6 This file is a HOWTO for Wireshark developers. It describes how to start coding
7 a Wireshark protocol dissector and the use of some of the important functions
10 This file is compiled to give in depth information on Wireshark.
11 It is by no means all inclusive and complete. Please feel free to send
12 remarks and patches to the developer mailing list.
16 Before starting to develop a new dissector, a "running" Wireshark build
17 environment is required - there's no such thing as a standalone "dissector
20 How to setup such an environment is platform dependent; detailed information
21 about these steps can be found in the "Developer's Guide" (available from:
22 http://www.wireshark.org) and in the INSTALL and README files of the sources
25 0.1. General README files.
27 You'll find additional information in the following README files:
29 - README.capture - the capture engine internals
30 - README.design - Wireshark software design - incomplete
31 - README.developer - this file
32 - README.display_filter - Display Filter Engine
33 - README.idl2wrs - CORBA IDL converter
34 - README.packaging - how to distribute a software package containing WS
35 - README.regression - regression testing of WS and TS
36 - README.stats_tree - a tree statistics counting specific packets
37 - README.tapping - "tap" a dissector to get protocol specific events
38 - README.xml-output - how to work with the PDML exported output
39 - wiretap/README.developer - how to add additional capture file types to
42 0.2. Dissector related README files.
44 You'll find additional dissector related information in the following README
47 - README.binarytrees - fast access to large data collections
48 - README.heuristic - what are heuristic dissectors and how to write them
49 - README.malloc - how to obtain "memory leak free" memory
50 - README.plugins - how to "pluginize" a dissector
51 - README.python - writing a dissector in PYTHON.
52 - README.request_response_tracking - how to track req./resp. times and such
56 James Coe <jammer[AT]cin.net>
57 Gilbert Ramirez <gram[AT]alumni.rice.edu>
58 Jeff Foster <jfoste[AT]woodward.com>
59 Olivier Abad <oabad[AT]cybercable.fr>
60 Laurent Deniel <laurent.deniel[AT]free.fr>
61 Gerald Combs <gerald[AT]wireshark.org>
62 Guy Harris <guy[AT]alum.mit.edu>
63 Ulf Lamping <ulf.lamping[AT]web.de>
65 1. Setting up your protocol dissector code.
67 This section provides skeleton code for a protocol dissector. It also explains
68 the basic functions needed to enter values in the traffic summary columns,
69 add to the protocol tree, and work with registered header fields.
75 Wireshark runs on many platforms, and can be compiled with a number of
76 different compilers; here are some rules for writing code that will work
77 on multiple platforms.
79 Don't use C++-style comments (comments beginning with "//" and running
80 to the end of the line); Wireshark's dissectors are written in C, and
81 thus run through C rather than C++ compilers, and not all C compilers
82 support C++-style comments (GCC does, but IBM's C compiler for AIX, for
83 example, doesn't do so by default).
85 In general, don't use C99 features since some C compilers used to compile
86 Wireshark don't support C99 (E.G. Microsoft C).
88 Don't initialize variables in their declaration with non-constant
89 values. Not all compilers support this. E.g. don't use
90 guint32 i = somearray[2];
96 Don't use zero-length arrays; not all compilers support them. If an
97 array would have no members, just leave it out.
99 Don't declare variables in the middle of executable code; not all C
100 compilers support that. Variables should be declared outside a
101 function, or at the beginning of a function or compound statement.
103 Don't use anonymous unions; not all compilers support them.
111 } u; /* have a name here */
114 Don't use "uchar", "u_char", "ushort", "u_short", "uint", "u_int",
115 "ulong", "u_long" or "boolean"; they aren't defined on all platforms.
116 If you want an 8-bit unsigned quantity, use "guint8"; if you want an
117 8-bit character value with the 8th bit not interpreted as a sign bit,
118 use "guchar"; if you want a 16-bit unsigned quantity, use "guint16";
119 if you want a 32-bit unsigned quantity, use "guint32"; and if you want
120 an "int-sized" unsigned quantity, use "guint"; if you want a boolean,
121 use "gboolean". Use "%d", "%u", "%x", and "%o" to print those types;
122 don't use "%ld", "%lu", "%lx", or "%lo", as longs are 64 bits long on
123 many platforms, but "guint32" is 32 bits long.
125 Don't use "long" to mean "signed 32-bit integer", and don't use
126 "unsigned long" to mean "unsigned 32-bit integer"; "long"s are 64 bits
127 long on many platforms. Use "gint32" for signed 32-bit integers and use
128 "guint32" for unsigned 32-bit integers.
130 Don't use "long" to mean "signed 64-bit integer" and don't use "unsigned
131 long" to mean "unsigned 64-bit integer"; "long"s are 32 bits long on
132 many other platforms. Don't use "long long" or "unsigned long long",
133 either, as not all platforms support them; use "gint64" or "guint64",
134 which will be defined as the appropriate types for 64-bit signed and
137 On LLP64 data model systems (notably 64-bit Windows), "int" and "long"
138 are 32 bits while "size_t" and "ptrdiff_t" are 64 bits. This means that
139 the following will generate a compiler warning:
142 i = strlen("hello, sailor"); /* Compiler warning */
144 Normally, you'd just make "i" a size_t. However, many GLib and Wireshark
145 functions won't accept a size_t on LLP64:
148 char greeting[] = "hello, sailor";
149 guint byte_after_greet;
151 i = strlen(greeting);
152 byte_after_greet = tvb_get_guint8(tvb, i); /* Compiler warning */
154 Try to use the appropriate data type when you can. When you can't, you
155 will have to cast to a compatible data type, e.g.
158 char greeting[] = "hello, sailor";
159 guint byte_after_greet;
161 i = strlen(greeting);
162 byte_after_greet = tvb_get_guint8(tvb, (gint) i); /* OK */
167 char greeting[] = "hello, sailor";
168 guint byte_after_greet;
170 i = (gint) strlen(greeting);
171 byte_after_greet = tvb_get_guint8(tvb, i); /* OK */
173 See http://www.unix.org/version2/whatsnew/lp64_wp.html for more
174 information on the sizes of common types in different data models.
176 When printing or displaying the values of 64-bit integral data types,
177 don't use "%lld", "%llu", "%llx", or "%llo" - not all platforms
178 support "%ll" for printing 64-bit integral data types. Instead, for
179 GLib routines, and routines that use them, such as all the routines in
180 Wireshark that take format arguments, use G_GINT64_MODIFIER, for example:
182 proto_tree_add_text(tree, tvb, offset, 8,
183 "Sequence Number: %" G_GINT64_MODIFIER "u",
186 When specifying an integral constant that doesn't fit in 32 bits, don't
187 use "LL" at the end of the constant - not all compilers use "LL" for
188 that. Instead, put the constant in a call to the "G_GINT64_CONSTANT()"
191 G_GINT64_CONSTANT(11644473600U)
197 Don't assume that you can scan through a va_list initialized by va_start
198 more than once without closing it with va_end and re-initializing it with
199 va_start. This applies even if you're not scanning through it yourself,
200 but are calling a routine that scans through it, such as vfprintf() or
201 one of the routines in Wireshark that takes a format and a va_list as an
202 argument. You must do
204 va_start(ap, format);
205 call_routine1(xxx, format, ap);
207 va_start(ap, format);
208 call_routine2(xxx, format, ap);
212 va_start(ap, format);
213 call_routine1(xxx, format, ap);
214 call_routine2(xxx, format, ap);
217 Don't use a label without a statement following it. For example,
227 will not work with all compilers - you have to do
237 with some statement, even if it's a null statement, after the label.
