "variadic macros", such as
376 #define DBG(format, args...) fprintf(stderr, format, ## args)
378 as not all C compilers support them. Use macros that take a fixed
379 number of arguments, such as
381 #define DBG0(format) fprintf(stderr, format)
382 #define DBG1(format, arg1) fprintf(stderr, format, arg1)
383 #define DBG2(format, arg1, arg2) fprintf(stderr, format, arg1, arg2)
389 #define DBG(args) printf args
395 as that's not supported by all compilers.
397 snprintf() -> g_snprintf()
398 snprintf() is not available on all platforms, so it's a good idea to use the
399 g_snprintf() function declared by <glib.h> instead.
401 tmpnam() -> mkstemp()
402 tmpnam is insecure and should not be used any more. Wireshark brings its
403 own mkstemp implementation for use on platforms that lack mkstemp.
404 Note: mkstemp does not accept NULL as a parameter.
406 The pointer returned by a call to "tvb_get_ptr()" is not guaranteed to be
407 aligned on any particular byte boundary; this means that you cannot
408 safely cast it to any data type other than a pointer to "char",
409 "unsigned char", "guint8", or other one-byte data types. You cannot,
410 for example, safely cast it to a pointer to a structure, and then access
411 the structure members directly; on some systems, unaligned accesses to
412 integral data types larger than 1 byte, and floating-point data types,
413 cause a trap, which will, at best, result in the OS slowly performing an
414 unaligned access for you, and will, on at least some platforms, cause
415 the program to be terminated.
417 Wireshark supports platforms with GLib 2.4[.x]/GTK+ 2.4[.x] or newer.
418 If a Glib/GTK+ mechanism is available only in Glib/GTK+ versions
419 newer than 2.4/2.4 then use "#if GTK_CHECK_VERSION(...)" to conditionally
420 compile code using that mechanism.
422 When different code must be used on UN*X and Win32, use a #if or #ifdef
423 that tests _WIN32, not WIN32. Try to write code portably whenever
424 possible, however; note that there are some routines in Wireshark with
425 platform-dependent implementations and platform-independent APIs, such
426 as the routines in epan/filesystem.c, allowing the code that calls it to
427 be written portably without #ifdefs.
429 1.1.2 String handling
431 Do not use functions such as strcat() or strcpy().
432 A lot of work has been done to remove the existing calls to these functions and
433 we do not want any new callers of these functions.
435 Instead use g_snprintf() since that function will if used correctly prevent
436 buffer overflows for large strings.
438 When using a buffer to create a string, do not use a buffer stored on the stack.
439 I.e. do not use a buffer declared as
443 instead allocate a buffer dynamically using the string-specific or plain emem
444 routines (see README.malloc) such as
446 emem_strbuf_t *strbuf;
447 strbuf = ep_strbuf_new_label("");
448 ep_strbuf_append_printf(strbuf, ...
454 #define MAX_BUFFER 1024
455 buffer=ep_alloc(MAX_BUFFER);
458 g_snprintf(buffer, MAX_BUFFER, ...
460 This avoids the stack from being corrupted in case there is a bug in your code
461 that accidentally writes beyond the end of the buffer.
464 If you write a routine that will create and return a pointer to a filled in
465 string and if that buffer will not be further processed or appended to after
466 the routine returns (except being added to the proto tree),
467 do not preallocate the buffer to fill in and pass as a parameter instead
468 pass a pointer to a pointer to the function and return a pointer to an
469 emem allocated buffer that will be automatically freed. (see README.malloc)
471 I.e. do not write code such as
473 foo_to_str(char *string, ... ){
479 foo_to_str(buffer, ...
480 proto_tree_add_text(... buffer ...
482 instead write the code as
484 foo_to_str(char **buffer, ...
486 *buffer=ep_alloc(MAX_BUFFER);
492 foo_to_str(&buffer, ...
493 proto_tree_add_text(... *buffer ...
495 Use ep_ allocated buffers. They are very fast and nice. These buffers are all
496 automatically free()d when the dissection of the current packet ends so you
497 don't have to worry about free()ing them explicitly in order to not leak memory.
498 Please read README.malloc.
500 Don't use non-ASCII characters in source files; not all compiler
501 environments will be using the same encoding for non-ASCII characters,
502 and at least one compiler (Microsoft's Visual C) will, in environments
503 with double-byte character encodings, such as many Asian environments,
504 fail if it sees a byte sequence in a source file that doesn't correspond
505 to a valid character. This causes source files using either an ISO
506 8859/n single-byte character encoding or UTF-8 to fail to compile. Even
507 if the compiler doesn't fail, there is no guarantee that the compiler,
508 or a developer's text editor, will interpret the characters the way you
509 intend them to be interpreted.
513 Wireshark is not guaranteed to read only network traces that contain correctly-
514 formed packets. Wireshark is commonly used to track down networking
515 problems, and the problems might be due to a buggy protocol implementation
516 sending out bad packets.
518 Therefore, protocol dissectors not only have to be able to handle
519 correctly-formed packets without, for example, crashing or looping
520 infinitely, they also have to be able to handle *incorrectly*-formed
521 packets without crashing or looping infinitely.
523 Here are some suggestions for making dissectors more robust in the face
524 of incorrectly-formed packets:
526 Do *NOT* use "g_assert()" or "g_assert_not_reached()" in dissectors.
527 *NO* value in a packet's data should be considered "wrong" in the sense
528 that it's a problem with the dissector if found; if it cannot do
529 anything else with a particular value from a packet's data, the
530 dissector should put into the protocol tree an indication that the
531 value is invalid, and should return. You can use the DISSECTOR_ASSERT
532 macro for that purpose.
534 If you are allocating a chunk of memory to contain data from a packet,
535 or to contain information derived from data in a packet, and the size of
536 the chunk of memory is derived from a size field in the packet, make
537 sure all the data is present in the packet before allocating the buffer.
540 1) Wireshark won't leak that chunk of memory if an attempt to
541 fetch data not present in the packet throws an exception.
545 2) it won't crash trying to allocate an absurdly-large chunk of
546 memory if the size field has a bogus large value.
548 If you're fetching into such a chunk of memory a string from the buffer,
549 and the string has a specified size, you can use "tvb_get_*_string()",
550 which will check whether the entire string is present before allocating
551 a buffer for the string, and will also put a trailing '\0' at the end of
554 If you're fetching into such a chunk of memory a 2-byte Unicode string
555 from the buffer, and the string has a specified size, you can use
556 "tvb_get_ephemeral_faked_unicode()", which will check whether the entire
557 string is present before allocating a buffer for the string, and will also
558 put a trailing '\0' at the end of the buffer. The resulting string will be
559 a sequence of single-byte characters; the only Unicode characters that
560 will be handled correctly are those in the ASCII range. (Wireshark's
561 ability to handle non-ASCII strings is limited; it needs to be
564 If you're fetching into such a chunk of memory a sequence of bytes from
565 the buffer, and the sequence has a specified size, you can use
566 "tvb_memdup()", which will check whether the entire sequence is present
567 before allocating a buffer for it.
569 Otherwise, you can check whether the data is present by using
570 "tvb_ensure_bytes_exist()" or by getting a pointer to the data by using
571 "tvb_get_ptr()", although note that there might be problems with using
572 the pointer from "tvb_get_ptr()" (see the item on this in the
573 Portability section above, and the next item below).
575 Note also that you should only fetch string data into a fixed-length
576 buffer if the code ensures that no more bytes than will fit into the
577 buffer are fetched ("the protocol ensures" isn't good enough, as
578 protocol specifications can't ensure only packets that conform to the
579 specification will be transmitted or that only packets for the protocol
580 in question will be interpreted as packets for that protocol by
581 Wireshark). If there's no maximum length of string data to be fetched,
582 routines such as "tvb_get_*_string()" are safer, as they allocate a buffer
583 large enough to hold the string. (Note that some variants of this call
584 require you to free the string once you're finished with it.)
586 If you have gotten a pointer using "tvb_get_ptr()", you must make sure
587 that you do not refer to any data past the length passed as the last
588 argument to "tvb_get_ptr()"; while the various "tvb_get" routines
589 perform bounds checking and throw an exception if you refer to data not
590 available in the tvbuff, direct references through a pointer gotten from
591 "tvb_get_ptr()" do not do any bounds checking.
593 If you have a loop that dissects a sequence of items, each of which has
594 a length field, with the offset in the tvbuff advanced by the length of
595 the item, then, if the length field is the total length of the item, and
596 thus can be zero, you *MUST* check for a zero-length item and abort the
597 loop if you see one. Otherwise, a zero-length item could cause the
598 dissector to loop infinitely. You should also check that the offset,
599 after having the length added to it, is greater than the offset before
600 the length was added to it, if the length field is greater than 24 bits
601 long, so that, if the length value is *very* large and adding it to the
602 offset causes an overflow, that overflow is detected.
604 If you are fetching a length field from the buffer, corresponding to the
605 length of a portion of the packet, and subtracting from that length a
606 value corresponding to the length of, for example, a header in the
607 packet portion in question, *ALWAYS* check that the value of the length
608 field is greater than or equal to the length you're subtracting from it,
609 and report an error in the packet and stop dissecting the packet if it's
610 less than the length you're subtracting from it. Otherwise, the
611 resulting length value will be negative, which will either cause errors
612 in the dissector or routines called by the dissector, or, if the value
613 is interpreted as an unsigned integer, will cause the value to be
614 interpreted as a very large positive value.
616 Any tvbuff offset that is added to as processing is done on a packet
617 should be stored in a 32-bit variable, such as an "int"; if you store it
618 in an 8-bit or 16-bit variable, you run the risk of the variable
621 sprintf() -> g_snprintf()
622 Prevent yourself from using the sprintf() function, as it does not test the
623 length of the given output buffer and might be writing into unintended memory
624 areas. This function is one of the main causes of security problems like buffer
625 exploits and many other bugs that are very hard to find. It's much better to
626 use the g_snprintf() function declared by <glib.h> instead.
628 You should test your dissector against incorrectly-formed packets. This
629 can be done using the randpkt and editcap utilities that come with the
630 Wireshark distribution. Testing using randpkt can be done by generating
631 output at the same layer as your protocol, and forcing Wireshark/TShark
632 to decode it as your protocol, e.g. if your protocol sits on top of UDP:
634 randpkt -c 50000 -t dns randpkt.pcap
635 tshark -nVr randpkt.pcap -d udp.port==53,<myproto>
637 Testing using editcap can be done using preexisting capture files and the
638 "-E" flag, which introduces errors in a capture file. E.g.:
640 editcap -E 0.03 infile.pcap outfile.pcap
641 tshark -nVr outfile.pcap
643 The script fuzz-test.sh is available to help automate these tests.
645 1.1.4 Name convention.
647 Wireshark uses the underscore_convention rather than the InterCapConvention for
648 function names, so new code should probably use underscores rather than
649 intercaps for functions and variable names. This is especially important if you
650 are writing code that will be called from outside your code. We are just
651 trying to keep things consistent for other developers.
653 1.1.5 White space convention.
655 Avoid using tab expansions different from 8 column widths, as not all
656 text editors in use by the developers support this. For a detailed
657 discussion of tabs, spaces, and indentation, see
659 http://www.jwz.org/doc/tabs-vs-spaces.html
661 When creating a new file, you are free to choose an indentation logic.
662 Most of the files in Wireshark tend to use 2-space or 4-space
663 indentation. You are encouraged to write a short comment on the
664 indentation logic at the beginning of this new file, especially if
665 you're using non-mod-8 tabs. The tabs-vs-spaces document above provides
666 examples of Emacs and vi modelines for this purpose.
668 When editing an existing file, try following the existing indentation
669 logic and even if it very tempting, never ever use a restyler/reindenter
670 utility on an existing file. If you run across wildly varying
671 indentation styles within the same file, it might be helpful to send a
672 note to wireshark-dev for guidance.
674 1.1.6 Compiler warnings
676 You should write code that is free of compiler warnings. Such warnings will
677 often indicate questionable code and sometimes even real bugs, so it's best
678 to avoid warnings at all.
680 The compiler flags in the Makefiles are set to "treat warnings as errors",
681 so your code won't even compile when warnings occur.
685 Wireshark requires certain things when setting up a protocol dissector.
686 Below is skeleton code for a dissector that you can copy to a file and
687 fill in. Your dissector should follow the naming convention of packet-
688 followed by the abbreviated name for the protocol. It is recommended
689 that where possible you keep to the IANA abbreviated name for the
690 protocol, if there is one, or a commonly-used abbreviation for the
693 Usually, you will put your newly created dissector file into the directory
694 epan/dissectors, just like all the other packet-....c files already in there.
696 Also, please add your dissector file to the corresponding makefile,
697 described in section "1.9 Editing Makefile.common to add your dissector" below.
699 Dissectors that use the dissector registration to register with a lower level
700 dissector don't need to define a prototype in the .h file. For other
701 dissectors the main dissector routine should have a prototype in a header
702 file whose name is "packet-", followed by the abbreviated name for the
703 protocol, followed by ".h"; any dissector file that calls your dissector
704 should be changed to include that file.
706 You may not need to include all the headers listed in the skeleton
707 below, and you may need to include additional headers. For example, the
716 is needed only if you are using a function from libpcre, e.g. the
717 "pcre_compile()" function.
719 The "$Id$" in the comment will be updated by Subversion when the file is
722 When creating a new file, it is fine to just write "$Id$" as Subversion will
723 automatically fill in the identifier at the time the file will be added to the
724 SVN repository (committed).
726 ------------------------------------Cut here------------------------------------
727 /* packet-PROTOABBREV.c
728 * Routines for PROTONAME dissection
729 * Copyright 200x, YOUR_NAME <YOUR_EMAIL_ADDRESS>
733 * Wireshark - Network traffic analyzer
734 * By Gerald Combs <gerald@wireshark.org>
735 * Copyright 1998 Gerald Combs
737 * Copied from WHATEVER_FILE_YOU_USED (where "WHATEVER_FILE_YOU_USED"
738 * is a dissector file; if you just copied this from README.developer,
739 * don't bother with the "Copied from" - you don't even need to put
740 * in a "Copied from" if you copied an existing dissector, especially
741 * if the bulk of the code in the new dissector is your code)
743 * This program is free software; you can redistribute it and/or modify
744 * it under the terms of the GNU General Public License as published by
745 * the Free Software Foundation; either version 2 of the License, or
746 * (at your option) any later version.
748 * This program is distributed in the hope that it will be useful,
749 * but WITHOUT ANY WARRANTY; without even the implied warranty of
750 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
751 * GNU General Public License for more details.
753 * You should have received a copy of the GNU General Public License along
754 * with this program; if not, write to the Free Software Foundation, Inc.,
755 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
768 #include <epan/packet.h>
769 #include <epan/prefs.h>
771 /* IF PROTO exposes code to other dissectors, then it must be exported
772 in a header file. If not, a header file is not needed at all. */
773 #include "packet-PROTOABBREV.h"
775 /* Forward declaration we need below (if using proto_reg_handoff...
776 as a prefs callback) */
777 void proto_reg_handoff_PROTOABBREV(void);
779 /* Initialize the protocol and registered fields */
780 static int proto_PROTOABBREV = -1;
781 static int hf_PROTOABBREV_FIELDABBREV = -1;
783 /* Global sample preference ("controls" display of numbers) */
784 static gboolean gPREF_HEX = FALSE;
785 /* Global sample port pref */
786 static guint gPORT_PREF = 1234;
788 /* Initialize the subtree pointers */
789 static gint ett_PROTOABBREV = -1;
791 /* Code to actually dissect the packets */
793 dissect_PROTOABBREV(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
796 /* Set up structures needed to add the protocol subtree and manage it */
798 proto_tree *PROTOABBREV_tree;
800 /* First, if at all possible, do some heuristics to check if the packet cannot
801 * possibly belong to your protocol. This is especially important for
802 * protocols directly on top of TCP or UDP where port collisions are
803 * common place (e.g., even though your protocol uses a well known port,
804 * someone else may set up, for example, a web server on that port which,
805 * if someone analyzed that web server's traffic in Wireshark, would result
806 * in Wireshark handing an HTTP packet to your dissector). For example:
808 /* Check that there's enough data */
809 if (tvb_length(tvb) < /* your protocol's smallest packet size */)
812 /* Get some values from the packet header, probably using tvb_get_*() */
813 if ( /* these values are not possible in PROTONAME */ )
814 /* This packet does not appear to belong to PROTONAME.
