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.python - writing a dissector in PYTHON.
52 - README.request_response_tracking - how to track req./resp. times and such
56 James Coe <jammer[AT]cin.net>
57 Gilbert Ramirez <gram[AT]alumni.rice.edu>
58 Jeff Foster <jfoste[AT]woodward.com>
59 Olivier Abad <oabad[AT]cybercable.fr>
60 Laurent Deniel <laurent.deniel[AT]free.fr>
61 Gerald Combs <gerald[AT]wireshark.org>
62 Guy Harris <guy[AT]alum.mit.edu>
63 Ulf Lamping <ulf.lamping[AT]web.de>
65 1. Setting up your protocol dissector code.
67 This section provides skeleton code for a protocol dissector. It also explains
68 the basic functions needed to enter values in the traffic summary columns,
69 add to the protocol tree, and work with registered header fields.
75 Wireshark runs on many platforms, and can be compiled with a number of
76 different compilers; here are some rules for writing code that will work
77 on multiple platforms.
79 Don't use C++-style comments (comments beginning with "//" and running
80 to the end of the line); Wireshark's dissectors are written in C, and
81 thus run through C rather than C++ compilers, and not all C compilers
82 support C++-style comments (GCC does, but IBM's C compiler for AIX, for
83 example, doesn't do so by default).
85 In general, don't use C99 features since some C compilers used to compile
86 Wireshark don't support C99 (E.G. Microsoft C).
88 Don't initialize variables in their declaration with non-constant
89 values. Not all compilers support this. E.g. don't use
90 guint32 i = somearray[2];
96 Don't use zero-length arrays; not all compilers support them. If an
97 array would have no members, just leave it out.
99 Don't declare variables in the middle of executable code; not all C
100 compilers support that. Variables should be declared outside a
101 function, or at the beginning of a function or compound statement.
103 Don't use anonymous unions; not all compilers support it.
110 } u; /* have a name here */
113 Don't use "uchar", "u_char", "ushort", "u_short", "uint", "u_int",
114 "ulong", "u_long" or "boolean"; they aren't defined on all platforms.
115 If you want an 8-bit unsigned quantity, use "guint8"; if you want an
116 8-bit character value with the 8th bit not interpreted as a sign bit,
117 use "guchar"; if you want a 16-bit unsigned quantity, use "guint16";
118 if you want a 32-bit unsigned quantity, use "guint32"; and if you want
119 an "int-sized" unsigned quantity, use "guint"; if you want a boolean,
120 use "gboolean". Use "%d", "%u", "%x", and "%o" to print those types;
121 don't use "%ld", "%lu", "%lx", or "%lo", as longs are 64 bits long on
122 many platforms, but "guint32" is 32 bits long.
124 Don't use "long" to mean "signed 32-bit integer", and don't use
125 "unsigned long" to mean "unsigned 32-bit integer"; "long"s are 64 bits
126 long on many platforms. Use "gint32" for signed 32-bit integers and use
127 "guint32" for unsigned 32-bit integers.
129 Don't use "long" to mean "signed 64-bit integer" and don't use "unsigned
130 long" to mean "unsigned 64-bit integer"; "long"s are 32 bits long on
131 many other platforms. Don't use "long long" or "unsigned long long",
132 either, as not all platforms support them; use "gint64" or "guint64",
133 which will be defined as the appropriate types for 64-bit signed and
136 On LLP64 data model systems (notably 64-bit Windows), "int" and "long"
137 are 32 bits while "size_t" and "ptrdiff_t" are 64 bits. This means that
138 the following will generate a compiler warning:
141 i = strlen("hello, sailor"); /* Compiler warning */
143 Normally, you'd just make "i" a size_t. However, many GLib and Wireshark
144 functions won't accept a size_t on LLP64:
147 char greeting[] = "hello, sailor";
148 guint byte_after_greet;
150 i = strlen(greeting);
151 byte_after_greet = tvb_get_guint8(tvb, i); /* Compiler warning */
153 Try to use the appropriate data type when you can. When you can't, you
154 will have to cast to a compatible data type, e.g.
157 char greeting[] = "hello, sailor";
158 guint byte_after_greet;
160 i = strlen(greeting);
161 byte_after_greet = tvb_get_guint8(tvb, (gint) i); /* OK */
166 char greeting[] = "hello, sailor";
167 guint byte_after_greet;
169 i = (gint) strlen(greeting);
170 byte_after_greet = tvb_get_guint8(tvb, i); /* OK */
172 See http://www.unix.org/version2/whatsnew/lp64_wp.html for more
173 information on the sizes of common types in different data models.
175 When printing or displaying the values of 64-bit integral data types,
176 don't use "%lld", "%llu", "%llx", or "%llo" - not all platforms
177 support "%ll" for printing 64-bit integral data types. Instead, for
178 GLib routines, and routines that use them, such as all the routines in
179 Wireshark that take format arguments, use G_GINT64_MODIFIER, for example:
181 proto_tree_add_text(tree, tvb, offset, 8,
182 "Sequence Number: %" G_GINT64_MODIFIER "u",
185 When specifying an integral constant that doesn't fit in 32 bits, don't
186 use "LL" at the end of the constant - not all compilers use "LL" for
187 that. Instead, put the constant in a call to the "G_GINT64_CONSTANT()"
190 G_GINT64_CONSTANT(11644473600U)
196 Don't assume that you can scan through a va_list initialized by va_start
197 more than once without closing it with va_end and re-initalizing it with
198 va_start. This applies even if you're not scanning through it yourself,
199 but are calling a routine that scans through it, such as vfprintf() or
200 one of the routines in Wireshark that takes a format and a va_list as an
201 argument. You must do
203 va_start(ap, format);
204 call_routine1(xxx, format, ap);
206 va_start(ap, format);
207 call_routine2(xxx, format, ap);
211 va_start(ap, format);
212 call_routine1(xxx, format, ap);
213 call_routine2(xxx, format, ap);
216 Don't use a label without a statement following it. For example,
226 will not work with all compilers - you have to do
236 with some statement, even if it's a null statement, after the label.
238 Don't use "bzero()", "bcopy()", or "bcmp()"; instead, use the ANSI C
241 "memset()" (with zero as the second argument, so that it sets
242 all the bytes to zero);
244 "memcpy()" or "memmove()" (note that the first and second
245 arguments to "memcpy()" are in the reverse order to the
246 arguments to "bcopy()"; note also that "bcopy()" is typically
247 guaranteed to work on overlapping memory regions, while
248 "memcpy()" isn't, so if you may be copying from one region to a
249 region that overlaps it, use "memmove()", not "memcpy()" - but
250 "memcpy()" might be faster as a result of not guaranteeing
251 correct operation on overlapping memory regions);
253 and "memcmp()" (note that "memcmp()" returns 0, 1, or -1, doing
254 an ordered comparison, rather than just returning 0 for "equal"
255 and 1 for "not equal", as "bcmp()" does).
257 Not all platforms necessarily have "bzero()"/"bcopy()"/"bcmp()", and
258 those that do might not declare them in the header file on which they're
259 declared on your platform.
261 Don't use "index()" or "rindex()"; instead, use the ANSI C equivalents,
262 "strchr()" and "strrchr()". Not all platforms necessarily have
263 "index()" or "rindex()", and those that do might not declare them in the
264 header file on which they're declared on your platform.
266 Don't fetch data from packets by getting a pointer to data in the packet
267 with "tvb_get_ptr()", casting that pointer to a pointer to a structure,
268 and dereferencing that pointer. That pointer won't necessarily be aligned
269 on the proper boundary, which can cause crashes on some platforms (even
270 if it doesn't crash on an x86-based PC); furthermore, the data in a
271 packet is not necessarily in the byte order of the machine on which
272 Wireshark is running. Use the tvbuff routines to extract individual
273 items from the packet, or use "proto_tree_add_item()" and let it extract
276 Don't use structures that overlay packet data, or into which you copy
277 packet data; the C programming language does not guarantee any
278 particular alignment of fields within a structure, and even the
279 extensions that try to guarantee that are compiler-specific and not
280 necessarily supported by all compilers used to build Wireshark. Using
281 bitfields in those structures is even worse; the order of bitfields
284 Don't use "ntohs()", "ntohl()", "htons()", or "htonl()"; the header
285 files required to define or declare them differ between platforms, and
286 you might be able to get away with not including the appropriate header
287 file on your platform but that might not work on other platforms.
288 Instead, use "g_ntohs()", "g_ntohl()", "g_htons()", and "g_htonl()";
289 those are declared by <glib.h>, and you'll need to include that anyway,
290 as Wireshark header files that all dissectors must include use stuff from
293 Don't fetch a little-endian value using "tvb_get_ntohs() or
294 "tvb_get_ntohl()" and then using "g_ntohs()", "g_htons()", "g_ntohl()",
295 or "g_htonl()" on the resulting value - the g_ routines in question
296 convert between network byte order (big-endian) and *host* byte order,
297 not *little-endian* byte order; not all machines on which Wireshark runs
298 are little-endian, even though PCs are. Fetch those values using
299 "tvb_get_letohs()" and "tvb_get_letohl()".
301 Don't put a comma after the last element of an enum - some compilers may
302 either warn about it (producing extra noise) or refuse to accept it.
304 Don't include <unistd.h> without protecting it with
312 and, if you're including it to get routines such as "open()", "close()",
313 "read()", and "write()" declared, also include <io.h> if present:
319 in order to declare the Windows C library routines "_open()",
320 "_close()", "_read()", and "_write()". Your file must include <glib.h>
321 - which many of the Wireshark header files include, so you might not have
322 to include it explicitly - in order to get "open()", "close()",
323 "read()", "write()", etc. mapped to "_open()", "_close()", "_read()",
326 Do not use "open()", "rename()", "mkdir()", "stat()", "unlink()", "remove()",
327 "fopen()", "freopen()" directly. Instead use "ws_open()", "ws_rename()",
328 "ws_mkdir()", "ws_stat()", "ws_unlink()", "ws_remove()", "ws_fopen()",
329 "ws_freopen()": these wrapper functions change the path and file name from
330 UTF8 to UTF16 on Windows allowing the functions to work correctly when the
331 path or file name contain non-ASCII characters.
333 When opening a file with "ws_fopen()", "ws_freopen()", or "ws_fdopen()", if
334 the file contains ASCII text, use "r", "w", "a", and so on as the open mode
335 - but if it contains binary data, use "rb", "wb", and so on. On
336 Windows, if a file is opened in a text mode, writing a byte with the
337 value of octal 12 (newline) to the file causes two bytes, one with the
338 value octal 15 (carriage return) and one with the value octal 12, to be
339 written to the file, and causes bytes with the value octal 15 to be
340 discarded when reading the file (to translate between C's UNIX-style
341 lines that end with newline and Windows' DEC-style lines that end with
342 carriage return/line feed).
344 In addition, that also means that when opening or creating a binary
345 file, you must use "ws_open()" (with O_CREAT and possibly O_TRUNC if the
346 file is to be created if it doesn't exist), and OR in the O_BINARY flag.
347 That flag is not present on most, if not all, UNIX systems, so you must
354 to properly define it for UNIX (it's not necessary on UNIX).
356 Don't use forward declarations of static arrays without a specified size
357 in a fashion such as this:
359 static const value_string foo_vals[];
363 static const value_string foo_vals[] = {
370 as some compilers will reject the first of those statements. Instead,
371 initialize the array at the point at which it's first declared, so that
374 Don't put a comma after the last tuple of an initializer of an array.
376 For #define names and enum member names, prefix the names with a tag so
377 as to avoid collisions with other names - this might be more of an issue
378 on Windows, as it appears to #define names such as DELETE and
381 Don't use the "numbered argument" feature that many UNIX printf's
384 g_snprintf(add_string, 30, " - (%1$d) (0x%1$04x)", value);
386 as not all UNIX printf's implement it, and Windows printf doesn't appear
387 to implement it. Use something like
389 g_snprintf(add_string, 30, " - (%d) (0x%04x)", value, value);
393 Don't use "variadic macros", such as
395 #define DBG(format, args...) fprintf(stderr, format, ## args)
397 as not all C compilers support them. Use macros that take a fixed
398 number of arguments, such as
400 #define DBG0(format) fprintf(stderr, format)
401 #define DBG1(format, arg1) fprintf(stderr, format, arg1)
402 #define DBG2(format, arg1, arg2) fprintf(stderr, format, arg1, arg2)
408 #define DBG(args) printf args
414 as that's not supported by all compilers.
416 snprintf() -> g_snprintf()
417 snprintf() is not available on all platforms, so it's a good idea to use the
418 g_snprintf() function declared by <glib.h> instead.
420 tmpnam() -> mkstemp()
421 tmpnam is insecure and should not be used any more. Wireshark brings its
422 own mkstemp implementation for use on platforms that lack mkstemp.
423 Note: mkstemp does not accept NULL as a parameter.
425 The pointer returned by a call to "tvb_get_ptr()" is not guaranteed to be
426 aligned on any particular byte boundary; this means that you cannot
427 safely cast it to any data type other than a pointer to "char",
428 "unsigned char", "guint8", or other one-byte data types. You cannot,
429 for example, safely cast it to a pointer to a structure, and then access
430 the structure members directly; on some systems, unaligned accesses to
431 integral data types larger than 1 byte, and floating-point data types,
432 cause a trap, which will, at best, result in the OS slowly performing an
433 unaligned access for you, and will, on at least some platforms, cause
434 the program to be terminated.
436 Wireshark supports platforms with GLib 2.4[.x]/GTK+ 2.4[.x] or newer.
437 If a Glib/GTK+ mechanism is available only in Glib/GTK+ versions
438 newer than 2.4/2.4 then use "#if GTK_CHECK_VERSION(...)" to conditionally
439 compile code using that mechanism.
441 When different code must be used on UN*X and Win32, use a #if or #ifdef
442 that tests _WIN32, not WIN32. Try to write code portably whenever
443 possible, however; note that there are some routines in Wireshark with
444 platform-dependent implementations and platform-independent APIs, such
445 as the routines in epan/filesystem.c, allowing the code that calls it to
446 be written portably without #ifdefs.
448 1.1.2 String handling
450 Do not use functions such as strcat() or strcpy().
451 A lot of work has been done to remove the existing calls to these functions and
452 we do not want any new callers of these functions.
454 Instead use g_snprintf() since that function will if used correctly prevent
455 buffer overflows for large strings.
457 When using a buffer to create a string, do not use a buffer stored on the stack.
458 I.e. do not use a buffer declared as
462 instead allocate a buffer dynamically using the string-specific or plain emem
463 routines (see README.malloc) such as
465 emem_strbuf_t *strbuf;
466 strbuf = ep_strbuf_new_label("");
467 ep_strbuf_append_printf(strbuf, ...
473 #define MAX_BUFFER 1024
474 buffer=ep_alloc(MAX_BUFFER);
477 g_snprintf(buffer, MAX_BUFFER, ...
479 This avoids the stack from being corrupted in case there is a bug in your code
480 that accidentally writes beyond the end of the buffer.
483 If you write a routine that will create and return a pointer to a filled in
484 string and if that buffer will not be further processed or appended to after
485 the routine returns (except being added to the proto tree),
486 do not preallocate the buffer to fill in and pass as a parameter instead
487 pass a pointer to a pointer to the function and return a pointer to an
488 emem allocated buffer that will be automatically freed. (see README.malloc)
490 I.e. do not write code such as
492 foo_to_str(char *string, ... ){
498 foo_to_str(buffer, ...
499 proto_tree_add_text(... buffer ...
501 instead write the code as
503 foo_to_str(char **buffer, ...
505 *buffer=ep_alloc(MAX_BUFFER);
511 foo_to_str(&buffer, ...
512 proto_tree_add_text(... *buffer ...
514 Use ep_ allocated buffers. They are very fast and nice. These buffers are all
515 automatically free()d when the dissection of the current packet ends so you
516 don't have to worry about free()ing them explicitly in order to not leak memory.
517 Please read README.malloc.
519 Don't use non-ASCII characters in source files; not all compiler
520 environments will be using the same encoding for non-ASCII characters,
521 and at least one compiler (Microsoft's Visual C) will, in environments
522 with double-byte character encodings, such as many Asian environments,
523 fail if it sees a byte sequence in a source file that doesn't correspond
524 to a valid character. This causes source files using either an ISO
525 8859/n single-byte character encoding or UTF-8 to fail to compile. Even
526 if the compiler doesn't fail, there is no guarantee that the compiler,
527 or a developer's text editor, will interpret the characters the way you
528 intend them to be interpreted.
532 Wireshark is not guaranteed to read only network traces that contain correctly-
533 formed packets. Wireshark is commonly used to track down networking
534 problems, and the problems might be due to a buggy protocol implementation
535 sending out bad packets.
537 Therefore, protocol dissectors not only have to be able to handle
538 correctly-formed packets without, for example, crashing or looping
539 infinitely, they also have to be able to handle *incorrectly*-formed
540 packets without crashing or looping infinitely.
542 Here are some suggestions for making dissectors more robust in the face
543 of incorrectly-formed packets:
545 Do *NOT* use "g_assert()" or "g_assert_not_reached()" in dissectors.
546 *NO* value in a packet's data should be considered "wrong" in the sense
547 that it's a problem with the dissector if found; if it cannot do
548 anything else with a particular value from a packet's data, the
549 dissector should put into the protocol tree an indication that the
550 value is invalid, and should return. The "expert" mechanism should be
551 used for that purpose.
553 If there is a case where you are checking not for an invalid data item
554 in the packet, but for a bug in the dissector (for example, an
555 assumption being made at a particular point in the code about the
556 internal state of the dissector), use the DISSECTOR_ASSERT macro for
557 that purpose; this will put into the protocol tree an indication that
558 the dissector has a bug in it, and will not crash the application.
560 If you are allocating a chunk of memory to contain data from a packet,
561 or to contain information derived from data in a packet, and the size of
562 the chunk of memory is derived from a size field in the packet, make
563 sure all the data is present in the packet before allocating the buffer.
566 1) Wireshark won't leak that chunk of memory if an attempt to
567 fetch data not present in the packet throws an exception.