239 Don't use "bzero()", "bcopy()", or "bcmp()"; instead, use the ANSI C
242 "memset()" (with zero as the second argument, so that it sets
243 all the bytes to zero);
245 "memcpy()" or "memmove()" (note that the first and second
246 arguments to "memcpy()" are in the reverse order to the
247 arguments to "bcopy()"; note also that "bcopy()" is typically
248 guaranteed to work on overlapping memory regions, while
249 "memcpy()" isn't, so if you may be copying from one region to a
250 region that overlaps it, use "memmove()", not "memcpy()" - but
251 "memcpy()" might be faster as a result of not guaranteeing
252 correct operation on overlapping memory regions);
254 and "memcmp()" (note that "memcmp()" returns 0, 1, or -1, doing
255 an ordered comparison, rather than just returning 0 for "equal"
256 and 1 for "not equal", as "bcmp()" does).
258 Not all platforms necessarily have "bzero()"/"bcopy()"/"bcmp()", and
259 those that do might not declare them in the header file on which they're
260 declared on your platform.
262 Don't use "index()" or "rindex()"; instead, use the ANSI C equivalents,
263 "strchr()" and "strrchr()". Not all platforms necessarily have
264 "index()" or "rindex()", and those that do might not declare them in the
265 header file on which they're declared on your platform.
267 Don't fetch data from packets by getting a pointer to data in the packet
268 with "tvb_get_ptr()", casting that pointer to a pointer to a structure,
269 and dereferencing that pointer. That pointer won't necessarily be aligned
270 on the proper boundary, which can cause crashes on some platforms (even
271 if it doesn't crash on an x86-based PC); furthermore, the data in a
272 packet is not necessarily in the byte order of the machine on which
273 Wireshark is running. Use the tvbuff routines to extract individual
274 items from the packet, or use "proto_tree_add_item()" and let it extract
277 Don't use structures that overlay packet data, or into which you copy
278 packet data; the C programming language does not guarantee any
279 particular alignment of fields within a structure, and even the
280 extensions that try to guarantee that are compiler-specific and not
281 necessarily supported by all compilers used to build Wireshark. Using
282 bitfields in those structures is even worse; the order of bitfields
285 Don't use "ntohs()", "ntohl()", "htons()", or "htonl()"; the header
286 files required to define or declare them differ between platforms, and
287 you might be able to get away with not including the appropriate header
288 file on your platform but that might not work on other platforms.
289 Instead, use "g_ntohs()", "g_ntohl()", "g_htons()", and "g_htonl()";
290 those are declared by <glib.h>, and you'll need to include that anyway,
291 as Wireshark header files that all dissectors must include use stuff from
294 Don't fetch a little-endian value using "tvb_get_ntohs() or
295 "tvb_get_ntohl()" and then using "g_ntohs()", "g_htons()", "g_ntohl()",
296 or "g_htonl()" on the resulting value - the g_ routines in question
297 convert between network byte order (big-endian) and *host* byte order,
298 not *little-endian* byte order; not all machines on which Wireshark runs
299 are little-endian, even though PCs are. Fetch those values using
300 "tvb_get_letohs()" and "tvb_get_letohl()".
302 Don't put a comma after the last element of an enum - some compilers may
303 either warn about it (producing extra noise) or refuse to accept it.
305 Don't include <unistd.h> without protecting it with
313 and, if you're including it to get routines such as "open()", "close()",
314 "read()", and "write()" declared, also include <io.h> if present:
320 in order to declare the Windows C library routines "_open()",
321 "_close()", "_read()", and "_write()". Your file must include <glib.h>
322 - which many of the Wireshark header files include, so you might not have
323 to include it explicitly - in order to get "open()", "close()",
324 "read()", "write()", etc. mapped to "_open()", "_close()", "_read()",
327 Do not use "open()", "rename()", "mkdir()", "stat()", "unlink()", "remove()",
328 "fopen()", "freopen()" directly. Instead use "ws_open()", "ws_rename()",
329 "ws_mkdir()", "ws_stat()", "ws_unlink()", "ws_remove()", "ws_fopen()",
330 "ws_freopen()": these wrapper functions change the path and file name from
331 UTF8 to UTF16 on Windows allowing the functions to work correctly when the
332 path or file name contain non-ASCII characters.
334 When opening a file with "ws_fopen()", "ws_freopen()", or "ws_fdopen()", if
335 the file contains ASCII text, use "r", "w", "a", and so on as the open mode
336 - but if it contains binary data, use "rb", "wb", and so on. On
337 Windows, if a file is opened in a text mode, writing a byte with the
338 value of octal 12 (newline) to the file causes two bytes, one with the
339 value octal 15 (carriage return) and one with the value octal 12, to be
340 written to the file, and causes bytes with the value octal 15 to be
341 discarded when reading the file (to translate between C's UNIX-style
342 lines that end with newline and Windows' DEC-style lines that end with
343 carriage return/line feed).
345 In addition, that also means that when opening or creating a binary
346 file, you must use "ws_open()" (with O_CREAT and possibly O_TRUNC if the
347 file is to be created if it doesn't exist), and OR in the O_BINARY flag.
348 That flag is not present on most, if not all, UNIX systems, so you must
355 to properly define it for UNIX (it's not necessary on UNIX).
357 Don't use forward declarations of static arrays without a specified size
358 in a fashion such as this:
360 static const value_string foo_vals[];
364 static const value_string foo_vals[] = {
371 as some compilers will reject the first of those statements. Instead,
372 initialize the array at the point at which it's first declared, so that
375 Don't put a comma after the last tuple of an initializer of an array.
377 For #define names and enum member names, prefix the names with a tag so
378 as to avoid collisions with other names - this might be more of an issue
379 on Windows, as it appears to #define names such as DELETE and
382 Don't use the "numbered argument" feature that many UNIX printf's
385 g_snprintf(add_string, 30, " - (%1$d) (0x%1$04x)", value);
387 as not all UNIX printf's implement it, and Windows printf doesn't appear
388 to implement it. Use something like
390 g_snprintf(add_string, 30, " - (%d) (0x%04x)", value, value);
394 Don't use "variadic macros", such as
396 #define DBG(format, args...) fprintf(stderr, format, ## args)
398 as not all C compilers support them. Use macros that take a fixed
399 number of arguments, such as
401 #define DBG0(format) fprintf(stderr, format)
402 #define DBG1(format, arg1) fprintf(stderr, format, arg1)
403 #define DBG2(format, arg1, arg2) fprintf(stderr, format, arg1, arg2)
409 #define DBG(args) printf args
415 as that's not supported by all compilers.
417 snprintf() -> g_snprintf()
418 snprintf() is not available on all platforms, so it's a good idea to use the
419 g_snprintf() function declared by <glib.h> instead.
421 tmpnam() -> mkstemp()
422 tmpnam is insecure and should not be used any more. Wireshark brings its
423 own mkstemp implementation for use on platforms that lack mkstemp.
424 Note: mkstemp does not accept NULL as a parameter.
426 The pointer returned by a call to "tvb_get_ptr()" is not guaranteed to be
427 aligned on any particular byte boundary; this means that you cannot
428 safely cast it to any data type other than a pointer to "char",
429 "unsigned char", "guint8", or other one-byte data types. You cannot,
430 for example, safely cast it to a pointer to a structure, and then access
431 the structure members directly; on some systems, unaligned accesses to
432 integral data types larger than 1 byte, and floating-point data types,
433 cause a trap, which will, at best, result in the OS slowly performing an
434 unaligned access for you, and will, on at least some platforms, cause
435 the program to be terminated.
