6 This file is a HOWTO for Wireshark developers. It describes how to start coding
7 a Wireshark protocol dissector and the use of some of the important functions
10 This file is compiled to give in depth information on Wireshark.
11 It is by no means all inclusive and complete. Please feel free to send
12 remarks and patches to the developer mailing list.
16 Before starting to develop a new dissector, a "running" Wireshark build
17 environment is required - there's no such thing as a standalone "dissector
20 How to setup such an environment is platform dependent; detailed information
21 about these steps can be found in the "Developer's Guide" (available from:
22 http://www.wireshark.org) and in the INSTALL and README files of the sources
25 0.1. General README files.
27 You'll find additional information in the following README files:
29 - README.capture - the capture engine internals
30 - README.design - Wireshark software design - incomplete
31 - README.developer - this file
32 - README.display_filter - Display Filter Engine
33 - README.idl2wrs - CORBA IDL converter
34 - README.packaging - how to distribute a software package containing WS
35 - README.regression - regression testing of WS and TS
36 - README.stats_tree - a tree statistics counting specific packets
37 - README.tapping - "tap" a dissector to get protocol specific events
38 - README.xml-output - how to work with the PDML exported output
39 - wiretap/README.developer - how to add additional capture file types to
42 0.2. Dissector related README files.
44 You'll find additional dissector related information in the following README
47 - README.binarytrees - fast access to large data collections
48 - README.heuristic - what are heuristic dissectors and how to write them
49 - README.malloc - how to obtain "memory leak free" memory
50 - README.plugins - how to "pluginize" a dissector
51 - README.request_response_tracking - how to track req./resp. times and such
55 James Coe <jammer[AT]cin.net>
56 Gilbert Ramirez <gram[AT]alumni.rice.edu>
57 Jeff Foster <jfoste[AT]woodward.com>
58 Olivier Abad <oabad[AT]cybercable.fr>
59 Laurent Deniel <laurent.deniel[AT]free.fr>
60 Gerald Combs <gerald[AT]wireshark.org>
61 Guy Harris <guy[AT]alum.mit.edu>
62 Ulf Lamping <ulf.lamping[AT]web.de>
64 1. Setting up your protocol dissector code.
66 This section provides skeleton code for a protocol dissector. It also explains
67 the basic functions needed to enter values in the traffic summary columns,
68 add to the protocol tree, and work with registered header fields.
74 Wireshark runs on many platforms, and can be compiled with a number of
75 different compilers; here are some rules for writing code that will work
76 on multiple platforms.
78 Don't use C++-style comments (comments beginning with "//" and running
79 to the end of the line); Wireshark's dissectors are written in C, and
80 thus run through C rather than C++ compilers, and not all C compilers
81 support C++-style comments (GCC does, but IBM's C compiler for AIX, for
82 example, doesn't do so by default).
84 Don't initialize variables in their declaration with non-constant
85 values. Not all compilers support this. E.g. don't use
86 guint32 i = somearray[2];
92 Don't use zero-length arrays; not all compilers support them. If an
93 array would have no members, just leave it out.
95 Don't declare variables in the middle of executable code; not all C
96 compilers support that. Variables should be declared outside a
97 function, or at the beginning of a function or compound statement.
99 Don't use anonymous unions; not all compilers support it.
106 } u; /* have a name here */
109 Don't use "uchar", "u_char", "ushort", "u_short", "uint", "u_int",
110 "ulong", "u_long" or "boolean"; they aren't defined on all platforms.
111 If you want an 8-bit unsigned quantity, use "guint8"; if you want an
112 8-bit character value with the 8th bit not interpreted as a sign bit,
113 use "guchar"; if you want a 16-bit unsigned quantity, use "guint16";
114 if you want a 32-bit unsigned quantity, use "guint32"; and if you want
115 an "int-sized" unsigned quantity, use "guint"; if you want a boolean,
116 use "gboolean". Use "%d", "%u", "%x", and "%o" to print those types;
117 don't use "%ld", "%lu", "%lx", or "%lo", as longs are 64 bits long on
118 many platforms, but "guint32" is 32 bits long.
120 Don't use "long" to mean "signed 32-bit integer", and don't use
121 "unsigned long" to mean "unsigned 32-bit integer"; "long"s are 64 bits
122 long on many platforms. Use "gint32" for signed 32-bit integers and use
123 "guint32" for unsigned 32-bit integers.
125 Don't use "long" to mean "signed 64-bit integer" and don't use "unsigned
126 long" to mean "unsigned 64-bit integer"; "long"s are 32 bits long on
127 many other platforms. Don't use "long long" or "unsigned long long",
128 either, as not all platforms support them; use "gint64" or "guint64",
129 which will be defined as the appropriate types for 64-bit signed and
132 On LLP64 data model systems (notably 64-bit Windows), "int" and "long"
133 are 32 bits while "size_t" and "ptrdiff_t" are 64 bits. This means that
134 the following will generate a compiler warning:
137 i = strlen("hello, sailor"); /* Compiler warning */
139 Normally, you'd just make "i" a size_t. However, many GLib and Wireshark
140 functions won't accept a size_t on LLP64:
143 char greeting[] = "hello, sailor";
144 guint byte_after_greet;
146 i = strlen(greeting);
147 byte_after_greet = tvb_get_guint8(tvb, i); /* Compiler warning */
149 Try to use the appropriate data type when you can. When you can't, you
150 will have to cast to a compatible data type, e.g.
153 char greeting[] = "hello, sailor";
154 guint byte_after_greet;
156 i = strlen(greeting);
157 byte_after_greet = tvb_get_guint8(tvb, (gint) i); /* OK */
162 char greeting[] = "hello, sailor";
163 guint byte_after_greet;
165 i = (gint) strlen(greeting);
166 byte_after_greet = tvb_get_guint8(tvb, i); /* OK */
168 See http://www.unix.org/version2/whatsnew/lp64_wp.html for more
169 information on the sizes of common types in different data models.
171 When printing or displaying the values of 64-bit integral data types,
172 don't use "%lld", "%llu", "%llx", or "%llo" - not all platforms
173 support "%ll" for printing 64-bit integral data types. Instead, for
174 GLib routines, and routines that use them, such as all the routines in
175 Wireshark that take format arguments, use G_GINT64_MODIFIER, for example:
177 proto_tree_add_text(tree, tvb, offset, 8,
178 "Sequence Number: %" G_GINT64_MODIFIER "u",
181 When specifying an integral constant that doesn't fit in 32 bits, don't
182 use "LL" at the end of the constant - not all compilers use "LL" for
183 that. Instead, put the constant in a call to the "G_GINT64_CONSTANT()"
186 G_GINT64_CONSTANT(11644473600U)
192 Don't use a label without a statement following it. For example,
202 will not work with all compilers - you have to do
212 with some statement, even if it's a null statement, after the label.
214 Don't use "bzero()", "bcopy()", or "bcmp()"; instead, use the ANSI C
217 "memset()" (with zero as the second argument, so that it sets
218 all the bytes to zero);
220 "memcpy()" or "memmove()" (note that the first and second
221 arguments to "memcpy()" are in the reverse order to the
222 arguments to "bcopy()"; note also that "bcopy()" is typically
223 guaranteed to work on overlapping memory regions, while
224 "memcpy()" isn't, so if you may be copying from one region to a
225 region that overlaps it, use "memmove()", not "memcpy()" - but
226 "memcpy()" might be faster as a result of not guaranteeing
227 correct operation on overlapping memory regions);
229 and "memcmp()" (note that "memcmp()" returns 0, 1, or -1, doing
230 an ordered comparison, rather than just returning 0 for "equal"
231 and 1 for "not equal", as "bcmp()" does).
233 Not all platforms necessarily have "bzero()"/"bcopy()"/"bcmp()", and
234 those that do might not declare them in the header file on which they're
235 declared on your platform.
237 Don't use "index()" or "rindex()"; instead, use the ANSI C equivalents,
238 "strchr()" and "strrchr()". Not all platforms necessarily have
239 "index()" or "rindex()", and those that do might not declare them in the
240 header file on which they're declared on your platform.
242 Don't fetch data from packets by getting a pointer to data in the packet
243 with "tvb_get_ptr()", casting that pointer to a pointer to a structure,
244 and dereferencing that pointer. That pointer won't necessarily be aligned
245 on the proper boundary, which can cause crashes on some platforms (even
246 if it doesn't crash on an x86-based PC); furthermore, the data in a
247 packet is not necessarily in the byte order of the machine on which
248 Wireshark is running. Use the tvbuff routines to extract individual
249 items from the packet, or use "proto_tree_add_item()" and let it extract
252 Don't use structures that overlay packet data, or into which you copy
253 packet data; the C programming language does not guarantee any
254 particular alignment of fields within a structure, and even the
255 extensions that try to guarantee that are compiler-specific and not
256 necessarily supported by all compilers used to build Wireshark. Using
257 bitfields in those structures is even worse; the order of bitfields
260 Don't use "ntohs()", "ntohl()", "htons()", or "htonl()"; the header
261 files required to define or declare them differ between platforms, and
262 you might be able to get away with not including the appropriate header
263 file on your platform but that might not work on other platforms.
264 Instead, use "g_ntohs()", "g_ntohl()", "g_htons()", and "g_htonl()";
265 those are declared by <glib.h>, and you'll need to include that anyway,
266 as Wireshark header files that all dissectors must include use stuff from
269 Don't fetch a little-endian value using "tvb_get_ntohs() or
270 "tvb_get_ntohl()" and then using "g_ntohs()", "g_htons()", "g_ntohl()",
271 or "g_htonl()" on the resulting value - the g_ routines in question
272 convert between network byte order (big-endian) and *host* byte order,
273 not *little-endian* byte order; not all machines on which Wireshark runs
274 are little-endian, even though PCs are. Fetch those values using
275 "tvb_get_letohs()" and "tvb_get_letohl()".
277 Don't put a comma after the last element of an enum - some compilers may
278 either warn about it (producing extra noise) or refuse to accept it.
280 Don't include <unistd.h> without protecting it with
288 and, if you're including it to get routines such as "open()", "close()",
289 "read()", and "write()" declared, also include <io.h> if present:
295 in order to declare the Windows C library routines "_open()",
296 "_close()", "_read()", and "_write()". Your file must include <glib.h>
297 - which many of the Wireshark header files include, so you might not have
298 to include it explicitly - in order to get "open()", "close()",
299 "read()", "write()", etc. mapped to "_open()", "_close()", "_read()",
302 Do not use "open()", "rename()", "mkdir()", "stat()", "unlink()", "remove()",
303 "fopen()", "freopen()" directly. Instead use "ws_open()", "ws_rename()",
304 "ws_mkdir()", "ws_stat()", "ws_unlink()", "ws_remove()", "ws_fopen()",
305 "ws_freopen()": these wrapper functions change the path and file name from
306 UTF8 to UTF16 on Windows allowing the functions to work correctly when the
307 path or file name contain non-ASCII characters.
309 When opening a file with "ws_fopen()", "ws_freopen()", or "ws_fdopen()", if
310 the file contains ASCII text, use "r", "w", "a", and so on as the open mode
311 - but if it contains binary data, use "rb", "wb", and so on. On
312 Windows, if a file is opened in a text mode, writing a byte with the
313 value of octal 12 (newline) to the file causes two bytes, one with the
314 value octal 15 (carriage return) and one with the value octal 12, to be
315 written to the file, and causes bytes with the value octal 15 to be
316 discarded when reading the file (to translate between C's UNIX-style
317 lines that end with newline and Windows' DEC-style lines that end with
318 carriage return/line feed).
320 In addition, that also means that when opening or creating a binary
321 file, you must use "ws_open()" (with O_CREAT and possibly O_TRUNC if the
322 file is to be created if it doesn't exist), and OR in the O_BINARY flag.
323 That flag is not present on most, if not all, UNIX systems, so you must
330 to properly define it for UNIX (it's not necessary on UNIX).
332 Don't use forward declarations of static arrays without a specified size
333 in a fashion such as this:
335 static const value_string foo_vals[];
339 static const value_string foo_vals[] = {
346 as some compilers will reject the first of those statements. Instead,
347 initialize the array at the point at which it's first declared, so that
350 Don't put a comma after the last tuple of an initializer of an array.
352 For #define names and enum member names, prefix the names with a tag so
353 as to avoid collisions with other names - this might be more of an issue
354 on Windows, as it appears to #define names such as DELETE and
357 Don't use the "numbered argument" feature that many UNIX printf's
360 g_snprintf(add_string, 30, " - (%1$d) (0x%1$04x)", value);
362 as not all UNIX printf's implement it, and Windows printf doesn't appear
363 to implement it. Use something like
365 g_snprintf(add_string, 30, " - (%d) (0x%04x)", value, value);
369 Don't use "variadic macros", such as
371 #define DBG(format, args...) fprintf(stderr, format, ## args)
373 as not all C compilers support them. Use macros that take a fixed
374 number of arguments, such as
376 #define DBG0(format) fprintf(stderr, format)
377 #define DBG1(format, arg1) fprintf(stderr, format, arg1)
378 #define DBG2(format, arg1, arg2) fprintf(stderr, format, arg1, arg2)
384 #define DBG(args) printf args
390 as that's not supported by all compilers.
392 snprintf() -> g_snprintf()
393 snprintf() is not available on all platforms, so it's a good idea to use the
394 g_snprintf() function declared by <glib.h> instead.
396 tmpnam() -> mkstemp()
397 tmpnam is insecure and should not be used any more. Wireshark brings its
398 own mkstemp implementation for use on platforms that lack mkstemp.
399 Note: mkstemp does not accept NULL as a parameter.
401 The pointer returned by a call to "tvb_get_ptr()" is not guaranteed to be
402 aligned on any particular byte boundary; this means that you cannot
403 safely cast it to any data type other than a pointer to "char",
404 "unsigned char", "guint8", or other one-byte data types. You cannot,
405 for example, safely cast it to a pointer to a structure, and then access
406 the structure members directly; on some systems, unaligned accesses to
407 integral data types larger than 1 byte, and floating-point data types,
408 cause a trap, which will, at best, result in the OS slowly performing an
409 unaligned access for you, and will, on at least some platforms, cause
410 the program to be terminated.
412 Wireshark supports platforms with GLib 2.4[.x]/GTK+ 2.4[.x] or newer.
413 If a Glib/GTK+ mechanism is available only in Glib/GTK+ versions
414 newer than 2.4/2.4 then use "#if GTK_CHECK_VERSION(...)" to conditionally
415 compile code using that mechanism.
417 When different code must be used on UN*X and Win32, use a #if or #ifdef
418 that tests _WIN32, not WIN32. Try to write code portably whenever
419 possible, however; note that there are some routines in Wireshark with
420 platform-dependent implementations and platform-independent APIs, such
421 as the routines in epan/filesystem.c, allowing the code that calls it to
422 be written portably without #ifdefs.
424 1.1.2 String handling
426 Do not use functions such as strcat() or strcpy().
427 A lot of work has been done to remove the existing calls to these functions and
428 we do not want any new callers of these functions.
430 Instead use g_snprintf() since that function will if used correctly prevent
431 buffer overflows for large strings.
433 When using a buffer to create a string, do not use a buffer stored on the stack.
434 I.e. do not use a buffer declared as
438 instead allocate a buffer dynamically using the string-specific or plain emem
439 routines (see README.malloc) such as
441 emem_strbuf_t *strbuf;
442 strbuf = ep_strbuf_new_label("");
443 ep_strbuf_append_printf(strbuf, ...
449 #define MAX_BUFFER 1024
450 buffer=ep_alloc(MAX_BUFFER);
453 g_snprintf(buffer, MAX_BUFFER, ...
455 This avoids the stack from being corrupted in case there is a bug in your code
456 that accidentally writes beyond the end of the buffer.
459 If you write a routine that will create and return a pointer to a filled in
460 string and if that buffer will not be further processed or appended to after
461 the routine returns (except being added to the proto tree),
462 do not preallocate the buffer to fill in and pass as a parameter instead
463 pass a pointer to a pointer to the function and return a pointer to an
464 emem allocated buffer that will be automatically freed. (see README.malloc)
466 I.e. do not write code such as
468 foo_to_str(char *string, ... ){
474 foo_to_str(buffer, ...
475 proto_tree_add_text(... buffer ...
477 instead write the code as
479 foo_to_str(char **buffer, ...
481 *buffer=ep_alloc(MAX_BUFFER);
487 foo_to_str(&buffer, ...
488 proto_tree_add_text(... *buffer ...
490 Use ep_ allocated buffers. They are very fast and nice. These buffers are all
491 automatically free()d when the dissection of the current packet ends so you
492 don't have to worry about free()ing them explicitly in order to not leak memory.
493 Please read README.malloc.
495 Don't use non-ASCII characters in source files; not all compiler
496 environments will be using the same encoding for non-ASCII characters,
497 and at least one compiler (Microsoft's Visual C) will, in environments
498 with double-byte character encodings, such as many Asian environments,
499 fail if it sees a byte sequence in a source file that doesn't correspond
500 to a valid character. This causes source files using either an ISO
501 8859/n single-byte character encoding or UTF-8 to fail to compile. Even
502 if the compiler doesn't fail, there is no guarantee that the compiler,
503 or a developer's text editor, will interpret the characters the way you
504 intend them to be interpreted.
508 Wireshark is not guaranteed to read only network traces that contain correctly-
509 formed packets. Wireshark is commonly used to track down networking
510 problems, and the problems might be due to a buggy protocol implementation
511 sending out bad packets.
513 Therefore, protocol dissectors not only have to be able to handle
514 correctly-formed packets without, for example, crashing or looping
515 infinitely, they also have to be able to handle *incorrectly*-formed
516 packets without crashing or looping infinitely.