815 * Return 0 to give another dissector a chance to dissect it.
819 /* Make entries in Protocol column and Info column on summary display */
820 if (check_col(pinfo->cinfo, COL_PROTOCOL))
821 col_set_str(pinfo->cinfo, COL_PROTOCOL, "PROTOABBREV");
823 /* This field shows up as the "Info" column in the display; you should use
824 it, if possible, to summarize what's in the packet, so that a user looking
825 at the list of packets can tell what type of packet it is. See section 1.5
826 for more information.
828 Before changing the contents of a column you should make sure the column is
829 active by calling "check_col(pinfo->cinfo, COL_*)". If it is not active
830 don't bother setting it.
832 If you are setting the column to a constant string, use "col_set_str()",
833 as it's more efficient than the other "col_set_XXX()" calls.
835 If you're setting it to a string you've constructed, or will be
836 appending to the column later, use "col_add_str()".
838 "col_add_fstr()" can be used instead of "col_add_str()"; it takes
839 "printf()"-like arguments. Don't use "col_add_fstr()" with a format
840 string of "%s" - just use "col_add_str()" or "col_set_str()", as it's
841 more efficient than "col_add_fstr()".
843 If you will be fetching any data from the packet before filling in
844 the Info column, clear that column first, in case the calls to fetch
845 data from the packet throw an exception because they're fetching data
846 past the end of the packet, so that the Info column doesn't have data
847 left over from the previous dissector; do
849 if (check_col(pinfo->cinfo, COL_INFO))
850 col_clear(pinfo->cinfo, COL_INFO);
854 if (check_col(pinfo->cinfo, COL_INFO))
855 col_set_str(pinfo->cinfo, COL_INFO, "XXX Request");
857 /* A protocol dissector can be called in 2 different ways:
859 (a) Operational dissection
861 In this mode, Wireshark is only interested in the way protocols
862 interact, protocol conversations are created, packets are
863 reassembled and handed over to higher-level protocol dissectors.
864 In this mode Wireshark does not build a so-called "protocol
867 (b) Detailed dissection
869 In this mode, Wireshark is also interested in all details of
870 a given protocol, so a "protocol tree" is created.
872 Wireshark distinguishes between the 2 modes with the proto_tree pointer:
876 In the interest of speed, if "tree" is NULL, avoid building a
877 protocol tree and adding stuff to it, or even looking at any packet
878 data needed only if you're building the protocol tree, if possible.
880 Note, however, that you must fill in column information, create
881 conversations, reassemble packets, build any other persistent state
882 needed for dissection, and call subdissectors regardless of whether
883 "tree" is NULL or not. This might be inconvenient to do without
884 doing most of the dissection work; the routines for adding items to
885 the protocol tree can be passed a null protocol tree pointer, in
886 which case they'll return a null item pointer, and
887 "proto_item_add_subtree()" returns a null tree pointer if passed a
888 null item pointer, so, if you're careful not to dereference any null
889 tree or item pointers, you can accomplish this by doing all the
890 dissection work. This might not be as efficient as skipping that
891 work if you're not building a protocol tree, but if the code would
892 have a lot of tests whether "tree" is null if you skipped that work,
893 you might still be better off just doing all that work regardless of
894 whether "tree" is null or not. */
897 /* NOTE: The offset and length values in the call to
898 "proto_tree_add_item()" define what data bytes to highlight in the hex
899 display window when the line in the protocol tree display
900 corresponding to that item is selected.
902 Supplying a length of -1 is the way to highlight all data from the
903 offset to the end of the packet. */
905 /* create display subtree for the protocol */
906 ti = proto_tree_add_item(tree, proto_PROTOABBREV, tvb, 0, -1, FALSE);
908 PROTOABBREV_tree = proto_item_add_subtree(ti, ett_PROTOABBREV);
910 /* add an item to the subtree, see section 1.6 for more information */
911 proto_tree_add_item(PROTOABBREV_tree,
912 hf_PROTOABBREV_FIELDABBREV, tvb, offset, len, FALSE);
915 /* Continue adding tree items to process the packet here */
920 /* If this protocol has a sub-dissector call it here, see section 1.8 */
922 /* Return the amount of data this dissector was able to dissect */
923 return tvb_length(tvb);
927 /* Register the protocol with Wireshark */
929 /* this format is require because a script is used to build the C function
930 that calls all the protocol registration.
934 proto_register_PROTOABBREV(void)
936 module_t *PROTOABBREV_module;
938 /* Setup list of header fields See Section 1.6.1 for details*/
939 static hf_register_info hf[] = {
940 { &hf_PROTOABBREV_FIELDABBREV,
941 { "FIELDNAME", "PROTOABBREV.FIELDABBREV",
942 FIELDTYPE, FIELDBASE, FIELDCONVERT, BITMASK,
943 "FIELDDESCR", HFILL }
947 /* Setup protocol subtree array */
948 static gint *ett[] = {
952 /* Register the protocol name and description */
953 proto_PROTOABBREV = proto_register_protocol("PROTONAME",
954 "PROTOSHORTNAME", "PROTOABBREV");
956 /* Required function calls to register the header fields and subtrees used */
957 proto_register_field_array(proto_PROTOABBREV, hf, array_length(hf));
958 proto_register_subtree_array(ett, array_length(ett));
960 /* Register preferences module (See Section 2.6 for more on preferences) */
961 /* (Registration of a prefs callback is not required if there are no */
962 /* prefs-dependent registration functions (eg: a port pref). */
963 /* See proto_reg_handoff below. */
964 /* If a prefs callback is not needed, use NULL instead of */
965 /* proto_reg_handoff_PROTOABBREV in the following). */
966 PROTOABBREV_module = prefs_register_protocol(proto_PROTOABBREV,
967 proto_reg_handoff_PROTOABBREV);
969 /* Register a sample preference */
970 prefs_register_bool_preference(PROTOABBREV_module, "show_hex",
971 "Display numbers in Hex",
972 "Enable to display numerical values in hexadecimal.",
975 /* Register a sample port preference */
976 prefs_register_uint_preference(PROTOABBREV_module, "tcp.port", "PROTOABBREV TCP Port",
977 " PROTOABBREV TCP port if other than the default",
980 /* If this dissector uses sub-dissector registration add a registration routine.
981 This exact format is required because a script is used to find these
982 routines and create the code that calls these routines.
984 If this function is registered as a prefs callback (see prefs_register_protocol
985 above) this function is also called by preferences whenever "Apply" is pressed;
986 In that case, it should accommodate being called more than once.
988 This form of the reg_handoff function is used if if you perform
989 registration functions which are dependent upon prefs. See below
990 for a simpler form which can be used if there are no
991 prefs-dependent registration functions.
994 proto_reg_handoff_PROTOABBREV(void)
996 static gboolean initialized = FALSE;
997 static dissector_handle_t PROTOABBREV_handle;
998 static int currentPort;
1002 /* Use new_create_dissector_handle() to indicate that dissect_PROTOABBREV()
1003 * returns the number of bytes it dissected (or 0 if it thinks the packet
1004 * does not belong to PROTONAME).
1006 PROTOABBREV_handle = new_create_dissector_handle(dissect_PROTOABBREV,
1008 dissector_add("PARENT_SUBFIELD", ID_VALUE, PROTOABBREV_handle);
1014 If you perform registration functions which are dependent upon
1015 prefs the you should de-register everything which was associated
1016 with the previous settings and re-register using the new prefs
1017 settings here. In general this means you need to keep track of
1018 the PROTOABBREV_handle and the value the preference had at the time
1019 you registered. The PROTOABBREV_handle value and the value of the
1020 preference can be saved using local statics in this
1021 function (proto_reg_handoff).
1024 dissector_delete("tcp.port", currentPort, PROTOABBREV_handle);
1027 currentPort = gPORT_PREF;
1029 dissector_add("tcp.port", currentPort, PROTOABBREV_handle);
1034 /* Simple form of proto_reg_handoff_PROTOABBREV which can be used if there are
1035 no prefs-dependent registration function calls.
1039 proto_reg_handoff_PROTOABBREV(void)
1041 dissector_handle_t PROTOABBREV_handle;
1043 /* Use new_create_dissector_handle() to indicate that dissect_PROTOABBREV()
1044 * returns the number of bytes it dissected (or 0 if it thinks the packet
1045 * does not belong to PROTONAME).
1047 PROTOABBREV_handle = new_create_dissector_handle(dissect_PROTOABBREV,
1049 dissector_add("PARENT_SUBFIELD", ID_VALUE, PROTOABBREV_handle);
1054 ------------------------------------Cut here------------------------------------
1056 1.3 Explanation of needed substitutions in code skeleton.
1058 In the above code block the following strings should be substituted with
1061 YOUR_NAME Your name, of course. You do want credit, don't you?
1062 It's the only payment you will receive....
1063 YOUR_EMAIL_ADDRESS Keep those cards and letters coming.
1064 WHATEVER_FILE_YOU_USED Add this line if you are using another file as a
1066 PROTONAME The name of the protocol; this is displayed in the
1067 top-level protocol tree item for that protocol.
1068 PROTOSHORTNAME An abbreviated name for the protocol; this is displayed
1069 in the "Preferences" dialog box if your dissector has
1070 any preferences, in the dialog box of enabled protocols,
1071 and in the dialog box for filter fields when constructing
1072 a filter expression.
1073 PROTOABBREV A name for the protocol for use in filter expressions;
1074 it shall contain only lower-case letters, digits, and
1076 FIELDNAME The displayed name for the header field.
1077 FIELDABBREV The abbreviated name for the header field. (NO SPACES)
1078 FIELDTYPE FT_NONE, FT_BOOLEAN, FT_UINT8, FT_UINT16, FT_UINT24,
1079 FT_UINT32, FT_UINT64, FT_INT8, FT_INT16, FT_INT24, FT_INT32,
1080 FT_INT64, FT_FLOAT, FT_DOUBLE, FT_ABSOLUTE_TIME,
1081 FT_RELATIVE_TIME, FT_STRING, FT_STRINGZ, FT_EBCDIC,
1082 FT_UINT_STRING, FT_ETHER, FT_BYTES, FT_UINT_BYTES, FT_IPv4,
1083 FT_IPv6, FT_IPXNET, FT_FRAMENUM, FT_PROTOCOL, FT_GUID, FT_OID
1084 FIELDBASE BASE_NONE, BASE_DEC, BASE_HEX, BASE_OCT, BASE_DEC_HEX,
1085 BASE_HEX_DEC, BASE_RANGE_STRING, BASE_CUSTOM
1086 FIELDCONVERT VALS(x), RVALS(x), TFS(x), NULL
1087 BITMASK Usually 0x0 unless using the TFS(x) field conversion.
1088 FIELDDESCR A brief description of the field, or NULL.
1089 PARENT_SUBFIELD Lower level protocol field used for lookup, i.e. "tcp.port"
1090 ID_VALUE Lower level protocol field value that identifies this protocol
1091 For example the TCP or UDP port number
1093 If, for example, PROTONAME is "Internet Bogosity Discovery Protocol",
1094 PROTOSHORTNAME would be "IBDP", and PROTOABBREV would be "ibdp". Try to
1095 conform with IANA names.
1097 1.4 The dissector and the data it receives.
1102 This is only needed if the dissector doesn't use self-registration to
1103 register itself with the lower level dissector, or if the protocol dissector
1104 wants/needs to expose code to other subdissectors.
1106 The dissector must be declared exactly as follows in the file
1107 packet-PROTOABBREV.h:
1110 dissect_PROTOABBREV(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree);
1113 1.4.2 Extracting data from packets.
1115 NOTE: See the file /epan/tvbuff.h for more details.
1117 The "tvb" argument to a dissector points to a buffer containing the raw
1118 data to be analyzed by the dissector; for example, for a protocol
1119 running atop UDP, it contains the UDP payload (but not the UDP header,
1120 or any protocol headers above it). A tvbuffer is an opaque data
1121 structure, the internal data structures are hidden and the data must be
1122 accessed via the tvbuffer accessors.
1126 Bit accessors for a maximum of 8-bits, 16-bits 32-bits and 64-bits:
1128 guint8 tvb_get_bits8(tvbuff_t *tvb, gint bit_offset, gint no_of_bits);
1129 guint16 tvb_get_bits16(tvbuff_t *tvb, gint bit_offset, gint no_of_bits,gboolean little_endian);
1130 guint32 tvb_get_bits32(tvbuff_t *tvb, gint bit_offset, gint no_of_bits,gboolean little_endian);
1131 guint64 tvb_get_bits64(tvbuff_t *tvb, gint bit_offset, gint no_of_bits,gboolean little_endian);
1133 Single-byte accessor:
1135 guint8 tvb_get_guint8(tvbuff_t*, gint offset);
1137 Network-to-host-order accessors for 16-bit integers (guint16), 24-bit
1138 integers, 32-bit integers (guint32), and 64-bit integers (guint64):
1140 guint16 tvb_get_ntohs(tvbuff_t*, gint offset);
1141 guint32 tvb_get_ntoh24(tvbuff_t*, gint offset);
1142 guint32 tvb_get_ntohl(tvbuff_t*, gint offset);
1143 guint64 tvb_get_ntoh64(tvbuff_t*, gint offset);
1145 Network-to-host-order accessors for single-precision and
1146 double-precision IEEE floating-point numbers:
1148 gfloat tvb_get_ntohieee_float(tvbuff_t*, gint offset);
1149 gdouble tvb_get_ntohieee_double(tvbuff_t*, gint offset);
1151 Little-Endian-to-host-order accessors for 16-bit integers (guint16),
1152 24-bit integers, 32-bit integers (guint32), and 64-bit integers
1155 guint16 tvb_get_letohs(tvbuff_t*, gint offset);
1156 guint32 tvb_get_letoh24(tvbuff_t*, gint offset);
1157 guint32 tvb_get_letohl(tvbuff_t*, gint offset);
1158 guint64 tvb_get_letoh64(tvbuff_t*, gint offset);
1160 Little-Endian-to-host-order accessors for single-precision and
1161 double-precision IEEE floating-point numbers:
1163 gfloat tvb_get_letohieee_float(tvbuff_t*, gint offset);
1164 gdouble tvb_get_letohieee_double(tvbuff_t*, gint offset);
1166 Accessors for IPv4 and IPv6 addresses:
1168 guint32 tvb_get_ipv4(tvbuff_t*, gint offset);
1169 void tvb_get_ipv6(tvbuff_t*, gint offset, struct e_in6_addr *addr);
1171 NOTE: IPv4 addresses are not to be converted to host byte order before
1172 being passed to "proto_tree_add_ipv4()". You should use "tvb_get_ipv4()"
1173 to fetch them, not "tvb_get_ntohl()" *OR* "tvb_get_letohl()" - don't,
1174 for example, try to use "tvb_get_ntohl()", find that it gives you the
1175 wrong answer on the PC on which you're doing development, and try
1176 "tvb_get_letohl()" instead, as "tvb_get_letohl()" will give the wrong
1177 answer on big-endian machines.
1181 void tvb_get_ntohguid(tvbuff_t *, gint offset, e_guid_t *guid);
1182 void tvb_get_letohguid(tvbuff_t *, gint offset, e_guid_t *guid);
1186 guint8 *tvb_get_string(tvbuff_t*, gint offset, gint length);
1187 guint8 *tvb_get_ephemeral_string(tvbuff_t*, gint offset, gint length);
1188 guint8 *tvb_get_seasonal_string(tvbuff_t*, gint offset, gint length);
1190 Returns a null-terminated buffer containing data from the specified
1191 tvbuff, starting at the specified offset, and containing the specified
1192 length worth of characters (the length of the buffer will be length+1,
1193 as it includes a null character to terminate the string).
1195 tvb_get_string() returns a buffer allocated by g_malloc() so you must
1196 g_free() it when you are finished with the string. Failure to g_free() this
1197 buffer will lead to memory leaks.