437 Wireshark supports platforms with GLib 2.14[.x]/GTK+ 2.12[.x] or newer.
438 If a Glib/GTK+ mechanism is available only in Glib/GTK+ versions newer
439 than 2.14/2.12 then use "#if GLIB_CHECK_VERSION(...)" or "#if
440 GTK_CHECK_VERSION(...)" to conditionally compile code using that
443 When different code must be used on UN*X and Win32, use a #if or #ifdef
444 that tests _WIN32, not WIN32. Try to write code portably whenever
445 possible, however; note that there are some routines in Wireshark with
446 platform-dependent implementations and platform-independent APIs, such
447 as the routines in epan/filesystem.c, allowing the code that calls it to
448 be written portably without #ifdefs.
450 1.1.2 String handling
452 Do not use functions such as strcat() or strcpy().
453 A lot of work has been done to remove the existing calls to these functions and
454 we do not want any new callers of these functions.
456 Instead use g_snprintf() since that function will if used correctly prevent
457 buffer overflows for large strings.
459 When using a buffer to create a string, do not use a buffer stored on the stack.
460 I.e. do not use a buffer declared as
464 instead allocate a buffer dynamically using the string-specific or plain emem
465 routines (see README.malloc) such as
467 emem_strbuf_t *strbuf;
468 strbuf = ep_strbuf_new_label("");
469 ep_strbuf_append_printf(strbuf, ...
475 #define MAX_BUFFER 1024
476 buffer=ep_alloc(MAX_BUFFER);
479 g_snprintf(buffer, MAX_BUFFER, ...
481 This avoids the stack from being corrupted in case there is a bug in your code
482 that accidentally writes beyond the end of the buffer.
485 If you write a routine that will create and return a pointer to a filled in
486 string and if that buffer will not be further processed or appended to after
487 the routine returns (except being added to the proto tree),
488 do not preallocate the buffer to fill in and pass as a parameter instead
489 pass a pointer to a pointer to the function and return a pointer to an
490 emem allocated buffer that will be automatically freed. (see README.malloc)
492 I.e. do not write code such as
494 foo_to_str(char *string, ... ){
500 foo_to_str(buffer, ...
501 proto_tree_add_text(... buffer ...
503 instead write the code as
505 foo_to_str(char **buffer, ...
507 *buffer=ep_alloc(MAX_BUFFER);
513 foo_to_str(&buffer, ...
514 proto_tree_add_text(... *buffer ...
516 Use ep_ allocated buffers. They are very fast and nice. These buffers are all
517 automatically free()d when the dissection of the current packet ends so you
518 don't have to worry about free()ing them explicitly in order to not leak memory.
519 Please read README.malloc.
521 Don't use non-ASCII characters in source files; not all compiler
522 environments will be using the same encoding for non-ASCII characters,
523 and at least one compiler (Microsoft's Visual C) will, in environments
524 with double-byte character encodings, such as many Asian environments,
525 fail if it sees a byte sequence in a source file that doesn't correspond
526 to a valid character. This causes source files using either an ISO
527 8859/n single-byte character encoding or UTF-8 to fail to compile. Even
528 if the compiler doesn't fail, there is no guarantee that the compiler,
529 or a developer's text editor, will interpret the characters the way you
530 intend them to be interpreted.
534 Wireshark is not guaranteed to read only network traces that contain correctly-
535 formed packets. Wireshark is commonly used to track down networking
536 problems, and the problems might be due to a buggy protocol implementation
537 sending out bad packets.
539 Therefore, protocol dissectors not only have to be able to handle
540 correctly-formed packets without, for example, crashing or looping
541 infinitely, they also have to be able to handle *incorrectly*-formed
542 packets without crashing or looping infinitely.
544 Here are some suggestions for making dissectors more robust in the face
545 of incorrectly-formed packets:
547 Do *NOT* use "g_assert()" or "g_assert_not_reached()" in dissectors.
548 *NO* value in a packet's data should be considered "wrong" in the sense
549 that it's a problem with the dissector if found; if it cannot do
550 anything else with a particular value from a packet's data, the
551 dissector should put into the protocol tree an indication that the
552 value is invalid, and should return. The "expert" mechanism should be
553 used for that purpose.
555 If there is a case where you are checking not for an invalid data item
556 in the packet, but for a bug in the dissector (for example, an
557 assumption being made at a particular point in the code about the
558 internal state of the dissector), use the DISSECTOR_ASSERT macro for
559 that purpose; this will put into the protocol tree an indication that
560 the dissector has a bug in it, and will not crash the application.
562 If you are allocating a chunk of memory to contain data from a packet,
563 or to contain information derived from data in a packet, and the size of
564 the chunk of memory is derived from a size field in the packet, make
565 sure all the data is present in the packet before allocating the buffer.
568 1) Wireshark won't leak that chunk of memory if an attempt to
569 fetch data not present in the packet throws an exception.
573 2) it won't crash trying to allocate an absurdly-large chunk of
574 memory if the size field has a bogus large value.
576 If you're fetching into such a chunk of memory a string from the buffer,
577 and the string has a specified size, you can use "tvb_get_*_string()",
578 which will check whether the entire string is present before allocating
579 a buffer for the string, and will also put a trailing '\0' at the end of
582 If you're fetching into such a chunk of memory a 2-byte Unicode string
583 from the buffer, and the string has a specified size, you can use
584 "tvb_get_ephemeral_faked_unicode()", which will check whether the entire
585 string is present before allocating a buffer for the string, and will also
586 put a trailing '\0' at the end of the buffer. The resulting string will be
587 a sequence of single-byte characters; the only Unicode characters that
588 will be handled correctly are those in the ASCII range. (Wireshark's
589 ability to handle non-ASCII strings is limited; it needs to be
592 If you're fetching into such a chunk of memory a sequence of bytes from
593 the buffer, and the sequence has a specified size, you can use
594 "tvb_memdup()", which will check whether the entire sequence is present
595 before allocating a buffer for it.
597 Otherwise, you can check whether the data is present by using
598 "tvb_ensure_bytes_exist()" or by getting a pointer to the data by using
599 "tvb_get_ptr()", although note that there might be problems with using
600 the pointer from "tvb_get_ptr()" (see the item on this in the
601 Portability section above, and the next item below).
603 Note also that you should only fetch string data into a fixed-length
604 buffer if the code ensures that no more bytes than will fit into the
605 buffer are fetched ("the protocol ensures" isn't good enough, as
606 protocol specifications can't ensure only packets that conform to the
607 specification will be transmitted or that only packets for the protocol
608 in question will be interpreted as packets for that protocol by
609 Wireshark). If there's no maximum length of string data to be fetched,
610 routines such as "tvb_get_*_string()" are safer, as they allocate a buffer
611 large enough to hold the string. (Note that some variants of this call
612 require you to free the string once you're finished with it.)
614 If you have gotten a pointer using "tvb_get_ptr()", you must make sure
615 that you do not refer to any data past the length passed as the last
616 argument to "tvb_get_ptr()"; while the various "tvb_get" routines
617 perform bounds checking and throw an exception if you refer to data not
618 available in the tvbuff, direct references through a pointer gotten from
619 "tvb_get_ptr()" do not do any bounds checking.