518 Here are some suggestions for making dissectors more robust in the face
519 of incorrectly-formed packets:
521 Do *NOT* use "g_assert()" or "g_assert_not_reached()" in dissectors.
522 *NO* value in a packet's data should be considered "wrong" in the sense
523 that it's a problem with the dissector if found; if it cannot do
524 anything else with a particular value from a packet's data, the
525 dissector should put into the protocol tree an indication that the
526 value is invalid, and should return. The "expert" mechanism should be
527 used for that purpose.
529 If there is a case where you are checking not for an invalid data item
530 in the packet, but for a bug in the dissector (for example, an
531 assumption being made at a particular point in the code about the
532 internal state of the dissector), use the DISSECTOR_ASSERT macro for
533 that purpose; this will put into the protocol tree an indication that
534 the dissector has a bug in it, and will not crash the application.
536 If you are allocating a chunk of memory to contain data from a packet,
537 or to contain information derived from data in a packet, and the size of
538 the chunk of memory is derived from a size field in the packet, make
539 sure all the data is present in the packet before allocating the buffer.
542 1) Wireshark won't leak that chunk of memory if an attempt to
543 fetch data not present in the packet throws an exception.
547 2) it won't crash trying to allocate an absurdly-large chunk of
548 memory if the size field has a bogus large value.
550 If you're fetching into such a chunk of memory a string from the buffer,
551 and the string has a specified size, you can use "tvb_get_*_string()",
552 which will check whether the entire string is present before allocating
553 a buffer for the string, and will also put a trailing '\0' at the end of
556 If you're fetching into such a chunk of memory a 2-byte Unicode string
557 from the buffer, and the string has a specified size, you can use
558 "tvb_get_ephemeral_faked_unicode()", which will check whether the entire
559 string is present before allocating a buffer for the string, and will also
560 put a trailing '\0' at the end of the buffer. The resulting string will be
561 a sequence of single-byte characters; the only Unicode characters that
562 will be handled correctly are those in the ASCII range. (Wireshark's
563 ability to handle non-ASCII strings is limited; it needs to be
566 If you're fetching into such a chunk of memory a sequence of bytes from
567 the buffer, and the sequence has a specified size, you can use
568 "tvb_memdup()", which will check whether the entire sequence is present
569 before allocating a buffer for it.
571 Otherwise, you can check whether the data is present by using
572 "tvb_ensure_bytes_exist()" or by getting a pointer to the data by using
573 "tvb_get_ptr()", although note that there might be problems with using
574 the pointer from "tvb_get_ptr()" (see the item on this in the
575 Portability section above, and the next item below).
577 Note also that you should only fetch string data into a fixed-length
578 buffer if the code ensures that no more bytes than will fit into the
579 buffer are fetched ("the protocol ensures" isn't good enough, as
580 protocol specifications can't ensure only packets that conform to the
581 specification will be transmitted or that only packets for the protocol
582 in question will be interpreted as packets for that protocol by
583 Wireshark). If there's no maximum length of string data to be fetched,
584 routines such as "tvb_get_*_string()" are safer, as they allocate a buffer
585 large enough to hold the string. (Note that some variants of this call
586 require you to free the string once you're finished with it.)
588 If you have gotten a pointer using "tvb_get_ptr()", you must make sure
589 that you do not refer to any data past the length passed as the last
590 argument to "tvb_get_ptr()"; while the various "tvb_get" routines
591 perform bounds checking and throw an exception if you refer to data not
592 available in the tvbuff, direct references through a pointer gotten from
593 "tvb_get_ptr()" do not do any bounds checking.
595 If you have a loop that dissects a sequence of items, each of which has
596 a length field, with the offset in the tvbuff advanced by the length of
597 the item, then, if the length field is the total length of the item, and
598 thus can be zero, you *MUST* check for a zero-length item and abort the
599 loop if you see one. Otherwise, a zero-length item could cause the
600 dissector to loop infinitely. You should also check that the offset,
601 after having the length added to it, is greater than the offset before
602 the length was added to it, if the length field is greater than 24 bits
603 long, so that, if the length value is *very* large and adding it to the
604 offset causes an overflow, that overflow is detected.
606 If you are fetching a length field from the buffer, corresponding to the
607 length of a portion of the packet, and subtracting from that length a
608 value corresponding to the length of, for example, a header in the
609 packet portion in question, *ALWAYS* check that the value of the length
610 field is greater than or equal to the length you're subtracting from it,
611 and report an error in the packet and stop dissecting the packet if it's
612 less than the length you're subtracting from it. Otherwise, the
613 resulting length value will be negative, which will either cause errors
614 in the dissector or routines called by the dissector, or, if the value
615 is interpreted as an unsigned integer, will cause the value to be
616 interpreted as a very large positive value.
618 Any tvbuff offset that is added to as processing is done on a packet
619 should be stored in a 32-bit variable, such as an "int"; if you store it
620 in an 8-bit or 16-bit variable, you run the risk of the variable
623 sprintf() -> g_snprintf()
624 Prevent yourself from using the sprintf() function, as it does not test the
625 length of the given output buffer and might be writing into unintended memory
626 areas. This function is one of the main causes of security problems like buffer
627 exploits and many other bugs that are very hard to find. It's much better to
628 use the g_snprintf() function declared by <glib.h> instead.
630 You should test your dissector against incorrectly-formed packets. This
631 can be done using the randpkt and editcap utilities that come with the
632 Wireshark distribution. Testing using randpkt can be done by generating
633 output at the same layer as your protocol, and forcing Wireshark/TShark
634 to decode it as your protocol, e.g. if your protocol sits on top of UDP:
636 randpkt -c 50000 -t dns randpkt.pcap
637 tshark -nVr randpkt.pcap -d udp.port==53,<myproto>
639 Testing using editcap can be done using preexisting capture files and the
640 "-E" flag, which introduces errors in a capture file. E.g.:
642 editcap -E 0.03 infile.pcap outfile.pcap
643 tshark -nVr outfile.pcap
645 The script fuzz-test.sh is available to help automate these tests.
647 1.1.4 Name convention.
649 Wireshark uses the underscore_convention rather than the InterCapConvention for
650 function names, so new code should probably use underscores rather than
651 intercaps for functions and variable names. This is especially important if you
652 are writing code that will be called from outside your code. We are just
653 trying to keep things consistent for other developers.
655 1.1.5 White space convention.
657 Avoid using tab expansions different from 8 column widths, as not all
658 text editors in use by the developers support this. For a detailed
659 discussion of tabs, spaces, and indentation, see
661 http://www.jwz.org/doc/tabs-vs-spaces.html
663 When creating a new file, you are free to choose an indentation logic.
664 Most of the files in Wireshark tend to use 2-space or 4-space
665 indentation. You are encouraged to write a short comment on the
666 indentation logic at the beginning of this new file, especially if
667 you're using non-mod-8 tabs. The tabs-vs-spaces document above provides
668 examples of Emacs and vi modelines for this purpose.
670 When editing an existing file, try following the existing indentation
671 logic and even if it very tempting, never ever use a restyler/reindenter
672 utility on an existing file. If you run across wildly varying
673 indentation styles within the same file, it might be helpful to send a
674 note to wireshark-dev for guidance.
676 1.1.6 Compiler warnings
678 You should write code that is free of compiler warnings. Such warnings will
679 often indicate questionable code and sometimes even real bugs, so it's best
680 to avoid warnings at all.
682 The compiler flags in the Makefiles are set to "treat warnings as errors",
683 so your code won't even compile when warnings occur.
687 Wireshark requires certain things when setting up a protocol dissector.
688 Below is skeleton code for a dissector that you can copy to a file and
689 fill in. Your dissector should follow the naming convention of packet-
690 followed by the abbreviated name for the protocol. It is recommended
691 that where possible you keep to the IANA abbreviated name for the
692 protocol, if there is one, or a commonly-used abbreviation for the
695 Usually, you will put your newly created dissector file into the directory
696 epan/dissectors, just like all the other packet-....c files already in there.
698 Also, please add your dissector file to the corresponding makefile,
699 described in section "1.9 Editing Makefile.common to add your dissector" below.
701 Dissectors that use the dissector registration to register with a lower level
702 dissector don't need to define a prototype in the .h file. For other
703 dissectors the main dissector routine should have a prototype in a header
704 file whose name is "packet-", followed by the abbreviated name for the
705 protocol, followed by ".h"; any dissector file that calls your dissector
706 should be changed to include that file.
708 You may not need to include all the headers listed in the skeleton
709 below, and you may need to include additional headers. For example, the
718 is needed only if you are using a function from libpcre, e.g. the
719 "pcre_compile()" function.
721 The "$Id$" in the comment will be updated by Subversion when the file is
724 When creating a new file, it is fine to just write "$Id$" as Subversion will
725 automatically fill in the identifier at the time the file will be added to the
726 SVN repository (committed).
728 ------------------------------------Cut here------------------------------------
729 /* packet-PROTOABBREV.c
730 * Routines for PROTONAME dissection
731 * Copyright 200x, YOUR_NAME <YOUR_EMAIL_ADDRESS>
735 * Wireshark - Network traffic analyzer
736 * By Gerald Combs <gerald@wireshark.org>
737 * Copyright 1998 Gerald Combs
739 * Copied from WHATEVER_FILE_YOU_USED (where "WHATEVER_FILE_YOU_USED"
740 * is a dissector file; if you just copied this from README.developer,
741 * don't bother with the "Copied from" - you don't even need to put
742 * in a "Copied from" if you copied an existing dissector, especially
743 * if the bulk of the code in the new dissector is your code)
745 * This program is free software; you can redistribute it and/or modify
746 * it under the terms of the GNU General Public License as published by
747 * the Free Software Foundation; either version 2 of the License, or
748 * (at your option) any later version.
750 * This program is distributed in the hope that it will be useful,
751 * but WITHOUT ANY WARRANTY; without even the implied warranty of
752 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
753 * GNU General Public License for more details.
755 * You should have received a copy of the GNU General Public License along
756 * with this program; if not, write to the Free Software Foundation, Inc.,
757 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
770 #include <epan/packet.h>
771 #include <epan/prefs.h>
773 /* IF PROTO exposes code to other dissectors, then it must be exported
774 in a header file. If not, a header file is not needed at all. */
775 #include "packet-PROTOABBREV.h"
777 /* Forward declaration we need below (if using proto_reg_handoff...
778 as a prefs callback) */
779 void proto_reg_handoff_PROTOABBREV(void);
781 /* Initialize the protocol and registered fields */
782 static int proto_PROTOABBREV = -1;
783 static int hf_PROTOABBREV_FIELDABBREV = -1;
785 /* Global sample preference ("controls" display of numbers) */
786 static gboolean gPREF_HEX = FALSE;
787 /* Global sample port pref */
788 static guint gPORT_PREF = 1234;
790 /* Initialize the subtree pointers */
791 static gint ett_PROTOABBREV = -1;
793 /* Code to actually dissect the packets */
795 dissect_PROTOABBREV(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
798 /* Set up structures needed to add the protocol subtree and manage it */
800 proto_tree *PROTOABBREV_tree;
802 /* First, if at all possible, do some heuristics to check if the packet cannot
803 * possibly belong to your protocol. This is especially important for
804 * protocols directly on top of TCP or UDP where port collisions are
805 * common place (e.g., even though your protocol uses a well known port,
806 * someone else may set up, for example, a web server on that port which,
807 * if someone analyzed that web server's traffic in Wireshark, would result
808 * in Wireshark handing an HTTP packet to your dissector). For example:
810 /* Check that there's enough data */
811 if (tvb_length(tvb) < /* your protocol's smallest packet size */)
814 /* Get some values from the packet header, probably using tvb_get_*() */
815 if ( /* these values are not possible in PROTONAME */ )
816 /* This packet does not appear to belong to PROTONAME.
817 * Return 0 to give another dissector a chance to dissect it.
821 /* Make entries in Protocol column and Info column on summary display */
822 col_set_str(pinfo->cinfo, COL_PROTOCOL, "PROTOABBREV");
824 /* This field shows up as the "Info" column in the display; you should use
825 it, if possible, to summarize what's in the packet, so that a user looking
826 at the list of packets can tell what type of packet it is. See section 1.5
827 for more information.
829 If you are setting the column to a constant string, use "col_set_str()",
830 as it's more efficient than the other "col_set_XXX()" calls.
832 If you're setting it to a string you've constructed, or will be
833 appending to the column later, use "col_add_str()".
835 "col_add_fstr()" can be used instead of "col_add_str()"; it takes
836 "printf()"-like arguments. Don't use "col_add_fstr()" with a format
837 string of "%s" - just use "col_add_str()" or "col_set_str()", as it's
838 more efficient than "col_add_fstr()".
840 If you will be fetching any data from the packet before filling in
841 the Info column, clear that column first, in case the calls to fetch
842 data from the packet throw an exception because they're fetching data
843 past the end of the packet, so that the Info column doesn't have data
844 left over from the previous dissector; do
846 col_clear(pinfo->cinfo, COL_INFO);
850 col_set_str(pinfo->cinfo, COL_INFO, "XXX Request");
852 /* A protocol dissector may be called in 2 different ways - with, or
853 without a non-null "tree" argument.
855 If the proto_tree argument is null, Wireshark does not need to use
856 the protocol tree information from your dissector, and therefore is
857 passing the dissector a null "tree" argument so that it doesn't
858 need to do work necessary to build the protocol tree.
860 In the interest of speed, if "tree" is NULL, avoid building a
861 protocol tree and adding stuff to it, or even looking at any packet
862 data needed only if you're building the protocol tree, if possible.
864 Note, however, that you must fill in column information, create
865 conversations, reassemble packets, build any other persistent state
866 needed for dissection, and call subdissectors regardless of whether
867 "tree" is NULL or not. This might be inconvenient to do without
868 doing most of the dissection work; the routines for adding items to
869 the protocol tree can be passed a null protocol tree pointer, in
870 which case they'll return a null item pointer, and
871 "proto_item_add_subtree()" returns a null tree pointer if passed a
872 null item pointer, so, if you're careful not to dereference any null
873 tree or item pointers, you can accomplish this by doing all the
874 dissection work. This might not be as efficient as skipping that
875 work if you're not building a protocol tree, but if the code would
876 have a lot of tests whether "tree" is null if you skipped that work,
877 you might still be better off just doing all that work regardless of
878 whether "tree" is null or not.
880 Note also that there is no guarantee, the first time the dissector is
881 called, whether "tree" will be null or not; your dissector must work
882 correctly, building or updating whatever state information is
883 necessary, in either case. */
886 /* NOTE: The offset and length values in the call to
887 "proto_tree_add_item()" define what data bytes to highlight in the hex
888 display window when the line in the protocol tree display
889 corresponding to that item is selected.
891 Supplying a length of -1 is the way to highlight all data from the
892 offset to the end of the packet. */
894 /* create display subtree for the protocol */
895 ti = proto_tree_add_item(tree, proto_PROTOABBREV, tvb, 0, -1, FALSE);
897 PROTOABBREV_tree = proto_item_add_subtree(ti, ett_PROTOABBREV);
899 /* add an item to the subtree, see section 1.6 for more information */
900 proto_tree_add_item(PROTOABBREV_tree,
901 hf_PROTOABBREV_FIELDABBREV, tvb, offset, len, FALSE);
904 /* Continue adding tree items to process the packet here */
909 /* If this protocol has a sub-dissector call it here, see section 1.8 */
911 /* Return the amount of data this dissector was able to dissect */
912 return tvb_length(tvb);
916 /* Register the protocol with Wireshark */
918 /* this format is require because a script is used to build the C function
919 that calls all the protocol registration.
923 proto_register_PROTOABBREV(void)
925 module_t *PROTOABBREV_module;
927 /* Setup list of header fields See Section 1.6.1 for details*/
928 static hf_register_info hf[] = {
929 { &hf_PROTOABBREV_FIELDABBREV,
930 { "FIELDNAME", "PROTOABBREV.FIELDABBREV",
931 FIELDTYPE, FIELDBASE, FIELDCONVERT, BITMASK,
932 "FIELDDESCR", HFILL }
936 /* Setup protocol subtree array */
937 static gint *ett[] = {
941 /* Register the protocol name and description */
942 proto_PROTOABBREV = proto_register_protocol("PROTONAME",
943 "PROTOSHORTNAME", "PROTOABBREV");
945 /* Required function calls to register the header fields and subtrees used */
946 proto_register_field_array(proto_PROTOABBREV, hf, array_length(hf));
947 proto_register_subtree_array(ett, array_length(ett));
949 /* Register preferences module (See Section 2.6 for more on preferences) */
950 /* (Registration of a prefs callback is not required if there are no */
951 /* prefs-dependent registration functions (eg: a port pref). */
952 /* See proto_reg_handoff below. */
953 /* If a prefs callback is not needed, use NULL instead of */
954 /* proto_reg_handoff_PROTOABBREV in the following). */
955 PROTOABBREV_module = prefs_register_protocol(proto_PROTOABBREV,
956 proto_reg_handoff_PROTOABBREV);
958 /* Register preferences module under preferences subtree.
959 Use this function instead of prefs_register_protocol if you want to group
960 preferences of several protocols under one preferences subtree.
961 Argument subtree identifies grouping tree node name, several subnodes can be
962 specified usign slash '/' (e.g. "OSI/X.500" - protocol preferences will be
963 accessible under Protocols->OSI->X.500-><PROTOSHORTNAME> preferences node.
965 PROTOABBREV_module = prefs_register_protocol_subtree(const char *subtree,
966 proto_PROTOABBREV, proto_reg_handoff_PROTOABBREV);
968 /* Register a sample preference */
969 prefs_register_bool_preference(PROTOABBREV_module, "show_hex",
970 "Display numbers in Hex",
971 "Enable to display numerical values in hexadecimal.",
974 /* Register a sample port preference */
975 prefs_register_uint_preference(PROTOABBREV_module, "tcp.port", "PROTOABBREV TCP Port",
976 " PROTOABBREV TCP port if other than the default",
981 /* If this dissector uses sub-dissector registration add a registration routine.