571 2) it won't crash trying to allocate an absurdly-large chunk of
572 memory if the size field has a bogus large value.
574 If you're fetching into such a chunk of memory a string from the buffer,
575 and the string has a specified size, you can use "tvb_get_*_string()",
576 which will check whether the entire string is present before allocating
577 a buffer for the string, and will also put a trailing '\0' at the end of
580 If you're fetching into such a chunk of memory a 2-byte Unicode string
581 from the buffer, and the string has a specified size, you can use
582 "tvb_get_ephemeral_faked_unicode()", which will check whether the entire
583 string is present before allocating a buffer for the string, and will also
584 put a trailing '\0' at the end of the buffer. The resulting string will be
585 a sequence of single-byte characters; the only Unicode characters that
586 will be handled correctly are those in the ASCII range. (Wireshark's
587 ability to handle non-ASCII strings is limited; it needs to be
590 If you're fetching into such a chunk of memory a sequence of bytes from
591 the buffer, and the sequence has a specified size, you can use
592 "tvb_memdup()", which will check whether the entire sequence is present
593 before allocating a buffer for it.
595 Otherwise, you can check whether the data is present by using
596 "tvb_ensure_bytes_exist()" or by getting a pointer to the data by using
597 "tvb_get_ptr()", although note that there might be problems with using
598 the pointer from "tvb_get_ptr()" (see the item on this in the
599 Portability section above, and the next item below).
601 Note also that you should only fetch string data into a fixed-length
602 buffer if the code ensures that no more bytes than will fit into the
603 buffer are fetched ("the protocol ensures" isn't good enough, as
604 protocol specifications can't ensure only packets that conform to the
605 specification will be transmitted or that only packets for the protocol
606 in question will be interpreted as packets for that protocol by
607 Wireshark). If there's no maximum length of string data to be fetched,
608 routines such as "tvb_get_*_string()" are safer, as they allocate a buffer
609 large enough to hold the string. (Note that some variants of this call
610 require you to free the string once you're finished with it.)
612 If you have gotten a pointer using "tvb_get_ptr()", you must make sure
613 that you do not refer to any data past the length passed as the last
614 argument to "tvb_get_ptr()"; while the various "tvb_get" routines
615 perform bounds checking and throw an exception if you refer to data not
616 available in the tvbuff, direct references through a pointer gotten from
617 "tvb_get_ptr()" do not do any bounds checking.
619 If you have a loop that dissects a sequence of items, each of which has
620 a length field, with the offset in the tvbuff advanced by the length of
621 the item, then, if the length field is the total length of the item, and
622 thus can be zero, you *MUST* check for a zero-length item and abort the
623 loop if you see one. Otherwise, a zero-length item could cause the
624 dissector to loop infinitely. You should also check that the offset,
625 after having the length added to it, is greater than the offset before
626 the length was added to it, if the length field is greater than 24 bits
627 long, so that, if the length value is *very* large and adding it to the
628 offset causes an overflow, that overflow is detected.
630 If you are fetching a length field from the buffer, corresponding to the
631 length of a portion of the packet, and subtracting from that length a
632 value corresponding to the length of, for example, a header in the
633 packet portion in question, *ALWAYS* check that the value of the length
634 field is greater than or equal to the length you're subtracting from it,
635 and report an error in the packet and stop dissecting the packet if it's
636 less than the length you're subtracting from it. Otherwise, the
637 resulting length value will be negative, which will either cause errors
638 in the dissector or routines called by the dissector, or, if the value
639 is interpreted as an unsigned integer, will cause the value to be
640 interpreted as a very large positive value.
642 Any tvbuff offset that is added to as processing is done on a packet
643 should be stored in a 32-bit variable, such as an "int"; if you store it
644 in an 8-bit or 16-bit variable, you run the risk of the variable
647 sprintf() -> g_snprintf()
648 Prevent yourself from using the sprintf() function, as it does not test the
649 length of the given output buffer and might be writing into unintended memory
650 areas. This function is one of the main causes of security problems like buffer
651 exploits and many other bugs that are very hard to find. It's much better to
652 use the g_snprintf() function declared by <glib.h> instead.
654 You should test your dissector against incorrectly-formed packets. This
655 can be done using the randpkt and editcap utilities that come with the
656 Wireshark distribution. Testing using randpkt can be done by generating
657 output at the same layer as your protocol, and forcing Wireshark/TShark
658 to decode it as your protocol, e.g. if your protocol sits on top of UDP:
660 randpkt -c 50000 -t dns randpkt.pcap
661 tshark -nVr randpkt.pcap -d udp.port==53,<myproto>
663 Testing using editcap can be done using preexisting capture files and the
664 "-E" flag, which introduces errors in a capture file. E.g.:
666 editcap -E 0.03 infile.pcap outfile.pcap
667 tshark -nVr outfile.pcap
669 The script fuzz-test.sh is available to help automate these tests.
671 1.1.4 Name convention.
673 Wireshark uses the underscore_convention rather than the InterCapConvention for
674 function names, so new code should probably use underscores rather than
675 intercaps for functions and variable names. This is especially important if you
676 are writing code that will be called from outside your code. We are just
677 trying to keep things consistent for other developers.
679 1.1.5 White space convention.
681 Avoid using tab expansions different from 8 column widths, as not all
682 text editors in use by the developers support this. For a detailed
683 discussion of tabs, spaces, and indentation, see
685 http://www.jwz.org/doc/tabs-vs-spaces.html
687 When creating a new file, you are free to choose an indentation logic.
688 Most of the files in Wireshark tend to use 2-space or 4-space
689 indentation. You are encouraged to write a short comment on the
690 indentation logic at the beginning of this new file, especially if
691 you're using non-mod-8 tabs. The tabs-vs-spaces document above provides
692 examples of Emacs and vi modelines for this purpose.
694 When editing an existing file, try following the existing indentation
695 logic and even if it very tempting, never ever use a restyler/reindenter
696 utility on an existing file. If you run across wildly varying
697 indentation styles within the same file, it might be helpful to send a
698 note to wireshark-dev for guidance.
700 1.1.6 Compiler warnings
702 You should write code that is free of compiler warnings. Such warnings will
703 often indicate questionable code and sometimes even real bugs, so it's best
704 to avoid warnings at all.
706 The compiler flags in the Makefiles are set to "treat warnings as errors",
707 so your code won't even compile when warnings occur.
711 Wireshark requires certain things when setting up a protocol dissector.
712 Below is skeleton code for a dissector that you can copy to a file and
713 fill in. Your dissector should follow the naming convention of packet-
714 followed by the abbreviated name for the protocol. It is recommended
715 that where possible you keep to the IANA abbreviated name for the
716 protocol, if there is one, or a commonly-used abbreviation for the
719 Usually, you will put your newly created dissector file into the directory
720 epan/dissectors, just like all the other packet-....c files already in there.
722 Also, please add your dissector file to the corresponding makefiles,
723 described in section "1.9 Editing Makefile.common and CMakeLists.txt
724 to add your dissector" below.
726 Dissectors that use the dissector registration to register with a lower level
727 dissector don't need to define a prototype in the .h file. For other
728 dissectors the main dissector routine should have a prototype in a header
729 file whose name is "packet-", followed by the abbreviated name for the
730 protocol, followed by ".h"; any dissector file that calls your dissector
731 should be changed to include that file.
733 You may not need to include all the headers listed in the skeleton
734 below, and you may need to include additional headers. For example, the
743 is needed only if you are using a function from libpcre, e.g. the
744 "pcre_compile()" function.
746 The stdio.h, stdlib.h and string.h header files should be included only as needed.
749 The "$Id$" in the comment will be updated by Subversion when the file is
752 When creating a new file, it is fine to just write "$Id$" as Subversion will
753 automatically fill in the identifier at the time the file will be added to the
754 SVN repository (committed).
756 ------------------------------------Cut here------------------------------------
757 /* packet-PROTOABBREV.c
758 * Routines for PROTONAME dissection
759 * Copyright 201x, YOUR_NAME <YOUR_EMAIL_ADDRESS>
763 * Wireshark - Network traffic analyzer
764 * By Gerald Combs <gerald@wireshark.org>
765 * Copyright 1998 Gerald Combs
767 * Copied from WHATEVER_FILE_YOU_USED (where "WHATEVER_FILE_YOU_USED"
768 * is a dissector file; if you just copied this from README.developer,
769 * don't bother with the "Copied from" - you don't even need to put
770 * in a "Copied from" if you copied an existing dissector, especially
771 * if the bulk of the code in the new dissector is your code)
773 * This program is free software; you can redistribute it and/or modify
774 * it under the terms of the GNU General Public License as published by
775 * the Free Software Foundation; either version 2 of the License, or
776 * (at your option) any later version.
778 * This program is distributed in the hope that it will be useful,
779 * but WITHOUT ANY WARRANTY; without even the implied warranty of
780 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
781 * GNU General Public License for more details.
783 * You should have received a copy of the GNU General Public License along
784 * with this program; if not, write to the Free Software Foundation, Inc.,
785 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
793 /* Include only as needed */
801 #include <epan/packet.h>
802 #include <epan/prefs.h>
804 /* IF PROTO exposes code to other dissectors, then it must be exported
805 in a header file. If not, a header file is not needed at all. */
806 #include "packet-PROTOABBREV.h"
808 /* Forward declaration we need below (if using proto_reg_handoff...
809 as a prefs callback) */
810 void proto_reg_handoff_PROTOABBREV(void);
812 /* Initialize the protocol and registered fields */
813 static int proto_PROTOABBREV = -1;
814 static int hf_PROTOABBREV_FIELDABBREV = -1;
816 /* Global sample preference ("controls" display of numbers) */
817 static gboolean gPREF_HEX = FALSE;
818 /* Global sample port pref */
819 static guint gPORT_PREF = 1234;
821 /* Initialize the subtree pointers */
822 static gint ett_PROTOABBREV = -1;
824 /* Code to actually dissect the packets */
826 dissect_PROTOABBREV(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
829 /* Set up structures needed to add the protocol subtree and manage it */
831 proto_tree *PROTOABBREV_tree;
833 /* First, if at all possible, do some heuristics to check if the packet cannot
834 * possibly belong to your protocol. This is especially important for
835 * protocols directly on top of TCP or UDP where port collisions are
836 * common place (e.g., even though your protocol uses a well known port,
837 * someone else may set up, for example, a web server on that port which,
838 * if someone analyzed that web server's traffic in Wireshark, would result
839 * in Wireshark handing an HTTP packet to your dissector). For example:
841 /* Check that there's enough data */
842 if (tvb_length(tvb) < /* your protocol's smallest packet size */)
845 /* Get some values from the packet header, probably using tvb_get_*() */
846 if ( /* these values are not possible in PROTONAME */ )
847 /* This packet does not appear to belong to PROTONAME.
848 * Return 0 to give another dissector a chance to dissect it.
852 /* Make entries in Protocol column and Info column on summary display */
853 col_set_str(pinfo->cinfo, COL_PROTOCOL, "PROTOABBREV");
855 /* This field shows up as the "Info" column in the display; you should use
856 it, if possible, to summarize what's in the packet, so that a user looking
857 at the list of packets can tell what type of packet it is. See section 1.5
858 for more information.
860 If you are setting the column to a constant string, use "col_set_str()",
861 as it's more efficient than the other "col_set_XXX()" calls.
863 If you're setting it to a string you've constructed, or will be
864 appending to the column later, use "col_add_str()".
866 "col_add_fstr()" can be used instead of "col_add_str()"; it takes
867 "printf()"-like arguments. Don't use "col_add_fstr()" with a format
868 string of "%s" - just use "col_add_str()" or "col_set_str()", as it's
869 more efficient than "col_add_fstr()".
871 If you will be fetching any data from the packet before filling in
872 the Info column, clear that column first, in case the calls to fetch
873 data from the packet throw an exception because they're fetching data
874 past the end of the packet, so that the Info column doesn't have data
875 left over from the previous dissector; do
877 col_clear(pinfo->cinfo, COL_INFO);
881 col_set_str(pinfo->cinfo, COL_INFO, "XXX Request");
883 /* A protocol dissector may be called in 2 different ways - with, or
884 without a non-null "tree" argument.
886 If the proto_tree argument is null, Wireshark does not need to use
887 the protocol tree information from your dissector, and therefore is
888 passing the dissector a null "tree" argument so that it doesn't
889 need to do work necessary to build the protocol tree.
891 In the interest of speed, if "tree" is NULL, avoid building a
892 protocol tree and adding stuff to it, or even looking at any packet
893 data needed only if you're building the protocol tree, if possible.
895 Note, however, that you must fill in column information, create
896 conversations, reassemble packets, build any other persistent state
897 needed for dissection, and call subdissectors regardless of whether
898 "tree" is NULL or not. This might be inconvenient to do without
899 doing most of the dissection work; the routines for adding items to
900 the protocol tree can be passed a null protocol tree pointer, in
901 which case they'll return a null item pointer, and
902 "proto_item_add_subtree()" returns a null tree pointer if passed a
903 null item pointer, so, if you're careful not to dereference any null
904 tree or item pointers, you can accomplish this by doing all the
905 dissection work. This might not be as efficient as skipping that
906 work if you're not building a protocol tree, but if the code would
907 have a lot of tests whether "tree" is null if you skipped that work,
908 you might still be better off just doing all that work regardless of
909 whether "tree" is null or not.
911 Note also that there is no guarantee, the first time the dissector is
912 called, whether "tree" will be null or not; your dissector must work
913 correctly, building or updating whatever state information is
914 necessary, in either case. */
917 /* NOTE: The offset and length values in the call to
918 "proto_tree_add_item()" define what data bytes to highlight in the hex
919 display window when the line in the protocol tree display
920 corresponding to that item is selected.
922 Supplying a length of -1 is the way to highlight all data from the
923 offset to the end of the packet. */
925 /* create display subtree for the protocol */
926 ti = proto_tree_add_item(tree, proto_PROTOABBREV, tvb, 0, -1, REP_NA);
928 PROTOABBREV_tree = proto_item_add_subtree(ti, ett_PROTOABBREV);
930 /* add an item to the subtree, see section 1.6 for more information */
931 proto_tree_add_item(PROTOABBREV_tree,
932 hf_PROTOABBREV_FIELDABBREV, tvb, offset, len, REP_xxx);
935 /* Continue adding tree items to process the packet here */
940 /* If this protocol has a sub-dissector call it here, see section 1.8 */
942 /* Return the amount of data this dissector was able to dissect */
943 return tvb_length(tvb);
947 /* Register the protocol with Wireshark */
949 /* this format is require because a script is used to build the C function
950 that calls all the protocol registration.
954 proto_register_PROTOABBREV(void)
956 module_t *PROTOABBREV_module;
958 /* Setup list of header fields See Section 1.6.1 for details*/
959 static hf_register_info hf[] = {
960 { &hf_PROTOABBREV_FIELDABBREV,
961 { "FIELDNAME", "PROTOABBREV.FIELDABBREV",
962 FIELDTYPE, FIELDDISPLAY, FIELDCONVERT, BITMASK,
963 "FIELDDESCR", HFILL }
967 /* Setup protocol subtree array */
968 static gint *ett[] = {
972 /* Register the protocol name and description */
973 proto_PROTOABBREV = proto_register_protocol("PROTONAME",
974 "PROTOSHORTNAME", "PROTOABBREV");
976 /* Required function calls to register the header fields and subtrees used */
977 proto_register_field_array(proto_PROTOABBREV, hf, array_length(hf));
978 proto_register_subtree_array(ett, array_length(ett));
980 /* Register preferences module (See Section 2.6 for more on preferences) */
981 /* (Registration of a prefs callback is not required if there are no */
982 /* prefs-dependent registration functions (eg: a port pref). */
983 /* See proto_reg_handoff below. */
984 /* If a prefs callback is not needed, use NULL instead of */
985 /* proto_reg_handoff_PROTOABBREV in the following). */
986 PROTOABBREV_module = prefs_register_protocol(proto_PROTOABBREV,
987 proto_reg_handoff_PROTOABBREV);
989 /* Register preferences module under preferences subtree.
990 Use this function instead of prefs_register_protocol if you want to group
991 preferences of several protocols under one preferences subtree.
992 Argument subtree identifies grouping tree node name, several subnodes can be
993 specified usign slash '/' (e.g. "OSI/X.500" - protocol preferences will be
994 accessible under Protocols->OSI->X.500-><PROTOSHORTNAME> preferences node.
996 PROTOABBREV_module = prefs_register_protocol_subtree(const char *subtree,
997 proto_PROTOABBREV, proto_reg_handoff_PROTOABBREV);
999 /* Register a sample preference */
1000 prefs_register_bool_preference(PROTOABBREV_module, "show_hex",
1001 "Display numbers in Hex",
1002 "Enable to display numerical values in hexadecimal.",
1005 /* Register a sample port preference */
1006 prefs_register_uint_preference(PROTOABBREV_module, "tcp.port", "PROTOABBREV TCP Port",
1007 " PROTOABBREV TCP port if other than the default",
1012 /* If this dissector uses sub-dissector registration add a registration routine.
1013 This exact format is required because a script is used to find these
1014 routines and create the code that calls these routines.
1016 If this function is registered as a prefs callback (see prefs_register_protocol
1017 above) this function is also called by preferences whenever "Apply" is pressed;
1018 In that case, it should accommodate being called more than once.
1020 This form of the reg_handoff function is used if if you perform
1021 registration functions which are dependent upon prefs. See below
1022 for a simpler form which can be used if there are no
1023 prefs-dependent registration functions.
1026 proto_reg_handoff_PROTOABBREV(void)
1028 static gboolean initialized = FALSE;
1029 static dissector_handle_t PROTOABBREV_handle;
1030 static int currentPort;
1034 /* Use new_create_dissector_handle() to indicate that dissect_PROTOABBREV()
1035 * returns the number of bytes it dissected (or 0 if it thinks the packet
1036 * does not belong to PROTONAME).