1199 tvb_get_ephemeral_string() returns a buffer allocated from a special heap
1200 with a lifetime until the next packet is dissected. You do not need to
1201 free() this buffer, it will happen automatically once the next packet is
1204 tvb_get_seasonal_string() returns a buffer allocated from a special heap
1205 with a lifetime of the current capture session. You do not need to
1206 free() this buffer, it will happen automatically once the a new capture or
1209 guint8 *tvb_get_stringz(tvbuff_t *tvb, gint offset, gint *lengthp);
1210 guint8 *tvb_get_ephemeral_stringz(tvbuff_t *tvb, gint offset, gint *lengthp);
1211 guint8 *tvb_get_seasonal_stringz(tvbuff_t *tvb, gint offset, gint *lengthp);
1213 Returns a null-terminated buffer, allocated with "g_malloc()",
1214 containing data from the specified tvbuff, starting at the
1215 specified offset, and containing all characters from the tvbuff up to
1216 and including a terminating null character in the tvbuff. "*lengthp"
1217 will be set to the length of the string, including the terminating null.
1219 tvb_get_stringz() returns a buffer allocated by g_malloc() so you must
1220 g_free() it when you are finished with the string. Failure to g_free() this
1221 buffer will lead to memory leaks.
1222 tvb_get_ephemeral_stringz() returns a buffer allocated from a special heap
1223 with a lifetime until the next packet is dissected. You do not need to
1224 free() this buffer, it will happen automatically once the next packet is
1227 tvb_get_seasonal_stringz() returns a buffer allocated from a special heap
1228 with a lifetime of the current capture session. You do not need to
1229 free() this buffer, it will happen automatically once the a new capture or
1232 guint8 *tvb_fake_unicode(tvbuff_t*, gint offset, gint length, gboolean little_endian);
1233 guint8 *tvb_get_ephemeral_faked_unicode(tvbuff_t*, gint offset, gint length, gboolean little_endian);
1235 Converts a 2-byte unicode string to an ASCII string.
1236 Returns a null-terminated buffer containing data from the specified
1237 tvbuff, starting at the specified offset, and containing the specified
1238 length worth of characters (the length of the buffer will be length+1,
1239 as it includes a null character to terminate the string).
1241 tvb_fake_unicode() returns a buffer allocated by g_malloc() so you must
1242 g_free() it when you are finished with the string. Failure to g_free() this
1243 buffer will lead to memory leaks.
1244 tvb_get_ephemeral_faked_unicode() returns a buffer allocated from a special
1245 heap with a lifetime until the next packet is dissected. You do not need to
1246 free() this buffer, it will happen automatically once the next packet is
1249 Byte Array Accessors:
1251 gchar *tvb_bytes_to_str(tvbuff_t *tvb, gint offset, gint len);
1253 Formats a bunch of data from a tvbuff as bytes, returning a pointer
1254 to the string with the data formatted as two hex digits for each byte.
1255 The string pointed to is stored in an "ep_alloc'd" buffer which will be freed
1256 before the next frame is dissected. The formatted string will contain the hex digits
1257 for at most the first 16 bytes of the data. If len is greater than 16 bytes, a
1258 trailing "..." will be added to the string.
1260 gchar *tvb_bytes_to_str_punct(tvbuff_t *tvb, gint offset, gint len, gchar punct);
1262 This function is similar to tvb_bytes_to_str(...) except that 'punct' is inserted
1263 between the hex representation of each byte.
1267 guint8* tvb_memcpy(tvbuff_t*, guint8* target, gint offset, gint length);
1269 Copies into the specified target the specified length's worth of data
1270 from the specified tvbuff, starting at the specified offset.
1272 guint8* tvb_memdup(tvbuff_t*, gint offset, gint length);
1273 guint8* ep_tvb_memdup(tvbuff_t*, gint offset, gint length);
1275 Returns a buffer, allocated with "g_malloc()", containing the specified
1276 length's worth of data from the specified tvbuff, starting at the
1277 specified offset. The ephemeral variant is freed automatically after the
1278 packet is dissected.
1281 /* WARNING! This function is possibly expensive, temporarily allocating
1282 * another copy of the packet data. Furthermore, it's dangerous because once
1283 * this pointer is given to the user, there's no guarantee that the user will
1284 * honor the 'length' and not overstep the boundaries of the buffer.
1286 guint8* tvb_get_ptr(tvbuff_t*, gint offset, gint length);
1288 The reason that tvb_get_ptr() might have to allocate a copy of its data
1289 only occurs with TVBUFF_COMPOSITES, data that spans multiple tvbuffers.
1290 If the user requests a pointer to a range of bytes that span the member
1291 tvbuffs that make up the TVBUFF_COMPOSITE, the data will have to be
1292 copied to another memory region to assure that all the bytes are
1297 1.5 Functions to handle columns in the traffic summary window.
1299 The topmost pane of the main window is a list of the packets in the
1300 capture, possibly filtered by a display filter.
1302 Each line corresponds to a packet, and has one or more columns, as
1303 configured by the user.
1305 Many of the columns are handled by code outside individual dissectors;
1306 most dissectors need only specify the value to put in the "Protocol" and
1309 Columns are specified by COL_ values; the COL_ value for the "Protocol"
1310 field, typically giving an abbreviated name for the protocol (but not
1311 the all-lower-case abbreviation used elsewhere) is COL_PROTOCOL, and the
1312 COL_ value for the "Info" field, giving a summary of the contents of the
1313 packet for that protocol, is COL_INFO.
1315 A value for a column should only be added if the user specified that it
1316 be displayed; to check whether a given column is to be displayed, call
1317 'check_col' with the COL_ value for that field as an argument - it will
1318 return TRUE if the column is to be displayed and FALSE if it is not to
1321 The value for a column can be specified with one of several functions,
1322 all of which take the 'fd' argument to the dissector as their first
1323 argument, and the COL_ value for the column as their second argument.
1325 1.5.1 The col_set_str function.
1327 'col_set_str' takes a string as its third argument, and sets the value
1328 for the column to that value. It assumes that the pointer passed to it
1329 points to a string constant or a static "const" array, not to a
1330 variable, as it doesn't copy the string, it merely saves the pointer
1331 value; the argument can itself be a variable, as long as it always
1332 points to a string constant or a static "const" array.
1334 It is more efficient than 'col_add_str' or 'col_add_fstr'; however, if
1335 the dissector will be using 'col_append_str' or 'col_append_fstr" to
1336 append more information to the column, the string will have to be copied
1337 anyway, so it's best to use 'col_add_str' rather than 'col_set_str' in
1340 For example, to set the "Protocol" column
1343 if (check_col(pinfo->cinfo, COL_PROTOCOL))
1344 col_set_str(pinfo->cinfo, COL_PROTOCOL, "PROTOABBREV");
1347 1.5.2 The col_add_str function.
1349 'col_add_str' takes a string as its third argument, and sets the value
1350 for the column to that value. It takes the same arguments as
1351 'col_set_str', but copies the string, so that if the string is, for
1352 example, an automatic variable that won't remain in scope when the
1353 dissector returns, it's safe to use.
1356 1.5.3 The col_add_fstr function.
1358 'col_add_fstr' takes a 'printf'-style format string as its third
1359 argument, and 'printf'-style arguments corresponding to '%' format
1360 items in that string as its subsequent arguments. For example, to set
1361 the "Info" field to "<XXX> request, <N> bytes", where "reqtype" is a
1362 string containing the type of the request in the packet and "n" is an
1363 unsigned integer containing the number of bytes in the request:
1365 if (check_col(pinfo->cinfo, COL_INFO))
1366 col_add_fstr(pinfo->cinfo, COL_INFO, "%s request, %u bytes",
1369 Don't use 'col_add_fstr' with a format argument of just "%s" -
1370 'col_add_str', or possibly even 'col_set_str' if the string that matches
1371 the "%s" is a static constant string, will do the same job more
1375 1.5.4 The col_clear function.
1377 If the Info column will be filled with information from the packet, that
1378 means that some data will be fetched from the packet before the Info
1379 column is filled in. If the packet is so small that the data in
1380 question cannot be fetched, the routines to fetch the data will throw an
1381 exception (see the comment at the beginning about tvbuffers improving
1382 the handling of short packets - the tvbuffers keep track of how much
1383 data is in the packet, and throw an exception on an attempt to fetch
1384 data past the end of the packet, so that the dissector won't process
1385 bogus data), causing the Info column not to be filled in.
1387 This means that the Info column will have data for the previous
1388 protocol, which would be confusing if, for example, the Protocol column
1389 had data for this protocol.
1391 Therefore, before a dissector fetches any data whatsoever from the
1392 packet (unless it's a heuristic dissector fetching data to determine
1393 whether the packet is one that it should dissect, in which case it
1394 should check, before fetching the data, whether there's any data to
1395 fetch; if there isn't, it should return FALSE), it should set the
1396 Protocol column and the Info column.
1398 If the Protocol column will ultimately be set to, for example, a value
1399 containing a protocol version number, with the version number being a
1400 field in the packet, the dissector should, before fetching the version
1401 number field or any other field from the packet, set it to a value
1402 without a version number, using 'col_set_str', and should later set it
1403 to a value with the version number after it's fetched the version
1406 If the Info column will ultimately be set to a value containing
1407 information from the packet, the dissector should, before fetching any
1408 fields from the packet, clear the column using 'col_clear' (which is
1409 more efficient than clearing it by calling 'col_set_str' or
1410 'col_add_str' with a null string), and should later set it to the real
1411 string after it's fetched the data to use when doing that.
1414 1.5.5 The col_append_str function.
1416 Sometimes the value of a column, especially the "Info" column, can't be
1417 conveniently constructed at a single point in the dissection process;
1418 for example, it might contain small bits of information from many of the
1419 fields in the packet. 'col_append_str' takes, as arguments, the same
1420 arguments as 'col_add_str', but the string is appended to the end of the
1421 current value for the column, rather than replacing the value for that
1422 column. (Note that no blank separates the appended string from the
1423 string to which it is appended; if you want a blank there, you must add
1424 it yourself as part of the string being appended.)
1427 1.5.6 The col_append_fstr function.
1429 'col_append_fstr' is to 'col_add_fstr' as 'col_append_str' is to
1430 'col_add_str' - it takes, as arguments, the same arguments as
1431 'col_add_fstr', but the formatted string is appended to the end of the
1432 current value for the column, rather than replacing the value for that
1435 1.5.7 The col_append_sep_str and col_append_sep_fstr functions.
1437 In specific situations the developer knows that a column's value will be
1438 created in a stepwise manner, where the appended values are listed. Both
1439 'col_append_sep_str' and 'col_append_sep_fstr' functions will add an item
1440 separator between two consecutive items, and will not add the separator at the
1441 beginning of the column. The remainder of the work both functions do is
1442 identical to what 'col_append_str' and 'col_append_fstr' do.
1444 1.5.8 The col_set_fence and col_prepend_fence_fstr functions.
1446 Sometimes a dissector may be called multiple times for different PDUs in the
1447 same frame (for example in the case of SCTP chunk bundling: several upper
1448 layer data packets may be contained in one SCTP packet). If the upper layer
1449 dissector calls 'col_set_str()' or 'col_clear()' on the Info column when it
1450 begins dissecting each of those PDUs then when the frame is fully dissected
1451 the Info column would contain only the string from the last PDU in the frame.
1452 The 'col_set_fence' function erects a "fence" in the column that prevents
1453 subsequent 'col_...' calls from clearing the data currently in that column.
1454 For example, the SCTP dissector calls 'col_set_fence' on the Info column
1455 after it has called any subdissectors for that chunk so that subdissectors
1456 of any subsequent chunks may only append to the Info column.
1457 'col_prepend_fence_fstr' prepends data before a fence (moving it if
1458 necessary). It will create a fence at the end of the prepended data if the
1459 fence does not already exist.
1462 1.5.9 The col_set_time function.
1464 The 'col_set_time' function takes an nstime value as its third argument.
1465 This nstime value is a relative value and will be added as such to the
1466 column. The fourth argument is the filtername holding this value. This
1467 way, rightclicking on the column makes it possible to build a filter
1468 based on the time-value.
1472 if (check_col(pinfo->cinfo, COL_REL_CONV_TIME)) {
1473 nstime_delta(&ts, &pinfo->fd->abs_ts, &tcpd->ts_first);
1474 col_set_time(pinfo->cinfo, COL_REL_CONV_TIME, &ts, "tcp.time_relative");
1478 1.6 Constructing the protocol tree.
1480 The middle pane of the main window, and the topmost pane of a packet
1481 popup window, are constructed from the "protocol tree" for a packet.
1483 The protocol tree, or proto_tree, is a GNode, the N-way tree structure
1484 available within GLIB. Of course the protocol dissectors don't care
1485 what a proto_tree really is; they just pass the proto_tree pointer as an
1486 argument to the routines which allow them to add items and new branches
1489 When a packet is selected in the packet-list pane, or a packet popup
1490 window is created, a new logical protocol tree (proto_tree) is created.
1491 The pointer to the proto_tree (in this case, 'protocol tree'), is passed
1492 to the top-level protocol dissector, and then to all subsequent protocol
1493 dissectors for that packet, and then the GUI tree is drawn via
1496 The logical proto_tree needs to know detailed information about the protocols
1497 and fields about which information will be collected from the dissection
1498 routines. By strictly defining (or "typing") the data that can be attached to a
1499 proto tree, searching and filtering becomes possible. This means that for
1500 every protocol and field (which I also call "header fields", since they are
1501 fields in the protocol headers) which might be attached to a tree, some
1502 information is needed.
1504 Every dissector routine will need to register its protocols and fields
1505 with the central protocol routines (in proto.c). At first I thought I
1506 might keep all the protocol and field information about all the
1507 dissectors in one file, but decentralization seemed like a better idea.
1508 That one file would have gotten very large; one small change would have
1509 required a re-compilation of the entire file. Also, by allowing
1510 registration of protocols and fields at run-time, loadable modules of
1511 protocol dissectors (perhaps even user-supplied) is feasible.
1513 To do this, each protocol should have a register routine, which will be
1514 called when Wireshark starts. The code to call the register routines is
1515 generated automatically; to arrange that a protocol's register routine
1516 be called at startup:
1518 the file containing a dissector's "register" routine must be
1519 added to "DISSECTOR_SRC" in "epan/dissectors/Makefile.common";
1521 the "register" routine must have a name of the form
1522 "proto_register_XXX";
1524 the "register" routine must take no argument, and return no
1527 the "register" routine's name must appear in the source file
1528 either at the beginning of the line, or preceded only by "void "
1529 at the beginning of the line (that would typically be the
1530 definition) - other white space shouldn't cause a problem, e.g.:
1532 void proto_register_XXX(void) {
1541 proto_register_XXX( void )
1548 and so on should work.
1550 For every protocol or field that a dissector wants to register, a variable of
1551 type int needs to be used to keep track of the protocol. The IDs are
1552 needed for establishing parent/child relationships between protocols and
1553 fields, as well as associating data with a particular field so that it
1554 can be stored in the logical tree and displayed in the GUI protocol
1557 Some dissectors will need to create branches within their tree to help
1558 organize header fields. These branches should be registered as header
1559 fields. Only true protocols should be registered as protocols. This is
1560 so that a display filter user interface knows how to distinguish
1561 protocols from fields.
1563 A protocol is registered with the name of the protocol and its
1566 Here is how the frame "protocol" is registered.
1570 proto_frame = proto_register_protocol (
1572 /* short name */ "Frame",
1573 /* abbrev */ "frame" );
1575 A header field is also registered with its name and abbreviation, but
1576 information about its data type is needed. It helps to look at
1577 the header_field_info struct to see what information is expected:
1579 struct header_field_info {
1584 const void *strings;
1592 A string representing the name of the field. This is the name
1593 that will appear in the graphical protocol tree. It must be a non-empty
1598 A string with an abbreviation of the field. We concatenate the
1599 abbreviation of the parent protocol with an abbreviation for the field,
1600 using a period as a separator. For example, the "src" field in an IP packet
1601 would have "ip.src" as an abbreviation. It is acceptable to have
1602 multiple levels of periods if, for example, you have fields in your
1603 protocol that are then subdivided into subfields. For example, TRMAC
1604 has multiple error fields, so the abbreviations follow this pattern:
1605 "trmac.errors.iso", "trmac.errors.noniso", etc.