982 This exact format is required because a script is used to find these
983 routines and create the code that calls these routines.
985 If this function is registered as a prefs callback (see prefs_register_protocol
986 above) this function is also called by preferences whenever "Apply" is pressed;
987 In that case, it should accommodate being called more than once.
989 This form of the reg_handoff function is used if if you perform
990 registration functions which are dependent upon prefs. See below
991 for a simpler form which can be used if there are no
992 prefs-dependent registration functions.
995 proto_reg_handoff_PROTOABBREV(void)
997 static gboolean initialized = FALSE;
998 static dissector_handle_t PROTOABBREV_handle;
999 static int currentPort;
1003 /* Use new_create_dissector_handle() to indicate that dissect_PROTOABBREV()
1004 * returns the number of bytes it dissected (or 0 if it thinks the packet
1005 * does not belong to PROTONAME).
1007 PROTOABBREV_handle = new_create_dissector_handle(dissect_PROTOABBREV,
1009 dissector_add("PARENT_SUBFIELD", ID_VALUE, PROTOABBREV_handle);
1015 If you perform registration functions which are dependent upon
1016 prefs the you should de-register everything which was associated
1017 with the previous settings and re-register using the new prefs
1018 settings here. In general this means you need to keep track of
1019 the PROTOABBREV_handle and the value the preference had at the time
1020 you registered. The PROTOABBREV_handle value and the value of the
1021 preference can be saved using local statics in this
1022 function (proto_reg_handoff).
1025 dissector_delete("tcp.port", currentPort, PROTOABBREV_handle);
1028 currentPort = gPORT_PREF;
1030 dissector_add("tcp.port", currentPort, PROTOABBREV_handle);
1035 /* Simple form of proto_reg_handoff_PROTOABBREV which can be used if there are
1036 no prefs-dependent registration function calls.
1040 proto_reg_handoff_PROTOABBREV(void)
1042 dissector_handle_t PROTOABBREV_handle;
1044 /* Use new_create_dissector_handle() to indicate that dissect_PROTOABBREV()
1045 * returns the number of bytes it dissected (or 0 if it thinks the packet
1046 * does not belong to PROTONAME).
1048 PROTOABBREV_handle = new_create_dissector_handle(dissect_PROTOABBREV,
1050 dissector_add("PARENT_SUBFIELD", ID_VALUE, PROTOABBREV_handle);
1055 ------------------------------------Cut here------------------------------------
1057 1.3 Explanation of needed substitutions in code skeleton.
1059 In the above code block the following strings should be substituted with
1062 YOUR_NAME Your name, of course. You do want credit, don't you?
1063 It's the only payment you will receive....
1064 YOUR_EMAIL_ADDRESS Keep those cards and letters coming.
1065 WHATEVER_FILE_YOU_USED Add this line if you are using another file as a
1067 PROTONAME The name of the protocol; this is displayed in the
1068 top-level protocol tree item for that protocol.
1069 PROTOSHORTNAME An abbreviated name for the protocol; this is displayed
1070 in the "Preferences" dialog box if your dissector has
1071 any preferences, in the dialog box of enabled protocols,
1072 and in the dialog box for filter fields when constructing
1073 a filter expression.
1074 PROTOABBREV A name for the protocol for use in filter expressions;
1075 it shall contain only lower-case letters, digits, and
1077 FIELDNAME The displayed name for the header field.
1078 FIELDABBREV The abbreviated name for the header field. (NO SPACES)
1079 FIELDTYPE FT_NONE, FT_BOOLEAN, FT_UINT8, FT_UINT16, FT_UINT24,
1080 FT_UINT32, FT_UINT64, FT_INT8, FT_INT16, FT_INT24, FT_INT32,
1081 FT_INT64, FT_FLOAT, FT_DOUBLE, FT_ABSOLUTE_TIME,
1082 FT_RELATIVE_TIME, FT_STRING, FT_STRINGZ, FT_EBCDIC,
1083 FT_UINT_STRING, FT_ETHER, FT_BYTES, FT_UINT_BYTES, FT_IPv4,
1084 FT_IPv6, FT_IPXNET, FT_FRAMENUM, FT_PROTOCOL, FT_GUID, FT_OID
1085 FIELDBASE For FT_UINT{8,16,24,32} and FT_INT{8,16,24,32):
1087 BASE_DEC, BASE_HEX, BASE_OCT, BASE_DEC_HEX, BASE_HEX_DEC,
1088 or BASE_CUSTOM, possibly ORed with BASE_RANGE_STRING
1090 For FT_ABSOLUTE_TIME:
1092 ABSOLUTE_TIME_LOCAL or ABSOLUTE_TIME_UTC
1094 For all other types:
1097 FIELDCONVERT VALS(x), RVALS(x), TFS(x), NULL
1098 BITMASK Usually 0x0 unless using the TFS(x) field conversion.
1099 FIELDDESCR A brief description of the field, or NULL.
1100 PARENT_SUBFIELD Lower level protocol field used for lookup, i.e. "tcp.port"
1101 ID_VALUE Lower level protocol field value that identifies this protocol
1102 For example the TCP or UDP port number
1104 If, for example, PROTONAME is "Internet Bogosity Discovery Protocol",
1105 PROTOSHORTNAME would be "IBDP", and PROTOABBREV would be "ibdp". Try to
1106 conform with IANA names.
1108 1.4 The dissector and the data it receives.
1113 This is only needed if the dissector doesn't use self-registration to
1114 register itself with the lower level dissector, or if the protocol dissector
1115 wants/needs to expose code to other subdissectors.
1117 The dissector must be declared exactly as follows in the file
1118 packet-PROTOABBREV.h:
1121 dissect_PROTOABBREV(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree);
1124 1.4.2 Extracting data from packets.
1126 NOTE: See the file /epan/tvbuff.h for more details.
1128 The "tvb" argument to a dissector points to a buffer containing the raw
1129 data to be analyzed by the dissector; for example, for a protocol
1130 running atop UDP, it contains the UDP payload (but not the UDP header,
1131 or any protocol headers above it). A tvbuffer is an opaque data
1132 structure, the internal data structures are hidden and the data must be
1133 accessed via the tvbuffer accessors.
1137 Bit accessors for a maximum of 8-bits, 16-bits 32-bits and 64-bits:
1139 guint8 tvb_get_bits8(tvbuff_t *tvb, gint bit_offset, gint no_of_bits);
1140 guint16 tvb_get_bits16(tvbuff_t *tvb, gint bit_offset, gint no_of_bits,gboolean little_endian);
1141 guint32 tvb_get_bits32(tvbuff_t *tvb, gint bit_offset, gint no_of_bits,gboolean little_endian);
1142 guint64 tvb_get_bits64(tvbuff_t *tvb, gint bit_offset, gint no_of_bits,gboolean little_endian);
1144 Single-byte accessor:
1146 guint8 tvb_get_guint8(tvbuff_t*, gint offset);
1148 Network-to-host-order accessors for 16-bit integers (guint16), 24-bit
1149 integers, 32-bit integers (guint32), and 64-bit integers (guint64):
1151 guint16 tvb_get_ntohs(tvbuff_t*, gint offset);
1152 guint32 tvb_get_ntoh24(tvbuff_t*, gint offset);
1153 guint32 tvb_get_ntohl(tvbuff_t*, gint offset);
1154 guint64 tvb_get_ntoh64(tvbuff_t*, gint offset);
1156 Network-to-host-order accessors for single-precision and
1157 double-precision IEEE floating-point numbers:
1159 gfloat tvb_get_ntohieee_float(tvbuff_t*, gint offset);
1160 gdouble tvb_get_ntohieee_double(tvbuff_t*, gint offset);
1162 Little-Endian-to-host-order accessors for 16-bit integers (guint16),
1163 24-bit integers, 32-bit integers (guint32), and 64-bit integers
1166 guint16 tvb_get_letohs(tvbuff_t*, gint offset);
1167 guint32 tvb_get_letoh24(tvbuff_t*, gint offset);
1168 guint32 tvb_get_letohl(tvbuff_t*, gint offset);
1169 guint64 tvb_get_letoh64(tvbuff_t*, gint offset);
1171 Little-Endian-to-host-order accessors for single-precision and
1172 double-precision IEEE floating-point numbers:
1174 gfloat tvb_get_letohieee_float(tvbuff_t*, gint offset);
1175 gdouble tvb_get_letohieee_double(tvbuff_t*, gint offset);
1177 Accessors for IPv4 and IPv6 addresses:
1179 guint32 tvb_get_ipv4(tvbuff_t*, gint offset);
1180 void tvb_get_ipv6(tvbuff_t*, gint offset, struct e_in6_addr *addr);
1182 NOTE: IPv4 addresses are not to be converted to host byte order before
1183 being passed to "proto_tree_add_ipv4()". You should use "tvb_get_ipv4()"
1184 to fetch them, not "tvb_get_ntohl()" *OR* "tvb_get_letohl()" - don't,
1185 for example, try to use "tvb_get_ntohl()", find that it gives you the
1186 wrong answer on the PC on which you're doing development, and try
1187 "tvb_get_letohl()" instead, as "tvb_get_letohl()" will give the wrong
1188 answer on big-endian machines.
1192 void tvb_get_ntohguid(tvbuff_t *, gint offset, e_guid_t *guid);
1193 void tvb_get_letohguid(tvbuff_t *, gint offset, e_guid_t *guid);
1197 guint8 *tvb_get_string(tvbuff_t*, gint offset, gint length);
1198 guint8 *tvb_get_ephemeral_string(tvbuff_t*, gint offset, gint length);
1199 guint8 *tvb_get_seasonal_string(tvbuff_t*, gint offset, gint length);
1201 Returns a null-terminated buffer containing data from the specified
1202 tvbuff, starting at the specified offset, and containing the specified
1203 length worth of characters (the length of the buffer will be length+1,
1204 as it includes a null character to terminate the string).
1206 tvb_get_string() returns a buffer allocated by g_malloc() so you must
1207 g_free() it when you are finished with the string. Failure to g_free() this
1208 buffer will lead to memory leaks.
1210 tvb_get_ephemeral_string() returns a buffer allocated from a special heap
1211 with a lifetime until the next packet is dissected. You do not need to
1212 free() this buffer, it will happen automatically once the next packet is
1215 tvb_get_seasonal_string() returns a buffer allocated from a special heap
1216 with a lifetime of the current capture session. You do not need to
1217 free() this buffer, it will happen automatically once the a new capture or
1220 guint8 *tvb_get_stringz(tvbuff_t *tvb, gint offset, gint *lengthp);
1221 guint8 *tvb_get_ephemeral_stringz(tvbuff_t *tvb, gint offset, gint *lengthp);
1222 guint8 *tvb_get_seasonal_stringz(tvbuff_t *tvb, gint offset, gint *lengthp);
1224 Returns a null-terminated buffer, allocated with "g_malloc()",
1225 containing data from the specified tvbuff, starting at the
1226 specified offset, and containing all characters from the tvbuff up to
1227 and including a terminating null character in the tvbuff. "*lengthp"
1228 will be set to the length of the string, including the terminating null.
1230 tvb_get_stringz() returns a buffer allocated by g_malloc() so you must
1231 g_free() it when you are finished with the string. Failure to g_free() this
1232 buffer will lead to memory leaks.
1233 tvb_get_ephemeral_stringz() returns a buffer allocated from a special heap
1234 with a lifetime until the next packet is dissected. You do not need to
1235 free() this buffer, it will happen automatically once the next packet is
1238 tvb_get_seasonal_stringz() returns a buffer allocated from a special heap
1239 with a lifetime of the current capture session. You do not need to
1240 free() this buffer, it will happen automatically once the a new capture or
1243 guint8 *tvb_fake_unicode(tvbuff_t*, gint offset, gint length, gboolean little_endian);
1244 guint8 *tvb_get_ephemeral_faked_unicode(tvbuff_t*, gint offset, gint length, gboolean little_endian);
1246 Converts a 2-byte unicode string to an ASCII string.
1247 Returns a null-terminated buffer containing data from the specified
1248 tvbuff, starting at the specified offset, and containing the specified
1249 length worth of characters (the length of the buffer will be length+1,
1250 as it includes a null character to terminate the string).
1252 tvb_fake_unicode() returns a buffer allocated by g_malloc() so you must
1253 g_free() it when you are finished with the string. Failure to g_free() this
1254 buffer will lead to memory leaks.
1255 tvb_get_ephemeral_faked_unicode() returns a buffer allocated from a special
1256 heap with a lifetime until the next packet is dissected. You do not need to
1257 free() this buffer, it will happen automatically once the next packet is
1260 Byte Array Accessors:
1262 gchar *tvb_bytes_to_str(tvbuff_t *tvb, gint offset, gint len);
1264 Formats a bunch of data from a tvbuff as bytes, returning a pointer
1265 to the string with the data formatted as two hex digits for each byte.
1266 The string pointed to is stored in an "ep_alloc'd" buffer which will be freed
1267 before the next frame is dissected. The formatted string will contain the hex digits
1268 for at most the first 16 bytes of the data. If len is greater than 16 bytes, a
1269 trailing "..." will be added to the string.
1271 gchar *tvb_bytes_to_str_punct(tvbuff_t *tvb, gint offset, gint len, gchar punct);
1273 This function is similar to tvb_bytes_to_str(...) except that 'punct' is inserted
1274 between the hex representation of each byte.
1278 guint8* tvb_memcpy(tvbuff_t*, guint8* target, gint offset, gint length);
1280 Copies into the specified target the specified length's worth of data
1281 from the specified tvbuff, starting at the specified offset.
1283 guint8* tvb_memdup(tvbuff_t*, gint offset, gint length);
1284 guint8* ep_tvb_memdup(tvbuff_t*, gint offset, gint length);
1286 Returns a buffer, allocated with "g_malloc()", containing the specified
1287 length's worth of data from the specified tvbuff, starting at the
1288 specified offset. The ephemeral variant is freed automatically after the
1289 packet is dissected.
1292 /* WARNING! This function is possibly expensive, temporarily allocating
1293 * another copy of the packet data. Furthermore, it's dangerous because once
1294 * this pointer is given to the user, there's no guarantee that the user will
1295 * honor the 'length' and not overstep the boundaries of the buffer.
1297 guint8* tvb_get_ptr(tvbuff_t*, gint offset, gint length);
1299 The reason that tvb_get_ptr() might have to allocate a copy of its data
1300 only occurs with TVBUFF_COMPOSITES, data that spans multiple tvbuffers.
1301 If the user requests a pointer to a range of bytes that span the member
1302 tvbuffs that make up the TVBUFF_COMPOSITE, the data will have to be
1303 copied to another memory region to assure that all the bytes are
1308 1.5 Functions to handle columns in the traffic summary window.
1310 The topmost pane of the main window is a list of the packets in the
1311 capture, possibly filtered by a display filter.
1313 Each line corresponds to a packet, and has one or more columns, as
1314 configured by the user.
1316 Many of the columns are handled by code outside individual dissectors;
1317 most dissectors need only specify the value to put in the "Protocol" and
1320 Columns are specified by COL_ values; the COL_ value for the "Protocol"
1321 field, typically giving an abbreviated name for the protocol (but not
1322 the all-lower-case abbreviation used elsewhere) is COL_PROTOCOL, and the
1323 COL_ value for the "Info" field, giving a summary of the contents of the
1324 packet for that protocol, is COL_INFO.
1326 The value for a column can be specified with one of several functions,
1327 all of which take the 'fd' argument to the dissector as their first
1328 argument, and the COL_ value for the column as their second argument.
1330 1.5.1 The col_set_str function.
1332 'col_set_str' takes a string as its third argument, and sets the value
1333 for the column to that value. It assumes that the pointer passed to it
1334 points to a string constant or a static "const" array, not to a
1335 variable, as it doesn't copy the string, it merely saves the pointer
1336 value; the argument can itself be a variable, as long as it always
1337 points to a string constant or a static "const" array.
1339 It is more efficient than 'col_add_str' or 'col_add_fstr'; however, if
1340 the dissector will be using 'col_append_str' or 'col_append_fstr" to
1341 append more information to the column, the string will have to be copied
1342 anyway, so it's best to use 'col_add_str' rather than 'col_set_str' in
1345 For example, to set the "Protocol" column
1348 col_set_str(pinfo->cinfo, COL_PROTOCOL, "PROTOABBREV");
1351 1.5.2 The col_add_str function.
1353 'col_add_str' takes a string as its third argument, and sets the value
1354 for the column to that value. It takes the same arguments as
1355 'col_set_str', but copies the string, so that if the string is, for
1356 example, an automatic variable that won't remain in scope when the
1357 dissector returns, it's safe to use.
1360 1.5.3 The col_add_fstr function.
1362 'col_add_fstr' takes a 'printf'-style format string as its third
1363 argument, and 'printf'-style arguments corresponding to '%' format
1364 items in that string as its subsequent arguments. For example, to set
1365 the "Info" field to "<XXX> request, <N> bytes", where "reqtype" is a
1366 string containing the type of the request in the packet and "n" is an
1367 unsigned integer containing the number of bytes in the request:
1369 col_add_fstr(pinfo->cinfo, COL_INFO, "%s request, %u bytes",
1372 Don't use 'col_add_fstr' with a format argument of just "%s" -
1373 'col_add_str', or possibly even 'col_set_str' if the string that matches
1374 the "%s" is a static constant string, will do the same job more
1378 1.5.4 The col_clear function.
1380 If the Info column will be filled with information from the packet, that
1381 means that some data will be fetched from the packet before the Info
1382 column is filled in. If the packet is so small that the data in
1383 question cannot be fetched, the routines to fetch the data will throw an
1384 exception (see the comment at the beginning about tvbuffers improving
1385 the handling of short packets - the tvbuffers keep track of how much
1386 data is in the packet, and throw an exception on an attempt to fetch
1387 data past the end of the packet, so that the dissector won't process
1388 bogus data), causing the Info column not to be filled in.