1038 PROTOABBREV_handle = new_create_dissector_handle(dissect_PROTOABBREV,
1040 dissector_add("PARENT_SUBFIELD", ID_VALUE, PROTOABBREV_handle);
1046 If you perform registration functions which are dependent upon
1047 prefs the you should de-register everything which was associated
1048 with the previous settings and re-register using the new prefs
1049 settings here. In general this means you need to keep track of
1050 the PROTOABBREV_handle and the value the preference had at the time
1051 you registered. The PROTOABBREV_handle value and the value of the
1052 preference can be saved using local statics in this
1053 function (proto_reg_handoff).
1056 dissector_delete("tcp.port", currentPort, PROTOABBREV_handle);
1059 currentPort = gPORT_PREF;
1061 dissector_add("tcp.port", currentPort, PROTOABBREV_handle);
1066 /* Simple form of proto_reg_handoff_PROTOABBREV which can be used if there are
1067 no prefs-dependent registration function calls.
1071 proto_reg_handoff_PROTOABBREV(void)
1073 dissector_handle_t PROTOABBREV_handle;
1075 /* Use new_create_dissector_handle() to indicate that dissect_PROTOABBREV()
1076 * returns the number of bytes it dissected (or 0 if it thinks the packet
1077 * does not belong to PROTONAME).
1079 PROTOABBREV_handle = new_create_dissector_handle(dissect_PROTOABBREV,
1081 dissector_add("PARENT_SUBFIELD", ID_VALUE, PROTOABBREV_handle);
1086 ------------------------------------Cut here------------------------------------
1088 1.3 Explanation of needed substitutions in code skeleton.
1090 In the above code block the following strings should be substituted with
1093 YOUR_NAME Your name, of course. You do want credit, don't you?
1094 It's the only payment you will receive....
1095 YOUR_EMAIL_ADDRESS Keep those cards and letters coming.
1096 WHATEVER_FILE_YOU_USED Add this line if you are using another file as a
1098 PROTONAME The name of the protocol; this is displayed in the
1099 top-level protocol tree item for that protocol.
1100 PROTOSHORTNAME An abbreviated name for the protocol; this is displayed
1101 in the "Preferences" dialog box if your dissector has
1102 any preferences, in the dialog box of enabled protocols,
1103 and in the dialog box for filter fields when constructing
1104 a filter expression.
1105 PROTOABBREV A name for the protocol for use in filter expressions;
1106 it shall contain only lower-case letters, digits, and
1108 FIELDNAME The displayed name for the header field.
1109 FIELDABBREV The abbreviated name for the header field. (NO SPACES)
1110 FIELDTYPE FT_NONE, FT_BOOLEAN, FT_UINT8, FT_UINT16, FT_UINT24,
1111 FT_UINT32, FT_UINT64, FT_INT8, FT_INT16, FT_INT24, FT_INT32,
1112 FT_INT64, FT_FLOAT, FT_DOUBLE, FT_ABSOLUTE_TIME,
1113 FT_RELATIVE_TIME, FT_STRING, FT_STRINGZ, FT_EBCDIC,
1114 FT_UINT_STRING, FT_ETHER, FT_BYTES, FT_UINT_BYTES, FT_IPv4,
1115 FT_IPv6, FT_IPXNET, FT_FRAMENUM, FT_PROTOCOL, FT_GUID, FT_OID
1116 FIELDDISPLAY For FT_UINT{8,16,24,32,64} and FT_INT{8,16,24,32,64):
1118 BASE_DEC, BASE_HEX, BASE_OCT, BASE_DEC_HEX, BASE_HEX_DEC,
1119 or BASE_CUSTOM, possibly ORed with BASE_RANGE_STRING
1121 For FT_ABSOLUTE_TIME:
1123 ABSOLUTE_TIME_LOCAL, ABSOLUTE_TIME_UTC, or
1124 ABSOLUTE_TIME_DOY_UTC
1126 For FT_BOOLEAN if BITMASK is non-zero:
1128 Number of bits in the field containing the FT_BOOLEAN
1131 For all other types:
1134 FIELDCONVERT VALS(x), RVALS(x), TFS(x), NULL
1135 BITMASK Usually 0x0 unless using the TFS(x) field conversion.
1136 FIELDDESCR A brief description of the field, or NULL. [Please do not use ""].
1137 PARENT_SUBFIELD Lower level protocol field used for lookup, i.e. "tcp.port"
1138 ID_VALUE Lower level protocol field value that identifies this protocol
1139 For example the TCP or UDP port number
1141 If, for example, PROTONAME is "Internet Bogosity Discovery Protocol",
1142 PROTOSHORTNAME would be "IBDP", and PROTOABBREV would be "ibdp". Try to
1143 conform with IANA names.
1145 1.4 The dissector and the data it receives.
1150 This is only needed if the dissector doesn't use self-registration to
1151 register itself with the lower level dissector, or if the protocol dissector
1152 wants/needs to expose code to other subdissectors.
1154 The dissector must be declared exactly as follows in the file
1155 packet-PROTOABBREV.h:
1158 dissect_PROTOABBREV(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree);
1161 1.4.2 Extracting data from packets.
1163 NOTE: See the file /epan/tvbuff.h for more details.
1165 The "tvb" argument to a dissector points to a buffer containing the raw
1166 data to be analyzed by the dissector; for example, for a protocol
1167 running atop UDP, it contains the UDP payload (but not the UDP header,
1168 or any protocol headers above it). A tvbuffer is an opaque data
1169 structure, the internal data structures are hidden and the data must be
1170 accessed via the tvbuffer accessors.
1174 Bit accessors for a maximum of 8-bits, 16-bits 32-bits and 64-bits:
1176 guint8 tvb_get_bits8(tvbuff_t *tvb, gint bit_offset, gint no_of_bits);
1177 guint16 tvb_get_bits16(tvbuff_t *tvb, gint bit_offset, gint no_of_bits,gboolean little_endian);
1178 guint32 tvb_get_bits32(tvbuff_t *tvb, gint bit_offset, gint no_of_bits,gboolean little_endian);
1179 guint64 tvb_get_bits64(tvbuff_t *tvb, gint bit_offset, gint no_of_bits,gboolean little_endian);
1181 Single-byte accessor:
1183 guint8 tvb_get_guint8(tvbuff_t*, gint offset);
1185 Network-to-host-order accessors for 16-bit integers (guint16), 24-bit
1186 integers, 32-bit integers (guint32), and 64-bit integers (guint64):
1188 guint16 tvb_get_ntohs(tvbuff_t*, gint offset);
1189 guint32 tvb_get_ntoh24(tvbuff_t*, gint offset);
1190 guint32 tvb_get_ntohl(tvbuff_t*, gint offset);
1191 guint64 tvb_get_ntoh64(tvbuff_t*, gint offset);
1193 Network-to-host-order accessors for single-precision and
1194 double-precision IEEE floating-point numbers:
1196 gfloat tvb_get_ntohieee_float(tvbuff_t*, gint offset);
1197 gdouble tvb_get_ntohieee_double(tvbuff_t*, gint offset);
1199 Little-Endian-to-host-order accessors for 16-bit integers (guint16),
1200 24-bit integers, 32-bit integers (guint32), and 64-bit integers
1203 guint16 tvb_get_letohs(tvbuff_t*, gint offset);
1204 guint32 tvb_get_letoh24(tvbuff_t*, gint offset);
1205 guint32 tvb_get_letohl(tvbuff_t*, gint offset);
1206 guint64 tvb_get_letoh64(tvbuff_t*, gint offset);
1208 Little-Endian-to-host-order accessors for single-precision and
1209 double-precision IEEE floating-point numbers:
1211 gfloat tvb_get_letohieee_float(tvbuff_t*, gint offset);
1212 gdouble tvb_get_letohieee_double(tvbuff_t*, gint offset);
1214 Accessors for IPv4 and IPv6 addresses:
1216 guint32 tvb_get_ipv4(tvbuff_t*, gint offset);
1217 void tvb_get_ipv6(tvbuff_t*, gint offset, struct e_in6_addr *addr);
1219 NOTE: IPv4 addresses are not to be converted to host byte order before
1220 being passed to "proto_tree_add_ipv4()". You should use "tvb_get_ipv4()"
1221 to fetch them, not "tvb_get_ntohl()" *OR* "tvb_get_letohl()" - don't,
1222 for example, try to use "tvb_get_ntohl()", find that it gives you the
1223 wrong answer on the PC on which you're doing development, and try
1224 "tvb_get_letohl()" instead, as "tvb_get_letohl()" will give the wrong
1225 answer on big-endian machines.
1229 void tvb_get_ntohguid(tvbuff_t *, gint offset, e_guid_t *guid);
1230 void tvb_get_letohguid(tvbuff_t *, gint offset, e_guid_t *guid);
1234 guint8 *tvb_get_string(tvbuff_t*, gint offset, gint length);
1235 guint8 *tvb_get_ephemeral_string(tvbuff_t*, gint offset, gint length);
1236 guint8 *tvb_get_seasonal_string(tvbuff_t*, gint offset, gint length);
1238 Returns a null-terminated buffer containing data from the specified
1239 tvbuff, starting at the specified offset, and containing the specified
1240 length worth of characters (the length of the buffer will be length+1,
1241 as it includes a null character to terminate the string).
1243 tvb_get_string() returns a buffer allocated by g_malloc() so you must
1244 g_free() it when you are finished with the string. Failure to g_free() this
1245 buffer will lead to memory leaks.
1247 tvb_get_ephemeral_string() returns a buffer allocated from a special heap
1248 with a lifetime until the next packet is dissected. You do not need to
1249 free() this buffer, it will happen automatically once the next packet is
1252 tvb_get_seasonal_string() returns a buffer allocated from a special heap
1253 with a lifetime of the current capture session. You do not need to
1254 free() this buffer, it will happen automatically once the a new capture or
1257 guint8 *tvb_get_stringz(tvbuff_t *tvb, gint offset, gint *lengthp);
1258 guint8 *tvb_get_ephemeral_stringz(tvbuff_t *tvb, gint offset, gint *lengthp);
1259 guint8 *tvb_get_seasonal_stringz(tvbuff_t *tvb, gint offset, gint *lengthp);
1261 Returns a null-terminated buffer, allocated with "g_malloc()",
1262 containing data from the specified tvbuff, starting at the
1263 specified offset, and containing all characters from the tvbuff up to
1264 and including a terminating null character in the tvbuff. "*lengthp"
1265 will be set to the length of the string, including the terminating null.
1267 tvb_get_stringz() returns a buffer allocated by g_malloc() so you must
1268 g_free() it when you are finished with the string. Failure to g_free() this
1269 buffer will lead to memory leaks.
1270 tvb_get_ephemeral_stringz() returns a buffer allocated from a special heap
1271 with a lifetime until the next packet is dissected. You do not need to
1272 free() this buffer, it will happen automatically once the next packet is
1275 tvb_get_seasonal_stringz() returns a buffer allocated from a special heap
1276 with a lifetime of the current capture session. You do not need to
1277 free() this buffer, it will happen automatically once the a new capture or
1280 guint8 *tvb_fake_unicode(tvbuff_t*, gint offset, gint length, gboolean little_endian);
1281 guint8 *tvb_get_ephemeral_faked_unicode(tvbuff_t*, gint offset, gint length, gboolean little_endian);
1283 Converts a 2-byte unicode string to an ASCII string.
1284 Returns a null-terminated buffer containing data from the specified
1285 tvbuff, starting at the specified offset, and containing the specified
1286 length worth of characters (the length of the buffer will be length+1,
1287 as it includes a null character to terminate the string).
1289 tvb_fake_unicode() returns a buffer allocated by g_malloc() so you must
1290 g_free() it when you are finished with the string. Failure to g_free() this
1291 buffer will lead to memory leaks.
1292 tvb_get_ephemeral_faked_unicode() returns a buffer allocated from a special
1293 heap with a lifetime until the next packet is dissected. You do not need to
1294 free() this buffer, it will happen automatically once the next packet is
1297 Byte Array Accessors:
1299 gchar *tvb_bytes_to_str(tvbuff_t *tvb, gint offset, gint len);
1301 Formats a bunch of data from a tvbuff as bytes, returning a pointer
1302 to the string with the data formatted as two hex digits for each byte.
1303 The string pointed to is stored in an "ep_alloc'd" buffer which will be freed
1304 before the next frame is dissected. The formatted string will contain the hex digits
1305 for at most the first 16 bytes of the data. If len is greater than 16 bytes, a
1306 trailing "..." will be added to the string.
1308 gchar *tvb_bytes_to_str_punct(tvbuff_t *tvb, gint offset, gint len, gchar punct);
1310 This function is similar to tvb_bytes_to_str(...) except that 'punct' is inserted
1311 between the hex representation of each byte.
1315 guint8* tvb_memcpy(tvbuff_t*, guint8* target, gint offset, gint length);
1317 Copies into the specified target the specified length's worth of data
1318 from the specified tvbuff, starting at the specified offset.
1320 guint8* tvb_memdup(tvbuff_t*, gint offset, gint length);
1321 guint8* ep_tvb_memdup(tvbuff_t*, gint offset, gint length);
1323 Returns a buffer, allocated with "g_malloc()", containing the specified
1324 length's worth of data from the specified tvbuff, starting at the
1325 specified offset. The ephemeral variant is freed automatically after the
1326 packet is dissected.
1329 /* WARNING! This function is possibly expensive, temporarily allocating
1330 * another copy of the packet data. Furthermore, it's dangerous because once
1331 * this pointer is given to the user, there's no guarantee that the user will
1332 * honor the 'length' and not overstep the boundaries of the buffer.
1334 guint8* tvb_get_ptr(tvbuff_t*, gint offset, gint length);
1336 The reason that tvb_get_ptr() might have to allocate a copy of its data
1337 only occurs with TVBUFF_COMPOSITES, data that spans multiple tvbuffers.
1338 If the user requests a pointer to a range of bytes that span the member
1339 tvbuffs that make up the TVBUFF_COMPOSITE, the data will have to be
1340 copied to another memory region to assure that all the bytes are
1345 1.5 Functions to handle columns in the traffic summary window.
1347 The topmost pane of the main window is a list of the packets in the
1348 capture, possibly filtered by a display filter.
1350 Each line corresponds to a packet, and has one or more columns, as
1351 configured by the user.
1353 Many of the columns are handled by code outside individual dissectors;
1354 most dissectors need only specify the value to put in the "Protocol" and
1357 Columns are specified by COL_ values; the COL_ value for the "Protocol"
1358 field, typically giving an abbreviated name for the protocol (but not
1359 the all-lower-case abbreviation used elsewhere) is COL_PROTOCOL, and the
1360 COL_ value for the "Info" field, giving a summary of the contents of the
1361 packet for that protocol, is COL_INFO.
1363 The value for a column can be specified with one of several functions,
1364 all of which take the 'fd' argument to the dissector as their first
1365 argument, and the COL_ value for the column as their second argument.
1367 1.5.1 The col_set_str function.
1369 'col_set_str' takes a string as its third argument, and sets the value
1370 for the column to that value. It assumes that the pointer passed to it
1371 points to a string constant or a static "const" array, not to a
1372 variable, as it doesn't copy the string, it merely saves the pointer
1373 value; the argument can itself be a variable, as long as it always
1374 points to a string constant or a static "const" array.
1376 It is more efficient than 'col_add_str' or 'col_add_fstr'; however, if
1377 the dissector will be using 'col_append_str' or 'col_append_fstr" to
1378 append more information to the column, the string will have to be copied
1379 anyway, so it's best to use 'col_add_str' rather than 'col_set_str' in
1382 For example, to set the "Protocol" column
1385 col_set_str(pinfo->cinfo, COL_PROTOCOL, "PROTOABBREV");
1388 1.5.2 The col_add_str function.
1390 'col_add_str' takes a string as its third argument, and sets the value
1391 for the column to that value. It takes the same arguments as
1392 'col_set_str', but copies the string, so that if the string is, for
1393 example, an automatic variable that won't remain in scope when the
1394 dissector returns, it's safe to use.
1397 1.5.3 The col_add_fstr function.
1399 'col_add_fstr' takes a 'printf'-style format string as its third
1400 argument, and 'printf'-style arguments corresponding to '%' format
1401 items in that string as its subsequent arguments. For example, to set
1402 the "Info" field to "<XXX> request, <N> bytes", where "reqtype" is a
1403 string containing the type of the request in the packet and "n" is an
1404 unsigned integer containing the number of bytes in the request:
1406 col_add_fstr(pinfo->cinfo, COL_INFO, "%s request, %u bytes",
1409 Don't use 'col_add_fstr' with a format argument of just "%s" -
1410 'col_add_str', or possibly even 'col_set_str' if the string that matches
1411 the "%s" is a static constant string, will do the same job more
1415 1.5.4 The col_clear function.
1417 If the Info column will be filled with information from the packet, that
1418 means that some data will be fetched from the packet before the Info
1419 column is filled in. If the packet is so small that the data in
1420 question cannot be fetched, the routines to fetch the data will throw an
1421 exception (see the comment at the beginning about tvbuffers improving
1422 the handling of short packets - the tvbuffers keep track of how much
1423 data is in the packet, and throw an exception on an attempt to fetch
1424 data past the end of the packet, so that the dissector won't process
1425 bogus data), causing the Info column not to be filled in.
1427 This means that the Info column will have data for the previous
1428 protocol, which would be confusing if, for example, the Protocol column
1429 had data for this protocol.
1431 Therefore, before a dissector fetches any data whatsoever from the
1432 packet (unless it's a heuristic dissector fetching data to determine
1433 whether the packet is one that it should dissect, in which case it
1434 should check, before fetching the data, whether there's any data to
1435 fetch; if there isn't, it should return FALSE), it should set the
1436 Protocol column and the Info column.
1438 If the Protocol column will ultimately be set to, for example, a value
1439 containing a protocol version number, with the version number being a
1440 field in the packet, the dissector should, before fetching the version
1441 number field or any other field from the packet, set it to a value
1442 without a version number, using 'col_set_str', and should later set it
1443 to a value with the version number after it's fetched the version
1446 If the Info column will ultimately be set to a value containing
1447 information from the packet, the dissector should, before fetching any
1448 fields from the packet, clear the column using 'col_clear' (which is
1449 more efficient than clearing it by calling 'col_set_str' or
1450 'col_add_str' with a null string), and should later set it to the real
1451 string after it's fetched the data to use when doing that.