1607 The abbreviation is the identifier used in a display filter. If it is
1608 an empty string then the field will not be filterable.
1612 The type of value this field holds. The current field types are:
1614 FT_NONE No field type. Used for fields that
1615 aren't given a value, and that can only
1616 be tested for presence or absence; a
1617 field that represents a data structure,
1618 with a subtree below it containing
1619 fields for the members of the structure,
1620 or that represents an array with a
1621 subtree below it containing fields for
1622 the members of the array, might be an
1624 FT_PROTOCOL Used for protocols which will be placing
1625 themselves as top-level items in the
1626 "Packet Details" pane of the UI.
1627 FT_BOOLEAN 0 means "false", any other value means
1629 FT_FRAMENUM A frame number; if this is used, the "Go
1630 To Corresponding Frame" menu item can
1632 FT_UINT8 An 8-bit unsigned integer.
1633 FT_UINT16 A 16-bit unsigned integer.
1634 FT_UINT24 A 24-bit unsigned integer.
1635 FT_UINT32 A 32-bit unsigned integer.
1636 FT_UINT64 A 64-bit unsigned integer.
1637 FT_INT8 An 8-bit signed integer.
1638 FT_INT16 A 16-bit signed integer.
1639 FT_INT24 A 24-bit signed integer.
1640 FT_INT32 A 32-bit signed integer.
1641 FT_INT64 A 64-bit signed integer.
1642 FT_FLOAT A single-precision floating point number.
1643 FT_DOUBLE A double-precision floating point number.
1644 FT_ABSOLUTE_TIME Seconds (4 bytes) and nanoseconds (4 bytes)
1645 of time displayed as month name, month day,
1646 year, hours, minutes, and seconds with 9
1647 digits after the decimal point.
1648 FT_RELATIVE_TIME Seconds (4 bytes) and nanoseconds (4 bytes)
1649 of time displayed as seconds and 9 digits
1650 after the decimal point.
1651 FT_STRING A string of characters, not necessarily
1652 NUL-terminated, but possibly NUL-padded.
1653 This, and the other string-of-characters
1654 types, are to be used for text strings,
1655 not raw binary data.
1656 FT_STRINGZ A NUL-terminated string of characters.
1657 FT_EBCDIC A string of characters, not necessarily
1658 NUL-terminated, but possibly NUL-padded.
1659 The data from the packet is converted from
1660 EBCDIC to ASCII before displaying to the user.
1661 FT_UINT_STRING A counted string of characters, consisting
1662 of a count (represented as an integral value,
1663 of width given in the proto_tree_add_item()
1664 call) followed immediately by that number of
1666 FT_ETHER A six octet string displayed in
1667 Ethernet-address format.
1668 FT_BYTES A string of bytes with arbitrary values;
1669 used for raw binary data.
1670 FT_UINT_BYTES A counted string of bytes, consisting
1671 of a count (represented as an integral value,
1672 of width given in the proto_tree_add_item()
1673 call) followed immediately by that number of
1674 arbitrary values; used for raw binary data.
1675 FT_IPv4 A version 4 IP address (4 bytes) displayed
1676 in dotted-quad IP address format (4
1677 decimal numbers separated by dots).
1678 FT_IPv6 A version 6 IP address (16 bytes) displayed
1679 in standard IPv6 address format.
1680 FT_IPXNET An IPX address displayed in hex as a 6-byte
1681 network number followed by a 6-byte station
1683 FT_GUID A Globally Unique Identifier
1684 FT_OID An ASN.1 Object Identifier
1686 Some of these field types are still not handled in the display filter
1687 routines, but the most common ones are. The FT_UINT* variables all
1688 represent unsigned integers, and the FT_INT* variables all represent
1689 signed integers; the number on the end represent how many bits are used
1690 to represent the number.
1694 The display field has a couple of overloaded uses. This is unfortunate,
1695 but since we're using C as an application programming language, this sometimes
1696 makes for cleaner programs. Right now I still think that overloading
1697 this variable was okay.
1699 For integer fields (FT_UINT* and FT_INT*), this variable represents the
1700 base in which you would like the value displayed. The acceptable bases
1710 BASE_DEC, BASE_HEX, and BASE_OCT are decimal, hexadecimal, and octal,
1711 respectively. BASE_DEC_HEX and BASE_HEX_DEC display value in two bases
1712 (the 1st representation followed by the 2nd in parenthesis).
1714 BASE_CUSTOM allows one to specify a callback function pointer that will
1715 format the value. The function pointer of the same type as defined by
1716 custom_fmt_func_t in epan/proto.h, specifically:
1718 void func(gchar *, guint32);
1720 The first argument is a pointer to a buffer of the ITEM_LABEL_LENGTH size
1721 and the second argument is the value to be formatted.
1723 For FT_BOOLEAN fields that are also bitfields, 'display' is used to tell
1724 the proto_tree how wide the parent bitfield is. With integers this is
1725 not needed since the type of integer itself (FT_UINT8, FT_UINT16,
1726 FT_UINT24, FT_UINT32, etc.) tells the proto_tree how wide the parent
1729 Additionally, BASE_NONE is used for 'display' as a NULL-value. That is,
1730 for non-integers and non-bitfield FT_BOOLEANs, you'll want to use BASE_NONE
1731 in the 'display' field. You may not use BASE_NONE for integers.
1733 It is possible that in the future we will record the endianness of
1734 integers. If so, it is likely that we'll use a bitmask on the display field
1735 so that integers would be represented as BEND|BASE_DEC or LEND|BASE_HEX.
1736 But that has not happened yet.
1740 Some integer fields, of type FT_UINT*, need labels to represent the true
1741 value of a field. You could think of those fields as having an
1742 enumerated data type, rather than an integral data type.
1744 A 'value_string' structure is a way to map values to strings.
1746 typedef struct _value_string {
1751 For fields of that type, you would declare an array of "value_string"s:
1753 static const value_string valstringname[] = {
1754 { INTVAL1, "Descriptive String 1" },
1755 { INTVAL2, "Descriptive String 2" },
1759 (the last entry in the array must have a NULL 'strptr' value, to
1760 indicate the end of the array). The 'strings' field would be set to
1761 'VALS(valstringname)'.
1763 If the field has a numeric rather than an enumerated type, the 'strings'
1764 field would be set to NULL.
1766 If the field has a numeric type that might logically fit in ranges of values
1767 one can use a range_string struct.
1769 Thus a 'range_string' structure is a way to map ranges to strings.
1771 typedef struct _range_string {
1774 const gchar *strptr;
1777 For fields of that type, you would declare an array of "range_string"s:
1779 static const range_string rvalstringname[] = {
1780 { INTVAL_MIN1, INTVALMAX1, "Descriptive String 1" },
1781 { INTVAL_MIN2, INTVALMAX2, "Descriptive String 2" },
1785 If INTVAL_MIN equals INTVAL_MAX for a given entry the range_string
1786 behavior collapses to the one of value_string.
1787 For FT_(U)INT* fields that need a 'range_string' struct, the 'strings' field
1788 would be set to 'RVALS(rvalstringname)'. Furthermore, 'display' field must be
1789 ORed with 'BASE_RANGE_STRING' (e.g. BASE_DEC|BASE_RANGE_STRING).
1791 FT_BOOLEANs have a default map of 0 = "False", 1 (or anything else) = "True".
1792 Sometimes it is useful to change the labels for boolean values (e.g.,
1793 to "Yes"/"No", "Fast"/"Slow", etc.). For these mappings, a struct called
1794 true_false_string is used.
1796 typedef struct true_false_string {
1799 } true_false_string;
1801 For Boolean fields for which "False" and "True" aren't the desired
1802 labels, you would declare a "true_false_string"s:
1804 static const true_false_string boolstringname = {
1809 Its two fields are pointers to the string representing truth, and the
1810 string representing falsehood. For FT_BOOLEAN fields that need a
1811 'true_false_string' struct, the 'strings' field would be set to
1812 'TFS(&boolstringname)'.
1814 If the Boolean field is to be displayed as "False" or "True", the
1815 'strings' field would be set to NULL.
1817 Wireshark predefines a whole range of ready made "true_false_string"s
1818 in tfs.h, included via packet.h.
1822 If the field is a bitfield, then the bitmask is the mask which will
1823 leave only the bits needed to make the field when ANDed with a value.
1824 The proto_tree routines will calculate 'bitshift' automatically
1825 from 'bitmask', by finding the rightmost set bit in the bitmask.
1826 This shift is applied before applying string mapping functions or
1828 If the field is not a bitfield, then bitmask should be set to 0.
1832 This is a string giving a proper description of the field. It should be
1833 at least one grammatically complete sentence, or NULL in which case the
1835 It is meant to provide a more detailed description of the field than the
1836 name alone provides. This information will be used in the man page, and
1837 in a future GUI display-filter creation tool. We might also add tooltips
1838 to the labels in the GUI protocol tree, in which case the blurb would
1839 be used as the tooltip text.
1842 1.6.1 Field Registration.
1844 Protocol registration is handled by creating an instance of the
1845 header_field_info struct (or an array of such structs), and
1846 calling the registration function along with the registration ID of
1847 the protocol that is the parent of the fields. Here is a complete example:
1849 static int proto_eg = -1;
1850 static int hf_field_a = -1;
1851 static int hf_field_b = -1;
1853 static hf_register_info hf[] = {
1856 { "Field A", "proto.field_a", FT_UINT8, BASE_HEX, NULL,
1857 0xf0, "Field A represents Apples", HFILL }},
1860 { "Field B", "proto.field_b", FT_UINT16, BASE_DEC, VALS(vs),
1861 0x0, "Field B represents Bananas", HFILL }}
1864 proto_eg = proto_register_protocol("Example Protocol",
1866 proto_register_field_array(proto_eg, hf, array_length(hf));
1868 Be sure that your array of hf_register_info structs is declared 'static',
1869 since the proto_register_field_array() function does not create a copy
1870 of the information in the array... it uses that static copy of the
1871 information that the compiler created inside your array. Here's the
1872 layout of the hf_register_info struct:
1874 typedef struct hf_register_info {
1875 int *p_id; /* pointer to parent variable */
1876 header_field_info hfinfo;
1879 Also be sure to use the handy array_length() macro found in packet.h
1880 to have the compiler compute the array length for you at compile time.
1882 If you don't have any fields to register, do *NOT* create a zero-length
1883 "hf" array; not all compilers used to compile Wireshark support them.
1884 Just omit the "hf" array, and the "proto_register_field_array()" call,
1887 It is OK to have header fields with a different format be registered with
1888 the same abbreviation. For instance, the following is valid:
1890 static hf_register_info hf[] = {
1892 { &hf_field_8bit, /* 8-bit version of proto.field */
1893 { "Field (8 bit)", "proto.field", FT_UINT8, BASE_DEC, NULL,
1894 0x00, "Field represents FOO", HFILL }},
1896 { &hf_field_32bit, /* 32-bit version of proto.field */
1897 { "Field (32 bit)", "proto.field", FT_UINT32, BASE_DEC, NULL,
1898 0x00, "Field represents FOO", HFILL }}
1901 This way a filter expression can match a header field, irrespective of the
1902 representation of it in the specific protocol context. This is interesting
1903 for protocols with variable-width header fields.
1905 The HFILL macro at the end of the struct will set reasonable default values
1906 for internally used fields.
1908 1.6.2 Adding Items and Values to the Protocol Tree.
1910 A protocol item is added to an existing protocol tree with one of a
1911 handful of proto_XXX_DO_YYY() functions.
1913 Remember that it only makes sense to add items to a protocol tree if its
1914 proto_tree pointer is not null. Should you add an item to a NULL tree, then
1915 the proto_XXX_DO_YYY() function will immediately return. The cost of this
1916 function call can be avoided by checking for the tree pointer.
1918 Subtrees can be made with the proto_item_add_subtree() function:
1920 item = proto_tree_add_item(....);
1921 new_tree = proto_item_add_subtree(item, tree_type);
1923 This will add a subtree under the item in question; a subtree can be
1924 created under an item made by any of the "proto_tree_add_XXX" functions,
1925 so that the tree can be given an arbitrary depth.
1927 Subtree types are integers, assigned by
1928 "proto_register_subtree_array()". To register subtree types, pass an
1929 array of pointers to "gint" variables to hold the subtree type values to
1930 "proto_register_subtree_array()":
1932 static gint ett_eg = -1;
1933 static gint ett_field_a = -1;
1935 static gint *ett[] = {
1940 proto_register_subtree_array(ett, array_length(ett));
1942 in your "register" routine, just as you register the protocol and the
1943 fields for that protocol.
1945 There are several functions that the programmer can use to add either
1946 protocol or field labels to the proto_tree:
1949 proto_tree_add_item(tree, id, tvb, start, length, little_endian);
1952 proto_tree_add_none_format(tree, id, tvb, start, length, format, ...);
1955 proto_tree_add_protocol_format(tree, id, tvb, start, length,
1959 proto_tree_add_bytes(tree, id, tvb, start, length, start_ptr);
1962 proto_tree_add_bytes_format(tree, id, tvb, start, length, start_ptr,
1966 proto_tree_add_bytes_format_value(tree, id, tvb, start, length,
1967 start_ptr, format, ...);
1970 proto_tree_add_time(tree, id, tvb, start, length, value_ptr);
1973 proto_tree_add_time_format(tree, id, tvb, start, length, value_ptr,
1977 proto_tree_add_time_format_value(tree, id, tvb, start, length,
1978 value_ptr, format, ...);
1981 proto_tree_add_ipxnet(tree, id, tvb, start, length, value);
1984 proto_tree_add_ipxnet_format(tree, id, tvb, start, length, value,
1988 proto_tree_add_ipxnet_format_value(tree, id, tvb, start, length,
1989 value, format, ...);
1992 proto_tree_add_ipv4(tree, id, tvb, start, length, value);
1995 proto_tree_add_ipv4_format(tree, id, tvb, start, length, value,
1999 proto_tree_add_ipv4_format_value(tree, id, tvb, start, length,
2000 value, format, ...);
2003 proto_tree_add_ipv6(tree, id, tvb, start, length, value_ptr);
2006 proto_tree_add_ipv6_format(tree, id, tvb, start, length, value_ptr,
2010 proto_tree_add_ipv6_format_value(tree, id, tvb, start, length,
2011 value_ptr, format, ...);
2014 proto_tree_add_ether(tree, id, tvb, start, length, value_ptr);
2017 proto_tree_add_ether_format(tree, id, tvb, start, length, value_ptr,
2021 proto_tree_add_ether_format_value(tree, id, tvb, start, length,
2022 value_ptr, format, ...);
2025 proto_tree_add_string(tree, id, tvb, start, length, value_ptr);
2028 proto_tree_add_string_format(tree, id, tvb, start, length, value_ptr,
2032 proto_tree_add_string_format_value(tree, id, tvb, start, length,
2033 value_ptr, format, ...);
2036 proto_tree_add_boolean(tree, id, tvb, start, length, value);
2039 proto_tree_add_boolean_format(tree, id, tvb, start, length, value,
2043 proto_tree_add_boolean_format_value(tree, id, tvb, start, length,
2044 value, format, ...);
2047 proto_tree_add_float(tree, id, tvb, start, length, value);
2050 proto_tree_add_float_format(tree, id, tvb, start, length, value,
2054 proto_tree_add_float_format_value(tree, id, tvb, start, length,
2055 value, format, ...);
2058 proto_tree_add_double(tree, id, tvb, start, length, value);
2061 proto_tree_add_double_format(tree, id, tvb, start, length, value,
2065 proto_tree_add_double_format_value(tree, id, tvb, start, length,
2066 value, format, ...);
2069 proto_tree_add_uint(tree, id, tvb, start, length, value);
2072 proto_tree_add_uint_format(tree, id, tvb, start, length, value,
2076 proto_tree_add_uint_format_value(tree, id, tvb, start, length,
2077 value, format, ...);
2080 proto_tree_add_uint64(tree, id, tvb, start, length, value);
2083 proto_tree_add_uint64_format(tree, id, tvb, start, length, value,
2087 proto_tree_add_uint64_format_value(tree, id, tvb, start, length,
2088 value, format, ...);
2091 proto_tree_add_int(tree, id, tvb, start, length, value);
2094 proto_tree_add_int_format(tree, id, tvb, start, length, value,
2098 proto_tree_add_int_format_value(tree, id, tvb, start, length,
2099 value, format, ...);
2102 proto_tree_add_int64(tree, id, tvb, start, length, value);
2105 proto_tree_add_int64_format(tree, id, tvb, start, length, value,
2109 proto_tree_add_int64_format_value(tree, id, tvb, start, length,
2110 value, format, ...);
2113 proto_tree_add_text(tree, tvb, start, length, format, ...);
2116 proto_tree_add_text_valist(tree, tvb, start, length, format, ap);
2119 proto_tree_add_guid(tree, id, tvb, start, length, value_ptr);
2122 proto_tree_add_guid_format(tree, id, tvb, start, length, value_ptr,
2126 proto_tree_add_guid_format_value(tree, id, tvb, start, length,
2127 value_ptr, format, ...);
2130 proto_tree_add_oid(tree, id, tvb, start, length, value_ptr);
2133 proto_tree_add_oid_format(tree, id, tvb, start, length, value_ptr,
2137 proto_tree_add_oid_format_value(tree, id, tvb, start, length,
2138 value_ptr, format, ...);
2141 proto_tree_add_bits_item(tree, id, tvb, bit_offset, no_of_bits,
2145 proto_tree_add_bits_ret_val(tree, id, tvb, bit_offset, no_of_bits,
2146 return_value, little_endian);
2149 proto_tree_add_bitmask(tree, tvb, start, header, ett, fields,
2153 proto_tree_add_bitmask_text(tree, tvb, offset, len, name, fallback,
2154 ett, fields, little_endian, flags);
2156 The 'tree' argument is the tree to which the item is to be added. The
2157 'tvb' argument is the tvbuff from which the item's value is being
2158 extracted; the 'start' argument is the offset from the beginning of that
2159 tvbuff of the item being added, and the 'length' argument is the length,
2160 in bytes, of the item, bit_offset is the offset in bits and no_of_bits
2161 is the lenght in bits.