621 If you have a loop that dissects a sequence of items, each of which has
622 a length field, with the offset in the tvbuff advanced by the length of
623 the item, then, if the length field is the total length of the item, and
624 thus can be zero, you *MUST* check for a zero-length item and abort the
625 loop if you see one. Otherwise, a zero-length item could cause the
626 dissector to loop infinitely. You should also check that the offset,
627 after having the length added to it, is greater than the offset before
628 the length was added to it, if the length field is greater than 24 bits
629 long, so that, if the length value is *very* large and adding it to the
630 offset causes an overflow, that overflow is detected.
634 for (i = {start}; i < {end}; i++)
636 loop, make sure that the type of the loop index variable is large enough
637 to hold the maximum {end} value plus 1; otherwise, the loop index
638 variable can overflow before it ever reaches its maximum value. In
639 particular, be very careful when using gint8, guint8, gint16, or guint16
640 variables as loop indices; you almost always want to use an "int"/"gint"
641 or "unsigned int"/"guint" as the loop index rather than a shorter type.
643 If you are fetching a length field from the buffer, corresponding to the
644 length of a portion of the packet, and subtracting from that length a
645 value corresponding to the length of, for example, a header in the
646 packet portion in question, *ALWAYS* check that the value of the length
647 field is greater than or equal to the length you're subtracting from it,
648 and report an error in the packet and stop dissecting the packet if it's
649 less than the length you're subtracting from it. Otherwise, the
650 resulting length value will be negative, which will either cause errors
651 in the dissector or routines called by the dissector, or, if the value
652 is interpreted as an unsigned integer, will cause the value to be
653 interpreted as a very large positive value.
655 Any tvbuff offset that is added to as processing is done on a packet
656 should be stored in a 32-bit variable, such as an "int"; if you store it
657 in an 8-bit or 16-bit variable, you run the risk of the variable
660 sprintf() -> g_snprintf()
661 Prevent yourself from using the sprintf() function, as it does not test the
662 length of the given output buffer and might be writing into unintended memory
663 areas. This function is one of the main causes of security problems like buffer
664 exploits and many other bugs that are very hard to find. It's much better to
665 use the g_snprintf() function declared by <glib.h> instead.
667 You should test your dissector against incorrectly-formed packets. This
668 can be done using the randpkt and editcap utilities that come with the
669 Wireshark distribution. Testing using randpkt can be done by generating
670 output at the same layer as your protocol, and forcing Wireshark/TShark
671 to decode it as your protocol, e.g. if your protocol sits on top of UDP:
673 randpkt -c 50000 -t dns randpkt.pcap
674 tshark -nVr randpkt.pcap -d udp.port==53,<myproto>
676 Testing using editcap can be done using preexisting capture files and the
677 "-E" flag, which introduces errors in a capture file. E.g.:
679 editcap -E 0.03 infile.pcap outfile.pcap
680 tshark -nVr outfile.pcap
682 The script fuzz-test.sh is available to help automate these tests.
684 1.1.4 Name convention.
686 Wireshark uses the underscore_convention rather than the InterCapConvention for
687 function names, so new code should probably use underscores rather than
688 intercaps for functions and variable names. This is especially important if you
689 are writing code that will be called from outside your code. We are just
690 trying to keep things consistent for other developers.
692 1.1.5 White space convention.
694 Avoid using tab expansions different from 8 column widths, as not all
695 text editors in use by the developers support this. For a detailed
696 discussion of tabs, spaces, and indentation, see
698 http://www.jwz.org/doc/tabs-vs-spaces.html
700 When creating a new file, you are free to choose an indentation logic.
701 Most of the files in Wireshark tend to use 2-space or 4-space
702 indentation. You are encouraged to write a short comment on the
703 indentation logic at the beginning of this new file, especially if
704 you're using non-mod-8 tabs. The tabs-vs-spaces document above provides
705 examples of Emacs and vi modelines for this purpose.
707 Please do not leave trailing whitespace (spaces/tabs) on lines.
709 When editing an existing file, try following the existing indentation
710 logic and even if it very tempting, never ever use a restyler/reindenter
711 utility on an existing file. If you run across wildly varying
712 indentation styles within the same file, it might be helpful to send a
713 note to wireshark-dev for guidance.
715 1.1.6 Compiler warnings
717 You should write code that is free of compiler warnings. Such warnings will
718 often indicate questionable code and sometimes even real bugs, so it's best
719 to avoid warnings at all.
721 The compiler flags in the Makefiles are set to "treat warnings as errors",
722 so your code won't even compile when warnings occur.
726 Wireshark requires certain things when setting up a protocol dissector.
727 Below is skeleton code for a dissector that you can copy to a file and
728 fill in. Your dissector should follow the naming convention of packet-
729 followed by the abbreviated name for the protocol. It is recommended
730 that where possible you keep to the IANA abbreviated name for the
731 protocol, if there is one, or a commonly-used abbreviation for the
734 Usually, you will put your newly created dissector file into the directory
735 epan/dissectors, just like all the other packet-....c files already in there.
737 Also, please add your dissector file to the corresponding makefiles,
738 described in section "1.9 Editing Makefile.common and CMakeLists.txt
739 to add your dissector" below.
741 Dissectors that use the dissector registration to register with a lower level
742 dissector don't need to define a prototype in the .h file. For other
743 dissectors the main dissector routine should have a prototype in a header
744 file whose name is "packet-", followed by the abbreviated name for the
745 protocol, followed by ".h"; any dissector file that calls your dissector
746 should be changed to include that file.
748 You may not need to include all the headers listed in the skeleton
749 below, and you may need to include additional headers.
751 The stdio.h, stdlib.h and string.h header files should be included only as needed.
754 The "$Id$" in the comment will be updated by Subversion when the file is
757 When creating a new file, it is fine to just write "$Id$" as Subversion will
758 automatically fill in the identifier at the time the file will be added to the
759 SVN repository (committed).
761 ------------------------------------Cut here------------------------------------
762 /* packet-PROTOABBREV.c
763 * Routines for PROTONAME dissection
764 * Copyright 201x, YOUR_NAME <YOUR_EMAIL_ADDRESS>
768 * Wireshark - Network traffic analyzer
769 * By Gerald Combs <gerald@wireshark.org>
770 * Copyright 1998 Gerald Combs
772 * Copied from WHATEVER_FILE_YOU_USED (where "WHATEVER_FILE_YOU_USED"
773 * is a dissector file; if you just copied this from README.developer,
774 * don't bother with the "Copied from" - you don't even need to put
775 * in a "Copied from" if you copied an existing dissector, especially
776 * if the bulk of the code in the new dissector is your code)
778 * This program is free software; you can redistribute it and/or modify
779 * it under the terms of the GNU General Public License as published by
780 * the Free Software Foundation; either version 2 of the License, or
781 * (at your option) any later version.
783 * This program is distributed in the hope that it will be useful,
784 * but WITHOUT ANY WARRANTY; without even the implied warranty of
785 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
786 * GNU General Public License for more details.
788 * You should have received a copy of the GNU General Public License along
789 * with this program; if not, write to the Free Software Foundation, Inc.,
790 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
798 /* Include only as needed */
806 #include <epan/packet.h>
807 #include <epan/prefs.h>
809 /* IF PROTO exposes code to other dissectors, then it must be exported
810 in a header file. If not, a header file is not needed at all. */
811 #include "packet-PROTOABBREV.h"
813 /* Forward declaration we need below (if using proto_reg_handoff...