1454 1.5.5 The col_append_str function.
1456 Sometimes the value of a column, especially the "Info" column, can't be
1457 conveniently constructed at a single point in the dissection process;
1458 for example, it might contain small bits of information from many of the
1459 fields in the packet. 'col_append_str' takes, as arguments, the same
1460 arguments as 'col_add_str', but the string is appended to the end of the
1461 current value for the column, rather than replacing the value for that
1462 column. (Note that no blank separates the appended string from the
1463 string to which it is appended; if you want a blank there, you must add
1464 it yourself as part of the string being appended.)
1467 1.5.6 The col_append_fstr function.
1469 'col_append_fstr' is to 'col_add_fstr' as 'col_append_str' is to
1470 'col_add_str' - it takes, as arguments, the same arguments as
1471 'col_add_fstr', but the formatted string is appended to the end of the
1472 current value for the column, rather than replacing the value for that
1475 1.5.7 The col_append_sep_str and col_append_sep_fstr functions.
1477 In specific situations the developer knows that a column's value will be
1478 created in a stepwise manner, where the appended values are listed. Both
1479 'col_append_sep_str' and 'col_append_sep_fstr' functions will add an item
1480 separator between two consecutive items, and will not add the separator at the
1481 beginning of the column. The remainder of the work both functions do is
1482 identical to what 'col_append_str' and 'col_append_fstr' do.
1484 1.5.8 The col_set_fence and col_prepend_fence_fstr functions.
1486 Sometimes a dissector may be called multiple times for different PDUs in the
1487 same frame (for example in the case of SCTP chunk bundling: several upper
1488 layer data packets may be contained in one SCTP packet). If the upper layer
1489 dissector calls 'col_set_str()' or 'col_clear()' on the Info column when it
1490 begins dissecting each of those PDUs then when the frame is fully dissected
1491 the Info column would contain only the string from the last PDU in the frame.
1492 The 'col_set_fence' function erects a "fence" in the column that prevents
1493 subsequent 'col_...' calls from clearing the data currently in that column.
1494 For example, the SCTP dissector calls 'col_set_fence' on the Info column
1495 after it has called any subdissectors for that chunk so that subdissectors
1496 of any subsequent chunks may only append to the Info column.
1497 'col_prepend_fence_fstr' prepends data before a fence (moving it if
1498 necessary). It will create a fence at the end of the prepended data if the
1499 fence does not already exist.
1502 1.5.9 The col_set_time function.
1504 The 'col_set_time' function takes an nstime value as its third argument.
1505 This nstime value is a relative value and will be added as such to the
1506 column. The fourth argument is the filtername holding this value. This
1507 way, rightclicking on the column makes it possible to build a filter
1508 based on the time-value.
1512 nstime_delta(&ts, &pinfo->fd->abs_ts, &tcpd->ts_first);
1513 col_set_time(pinfo->cinfo, COL_REL_CONV_TIME, &ts, "tcp.time_relative");
1516 1.6 Constructing the protocol tree.
1518 The middle pane of the main window, and the topmost pane of a packet
1519 popup window, are constructed from the "protocol tree" for a packet.
1521 The protocol tree, or proto_tree, is a GNode, the N-way tree structure
1522 available within GLIB. Of course the protocol dissectors don't care
1523 what a proto_tree really is; they just pass the proto_tree pointer as an
1524 argument to the routines which allow them to add items and new branches
1527 When a packet is selected in the packet-list pane, or a packet popup
1528 window is created, a new logical protocol tree (proto_tree) is created.
1529 The pointer to the proto_tree (in this case, 'protocol tree'), is passed
1530 to the top-level protocol dissector, and then to all subsequent protocol
1531 dissectors for that packet, and then the GUI tree is drawn via
1534 The logical proto_tree needs to know detailed information about the protocols
1535 and fields about which information will be collected from the dissection
1536 routines. By strictly defining (or "typing") the data that can be attached to a
1537 proto tree, searching and filtering becomes possible. This means that for
1538 every protocol and field (which I also call "header fields", since they are
1539 fields in the protocol headers) which might be attached to a tree, some
1540 information is needed.
1542 Every dissector routine will need to register its protocols and fields
1543 with the central protocol routines (in proto.c). At first I thought I
1544 might keep all the protocol and field information about all the
1545 dissectors in one file, but decentralization seemed like a better idea.
1546 That one file would have gotten very large; one small change would have
1547 required a re-compilation of the entire file. Also, by allowing
1548 registration of protocols and fields at run-time, loadable modules of
1549 protocol dissectors (perhaps even user-supplied) is feasible.
1551 To do this, each protocol should have a register routine, which will be
1552 called when Wireshark starts. The code to call the register routines is
1553 generated automatically; to arrange that a protocol's register routine
1554 be called at startup:
1556 the file containing a dissector's "register" routine must be
1557 added to "DISSECTOR_SRC" in "epan/dissectors/Makefile.common"
1558 (and in "epan/CMakeLists.txt");
1560 the "register" routine must have a name of the form
1561 "proto_register_XXX";
1563 the "register" routine must take no argument, and return no
1566 the "register" routine's name must appear in the source file
1567 either at the beginning of the line, or preceded only by "void "
1568 at the beginning of the line (that would typically be the
1569 definition) - other white space shouldn't cause a problem, e.g.:
1571 void proto_register_XXX(void) {
1580 proto_register_XXX( void )
1587 and so on should work.
1589 For every protocol or field that a dissector wants to register, a variable of
1590 type int needs to be used to keep track of the protocol. The IDs are
1591 needed for establishing parent/child relationships between protocols and
1592 fields, as well as associating data with a particular field so that it
1593 can be stored in the logical tree and displayed in the GUI protocol
1596 Some dissectors will need to create branches within their tree to help
1597 organize header fields. These branches should be registered as header
1598 fields. Only true protocols should be registered as protocols. This is
1599 so that a display filter user interface knows how to distinguish
1600 protocols from fields.
1602 A protocol is registered with the name of the protocol and its
1605 Here is how the frame "protocol" is registered.
1609 proto_frame = proto_register_protocol (
1611 /* short name */ "Frame",
1612 /* abbrev */ "frame" );
1614 A header field is also registered with its name and abbreviation, but
1615 information about its data type is needed. It helps to look at
1616 the header_field_info struct to see what information is expected:
1618 struct header_field_info {
1623 const void *strings;
1631 A string representing the name of the field. This is the name
1632 that will appear in the graphical protocol tree. It must be a non-empty
1637 A string with an abbreviation of the field. We concatenate the
1638 abbreviation of the parent protocol with an abbreviation for the field,
1639 using a period as a separator. For example, the "src" field in an IP packet
1640 would have "ip.src" as an abbreviation. It is acceptable to have
1641 multiple levels of periods if, for example, you have fields in your
1642 protocol that are then subdivided into subfields. For example, TRMAC
1643 has multiple error fields, so the abbreviations follow this pattern:
1644 "trmac.errors.iso", "trmac.errors.noniso", etc.
1646 The abbreviation is the identifier used in a display filter. If it is
1647 an empty string then the field will not be filterable.
1651 The type of value this field holds. The current field types are:
1653 FT_NONE No field type. Used for fields that
1654 aren't given a value, and that can only
1655 be tested for presence or absence; a
1656 field that represents a data structure,
1657 with a subtree below it containing
1658 fields for the members of the structure,
1659 or that represents an array with a
1660 subtree below it containing fields for
1661 the members of the array, might be an
1663 FT_PROTOCOL Used for protocols which will be placing
1664 themselves as top-level items in the
1665 "Packet Details" pane of the UI.
1666 FT_BOOLEAN 0 means "false", any other value means
1668 FT_FRAMENUM A frame number; if this is used, the "Go
1669 To Corresponding Frame" menu item can
1671 FT_UINT8 An 8-bit unsigned integer.
1672 FT_UINT16 A 16-bit unsigned integer.
1673 FT_UINT24 A 24-bit unsigned integer.
1674 FT_UINT32 A 32-bit unsigned integer.
1675 FT_UINT64 A 64-bit unsigned integer.
1676 FT_INT8 An 8-bit signed integer.
1677 FT_INT16 A 16-bit signed integer.
1678 FT_INT24 A 24-bit signed integer.
1679 FT_INT32 A 32-bit signed integer.
1680 FT_INT64 A 64-bit signed integer.
1681 FT_FLOAT A single-precision floating point number.
1682 FT_DOUBLE A double-precision floating point number.
1683 FT_ABSOLUTE_TIME Seconds (4 bytes) and nanoseconds (4 bytes)
1684 of time since January 1, 1970, midnight
1685 UTC, displayed as the date, followed by
1686 the time, as hours, minutes, and seconds
1687 with 9 digits after the decimal point.
1688 FT_RELATIVE_TIME Seconds (4 bytes) and nanoseconds (4 bytes)
1689 of time relative to an arbitrary time.
1690 displayed as seconds and 9 digits
1691 after the decimal point.
1692 FT_STRING A string of characters, not necessarily
1693 NUL-terminated, but possibly NUL-padded.
1694 This, and the other string-of-characters
1695 types, are to be used for text strings,
1696 not raw binary data.
1697 FT_STRINGZ A NUL-terminated string of characters.
1698 FT_EBCDIC A string of characters, not necessarily
1699 NUL-terminated, but possibly NUL-padded.
1700 The data from the packet is converted from
1701 EBCDIC to ASCII before displaying to the user.
1702 FT_UINT_STRING A counted string of characters, consisting
1703 of a count (represented as an integral value,
1704 of width given in the proto_tree_add_item()
1705 call) followed immediately by that number of
1707 FT_ETHER A six octet string displayed in
1708 Ethernet-address format.
1709 FT_BYTES A string of bytes with arbitrary values;
1710 used for raw binary data.
1711 FT_UINT_BYTES A counted string of bytes, consisting
1712 of a count (represented as an integral value,
1713 of width given in the proto_tree_add_item()
1714 call) followed immediately by that number of
1715 arbitrary values; used for raw binary data.
1716 FT_IPv4 A version 4 IP address (4 bytes) displayed
1717 in dotted-quad IP address format (4
1718 decimal numbers separated by dots).
1719 FT_IPv6 A version 6 IP address (16 bytes) displayed
1720 in standard IPv6 address format.
1721 FT_IPXNET An IPX address displayed in hex as a 6-byte
1722 network number followed by a 6-byte station
1724 FT_GUID A Globally Unique Identifier
1725 FT_OID An ASN.1 Object Identifier
1727 Some of these field types are still not handled in the display filter
1728 routines, but the most common ones are. The FT_UINT* variables all
1729 represent unsigned integers, and the FT_INT* variables all represent
1730 signed integers; the number on the end represent how many bits are used
1731 to represent the number.
1733 Some constraints are imposed on the header fields depending on the type
1734 (e.g. FT_BYTES) of the field. Fields of type FT_ABSOLUTE_TIME must use
1735 'ABSOLUTE_TIME_{LOCAL,UTC,DOY_UTC}, NULL, 0x0' as values for the
1736 'display, 'strings', and 'bitmask' fields, and all other non-integral
1737 types (i.e.. types that are _not_ FT_INT* and FT_UINT*) must use
1738 'BASE_NONE, NULL, 0x0' as values for the 'display', 'strings', 'bitmask'
1739 fields. The reason is simply that the type itself implictly defines the
1740 nature of 'display', 'strings', 'bitmask'.
1744 The display field has a couple of overloaded uses. This is unfortunate,
1745 but since we're using C as an application programming language, this sometimes
1746 makes for cleaner programs. Right now I still think that overloading
1747 this variable was okay.
1749 For integer fields (FT_UINT* and FT_INT*), this variable represents the
1750 base in which you would like the value displayed. The acceptable bases
1760 BASE_DEC, BASE_HEX, and BASE_OCT are decimal, hexadecimal, and octal,
1761 respectively. BASE_DEC_HEX and BASE_HEX_DEC display value in two bases
1762 (the 1st representation followed by the 2nd in parenthesis).
1764 BASE_CUSTOM allows one to specify a callback function pointer that will
1765 format the value. The function pointer of the same type as defined by
1766 custom_fmt_func_t in epan/proto.h, specifically:
1768 void func(gchar *, guint32);
1770 The first argument is a pointer to a buffer of the ITEM_LABEL_LENGTH size
1771 and the second argument is the value to be formatted.
1773 For FT_BOOLEAN fields that are also bitfields (i.e. 'bitmask' is non-zero),
1774 'display' is used to tell the proto_tree how wide the parent bitfield is.
1775 With integers this is not needed since the type of integer itself
1776 (FT_UINT8, FT_UINT16, FT_UINT24, FT_UINT32, etc.) tells the proto_tree how
1777 wide the parent bitfield is.
1779 For FT_ABSOLUTE_TIME fields, 'display' is used to indicate whether the
1780 time is to be displayed as a time in the time zone for the machine on
1781 which Wireshark/TShark is running or as UTC and, for UTC, whether the
1782 date should be displayed as "{monthname}, {month} {day_of_month},
1783 {year}" or as "{year/day_of_year}".
1785 Additionally, BASE_NONE is used for 'display' as a NULL-value. That is, for
1786 non-integers other than FT_ABSOLUTE_TIME fields, and non-bitfield
1787 FT_BOOLEANs, you'll want to use BASE_NONE in the 'display' field. You may
1788 not use BASE_NONE for integers.
1790 It is possible that in the future we will record the endianness of
1791 integers. If so, it is likely that we'll use a bitmask on the display field
1792 so that integers would be represented as BEND|BASE_DEC or LEND|BASE_HEX.
1793 But that has not happened yet; note that there are protocols for which
1794 no endianness is specified, such as the X11 protocol and the DCE RPC
1795 protocol, so it would not be possible to record the endianness of all
1800 Some integer fields, of type FT_UINT*, need labels to represent the true
1801 value of a field. You could think of those fields as having an
1802 enumerated data type, rather than an integral data type.
1804 A 'value_string' structure is a way to map values to strings.
1806 typedef struct _value_string {
1811 For fields of that type, you would declare an array of "value_string"s:
1813 static const value_string valstringname[] = {
1814 { INTVAL1, "Descriptive String 1" },
1815 { INTVAL2, "Descriptive String 2" },
1819 (the last entry in the array must have a NULL 'strptr' value, to
1820 indicate the end of the array). The 'strings' field would be set to
1821 'VALS(valstringname)'.
1823 If the field has a numeric rather than an enumerated type, the 'strings'
1824 field would be set to NULL.
1826 You can also use an extended version of the value_string for faster lookups.
1827 It requires a value_string as input.
1828 It will use the value as a pointer to the string if all values from 0 to max
1829 are present in the array; otherwise if the values are in assending order
1830 a binary search will be used. The init macro will perform a check on the value string
1831 the first time it is used to determine which search algorithm fits and fall back to a linear search
1832 if the value_string does not meet the criteria above.
1834 Use this macro to initialise the extended value_string:
1836 static value_string_ext valstringname_ext = VALUE_STRING_EXT_INIT(valstringname);
1838 For FT_(U)INT* fields that need a 'valstringname_ext' struct, the 'strings' field
1839 would be set to '&valstringname_ext)'. Furthermore, 'display' field must be
1840 ORed with 'BASE_EXT_STRING' (e.g. BASE_DEC|BASE_EXT_STRING).
1843 If the field has a numeric type that might logically fit in ranges of values
1844 one can use a range_string struct.
1846 Thus a 'range_string' structure is a way to map ranges to strings.
1848 typedef struct _range_string {
1851 const gchar *strptr;
1854 For fields of that type, you would declare an array of "range_string"s:
1856 static const range_string rvalstringname[] = {
1857 { INTVAL_MIN1, INTVALMAX1, "Descriptive String 1" },
1858 { INTVAL_MIN2, INTVALMAX2, "Descriptive String 2" },
1862 If INTVAL_MIN equals INTVAL_MAX for a given entry the range_string
1863 behavior collapses to the one of value_string.
1864 For FT_(U)INT* fields that need a 'range_string' struct, the 'strings' field
1865 would be set to 'RVALS(rvalstringname)'. Furthermore, 'display' field must be
1866 ORed with 'BASE_RANGE_STRING' (e.g. BASE_DEC|BASE_RANGE_STRING).
1868 FT_BOOLEANs have a default map of 0 = "False", 1 (or anything else) = "True".
1869 Sometimes it is useful to change the labels for boolean values (e.g.,
1870 to "Yes"/"No", "Fast"/"Slow", etc.). For these mappings, a struct called
1871 true_false_string is used.
1873 typedef struct true_false_string {
1876 } true_false_string;
1878 For Boolean fields for which "False" and "True" aren't the desired
1879 labels, you would declare a "true_false_string"s:
1881 static const true_false_string boolstringname = {
1886 Its two fields are pointers to the string representing truth, and the
1887 string representing falsehood. For FT_BOOLEAN fields that need a
1888 'true_false_string' struct, the 'strings' field would be set to
1889 'TFS(&boolstringname)'.
1891 If the Boolean field is to be displayed as "False" or "True", the
1892 'strings' field would be set to NULL.
1894 Wireshark predefines a whole range of ready made "true_false_string"s
1895 in tfs.h, included via packet.h.
1899 If the field is a bitfield, then the bitmask is the mask which will
1900 leave only the bits needed to make the field when ANDed with a value.
1901 The proto_tree routines will calculate 'bitshift' automatically
1902 from 'bitmask', by finding the rightmost set bit in the bitmask.
1903 This shift is applied before applying string mapping functions or
1905 If the field is not a bitfield, then bitmask should be set to 0.
1909 This is a string giving a proper description of the field. It should be
1910 at least one grammatically complete sentence, or NULL in which case the
1911 name field is used. (Please do not use "").
1912 It is meant to provide a more detailed description of the field than the
1913 name alone provides. This information will be used in the man page, and
1914 in a future GUI display-filter creation tool. We might also add tooltips
1915 to the labels in the GUI protocol tree, in which case the blurb would
1916 be used as the tooltip text.