2163 The length of some items cannot be determined until the item has been
2164 dissected; to add such an item, add it with a length of -1, and, when the
2165 dissection is complete, set the length with 'proto_item_set_len()':
2168 proto_item_set_len(ti, length);
2170 The "ti" argument is the value returned by the call that added the item
2171 to the tree, and the "length" argument is the length of the item.
2173 proto_tree_add_item()
2174 ---------------------
2175 proto_tree_add_item is used when you wish to do no special formatting.
2176 The item added to the GUI tree will contain the name (as passed in the
2177 proto_register_*() function) and a value. The value will be fetched
2178 from the tvbuff by proto_tree_add_item(), based on the type of the field
2179 and, for integral and Boolean fields, the byte order of the value; the
2180 byte order is specified by the 'little_endian' argument, which is TRUE
2181 if the value is little-endian and FALSE if it is big-endian.
2183 Now that definitions of fields have detailed information about bitfield
2184 fields, you can use proto_tree_add_item() with no extra processing to
2185 add bitfield values to your tree. Here's an example. Take the Format
2186 Identifier (FID) field in the Transmission Header (TH) portion of the SNA
2187 protocol. The FID is the high nibble of the first byte of the TH. The
2188 FID would be registered like this:
2190 name = "Format Identifier"
2191 abbrev = "sna.th.fid"
2194 strings = sna_th_fid_vals
2197 The bitmask contains the value which would leave only the FID if bitwise-ANDed
2198 against the parent field, the first byte of the TH.
2200 The code to add the FID to the tree would be;
2202 proto_tree_add_item(bf_tree, hf_sna_th_fid, tvb, offset, 1, TRUE);
2204 The definition of the field already has the information about bitmasking
2205 and bitshifting, so it does the work of masking and shifting for us!
2206 This also means that you no longer have to create value_string structs
2207 with the values bitshifted. The value_string for FID looks like this,
2208 even though the FID value is actually contained in the high nibble.
2209 (You'd expect the values to be 0x0, 0x10, 0x20, etc.)
2211 /* Format Identifier */
2212 static const value_string sna_th_fid_vals[] = {
2213 { 0x0, "SNA device <--> Non-SNA Device" },
2214 { 0x1, "Subarea Node <--> Subarea Node" },
2215 { 0x2, "Subarea Node <--> PU2" },
2216 { 0x3, "Subarea Node or SNA host <--> Subarea Node" },
2219 { 0xf, "Adjacent Subarea Nodes" },
2223 The final implication of this is that display filters work the way you'd
2224 naturally expect them to. You'd type "sna.th.fid == 0xf" to find Adjacent
2225 Subarea Nodes. The user does not have to shift the value of the FID to
2226 the high nibble of the byte ("sna.th.fid == 0xf0") as was necessary
2229 proto_tree_add_protocol_format()
2230 --------------------------------
2231 proto_tree_add_protocol_format is used to add the top-level item for the
2232 protocol when the dissector routine wants complete control over how the
2233 field and value will be represented on the GUI tree. The ID value for
2234 the protocol is passed in as the "id" argument; the rest of the
2235 arguments are a "printf"-style format and any arguments for that format.
2236 The caller must include the name of the protocol in the format; it is
2237 not added automatically as in proto_tree_add_item().
2239 proto_tree_add_none_format()
2240 ----------------------------
2241 proto_tree_add_none_format is used to add an item of type FT_NONE.
2242 The caller must include the name of the field in the format; it is
2243 not added automatically as in proto_tree_add_item().
2245 proto_tree_add_bytes()
2246 proto_tree_add_time()
2247 proto_tree_add_ipxnet()
2248 proto_tree_add_ipv4()
2249 proto_tree_add_ipv6()
2250 proto_tree_add_ether()
2251 proto_tree_add_string()
2252 proto_tree_add_boolean()
2253 proto_tree_add_float()
2254 proto_tree_add_double()
2255 proto_tree_add_uint()
2256 proto_tree_add_uint64()
2257 proto_tree_add_int()
2258 proto_tree_add_int64()
2259 proto_tree_add_guid()
2260 proto_tree_add_oid()
2261 ------------------------
2262 These routines are used to add items to the protocol tree if either:
2264 the value of the item to be added isn't just extracted from the
2265 packet data, but is computed from data in the packet;
2267 the value was fetched into a variable.
2269 The 'value' argument has the value to be added to the tree.
2271 NOTE: in all cases where the 'value' argument is a pointer, a copy is
2272 made of the object pointed to; if you have dynamically allocated a
2273 buffer for the object, that buffer will not be freed when the protocol
2274 tree is freed - you must free the buffer yourself when you don't need it
2277 For proto_tree_add_bytes(), the 'value_ptr' argument is a pointer to a
2280 For proto_tree_add_time(), the 'value_ptr' argument is a pointer to an
2281 "nstime_t", which is a structure containing the time to be added; it has
2282 'secs' and 'nsecs' members, giving the integral part and the fractional
2283 part of a time in units of seconds, with 'nsecs' being the number of
2284 nanoseconds. For absolute times, "secs" is a UNIX-style seconds since
2285 January 1, 1970, 00:00:00 GMT value.
2287 For proto_tree_add_ipxnet(), the 'value' argument is a 32-bit IPX
2290 For proto_tree_add_ipv4(), the 'value' argument is a 32-bit IPv4
2291 address, in network byte order.
2293 For proto_tree_add_ipv6(), the 'value_ptr' argument is a pointer to a
2294 128-bit IPv6 address.
2296 For proto_tree_add_ether(), the 'value_ptr' argument is a pointer to a
2299 For proto_tree_add_string(), the 'value_ptr' argument is a pointer to a
2302 For proto_tree_add_boolean(), the 'value' argument is a 32-bit integer.
2303 It is masked and shifted as defined by the field info after which zero
2304 means "false", and non-zero means "true".
2306 For proto_tree_add_float(), the 'value' argument is a 'float' in the
2307 host's floating-point format.
2309 For proto_tree_add_double(), the 'value' argument is a 'double' in the
2310 host's floating-point format.
2312 For proto_tree_add_uint(), the 'value' argument is a 32-bit unsigned
2313 integer value, in host byte order. (This routine cannot be used to add
2316 For proto_tree_add_uint64(), the 'value' argument is a 64-bit unsigned
2317 integer value, in host byte order.
2319 For proto_tree_add_int(), the 'value' argument is a 32-bit signed
2320 integer value, in host byte order. (This routine cannot be used to add
2323 For proto_tree_add_int64(), the 'value' argument is a 64-bit signed
2324 integer value, in host byte order.
2326 For proto_tree_add_guid(), the 'value_ptr' argument is a pointer to an
2329 For proto_tree_add_oid(), the 'value_ptr' argument is a pointer to an
2330 ASN.1 Object Identifier.
2332 proto_tree_add_bytes_format()
2333 proto_tree_add_time_format()
2334 proto_tree_add_ipxnet_format()
2335 proto_tree_add_ipv4_format()
2336 proto_tree_add_ipv6_format()
2337 proto_tree_add_ether_format()
2338 proto_tree_add_string_format()
2339 proto_tree_add_boolean_format()
2340 proto_tree_add_float_format()
2341 proto_tree_add_double_format()
2342 proto_tree_add_uint_format()
2343 proto_tree_add_uint64_format()
2344 proto_tree_add_int_format()
2345 proto_tree_add_int64_format()
2346 proto_tree_add_guid_format()
2347 proto_tree_add_oid_format()
2348 ----------------------------
2349 These routines are used to add items to the protocol tree when the
2350 dissector routine wants complete control over how the field and value
2351 will be represented on the GUI tree. The argument giving the value is
2352 the same as the corresponding proto_tree_add_XXX() function; the rest of
2353 the arguments are a "printf"-style format and any arguments for that
2354 format. The caller must include the name of the field in the format; it
2355 is not added automatically as in the proto_tree_add_XXX() functions.
2357 proto_tree_add_bytes_format_value()
2358 proto_tree_add_time_format_value()
2359 proto_tree_add_ipxnet_format_value()
2360 proto_tree_add_ipv4_format_value()
2361 proto_tree_add_ipv6_format_value()
2362 proto_tree_add_ether_format_value()
2363 proto_tree_add_string_format_value()
2364 proto_tree_add_boolean_format_value()
2365 proto_tree_add_float_format_value()
2366 proto_tree_add_double_format_value()
2367 proto_tree_add_uint_format_value()
2368 proto_tree_add_uint64_format_value()
2369 proto_tree_add_int_format_value()
2370 proto_tree_add_int64_format_value()
2371 proto_tree_add_guid_format_value()
2372 proto_tree_add_oid_format_value()
2373 ------------------------------------
2375 These routines are used to add items to the protocol tree when the
2376 dissector routine wants complete control over how the value will be
2377 represented on the GUI tree. The argument giving the value is the same
2378 as the corresponding proto_tree_add_XXX() function; the rest of the
2379 arguments are a "printf"-style format and any arguments for that format.
2380 With these routines, unlike the proto_tree_add_XXX_format() routines,
2381 the name of the field is added automatically as in the
2382 proto_tree_add_XXX() functions; only the value is added with the format.
2384 proto_tree_add_text()
2385 ---------------------
2386 proto_tree_add_text() is used to add a label to the GUI tree. It will
2387 contain no value, so it is not searchable in the display filter process.
2388 This function was needed in the transition from the old-style proto_tree
2389 to this new-style proto_tree so that Wireshark would still decode all
2390 protocols w/o being able to filter on all protocols and fields.
2391 Otherwise we would have had to cripple Wireshark's functionality while we
2392 converted all the old-style proto_tree calls to the new-style proto_tree
2393 calls. In other words, you should not use this in new code unless you've got
2394 a specific reason (see below).
2396 This can also be used for items with subtrees, which may not have values
2397 themselves - the items in the subtree are the ones with values.
2399 For a subtree, the label on the subtree might reflect some of the items
2400 in the subtree. This means the label can't be set until at least some
2401 of the items in the subtree have been dissected. To do this, use
2402 'proto_item_set_text()' or 'proto_item_append_text()':
2405 proto_item_set_text(proto_item *ti, ...);
2408 proto_item_append_text(proto_item *ti, ...);
2410 'proto_item_set_text()' takes as an argument the value returned by
2411 'proto_tree_add_text()', a 'printf'-style format string, and a set of
2412 arguments corresponding to '%' format items in that string, and replaces
2413 the text for the item created by 'proto_tree_add_text()' with the result
2414 of applying the arguments to the format string.
2416 'proto_item_append_text()' is similar, but it appends to the text for
2417 the item the result of applying the arguments to the format string.
2419 For example, early in the dissection, one might do:
2421 ti = proto_tree_add_text(tree, tvb, offset, length, <label>);
2425 proto_item_set_text(ti, "%s: %s", type, value);
2427 after the "type" and "value" fields have been extracted and dissected.
2428 <label> would be a label giving what information about the subtree is
2429 available without dissecting any of the data in the subtree.
2431 Note that an exception might be thrown when trying to extract the values of
2432 the items used to set the label, if not all the bytes of the item are
2433 available. Thus, one should create the item with text that is as
2434 meaningful as possible, and set it or append additional information to
2435 it as the values needed to supply that information are extracted.
2437 proto_tree_add_text_valist()
2438 ----------------------------
2439 This is like proto_tree_add_text(), but takes, as the last argument, a
2440 'va_list'; it is used to allow routines that take a printf-like
2441 variable-length list of arguments to add a text item to the protocol
2444 proto_tree_add_bits_item()
2445 --------------------------
2446 Adds a number of bits to the protocol tree which does not have to be byte
2447 aligned. The offset and length is in bits.
2450 ..10 1010 10.. .... "value" (formatted as FT_ indicates).
2452 proto_tree_add_bits_ret_val()
2453 -----------------------------
2454 Works in the same way but also returns the value of the read bits.
2456 proto_tree_add_bitmask() and proto_tree_add_bitmask_text()
2457 ----------------------------------------------------------
2458 This function provides an easy to use and convenient helper function
2459 to manage many types of common bitmasks that occur in protocols.
2461 This function will dissect a 1/2/3/4 byte large bitmask into its individual
2463 header is an integer type and must be of type FT_[U]INT{8|16|24|32} and
2464 represents the entire width of the bitmask.
2466 'header' and 'ett' are the hf fields and ett field respectively to create an
2467 expansion that covers the 1-4 bytes of the bitmask.
2469 'fields' is a NULL terminated array of pointers to hf fields representing
2470 the individual subfields of the bitmask. These fields must either be integers
2471 of the same byte width as 'header' or of the type FT_BOOLEAN.
2472 Each of the entries in 'fields' will be dissected as an item under the
2473 'header' expansion and also IF the field is a boolean and IF it is set to 1,
2474 then the name of that boolean field will be printed on the 'header' expansion
2475 line. For integer type subfields that have a value_string defined, the
2476 matched string from that value_string will be printed on the expansion line
2479 Example: (from the SCSI dissector)
2480 static int hf_scsi_inq_peripheral = -1;
2481 static int hf_scsi_inq_qualifier = -1;
2482 static int hf_scsi_inq_devtype = -1;
2484 static gint ett_scsi_inq_peripheral = -1;
2486 static const int *peripheal_fields[] = {
2487 &hf_scsi_inq_qualifier,
2488 &hf_scsi_inq_devtype,
2492 /* Qualifier and DeviceType */
2493 proto_tree_add_bitmask(tree, tvb, offset, hf_scsi_inq_peripheral,
2494 ett_scsi_inq_peripheral, peripheal_fields, FALSE);
2497 { &hf_scsi_inq_peripheral,
2498 {"Peripheral", "scsi.inquiry.preipheral", FT_UINT8, BASE_HEX,
2499 NULL, 0, NULL, HFILL}},
2500 { &hf_scsi_inq_qualifier,
2501 {"Qualifier", "scsi.inquiry.qualifier", FT_UINT8, BASE_HEX,
2502 VALS (scsi_qualifier_val), 0xE0, NULL, HFILL}},
2503 { &hf_scsi_inq_devtype,
2504 {"Device Type", "scsi.inquiry.devtype", FT_UINT8, BASE_HEX,
2505 VALS (scsi_devtype_val), SCSI_DEV_BITS, NULL, HFILL}},
2508 Which provides very pretty dissection of this one byte bitmask.
2510 Peripheral: 0x05, Qualifier: Device type is connected to logical unit, Device Type: CD-ROM
2511 000. .... = Qualifier: Device type is connected to logical unit (0x00)
2512 ...0 0101 = Device Type: CD-ROM (0x05)
2514 The proto_tree_add_bitmask_text() function is an extended version of
2515 the proto_tree_add_bitmask() function. In addition, it allows to:
2516 - Provide a leading text (e.g. "Flags: ") that will appear before
2517 the comma-separated list of field values
2518 - Provide a fallback text (e.g. "None") that will be appended if
2519 no fields warranted a change to the top-level title.