814 as a prefs callback) */
815 void proto_reg_handoff_PROTOABBREV(void);
817 /* Initialize the protocol and registered fields */
818 static int proto_PROTOABBREV = -1;
819 static int hf_PROTOABBREV_FIELDABBREV = -1;
821 /* Global sample preference ("controls" display of numbers) */
822 static gboolean gPREF_HEX = FALSE;
823 /* Global sample port pref */
824 static guint gPORT_PREF = 1234;
826 /* Initialize the subtree pointers */
827 static gint ett_PROTOABBREV = -1;
829 /* Code to actually dissect the packets */
831 dissect_PROTOABBREV(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
834 /* Set up structures needed to add the protocol subtree and manage it */
836 proto_tree *PROTOABBREV_tree;
838 /* First, if at all possible, do some heuristics to check if the packet cannot
839 * possibly belong to your protocol. This is especially important for
840 * protocols directly on top of TCP or UDP where port collisions are
841 * common place (e.g., even though your protocol uses a well known port,
842 * someone else may set up, for example, a web server on that port which,
843 * if someone analyzed that web server's traffic in Wireshark, would result
844 * in Wireshark handing an HTTP packet to your dissector). For example:
846 /* Check that there's enough data */
847 if (tvb_length(tvb) < /* your protocol's smallest packet size */)
850 /* Get some values from the packet header, probably using tvb_get_*() */
851 if ( /* these values are not possible in PROTONAME */ )
852 /* This packet does not appear to belong to PROTONAME.
853 * Return 0 to give another dissector a chance to dissect it.
857 /* Make entries in Protocol column and Info column on summary display */
858 col_set_str(pinfo->cinfo, COL_PROTOCOL, "PROTOABBREV");
860 /* This field shows up as the "Info" column in the display; you should use
861 it, if possible, to summarize what's in the packet, so that a user looking
862 at the list of packets can tell what type of packet it is. See section 1.5
863 for more information.
865 If you are setting the column to a constant string, use "col_set_str()",
866 as it's more efficient than the other "col_set_XXX()" calls.
868 If you're setting it to a string you've constructed, or will be
869 appending to the column later, use "col_add_str()".
871 "col_add_fstr()" can be used instead of "col_add_str()"; it takes
872 "printf()"-like arguments. Don't use "col_add_fstr()" with a format
873 string of "%s" - just use "col_add_str()" or "col_set_str()", as it's
874 more efficient than "col_add_fstr()".
876 If you will be fetching any data from the packet before filling in
877 the Info column, clear that column first, in case the calls to fetch
878 data from the packet throw an exception because they're fetching data
879 past the end of the packet, so that the Info column doesn't have data
880 left over from the previous dissector; do
882 col_clear(pinfo->cinfo, COL_INFO);
886 col_set_str(pinfo->cinfo, COL_INFO, "XXX Request");
888 /* A protocol dissector may be called in 2 different ways - with, or
889 without a non-null "tree" argument.
891 If the proto_tree argument is null, Wireshark does not need to use
892 the protocol tree information from your dissector, and therefore is
893 passing the dissector a null "tree" argument so that it doesn't
894 need to do work necessary to build the protocol tree.
896 In the interest of speed, if "tree" is NULL, avoid building a
897 protocol tree and adding stuff to it, or even looking at any packet
898 data needed only if you're building the protocol tree, if possible.
900 Note, however, that you must fill in column information, create
901 conversations, reassemble packets, build any other persistent state
902 needed for dissection, and call subdissectors regardless of whether
903 "tree" is NULL or not. This might be inconvenient to do without
904 doing most of the dissection work; the routines for adding items to
905 the protocol tree can be passed a null protocol tree pointer, in
906 which case they'll return a null item pointer, and
907 "proto_item_add_subtree()" returns a null tree pointer if passed a
908 null item pointer, so, if you're careful not to dereference any null
909 tree or item pointers, you can accomplish this by doing all the
910 dissection work. This might not be as efficient as skipping that
911 work if you're not building a protocol tree, but if the code would
912 have a lot of tests whether "tree" is null if you skipped that work,
913 you might still be better off just doing all that work regardless of
914 whether "tree" is null or not.
916 Note also that there is no guarantee, the first time the dissector is
917 called, whether "tree" will be null or not; your dissector must work
918 correctly, building or updating whatever state information is
919 necessary, in either case. */
922 /* NOTE: The offset and length values in the call to
923 "proto_tree_add_item()" define what data bytes to highlight in the hex
924 display window when the line in the protocol tree display
925 corresponding to that item is selected.
927 Supplying a length of -1 is the way to highlight all data from the
928 offset to the end of the packet. */
930 /* create display subtree for the protocol */
931 ti = proto_tree_add_item(tree, proto_PROTOABBREV, tvb, 0, -1, ENC_NA);
933 PROTOABBREV_tree = proto_item_add_subtree(ti, ett_PROTOABBREV);
935 /* add an item to the subtree, see section 1.6 for more information */
936 proto_tree_add_item(PROTOABBREV_tree,
937 hf_PROTOABBREV_FIELDABBREV, tvb, offset, len, ENC_xxx);
940 /* Continue adding tree items to process the packet here */
945 /* If this protocol has a sub-dissector call it here, see section 1.8 */
947 /* Return the amount of data this dissector was able to dissect */
948 return tvb_length(tvb);
952 /* Register the protocol with Wireshark */
954 /* this format is require because a script is used to build the C function
955 that calls all the protocol registration.
959 proto_register_PROTOABBREV(void)
961 module_t *PROTOABBREV_module;
963 /* Setup list of header fields See Section 1.6.1 for details*/
964 static hf_register_info hf[] = {
965 { &hf_PROTOABBREV_FIELDABBREV,
966 { "FIELDNAME", "PROTOABBREV.FIELDABBREV",
967 FIELDTYPE, FIELDDISPLAY, FIELDCONVERT, BITMASK,
968 "FIELDDESCR", HFILL }
972 /* Setup protocol subtree array */
973 static gint *ett[] = {
977 /* Register the protocol name and description */
978 proto_PROTOABBREV = proto_register_protocol("PROTONAME",
979 "PROTOSHORTNAME", "PROTOABBREV");
981 /* Required function calls to register the header fields and subtrees used */
982 proto_register_field_array(proto_PROTOABBREV, hf, array_length(hf));
983 proto_register_subtree_array(ett, array_length(ett));
985 /* Register preferences module (See Section 2.6 for more on preferences) */
986 /* (Registration of a prefs callback is not required if there are no */
987 /* prefs-dependent registration functions (eg: a port pref). */
988 /* See proto_reg_handoff below. */
989 /* If a prefs callback is not needed, use NULL instead of */
990 /* proto_reg_handoff_PROTOABBREV in the following). */
991 PROTOABBREV_module = prefs_register_protocol(proto_PROTOABBREV,
992 proto_reg_handoff_PROTOABBREV);
994 /* Register preferences module under preferences subtree.
995 Use this function instead of prefs_register_protocol if you want to group
996 preferences of several protocols under one preferences subtree.
997 Argument subtree identifies grouping tree node name, several subnodes can be
998 specified using slash '/' (e.g. "OSI/X.500" - protocol preferences will be
999 accessible under Protocols->OSI->X.500-><PROTOSHORTNAME> preferences node.
1001 PROTOABBREV_module = prefs_register_protocol_subtree(const char *subtree,
1002 proto_PROTOABBREV, proto_reg_handoff_PROTOABBREV);
1004 /* Register a sample preference */
1005 prefs_register_bool_preference(PROTOABBREV_module, "show_hex",
1006 "Display numbers in Hex",
1007 "Enable to display numerical values in hexadecimal.",
1010 /* Register a sample port preference */
1011 prefs_register_uint_preference(PROTOABBREV_module, "tcp.port", "PROTOABBREV TCP Port",
1012 " PROTOABBREV TCP port if other than the default",
1017 /* If this dissector uses sub-dissector registration add a registration routine.