1390 This means that the Info column will have data for the previous
1391 protocol, which would be confusing if, for example, the Protocol column
1392 had data for this protocol.
1394 Therefore, before a dissector fetches any data whatsoever from the
1395 packet (unless it's a heuristic dissector fetching data to determine
1396 whether the packet is one that it should dissect, in which case it
1397 should check, before fetching the data, whether there's any data to
1398 fetch; if there isn't, it should return FALSE), it should set the
1399 Protocol column and the Info column.
1401 If the Protocol column will ultimately be set to, for example, a value
1402 containing a protocol version number, with the version number being a
1403 field in the packet, the dissector should, before fetching the version
1404 number field or any other field from the packet, set it to a value
1405 without a version number, using 'col_set_str', and should later set it
1406 to a value with the version number after it's fetched the version
1409 If the Info column will ultimately be set to a value containing
1410 information from the packet, the dissector should, before fetching any
1411 fields from the packet, clear the column using 'col_clear' (which is
1412 more efficient than clearing it by calling 'col_set_str' or
1413 'col_add_str' with a null string), and should later set it to the real
1414 string after it's fetched the data to use when doing that.
1417 1.5.5 The col_append_str function.
1419 Sometimes the value of a column, especially the "Info" column, can't be
1420 conveniently constructed at a single point in the dissection process;
1421 for example, it might contain small bits of information from many of the
1422 fields in the packet. 'col_append_str' takes, as arguments, the same
1423 arguments as 'col_add_str', but the string is appended to the end of the
1424 current value for the column, rather than replacing the value for that
1425 column. (Note that no blank separates the appended string from the
1426 string to which it is appended; if you want a blank there, you must add
1427 it yourself as part of the string being appended.)
1430 1.5.6 The col_append_fstr function.
1432 'col_append_fstr' is to 'col_add_fstr' as 'col_append_str' is to
1433 'col_add_str' - it takes, as arguments, the same arguments as
1434 'col_add_fstr', but the formatted string is appended to the end of the
1435 current value for the column, rather than replacing the value for that
1438 1.5.7 The col_append_sep_str and col_append_sep_fstr functions.
1440 In specific situations the developer knows that a column's value will be
1441 created in a stepwise manner, where the appended values are listed. Both
1442 'col_append_sep_str' and 'col_append_sep_fstr' functions will add an item
1443 separator between two consecutive items, and will not add the separator at the
1444 beginning of the column. The remainder of the work both functions do is
1445 identical to what 'col_append_str' and 'col_append_fstr' do.
1447 1.5.8 The col_set_fence and col_prepend_fence_fstr functions.
1449 Sometimes a dissector may be called multiple times for different PDUs in the
1450 same frame (for example in the case of SCTP chunk bundling: several upper
1451 layer data packets may be contained in one SCTP packet). If the upper layer
1452 dissector calls 'col_set_str()' or 'col_clear()' on the Info column when it
1453 begins dissecting each of those PDUs then when the frame is fully dissected
1454 the Info column would contain only the string from the last PDU in the frame.
1455 The 'col_set_fence' function erects a "fence" in the column that prevents
1456 subsequent 'col_...' calls from clearing the data currently in that column.
1457 For example, the SCTP dissector calls 'col_set_fence' on the Info column
1458 after it has called any subdissectors for that chunk so that subdissectors
1459 of any subsequent chunks may only append to the Info column.
1460 'col_prepend_fence_fstr' prepends data before a fence (moving it if
1461 necessary). It will create a fence at the end of the prepended data if the
1462 fence does not already exist.
1465 1.5.9 The col_set_time function.
1467 The 'col_set_time' function takes an nstime value as its third argument.
1468 This nstime value is a relative value and will be added as such to the
1469 column. The fourth argument is the filtername holding this value. This
1470 way, rightclicking on the column makes it possible to build a filter
1471 based on the time-value.
1475 nstime_delta(&ts, &pinfo->fd->abs_ts, &tcpd->ts_first);
1476 col_set_time(pinfo->cinfo, COL_REL_CONV_TIME, &ts, "tcp.time_relative");
1479 1.6 Constructing the protocol tree.
1481 The middle pane of the main window, and the topmost pane of a packet
1482 popup window, are constructed from the "protocol tree" for a packet.
1484 The protocol tree, or proto_tree, is a GNode, the N-way tree structure
1485 available within GLIB. Of course the protocol dissectors don't care
1486 what a proto_tree really is; they just pass the proto_tree pointer as an
1487 argument to the routines which allow them to add items and new branches
1490 When a packet is selected in the packet-list pane, or a packet popup
1491 window is created, a new logical protocol tree (proto_tree) is created.
1492 The pointer to the proto_tree (in this case, 'protocol tree'), is passed
1493 to the top-level protocol dissector, and then to all subsequent protocol
1494 dissectors for that packet, and then the GUI tree is drawn via
1497 The logical proto_tree needs to know detailed information about the protocols
1498 and fields about which information will be collected from the dissection
1499 routines. By strictly defining (or "typing") the data that can be attached to a
1500 proto tree, searching and filtering becomes possible. This means that for
1501 every protocol and field (which I also call "header fields", since they are
1502 fields in the protocol headers) which might be attached to a tree, some
1503 information is needed.
1505 Every dissector routine will need to register its protocols and fields
1506 with the central protocol routines (in proto.c). At first I thought I
1507 might keep all the protocol and field information about all the
1508 dissectors in one file, but decentralization seemed like a better idea.
1509 That one file would have gotten very large; one small change would have
1510 required a re-compilation of the entire file. Also, by allowing
1511 registration of protocols and fields at run-time, loadable modules of
1512 protocol dissectors (perhaps even user-supplied) is feasible.
1514 To do this, each protocol should have a register routine, which will be
1515 called when Wireshark starts. The code to call the register routines is
1516 generated automatically; to arrange that a protocol's register routine
1517 be called at startup:
1519 the file containing a dissector's "register" routine must be
1520 added to "DISSECTOR_SRC" in "epan/dissectors/Makefile.common";
1522 the "register" routine must have a name of the form
1523 "proto_register_XXX";
1525 the "register" routine must take no argument, and return no
1528 the "register" routine's name must appear in the source file
1529 either at the beginning of the line, or preceded only by "void "
1530 at the beginning of the line (that would typically be the
1531 definition) - other white space shouldn't cause a problem, e.g.:
1533 void proto_register_XXX(void) {
1542 proto_register_XXX( void )
1549 and so on should work.
1551 For every protocol or field that a dissector wants to register, a variable of
1552 type int needs to be used to keep track of the protocol. The IDs are
1553 needed for establishing parent/child relationships between protocols and
1554 fields, as well as associating data with a particular field so that it
1555 can be stored in the logical tree and displayed in the GUI protocol
1558 Some dissectors will need to create branches within their tree to help
1559 organize header fields. These branches should be registered as header
1560 fields. Only true protocols should be registered as protocols. This is
1561 so that a display filter user interface knows how to distinguish
1562 protocols from fields.
1564 A protocol is registered with the name of the protocol and its
1567 Here is how the frame "protocol" is registered.
1571 proto_frame = proto_register_protocol (
1573 /* short name */ "Frame",
1574 /* abbrev */ "frame" );
1576 A header field is also registered with its name and abbreviation, but
1577 information about its data type is needed. It helps to look at
1578 the header_field_info struct to see what information is expected:
1580 struct header_field_info {
1585 const void *strings;
1593 A string representing the name of the field. This is the name
1594 that will appear in the graphical protocol tree. It must be a non-empty
1599 A string with an abbreviation of the field. We concatenate the
1600 abbreviation of the parent protocol with an abbreviation for the field,
1601 using a period as a separator. For example, the "src" field in an IP packet
1602 would have "ip.src" as an abbreviation. It is acceptable to have
1603 multiple levels of periods if, for example, you have fields in your
1604 protocol that are then subdivided into subfields. For example, TRMAC
1605 has multiple error fields, so the abbreviations follow this pattern:
1606 "trmac.errors.iso", "trmac.errors.noniso", etc.
1608 The abbreviation is the identifier used in a display filter. If it is
1609 an empty string then the field will not be filterable.
1613 The type of value this field holds. The current field types are:
1615 FT_NONE No field type. Used for fields that
1616 aren't given a value, and that can only
1617 be tested for presence or absence; a
1618 field that represents a data structure,
1619 with a subtree below it containing
1620 fields for the members of the structure,
1621 or that represents an array with a
1622 subtree below it containing fields for
1623 the members of the array, might be an
1625 FT_PROTOCOL Used for protocols which will be placing
1626 themselves as top-level items in the
1627 "Packet Details" pane of the UI.
1628 FT_BOOLEAN 0 means "false", any other value means
1630 FT_FRAMENUM A frame number; if this is used, the "Go
1631 To Corresponding Frame" menu item can
1633 FT_UINT8 An 8-bit unsigned integer.
1634 FT_UINT16 A 16-bit unsigned integer.
1635 FT_UINT24 A 24-bit unsigned integer.
1636 FT_UINT32 A 32-bit unsigned integer.
1637 FT_UINT64 A 64-bit unsigned integer.
1638 FT_INT8 An 8-bit signed integer.
1639 FT_INT16 A 16-bit signed integer.
1640 FT_INT24 A 24-bit signed integer.
1641 FT_INT32 A 32-bit signed integer.
1642 FT_INT64 A 64-bit signed integer.
1643 FT_FLOAT A single-precision floating point number.
1644 FT_DOUBLE A double-precision floating point number.
1645 FT_ABSOLUTE_TIME Seconds (4 bytes) and nanoseconds (4 bytes)
1646 of time displayed as month name, month day,
1647 year, hours, minutes, and seconds with 9
1648 digits after the decimal point.
1649 FT_RELATIVE_TIME Seconds (4 bytes) and nanoseconds (4 bytes)
1650 of time displayed as seconds and 9 digits
1651 after the decimal point.
1652 FT_STRING A string of characters, not necessarily
1653 NUL-terminated, but possibly NUL-padded.
1654 This, and the other string-of-characters
1655 types, are to be used for text strings,
1656 not raw binary data.
1657 FT_STRINGZ A NUL-terminated string of characters.
1658 FT_EBCDIC A string of characters, not necessarily
1659 NUL-terminated, but possibly NUL-padded.
1660 The data from the packet is converted from
1661 EBCDIC to ASCII before displaying to the user.
1662 FT_UINT_STRING A counted string of characters, consisting
1663 of a count (represented as an integral value,
1664 of width given in the proto_tree_add_item()
1665 call) followed immediately by that number of
1667 FT_ETHER A six octet string displayed in
1668 Ethernet-address format.
1669 FT_BYTES A string of bytes with arbitrary values;
1670 used for raw binary data.
1671 FT_UINT_BYTES A counted string of bytes, consisting
1672 of a count (represented as an integral value,
1673 of width given in the proto_tree_add_item()
1674 call) followed immediately by that number of
1675 arbitrary values; used for raw binary data.
1676 FT_IPv4 A version 4 IP address (4 bytes) displayed
1677 in dotted-quad IP address format (4
1678 decimal numbers separated by dots).
1679 FT_IPv6 A version 6 IP address (16 bytes) displayed
1680 in standard IPv6 address format.
1681 FT_IPXNET An IPX address displayed in hex as a 6-byte
1682 network number followed by a 6-byte station
1684 FT_GUID A Globally Unique Identifier
1685 FT_OID An ASN.1 Object Identifier
1687 Some of these field types are still not handled in the display filter
1688 routines, but the most common ones are. The FT_UINT* variables all
1689 represent unsigned integers, and the FT_INT* variables all represent
1690 signed integers; the number on the end represent how many bits are used
1691 to represent the number.
1693 Some constraints are imposed on the header fields depending on the type
1694 (e.g. FT_BYTES) of the field. Fields of type FT_ABSOLUTE_TIME must use
1695 'ABSOLUTE_TIME_{LOCAL,UTC}, NULL, 0x0' as values for the 'display,
1696 'strings', and 'bitmask' fields, and all other non-integral types (i.e..
1697 types that are _not_ FT_INT* and FT_UINT*) must use 'BASE_NONE, NULL, 0x0'
1698 as values for the 'display', 'strings', 'bitmask' fields. The reason is
1699 simply that the type itself implictly defines the nature of 'display',
1700 'strings', 'bitmask'.
1704 The display field has a couple of overloaded uses. This is unfortunate,
1705 but since we're using C as an application programming language, this sometimes
1706 makes for cleaner programs. Right now I still think that overloading
1707 this variable was okay.
1709 For integer fields (FT_UINT* and FT_INT*), this variable represents the
1710 base in which you would like the value displayed. The acceptable bases
1720 BASE_DEC, BASE_HEX, and BASE_OCT are decimal, hexadecimal, and octal,
1721 respectively. BASE_DEC_HEX and BASE_HEX_DEC display value in two bases
1722 (the 1st representation followed by the 2nd in parenthesis).
1724 BASE_CUSTOM allows one to specify a callback function pointer that will
1725 format the value. The function pointer of the same type as defined by
1726 custom_fmt_func_t in epan/proto.h, specifically:
1728 void func(gchar *, guint32);
1730 The first argument is a pointer to a buffer of the ITEM_LABEL_LENGTH size
1731 and the second argument is the value to be formatted.
1733 For FT_BOOLEAN fields that are also bitfields (i.e. 'bitmask' is non-zero),
1734 'display' is used to tell the proto_tree how wide the parent bitfield is.
1735 With integers this is not needed since the type of integer itself
1736 (FT_UINT8, FT_UINT16, FT_UINT24, FT_UINT32, etc.) tells the proto_tree how
1737 wide the parent bitfield is.
1739 For FT_ABSOLUTE_TIME fields, 'display' is used to indicate whether the
1740 time is to be displayed as a time in the time zone for the machine on
1741 which Wireshark/TShark is running or as UTC.
1743 Additionally, BASE_NONE is used for 'display' as a NULL-value. That is, for
1744 for non-integers other than FT_ABSOLUTE_TIME fields, and non-bitfield
1745 FT_BOOLEANs, you'll want to use BASE_NONE in the 'display' field. You may
1746 not use BASE_NONE for integers.
1748 It is possible that in the future we will record the endianness of
1749 integers. If so, it is likely that we'll use a bitmask on the display field
1750 so that integers would be represented as BEND|BASE_DEC or LEND|BASE_HEX.
1751 But that has not happened yet; note that there are protocols for which
1752 no endianness is specified, such as the X11 protocol and the DCE RPC
1753 protocol, so it would not be possible to record the endianness of all
1758 Some integer fields, of type FT_UINT*, need labels to represent the true
1759 value of a field. You could think of those fields as having an
1760 enumerated data type, rather than an integral data type.
1762 A 'value_string' structure is a way to map values to strings.
1764 typedef struct _value_string {
1769 For fields of that type, you would declare an array of "value_string"s:
1771 static const value_string valstringname[] = {
1772 { INTVAL1, "Descriptive String 1" },
1773 { INTVAL2, "Descriptive String 2" },
1777 (the last entry in the array must have a NULL 'strptr' value, to
1778 indicate the end of the array). The 'strings' field would be set to
1779 'VALS(valstringname)'.
1781 If the field has a numeric rather than an enumerated type, the 'strings'
1782 field would be set to NULL.
1784 If the field has a numeric type that might logically fit in ranges of values
1785 one can use a range_string struct.
1787 Thus a 'range_string' structure is a way to map ranges to strings.
1789 typedef struct _range_string {
1792 const gchar *strptr;
1795 For fields of that type, you would declare an array of "range_string"s:
1797 static const range_string rvalstringname[] = {
1798 { INTVAL_MIN1, INTVALMAX1, "Descriptive String 1" },
1799 { INTVAL_MIN2, INTVALMAX2, "Descriptive String 2" },
1803 If INTVAL_MIN equals INTVAL_MAX for a given entry the range_string
1804 behavior collapses to the one of value_string.
1805 For FT_(U)INT* fields that need a 'range_string' struct, the 'strings' field
1806 would be set to 'RVALS(rvalstringname)'. Furthermore, 'display' field must be
1807 ORed with 'BASE_RANGE_STRING' (e.g. BASE_DEC|BASE_RANGE_STRING).
1809 FT_BOOLEANs have a default map of 0 = "False", 1 (or anything else) = "True".
1810 Sometimes it is useful to change the labels for boolean values (e.g.,
1811 to "Yes"/"No", "Fast"/"Slow", etc.). For these mappings, a struct called
1812 true_false_string is used.
1814 typedef struct true_false_string {
1817 } true_false_string;
1819 For Boolean fields for which "False" and "True" aren't the desired
1820 labels, you would declare a "true_false_string"s:
1822 static const true_false_string boolstringname = {
1827 Its two fields are pointers to the string representing truth, and the
1828 string representing falsehood. For FT_BOOLEAN fields that need a
1829 'true_false_string' struct, the 'strings' field would be set to
1830 'TFS(&boolstringname)'.
1832 If the Boolean field is to be displayed as "False" or "True", the
1833 'strings' field would be set to NULL.
1835 Wireshark predefines a whole range of ready made "true_false_string"s
1836 in tfs.h, included via packet.h.
1840 If the field is a bitfield, then the bitmask is the mask which will
1841 leave only the bits needed to make the field when ANDed with a value.
1842 The proto_tree routines will calculate 'bitshift' automatically
1843 from 'bitmask', by finding the rightmost set bit in the bitmask.
1844 This shift is applied before applying string mapping functions or
1846 If the field is not a bitfield, then bitmask should be set to 0.
1850 This is a string giving a proper description of the field. It should be
1851 at least one grammatically complete sentence, or NULL in which case the
1853 It is meant to provide a more detailed description of the field than the
1854 name alone provides. This information will be used in the man page, and
1855 in a future GUI display-filter creation tool. We might also add tooltips
1856 to the labels in the GUI protocol tree, in which case the blurb would
1857 be used as the tooltip text.