2520 - Using flags, specify which fields will affect the top-level title.
2522 There are the following flags defined:
2524 BMT_NO_APPEND - the title is taken "as-is" from the 'name' argument.
2525 BMT_NO_INT - only boolean flags are added to the title.
2526 BMT_NO_FALSE - boolean flags are only added to the title if they are set.
2527 BMT_NO_TFS - only add flag name to the title, do not use true_false_string
2529 The proto_tree_add_bitmask() behavior can be obtained by providing
2530 both 'name' and 'fallback' arguments as NULL, and a flags of
2531 (BMT_NO_FALSE|BMT_NO_TFS).
2533 PROTO_ITEM_SET_GENERATED()
2534 --------------------------
2535 PROTO_ITEM_SET_GENERATED is used to mark fields as not being read from the
2536 captured data directly, but inferred from one or more values.
2538 One of the primary uses of this is the presentation of verification of
2539 checksums. Every IP packet has a checksum line, which can present the result
2540 of the checksum verification, if enabled in the preferences. The result is
2541 presented as a subtree, where the result is enclosed in square brackets
2542 indicating a generated field.
2544 Header checksum: 0x3d42 [correct]
2548 PROTO_ITEM_SET_HIDDEN()
2549 -----------------------
2550 PROTO_ITEM_SET_HIDDEN is used to hide fields, which have already been added
2551 to the tree, from being visible in the displayed tree.
2553 NOTE that creating hidden fields is actually quite a bad idea from a UI design
2554 perspective because the user (someone who did not write nor has ever seen the
2555 code) has no way of knowing that hidden fields are there to be filtered on
2556 thus defeating the whole purpose of putting them there. A Better Way might
2557 be to add the fields (that might otherwise be hidden) to a subtree where they
2558 won't be seen unless the user opens the subtree--but they can be found if the
2561 One use for hidden fields (which would be better implemented using visible
2562 fields in a subtree) follows: The caller may want a value to be
2563 included in a tree so that the packet can be filtered on this field, but
2564 the representation of that field in the tree is not appropriate. An
2565 example is the token-ring routing information field (RIF). The best way
2566 to show the RIF in a GUI is by a sequence of ring and bridge numbers.
2567 Rings are 3-digit hex numbers, and bridges are single hex digits:
2569 RIF: 001-A-013-9-C0F-B-555
2571 In the case of RIF, the programmer should use a field with no value and
2572 use proto_tree_add_none_format() to build the above representation. The
2573 programmer can then add the ring and bridge values, one-by-one, with
2574 proto_tree_add_item() and hide them with PROTO_ITEM_SET_HIDDEN() so that the
2575 user can then filter on or search for a particular ring or bridge. Here's a
2576 skeleton of how the programmer might code this.
2579 rif = create_rif_string(...);
2581 proto_tree_add_none_format(tree, hf_tr_rif_label, ..., "RIF: %s", rif);
2583 for(i = 0; i < num_rings; i++) {
2586 pi = proto_tree_add_item(tree, hf_tr_rif_ring, ..., FALSE);
2587 PROTO_ITEM_SET_HIDDEN(pi);
2589 for(i = 0; i < num_rings - 1; i++) {
2592 pi = proto_tree_add_item(tree, hf_tr_rif_bridge, ..., FALSE);
2593 PROTO_ITEM_SET_HIDDEN(pi);
2596 The logical tree has these items:
2598 hf_tr_rif_label, text="RIF: 001-A-013-9-C0F-B-555", value = NONE
2599 hf_tr_rif_ring, hidden, value=0x001
2600 hf_tr_rif_bridge, hidden, value=0xA
2601 hf_tr_rif_ring, hidden, value=0x013
2602 hf_tr_rif_bridge, hidden, value=0x9
2603 hf_tr_rif_ring, hidden, value=0xC0F
2604 hf_tr_rif_bridge, hidden, value=0xB
2605 hf_tr_rif_ring, hidden, value=0x555
2607 GUI or print code will not display the hidden fields, but a display
2608 filter or "packet grep" routine will still see the values. The possible
2609 filter is then possible:
2611 tr.rif_ring eq 0x013
2615 PROTO_ITEM_SET_URL is used to mark fields as containing a URL. This can only
2616 be done with fields of type FT_STRING(Z). If these fields are presented they
2617 are underlined, as could be done in a browser. These fields are sensitive to
2618 clicks as well, launching the configured browser with this URL as parameter.
2620 1.7 Utility routines.
2622 1.7.1 match_strval and val_to_str.
2624 A dissector may need to convert a value to a string, using a
2625 'value_string' structure, by hand, rather than by declaring a field with
2626 an associated 'value_string' structure; this might be used, for example,
2627 to generate a COL_INFO line for a frame.
2629 'match_strval()' will do that:
2632 match_strval(guint32 val, const value_string *vs)
2634 It will look up the value 'val' in the 'value_string' table pointed to
2635 by 'vs', and return either the corresponding string, or NULL if the
2636 value could not be found in the table. Note that, unless 'val' is
2637 guaranteed to be a value in the 'value_string' table ("guaranteed" as in
2638 "the code has already checked that it's one of those values" or "the
2639 table handles all possible values of the size of 'val'", not "the
2640 protocol spec says it has to be" - protocol specs do not prevent invalid
2641 packets from being put onto a network or into a purported packet capture
2642 file), you must check whether 'match_strval()' returns NULL, and arrange
2643 that its return value not be dereferenced if it's NULL. 'val_to_str()'
2644 can be used to generate a string for values not found in the table:
2647 val_to_str(guint32 val, const value_string *vs, const char *fmt)
2649 If the value 'val' is found in the 'value_string' table pointed to by
2650 'vs', 'val_to_str' will return the corresponding string; otherwise, it
2651 will use 'fmt' as an 'sprintf'-style format, with 'val' as an argument,
2652 to generate a string, and will return a pointer to that string.
2653 You can use it in a call to generate a COL_INFO line for a frame such as
2655 col_add_fstr(COL_INFO, ", %s", val_to_str(val, table, "Unknown %d"));
2657 1.7.2 match_strrval and rval_to_str.
2659 A dissector may need to convert a range of values to a string, using a
2660 'range_string' structure.
2662 'match_strrval()' will do that:
2665 match_strrval(guint32 val, const range_string *rs)
2667 It will look up the value 'val' in the 'range_string' table pointed to
2668 by 'rs', and return either the corresponding string, or NULL if the
2669 value could not be found in the table. Please note that its base
2670 behavior is inherited from match_strval().
2672 'rval_to_str()' can be used to generate a string for values not found in
2676 rval_to_str(guint32 val, const range_string *rs, const char *fmt)
2678 If the value 'val' is found in the 'range_string' table pointed to by
2679 'rs', 'rval_to_str' will return the corresponding string; otherwise, it
2680 will use 'fmt' as an 'sprintf'-style format, with 'val' as an argument,
2681 to generate a string, and will return a pointer to that string. Please
2682 note that its base behavior is inherited from match_strval().
2684 1.8 Calling Other Dissectors.
2686 As each dissector completes its portion of the protocol analysis, it
2687 is expected to create a new tvbuff of type TVBUFF_SUBSET which
2688 contains the payload portion of the protocol (that is, the bytes
2689 that are relevant to the next dissector).
2691 The syntax for creating a new TVBUFF_SUBSET is:
2693 next_tvb = tvb_new_subset(tvb, offset, length, reported_length)
2696 tvb is the tvbuff that the dissector has been working on. It
2697 can be a tvbuff of any type.
2699 next_tvb is the new TVBUFF_SUBSET.
2701 offset is the byte offset of 'tvb' at which the new tvbuff
2702 should start. The first byte is the 0th byte.
2704 length is the number of bytes in the new TVBUFF_SUBSET. A length
2705 argument of -1 says to use as many bytes as are available in
2708 reported_length is the number of bytes that the current protocol
2709 says should be in the payload. A reported_length of -1 says that
2710 the protocol doesn't say anything about the size of its payload.
2713 An example from packet-ipx.c -
2716 dissect_ipx(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
2719 int reported_length, available_length;
2722 /* Make the next tvbuff */
2724 /* IPX does have a length value in the header, so calculate report_length */
2725 Set this to -1 if there isn't any length information in the protocol
2727 reported_length = ipx_length - IPX_HEADER_LEN;
2729 /* Calculate the available data in the packet,
2730 set this to -1 to use all the data in the tv_buffer
2732 available_length = tvb_length(tvb) - IPX_HEADER_LEN;
2734 /* Create the tvbuffer for the next dissector */
2735 next_tvb = tvb_new_subset(tvb, IPX_HEADER_LEN,
2736 MIN(available_length, reported_length),
2739 /* call the next dissector */
2740 dissector_next( next_tvb, pinfo, tree);
2743 1.9 Editing Makefile.common to add your dissector.
2745 To arrange that your dissector will be built as part of Wireshark, you
2746 must add the name of the source file for your dissector to the
2747 'DISSECTOR_SRC' macro in the 'Makefile.common' file in the 'epan/dissectors'
2748 directory. (Note that this is for modern versions of UNIX, so there
2749 is no 14-character limitation on file names, and for modern versions of
2750 Windows, so there is no 8.3-character limitation on file names.)
2752 If your dissector also has its own header file or files, you must add
2753 them to the 'DISSECTOR_INCLUDES' macro in the 'Makefile.common' file in
2754 the 'epan/dissectors' directory, so that it's included when release source
2755 tarballs are built (otherwise, the source in the release tarballs won't
2758 1.10 Using the SVN source code tree.
2760 See <http://www.wireshark.org/develop.html>
2762 1.11 Submitting code for your new dissector.
2764 - VERIFY that your dissector code does not use prohibited or deprecated APIs
2766 perl <wireshark_root>/tools/checkAPIs.pl <source-filename(s)>
2768 - TEST YOUR DISSECTOR BEFORE SUBMITTING IT.
2769 Use fuzz-test.sh and/or randpkt against your dissector. These are
2770 described at <http://wiki.wireshark.org/FuzzTesting>.
2772 - Subscribe to <mailto:wireshark-dev[AT]wireshark.org> by sending an email to
2773 <mailto:wireshark-dev-request[AT]wireshark.org?body="help"> or visiting
2774 <http://www.wireshark.org/lists/>.
2776 - 'svn add' all the files of your new dissector.
2778 - 'svn diff' the workspace and save the result to a file.
2780 - Edit the diff file - remove any changes unrelated to your new dissector,
2781 e.g. changes in config.nmake
2783 - Submit a bug report to the Wireshark bug database, found at
2784 <http://bugs.wireshark.org>, qualified as an enhancement and attach your
2785 diff file there. Set the review request flag to '?' so it will pop up in
2786 the patch review list.
2788 - Create a Wiki page on the protocol at <http://wiki.wireshark.org>.
2789 A template is provided so it is easy to setup in a consistent style.
2791 - If possible, add sample capture files to the sample captures page at
2792 <http://wiki.wireshark.org/SampleCaptures>. These files are used by
2793 the automated build system for fuzz testing.
2795 - If you find that you are contributing a lot to wireshark on an ongoing
2796 basis you can request to become a committer which will allow you to
2797 commit files to subversion directly.
2799 2. Advanced dissector topics.
2803 Some of the advanced features are being worked on constantly. When using them
2804 it is wise to check the relevant header and source files for additional details.
2806 2.2 Following "conversations".
2808 In wireshark a conversation is defined as a series of data packets between two
2809 address:port combinations. A conversation is not sensitive to the direction of
2810 the packet. The same conversation will be returned for a packet bound from
2811 ServerA:1000 to ClientA:2000 and the packet from ClientA:2000 to ServerA:1000.
2813 There are five routines that you will use to work with a conversation:
2814 conversation_new, find_conversation, conversation_add_proto_data,
2815 conversation_get_proto_data, and conversation_delete_proto_data.
2818 2.2.1 The conversation_init function.
2820 This is an internal routine for the conversation code. As such you
2821 will not have to call this routine. Just be aware that this routine is
2822 called at the start of each capture and before the packets are filtered
2823 with a display filter. The routine will destroy all stored
2824 conversations. This routine does NOT clean up any data pointers that are
2825 passed in the conversation_new 'data' variable. You are responsible for
2826 this clean up if you pass a malloc'ed pointer in this variable.
2828 See item 2.2.8 for more information about the 'data' pointer.
2831 2.2.2 The conversation_new function.
2833 This routine will create a new conversation based upon two address/port
2834 pairs. If you want to associate with the conversation a pointer to a
2835 private data structure you must use the conversation_add_proto_data
2836 function. The ptype variable is used to differentiate between
2837 conversations over different protocols, i.e. TCP and UDP. The options
2838 variable is used to define a conversation that will accept any destination
2839 address and/or port. Set options = 0 if the destination port and address
2840 are know when conversation_new is called. See section 2.4 for more
2841 information on usage of the options parameter.
2843 The conversation_new prototype:
2844 conversation_t *conversation_new(guint32 setup_frame, address *addr1,
2845 address *addr2, port_type ptype, guint32 port1, guint32 port2,
2849 guint32 setup_frame = The lowest numbered frame for this conversation
2850 address* addr1 = first data packet address
2851 address* addr2 = second data packet address
2852 port_type ptype = port type, this is defined in packet.h
2853 guint32 port1 = first data packet port
2854 guint32 port2 = second data packet port
2855 guint options = conversation options, NO_ADDR2 and/or NO_PORT2
2857 setup_frame indicates the first frame for this conversation, and is used to
2858 distinguish multiple conversations with the same addr1/port1 and addr2/port2
2859 pair that occur within the same capture session.
2861 "addr1" and "port1" are the first address/port pair; "addr2" and "port2"
2862 are the second address/port pair. A conversation doesn't have source
2863 and destination address/port pairs - packets in a conversation go in
2864 both directions - so "addr1"/"port1" may be the source or destination
2865 address/port pair; "addr2"/"port2" would be the other pair.
2867 If NO_ADDR2 is specified, the conversation is set up so that a
2868 conversation lookup will match only the "addr1" address; if NO_PORT2 is
2869 specified, the conversation is set up so that a conversation lookup will
2870 match only the "port1" port; if both are specified, i.e.
2871 NO_ADDR2|NO_PORT2, the conversation is set up so that the lookup will
2872 match only the "addr1"/"port1" address/port pair. This can be used if a
2873 packet indicates that, later in the capture, a conversation will be
2874 created using certain addresses and ports, in the case where the packet
2875 doesn't specify the addresses and ports of both sides.
2877 2.2.3 The find_conversation function.
2879 Call this routine to look up a conversation. If no conversation is found,
2880 the routine will return a NULL value.