1018 This exact format is required because a script is used to find these
1019 routines and create the code that calls these routines.
1021 If this function is registered as a prefs callback (see prefs_register_protocol
1022 above) this function is also called by preferences whenever "Apply" is pressed;
1023 In that case, it should accommodate being called more than once.
1025 This form of the reg_handoff function is used if if you perform
1026 registration functions which are dependent upon prefs. See below
1027 for a simpler form which can be used if there are no
1028 prefs-dependent registration functions.
1031 proto_reg_handoff_PROTOABBREV(void)
1033 static gboolean initialized = FALSE;
1034 static dissector_handle_t PROTOABBREV_handle;
1035 static int currentPort;
1039 /* Use new_create_dissector_handle() to indicate that dissect_PROTOABBREV()
1040 * returns the number of bytes it dissected (or 0 if it thinks the packet
1041 * does not belong to PROTONAME).
1043 PROTOABBREV_handle = new_create_dissector_handle(dissect_PROTOABBREV,
1049 If you perform registration functions which are dependent upon
1050 prefs the you should de-register everything which was associated
1051 with the previous settings and re-register using the new prefs
1052 settings here. In general this means you need to keep track of
1053 the PROTOABBREV_handle and the value the preference had at the time
1054 you registered. The PROTOABBREV_handle value and the value of the
1055 preference can be saved using local statics in this
1056 function (proto_reg_handoff).
1059 dissector_delete_uint("tcp.port", currentPort, PROTOABBREV_handle);
1062 currentPort = gPORT_PREF;
1064 dissector_add_uint("tcp.port", currentPort, PROTOABBREV_handle);
1069 /* Simple form of proto_reg_handoff_PROTOABBREV which can be used if there are
1070 no prefs-dependent registration function calls.
1074 proto_reg_handoff_PROTOABBREV(void)
1076 dissector_handle_t PROTOABBREV_handle;
1078 /* Use new_create_dissector_handle() to indicate that dissect_PROTOABBREV()
1079 * returns the number of bytes it dissected (or 0 if it thinks the packet
1080 * does not belong to PROTONAME).
1082 PROTOABBREV_handle = new_create_dissector_handle(dissect_PROTOABBREV,
1084 dissector_add_uint("PARENT_SUBFIELD", ID_VALUE, PROTOABBREV_handle);
1090 * Editor modelines - http://www.wireshark.org/tools/modelines.html
1095 * indent-tabs-mode: nil
1098 * vi: set shiftwidth=4 tabstop=8 expandtab:
1099 * :indentSize=4:tabSize=8:noTabs=true:
1103 ------------------------------------Cut here------------------------------------
1105 1.3 Explanation of needed substitutions in code skeleton.
1107 In the above code block the following strings should be substituted with
1110 YOUR_NAME Your name, of course. You do want credit, don't you?
1111 It's the only payment you will receive....
1112 YOUR_EMAIL_ADDRESS Keep those cards and letters coming.
1113 WHATEVER_FILE_YOU_USED Add this line if you are using another file as a
1115 PROTONAME The name of the protocol; this is displayed in the
1116 top-level protocol tree item for that protocol.
1117 PROTOSHORTNAME An abbreviated name for the protocol; this is displayed
1118 in the "Preferences" dialog box if your dissector has
1119 any preferences, in the dialog box of enabled protocols,
1120 and in the dialog box for filter fields when constructing
1121 a filter expression.
1122 PROTOABBREV A name for the protocol for use in filter expressions;
1123 it shall contain only lower-case letters, digits, and
1125 FIELDNAME The displayed name for the header field.
1126 FIELDABBREV The abbreviated name for the header field. (NO SPACES)
1127 FIELDTYPE FT_NONE, FT_BOOLEAN, FT_UINT8, FT_UINT16, FT_UINT24,
1128 FT_UINT32, FT_UINT64, FT_INT8, FT_INT16, FT_INT24, FT_INT32,
1129 FT_INT64, FT_FLOAT, FT_DOUBLE, FT_ABSOLUTE_TIME,
1130 FT_RELATIVE_TIME, FT_STRING, FT_STRINGZ, FT_EUI64,
1131 FT_UINT_STRING, FT_ETHER, FT_BYTES, FT_UINT_BYTES, FT_IPv4,
1132 FT_IPv6, FT_IPXNET, FT_FRAMENUM, FT_PROTOCOL, FT_GUID, FT_OID
1133 FIELDDISPLAY For FT_UINT{8,16,24,32,64} and FT_INT{8,16,24,32,64):
1135 BASE_DEC, BASE_HEX, BASE_OCT, BASE_DEC_HEX, BASE_HEX_DEC,
1136 or BASE_CUSTOM, possibly ORed with BASE_RANGE_STRING
1138 For FT_ABSOLUTE_TIME:
1140 ABSOLUTE_TIME_LOCAL, ABSOLUTE_TIME_UTC, or
1141 ABSOLUTE_TIME_DOY_UTC
1143 For FT_BOOLEAN if BITMASK is non-zero:
1145 Number of bits in the field containing the FT_BOOLEAN
1148 For all other types:
1151 FIELDCONVERT VALS(x), RVALS(x), TFS(x), NULL
1152 BITMASK Usually 0x0 unless using the TFS(x) field conversion.
1153 FIELDDESCR A brief description of the field, or NULL. [Please do not use ""].
1154 PARENT_SUBFIELD Lower level protocol field used for lookup, i.e. "tcp.port"
1155 ID_VALUE Lower level protocol field value that identifies this protocol
1156 For example the TCP or UDP port number
1158 If, for example, PROTONAME is "Internet Bogosity Discovery Protocol",
1159 PROTOSHORTNAME would be "IBDP", and PROTOABBREV would be "ibdp". Try to
1160 conform with IANA names.
1162 1.4 The dissector and the data it receives.
1167 This is only needed if the dissector doesn't use self-registration to
1168 register itself with the lower level dissector, or if the protocol dissector
1169 wants/needs to expose code to other subdissectors.
1171 The dissector must be declared exactly as follows in the file
1172 packet-PROTOABBREV.h:
1175 dissect_PROTOABBREV(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree);
1178 1.4.2 Extracting data from packets.
1180 NOTE: See the file /epan/tvbuff.h for more details.
1182 The "tvb" argument to a dissector points to a buffer containing the raw
1183 data to be analyzed by the dissector; for example, for a protocol
1184 running atop UDP, it contains the UDP payload (but not the UDP header,
1185 or any protocol headers above it). A tvbuffer is an opaque data
1186 structure, the internal data structures are hidden and the data must be
1187 accessed via the tvbuffer accessors.