1860 1.6.1 Field Registration.
1862 Protocol registration is handled by creating an instance of the
1863 header_field_info struct (or an array of such structs), and
1864 calling the registration function along with the registration ID of
1865 the protocol that is the parent of the fields. Here is a complete example:
1867 static int proto_eg = -1;
1868 static int hf_field_a = -1;
1869 static int hf_field_b = -1;
1871 static hf_register_info hf[] = {
1874 { "Field A", "proto.field_a", FT_UINT8, BASE_HEX, NULL,
1875 0xf0, "Field A represents Apples", HFILL }},
1878 { "Field B", "proto.field_b", FT_UINT16, BASE_DEC, VALS(vs),
1879 0x0, "Field B represents Bananas", HFILL }}
1882 proto_eg = proto_register_protocol("Example Protocol",
1884 proto_register_field_array(proto_eg, hf, array_length(hf));
1886 Be sure that your array of hf_register_info structs is declared 'static',
1887 since the proto_register_field_array() function does not create a copy
1888 of the information in the array... it uses that static copy of the
1889 information that the compiler created inside your array. Here's the
1890 layout of the hf_register_info struct:
1892 typedef struct hf_register_info {
1893 int *p_id; /* pointer to parent variable */
1894 header_field_info hfinfo;
1897 Also be sure to use the handy array_length() macro found in packet.h
1898 to have the compiler compute the array length for you at compile time.
1900 If you don't have any fields to register, do *NOT* create a zero-length
1901 "hf" array; not all compilers used to compile Wireshark support them.
1902 Just omit the "hf" array, and the "proto_register_field_array()" call,
1905 It is OK to have header fields with a different format be registered with
1906 the same abbreviation. For instance, the following is valid:
1908 static hf_register_info hf[] = {
1910 { &hf_field_8bit, /* 8-bit version of proto.field */
1911 { "Field (8 bit)", "proto.field", FT_UINT8, BASE_DEC, NULL,
1912 0x00, "Field represents FOO", HFILL }},
1914 { &hf_field_32bit, /* 32-bit version of proto.field */
1915 { "Field (32 bit)", "proto.field", FT_UINT32, BASE_DEC, NULL,
1916 0x00, "Field represents FOO", HFILL }}
1919 This way a filter expression can match a header field, irrespective of the
1920 representation of it in the specific protocol context. This is interesting
1921 for protocols with variable-width header fields.
1923 The HFILL macro at the end of the struct will set reasonable default values
1924 for internally used fields.
1926 1.6.2 Adding Items and Values to the Protocol Tree.
1928 A protocol item is added to an existing protocol tree with one of a
1929 handful of proto_XXX_DO_YYY() functions.
1931 Remember that it only makes sense to add items to a protocol tree if its
1932 proto_tree pointer is not null. Should you add an item to a NULL tree, then
1933 the proto_XXX_DO_YYY() function will immediately return. The cost of this
1934 function call can be avoided by checking for the tree pointer.
1936 Subtrees can be made with the proto_item_add_subtree() function:
1938 item = proto_tree_add_item(....);
1939 new_tree = proto_item_add_subtree(item, tree_type);
1941 This will add a subtree under the item in question; a subtree can be
1942 created under an item made by any of the "proto_tree_add_XXX" functions,
1943 so that the tree can be given an arbitrary depth.
1945 Subtree types are integers, assigned by
1946 "proto_register_subtree_array()". To register subtree types, pass an
1947 array of pointers to "gint" variables to hold the subtree type values to
1948 "proto_register_subtree_array()":
1950 static gint ett_eg = -1;
1951 static gint ett_field_a = -1;
1953 static gint *ett[] = {
1958 proto_register_subtree_array(ett, array_length(ett));
1960 in your "register" routine, just as you register the protocol and the
1961 fields for that protocol.
1963 There are several functions that the programmer can use to add either
1964 protocol or field labels to the proto_tree:
1967 proto_tree_add_item(tree, id, tvb, start, length, little_endian);
1970 proto_tree_add_none_format(tree, id, tvb, start, length, format, ...);
1973 proto_tree_add_protocol_format(tree, id, tvb, start, length,
1977 proto_tree_add_bytes(tree, id, tvb, start, length, start_ptr);
1980 proto_tree_add_bytes_format(tree, id, tvb, start, length, start_ptr,
1984 proto_tree_add_bytes_format_value(tree, id, tvb, start, length,
1985 start_ptr, format, ...);
1988 proto_tree_add_time(tree, id, tvb, start, length, value_ptr);
1991 proto_tree_add_time_format(tree, id, tvb, start, length, value_ptr,
1995 proto_tree_add_time_format_value(tree, id, tvb, start, length,
1996 value_ptr, format, ...);
1999 proto_tree_add_ipxnet(tree, id, tvb, start, length, value);
2002 proto_tree_add_ipxnet_format(tree, id, tvb, start, length, value,
2006 proto_tree_add_ipxnet_format_value(tree, id, tvb, start, length,
2007 value, format, ...);
2010 proto_tree_add_ipv4(tree, id, tvb, start, length, value);
2013 proto_tree_add_ipv4_format(tree, id, tvb, start, length, value,
2017 proto_tree_add_ipv4_format_value(tree, id, tvb, start, length,
2018 value, format, ...);
2021 proto_tree_add_ipv6(tree, id, tvb, start, length, value_ptr);
2024 proto_tree_add_ipv6_format(tree, id, tvb, start, length, value_ptr,
2028 proto_tree_add_ipv6_format_value(tree, id, tvb, start, length,
2029 value_ptr, format, ...);
2032 proto_tree_add_ether(tree, id, tvb, start, length, value_ptr);
2035 proto_tree_add_ether_format(tree, id, tvb, start, length, value_ptr,
2039 proto_tree_add_ether_format_value(tree, id, tvb, start, length,
2040 value_ptr, format, ...);
2043 proto_tree_add_string(tree, id, tvb, start, length, value_ptr);
2046 proto_tree_add_string_format(tree, id, tvb, start, length, value_ptr,
2050 proto_tree_add_string_format_value(tree, id, tvb, start, length,
2051 value_ptr, format, ...);
2054 proto_tree_add_boolean(tree, id, tvb, start, length, value);
2057 proto_tree_add_boolean_format(tree, id, tvb, start, length, value,
2061 proto_tree_add_boolean_format_value(tree, id, tvb, start, length,
2062 value, format, ...);
2065 proto_tree_add_float(tree, id, tvb, start, length, value);
2068 proto_tree_add_float_format(tree, id, tvb, start, length, value,
2072 proto_tree_add_float_format_value(tree, id, tvb, start, length,
2073 value, format, ...);
2076 proto_tree_add_double(tree, id, tvb, start, length, value);
2079 proto_tree_add_double_format(tree, id, tvb, start, length, value,
2083 proto_tree_add_double_format_value(tree, id, tvb, start, length,
2084 value, format, ...);
2087 proto_tree_add_uint(tree, id, tvb, start, length, value);
2090 proto_tree_add_uint_format(tree, id, tvb, start, length, value,
2094 proto_tree_add_uint_format_value(tree, id, tvb, start, length,
2095 value, format, ...);
2098 proto_tree_add_uint64(tree, id, tvb, start, length, value);
2101 proto_tree_add_uint64_format(tree, id, tvb, start, length, value,
2105 proto_tree_add_uint64_format_value(tree, id, tvb, start, length,
2106 value, format, ...);
2109 proto_tree_add_int(tree, id, tvb, start, length, value);
2112 proto_tree_add_int_format(tree, id, tvb, start, length, value,
2116 proto_tree_add_int_format_value(tree, id, tvb, start, length,
2117 value, format, ...);
2120 proto_tree_add_int64(tree, id, tvb, start, length, value);
2123 proto_tree_add_int64_format(tree, id, tvb, start, length, value,
2127 proto_tree_add_int64_format_value(tree, id, tvb, start, length,
2128 value, format, ...);
2131 proto_tree_add_text(tree, tvb, start, length, format, ...);
2134 proto_tree_add_text_valist(tree, tvb, start, length, format, ap);
2137 proto_tree_add_guid(tree, id, tvb, start, length, value_ptr);
2140 proto_tree_add_guid_format(tree, id, tvb, start, length, value_ptr,
2144 proto_tree_add_guid_format_value(tree, id, tvb, start, length,
2145 value_ptr, format, ...);
2148 proto_tree_add_oid(tree, id, tvb, start, length, value_ptr);
2151 proto_tree_add_oid_format(tree, id, tvb, start, length, value_ptr,
2155 proto_tree_add_oid_format_value(tree, id, tvb, start, length,
2156 value_ptr, format, ...);
2159 proto_tree_add_bits_item(tree, id, tvb, bit_offset, no_of_bits,
2163 proto_tree_add_bits_ret_val(tree, id, tvb, bit_offset, no_of_bits,
2164 return_value, little_endian);
2167 proto_tree_add_bitmask(tree, tvb, start, header, ett, fields,
2171 proto_tree_add_bitmask_text(tree, tvb, offset, len, name, fallback,
2172 ett, fields, little_endian, flags);
2174 The 'tree' argument is the tree to which the item is to be added. The
2175 'tvb' argument is the tvbuff from which the item's value is being
2176 extracted; the 'start' argument is the offset from the beginning of that
2177 tvbuff of the item being added, and the 'length' argument is the length,
2178 in bytes, of the item, bit_offset is the offset in bits and no_of_bits
2179 is the length in bits.
2181 The length of some items cannot be determined until the item has been
2182 dissected; to add such an item, add it with a length of -1, and, when the
2183 dissection is complete, set the length with 'proto_item_set_len()':
2186 proto_item_set_len(ti, length);
2188 The "ti" argument is the value returned by the call that added the item
2189 to the tree, and the "length" argument is the length of the item.
2191 proto_tree_add_item()
2192 ---------------------
2193 proto_tree_add_item is used when you wish to do no special formatting.
2194 The item added to the GUI tree will contain the name (as passed in the
2195 proto_register_*() function) and a value. The value will be fetched
2196 from the tvbuff by proto_tree_add_item(), based on the type of the field
2197 and, for integral and Boolean fields, the byte order of the value; the
2198 byte order is specified by the 'little_endian' argument, which is TRUE
2199 if the value is little-endian and FALSE if it is big-endian.
2201 Now that definitions of fields have detailed information about bitfield
2202 fields, you can use proto_tree_add_item() with no extra processing to
2203 add bitfield values to your tree. Here's an example. Take the Format
2204 Identifier (FID) field in the Transmission Header (TH) portion of the SNA
2205 protocol. The FID is the high nibble of the first byte of the TH. The
2206 FID would be registered like this:
2208 name = "Format Identifier"
2209 abbrev = "sna.th.fid"
2212 strings = sna_th_fid_vals
2215 The bitmask contains the value which would leave only the FID if bitwise-ANDed
2216 against the parent field, the first byte of the TH.
2218 The code to add the FID to the tree would be;
2220 proto_tree_add_item(bf_tree, hf_sna_th_fid, tvb, offset, 1, TRUE);
2222 The definition of the field already has the information about bitmasking
2223 and bitshifting, so it does the work of masking and shifting for us!
2224 This also means that you no longer have to create value_string structs
2225 with the values bitshifted. The value_string for FID looks like this,
2226 even though the FID value is actually contained in the high nibble.
2227 (You'd expect the values to be 0x0, 0x10, 0x20, etc.)
2229 /* Format Identifier */
2230 static const value_string sna_th_fid_vals[] = {
2231 { 0x0, "SNA device <--> Non-SNA Device" },
2232 { 0x1, "Subarea Node <--> Subarea Node" },
2233 { 0x2, "Subarea Node <--> PU2" },
2234 { 0x3, "Subarea Node or SNA host <--> Subarea Node" },
2237 { 0xf, "Adjacent Subarea Nodes" },
2241 The final implication of this is that display filters work the way you'd
2242 naturally expect them to. You'd type "sna.th.fid == 0xf" to find Adjacent
2243 Subarea Nodes. The user does not have to shift the value of the FID to
2244 the high nibble of the byte ("sna.th.fid == 0xf0") as was necessary
2247 proto_tree_add_protocol_format()
2248 --------------------------------
2249 proto_tree_add_protocol_format is used to add the top-level item for the
2250 protocol when the dissector routine wants complete control over how the
2251 field and value will be represented on the GUI tree. The ID value for
2252 the protocol is passed in as the "id" argument; the rest of the
2253 arguments are a "printf"-style format and any arguments for that format.
2254 The caller must include the name of the protocol in the format; it is
2255 not added automatically as in proto_tree_add_item().
2257 proto_tree_add_none_format()
2258 ----------------------------
2259 proto_tree_add_none_format is used to add an item of type FT_NONE.
2260 The caller must include the name of the field in the format; it is
2261 not added automatically as in proto_tree_add_item().
2263 proto_tree_add_bytes()
2264 proto_tree_add_time()
2265 proto_tree_add_ipxnet()
2266 proto_tree_add_ipv4()
2267 proto_tree_add_ipv6()
2268 proto_tree_add_ether()
2269 proto_tree_add_string()
2270 proto_tree_add_boolean()
2271 proto_tree_add_float()
2272 proto_tree_add_double()
2273 proto_tree_add_uint()
2274 proto_tree_add_uint64()
2275 proto_tree_add_int()
2276 proto_tree_add_int64()
2277 proto_tree_add_guid()
2278 proto_tree_add_oid()
2279 ------------------------
2280 These routines are used to add items to the protocol tree if either:
2282 the value of the item to be added isn't just extracted from the
2283 packet data, but is computed from data in the packet;
2285 the value was fetched into a variable.
2287 The 'value' argument has the value to be added to the tree.
2289 NOTE: in all cases where the 'value' argument is a pointer, a copy is
2290 made of the object pointed to; if you have dynamically allocated a
2291 buffer for the object, that buffer will not be freed when the protocol
2292 tree is freed - you must free the buffer yourself when you don't need it
2295 For proto_tree_add_bytes(), the 'value_ptr' argument is a pointer to a
2298 For proto_tree_add_time(), the 'value_ptr' argument is a pointer to an
2299 "nstime_t", which is a structure containing the time to be added; it has
2300 'secs' and 'nsecs' members, giving the integral part and the fractional
2301 part of a time in units of seconds, with 'nsecs' being the number of
2302 nanoseconds. For absolute times, "secs" is a UNIX-style seconds since
2303 January 1, 1970, 00:00:00 GMT value.
2305 For proto_tree_add_ipxnet(), the 'value' argument is a 32-bit IPX
2308 For proto_tree_add_ipv4(), the 'value' argument is a 32-bit IPv4
2309 address, in network byte order.
2311 For proto_tree_add_ipv6(), the 'value_ptr' argument is a pointer to a
2312 128-bit IPv6 address.
2314 For proto_tree_add_ether(), the 'value_ptr' argument is a pointer to a
2317 For proto_tree_add_string(), the 'value_ptr' argument is a pointer to a
2320 For proto_tree_add_boolean(), the 'value' argument is a 32-bit integer.
2321 It is masked and shifted as defined by the field info after which zero
2322 means "false", and non-zero means "true".
2324 For proto_tree_add_float(), the 'value' argument is a 'float' in the
2325 host's floating-point format.
2327 For proto_tree_add_double(), the 'value' argument is a 'double' in the
2328 host's floating-point format.
2330 For proto_tree_add_uint(), the 'value' argument is a 32-bit unsigned
2331 integer value, in host byte order. (This routine cannot be used to add
2334 For proto_tree_add_uint64(), the 'value' argument is a 64-bit unsigned
2335 integer value, in host byte order.
2337 For proto_tree_add_int(), the 'value' argument is a 32-bit signed
2338 integer value, in host byte order. (This routine cannot be used to add
2341 For proto_tree_add_int64(), the 'value' argument is a 64-bit signed
2342 integer value, in host byte order.
2344 For proto_tree_add_guid(), the 'value_ptr' argument is a pointer to an
2347 For proto_tree_add_oid(), the 'value_ptr' argument is a pointer to an
2348 ASN.1 Object Identifier.
2350 proto_tree_add_bytes_format()
2351 proto_tree_add_time_format()
2352 proto_tree_add_ipxnet_format()
2353 proto_tree_add_ipv4_format()
2354 proto_tree_add_ipv6_format()
2355 proto_tree_add_ether_format()
2356 proto_tree_add_string_format()
2357 proto_tree_add_boolean_format()
2358 proto_tree_add_float_format()
2359 proto_tree_add_double_format()
2360 proto_tree_add_uint_format()
2361 proto_tree_add_uint64_format()
2362 proto_tree_add_int_format()
2363 proto_tree_add_int64_format()
2364 proto_tree_add_guid_format()
2365 proto_tree_add_oid_format()
2366 ----------------------------
2367 These routines are used to add items to the protocol tree when the
2368 dissector routine wants complete control over how the field and value
2369 will be represented on the GUI tree. The argument giving the value is
2370 the same as the corresponding proto_tree_add_XXX() function; the rest of
2371 the arguments are a "printf"-style format and any arguments for that
2372 format. The caller must include the name of the field in the format; it
2373 is not added automatically as in the proto_tree_add_XXX() functions.
2375 proto_tree_add_bytes_format_value()
2376 proto_tree_add_time_format_value()
2377 proto_tree_add_ipxnet_format_value()
2378 proto_tree_add_ipv4_format_value()
2379 proto_tree_add_ipv6_format_value()
2380 proto_tree_add_ether_format_value()
2381 proto_tree_add_string_format_value()
2382 proto_tree_add_boolean_format_value()
2383 proto_tree_add_float_format_value()
2384 proto_tree_add_double_format_value()
2385 proto_tree_add_uint_format_value()
2386 proto_tree_add_uint64_format_value()
2387 proto_tree_add_int_format_value()
2388 proto_tree_add_int64_format_value()
2389 proto_tree_add_guid_format_value()
2390 proto_tree_add_oid_format_value()
2391 ------------------------------------
2393 These routines are used to add items to the protocol tree when the
2394 dissector routine wants complete control over how the value will be
2395 represented on the GUI tree. The argument giving the value is the same
2396 as the corresponding proto_tree_add_XXX() function; the rest of the
2397 arguments are a "printf"-style format and any arguments for that format.