2882 The find_conversation prototype:
2884 conversation_t *find_conversation(guint32 frame_num, address *addr_a,
2885 address *addr_b, port_type ptype, guint32 port_a, guint32 port_b,
2889 guint32 frame_num = a frame number to match
2890 address* addr_a = first address
2891 address* addr_b = second address
2892 port_type ptype = port type
2893 guint32 port_a = first data packet port
2894 guint32 port_b = second data packet port
2895 guint options = conversation options, NO_ADDR_B and/or NO_PORT_B
2897 frame_num is a frame number to match. The conversation returned is where
2898 (frame_num >= conversation->setup_frame
2899 && frame_num < conversation->next->setup_frame)
2900 Suppose there are a total of 3 conversations (A, B, and C) that match
2901 addr_a/port_a and addr_b/port_b, where the setup_frame used in
2902 conversation_new() for A, B and C are 10, 50, and 100 respectively. The
2903 frame_num passed in find_conversation is compared to the setup_frame of each
2904 conversation. So if (frame_num >= 10 && frame_num < 50), conversation A is
2905 returned. If (frame_num >= 50 && frame_num < 100), conversation B is returned.
2906 If (frame_num >= 100) conversation C is returned.
2908 "addr_a" and "port_a" are the first address/port pair; "addr_b" and
2909 "port_b" are the second address/port pair. Again, as a conversation
2910 doesn't have source and destination address/port pairs, so
2911 "addr_a"/"port_a" may be the source or destination address/port pair;
2912 "addr_b"/"port_b" would be the other pair. The search will match the
2913 "a" address/port pair against both the "1" and "2" address/port pairs,
2914 and match the "b" address/port pair against both the "2" and "1"
2915 address/port pairs; you don't have to worry about which side the "a" or
2916 "b" pairs correspond to.
2918 If the NO_ADDR_B flag was specified to "find_conversation()", the
2919 "addr_b" address will be treated as matching any "wildcarded" address;
2920 if the NO_PORT_B flag was specified, the "port_b" port will be treated
2921 as matching any "wildcarded" port. If both flags are specified, i.e.
2922 NO_ADDR_B|NO_PORT_B, the "addr_b" address will be treated as matching
2923 any "wildcarded" address and the "port_b" port will be treated as
2924 matching any "wildcarded" port.
2927 2.2.4 The conversation_add_proto_data function.
2929 Once you have created a conversation with conversation_new, you can
2930 associate data with it using this function.
2932 The conversation_add_proto_data prototype:
2934 void conversation_add_proto_data(conversation_t *conv, int proto,
2938 conversation_t *conv = the conversation in question
2939 int proto = registered protocol number
2940 void *data = dissector data structure
2942 "conversation" is the value returned by conversation_new. "proto" is a
2943 unique protocol number created with proto_register_protocol. Protocols
2944 are typically registered in the proto_register_XXXX section of your
2945 dissector. "data" is a pointer to the data you wish to associate with the
2946 conversation. Using the protocol number allows several dissectors to
2947 associate data with a given conversation.
2950 2.2.5 The conversation_get_proto_data function.
2952 After you have located a conversation with find_conversation, you can use
2953 this function to retrieve any data associated with it.
2955 The conversation_get_proto_data prototype:
2957 void *conversation_get_proto_data(conversation_t *conv, int proto);
2960 conversation_t *conv = the conversation in question
2961 int proto = registered protocol number
2963 "conversation" is the conversation created with conversation_new. "proto"
2964 is a unique protocol number created with proto_register_protocol,
2965 typically in the proto_register_XXXX portion of a dissector. The function
2966 returns a pointer to the data requested, or NULL if no data was found.
2969 2.2.6 The conversation_delete_proto_data function.
2971 After you are finished with a conversation, you can remove your association
2972 with this function. Please note that ONLY the conversation entry is
2973 removed. If you have allocated any memory for your data, you must free it
2976 The conversation_delete_proto_data prototype:
2978 void conversation_delete_proto_data(conversation_t *conv, int proto);
2981 conversation_t *conv = the conversation in question
2982 int proto = registered protocol number
2984 "conversation" is the conversation created with conversation_new. "proto"
2985 is a unique protocol number created with proto_register_protocol,
2986 typically in the proto_register_XXXX portion of a dissector.
2989 2.2.7 Using timestamps relative to the conversation
2991 There is a framework to calculate timestamps relative to the start of the
2992 conversation. First of all the timestamp of the first packet that has been
2993 seen in the conversation must be kept in the protocol data to be able
2994 to calculate the timestamp of the current packet relative to the start
2995 of the conversation. The timestamp of the last packet that was seen in the
2996 conversation should also be kept in the protocol data. This way the
2997 delta time between the current packet and the previous packet in the
2998 conversation can be calculated.
3000 So add the following items to the struct that is used for the protocol data:
3005 The ts_prev value should only be set during the first run through the
3006 packets (ie pinfo->fd->flags.visited is false).
3008 Next step is to use the per-packet information (described in section 2.5)
3009 to keep the calculated delta timestamp, as it can only be calculated
3010 on the first run through the packets. This is because a packet can be
3011 selected in random order once the whole file has been read.
3013 After calculating the conversation timestamps, it is time to put them in
3014 the appropriate columns with the function 'col_set_time' (described in
3015 section 1.5.9). There are two columns for conversation timestamps:
3017 COL_REL_CONV_TIME, /* Relative time to beginning of conversation */
3018 COL_DELTA_CONV_TIME,/* Delta time to last frame in conversation */
3020 Last but not least, there MUST be a preference in each dissector that
3021 uses conversation timestamps that makes it possible to enable and
3022 disable the calculation of conversation timestamps. The main argument
3023 for this is that a higher level conversation is able to overwrite
3024 the values of lowel level conversations in these two columns. Being
3025 able to actively select which protocols may overwrite the conversation
3026 timestamp columns gives the user the power to control these columns.
3027 (A second reason is that conversation timestamps use the per-packet
3028 data structure which uses additional memory, which should be avoided
3029 if these timestamps are not needed)
3031 Have a look at the differences to packet-tcp.[ch] in SVN 22966 and
3032 SVN 23058 to see the implementation of conversation timestamps for
3036 2.2.8 The example conversation code with GMemChunk's.
3038 For a conversation between two IP addresses and ports you can use this as an
3039 example. This example uses the GMemChunk to allocate memory and stores the data
3040 pointer in the conversation 'data' variable.
3042 NOTE: Remember to register the init routine (my_dissector_init) in the
3043 protocol_register routine.
3046 /************************ Global values ************************/
3048 /* the number of entries in the memory chunk array */
3049 #define my_init_count 10
3051 /* define your structure here */
3056 /* the GMemChunk base structure */
3057 static GMemChunk *my_vals = NULL;
3059 /* Registered protocol number */
3060 static int my_proto = -1;
3063 /********************* in the dissector routine *********************/
3065 /* the local variables in the dissector */
3067 conversation_t *conversation;
3068 my_entry_t *data_ptr;
3071 /* look up the conversation */
3073 conversation = find_conversation(pinfo->fd->num, &pinfo->src, &pinfo->dst,
3074 pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
3076 /* if conversation found get the data pointer that you stored */
3078 data_ptr = (my_entry_t*)conversation_get_proto_data(conversation, my_proto);
3081 /* new conversation create local data structure */
3083 data_ptr = g_mem_chunk_alloc(my_vals);
3085 /*** add your code here to setup the new data structure ***/
3087 /* create the conversation with your data pointer */
3089 conversation = conversation_new(pinfo->fd->num, &pinfo->src, &pinfo->dst, pinfo->ptype,
3090 pinfo->srcport, pinfo->destport, 0);
3091 conversation_add_proto_data(conversation, my_proto, (void *)data_ptr);
3094 /* at this point the conversation data is ready */
3097 /******************* in the dissector init routine *******************/
3099 #define my_init_count 20
3102 my_dissector_init(void)
3105 /* destroy memory chunks if needed */
3108 g_mem_chunk_destroy(my_vals);
3110 /* now create memory chunks */
3112 my_vals = g_mem_chunk_new("my_proto_vals",
3114 my_init_count * sizeof(my_entry_t),
3118 /***************** in the protocol register routine *****************/
3120 /* register re-init routine */
3122 register_init_routine(&my_dissector_init);
3124 my_proto = proto_register_protocol("My Protocol", "My Protocol", "my_proto");
3127 2.2.9 An example conversation code that starts at a specific frame number.
3129 Sometimes a dissector has determined that a new conversation is needed that
3130 starts at a specific frame number, when a capture session encompasses multiple
3131 conversation that reuse the same src/dest ip/port pairs. You can use the
3132 conversation->setup_frame returned by find_conversation with
3133 pinfo->fd->num to determine whether or not there already exists a conversation
3134 that starts at the specific frame number.
3136 /* in the dissector routine */
3138 conversation = find_conversation(pinfo->fd->num, &pinfo->src, &pinfo->dst,
3139 pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
3140 if (conversation == NULL || (conversation->setup_frame != pinfo->fd->num)) {
3141 /* It's not part of any conversation or the returned
3142 * conversation->setup_frame doesn't match the current frame
3145 conversation = conversation_new(pinfo->fd->num, &pinfo->src,
3146 &pinfo->dst, pinfo->ptype, pinfo->srcport, pinfo->destport,
3151 2.2.10 The example conversation code using conversation index field.
3153 Sometimes the conversation isn't enough to define a unique data storage
3154 value for the network traffic. For example if you are storing information
3155 about requests carried in a conversation, the request may have an
3156 identifier that is used to define the request. In this case the
3157 conversation and the identifier are required to find the data storage
3158 pointer. You can use the conversation data structure index value to
3159 uniquely define the conversation.
3161 See packet-afs.c for an example of how to use the conversation index. In
3162 this dissector multiple requests are sent in the same conversation. To store
3163 information for each request the dissector has an internal hash table based
3164 upon the conversation index and values inside the request packets.
3167 /* in the dissector routine */
3169 /* to find a request value, first lookup conversation to get index */
3170 /* then used the conversation index, and request data to find data */
3171 /* in the local hash table */
3173 conversation = find_conversation(pinfo->fd->num, &pinfo->src, &pinfo->dst,
3174 pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
3175 if (conversation == NULL) {
3176 /* It's not part of any conversation - create a new one. */
3177 conversation = conversation_new(pinfo->fd->num, &pinfo->src,
3178 &pinfo->dst, pinfo->ptype, pinfo->srcport, pinfo->destport,
3182 request_key.conversation = conversation->index;
3183 request_key.service = pntohs(&rxh->serviceId);
3184 request_key.callnumber = pntohl(&rxh->callNumber);
3186 request_val = (struct afs_request_val *)g_hash_table_lookup(
3187 afs_request_hash, &request_key);
3189 /* only allocate a new hash element when it's a request */
3191 if (!request_val && !reply)
3193 new_request_key = g_mem_chunk_alloc(afs_request_keys);
3194 *new_request_key = request_key;
3196 request_val = g_mem_chunk_alloc(afs_request_vals);
3197 request_val -> opcode = pntohl(&afsh->opcode);
3198 opcode = request_val->opcode;
3200 g_hash_table_insert(afs_request_hash, new_request_key,
3206 2.3 Dynamic conversation dissector registration.
3209 NOTE: This sections assumes that all information is available to
3210 create a complete conversation, source port/address and
3211 destination port/address. If either the destination port or
3212 address is know, see section 2.4 Dynamic server port dissector
3215 For protocols that negotiate a secondary port connection, for example
3216 packet-msproxy.c, a conversation can install a dissector to handle
3217 the secondary protocol dissection. After the conversation is created
3218 for the negotiated ports use the conversation_set_dissector to define
3219 the dissection routine.
3220 Before we create these conversations or assign a dissector to them we should
3221 first check that the conversation does not already exist and if it exists
3222 whether it is registered to our protocol or not.
3223 We should do this because it is uncommon but it does happen that multiple
3224 different protocols can use the same socketpair during different stages of
3225 an application cycle. By keeping track of the frame number a conversation
3226 was started in wireshark can still tell these different protocols apart.
3228 The second argument to conversation_set_dissector is a dissector handle,
3229 which is created with a call to create_dissector_handle or
3232 create_dissector_handle takes as arguments a pointer to the dissector
3233 function and a protocol ID as returned by proto_register_protocol;
3234 register_dissector takes as arguments a string giving a name for the
3235 dissector, a pointer to the dissector function, and a protocol ID.
3237 The protocol ID is the ID for the protocol dissected by the function.
3238 The function will not be called if the protocol has been disabled by the
3239 user; instead, the data for the protocol will be dissected as raw data.
3243 /* the handle for the dynamic dissector *
3244 static dissector_handle_t sub_dissector_handle;
3246 /* prototype for the dynamic dissector */
3247 static void sub_dissector(tvbuff_t *tvb, packet_info *pinfo,
3250 /* in the main protocol dissector, where the next dissector is setup */
3252 /* if conversation has a data field, create it and load structure */
3254 /* First check if a conversation already exists for this
3257 conversation = find_conversation(pinfo->fd->num,
3258 &pinfo->src, &pinfo->dst, protocol,
3259 src_port, dst_port, new_conv_info, 0);
3261 /* If there is no such conversation, or if there is one but for
3262 someone else's protocol then we just create a new conversation
3263 and assign our protocol to it.
3265 if ( (conversation == NULL) ||
3266 (conversation->dissector_handle != sub_dissector_handle) ) {
3267 new_conv_info = g_mem_chunk_alloc(new_conv_vals);
3268 new_conv_info->data1 = value1;
3270 /* create the conversation for the dynamic port */
3271 conversation = conversation_new(pinfo->fd->num,
3272 &pinfo->src, &pinfo->dst, protocol,
3273 src_port, dst_port, new_conv_info, 0);
3275 /* set the dissector for the new conversation */
3276 conversation_set_dissector(conversation, sub_dissector_handle);
3281 proto_register_PROTOABBREV(void)
3285 sub_dissector_handle = create_dissector_handle(sub_dissector,
3291 2.4 Dynamic server port dissector registration.
3293 NOTE: While this example used both NO_ADDR2 and NO_PORT2 to create a
3294 conversation with only one port and address set, this isn't a
3295 requirement. Either the second port or the second address can be set
3296 when the conversation is created.
3298 For protocols that define a server address and port for a secondary
3299 protocol, a conversation can be used to link a protocol dissector to
3300 the server port and address. The key is to create the new
3301 conversation with the second address and port set to the "accept
3304 Some server applications can use the same port for different protocols during
3305 different stages of a transaction. For example it might initially use SNMP
3306 to perform some discovery and later switch to use TFTP using the same port.
3307 In order to handle this properly we must first check whether such a
3308 conversation already exists or not and if it exists we also check whether the
3309 registered dissector_handle for that conversation is "our" dissector or not.
3310 If not we create a new conversation on top of the previous one and set this new
3311 conversation to use our protocol.
3312 Since wireshark keeps track of the frame number where a conversation started
3313 wireshark will still be able to keep the packets apart even though they do use
3314 the same socketpair.
3315 (See packet-tftp.c and packet-snmp.c for examples of this)
3317 There are two support routines that will allow the second port and/or
3318 address to be set later.
3320 conversation_set_port2( conversation_t *conv, guint32 port);
3321 conversation_set_addr2( conversation_t *conv, address addr);
3323 These routines will change the second address or port for the
3324 conversation. So, the server port conversation will be converted into a
3325 more complete conversation definition. Don't use these routines if you
3326 want to create a conversation between the server and client and retain the
3327 server port definition, you must create a new conversation.
3332 /* the handle for the dynamic dissector *
3333 static dissector_handle_t sub_dissector_handle;
3337 /* in the main protocol dissector, where the next dissector is setup */
3339 /* if conversation has a data field, create it and load structure */
3341 new_conv_info = g_mem_chunk_alloc(new_conv_vals);
3342 new_conv_info->data1 = value1;
3344 /* create the conversation for the dynamic server address and port */
3345 /* NOTE: The second address and port values don't matter because the */
3346 /* NO_ADDR2 and NO_PORT2 options are set. */
3348 /* First check if a conversation already exists for this
3351 conversation = find_conversation(pinfo->fd->num,
3352 &server_src_addr, 0, protocol,
3353 server_src_port, 0, NO_ADDR2 | NO_PORT_B);
3354 /* If there is no such conversation, or if there is one but for
3355 someone else's protocol then we just create a new conversation
3356 and assign our protocol to it.