1191 Bit accessors for a maximum of 8-bits, 16-bits 32-bits and 64-bits:
1193 guint8 tvb_get_bits8(tvbuff_t *tvb, gint bit_offset, gint no_of_bits);
1194 guint16 tvb_get_bits16(tvbuff_t *tvb, gint bit_offset, gint no_of_bits,gboolean little_endian);
1195 guint32 tvb_get_bits32(tvbuff_t *tvb, gint bit_offset, gint no_of_bits,gboolean little_endian);
1196 guint64 tvb_get_bits64(tvbuff_t *tvb, gint bit_offset, gint no_of_bits,gboolean little_endian);
1198 Single-byte accessor:
1200 guint8 tvb_get_guint8(tvbuff_t*, gint offset);
1202 Network-to-host-order accessors for 16-bit integers (guint16), 24-bit
1203 integers, 32-bit integers (guint32), 40-bit integers, 48-bit integers,
1204 56-bit integers and 64-bit integers (guint64):
1206 guint16 tvb_get_ntohs(tvbuff_t*, gint offset);
1207 guint32 tvb_get_ntoh24(tvbuff_t*, gint offset);
1208 guint32 tvb_get_ntohl(tvbuff_t*, gint offset);
1209 guint64 tvb_get_ntoh40(tvbuff_t*, gint offset);
1210 guint64 tvb_get_ntoh48(tvbuff_t*, gint offset);
1211 guint64 tvb_get_ntoh56(tvbuff_t*, gint offset);
1212 guint64 tvb_get_ntoh64(tvbuff_t*, gint offset);
1214 Network-to-host-order accessors for single-precision and
1215 double-precision IEEE floating-point numbers:
1217 gfloat tvb_get_ntohieee_float(tvbuff_t*, gint offset);
1218 gdouble tvb_get_ntohieee_double(tvbuff_t*, gint offset);
1220 Little-Endian-to-host-order accessors for 16-bit integers (guint16),
1221 24-bit integers, 32-bit integers (guint32), 40-bit integers, 48-bit
1222 integers, 56-bit integers, and 64-bit integers (guint64):
1224 guint16 tvb_get_letohs(tvbuff_t*, gint offset);
1225 guint32 tvb_get_letoh24(tvbuff_t*, gint offset);
1226 guint32 tvb_get_letohl(tvbuff_t*, gint offset);
1227 guint64 tvb_get_letoh40(tvbuff_t*, gint offset);
1228 guint64 tvb_get_letoh48(tvbuff_t*, gint offset);
1229 guint64 tvb_get_letoh56(tvbuff_t*, gint offset);
1230 guint64 tvb_get_letoh64(tvbuff_t*, gint offset);
1232 Little-Endian-to-host-order accessors for single-precision and
1233 double-precision IEEE floating-point numbers:
1235 gfloat tvb_get_letohieee_float(tvbuff_t*, gint offset);
1236 gdouble tvb_get_letohieee_double(tvbuff_t*, gint offset);
1238 Accessors for IPv4 and IPv6 addresses:
1240 guint32 tvb_get_ipv4(tvbuff_t*, gint offset);
1241 void tvb_get_ipv6(tvbuff_t*, gint offset, struct e_in6_addr *addr);
1243 NOTE: IPv4 addresses are not to be converted to host byte order before
1244 being passed to "proto_tree_add_ipv4()". You should use "tvb_get_ipv4()"
1245 to fetch them, not "tvb_get_ntohl()" *OR* "tvb_get_letohl()" - don't,
1246 for example, try to use "tvb_get_ntohl()", find that it gives you the
1247 wrong answer on the PC on which you're doing development, and try
1248 "tvb_get_letohl()" instead, as "tvb_get_letohl()" will give the wrong
1249 answer on big-endian machines.
1253 void tvb_get_ntohguid(tvbuff_t *, gint offset, e_guid_t *guid);
1254 void tvb_get_letohguid(tvbuff_t *, gint offset, e_guid_t *guid);
1258 guint8 *tvb_get_string(tvbuff_t*, gint offset, gint length);
1259 gchar *tvb_get_unicode_string(tvbuff_t *tvb, const gint offset, gint length, const guint encoding);
1260 guint8 *tvb_get_ephemeral_string(tvbuff_t*, gint offset, gint length);
1261 gchar *tvb_get_ephemeral_unicode_string(tvbuff_t *tvb, const gint offset, gint length, const guint encoding);
1262 guint8 *tvb_get_seasonal_string(tvbuff_t*, gint offset, gint length);
1264 Returns a null-terminated buffer containing data from the specified
1265 tvbuff, starting at the specified offset, and containing the specified
1266 length worth of characters (the length of the buffer will be length+1,
1267 as it includes a null character to terminate the string).
1269 tvb_get_string() returns a buffer allocated by g_malloc() so you must
1270 g_free() it when you are finished with the string. Failure to g_free() this
1271 buffer will lead to memory leaks.
1273 tvb_get_unicode_string() is a unicode (UTF-16) version of above. This
1274 is intended for reading UTF-16 unicode strings out of a tvbuff and
1275 returning them as a UTF-8 string for use in Wireshark. The offset and
1276 returned length pointer are in bytes, not UTF-16 characters.
1278 tvb_get_ephemeral_string() returns a buffer allocated from a special heap
1279 with a lifetime until the next packet is dissected. You do not need to
1280 free() this buffer, it will happen automatically once the next packet is
1283 tvb_get_ephemeral_unicode_string() is a unicode (UTF-16) version of above.
1284 This is intended for reading UTF-16 unicode strings out of a tvbuff and
1285 returning them as a UTF-8 string for use in Wireshark. The offset and
1286 returned length pointer are in bytes, not UTF-16 characters.
1288 tvb_get_seasonal_string() returns a buffer allocated from a special heap
1289 with a lifetime of the current capture session. You do not need to
1290 free() this buffer, it will happen automatically once the a new capture or
1293 guint8 *tvb_get_stringz(tvbuff_t *tvb, gint offset, gint *lengthp);
1294 const guint8 *tvb_get_const stringz(tvbuff_t *tvb, gint offset, gint *lengthp);
1295 guint8 *tvb_get_ephemeral_stringz(tvbuff_t *tvb, gint offset, gint *lengthp);
1296 gchar *tvb_get_ephemeral_unicode_stringz(tvbuff_t *tvb, const gint offset, gint *lengthp, const guint encoding);
1297 guint8 *tvb_get_seasonal_stringz(tvbuff_t *tvb, gint offset, gint *lengthp);
1299 Returns a null-terminated buffer containing data from the specified tvbuff,
1300 starting at the specified offset, and containing all characters from the
1301 tvbuff up to and including a terminating null character in the tvbuff.
1302 "*lengthp" will be set to the length of the string, including the terminating
1305 tvb_get_stringz() returns a buffer allocated by g_malloc() so you must
1306 g_free() it when you are finished with the string. Failure to g_free() this
1307 buffer will lead to memory leaks.
1309 tvb_get_const_stringz() returns a pointer to the (const) string in the tvbuff.
1310 You do not need to free() this buffer, it will happen automatically once the
1311 next packet is dissected. This function is slightly more efficient than the
1312 others because it does not allocate memory and copy the string.
1314 tvb_get_ephemeral_stringz() returns a buffer allocated from a special heap
1315 with a lifetime until the next packet is dissected. You do not need to
1316 free() this buffer, it will happen automatically once the next packet is
1319 tvb_get_ephemeral_unicode_stringz() is a unicode (UTF-16) version of
1320 above. This is intended for reading UTF-16 unicode strings out of a tvbuff
1321 and returning them as a UTF-8 string for use in Wireshark. The offset and
1322 returned length pointer are in bytes, not UTF-16 characters.
1324 tvb_get_seasonal_stringz() returns a buffer allocated from a special heap
1325 with a lifetime of the current capture session. You do not need to
1326 free() this buffer, it will happen automatically once the a new capture or
1329 tvb_fake_unicode() has been superseded by tvb_get_unicode_string(), which
1330 properly handles Unicode (UTF-16) strings by converting them to UTF-8.
1332 tvb_get_ephemeral_faked_unicode() has been superseded by
1333 tvb_get_ephemeral_string(), which properly handles Unicode (UTF-16) strings by
1334 converting them to UTF-8.
1336 Byte Array Accessors:
1338 gchar *tvb_bytes_to_str(tvbuff_t *tvb, gint offset, gint len);
1340 Formats a bunch of data from a tvbuff as bytes, returning a pointer
1341 to the string with the data formatted as two hex digits for each byte.