1919 1.6.1 Field Registration.
1921 Protocol registration is handled by creating an instance of the
1922 header_field_info struct (or an array of such structs), and
1923 calling the registration function along with the registration ID of
1924 the protocol that is the parent of the fields. Here is a complete example:
1926 static int proto_eg = -1;
1927 static int hf_field_a = -1;
1928 static int hf_field_b = -1;
1930 static hf_register_info hf[] = {
1933 { "Field A", "proto.field_a", FT_UINT8, BASE_HEX, NULL,
1934 0xf0, "Field A represents Apples", HFILL }},
1937 { "Field B", "proto.field_b", FT_UINT16, BASE_DEC, VALS(vs),
1938 0x0, "Field B represents Bananas", HFILL }}
1941 proto_eg = proto_register_protocol("Example Protocol",
1943 proto_register_field_array(proto_eg, hf, array_length(hf));
1945 Be sure that your array of hf_register_info structs is declared 'static',
1946 since the proto_register_field_array() function does not create a copy
1947 of the information in the array... it uses that static copy of the
1948 information that the compiler created inside your array. Here's the
1949 layout of the hf_register_info struct:
1951 typedef struct hf_register_info {
1952 int *p_id; /* pointer to parent variable */
1953 header_field_info hfinfo;
1956 Also be sure to use the handy array_length() macro found in packet.h
1957 to have the compiler compute the array length for you at compile time.
1959 If you don't have any fields to register, do *NOT* create a zero-length
1960 "hf" array; not all compilers used to compile Wireshark support them.
1961 Just omit the "hf" array, and the "proto_register_field_array()" call,
1964 It is OK to have header fields with a different format be registered with
1965 the same abbreviation. For instance, the following is valid:
1967 static hf_register_info hf[] = {
1969 { &hf_field_8bit, /* 8-bit version of proto.field */
1970 { "Field (8 bit)", "proto.field", FT_UINT8, BASE_DEC, NULL,
1971 0x00, "Field represents FOO", HFILL }},
1973 { &hf_field_32bit, /* 32-bit version of proto.field */
1974 { "Field (32 bit)", "proto.field", FT_UINT32, BASE_DEC, NULL,
1975 0x00, "Field represents FOO", HFILL }}
1978 This way a filter expression can match a header field, irrespective of the
1979 representation of it in the specific protocol context. This is interesting
1980 for protocols with variable-width header fields.
1982 The HFILL macro at the end of the struct will set reasonable default values
1983 for internally used fields.
1985 1.6.2 Adding Items and Values to the Protocol Tree.
1987 A protocol item is added to an existing protocol tree with one of a
1988 handful of proto_XXX_DO_YYY() functions.
1990 Remember that it only makes sense to add items to a protocol tree if its
1991 proto_tree pointer is not null. Should you add an item to a NULL tree, then
1992 the proto_XXX_DO_YYY() function will immediately return. The cost of this
1993 function call can be avoided by checking for the tree pointer.
1995 Subtrees can be made with the proto_item_add_subtree() function:
1997 item = proto_tree_add_item(....);
1998 new_tree = proto_item_add_subtree(item, tree_type);
2000 This will add a subtree under the item in question; a subtree can be
2001 created under an item made by any of the "proto_tree_add_XXX" functions,
2002 so that the tree can be given an arbitrary depth.
2004 Subtree types are integers, assigned by
2005 "proto_register_subtree_array()". To register subtree types, pass an
2006 array of pointers to "gint" variables to hold the subtree type values to
2007 "proto_register_subtree_array()":
2009 static gint ett_eg = -1;
2010 static gint ett_field_a = -1;
2012 static gint *ett[] = {
2017 proto_register_subtree_array(ett, array_length(ett));
2019 in your "register" routine, just as you register the protocol and the
2020 fields for that protocol.
2022 There are several functions that the programmer can use to add either
2023 protocol or field labels to the proto_tree:
2026 proto_tree_add_item(tree, id, tvb, start, length, encoding);
2029 proto_tree_add_none_format(tree, id, tvb, start, length, format, ...);
2032 proto_tree_add_protocol_format(tree, id, tvb, start, length,
2036 proto_tree_add_bytes(tree, id, tvb, start, length, start_ptr);
2039 proto_tree_add_bytes_format(tree, id, tvb, start, length, start_ptr,
2043 proto_tree_add_bytes_format_value(tree, id, tvb, start, length,
2044 start_ptr, format, ...);
2047 proto_tree_add_time(tree, id, tvb, start, length, value_ptr);
2050 proto_tree_add_time_format(tree, id, tvb, start, length, value_ptr,
2054 proto_tree_add_time_format_value(tree, id, tvb, start, length,
2055 value_ptr, format, ...);
2058 proto_tree_add_ipxnet(tree, id, tvb, start, length, value);
2061 proto_tree_add_ipxnet_format(tree, id, tvb, start, length, value,
2065 proto_tree_add_ipxnet_format_value(tree, id, tvb, start, length,
2066 value, format, ...);
2069 proto_tree_add_ipv4(tree, id, tvb, start, length, value);
2072 proto_tree_add_ipv4_format(tree, id, tvb, start, length, value,
2076 proto_tree_add_ipv4_format_value(tree, id, tvb, start, length,
2077 value, format, ...);
2080 proto_tree_add_ipv6(tree, id, tvb, start, length, value_ptr);
2083 proto_tree_add_ipv6_format(tree, id, tvb, start, length, value_ptr,
2087 proto_tree_add_ipv6_format_value(tree, id, tvb, start, length,
2088 value_ptr, format, ...);
2091 proto_tree_add_ether(tree, id, tvb, start, length, value_ptr);
2094 proto_tree_add_ether_format(tree, id, tvb, start, length, value_ptr,
2098 proto_tree_add_ether_format_value(tree, id, tvb, start, length,
2099 value_ptr, format, ...);
2102 proto_tree_add_string(tree, id, tvb, start, length, value_ptr);
2105 proto_tree_add_string_format(tree, id, tvb, start, length, value_ptr,
2109 proto_tree_add_string_format_value(tree, id, tvb, start, length,
2110 value_ptr, format, ...);
2113 proto_tree_add_boolean(tree, id, tvb, start, length, value);
2116 proto_tree_add_boolean_format(tree, id, tvb, start, length, value,
2120 proto_tree_add_boolean_format_value(tree, id, tvb, start, length,
2121 value, format, ...);
2124 proto_tree_add_float(tree, id, tvb, start, length, value);
2127 proto_tree_add_float_format(tree, id, tvb, start, length, value,
2131 proto_tree_add_float_format_value(tree, id, tvb, start, length,
2132 value, format, ...);
2135 proto_tree_add_double(tree, id, tvb, start, length, value);
2138 proto_tree_add_double_format(tree, id, tvb, start, length, value,
2142 proto_tree_add_double_format_value(tree, id, tvb, start, length,
2143 value, format, ...);
2146 proto_tree_add_uint(tree, id, tvb, start, length, value);
2149 proto_tree_add_uint_format(tree, id, tvb, start, length, value,
2153 proto_tree_add_uint_format_value(tree, id, tvb, start, length,
2154 value, format, ...);
2157 proto_tree_add_uint64(tree, id, tvb, start, length, value);
2160 proto_tree_add_uint64_format(tree, id, tvb, start, length, value,
2164 proto_tree_add_uint64_format_value(tree, id, tvb, start, length,
2165 value, format, ...);
2168 proto_tree_add_int(tree, id, tvb, start, length, value);
2171 proto_tree_add_int_format(tree, id, tvb, start, length, value,
2175 proto_tree_add_int_format_value(tree, id, tvb, start, length,
2176 value, format, ...);
2179 proto_tree_add_int64(tree, id, tvb, start, length, value);
2182 proto_tree_add_int64_format(tree, id, tvb, start, length, value,
2186 proto_tree_add_int64_format_value(tree, id, tvb, start, length,
2187 value, format, ...);
2190 proto_tree_add_text(tree, tvb, start, length, format, ...);
2193 proto_tree_add_text_valist(tree, tvb, start, length, format, ap);
2196 proto_tree_add_guid(tree, id, tvb, start, length, value_ptr);
2199 proto_tree_add_guid_format(tree, id, tvb, start, length, value_ptr,
2203 proto_tree_add_guid_format_value(tree, id, tvb, start, length,
2204 value_ptr, format, ...);
2207 proto_tree_add_oid(tree, id, tvb, start, length, value_ptr);
2210 proto_tree_add_oid_format(tree, id, tvb, start, length, value_ptr,
2214 proto_tree_add_oid_format_value(tree, id, tvb, start, length,
2215 value_ptr, format, ...);
2218 proto_tree_add_bits_item(tree, id, tvb, bit_offset, no_of_bits,
2222 proto_tree_add_bits_ret_val(tree, id, tvb, bit_offset, no_of_bits,
2223 return_value, little_endian);
2226 proto_tree_add_bitmask(tree, tvb, start, header, ett, fields,
2230 proto_tree_add_bitmask_text(tree, tvb, offset, len, name, fallback,
2231 ett, fields, little_endian, flags);
2233 The 'tree' argument is the tree to which the item is to be added. The
2234 'tvb' argument is the tvbuff from which the item's value is being
2235 extracted; the 'start' argument is the offset from the beginning of that
2236 tvbuff of the item being added, and the 'length' argument is the length,
2237 in bytes, of the item, bit_offset is the offset in bits and no_of_bits
2238 is the length in bits.
2240 The length of some items cannot be determined until the item has been
2241 dissected; to add such an item, add it with a length of -1, and, when the
2242 dissection is complete, set the length with 'proto_item_set_len()':
2245 proto_item_set_len(ti, length);
2247 The "ti" argument is the value returned by the call that added the item
2248 to the tree, and the "length" argument is the length of the item.
2250 proto_tree_add_item()
2251 ---------------------
2252 proto_tree_add_item is used when you wish to do no special formatting.
2253 The item added to the GUI tree will contain the name (as passed in the
2254 proto_register_*() function) and a value. The value will be fetched
2255 from the tvbuff by proto_tree_add_item(), based on the type of the field
2256 and, for integral and Boolean fields, the byte order of the value; the
2257 byte order, for items for which that's relevant, is specified by the
2258 'encoding' argument, which is REP_LITTLE_ENDIAN if the value is
2259 little-endian and REP_BIG_ENDIAN if it is big-endian. If the byte order
2260 is not relevant, use REP_NA (Not Applicable). In the future, other
2261 elements of the encoding, such as the character encoding for
2262 character strings, might be supported.
2264 Now that definitions of fields have detailed information about bitfield
2265 fields, you can use proto_tree_add_item() with no extra processing to
2266 add bitfield values to your tree. Here's an example. Take the Format
2267 Identifier (FID) field in the Transmission Header (TH) portion of the SNA
2268 protocol. The FID is the high nibble of the first byte of the TH. The
2269 FID would be registered like this:
2271 name = "Format Identifier"
2272 abbrev = "sna.th.fid"
2275 strings = sna_th_fid_vals
2278 The bitmask contains the value which would leave only the FID if bitwise-ANDed
2279 against the parent field, the first byte of the TH.
2281 The code to add the FID to the tree would be;
2283 proto_tree_add_item(bf_tree, hf_sna_th_fid, tvb, offset, 1,
2286 The definition of the field already has the information about bitmasking
2287 and bitshifting, so it does the work of masking and shifting for us!
2288 This also means that you no longer have to create value_string structs
2289 with the values bitshifted. The value_string for FID looks like this,
2290 even though the FID value is actually contained in the high nibble.
2291 (You'd expect the values to be 0x0, 0x10, 0x20, etc.)
2293 /* Format Identifier */
2294 static const value_string sna_th_fid_vals[] = {
2295 { 0x0, "SNA device <--> Non-SNA Device" },
2296 { 0x1, "Subarea Node <--> Subarea Node" },
2297 { 0x2, "Subarea Node <--> PU2" },
2298 { 0x3, "Subarea Node or SNA host <--> Subarea Node" },
2301 { 0xf, "Adjacent Subarea Nodes" },
2305 The final implication of this is that display filters work the way you'd
2306 naturally expect them to. You'd type "sna.th.fid == 0xf" to find Adjacent
2307 Subarea Nodes. The user does not have to shift the value of the FID to
2308 the high nibble of the byte ("sna.th.fid == 0xf0") as was necessary
2311 proto_tree_add_protocol_format()
2312 --------------------------------
2313 proto_tree_add_protocol_format is used to add the top-level item for the
2314 protocol when the dissector routine wants complete control over how the
2315 field and value will be represented on the GUI tree. The ID value for
2316 the protocol is passed in as the "id" argument; the rest of the
2317 arguments are a "printf"-style format and any arguments for that format.
2318 The caller must include the name of the protocol in the format; it is
2319 not added automatically as in proto_tree_add_item().
2321 proto_tree_add_none_format()
2322 ----------------------------
2323 proto_tree_add_none_format is used to add an item of type FT_NONE.
2324 The caller must include the name of the field in the format; it is
2325 not added automatically as in proto_tree_add_item().
2327 proto_tree_add_bytes()
2328 proto_tree_add_time()
2329 proto_tree_add_ipxnet()
2330 proto_tree_add_ipv4()
2331 proto_tree_add_ipv6()
2332 proto_tree_add_ether()
2333 proto_tree_add_string()
2334 proto_tree_add_boolean()
2335 proto_tree_add_float()
2336 proto_tree_add_double()
2337 proto_tree_add_uint()
2338 proto_tree_add_uint64()
2339 proto_tree_add_int()
2340 proto_tree_add_int64()
2341 proto_tree_add_guid()
2342 proto_tree_add_oid()
2343 ------------------------
2344 These routines are used to add items to the protocol tree if either:
2346 the value of the item to be added isn't just extracted from the
2347 packet data, but is computed from data in the packet;
2349 the value was fetched into a variable.
2351 The 'value' argument has the value to be added to the tree.
2353 NOTE: in all cases where the 'value' argument is a pointer, a copy is
2354 made of the object pointed to; if you have dynamically allocated a
2355 buffer for the object, that buffer will not be freed when the protocol
2356 tree is freed - you must free the buffer yourself when you don't need it
2359 For proto_tree_add_bytes(), the 'value_ptr' argument is a pointer to a
2362 For proto_tree_add_time(), the 'value_ptr' argument is a pointer to an
2363 "nstime_t", which is a structure containing the time to be added; it has
2364 'secs' and 'nsecs' members, giving the integral part and the fractional
2365 part of a time in units of seconds, with 'nsecs' being the number of
2366 nanoseconds. For absolute times, "secs" is a UNIX-style seconds since
2367 January 1, 1970, 00:00:00 GMT value.
2369 For proto_tree_add_ipxnet(), the 'value' argument is a 32-bit IPX
2372 For proto_tree_add_ipv4(), the 'value' argument is a 32-bit IPv4
2373 address, in network byte order.
2375 For proto_tree_add_ipv6(), the 'value_ptr' argument is a pointer to a
2376 128-bit IPv6 address.
2378 For proto_tree_add_ether(), the 'value_ptr' argument is a pointer to a
2381 For proto_tree_add_string(), the 'value_ptr' argument is a pointer to a
2384 For proto_tree_add_boolean(), the 'value' argument is a 32-bit integer.
2385 It is masked and shifted as defined by the field info after which zero
2386 means "false", and non-zero means "true".
2388 For proto_tree_add_float(), the 'value' argument is a 'float' in the
2389 host's floating-point format.
2391 For proto_tree_add_double(), the 'value' argument is a 'double' in the
2392 host's floating-point format.
2394 For proto_tree_add_uint(), the 'value' argument is a 32-bit unsigned
2395 integer value, in host byte order. (This routine cannot be used to add
2398 For proto_tree_add_uint64(), the 'value' argument is a 64-bit unsigned
2399 integer value, in host byte order.
2401 For proto_tree_add_int(), the 'value' argument is a 32-bit signed
2402 integer value, in host byte order. (This routine cannot be used to add
2405 For proto_tree_add_int64(), the 'value' argument is a 64-bit signed
2406 integer value, in host byte order.
2408 For proto_tree_add_guid(), the 'value_ptr' argument is a pointer to an
2411 For proto_tree_add_oid(), the 'value_ptr' argument is a pointer to an
2412 ASN.1 Object Identifier.
2414 proto_tree_add_bytes_format()
2415 proto_tree_add_time_format()
2416 proto_tree_add_ipxnet_format()
2417 proto_tree_add_ipv4_format()
2418 proto_tree_add_ipv6_format()
2419 proto_tree_add_ether_format()
2420 proto_tree_add_string_format()
2421 proto_tree_add_boolean_format()
2422 proto_tree_add_float_format()
2423 proto_tree_add_double_format()
2424 proto_tree_add_uint_format()
2425 proto_tree_add_uint64_format()
2426 proto_tree_add_int_format()
2427 proto_tree_add_int64_format()
2428 proto_tree_add_guid_format()
2429 proto_tree_add_oid_format()
2430 ----------------------------
2431 These routines are used to add items to the protocol tree when the
2432 dissector routine wants complete control over how the field and value
2433 will be represented on the GUI tree. The argument giving the value is
2434 the same as the corresponding proto_tree_add_XXX() function; the rest of
2435 the arguments are a "printf"-style format and any arguments for that
2436 format. The caller must include the name of the field in the format; it
2437 is not added automatically as in the proto_tree_add_XXX() functions.
2439 proto_tree_add_bytes_format_value()
2440 proto_tree_add_time_format_value()
2441 proto_tree_add_ipxnet_format_value()
2442 proto_tree_add_ipv4_format_value()
2443 proto_tree_add_ipv6_format_value()
2444 proto_tree_add_ether_format_value()
2445 proto_tree_add_string_format_value()
2446 proto_tree_add_boolean_format_value()
2447 proto_tree_add_float_format_value()
2448 proto_tree_add_double_format_value()
2449 proto_tree_add_uint_format_value()
2450 proto_tree_add_uint64_format_value()
2451 proto_tree_add_int_format_value()
2452 proto_tree_add_int64_format_value()
2453 proto_tree_add_guid_format_value()
2454 proto_tree_add_oid_format_value()
2455 ------------------------------------
2457 These routines are used to add items to the protocol tree when the
2458 dissector routine wants complete control over how the value will be
2459 represented on the GUI tree. The argument giving the value is the same
2460 as the corresponding proto_tree_add_XXX() function; the rest of the
2461 arguments are a "printf"-style format and any arguments for that format.