2398 With these routines, unlike the proto_tree_add_XXX_format() routines,
2399 the name of the field is added automatically as in the
2400 proto_tree_add_XXX() functions; only the value is added with the format.
2402 proto_tree_add_text()
2403 ---------------------
2404 proto_tree_add_text() is used to add a label to the GUI tree. It will
2405 contain no value, so it is not searchable in the display filter process.
2406 This function was needed in the transition from the old-style proto_tree
2407 to this new-style proto_tree so that Wireshark would still decode all
2408 protocols w/o being able to filter on all protocols and fields.
2409 Otherwise we would have had to cripple Wireshark's functionality while we
2410 converted all the old-style proto_tree calls to the new-style proto_tree
2411 calls. In other words, you should not use this in new code unless you've got
2412 a specific reason (see below).
2414 This can also be used for items with subtrees, which may not have values
2415 themselves - the items in the subtree are the ones with values.
2417 For a subtree, the label on the subtree might reflect some of the items
2418 in the subtree. This means the label can't be set until at least some
2419 of the items in the subtree have been dissected. To do this, use
2420 'proto_item_set_text()' or 'proto_item_append_text()':
2423 proto_item_set_text(proto_item *ti, ...);
2426 proto_item_append_text(proto_item *ti, ...);
2428 'proto_item_set_text()' takes as an argument the value returned by
2429 'proto_tree_add_text()', a 'printf'-style format string, and a set of
2430 arguments corresponding to '%' format items in that string, and replaces
2431 the text for the item created by 'proto_tree_add_text()' with the result
2432 of applying the arguments to the format string.
2434 'proto_item_append_text()' is similar, but it appends to the text for
2435 the item the result of applying the arguments to the format string.
2437 For example, early in the dissection, one might do:
2439 ti = proto_tree_add_text(tree, tvb, offset, length, <label>);
2443 proto_item_set_text(ti, "%s: %s", type, value);
2445 after the "type" and "value" fields have been extracted and dissected.
2446 <label> would be a label giving what information about the subtree is
2447 available without dissecting any of the data in the subtree.
2449 Note that an exception might be thrown when trying to extract the values of
2450 the items used to set the label, if not all the bytes of the item are
2451 available. Thus, one should create the item with text that is as
2452 meaningful as possible, and set it or append additional information to
2453 it as the values needed to supply that information are extracted.
2455 proto_tree_add_text_valist()
2456 ----------------------------
2457 This is like proto_tree_add_text(), but takes, as the last argument, a
2458 'va_list'; it is used to allow routines that take a printf-like
2459 variable-length list of arguments to add a text item to the protocol
2462 proto_tree_add_bits_item()
2463 --------------------------
2464 Adds a number of bits to the protocol tree which does not have to be byte
2465 aligned. The offset and length is in bits.
2468 ..10 1010 10.. .... "value" (formatted as FT_ indicates).
2470 proto_tree_add_bits_ret_val()
2471 -----------------------------
2472 Works in the same way but also returns the value of the read bits.
2474 proto_tree_add_bitmask() and proto_tree_add_bitmask_text()
2475 ----------------------------------------------------------
2476 This function provides an easy to use and convenient helper function
2477 to manage many types of common bitmasks that occur in protocols.
2479 This function will dissect a 1/2/3/4 byte large bitmask into its individual
2481 header is an integer type and must be of type FT_[U]INT{8|16|24|32} and
2482 represents the entire width of the bitmask.
2484 'header' and 'ett' are the hf fields and ett field respectively to create an
2485 expansion that covers the 1-4 bytes of the bitmask.
2487 'fields' is a NULL terminated array of pointers to hf fields representing
2488 the individual subfields of the bitmask. These fields must either be integers
2489 of the same byte width as 'header' or of the type FT_BOOLEAN.
2490 Each of the entries in 'fields' will be dissected as an item under the
2491 'header' expansion and also IF the field is a boolean and IF it is set to 1,
2492 then the name of that boolean field will be printed on the 'header' expansion
2493 line. For integer type subfields that have a value_string defined, the
2494 matched string from that value_string will be printed on the expansion line
2497 Example: (from the SCSI dissector)
2498 static int hf_scsi_inq_peripheral = -1;
2499 static int hf_scsi_inq_qualifier = -1;
2500 static int hf_scsi_inq_devtype = -1;
2502 static gint ett_scsi_inq_peripheral = -1;
2504 static const int *peripheal_fields[] = {
2505 &hf_scsi_inq_qualifier,
2506 &hf_scsi_inq_devtype,
2510 /* Qualifier and DeviceType */
2511 proto_tree_add_bitmask(tree, tvb, offset, hf_scsi_inq_peripheral,
2512 ett_scsi_inq_peripheral, peripheal_fields, FALSE);
2515 { &hf_scsi_inq_peripheral,
2516 {"Peripheral", "scsi.inquiry.preipheral", FT_UINT8, BASE_HEX,
2517 NULL, 0, NULL, HFILL}},
2518 { &hf_scsi_inq_qualifier,
2519 {"Qualifier", "scsi.inquiry.qualifier", FT_UINT8, BASE_HEX,
2520 VALS (scsi_qualifier_val), 0xE0, NULL, HFILL}},
2521 { &hf_scsi_inq_devtype,
2522 {"Device Type", "scsi.inquiry.devtype", FT_UINT8, BASE_HEX,
2523 VALS (scsi_devtype_val), SCSI_DEV_BITS, NULL, HFILL}},
2526 Which provides very pretty dissection of this one byte bitmask.
2528 Peripheral: 0x05, Qualifier: Device type is connected to logical unit, Device Type: CD-ROM
2529 000. .... = Qualifier: Device type is connected to logical unit (0x00)
2530 ...0 0101 = Device Type: CD-ROM (0x05)
2532 The proto_tree_add_bitmask_text() function is an extended version of
2533 the proto_tree_add_bitmask() function. In addition, it allows to:
2534 - Provide a leading text (e.g. "Flags: ") that will appear before
2535 the comma-separated list of field values
2536 - Provide a fallback text (e.g. "None") that will be appended if
2537 no fields warranted a change to the top-level title.
2538 - Using flags, specify which fields will affect the top-level title.
2540 There are the following flags defined:
2542 BMT_NO_APPEND - the title is taken "as-is" from the 'name' argument.
2543 BMT_NO_INT - only boolean flags are added to the title.
2544 BMT_NO_FALSE - boolean flags are only added to the title if they are set.
2545 BMT_NO_TFS - only add flag name to the title, do not use true_false_string
2547 The proto_tree_add_bitmask() behavior can be obtained by providing
2548 both 'name' and 'fallback' arguments as NULL, and a flags of
2549 (BMT_NO_FALSE|BMT_NO_TFS).
2551 PROTO_ITEM_SET_GENERATED()
2552 --------------------------
2553 PROTO_ITEM_SET_GENERATED is used to mark fields as not being read from the
2554 captured data directly, but inferred from one or more values.
2556 One of the primary uses of this is the presentation of verification of
2557 checksums. Every IP packet has a checksum line, which can present the result
2558 of the checksum verification, if enabled in the preferences. The result is
2559 presented as a subtree, where the result is enclosed in square brackets
2560 indicating a generated field.
2562 Header checksum: 0x3d42 [correct]
2566 PROTO_ITEM_SET_HIDDEN()
2567 -----------------------
2568 PROTO_ITEM_SET_HIDDEN is used to hide fields, which have already been added
2569 to the tree, from being visible in the displayed tree.
2571 NOTE that creating hidden fields is actually quite a bad idea from a UI design
2572 perspective because the user (someone who did not write nor has ever seen the
2573 code) has no way of knowing that hidden fields are there to be filtered on
2574 thus defeating the whole purpose of putting them there. A Better Way might
2575 be to add the fields (that might otherwise be hidden) to a subtree where they
2576 won't be seen unless the user opens the subtree--but they can be found if the
2579 One use for hidden fields (which would be better implemented using visible
2580 fields in a subtree) follows: The caller may want a value to be
2581 included in a tree so that the packet can be filtered on this field, but
2582 the representation of that field in the tree is not appropriate. An
2583 example is the token-ring routing information field (RIF). The best way
2584 to show the RIF in a GUI is by a sequence of ring and bridge numbers.
2585 Rings are 3-digit hex numbers, and bridges are single hex digits:
2587 RIF: 001-A-013-9-C0F-B-555
2589 In the case of RIF, the programmer should use a field with no value and
2590 use proto_tree_add_none_format() to build the above representation. The
2591 programmer can then add the ring and bridge values, one-by-one, with
2592 proto_tree_add_item() and hide them with PROTO_ITEM_SET_HIDDEN() so that the
2593 user can then filter on or search for a particular ring or bridge. Here's a
2594 skeleton of how the programmer might code this.
2597 rif = create_rif_string(...);
2599 proto_tree_add_none_format(tree, hf_tr_rif_label, ..., "RIF: %s", rif);
2601 for(i = 0; i < num_rings; i++) {
2604 pi = proto_tree_add_item(tree, hf_tr_rif_ring, ..., FALSE);
2605 PROTO_ITEM_SET_HIDDEN(pi);
2607 for(i = 0; i < num_rings - 1; i++) {
2610 pi = proto_tree_add_item(tree, hf_tr_rif_bridge, ..., FALSE);
2611 PROTO_ITEM_SET_HIDDEN(pi);
2614 The logical tree has these items:
2616 hf_tr_rif_label, text="RIF: 001-A-013-9-C0F-B-555", value = NONE
2617 hf_tr_rif_ring, hidden, value=0x001
2618 hf_tr_rif_bridge, hidden, value=0xA
2619 hf_tr_rif_ring, hidden, value=0x013
2620 hf_tr_rif_bridge, hidden, value=0x9
2621 hf_tr_rif_ring, hidden, value=0xC0F
2622 hf_tr_rif_bridge, hidden, value=0xB
2623 hf_tr_rif_ring, hidden, value=0x555
2625 GUI or print code will not display the hidden fields, but a display
2626 filter or "packet grep" routine will still see the values. The possible
2627 filter is then possible:
2629 tr.rif_ring eq 0x013
2633 PROTO_ITEM_SET_URL is used to mark fields as containing a URL. This can only
2634 be done with fields of type FT_STRING(Z). If these fields are presented they
2635 are underlined, as could be done in a browser. These fields are sensitive to
2636 clicks as well, launching the configured browser with this URL as parameter.
2638 1.7 Utility routines.
2640 1.7.1 match_strval and val_to_str.
2642 A dissector may need to convert a value to a string, using a
2643 'value_string' structure, by hand, rather than by declaring a field with
2644 an associated 'value_string' structure; this might be used, for example,
2645 to generate a COL_INFO line for a frame.
2647 'match_strval()' will do that:
2650 match_strval(guint32 val, const value_string *vs)
2652 It will look up the value 'val' in the 'value_string' table pointed to
2653 by 'vs', and return either the corresponding string, or NULL if the
2654 value could not be found in the table. Note that, unless 'val' is
2655 guaranteed to be a value in the 'value_string' table ("guaranteed" as in
2656 "the code has already checked that it's one of those values" or "the
2657 table handles all possible values of the size of 'val'", not "the
2658 protocol spec says it has to be" - protocol specs do not prevent invalid
2659 packets from being put onto a network or into a purported packet capture
2660 file), you must check whether 'match_strval()' returns NULL, and arrange
2661 that its return value not be dereferenced if it's NULL. 'val_to_str()'
2662 can be used to generate a string for values not found in the table:
2665 val_to_str(guint32 val, const value_string *vs, const char *fmt)
2667 If the value 'val' is found in the 'value_string' table pointed to by
2668 'vs', 'val_to_str' will return the corresponding string; otherwise, it
2669 will use 'fmt' as an 'sprintf'-style format, with 'val' as an argument,
2670 to generate a string, and will return a pointer to that string.
2671 You can use it in a call to generate a COL_INFO line for a frame such as
2673 col_add_fstr(COL_INFO, ", %s", val_to_str(val, table, "Unknown %d"));
2675 1.7.2 match_strrval and rval_to_str.
2677 A dissector may need to convert a range of values to a string, using a
2678 'range_string' structure.
2680 'match_strrval()' will do that:
2683 match_strrval(guint32 val, const range_string *rs)
2685 It will look up the value 'val' in the 'range_string' table pointed to
2686 by 'rs', and return either the corresponding string, or NULL if the
2687 value could not be found in the table. Please note that its base
2688 behavior is inherited from match_strval().
2690 'rval_to_str()' can be used to generate a string for values not found in
2694 rval_to_str(guint32 val, const range_string *rs, const char *fmt)
2696 If the value 'val' is found in the 'range_string' table pointed to by
2697 'rs', 'rval_to_str' will return the corresponding string; otherwise, it
2698 will use 'fmt' as an 'sprintf'-style format, with 'val' as an argument,
2699 to generate a string, and will return a pointer to that string. Please
2700 note that its base behavior is inherited from match_strval().
2702 1.8 Calling Other Dissectors.
2704 As each dissector completes its portion of the protocol analysis, it
2705 is expected to create a new tvbuff of type TVBUFF_SUBSET which
2706 contains the payload portion of the protocol (that is, the bytes
2707 that are relevant to the next dissector).
2709 The syntax for creating a new TVBUFF_SUBSET is:
2711 next_tvb = tvb_new_subset(tvb, offset, length, reported_length)
2714 tvb is the tvbuff that the dissector has been working on. It
2715 can be a tvbuff of any type.
2717 next_tvb is the new TVBUFF_SUBSET.
2719 offset is the byte offset of 'tvb' at which the new tvbuff
2720 should start. The first byte is the 0th byte.
2722 length is the number of bytes in the new TVBUFF_SUBSET. A length
2723 argument of -1 says to use as many bytes as are available in
2726 reported_length is the number of bytes that the current protocol
2727 says should be in the payload. A reported_length of -1 says that
2728 the protocol doesn't say anything about the size of its payload.
2731 An example from packet-ipx.c -
2734 dissect_ipx(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
2737 int reported_length, available_length;
2740 /* Make the next tvbuff */
2742 /* IPX does have a length value in the header, so calculate report_length */
2743 Set this to -1 if there isn't any length information in the protocol
2745 reported_length = ipx_length - IPX_HEADER_LEN;
2747 /* Calculate the available data in the packet,
2748 set this to -1 to use all the data in the tv_buffer
2750 available_length = tvb_length(tvb) - IPX_HEADER_LEN;
2752 /* Create the tvbuffer for the next dissector */
2753 next_tvb = tvb_new_subset(tvb, IPX_HEADER_LEN,
2754 MIN(available_length, reported_length),
2757 /* call the next dissector */
2758 dissector_next( next_tvb, pinfo, tree);
2761 1.9 Editing Makefile.common to add your dissector.
2763 To arrange that your dissector will be built as part of Wireshark, you
2764 must add the name of the source file for your dissector to the
2765 'DISSECTOR_SRC' macro in the 'Makefile.common' file in the 'epan/dissectors'
2766 directory. (Note that this is for modern versions of UNIX, so there
2767 is no 14-character limitation on file names, and for modern versions of
2768 Windows, so there is no 8.3-character limitation on file names.)
2770 If your dissector also has its own header file or files, you must add
2771 them to the 'DISSECTOR_INCLUDES' macro in the 'Makefile.common' file in
2772 the 'epan/dissectors' directory, so that it's included when release source
2773 tarballs are built (otherwise, the source in the release tarballs won't
2776 1.10 Using the SVN source code tree.
2778 See <http://www.wireshark.org/develop.html>
2780 1.11 Submitting code for your new dissector.
2782 - VERIFY that your dissector code does not use prohibited or deprecated APIs
2784 perl <wireshark_root>/tools/checkAPIs.pl <source-filename(s)>
2786 - TEST YOUR DISSECTOR BEFORE SUBMITTING IT.
2787 Use fuzz-test.sh and/or randpkt against your dissector. These are
2788 described at <http://wiki.wireshark.org/FuzzTesting>.
2790 - Subscribe to <mailto:wireshark-dev[AT]wireshark.org> by sending an email to
2791 <mailto:wireshark-dev-request[AT]wireshark.org?body="help"> or visiting
2792 <http://www.wireshark.org/lists/>.
2794 - 'svn add' all the files of your new dissector.
2796 - 'svn diff' the workspace and save the result to a file.
2798 - Edit the diff file - remove any changes unrelated to your new dissector,
2799 e.g. changes in config.nmake
2801 - Submit a bug report to the Wireshark bug database, found at
2802 <http://bugs.wireshark.org>, qualified as an enhancement and attach your
2803 diff file there. Set the review request flag to '?' so it will pop up in
2804 the patch review list.
2806 - Create a Wiki page on the protocol at <http://wiki.wireshark.org>.
2807 A template is provided so it is easy to setup in a consistent style.
2809 - If possible, add sample capture files to the sample captures page at
2810 <http://wiki.wireshark.org/SampleCaptures>. These files are used by
2811 the automated build system for fuzz testing.
2813 - If you find that you are contributing a lot to wireshark on an ongoing
2814 basis you can request to become a committer which will allow you to
2815 commit files to subversion directly.
2817 2. Advanced dissector topics.
2821 Some of the advanced features are being worked on constantly. When using them
2822 it is wise to check the relevant header and source files for additional details.
2824 2.2 Following "conversations".
2826 In wireshark a conversation is defined as a series of data packets between two
2827 address:port combinations. A conversation is not sensitive to the direction of
2828 the packet. The same conversation will be returned for a packet bound from
2829 ServerA:1000 to ClientA:2000 and the packet from ClientA:2000 to ServerA:1000.
2831 There are five routines that you will use to work with a conversation:
2832 conversation_new, find_conversation, conversation_add_proto_data,
2833 conversation_get_proto_data, and conversation_delete_proto_data.