3358 if ( (conversation == NULL) ||
3359 (conversation->dissector_handle != sub_dissector_handle) ) {
3360 conversation = conversation_new(pinfo->fd->num,
3361 &server_src_addr, 0, protocol,
3362 server_src_port, 0, new_conv_info, NO_ADDR2 | NO_PORT2);
3364 /* set the dissector for the new conversation */
3365 conversation_set_dissector(conversation, sub_dissector_handle);
3368 2.5 Per-packet information.
3370 Information can be stored for each data packet that is processed by the
3371 dissector. The information is added with the p_add_proto_data function and
3372 retrieved with the p_get_proto_data function. The data pointers passed into
3373 the p_add_proto_data are not managed by the proto_data routines. If you use
3374 malloc or any other dynamic memory allocation scheme, you must release the
3375 data when it isn't required.
3378 p_add_proto_data(frame_data *fd, int proto, void *proto_data)
3380 p_get_proto_data(frame_data *fd, int proto)
3383 fd - The fd pointer in the pinfo structure, pinfo->fd
3384 proto - Protocol id returned by the proto_register_protocol call
3385 during initialization
3386 proto_data - pointer to the dissector data.
3389 2.6 User Preferences.
3391 If the dissector has user options, there is support for adding these preferences
3392 to a configuration dialog.
3394 You must register the module with the preferences routine with -
3396 module_t *prefs_register_protocol(proto_id, void (*apply_cb)(void))
3398 Where: proto_id - the value returned by "proto_register_protocol()" when
3399 the protocol was registered.
3400 apply_cb - Callback routine that is called when preferences are
3401 applied. It may be NULL, which inhibits the callback.
3403 Then you can register the fields that can be configured by the user with these
3406 /* Register a preference with an unsigned integral value. */
3407 void prefs_register_uint_preference(module_t *module, const char *name,
3408 const char *title, const char *description, guint base, guint *var);
3410 /* Register a preference with an Boolean value. */
3411 void prefs_register_bool_preference(module_t *module, const char *name,
3412 const char *title, const char *description, gboolean *var);
3414 /* Register a preference with an enumerated value. */
3415 void prefs_register_enum_preference(module_t *module, const char *name,
3416 const char *title, const char *description, gint *var,
3417 const enum_val_t *enumvals, gboolean radio_buttons)
3419 /* Register a preference with a character-string value. */
3420 void prefs_register_string_preference(module_t *module, const char *name,
3421 const char *title, const char *description, char **var)
3423 /* Register a preference with a range of unsigned integers (e.g.,
3426 void prefs_register_range_preference(module_t *module, const char *name,
3427 const char *title, const char *description, range_t *var,
3430 Where: module - Returned by the prefs_register_protocol routine
3431 name - This is appended to the name of the protocol, with a
3432 "." between them, to construct a name that identifies
3433 the field in the preference file; the name itself
3434 should not include the protocol name, as the name in
3435 the preference file will already have it
3436 title - Field title in the preferences dialog
3437 description - Comments added to the preference file above the
3439 var - pointer to the storage location that is updated when the
3440 field is changed in the preference dialog box
3441 base - Base that the unsigned integer is expected to be in,
3443 enumvals - an array of enum_val_t structures. This must be
3444 NULL-terminated; the members of that structure are:
3446 a short name, to be used with the "-o" flag - it
3447 should not contain spaces or upper-case letters,
3448 so that it's easier to put in a command line;
3450 a description, which is used in the GUI (and
3451 which, for compatibility reasons, is currently
3452 what's written to the preferences file) - it can
3453 contain spaces, capital letters, punctuation,
3456 the numerical value corresponding to that name
3458 radio_buttons - TRUE if the field is to be displayed in the
3459 preferences dialog as a set of radio buttons,
3460 FALSE if it is to be displayed as an option
3462 max_value - The maximum allowed value for a range (0 is the minimum).
3464 An example from packet-beep.c -
3466 proto_beep = proto_register_protocol("Blocks Extensible Exchange Protocol",
3471 /* Register our configuration options for BEEP, particularly our port */
3473 beep_module = prefs_register_protocol(proto_beep, proto_reg_handoff_beep);
3475 prefs_register_uint_preference(beep_module, "tcp.port", "BEEP TCP Port",
3476 "Set the port for BEEP messages (if other"
3477 " than the default of 10288)",
3478 10, &global_beep_tcp_port);
3480 prefs_register_bool_preference(beep_module, "strict_header_terminator",
3481 "BEEP Header Requires CRLF",
3482 "Specifies that BEEP requires CRLF as a "
3483 "terminator, and not just CR or LF",
3484 &global_beep_strict_term);
3486 This will create preferences "beep.tcp.port" and
3487 "beep.strict_header_terminator", the first of which is an unsigned
3488 integer and the second of which is a Boolean.
3490 Note that a warning will pop up if you've saved such preference to the
3491 preference file and you subsequently take the code out. The way to make
3492 a preference obsolete is to register it as such:
3494 /* Register a preference that used to be supported but no longer is. */
3495 void prefs_register_obsolete_preference(module_t *module,
3498 2.7 Reassembly/desegmentation for protocols running atop TCP.
3500 There are two main ways of reassembling a Protocol Data Unit (PDU) which
3501 spans across multiple TCP segments. The first approach is simpler, but
3502 assumes you are running atop of TCP when this occurs (but your dissector
3503 might run atop of UDP, too, for example), and that your PDUs consist of a
3504 fixed amount of data that includes enough information to determine the PDU
3505 length, possibly followed by additional data. The second method is more
3506 generic but requires more code and is less efficient.
3508 2.7.1 Using tcp_dissect_pdus().
3510 For the first method, you register two different dissection methods, one
3511 for the TCP case, and one for the other cases. It is a good idea to
3512 also have a dissect_PROTO_common function which will parse the generic
3513 content that you can find in all PDUs which is called from
3514 dissect_PROTO_tcp when the reassembly is complete and from
3515 dissect_PROTO_udp (or dissect_PROTO_other).
3517 To register the distinct dissector functions, consider the following
3518 example, stolen from packet-dns.c:
3520 dissector_handle_t dns_udp_handle;
3521 dissector_handle_t dns_tcp_handle;
3522 dissector_handle_t mdns_udp_handle;
3524 dns_udp_handle = create_dissector_handle(dissect_dns_udp,
3526 dns_tcp_handle = create_dissector_handle(dissect_dns_tcp,
3528 mdns_udp_handle = create_dissector_handle(dissect_mdns_udp,
3531 dissector_add("udp.port", UDP_PORT_DNS, dns_udp_handle);
3532 dissector_add("tcp.port", TCP_PORT_DNS, dns_tcp_handle);
3533 dissector_add("udp.port", UDP_PORT_MDNS, mdns_udp_handle);
3534 dissector_add("tcp.port", TCP_PORT_MDNS, dns_tcp_handle);
3536 The dissect_dns_udp function does very little work and calls
3537 dissect_dns_common, while dissect_dns_tcp calls tcp_dissect_pdus with a
3538 reference to a callback which will be called with reassembled data:
3541 dissect_dns_tcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
3543 tcp_dissect_pdus(tvb, pinfo, tree, dns_desegment, 2,
3544 get_dns_pdu_len, dissect_dns_tcp_pdu);
3547 (The dissect_dns_tcp_pdu function acts similarly to dissect_dns_udp.)
3548 The arguments to tcp_dissect_pdus are:
3550 the tvbuff pointer, packet_info pointer, and proto_tree pointer
3551 passed to the dissector;
3553 a gboolean flag indicating whether desegmentation is enabled for
3556 the number of bytes of PDU data required to determine the length
3559 a routine that takes as arguments a packet_info pointer, a tvbuff
3560 pointer and an offset value representing the offset into the tvbuff
3561 at which a PDU begins and should return - *without* throwing an
3562 exception (it is guaranteed that the number of bytes specified by the
3563 previous argument to tcp_dissect_pdus is available, but more data
3564 might not be available, so don't refer to any data past that) - the
3565 total length of the PDU, in bytes;
3567 a routine that's passed a tvbuff pointer, packet_info pointer,
3568 and proto_tree pointer, with the tvbuff containing a
3569 possibly-reassembled PDU, and that should dissect that PDU.
3571 2.7.2 Modifying the pinfo struct.
3573 The second reassembly mode is preferred when the dissector cannot determine
3574 how many bytes it will need to read in order to determine the size of a PDU.
3575 It may also be useful if your dissector needs to support reassembly from
3576 protocols other than TCP.
3578 Your dissect_PROTO will initially be passed a tvbuff containing the payload of
3579 the first packet. It should dissect as much data as it can, noting that it may
3580 contain more than one complete PDU. If the end of the provided tvbuff coincides
3581 with the end of a PDU then all is well and your dissector can just return as
3582 normal. (If it is a new-style dissector, it should return the number of bytes
3583 successfully processed.)
3585 If the dissector discovers that the end of the tvbuff does /not/ coincide with
3586 the end of a PDU, (ie, there is half of a PDU at the end of the tvbuff), it can
3587 indicate this to the parent dissector, by updating the pinfo struct. The
3588 desegment_offset field is the offset in the tvbuff at which the dissector will
3589 continue processing when next called. The desegment_len field should contain
3590 the estimated number of additional bytes required for completing the PDU. Next
3591 time your dissect_PROTO is called, it will be passed a tvbuff composed of the
3592 end of the data from the previous tvbuff together with desegment_len more bytes.
3594 If the dissector cannot tell how many more bytes it will need, it should set
3595 desegment_len=DESEGMENT_ONE_MORE_SEGMENT; it will then be called again as soon
3596 as any more data becomes available. Dissectors should set the desegment_len to a
3597 reasonable value when possible rather than always setting
3598 DESEGMENT_ONE_MORE_SEGMENT as it will generally be more efficient. Also, you
3599 *must not* set desegment_len=1 in this case, in the hope that you can change
3600 your mind later: once you return a positive value from desegment_len, your PDU
3601 boundary is set in stone.
3603 static hf_register_info hf[] = {
3605 {"C String", "c.string", FT_STRING, BASE_NONE, NULL, 0x0,
3611 * Dissect a buffer containing C strings.
3613 * @param tvb The buffer to dissect.
3614 * @param pinfo Packet Info.
3615 * @param tree The protocol tree.
3617 static void dissect_cstr(tvbuff_t * tvb, packet_info * pinfo, proto_tree * tree)
3620 while(offset < tvb_reported_length(tvb)) {
3621 gint available = tvb_reported_length_remaining(tvb, offset);
3622 gint len = tvb_strnlen(tvb, offset, available);
3625 /* we ran out of data: ask for more */
3626 pinfo->desegment_offset = offset;
3627 pinfo->desegment_len = DESEGMENT_ONE_MORE_SEGMENT;
3631 if (check_col(pinfo->cinfo, COL_INFO)) {
3632 col_set_str(pinfo->cinfo, COL_INFO, "C String");
3635 len += 1; /* Add one for the '\0' */
3638 proto_tree_add_item(tree, hf_cstring, tvb, offset, len, FALSE);
3640 offset += (guint)len;
3643 /* if we get here, then the end of the tvb coincided with the end of a
3644 string. Happy days. */
3647 This simple dissector will repeatedly return DESEGMENT_ONE_MORE_SEGMENT
3648 requesting more data until the tvbuff contains a complete C string. The C string
3649 will then be added to the protocol tree. Note that there may be more
3650 than one complete C string in the tvbuff, so the dissection is done in a
3655 The ptvcursor API allows a simpler approach to writing dissectors for
3656 simple protocols. The ptvcursor API works best for protocols whose fields
3657 are static and whose format does not depend on the value of other fields.
3658 However, even if only a portion of your protocol is statically defined,
3659 then that portion could make use of ptvcursors.
3661 The ptvcursor API lets you extract data from a tvbuff, and add it to a
3662 protocol tree in one step. It also keeps track of the position in the
3663 tvbuff so that you can extract data again without having to compute any
3664 offsets --- hence the "cursor" name of the API.
3666 The three steps for a simple protocol are:
3667 1. Create a new ptvcursor with ptvcursor_new()
3668 2. Add fields with multiple calls of ptvcursor_add()
3669 3. Delete the ptvcursor with ptvcursor_free()
3671 ptvcursor offers the possibility to add subtrees in the tree as well. It can be
3672 done in very simple steps :
3673 1. Create a new subtree with ptvcursor_push_subtree(). The old subtree is
3674 pushed in a stack and the new subtree will be used by ptvcursor.
3675 2. Add fields with multiple calls of ptvcursor_add(). The fields will be
3676 added in the new subtree created at the previous step.
3677 3. Pop the previous subtree with ptvcursor_pop_subtree(). The previous
3678 subtree is again used by ptvcursor.
3679 Note that at the end of the parsing of a packet you must have popped each
3680 subtree you pushed. If it's not the case, the dissector will generate an error.
3682 To use the ptvcursor API, include the "ptvcursor.h" file. The PGM dissector
3683 is an example of how to use it. You don't need to look at it as a guide;
3684 instead, the API description here should be good enough.
3686 2.8.1 ptvcursor API.
3689 ptvcursor_new(proto_tree* tree, tvbuff_t* tvb, gint offset)
3690 This creates a new ptvcursor_t object for iterating over a tvbuff.
3691 You must call this and use this ptvcursor_t object so you can use the
3695 ptvcursor_add(ptvcursor_t* ptvc, int hf, gint length, gboolean endianness)
3696 This will extract 'length' bytes from the tvbuff and place it in
3697 the proto_tree as field 'hf', which is a registered header_field. The
3698 pointer to the proto_item that is created is passed back to you. Internally,
3699 the ptvcursor advances its cursor so the next call to ptvcursor_add
3700 starts where this call finished. The 'endianness' parameter matters for
3701 FT_UINT* and FT_INT* fields.
3704 ptvcursor_add_no_advance(ptvcursor_t* ptvc, int hf, gint length, gboolean endianness)
3705 Like ptvcursor_add, but does not advance the internal cursor.
3708 ptvcursor_advance(ptvcursor_t* ptvc, gint length)
3709 Advances the internal cursor without adding anything to the proto_tree.
3712 ptvcursor_free(ptvcursor_t* ptvc)
3713 Frees the memory associated with the ptvcursor. You must call this
3714 after your dissection with the ptvcursor API is completed.
3718 ptvcursor_push_subtree(ptvcursor_t* ptvc, proto_item* it, gint ett_subtree)
3719 Pushes the current subtree in the tree stack of the cursor, creates a new
3720 one and sets this one as the working tree.
3723 ptvcursor_pop_subtree(ptvcursor_t* ptvc);
3724 Pops a subtree in the tree stack of the cursor
3727 ptvcursor_add_with_subtree(ptvcursor_t* ptvc, int hfindex, gint length,
3728 gboolean little_endian, gint ett_subtree);
3729 Adds an item to the tree and creates a subtree.
3730 If the length is unknown, length may be defined as SUBTREE_UNDEFINED_LENGTH.
3731 In this case, at the next pop, the item length will be equal to the advancement
3732 of the cursor since the creation of the subtree.
3735 ptvcursor_add_text_with_subtree(ptvcursor_t* ptvc, gint length,
3736 gint ett_subtree, const char* format, ...);
3737 Add a text node to the tree and create a subtree.
3738 If the length is unknown, length may be defined as SUBTREE_UNDEFINED_LENGTH.
3739 In this case, at the next pop, the item length will be equal to the advancement
3740 of the cursor since the creation of the subtree.
3742 2.8.2 Miscellaneous functions.
3745 ptvcursor_tvbuff(ptvcursor_t* ptvc)
3746 Returns the tvbuff associated with the ptvcursor.
3749 ptvcursor_current_offset(ptvcursor_t* ptvc)
3750 Returns the current offset.
3753 ptvcursor_tree(ptvcursor_t* ptvc)
3754 Returns the proto_tree associated with the ptvcursor.
3757 ptvcursor_set_tree(ptvcursor_t* ptvc, proto_tree *tree)
3758 Sets a new proto_tree for the ptvcursor.
3761 ptvcursor_set_subtree(ptvcursor_t* ptvc, proto_item* it, gint ett_subtree);
3762 Creates a subtree and adds it to the cursor as the working tree but does
3763 not save the old working tree.