2462 With these routines, unlike the proto_tree_add_XXX_format() routines,
2463 the name of the field is added automatically as in the
2464 proto_tree_add_XXX() functions; only the value is added with the format.
2466 proto_tree_add_text()
2467 ---------------------
2468 proto_tree_add_text() is used to add a label to the GUI tree. It will
2469 contain no value, so it is not searchable in the display filter process.
2470 This function was needed in the transition from the old-style proto_tree
2471 to this new-style proto_tree so that Wireshark would still decode all
2472 protocols w/o being able to filter on all protocols and fields.
2473 Otherwise we would have had to cripple Wireshark's functionality while we
2474 converted all the old-style proto_tree calls to the new-style proto_tree
2475 calls. In other words, you should not use this in new code unless you've got
2476 a specific reason (see below).
2478 This can also be used for items with subtrees, which may not have values
2479 themselves - the items in the subtree are the ones with values.
2481 For a subtree, the label on the subtree might reflect some of the items
2482 in the subtree. This means the label can't be set until at least some
2483 of the items in the subtree have been dissected. To do this, use
2484 'proto_item_set_text()' or 'proto_item_append_text()':
2487 proto_item_set_text(proto_item *ti, ...);
2490 proto_item_append_text(proto_item *ti, ...);
2492 'proto_item_set_text()' takes as an argument the value returned by
2493 'proto_tree_add_text()', a 'printf'-style format string, and a set of
2494 arguments corresponding to '%' format items in that string, and replaces
2495 the text for the item created by 'proto_tree_add_text()' with the result
2496 of applying the arguments to the format string.
2498 'proto_item_append_text()' is similar, but it appends to the text for
2499 the item the result of applying the arguments to the format string.
2501 For example, early in the dissection, one might do:
2503 ti = proto_tree_add_text(tree, tvb, offset, length, <label>);
2507 proto_item_set_text(ti, "%s: %s", type, value);
2509 after the "type" and "value" fields have been extracted and dissected.
2510 <label> would be a label giving what information about the subtree is
2511 available without dissecting any of the data in the subtree.
2513 Note that an exception might be thrown when trying to extract the values of
2514 the items used to set the label, if not all the bytes of the item are
2515 available. Thus, one should create the item with text that is as
2516 meaningful as possible, and set it or append additional information to
2517 it as the values needed to supply that information are extracted.
2519 proto_tree_add_text_valist()
2520 ----------------------------
2521 This is like proto_tree_add_text(), but takes, as the last argument, a
2522 'va_list'; it is used to allow routines that take a printf-like
2523 variable-length list of arguments to add a text item to the protocol
2526 proto_tree_add_bits_item()
2527 --------------------------
2528 Adds a number of bits to the protocol tree which does not have to be byte
2529 aligned. The offset and length is in bits.
2532 ..10 1010 10.. .... "value" (formatted as FT_ indicates).
2534 proto_tree_add_bits_ret_val()
2535 -----------------------------
2536 Works in the same way but also returns the value of the read bits.
2538 proto_tree_add_bitmask() and proto_tree_add_bitmask_text()
2539 ----------------------------------------------------------
2540 This function provides an easy to use and convenient helper function
2541 to manage many types of common bitmasks that occur in protocols.
2543 This function will dissect a 1/2/3/4 byte large bitmask into its individual
2545 header is an integer type and must be of type FT_[U]INT{8|16|24|32} and
2546 represents the entire width of the bitmask.
2548 'header' and 'ett' are the hf fields and ett field respectively to create an
2549 expansion that covers the 1-4 bytes of the bitmask.
2551 'fields' is a NULL terminated array of pointers to hf fields representing
2552 the individual subfields of the bitmask. These fields must either be integers
2553 of the same byte width as 'header' or of the type FT_BOOLEAN.
2554 Each of the entries in 'fields' will be dissected as an item under the
2555 'header' expansion and also IF the field is a boolean and IF it is set to 1,
2556 then the name of that boolean field will be printed on the 'header' expansion
2557 line. For integer type subfields that have a value_string defined, the
2558 matched string from that value_string will be printed on the expansion line
2561 Example: (from the SCSI dissector)
2562 static int hf_scsi_inq_peripheral = -1;
2563 static int hf_scsi_inq_qualifier = -1;
2564 static int hf_scsi_inq_devtype = -1;
2566 static gint ett_scsi_inq_peripheral = -1;
2568 static const int *peripheal_fields[] = {
2569 &hf_scsi_inq_qualifier,
2570 &hf_scsi_inq_devtype,
2574 /* Qualifier and DeviceType */
2575 proto_tree_add_bitmask(tree, tvb, offset, hf_scsi_inq_peripheral,
2576 ett_scsi_inq_peripheral, peripheal_fields, FALSE);
2579 { &hf_scsi_inq_peripheral,
2580 {"Peripheral", "scsi.inquiry.preipheral", FT_UINT8, BASE_HEX,
2581 NULL, 0, NULL, HFILL}},
2582 { &hf_scsi_inq_qualifier,
2583 {"Qualifier", "scsi.inquiry.qualifier", FT_UINT8, BASE_HEX,
2584 VALS (scsi_qualifier_val), 0xE0, NULL, HFILL}},
2585 { &hf_scsi_inq_devtype,
2586 {"Device Type", "scsi.inquiry.devtype", FT_UINT8, BASE_HEX,
2587 VALS (scsi_devtype_val), SCSI_DEV_BITS, NULL, HFILL}},
2590 Which provides very pretty dissection of this one byte bitmask.
2592 Peripheral: 0x05, Qualifier: Device type is connected to logical unit, Device Type: CD-ROM
2593 000. .... = Qualifier: Device type is connected to logical unit (0x00)
2594 ...0 0101 = Device Type: CD-ROM (0x05)
2596 The proto_tree_add_bitmask_text() function is an extended version of
2597 the proto_tree_add_bitmask() function. In addition, it allows to:
2598 - Provide a leading text (e.g. "Flags: ") that will appear before
2599 the comma-separated list of field values
2600 - Provide a fallback text (e.g. "None") that will be appended if
2601 no fields warranted a change to the top-level title.
2602 - Using flags, specify which fields will affect the top-level title.
2604 There are the following flags defined:
2606 BMT_NO_APPEND - the title is taken "as-is" from the 'name' argument.
2607 BMT_NO_INT - only boolean flags are added to the title.
2608 BMT_NO_FALSE - boolean flags are only added to the title if they are set.
2609 BMT_NO_TFS - only add flag name to the title, do not use true_false_string
2611 The proto_tree_add_bitmask() behavior can be obtained by providing
2612 both 'name' and 'fallback' arguments as NULL, and a flags of
2613 (BMT_NO_FALSE|BMT_NO_TFS).
2615 PROTO_ITEM_SET_GENERATED()
2616 --------------------------
2617 PROTO_ITEM_SET_GENERATED is used to mark fields as not being read from the
2618 captured data directly, but inferred from one or more values.
2620 One of the primary uses of this is the presentation of verification of
2621 checksums. Every IP packet has a checksum line, which can present the result
2622 of the checksum verification, if enabled in the preferences. The result is
2623 presented as a subtree, where the result is enclosed in square brackets
2624 indicating a generated field.
2626 Header checksum: 0x3d42 [correct]
2630 PROTO_ITEM_SET_HIDDEN()
2631 -----------------------
2632 PROTO_ITEM_SET_HIDDEN is used to hide fields, which have already been added
2633 to the tree, from being visible in the displayed tree.
2635 NOTE that creating hidden fields is actually quite a bad idea from a UI design
2636 perspective because the user (someone who did not write nor has ever seen the
2637 code) has no way of knowing that hidden fields are there to be filtered on
2638 thus defeating the whole purpose of putting them there. A Better Way might
2639 be to add the fields (that might otherwise be hidden) to a subtree where they
2640 won't be seen unless the user opens the subtree--but they can be found if the
2643 One use for hidden fields (which would be better implemented using visible
2644 fields in a subtree) follows: The caller may want a value to be
2645 included in a tree so that the packet can be filtered on this field, but
2646 the representation of that field in the tree is not appropriate. An
2647 example is the token-ring routing information field (RIF). The best way
2648 to show the RIF in a GUI is by a sequence of ring and bridge numbers.
2649 Rings are 3-digit hex numbers, and bridges are single hex digits:
2651 RIF: 001-A-013-9-C0F-B-555
2653 In the case of RIF, the programmer should use a field with no value and
2654 use proto_tree_add_none_format() to build the above representation. The
2655 programmer can then add the ring and bridge values, one-by-one, with
2656 proto_tree_add_item() and hide them with PROTO_ITEM_SET_HIDDEN() so that the
2657 user can then filter on or search for a particular ring or bridge. Here's a
2658 skeleton of how the programmer might code this.
2661 rif = create_rif_string(...);
2663 proto_tree_add_none_format(tree, hf_tr_rif_label, ..., "RIF: %s", rif);
2665 for(i = 0; i < num_rings; i++) {
2668 pi = proto_tree_add_item(tree, hf_tr_rif_ring, ...,
2670 PROTO_ITEM_SET_HIDDEN(pi);
2672 for(i = 0; i < num_rings - 1; i++) {
2675 pi = proto_tree_add_item(tree, hf_tr_rif_bridge, ...,
2677 PROTO_ITEM_SET_HIDDEN(pi);
2680 The logical tree has these items:
2682 hf_tr_rif_label, text="RIF: 001-A-013-9-C0F-B-555", value = NONE
2683 hf_tr_rif_ring, hidden, value=0x001
2684 hf_tr_rif_bridge, hidden, value=0xA
2685 hf_tr_rif_ring, hidden, value=0x013
2686 hf_tr_rif_bridge, hidden, value=0x9
2687 hf_tr_rif_ring, hidden, value=0xC0F
2688 hf_tr_rif_bridge, hidden, value=0xB
2689 hf_tr_rif_ring, hidden, value=0x555
2691 GUI or print code will not display the hidden fields, but a display
2692 filter or "packet grep" routine will still see the values. The possible
2693 filter is then possible:
2695 tr.rif_ring eq 0x013
2699 PROTO_ITEM_SET_URL is used to mark fields as containing a URL. This can only
2700 be done with fields of type FT_STRING(Z). If these fields are presented they
2701 are underlined, as could be done in a browser. These fields are sensitive to
2702 clicks as well, launching the configured browser with this URL as parameter.
2704 1.7 Utility routines.
2706 1.7.1 match_strval and val_to_str.
2708 A dissector may need to convert a value to a string, using a
2709 'value_string' structure, by hand, rather than by declaring a field with
2710 an associated 'value_string' structure; this might be used, for example,
2711 to generate a COL_INFO line for a frame.
2713 'match_strval()' will do that:
2716 match_strval(guint32 val, const value_string *vs)
2718 It will look up the value 'val' in the 'value_string' table pointed to
2719 by 'vs', and return either the corresponding string, or NULL if the
2720 value could not be found in the table. Note that, unless 'val' is
2721 guaranteed to be a value in the 'value_string' table ("guaranteed" as in
2722 "the code has already checked that it's one of those values" or "the
2723 table handles all possible values of the size of 'val'", not "the
2724 protocol spec says it has to be" - protocol specs do not prevent invalid
2725 packets from being put onto a network or into a purported packet capture
2726 file), you must check whether 'match_strval()' returns NULL, and arrange
2727 that its return value not be dereferenced if it's NULL. 'val_to_str()'
2728 can be used to generate a string for values not found in the table:
2731 val_to_str(guint32 val, const value_string *vs, const char *fmt)
2733 If the value 'val' is found in the 'value_string' table pointed to by
2734 'vs', 'val_to_str' will return the corresponding string; otherwise, it
2735 will use 'fmt' as an 'sprintf'-style format, with 'val' as an argument,
2736 to generate a string, and will return a pointer to that string.
2737 You can use it in a call to generate a COL_INFO line for a frame such as
2739 col_add_fstr(COL_INFO, ", %s", val_to_str(val, table, "Unknown %d"));
2741 1.7.2 match_strrval and rval_to_str.
2743 A dissector may need to convert a range of values to a string, using a
2744 'range_string' structure.
2746 'match_strrval()' will do that:
2749 match_strrval(guint32 val, const range_string *rs)
2751 It will look up the value 'val' in the 'range_string' table pointed to
2752 by 'rs', and return either the corresponding string, or NULL if the
2753 value could not be found in the table. Please note that its base
2754 behavior is inherited from match_strval().
2756 'rval_to_str()' can be used to generate a string for values not found in
2760 rval_to_str(guint32 val, const range_string *rs, const char *fmt)
2762 If the value 'val' is found in the 'range_string' table pointed to by
2763 'rs', 'rval_to_str' will return the corresponding string; otherwise, it
2764 will use 'fmt' as an 'sprintf'-style format, with 'val' as an argument,
2765 to generate a string, and will return a pointer to that string. Please
2766 note that its base behavior is inherited from match_strval().
2768 1.8 Calling Other Dissectors.
2770 As each dissector completes its portion of the protocol analysis, it
2771 is expected to create a new tvbuff of type TVBUFF_SUBSET which
2772 contains the payload portion of the protocol (that is, the bytes
2773 that are relevant to the next dissector).
2775 The syntax for creating a new TVBUFF_SUBSET is:
2777 next_tvb = tvb_new_subset(tvb, offset, length, reported_length)
2780 tvb is the tvbuff that the dissector has been working on. It
2781 can be a tvbuff of any type.
2783 next_tvb is the new TVBUFF_SUBSET.
2785 offset is the byte offset of 'tvb' at which the new tvbuff
2786 should start. The first byte is the 0th byte.
2788 length is the number of bytes in the new TVBUFF_SUBSET. A length
2789 argument of -1 says to use as many bytes as are available in
2792 reported_length is the number of bytes that the current protocol
2793 says should be in the payload. A reported_length of -1 says that
2794 the protocol doesn't say anything about the size of its payload.
2797 An example from packet-ipx.c -
2800 dissect_ipx(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
2803 int reported_length, available_length;
2806 /* Make the next tvbuff */
2808 /* IPX does have a length value in the header, so calculate report_length */
2809 Set this to -1 if there isn't any length information in the protocol
2811 reported_length = ipx_length - IPX_HEADER_LEN;
2813 /* Calculate the available data in the packet,
2814 set this to -1 to use all the data in the tv_buffer
2816 available_length = tvb_length(tvb) - IPX_HEADER_LEN;
2818 /* Create the tvbuffer for the next dissector */
2819 next_tvb = tvb_new_subset(tvb, IPX_HEADER_LEN,
2820 MIN(available_length, reported_length),
2823 /* call the next dissector */
2824 dissector_next( next_tvb, pinfo, tree);
2827 1.9 Editing Makefile.common and CMakeLists.txt to add your dissector.
2829 To arrange that your dissector will be built as part of Wireshark, you
2830 must add the name of the source file for your dissector to the
2831 'DISSECTOR_SRC' macro in the 'Makefile.common' file in the 'epan/dissectors'
2832 directory. (Note that this is for modern versions of UNIX, so there
2833 is no 14-character limitation on file names, and for modern versions of
2834 Windows, so there is no 8.3-character limitation on file names.)
2836 If your dissector also has its own header file or files, you must add
2837 them to the 'DISSECTOR_INCLUDES' macro in the 'Makefile.common' file in
2838 the 'epan/dissectors' directory, so that it's included when release source
2839 tarballs are built (otherwise, the source in the release tarballs won't
2842 In addition to the above, you should add your dissector source file name
2843 to the DISSECTOR_SRC section of epan/CMakeLists.txt
2846 1.10 Using the SVN source code tree.
2848 See <http://www.wireshark.org/develop.html>
2850 1.11 Submitting code for your new dissector.
2852 - VERIFY that your dissector code does not use prohibited or deprecated APIs
2854 perl <wireshark_root>/tools/checkAPIs.pl <source-filename(s)>
2856 - TEST YOUR DISSECTOR BEFORE SUBMITTING IT.
2857 Use fuzz-test.sh and/or randpkt against your dissector. These are
2858 described at <http://wiki.wireshark.org/FuzzTesting>.
2860 - Subscribe to <mailto:wireshark-dev[AT]wireshark.org> by sending an email to
2861 <mailto:wireshark-dev-request[AT]wireshark.org?body="help"> or visiting
2862 <http://www.wireshark.org/lists/>.
2864 - 'svn add' all the files of your new dissector.
2866 - 'svn diff' the workspace and save the result to a file.
2868 - Edit the diff file - remove any changes unrelated to your new dissector,
2869 e.g. changes in config.nmake
2871 - Submit a bug report to the Wireshark bug database, found at
2872 <http://bugs.wireshark.org>, qualified as an enhancement and attach your
2873 diff file there. Set the review request flag to '?' so it will pop up in
2874 the patch review list.
2876 - Create a Wiki page on the protocol at <http://wiki.wireshark.org>.
2877 A template is provided so it is easy to setup in a consistent style.
2878 See: <http://wiki.wireshark.org/HowToEdit>
2879 and <http://wiki.wireshark.org/ProtocolReference>
2881 - If possible, add sample capture files to the sample captures page at
2882 <http://wiki.wireshark.org/SampleCaptures>. These files are used by
2883 the automated build system for fuzz testing.
2885 - If you find that you are contributing a lot to wireshark on an ongoing
2886 basis you can request to become a committer which will allow you to
2887 commit files to subversion directly.
2889 2. Advanced dissector topics.
2893 Some of the advanced features are being worked on constantly. When using them
2894 it is wise to check the relevant header and source files for additional details.
2896 2.2 Following "conversations".