2836 2.2.1 The conversation_init function.
2838 This is an internal routine for the conversation code. As such you
2839 will not have to call this routine. Just be aware that this routine is
2840 called at the start of each capture and before the packets are filtered
2841 with a display filter. The routine will destroy all stored
2842 conversations. This routine does NOT clean up any data pointers that are
2843 passed in the conversation_new 'data' variable. You are responsible for
2844 this clean up if you pass a malloc'ed pointer in this variable.
2846 See item 2.2.8 for more information about the 'data' pointer.
2849 2.2.2 The conversation_new function.
2851 This routine will create a new conversation based upon two address/port
2852 pairs. If you want to associate with the conversation a pointer to a
2853 private data structure you must use the conversation_add_proto_data
2854 function. The ptype variable is used to differentiate between
2855 conversations over different protocols, i.e. TCP and UDP. The options
2856 variable is used to define a conversation that will accept any destination
2857 address and/or port. Set options = 0 if the destination port and address
2858 are know when conversation_new is called. See section 2.4 for more
2859 information on usage of the options parameter.
2861 The conversation_new prototype:
2862 conversation_t *conversation_new(guint32 setup_frame, address *addr1,
2863 address *addr2, port_type ptype, guint32 port1, guint32 port2,
2867 guint32 setup_frame = The lowest numbered frame for this conversation
2868 address* addr1 = first data packet address
2869 address* addr2 = second data packet address
2870 port_type ptype = port type, this is defined in packet.h
2871 guint32 port1 = first data packet port
2872 guint32 port2 = second data packet port
2873 guint options = conversation options, NO_ADDR2 and/or NO_PORT2
2875 setup_frame indicates the first frame for this conversation, and is used to
2876 distinguish multiple conversations with the same addr1/port1 and addr2/port2
2877 pair that occur within the same capture session.
2879 "addr1" and "port1" are the first address/port pair; "addr2" and "port2"
2880 are the second address/port pair. A conversation doesn't have source
2881 and destination address/port pairs - packets in a conversation go in
2882 both directions - so "addr1"/"port1" may be the source or destination
2883 address/port pair; "addr2"/"port2" would be the other pair.
2885 If NO_ADDR2 is specified, the conversation is set up so that a
2886 conversation lookup will match only the "addr1" address; if NO_PORT2 is
2887 specified, the conversation is set up so that a conversation lookup will
2888 match only the "port1" port; if both are specified, i.e.
2889 NO_ADDR2|NO_PORT2, the conversation is set up so that the lookup will
2890 match only the "addr1"/"port1" address/port pair. This can be used if a
2891 packet indicates that, later in the capture, a conversation will be
2892 created using certain addresses and ports, in the case where the packet
2893 doesn't specify the addresses and ports of both sides.
2895 2.2.3 The find_conversation function.
2897 Call this routine to look up a conversation. If no conversation is found,
2898 the routine will return a NULL value.
2900 The find_conversation prototype:
2902 conversation_t *find_conversation(guint32 frame_num, address *addr_a,
2903 address *addr_b, port_type ptype, guint32 port_a, guint32 port_b,
2907 guint32 frame_num = a frame number to match
2908 address* addr_a = first address
2909 address* addr_b = second address
2910 port_type ptype = port type
2911 guint32 port_a = first data packet port
2912 guint32 port_b = second data packet port
2913 guint options = conversation options, NO_ADDR_B and/or NO_PORT_B
2915 frame_num is a frame number to match. The conversation returned is where
2916 (frame_num >= conversation->setup_frame
2917 && frame_num < conversation->next->setup_frame)
2918 Suppose there are a total of 3 conversations (A, B, and C) that match
2919 addr_a/port_a and addr_b/port_b, where the setup_frame used in
2920 conversation_new() for A, B and C are 10, 50, and 100 respectively. The
2921 frame_num passed in find_conversation is compared to the setup_frame of each
2922 conversation. So if (frame_num >= 10 && frame_num < 50), conversation A is
2923 returned. If (frame_num >= 50 && frame_num < 100), conversation B is returned.
2924 If (frame_num >= 100) conversation C is returned.
2926 "addr_a" and "port_a" are the first address/port pair; "addr_b" and
2927 "port_b" are the second address/port pair. Again, as a conversation
2928 doesn't have source and destination address/port pairs, so
2929 "addr_a"/"port_a" may be the source or destination address/port pair;
2930 "addr_b"/"port_b" would be the other pair. The search will match the
2931 "a" address/port pair against both the "1" and "2" address/port pairs,
2932 and match the "b" address/port pair against both the "2" and "1"
2933 address/port pairs; you don't have to worry about which side the "a" or
2934 "b" pairs correspond to.
2936 If the NO_ADDR_B flag was specified to "find_conversation()", the
2937 "addr_b" address will be treated as matching any "wildcarded" address;
2938 if the NO_PORT_B flag was specified, the "port_b" port will be treated
2939 as matching any "wildcarded" port. If both flags are specified, i.e.
2940 NO_ADDR_B|NO_PORT_B, the "addr_b" address will be treated as matching
2941 any "wildcarded" address and the "port_b" port will be treated as
2942 matching any "wildcarded" port.
2945 2.2.4 The conversation_add_proto_data function.
2947 Once you have created a conversation with conversation_new, you can
2948 associate data with it using this function.
2950 The conversation_add_proto_data prototype:
2952 void conversation_add_proto_data(conversation_t *conv, int proto,
2956 conversation_t *conv = the conversation in question
2957 int proto = registered protocol number
2958 void *data = dissector data structure
2960 "conversation" is the value returned by conversation_new. "proto" is a
2961 unique protocol number created with proto_register_protocol. Protocols
2962 are typically registered in the proto_register_XXXX section of your
2963 dissector. "data" is a pointer to the data you wish to associate with the
2964 conversation. Using the protocol number allows several dissectors to
2965 associate data with a given conversation.
2968 2.2.5 The conversation_get_proto_data function.
2970 After you have located a conversation with find_conversation, you can use
2971 this function to retrieve any data associated with it.
2973 The conversation_get_proto_data prototype:
2975 void *conversation_get_proto_data(conversation_t *conv, int proto);
2978 conversation_t *conv = the conversation in question
2979 int proto = registered protocol number
2981 "conversation" is the conversation created with conversation_new. "proto"
2982 is a unique protocol number created with proto_register_protocol,
2983 typically in the proto_register_XXXX portion of a dissector. The function
2984 returns a pointer to the data requested, or NULL if no data was found.
2987 2.2.6 The conversation_delete_proto_data function.
2989 After you are finished with a conversation, you can remove your association
2990 with this function. Please note that ONLY the conversation entry is
2991 removed. If you have allocated any memory for your data, you must free it
2994 The conversation_delete_proto_data prototype:
2996 void conversation_delete_proto_data(conversation_t *conv, int proto);
2999 conversation_t *conv = the conversation in question
3000 int proto = registered protocol number
3002 "conversation" is the conversation created with conversation_new. "proto"
3003 is a unique protocol number created with proto_register_protocol,
3004 typically in the proto_register_XXXX portion of a dissector.
3007 2.2.7 Using timestamps relative to the conversation
3009 There is a framework to calculate timestamps relative to the start of the
3010 conversation. First of all the timestamp of the first packet that has been
3011 seen in the conversation must be kept in the protocol data to be able
3012 to calculate the timestamp of the current packet relative to the start
3013 of the conversation. The timestamp of the last packet that was seen in the
3014 conversation should also be kept in the protocol data. This way the
3015 delta time between the current packet and the previous packet in the
3016 conversation can be calculated.
3018 So add the following items to the struct that is used for the protocol data:
3023 The ts_prev value should only be set during the first run through the
3024 packets (ie pinfo->fd->flags.visited is false).
3026 Next step is to use the per-packet information (described in section 2.5)
3027 to keep the calculated delta timestamp, as it can only be calculated
3028 on the first run through the packets. This is because a packet can be
3029 selected in random order once the whole file has been read.
3031 After calculating the conversation timestamps, it is time to put them in
3032 the appropriate columns with the function 'col_set_time' (described in
3033 section 1.5.9). There are two columns for conversation timestamps:
3035 COL_REL_CONV_TIME, /* Relative time to beginning of conversation */
3036 COL_DELTA_CONV_TIME,/* Delta time to last frame in conversation */
3038 Last but not least, there MUST be a preference in each dissector that
3039 uses conversation timestamps that makes it possible to enable and
3040 disable the calculation of conversation timestamps. The main argument
3041 for this is that a higher level conversation is able to overwrite
3042 the values of lowel level conversations in these two columns. Being
3043 able to actively select which protocols may overwrite the conversation
3044 timestamp columns gives the user the power to control these columns.
3045 (A second reason is that conversation timestamps use the per-packet
3046 data structure which uses additional memory, which should be avoided
3047 if these timestamps are not needed)
3049 Have a look at the differences to packet-tcp.[ch] in SVN 22966 and
3050 SVN 23058 to see the implementation of conversation timestamps for
3054 2.2.8 The example conversation code with GMemChunk's.
3056 For a conversation between two IP addresses and ports you can use this as an
3057 example. This example uses the GMemChunk to allocate memory and stores the data
3058 pointer in the conversation 'data' variable.
3060 NOTE: Remember to register the init routine (my_dissector_init) in the
3061 protocol_register routine.
3064 /************************ Global values ************************/
3066 /* the number of entries in the memory chunk array */
3067 #define my_init_count 10
3069 /* define your structure here */
3074 /* the GMemChunk base structure */
3075 static GMemChunk *my_vals = NULL;
3077 /* Registered protocol number */
3078 static int my_proto = -1;
3081 /********************* in the dissector routine *********************/
3083 /* the local variables in the dissector */
3085 conversation_t *conversation;
3086 my_entry_t *data_ptr;
3089 /* look up the conversation */
3091 conversation = find_conversation(pinfo->fd->num, &pinfo->src, &pinfo->dst,
3092 pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
3094 /* if conversation found get the data pointer that you stored */
3096 data_ptr = (my_entry_t*)conversation_get_proto_data(conversation, my_proto);
3099 /* new conversation create local data structure */
3101 data_ptr = g_mem_chunk_alloc(my_vals);
3103 /*** add your code here to setup the new data structure ***/
3105 /* create the conversation with your data pointer */
3107 conversation = conversation_new(pinfo->fd->num, &pinfo->src, &pinfo->dst, pinfo->ptype,
3108 pinfo->srcport, pinfo->destport, 0);
3109 conversation_add_proto_data(conversation, my_proto, (void *)data_ptr);
3112 /* at this point the conversation data is ready */
3115 /******************* in the dissector init routine *******************/
3117 #define my_init_count 20
3120 my_dissector_init(void)
3123 /* destroy memory chunks if needed */
3126 g_mem_chunk_destroy(my_vals);
3128 /* now create memory chunks */
3130 my_vals = g_mem_chunk_new("my_proto_vals",
3132 my_init_count * sizeof(my_entry_t),
3136 /***************** in the protocol register routine *****************/
3138 /* register re-init routine */
3140 register_init_routine(&my_dissector_init);
3142 my_proto = proto_register_protocol("My Protocol", "My Protocol", "my_proto");
3145 2.2.9 An example conversation code that starts at a specific frame number.
3147 Sometimes a dissector has determined that a new conversation is needed that
3148 starts at a specific frame number, when a capture session encompasses multiple
3149 conversation that reuse the same src/dest ip/port pairs. You can use the
3150 conversation->setup_frame returned by find_conversation with
3151 pinfo->fd->num to determine whether or not there already exists a conversation
3152 that starts at the specific frame number.
3154 /* in the dissector routine */
3156 conversation = find_conversation(pinfo->fd->num, &pinfo->src, &pinfo->dst,
3157 pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
3158 if (conversation == NULL || (conversation->setup_frame != pinfo->fd->num)) {
3159 /* It's not part of any conversation or the returned
3160 * conversation->setup_frame doesn't match the current frame
3163 conversation = conversation_new(pinfo->fd->num, &pinfo->src,
3164 &pinfo->dst, pinfo->ptype, pinfo->srcport, pinfo->destport,
3169 2.2.10 The example conversation code using conversation index field.
3171 Sometimes the conversation isn't enough to define a unique data storage
3172 value for the network traffic. For example if you are storing information
3173 about requests carried in a conversation, the request may have an
3174 identifier that is used to define the request. In this case the
3175 conversation and the identifier are required to find the data storage
3176 pointer. You can use the conversation data structure index value to
3177 uniquely define the conversation.
3179 See packet-afs.c for an example of how to use the conversation index. In
3180 this dissector multiple requests are sent in the same conversation. To store
3181 information for each request the dissector has an internal hash table based
3182 upon the conversation index and values inside the request packets.
3185 /* in the dissector routine */
3187 /* to find a request value, first lookup conversation to get index */
3188 /* then used the conversation index, and request data to find data */
3189 /* in the local hash table */
3191 conversation = find_conversation(pinfo->fd->num, &pinfo->src, &pinfo->dst,
3192 pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
3193 if (conversation == NULL) {
3194 /* It's not part of any conversation - create a new one. */
3195 conversation = conversation_new(pinfo->fd->num, &pinfo->src,
3196 &pinfo->dst, pinfo->ptype, pinfo->srcport, pinfo->destport,
3200 request_key.conversation = conversation->index;
3201 request_key.service = pntohs(&rxh->serviceId);
3202 request_key.callnumber = pntohl(&rxh->callNumber);
3204 request_val = (struct afs_request_val *)g_hash_table_lookup(
3205 afs_request_hash, &request_key);
3207 /* only allocate a new hash element when it's a request */
3209 if (!request_val && !reply)
3211 new_request_key = g_mem_chunk_alloc(afs_request_keys);
3212 *new_request_key = request_key;
3214 request_val = g_mem_chunk_alloc(afs_request_vals);
3215 request_val -> opcode = pntohl(&afsh->opcode);
3216 opcode = request_val->opcode;
3218 g_hash_table_insert(afs_request_hash, new_request_key,
3224 2.3 Dynamic conversation dissector registration.
3227 NOTE: This sections assumes that all information is available to
3228 create a complete conversation, source port/address and
3229 destination port/address. If either the destination port or
3230 address is know, see section 2.4 Dynamic server port dissector
3233 For protocols that negotiate a secondary port connection, for example
3234 packet-msproxy.c, a conversation can install a dissector to handle
3235 the secondary protocol dissection. After the conversation is created
3236 for the negotiated ports use the conversation_set_dissector to define
3237 the dissection routine.
3238 Before we create these conversations or assign a dissector to them we should
3239 first check that the conversation does not already exist and if it exists
3240 whether it is registered to our protocol or not.
3241 We should do this because it is uncommon but it does happen that multiple
3242 different protocols can use the same socketpair during different stages of
3243 an application cycle. By keeping track of the frame number a conversation
3244 was started in wireshark can still tell these different protocols apart.
3246 The second argument to conversation_set_dissector is a dissector handle,
3247 which is created with a call to create_dissector_handle or
3250 create_dissector_handle takes as arguments a pointer to the dissector
3251 function and a protocol ID as returned by proto_register_protocol;
3252 register_dissector takes as arguments a string giving a name for the
3253 dissector, a pointer to the dissector function, and a protocol ID.
3255 The protocol ID is the ID for the protocol dissected by the function.
3256 The function will not be called if the protocol has been disabled by the
3257 user; instead, the data for the protocol will be dissected as raw data.
3261 /* the handle for the dynamic dissector *
3262 static dissector_handle_t sub_dissector_handle;
3264 /* prototype for the dynamic dissector */
3265 static void sub_dissector(tvbuff_t *tvb, packet_info *pinfo,
3268 /* in the main protocol dissector, where the next dissector is setup */
3270 /* if conversation has a data field, create it and load structure */
3272 /* First check if a conversation already exists for this
3275 conversation = find_conversation(pinfo->fd->num,
3276 &pinfo->src, &pinfo->dst, protocol,
3277 src_port, dst_port, new_conv_info, 0);
3279 /* If there is no such conversation, or if there is one but for
3280 someone else's protocol then we just create a new conversation
3281 and assign our protocol to it.
3283 if ( (conversation == NULL) ||
3284 (conversation->dissector_handle != sub_dissector_handle) ) {
3285 new_conv_info = g_mem_chunk_alloc(new_conv_vals);
3286 new_conv_info->data1 = value1;
3288 /* create the conversation for the dynamic port */
3289 conversation = conversation_new(pinfo->fd->num,
3290 &pinfo->src, &pinfo->dst, protocol,
3291 src_port, dst_port, new_conv_info, 0);
3293 /* set the dissector for the new conversation */
3294 conversation_set_dissector(conversation, sub_dissector_handle);
3299 proto_register_PROTOABBREV(void)
3303 sub_dissector_handle = create_dissector_handle(sub_dissector,
3309 2.4 Dynamic server port dissector registration.
3311 NOTE: While this example used both NO_ADDR2 and NO_PORT2 to create a
3312 conversation with only one port and address set, this isn't a
3313 requirement. Either the second port or the second address can be set
3314 when the conversation is created.
3316 For protocols that define a server address and port for a secondary
3317 protocol, a conversation can be used to link a protocol dissector to
3318 the server port and address. The key is to create the new
3319 conversation with the second address and port set to the "accept
3322 Some server applications can use the same port for different protocols during
3323 different stages of a transaction. For example it might initially use SNMP
3324 to perform some discovery and later switch to use TFTP using the same port.
3325 In order to handle this properly we must first check whether such a
3326 conversation already exists or not and if it exists we also check whether the
3327 registered dissector_handle for that conversation is "our" dissector or not.
3328 If not we create a new conversation on top of the previous one and set this new
3329 conversation to use our protocol.