2898 In wireshark a conversation is defined as a series of data packets between two
2899 address:port combinations. A conversation is not sensitive to the direction of
2900 the packet. The same conversation will be returned for a packet bound from
2901 ServerA:1000 to ClientA:2000 and the packet from ClientA:2000 to ServerA:1000.
2903 There are five routines that you will use to work with a conversation:
2904 conversation_new, find_conversation, conversation_add_proto_data,
2905 conversation_get_proto_data, and conversation_delete_proto_data.
2908 2.2.1 The conversation_init function.
2910 This is an internal routine for the conversation code. As such you
2911 will not have to call this routine. Just be aware that this routine is
2912 called at the start of each capture and before the packets are filtered
2913 with a display filter. The routine will destroy all stored
2914 conversations. This routine does NOT clean up any data pointers that are
2915 passed in the conversation_new 'data' variable. You are responsible for
2916 this clean up if you pass a malloc'ed pointer in this variable.
2918 See item 2.2.8 for more information about the 'data' pointer.
2921 2.2.2 The conversation_new function.
2923 This routine will create a new conversation based upon two address/port
2924 pairs. If you want to associate with the conversation a pointer to a
2925 private data structure you must use the conversation_add_proto_data
2926 function. The ptype variable is used to differentiate between
2927 conversations over different protocols, i.e. TCP and UDP. The options
2928 variable is used to define a conversation that will accept any destination
2929 address and/or port. Set options = 0 if the destination port and address
2930 are know when conversation_new is called. See section 2.4 for more
2931 information on usage of the options parameter.
2933 The conversation_new prototype:
2934 conversation_t *conversation_new(guint32 setup_frame, address *addr1,
2935 address *addr2, port_type ptype, guint32 port1, guint32 port2,
2939 guint32 setup_frame = The lowest numbered frame for this conversation
2940 address* addr1 = first data packet address
2941 address* addr2 = second data packet address
2942 port_type ptype = port type, this is defined in packet.h
2943 guint32 port1 = first data packet port
2944 guint32 port2 = second data packet port
2945 guint options = conversation options, NO_ADDR2 and/or NO_PORT2
2947 setup_frame indicates the first frame for this conversation, and is used to
2948 distinguish multiple conversations with the same addr1/port1 and addr2/port2
2949 pair that occur within the same capture session.
2951 "addr1" and "port1" are the first address/port pair; "addr2" and "port2"
2952 are the second address/port pair. A conversation doesn't have source
2953 and destination address/port pairs - packets in a conversation go in
2954 both directions - so "addr1"/"port1" may be the source or destination
2955 address/port pair; "addr2"/"port2" would be the other pair.
2957 If NO_ADDR2 is specified, the conversation is set up so that a
2958 conversation lookup will match only the "addr1" address; if NO_PORT2 is
2959 specified, the conversation is set up so that a conversation lookup will
2960 match only the "port1" port; if both are specified, i.e.
2961 NO_ADDR2|NO_PORT2, the conversation is set up so that the lookup will
2962 match only the "addr1"/"port1" address/port pair. This can be used if a
2963 packet indicates that, later in the capture, a conversation will be
2964 created using certain addresses and ports, in the case where the packet
2965 doesn't specify the addresses and ports of both sides.
2967 2.2.3 The find_conversation function.
2969 Call this routine to look up a conversation. If no conversation is found,
2970 the routine will return a NULL value.
2972 The find_conversation prototype:
2974 conversation_t *find_conversation(guint32 frame_num, address *addr_a,
2975 address *addr_b, port_type ptype, guint32 port_a, guint32 port_b,
2979 guint32 frame_num = a frame number to match
2980 address* addr_a = first address
2981 address* addr_b = second address
2982 port_type ptype = port type
2983 guint32 port_a = first data packet port
2984 guint32 port_b = second data packet port
2985 guint options = conversation options, NO_ADDR_B and/or NO_PORT_B
2987 frame_num is a frame number to match. The conversation returned is where
2988 (frame_num >= conversation->setup_frame
2989 && frame_num < conversation->next->setup_frame)
2990 Suppose there are a total of 3 conversations (A, B, and C) that match
2991 addr_a/port_a and addr_b/port_b, where the setup_frame used in
2992 conversation_new() for A, B and C are 10, 50, and 100 respectively. The
2993 frame_num passed in find_conversation is compared to the setup_frame of each
2994 conversation. So if (frame_num >= 10 && frame_num < 50), conversation A is
2995 returned. If (frame_num >= 50 && frame_num < 100), conversation B is returned.
2996 If (frame_num >= 100) conversation C is returned.
2998 "addr_a" and "port_a" are the first address/port pair; "addr_b" and
2999 "port_b" are the second address/port pair. Again, as a conversation
3000 doesn't have source and destination address/port pairs, so
3001 "addr_a"/"port_a" may be the source or destination address/port pair;
3002 "addr_b"/"port_b" would be the other pair. The search will match the
3003 "a" address/port pair against both the "1" and "2" address/port pairs,
3004 and match the "b" address/port pair against both the "2" and "1"
3005 address/port pairs; you don't have to worry about which side the "a" or
3006 "b" pairs correspond to.
3008 If the NO_ADDR_B flag was specified to "find_conversation()", the
3009 "addr_b" address will be treated as matching any "wildcarded" address;
3010 if the NO_PORT_B flag was specified, the "port_b" port will be treated
3011 as matching any "wildcarded" port. If both flags are specified, i.e.
3012 NO_ADDR_B|NO_PORT_B, the "addr_b" address will be treated as matching
3013 any "wildcarded" address and the "port_b" port will be treated as
3014 matching any "wildcarded" port.
3017 2.2.4 The find_or_create_conversation function.
3019 This convenience function will create find an existing conversation (by calling
3020 find_conversation()) and, if a conversation does not already exist, create a
3021 new conversation by calling conversation_new().
3023 The find_or_create_conversation prototype:
3025 extern conversation_t *find_or_create_conversation(packet_info *pinfo);
3028 packet_info *pinfo = the packet_info structure
3030 The frame number and the addresses necessary for find_conversation() and
3031 conversation_new() are taken from the pinfo structure (as is commonly done)
3032 and no 'options' are used.
3035 2.2.5 The conversation_add_proto_data function.
3037 Once you have created a conversation with conversation_new, you can
3038 associate data with it using this function.
3040 The conversation_add_proto_data prototype:
3042 void conversation_add_proto_data(conversation_t *conv, int proto,
3046 conversation_t *conv = the conversation in question
3047 int proto = registered protocol number
3048 void *data = dissector data structure
3050 "conversation" is the value returned by conversation_new. "proto" is a
3051 unique protocol number created with proto_register_protocol. Protocols
3052 are typically registered in the proto_register_XXXX section of your
3053 dissector. "data" is a pointer to the data you wish to associate with the
3054 conversation. Using the protocol number allows several dissectors to
3055 associate data with a given conversation.
3058 2.2.6 The conversation_get_proto_data function.
3060 After you have located a conversation with find_conversation, you can use
3061 this function to retrieve any data associated with it.
3063 The conversation_get_proto_data prototype:
3065 void *conversation_get_proto_data(conversation_t *conv, int proto);
3068 conversation_t *conv = the conversation in question
3069 int proto = registered protocol number
3071 "conversation" is the conversation created with conversation_new. "proto"
3072 is a unique protocol number created with proto_register_protocol,
3073 typically in the proto_register_XXXX portion of a dissector. The function
3074 returns a pointer to the data requested, or NULL if no data was found.
3077 2.2.7 The conversation_delete_proto_data function.
3079 After you are finished with a conversation, you can remove your association
3080 with this function. Please note that ONLY the conversation entry is
3081 removed. If you have allocated any memory for your data, you must free it
3084 The conversation_delete_proto_data prototype:
3086 void conversation_delete_proto_data(conversation_t *conv, int proto);
3089 conversation_t *conv = the conversation in question
3090 int proto = registered protocol number
3092 "conversation" is the conversation created with conversation_new. "proto"
3093 is a unique protocol number created with proto_register_protocol,
3094 typically in the proto_register_XXXX portion of a dissector.
3097 2.2.8 Using timestamps relative to the conversation
3099 There is a framework to calculate timestamps relative to the start of the
3100 conversation. First of all the timestamp of the first packet that has been
3101 seen in the conversation must be kept in the protocol data to be able
3102 to calculate the timestamp of the current packet relative to the start
3103 of the conversation. The timestamp of the last packet that was seen in the
3104 conversation should also be kept in the protocol data. This way the
3105 delta time between the current packet and the previous packet in the
3106 conversation can be calculated.
3108 So add the following items to the struct that is used for the protocol data:
3113 The ts_prev value should only be set during the first run through the
3114 packets (ie pinfo->fd->flags.visited is false).
3116 Next step is to use the per-packet information (described in section 2.5)
3117 to keep the calculated delta timestamp, as it can only be calculated
3118 on the first run through the packets. This is because a packet can be
3119 selected in random order once the whole file has been read.
3121 After calculating the conversation timestamps, it is time to put them in
3122 the appropriate columns with the function 'col_set_time' (described in
3123 section 1.5.9). There are two columns for conversation timestamps:
3125 COL_REL_CONV_TIME, /* Relative time to beginning of conversation */
3126 COL_DELTA_CONV_TIME,/* Delta time to last frame in conversation */
3128 Last but not least, there MUST be a preference in each dissector that
3129 uses conversation timestamps that makes it possible to enable and
3130 disable the calculation of conversation timestamps. The main argument
3131 for this is that a higher level conversation is able to overwrite
3132 the values of lowel level conversations in these two columns. Being
3133 able to actively select which protocols may overwrite the conversation
3134 timestamp columns gives the user the power to control these columns.
3135 (A second reason is that conversation timestamps use the per-packet
3136 data structure which uses additional memory, which should be avoided
3137 if these timestamps are not needed)
3139 Have a look at the differences to packet-tcp.[ch] in SVN 22966 and
3140 SVN 23058 to see the implementation of conversation timestamps for
3144 2.2.9 The example conversation code with GMemChunk's.
3146 For a conversation between two IP addresses and ports you can use this as an
3147 example. This example uses the GMemChunk to allocate memory and stores the data
3148 pointer in the conversation 'data' variable.
3150 NOTE: Remember to register the init routine (my_dissector_init) in the
3151 protocol_register routine.
3154 /************************ Global values ************************/
3156 /* the number of entries in the memory chunk array */
3157 #define my_init_count 10
3159 /* define your structure here */
3164 /* the GMemChunk base structure */
3165 static GMemChunk *my_vals = NULL;
3167 /* Registered protocol number */
3168 static int my_proto = -1;
3171 /********************* in the dissector routine *********************/
3173 /* the local variables in the dissector */
3175 conversation_t *conversation;
3176 my_entry_t *data_ptr;
3179 /* look up the conversation */
3181 conversation = find_conversation(pinfo->fd->num, &pinfo->src, &pinfo->dst,
3182 pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
3184 /* if conversation found get the data pointer that you stored */
3186 data_ptr = (my_entry_t*)conversation_get_proto_data(conversation, my_proto);
3189 /* new conversation create local data structure */
3191 data_ptr = g_mem_chunk_alloc(my_vals);
3193 /*** add your code here to setup the new data structure ***/
3195 /* create the conversation with your data pointer */
3197 conversation = conversation_new(pinfo->fd->num, &pinfo->src, &pinfo->dst, pinfo->ptype,
3198 pinfo->srcport, pinfo->destport, 0);
3199 conversation_add_proto_data(conversation, my_proto, (void *)data_ptr);
3202 /* at this point the conversation data is ready */
3205 /******************* in the dissector init routine *******************/
3207 #define my_init_count 20
3210 my_dissector_init(void)
3213 /* destroy memory chunks if needed */
3216 g_mem_chunk_destroy(my_vals);
3218 /* now create memory chunks */
3220 my_vals = g_mem_chunk_new("my_proto_vals",
3222 my_init_count * sizeof(my_entry_t),
3226 /***************** in the protocol register routine *****************/
3228 /* register re-init routine */
3230 register_init_routine(&my_dissector_init);
3232 my_proto = proto_register_protocol("My Protocol", "My Protocol", "my_proto");
3235 2.2.10 An example conversation code that starts at a specific frame number.
3237 Sometimes a dissector has determined that a new conversation is needed that
3238 starts at a specific frame number, when a capture session encompasses multiple
3239 conversation that reuse the same src/dest ip/port pairs. You can use the
3240 conversation->setup_frame returned by find_conversation with
3241 pinfo->fd->num to determine whether or not there already exists a conversation
3242 that starts at the specific frame number.
3244 /* in the dissector routine */
3246 conversation = find_conversation(pinfo->fd->num, &pinfo->src, &pinfo->dst,
3247 pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
3248 if (conversation == NULL || (conversation->setup_frame != pinfo->fd->num)) {
3249 /* It's not part of any conversation or the returned
3250 * conversation->setup_frame doesn't match the current frame
3253 conversation = conversation_new(pinfo->fd->num, &pinfo->src,
3254 &pinfo->dst, pinfo->ptype, pinfo->srcport, pinfo->destport,
3259 2.2.11 The example conversation code using conversation index field.
3261 Sometimes the conversation isn't enough to define a unique data storage
3262 value for the network traffic. For example if you are storing information
3263 about requests carried in a conversation, the request may have an
3264 identifier that is used to define the request. In this case the
3265 conversation and the identifier are required to find the data storage
3266 pointer. You can use the conversation data structure index value to
3267 uniquely define the conversation.
3269 See packet-afs.c for an example of how to use the conversation index. In
3270 this dissector multiple requests are sent in the same conversation. To store
3271 information for each request the dissector has an internal hash table based
3272 upon the conversation index and values inside the request packets.
3275 /* in the dissector routine */
3277 /* to find a request value, first lookup conversation to get index */
3278 /* then used the conversation index, and request data to find data */
3279 /* in the local hash table */
3281 conversation = find_or_create_conversation(pinfo);
3283 request_key.conversation = conversation->index;
3284 request_key.service = pntohs(&rxh->serviceId);
3285 request_key.callnumber = pntohl(&rxh->callNumber);
3287 request_val = (struct afs_request_val *)g_hash_table_lookup(
3288 afs_request_hash, &request_key);
3290 /* only allocate a new hash element when it's a request */
3292 if (!request_val && !reply)
3294 new_request_key = g_mem_chunk_alloc(afs_request_keys);
3295 *new_request_key = request_key;
3297 request_val = g_mem_chunk_alloc(afs_request_vals);
3298 request_val -> opcode = pntohl(&afsh->opcode);
3299 opcode = request_val->opcode;
3301 g_hash_table_insert(afs_request_hash, new_request_key,
3307 2.3 Dynamic conversation dissector registration.
3310 NOTE: This sections assumes that all information is available to
3311 create a complete conversation, source port/address and
3312 destination port/address. If either the destination port or
3313 address is know, see section 2.4 Dynamic server port dissector
3316 For protocols that negotiate a secondary port connection, for example
3317 packet-msproxy.c, a conversation can install a dissector to handle
3318 the secondary protocol dissection. After the conversation is created
3319 for the negotiated ports use the conversation_set_dissector to define
3320 the dissection routine.
3321 Before we create these conversations or assign a dissector to them we should
3322 first check that the conversation does not already exist and if it exists
3323 whether it is registered to our protocol or not.
3324 We should do this because it is uncommon but it does happen that multiple
3325 different protocols can use the same socketpair during different stages of
3326 an application cycle. By keeping track of the frame number a conversation
3327 was started in wireshark can still tell these different protocols apart.
3329 The second argument to conversation_set_dissector is a dissector handle,
3330 which is created with a call to create_dissector_handle or
3333 create_dissector_handle takes as arguments a pointer to the dissector
3334 function and a protocol ID as returned by proto_register_protocol;
3335 register_dissector takes as arguments a string giving a name for the
3336 dissector, a pointer to the dissector function, and a protocol ID.
3338 The protocol ID is the ID for the protocol dissected by the function.
3339 The function will not be called if the protocol has been disabled by the
3340 user; instead, the data for the protocol will be dissected as raw data.
3344 /* the handle for the dynamic dissector *
3345 static dissector_handle_t sub_dissector_handle;
3347 /* prototype for the dynamic dissector */
3348 static void sub_dissector(tvbuff_t *tvb, packet_info *pinfo,
3351 /* in the main protocol dissector, where the next dissector is setup */
3353 /* if conversation has a data field, create it and load structure */
3355 /* First check if a conversation already exists for this
3358 conversation = find_conversation(pinfo->fd->num,
3359 &pinfo->src, &pinfo->dst, protocol,
3360 src_port, dst_port, new_conv_info, 0);
3362 /* If there is no such conversation, or if there is one but for
3363 someone else's protocol then we just create a new conversation
3364 and assign our protocol to it.
3366 if ( (conversation == NULL) ||
3367 (conversation->dissector_handle != sub_dissector_handle) ) {
3368 new_conv_info = g_mem_chunk_alloc(new_conv_vals);
3369 new_conv_info->data1 = value1;
3371 /* create the conversation for the dynamic port */
3372 conversation = conversation_new(pinfo->fd->num,
3373 &pinfo->src, &pinfo->dst, protocol,
3374 src_port, dst_port, new_conv_info, 0);
3376 /* set the dissector for the new conversation */
3377 conversation_set_dissector(conversation, sub_dissector_handle);
3382 proto_register_PROTOABBREV(void)
3386 sub_dissector_handle = create_dissector_handle(sub_dissector,
3392 2.4 Dynamic server port dissector registration.
3394 NOTE: While this example used both NO_ADDR2 and NO_PORT2 to create a
3395 conversation with only one port and address set, this isn't a
3396 requirement. Either the second port or the second address can be set
3397 when the conversation is created.
3399 For protocols that define a server address and port for a secondary
3400 protocol, a conversation can be used to link a protocol dissector to
3401 the server port and address. The key is to create the new
3402 conversation with the second address and port set to the "accept
3405 Some server applications can use the same port for different protocols during
3406 different stages of a transaction. For example it might initially use SNMP
3407 to perform some discovery and later switch to use TFTP using the same port.