3330 Since wireshark keeps track of the frame number where a conversation started
3331 wireshark will still be able to keep the packets apart even though they do use
3332 the same socketpair.
3333 (See packet-tftp.c and packet-snmp.c for examples of this)
3335 There are two support routines that will allow the second port and/or
3336 address to be set later.
3338 conversation_set_port2( conversation_t *conv, guint32 port);
3339 conversation_set_addr2( conversation_t *conv, address addr);
3341 These routines will change the second address or port for the
3342 conversation. So, the server port conversation will be converted into a
3343 more complete conversation definition. Don't use these routines if you
3344 want to create a conversation between the server and client and retain the
3345 server port definition, you must create a new conversation.
3350 /* the handle for the dynamic dissector *
3351 static dissector_handle_t sub_dissector_handle;
3355 /* in the main protocol dissector, where the next dissector is setup */
3357 /* if conversation has a data field, create it and load structure */
3359 new_conv_info = g_mem_chunk_alloc(new_conv_vals);
3360 new_conv_info->data1 = value1;
3362 /* create the conversation for the dynamic server address and port */
3363 /* NOTE: The second address and port values don't matter because the */
3364 /* NO_ADDR2 and NO_PORT2 options are set. */
3366 /* First check if a conversation already exists for this
3369 conversation = find_conversation(pinfo->fd->num,
3370 &server_src_addr, 0, protocol,
3371 server_src_port, 0, NO_ADDR2 | NO_PORT_B);
3372 /* If there is no such conversation, or if there is one but for
3373 someone else's protocol then we just create a new conversation
3374 and assign our protocol to it.
3376 if ( (conversation == NULL) ||
3377 (conversation->dissector_handle != sub_dissector_handle) ) {
3378 conversation = conversation_new(pinfo->fd->num,
3379 &server_src_addr, 0, protocol,
3380 server_src_port, 0, new_conv_info, NO_ADDR2 | NO_PORT2);
3382 /* set the dissector for the new conversation */
3383 conversation_set_dissector(conversation, sub_dissector_handle);
3386 2.5 Per-packet information.
3388 Information can be stored for each data packet that is processed by the
3389 dissector. The information is added with the p_add_proto_data function and
3390 retrieved with the p_get_proto_data function. The data pointers passed into
3391 the p_add_proto_data are not managed by the proto_data routines. If you use
3392 malloc or any other dynamic memory allocation scheme, you must release the
3393 data when it isn't required.
3396 p_add_proto_data(frame_data *fd, int proto, void *proto_data)
3398 p_get_proto_data(frame_data *fd, int proto)
3401 fd - The fd pointer in the pinfo structure, pinfo->fd
3402 proto - Protocol id returned by the proto_register_protocol call
3403 during initialization
3404 proto_data - pointer to the dissector data.
3407 2.6 User Preferences.
3409 If the dissector has user options, there is support for adding these preferences
3410 to a configuration dialog.
3412 You must register the module with the preferences routine with -
3414 module_t *prefs_register_protocol(proto_id, void (*apply_cb)(void))
3416 module_t *prefs_register_protocol_subtree(const char *subtree, int id,
3417 void (*apply_cb)(void));
3420 Where: proto_id - the value returned by "proto_register_protocol()" when
3421 the protocol was registered.
3422 apply_cb - Callback routine that is called when preferences are
3423 applied. It may be NULL, which inhibits the callback.
3424 subtree - grouping preferences tree node name (several protocols can
3425 be grouped under one preferences subtree)
3427 Then you can register the fields that can be configured by the user with these
3430 /* Register a preference with an unsigned integral value. */
3431 void prefs_register_uint_preference(module_t *module, const char *name,
3432 const char *title, const char *description, guint base, guint *var);
3434 /* Register a preference with an Boolean value. */
3435 void prefs_register_bool_preference(module_t *module, const char *name,
3436 const char *title, const char *description, gboolean *var);
3438 /* Register a preference with an enumerated value. */
3439 void prefs_register_enum_preference(module_t *module, const char *name,
3440 const char *title, const char *description, gint *var,
3441 const enum_val_t *enumvals, gboolean radio_buttons)
3443 /* Register a preference with a character-string value. */
3444 void prefs_register_string_preference(module_t *module, const char *name,
3445 const char *title, const char *description, char **var)
3447 /* Register a preference with a range of unsigned integers (e.g.,
3450 void prefs_register_range_preference(module_t *module, const char *name,
3451 const char *title, const char *description, range_t *var,
3454 Where: module - Returned by the prefs_register_protocol routine
3455 name - This is appended to the name of the protocol, with a
3456 "." between them, to construct a name that identifies
3457 the field in the preference file; the name itself
3458 should not include the protocol name, as the name in
3459 the preference file will already have it
3460 title - Field title in the preferences dialog
3461 description - Comments added to the preference file above the
3463 var - pointer to the storage location that is updated when the
3464 field is changed in the preference dialog box
3465 base - Base that the unsigned integer is expected to be in,
3467 enumvals - an array of enum_val_t structures. This must be
3468 NULL-terminated; the members of that structure are:
3470 a short name, to be used with the "-o" flag - it
3471 should not contain spaces or upper-case letters,
3472 so that it's easier to put in a command line;
3474 a description, which is used in the GUI (and
3475 which, for compatibility reasons, is currently
3476 what's written to the preferences file) - it can
3477 contain spaces, capital letters, punctuation,
3480 the numerical value corresponding to that name
3482 radio_buttons - TRUE if the field is to be displayed in the
3483 preferences dialog as a set of radio buttons,
3484 FALSE if it is to be displayed as an option
3486 max_value - The maximum allowed value for a range (0 is the minimum).
3488 An example from packet-beep.c -
3490 proto_beep = proto_register_protocol("Blocks Extensible Exchange Protocol",
3495 /* Register our configuration options for BEEP, particularly our port */
3497 beep_module = prefs_register_protocol(proto_beep, proto_reg_handoff_beep);
3499 prefs_register_uint_preference(beep_module, "tcp.port", "BEEP TCP Port",
3500 "Set the port for BEEP messages (if other"
3501 " than the default of 10288)",
3502 10, &global_beep_tcp_port);
3504 prefs_register_bool_preference(beep_module, "strict_header_terminator",
3505 "BEEP Header Requires CRLF",
3506 "Specifies that BEEP requires CRLF as a "
3507 "terminator, and not just CR or LF",
3508 &global_beep_strict_term);
3510 This will create preferences "beep.tcp.port" and
3511 "beep.strict_header_terminator", the first of which is an unsigned
3512 integer and the second of which is a Boolean.
3514 Note that a warning will pop up if you've saved such preference to the
3515 preference file and you subsequently take the code out. The way to make
3516 a preference obsolete is to register it as such:
3518 /* Register a preference that used to be supported but no longer is. */
3519 void prefs_register_obsolete_preference(module_t *module,
3522 2.7 Reassembly/desegmentation for protocols running atop TCP.
3524 There are two main ways of reassembling a Protocol Data Unit (PDU) which
3525 spans across multiple TCP segments. The first approach is simpler, but
3526 assumes you are running atop of TCP when this occurs (but your dissector
3527 might run atop of UDP, too, for example), and that your PDUs consist of a
3528 fixed amount of data that includes enough information to determine the PDU
3529 length, possibly followed by additional data. The second method is more
3530 generic but requires more code and is less efficient.
3532 2.7.1 Using tcp_dissect_pdus().
3534 For the first method, you register two different dissection methods, one
3535 for the TCP case, and one for the other cases. It is a good idea to
3536 also have a dissect_PROTO_common function which will parse the generic
3537 content that you can find in all PDUs which is called from
3538 dissect_PROTO_tcp when the reassembly is complete and from
3539 dissect_PROTO_udp (or dissect_PROTO_other).
3541 To register the distinct dissector functions, consider the following
3542 example, stolen from packet-dns.c:
3544 dissector_handle_t dns_udp_handle;
3545 dissector_handle_t dns_tcp_handle;
3546 dissector_handle_t mdns_udp_handle;
3548 dns_udp_handle = create_dissector_handle(dissect_dns_udp,
3550 dns_tcp_handle = create_dissector_handle(dissect_dns_tcp,
3552 mdns_udp_handle = create_dissector_handle(dissect_mdns_udp,
3555 dissector_add("udp.port", UDP_PORT_DNS, dns_udp_handle);
3556 dissector_add("tcp.port", TCP_PORT_DNS, dns_tcp_handle);
3557 dissector_add("udp.port", UDP_PORT_MDNS, mdns_udp_handle);
3558 dissector_add("tcp.port", TCP_PORT_MDNS, dns_tcp_handle);
3560 The dissect_dns_udp function does very little work and calls
3561 dissect_dns_common, while dissect_dns_tcp calls tcp_dissect_pdus with a
3562 reference to a callback which will be called with reassembled data:
3565 dissect_dns_tcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
3567 tcp_dissect_pdus(tvb, pinfo, tree, dns_desegment, 2,
3568 get_dns_pdu_len, dissect_dns_tcp_pdu);
3571 (The dissect_dns_tcp_pdu function acts similarly to dissect_dns_udp.)
3572 The arguments to tcp_dissect_pdus are:
3574 the tvbuff pointer, packet_info pointer, and proto_tree pointer
3575 passed to the dissector;
3577 a gboolean flag indicating whether desegmentation is enabled for
3580 the number of bytes of PDU data required to determine the length
3583 a routine that takes as arguments a packet_info pointer, a tvbuff
3584 pointer and an offset value representing the offset into the tvbuff
3585 at which a PDU begins and should return - *without* throwing an
3586 exception (it is guaranteed that the number of bytes specified by the
3587 previous argument to tcp_dissect_pdus is available, but more data
3588 might not be available, so don't refer to any data past that) - the
3589 total length of the PDU, in bytes;
3591 a routine that's passed a tvbuff pointer, packet_info pointer,
3592 and proto_tree pointer, with the tvbuff containing a
3593 possibly-reassembled PDU, and that should dissect that PDU.
3595 2.7.2 Modifying the pinfo struct.
3597 The second reassembly mode is preferred when the dissector cannot determine
3598 how many bytes it will need to read in order to determine the size of a PDU.
3599 It may also be useful if your dissector needs to support reassembly from
3600 protocols other than TCP.
3602 Your dissect_PROTO will initially be passed a tvbuff containing the payload of
3603 the first packet. It should dissect as much data as it can, noting that it may
3604 contain more than one complete PDU. If the end of the provided tvbuff coincides
3605 with the end of a PDU then all is well and your dissector can just return as
3606 normal. (If it is a new-style dissector, it should return the number of bytes
3607 successfully processed.)
3609 If the dissector discovers that the end of the tvbuff does /not/ coincide with
3610 the end of a PDU, (ie, there is half of a PDU at the end of the tvbuff), it can
3611 indicate this to the parent dissector, by updating the pinfo struct. The
3612 desegment_offset field is the offset in the tvbuff at which the dissector will
3613 continue processing when next called. The desegment_len field should contain
3614 the estimated number of additional bytes required for completing the PDU. Next
3615 time your dissect_PROTO is called, it will be passed a tvbuff composed of the
3616 end of the data from the previous tvbuff together with desegment_len more bytes.
3618 If the dissector cannot tell how many more bytes it will need, it should set
3619 desegment_len=DESEGMENT_ONE_MORE_SEGMENT; it will then be called again as soon
3620 as any more data becomes available. Dissectors should set the desegment_len to a
3621 reasonable value when possible rather than always setting
3622 DESEGMENT_ONE_MORE_SEGMENT as it will generally be more efficient. Also, you
3623 *must not* set desegment_len=1 in this case, in the hope that you can change
3624 your mind later: once you return a positive value from desegment_len, your PDU
3625 boundary is set in stone.
3627 static hf_register_info hf[] = {
3629 {"C String", "c.string", FT_STRING, BASE_NONE, NULL, 0x0,
3635 * Dissect a buffer containing C strings.
3637 * @param tvb The buffer to dissect.
3638 * @param pinfo Packet Info.
3639 * @param tree The protocol tree.
3641 static void dissect_cstr(tvbuff_t * tvb, packet_info * pinfo, proto_tree * tree)
3644 while(offset < tvb_reported_length(tvb)) {
3645 gint available = tvb_reported_length_remaining(tvb, offset);
3646 gint len = tvb_strnlen(tvb, offset, available);
3649 /* we ran out of data: ask for more */
3650 pinfo->desegment_offset = offset;
3651 pinfo->desegment_len = DESEGMENT_ONE_MORE_SEGMENT;
3655 col_set_str(pinfo->cinfo, COL_INFO, "C String");
3657 len += 1; /* Add one for the '\0' */
3660 proto_tree_add_item(tree, hf_cstring, tvb, offset, len, FALSE);
3662 offset += (guint)len;
3665 /* if we get here, then the end of the tvb coincided with the end of a
3666 string. Happy days. */
3669 This simple dissector will repeatedly return DESEGMENT_ONE_MORE_SEGMENT
3670 requesting more data until the tvbuff contains a complete C string. The C string
3671 will then be added to the protocol tree. Note that there may be more
3672 than one complete C string in the tvbuff, so the dissection is done in a
3677 The ptvcursor API allows a simpler approach to writing dissectors for
3678 simple protocols. The ptvcursor API works best for protocols whose fields
3679 are static and whose format does not depend on the value of other fields.
3680 However, even if only a portion of your protocol is statically defined,
3681 then that portion could make use of ptvcursors.
3683 The ptvcursor API lets you extract data from a tvbuff, and add it to a
3684 protocol tree in one step. It also keeps track of the position in the
3685 tvbuff so that you can extract data again without having to compute any
3686 offsets --- hence the "cursor" name of the API.
3688 The three steps for a simple protocol are:
3689 1. Create a new ptvcursor with ptvcursor_new()
3690 2. Add fields with multiple calls of ptvcursor_add()
3691 3. Delete the ptvcursor with ptvcursor_free()
3693 ptvcursor offers the possibility to add subtrees in the tree as well. It can be
3694 done in very simple steps :
3695 1. Create a new subtree with ptvcursor_push_subtree(). The old subtree is
3696 pushed in a stack and the new subtree will be used by ptvcursor.
3697 2. Add fields with multiple calls of ptvcursor_add(). The fields will be
3698 added in the new subtree created at the previous step.
3699 3. Pop the previous subtree with ptvcursor_pop_subtree(). The previous
3700 subtree is again used by ptvcursor.
3701 Note that at the end of the parsing of a packet you must have popped each
3702 subtree you pushed. If it's not the case, the dissector will generate an error.
3704 To use the ptvcursor API, include the "ptvcursor.h" file. The PGM dissector
3705 is an example of how to use it. You don't need to look at it as a guide;
3706 instead, the API description here should be good enough.
3708 2.8.1 ptvcursor API.
3711 ptvcursor_new(proto_tree* tree, tvbuff_t* tvb, gint offset)
3712 This creates a new ptvcursor_t object for iterating over a tvbuff.
3713 You must call this and use this ptvcursor_t object so you can use the
3717 ptvcursor_add(ptvcursor_t* ptvc, int hf, gint length, gboolean endianness)
3718 This will extract 'length' bytes from the tvbuff and place it in
3719 the proto_tree as field 'hf', which is a registered header_field. The
3720 pointer to the proto_item that is created is passed back to you. Internally,
3721 the ptvcursor advances its cursor so the next call to ptvcursor_add
3722 starts where this call finished. The 'endianness' parameter matters for
3723 FT_UINT* and FT_INT* fields.
3726 ptvcursor_add_no_advance(ptvcursor_t* ptvc, int hf, gint length, gboolean endianness)
3727 Like ptvcursor_add, but does not advance the internal cursor.
3730 ptvcursor_advance(ptvcursor_t* ptvc, gint length)
3731 Advances the internal cursor without adding anything to the proto_tree.
3734 ptvcursor_free(ptvcursor_t* ptvc)
3735 Frees the memory associated with the ptvcursor. You must call this
3736 after your dissection with the ptvcursor API is completed.
3740 ptvcursor_push_subtree(ptvcursor_t* ptvc, proto_item* it, gint ett_subtree)
3741 Pushes the current subtree in the tree stack of the cursor, creates a new
3742 one and sets this one as the working tree.
3745 ptvcursor_pop_subtree(ptvcursor_t* ptvc);
3746 Pops a subtree in the tree stack of the cursor
3749 ptvcursor_add_with_subtree(ptvcursor_t* ptvc, int hfindex, gint length,
3750 gboolean little_endian, gint ett_subtree);
3751 Adds an item to the tree and creates a subtree.
3752 If the length is unknown, length may be defined as SUBTREE_UNDEFINED_LENGTH.
3753 In this case, at the next pop, the item length will be equal to the advancement
3754 of the cursor since the creation of the subtree.
3757 ptvcursor_add_text_with_subtree(ptvcursor_t* ptvc, gint length,
3758 gint ett_subtree, const char* format, ...);
3759 Add a text node to the tree and create a subtree.
3760 If the length is unknown, length may be defined as SUBTREE_UNDEFINED_LENGTH.
3761 In this case, at the next pop, the item length will be equal to the advancement
3762 of the cursor since the creation of the subtree.
3764 2.8.2 Miscellaneous functions.
3767 ptvcursor_tvbuff(ptvcursor_t* ptvc)
3768 Returns the tvbuff associated with the ptvcursor.
3771 ptvcursor_current_offset(ptvcursor_t* ptvc)
3772 Returns the current offset.
3775 ptvcursor_tree(ptvcursor_t* ptvc)
3776 Returns the proto_tree associated with the ptvcursor.
3779 ptvcursor_set_tree(ptvcursor_t* ptvc, proto_tree *tree)
3780 Sets a new proto_tree for the ptvcursor.
3783 ptvcursor_set_subtree(ptvcursor_t* ptvc, proto_item* it, gint ett_subtree);
3784 Creates a subtree and adds it to the cursor as the working tree but does
3785 not save the old working tree.