3408 In order to handle this properly we must first check whether such a
3409 conversation already exists or not and if it exists we also check whether the
3410 registered dissector_handle for that conversation is "our" dissector or not.
3411 If not we create a new conversation on top of the previous one and set this new
3412 conversation to use our protocol.
3413 Since wireshark keeps track of the frame number where a conversation started
3414 wireshark will still be able to keep the packets apart even though they do use
3415 the same socketpair.
3416 (See packet-tftp.c and packet-snmp.c for examples of this)
3418 There are two support routines that will allow the second port and/or
3419 address to be set later.
3421 conversation_set_port2( conversation_t *conv, guint32 port);
3422 conversation_set_addr2( conversation_t *conv, address addr);
3424 These routines will change the second address or port for the
3425 conversation. So, the server port conversation will be converted into a
3426 more complete conversation definition. Don't use these routines if you
3427 want to create a conversation between the server and client and retain the
3428 server port definition, you must create a new conversation.
3433 /* the handle for the dynamic dissector *
3434 static dissector_handle_t sub_dissector_handle;
3438 /* in the main protocol dissector, where the next dissector is setup */
3440 /* if conversation has a data field, create it and load structure */
3442 new_conv_info = g_mem_chunk_alloc(new_conv_vals);
3443 new_conv_info->data1 = value1;
3445 /* create the conversation for the dynamic server address and port */
3446 /* NOTE: The second address and port values don't matter because the */
3447 /* NO_ADDR2 and NO_PORT2 options are set. */
3449 /* First check if a conversation already exists for this
3452 conversation = find_conversation(pinfo->fd->num,
3453 &server_src_addr, 0, protocol,
3454 server_src_port, 0, NO_ADDR2 | NO_PORT_B);
3455 /* If there is no such conversation, or if there is one but for
3456 someone else's protocol then we just create a new conversation
3457 and assign our protocol to it.
3459 if ( (conversation == NULL) ||
3460 (conversation->dissector_handle != sub_dissector_handle) ) {
3461 conversation = conversation_new(pinfo->fd->num,
3462 &server_src_addr, 0, protocol,
3463 server_src_port, 0, new_conv_info, NO_ADDR2 | NO_PORT2);
3465 /* set the dissector for the new conversation */
3466 conversation_set_dissector(conversation, sub_dissector_handle);
3469 2.5 Per-packet information.
3471 Information can be stored for each data packet that is processed by the
3472 dissector. The information is added with the p_add_proto_data function and
3473 retrieved with the p_get_proto_data function. The data pointers passed into
3474 the p_add_proto_data are not managed by the proto_data routines. If you use
3475 malloc or any other dynamic memory allocation scheme, you must release the
3476 data when it isn't required.
3479 p_add_proto_data(frame_data *fd, int proto, void *proto_data)
3481 p_get_proto_data(frame_data *fd, int proto)
3484 fd - The fd pointer in the pinfo structure, pinfo->fd
3485 proto - Protocol id returned by the proto_register_protocol call
3486 during initialization
3487 proto_data - pointer to the dissector data.
3490 2.6 User Preferences.
3492 If the dissector has user options, there is support for adding these preferences
3493 to a configuration dialog.
3495 You must register the module with the preferences routine with -
3497 module_t *prefs_register_protocol(proto_id, void (*apply_cb)(void))
3499 module_t *prefs_register_protocol_subtree(const char *subtree, int id,
3500 void (*apply_cb)(void));
3503 Where: proto_id - the value returned by "proto_register_protocol()" when
3504 the protocol was registered.
3505 apply_cb - Callback routine that is called when preferences are
3506 applied. It may be NULL, which inhibits the callback.
3507 subtree - grouping preferences tree node name (several protocols can
3508 be grouped under one preferences subtree)
3510 Then you can register the fields that can be configured by the user with these
3513 /* Register a preference with an unsigned integral value. */
3514 void prefs_register_uint_preference(module_t *module, const char *name,
3515 const char *title, const char *description, guint base, guint *var);
3517 /* Register a preference with an Boolean value. */
3518 void prefs_register_bool_preference(module_t *module, const char *name,
3519 const char *title, const char *description, gboolean *var);
3521 /* Register a preference with an enumerated value. */
3522 void prefs_register_enum_preference(module_t *module, const char *name,
3523 const char *title, const char *description, gint *var,
3524 const enum_val_t *enumvals, gboolean radio_buttons)
3526 /* Register a preference with a character-string value. */
3527 void prefs_register_string_preference(module_t *module, const char *name,
3528 const char *title, const char *description, char **var)
3530 /* Register a preference with a range of unsigned integers (e.g.,
3533 void prefs_register_range_preference(module_t *module, const char *name,
3534 const char *title, const char *description, range_t *var,
3537 Where: module - Returned by the prefs_register_protocol routine
3538 name - This is appended to the name of the protocol, with a
3539 "." between them, to construct a name that identifies
3540 the field in the preference file; the name itself
3541 should not include the protocol name, as the name in
3542 the preference file will already have it
3543 title - Field title in the preferences dialog
3544 description - Comments added to the preference file above the
3546 var - pointer to the storage location that is updated when the
3547 field is changed in the preference dialog box
3548 base - Base that the unsigned integer is expected to be in,
3550 enumvals - an array of enum_val_t structures. This must be
3551 NULL-terminated; the members of that structure are:
3553 a short name, to be used with the "-o" flag - it
3554 should not contain spaces or upper-case letters,
3555 so that it's easier to put in a command line;
3557 a description, which is used in the GUI (and
3558 which, for compatibility reasons, is currently
3559 what's written to the preferences file) - it can
3560 contain spaces, capital letters, punctuation,
3563 the numerical value corresponding to that name
3565 radio_buttons - TRUE if the field is to be displayed in the
3566 preferences dialog as a set of radio buttons,
3567 FALSE if it is to be displayed as an option
3569 max_value - The maximum allowed value for a range (0 is the minimum).
3571 An example from packet-beep.c -
3573 proto_beep = proto_register_protocol("Blocks Extensible Exchange Protocol",
3578 /* Register our configuration options for BEEP, particularly our port */
3580 beep_module = prefs_register_protocol(proto_beep, proto_reg_handoff_beep);
3582 prefs_register_uint_preference(beep_module, "tcp.port", "BEEP TCP Port",
3583 "Set the port for BEEP messages (if other"
3584 " than the default of 10288)",
3585 10, &global_beep_tcp_port);
3587 prefs_register_bool_preference(beep_module, "strict_header_terminator",
3588 "BEEP Header Requires CRLF",
3589 "Specifies that BEEP requires CRLF as a "
3590 "terminator, and not just CR or LF",
3591 &global_beep_strict_term);
3593 This will create preferences "beep.tcp.port" and
3594 "beep.strict_header_terminator", the first of which is an unsigned
3595 integer and the second of which is a Boolean.
3597 Note that a warning will pop up if you've saved such preference to the
3598 preference file and you subsequently take the code out. The way to make
3599 a preference obsolete is to register it as such:
3601 /* Register a preference that used to be supported but no longer is. */
3602 void prefs_register_obsolete_preference(module_t *module,
3605 2.7 Reassembly/desegmentation for protocols running atop TCP.
3607 There are two main ways of reassembling a Protocol Data Unit (PDU) which
3608 spans across multiple TCP segments. The first approach is simpler, but
3609 assumes you are running atop of TCP when this occurs (but your dissector
3610 might run atop of UDP, too, for example), and that your PDUs consist of a
3611 fixed amount of data that includes enough information to determine the PDU
3612 length, possibly followed by additional data. The second method is more
3613 generic but requires more code and is less efficient.
3615 2.7.1 Using tcp_dissect_pdus().
3617 For the first method, you register two different dissection methods, one
3618 for the TCP case, and one for the other cases. It is a good idea to
3619 also have a dissect_PROTO_common function which will parse the generic
3620 content that you can find in all PDUs which is called from
3621 dissect_PROTO_tcp when the reassembly is complete and from
3622 dissect_PROTO_udp (or dissect_PROTO_other).
3624 To register the distinct dissector functions, consider the following
3625 example, stolen from packet-dns.c:
3627 dissector_handle_t dns_udp_handle;
3628 dissector_handle_t dns_tcp_handle;
3629 dissector_handle_t mdns_udp_handle;
3631 dns_udp_handle = create_dissector_handle(dissect_dns_udp,
3633 dns_tcp_handle = create_dissector_handle(dissect_dns_tcp,
3635 mdns_udp_handle = create_dissector_handle(dissect_mdns_udp,
3638 dissector_add("udp.port", UDP_PORT_DNS, dns_udp_handle);
3639 dissector_add("tcp.port", TCP_PORT_DNS, dns_tcp_handle);
3640 dissector_add("udp.port", UDP_PORT_MDNS, mdns_udp_handle);
3641 dissector_add("tcp.port", TCP_PORT_MDNS, dns_tcp_handle);
3643 The dissect_dns_udp function does very little work and calls
3644 dissect_dns_common, while dissect_dns_tcp calls tcp_dissect_pdus with a
3645 reference to a callback which will be called with reassembled data:
3648 dissect_dns_tcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
3650 tcp_dissect_pdus(tvb, pinfo, tree, dns_desegment, 2,
3651 get_dns_pdu_len, dissect_dns_tcp_pdu);
3654 (The dissect_dns_tcp_pdu function acts similarly to dissect_dns_udp.)
3655 The arguments to tcp_dissect_pdus are:
3657 the tvbuff pointer, packet_info pointer, and proto_tree pointer
3658 passed to the dissector;
3660 a gboolean flag indicating whether desegmentation is enabled for
3663 the number of bytes of PDU data required to determine the length
3666 a routine that takes as arguments a packet_info pointer, a tvbuff
3667 pointer and an offset value representing the offset into the tvbuff
3668 at which a PDU begins and should return - *without* throwing an
3669 exception (it is guaranteed that the number of bytes specified by the
3670 previous argument to tcp_dissect_pdus is available, but more data
3671 might not be available, so don't refer to any data past that) - the
3672 total length of the PDU, in bytes;
3674 a routine that's passed a tvbuff pointer, packet_info pointer,
3675 and proto_tree pointer, with the tvbuff containing a
3676 possibly-reassembled PDU, and that should dissect that PDU.
3678 2.7.2 Modifying the pinfo struct.
3680 The second reassembly mode is preferred when the dissector cannot determine
3681 how many bytes it will need to read in order to determine the size of a PDU.
3682 It may also be useful if your dissector needs to support reassembly from
3683 protocols other than TCP.
3685 Your dissect_PROTO will initially be passed a tvbuff containing the payload of
3686 the first packet. It should dissect as much data as it can, noting that it may
3687 contain more than one complete PDU. If the end of the provided tvbuff coincides
3688 with the end of a PDU then all is well and your dissector can just return as
3689 normal. (If it is a new-style dissector, it should return the number of bytes
3690 successfully processed.)
3692 If the dissector discovers that the end of the tvbuff does /not/ coincide with
3693 the end of a PDU, (ie, there is half of a PDU at the end of the tvbuff), it can
3694 indicate this to the parent dissector, by updating the pinfo struct. The
3695 desegment_offset field is the offset in the tvbuff at which the dissector will
3696 continue processing when next called. The desegment_len field should contain
3697 the estimated number of additional bytes required for completing the PDU. Next
3698 time your dissect_PROTO is called, it will be passed a tvbuff composed of the
3699 end of the data from the previous tvbuff together with desegment_len more bytes.
3701 If the dissector cannot tell how many more bytes it will need, it should set
3702 desegment_len=DESEGMENT_ONE_MORE_SEGMENT; it will then be called again as soon
3703 as any more data becomes available. Dissectors should set the desegment_len to a
3704 reasonable value when possible rather than always setting
3705 DESEGMENT_ONE_MORE_SEGMENT as it will generally be more efficient. Also, you
3706 *must not* set desegment_len=1 in this case, in the hope that you can change
3707 your mind later: once you return a positive value from desegment_len, your PDU
3708 boundary is set in stone.
3710 static hf_register_info hf[] = {
3712 {"C String", "c.string", FT_STRING, BASE_NONE, NULL, 0x0,
3718 * Dissect a buffer containing C strings.
3720 * @param tvb The buffer to dissect.
3721 * @param pinfo Packet Info.
3722 * @param tree The protocol tree.
3724 static void dissect_cstr(tvbuff_t * tvb, packet_info * pinfo, proto_tree * tree)
3727 while(offset < tvb_reported_length(tvb)) {
3728 gint available = tvb_reported_length_remaining(tvb, offset);
3729 gint len = tvb_strnlen(tvb, offset, available);
3732 /* we ran out of data: ask for more */
3733 pinfo->desegment_offset = offset;
3734 pinfo->desegment_len = DESEGMENT_ONE_MORE_SEGMENT;
3738 col_set_str(pinfo->cinfo, COL_INFO, "C String");
3740 len += 1; /* Add one for the '\0' */
3743 proto_tree_add_item(tree, hf_cstring, tvb, offset, len,
3746 offset += (guint)len;
3749 /* if we get here, then the end of the tvb coincided with the end of a
3750 string. Happy days. */
3753 This simple dissector will repeatedly return DESEGMENT_ONE_MORE_SEGMENT
3754 requesting more data until the tvbuff contains a complete C string. The C string
3755 will then be added to the protocol tree. Note that there may be more
3756 than one complete C string in the tvbuff, so the dissection is done in a
3761 The ptvcursor API allows a simpler approach to writing dissectors for
3762 simple protocols. The ptvcursor API works best for protocols whose fields
3763 are static and whose format does not depend on the value of other fields.
3764 However, even if only a portion of your protocol is statically defined,
3765 then that portion could make use of ptvcursors.
3767 The ptvcursor API lets you extract data from a tvbuff, and add it to a
3768 protocol tree in one step. It also keeps track of the position in the
3769 tvbuff so that you can extract data again without having to compute any
3770 offsets --- hence the "cursor" name of the API.
3772 The three steps for a simple protocol are:
3773 1. Create a new ptvcursor with ptvcursor_new()
3774 2. Add fields with multiple calls of ptvcursor_add()
3775 3. Delete the ptvcursor with ptvcursor_free()
3777 ptvcursor offers the possibility to add subtrees in the tree as well. It can be
3778 done in very simple steps :
3779 1. Create a new subtree with ptvcursor_push_subtree(). The old subtree is
3780 pushed in a stack and the new subtree will be used by ptvcursor.
3781 2. Add fields with multiple calls of ptvcursor_add(). The fields will be
3782 added in the new subtree created at the previous step.
3783 3. Pop the previous subtree with ptvcursor_pop_subtree(). The previous
3784 subtree is again used by ptvcursor.
3785 Note that at the end of the parsing of a packet you must have popped each
3786 subtree you pushed. If it's not the case, the dissector will generate an error.
3788 To use the ptvcursor API, include the "ptvcursor.h" file. The PGM dissector
3789 is an example of how to use it. You don't need to look at it as a guide;
3790 instead, the API description here should be good enough.
3792 2.8.1 ptvcursor API.
3795 ptvcursor_new(proto_tree* tree, tvbuff_t* tvb, gint offset)
3796 This creates a new ptvcursor_t object for iterating over a tvbuff.
3797 You must call this and use this ptvcursor_t object so you can use the
3801 ptvcursor_add(ptvcursor_t* ptvc, int hf, gint length, gboolean endianness)
3802 This will extract 'length' bytes from the tvbuff and place it in
3803 the proto_tree as field 'hf', which is a registered header_field. The
3804 pointer to the proto_item that is created is passed back to you. Internally,
3805 the ptvcursor advances its cursor so the next call to ptvcursor_add
3806 starts where this call finished. The 'endianness' parameter matters for
3807 FT_UINT* and FT_INT* fields.
3810 ptvcursor_add_no_advance(ptvcursor_t* ptvc, int hf, gint length, gboolean endianness)
3811 Like ptvcursor_add, but does not advance the internal cursor.
3814 ptvcursor_advance(ptvcursor_t* ptvc, gint length)
3815 Advances the internal cursor without adding anything to the proto_tree.
3818 ptvcursor_free(ptvcursor_t* ptvc)
3819 Frees the memory associated with the ptvcursor. You must call this
3820 after your dissection with the ptvcursor API is completed.
3824 ptvcursor_push_subtree(ptvcursor_t* ptvc, proto_item* it, gint ett_subtree)
3825 Pushes the current subtree in the tree stack of the cursor, creates a new
3826 one and sets this one as the working tree.
3829 ptvcursor_pop_subtree(ptvcursor_t* ptvc);
3830 Pops a subtree in the tree stack of the cursor
3833 ptvcursor_add_with_subtree(ptvcursor_t* ptvc, int hfindex, gint length,
3834 gboolean little_endian, gint ett_subtree);
3835 Adds an item to the tree and creates a subtree.
3836 If the length is unknown, length may be defined as SUBTREE_UNDEFINED_LENGTH.
3837 In this case, at the next pop, the item length will be equal to the advancement
3838 of the cursor since the creation of the subtree.
3841 ptvcursor_add_text_with_subtree(ptvcursor_t* ptvc, gint length,
3842 gint ett_subtree, const char* format, ...);
3843 Add a text node to the tree and create a subtree.
3844 If the length is unknown, length may be defined as SUBTREE_UNDEFINED_LENGTH.
3845 In this case, at the next pop, the item length will be equal to the advancement
3846 of the cursor since the creation of the subtree.
3848 2.8.2 Miscellaneous functions.
3851 ptvcursor_tvbuff(ptvcursor_t* ptvc)
3852 Returns the tvbuff associated with the ptvcursor.
3855 ptvcursor_current_offset(ptvcursor_t* ptvc)
3856 Returns the current offset.
3859 ptvcursor_tree(ptvcursor_t* ptvc)
3860 Returns the proto_tree associated with the ptvcursor.
3863 ptvcursor_set_tree(ptvcursor_t* ptvc, proto_tree *tree)
3864 Sets a new proto_tree for the ptvcursor.
3867 ptvcursor_set_subtree(ptvcursor_t* ptvc, proto_item* it, gint ett_subtree);
3868 Creates a subtree and adds it to the cursor as the working tree but does
3869 not save the old working tree.