1342 The string pointed to is stored in an "ep_alloc'd" buffer which will be freed
1343 before the next frame is dissected. The formatted string will contain the hex digits
1344 for at most the first 16 bytes of the data. If len is greater than 16 bytes, a
1345 trailing "..." will be added to the string.
1347 gchar *tvb_bytes_to_str_punct(tvbuff_t *tvb, gint offset, gint len, gchar punct);
1349 This function is similar to tvb_bytes_to_str(...) except that 'punct' is inserted
1350 between the hex representation of each byte.
1352 gchar *tvb_bcd_dig_to_ep_str(tvbuff_t *tvb, const gint offset, const gint len, dgt_set_t *dgt, gboolean skip_first);
1354 Given a tvbuff, an offset into the tvbuff, and a length that starts
1355 at that offset (which may be -1 for "all the way to the end of the
1356 tvbuff"), fetch BCD encoded digits from a tvbuff starting from either
1357 the low or high half byte, formatting the digits according to an input digit set,
1358 if NUll a default digit set of 0-9 returning "?" for overdecadic digits will be used.
1359 A pointer to the EP allocated string will be returned.
1360 Note: a tvbuff content of 0xf is considered a 'filler' and will end the conversion.
1363 guint8* tvb_memcpy(tvbuff_t*, guint8* target, gint offset, gint length);
1365 Copies into the specified target the specified length's worth of data
1366 from the specified tvbuff, starting at the specified offset.
1368 guint8* tvb_memdup(tvbuff_t*, gint offset, gint length);
1369 guint8* ep_tvb_memdup(tvbuff_t*, gint offset, gint length);
1371 Returns a buffer, allocated with "g_malloc()", containing the specified
1372 length's worth of data from the specified tvbuff, starting at the
1373 specified offset. The ephemeral variant is freed automatically after the
1374 packet is dissected.
1377 /* WARNING! This function is possibly expensive, temporarily allocating
1378 * another copy of the packet data. Furthermore, it's dangerous because once
1379 * this pointer is given to the user, there's no guarantee that the user will
1380 * honor the 'length' and not overstep the boundaries of the buffer.
1382 guint8* tvb_get_ptr(tvbuff_t*, gint offset, gint length);
1384 The reason that tvb_get_ptr() might have to allocate a copy of its data
1385 only occurs with TVBUFF_COMPOSITES, data that spans multiple tvbuffers.
1386 If the user requests a pointer to a range of bytes that span the member
1387 tvbuffs that make up the TVBUFF_COMPOSITE, the data will have to be
1388 copied to another memory region to assure that all the bytes are
1393 1.5 Functions to handle columns in the traffic summary window.
1395 The topmost pane of the main window is a list of the packets in the
1396 capture, possibly filtered by a display filter.
1398 Each line corresponds to a packet, and has one or more columns, as
1399 configured by the user.
1401 Many of the columns are handled by code outside individual dissectors;
1402 most dissectors need only specify the value to put in the "Protocol" and
1405 Columns are specified by COL_ values; the COL_ value for the "Protocol"
1406 field, typically giving an abbreviated name for the protocol (but not
1407 the all-lower-case abbreviation used elsewhere) is COL_PROTOCOL, and the
1408 COL_ value for the "Info" field, giving a summary of the contents of the
1409 packet for that protocol, is COL_INFO.
1411 The value for a column can be specified with one of several functions,
1412 all of which take the 'fd' argument to the dissector as their first
1413 argument, and the COL_ value for the column as their second argument.
1415 1.5.1 The col_set_str function.
1417 'col_set_str' takes a string as its third argument, and sets the value
1418 for the column to that value. It assumes that the pointer passed to it
1419 points to a string constant or a static "const" array, not to a
1420 variable, as it doesn't copy the string, it merely saves the pointer
1421 value; the argument can itself be a variable, as long as it always
1422 points to a string constant or a static "const" array.
1424 It is more efficient than 'col_add_str' or 'col_add_fstr'; however, if
1425 the dissector will be using 'col_append_str' or 'col_append_fstr" to
1426 append more information to the column, the string will have to be copied
1427 anyway, so it's best to use 'col_add_str' rather than 'col_set_str' in
1430 For example, to set the "Protocol" column
1433 col_set_str(pinfo->cinfo, COL_PROTOCOL, "PROTOABBREV");
1436 1.5.2 The col_add_str function.
1438 'col_add_str' takes a string as its third argument, and sets the value
1439 for the column to that value. It takes the same arguments as
1440 'col_set_str', but copies the string, so that if the string is, for
1441 example, an automatic variable that won't remain in scope when the
1442 dissector returns, it's safe to use.
1445 1.5.3 The col_add_fstr function.
1447 'col_add_fstr' takes a 'printf'-style format string as its third
1448 argument, and 'printf'-style arguments corresponding to '%' format
1449 items in that string as its subsequent arguments. For example, to set
1450 the "Info" field to "<XXX> request, <N> bytes", where "reqtype" is a
1451 string containing the type of the request in the packet and "n" is an
1452 unsigned integer containing the number of bytes in the request:
1454 col_add_fstr(pinfo->cinfo, COL_INFO, "%s request, %u bytes",
1457 Don't use 'col_add_fstr' with a format argument of just "%s" -
1458 'col_add_str', or possibly even 'col_set_str' if the string that matches
1459 the "%s" is a static constant string, will do the same job more
1463 1.5.4 The col_clear function.
1465 If the Info column will be filled with information from the packet, that
1466 means that some data will be fetched from the packet before the Info
1467 column is filled in. If the packet is so small that the data in
1468 question cannot be fetched, the routines to fetch the data will throw an
1469 exception (see the comment at the beginning about tvbuffers improving
1470 the handling of short packets - the tvbuffers keep track of how much
1471 data is in the packet, and throw an exception on an attempt to fetch
1472 data past the end of the packet, so that the dissector won't process
1473 bogus data), causing the Info column not to be filled in.
1475 This means that the Info column will have data for the previous
1476 protocol, which would be confusing if, for example, the Protocol column
1477 had data for this protocol.
1479 Therefore, before a dissector fetches any data whatsoever from the
1480 packet (unless it's a heuristic dissector fetching data to determine
1481 whether the packet is one that it should dissect, in which case it
1482 should check, before fetching the data, whether there's any data to
1483 fetch; if there isn't, it should return FALSE), it should set the
1484 Protocol column and the Info column.
1486 If the Protocol column will ultimately be set to, for example, a value
1487 containing a protocol version number, with the version number being a
1488 field in the packet, the dissector should, before fetching the version
1489 number field or any other field from the packet, set it to a value
1490 without a version number, using 'col_set_str', and should later set it
1491 to a value with the version number after it's fetched the version
1494 If the Info column will ultimately be set to a value containing
1495 information from the packet, the dissector should, before fetching any
1496 fields from the packet, clear the column using 'col_clear' (which is
1497 more efficient than clearing it by calling 'col_set_str' or
1498 'col_add_str' with a null string), and should later set it to the real
1499 string after it's fetched the data to use when doing that.
1502 1.5.5 The col_append_str function.
1504 Sometimes the value of a column, especially the "Info" column, can't be
1505 conveniently constructed at a single point in the dissection process;
1506 for example, it might contain small bits of information from many of the
1507 fields in the packet. 'col_append_str' takes, as arguments, the same
1508 arguments as 'col_add_str', but the string is appended to the end of the
1509 current value for the column, rather than replacing the value for that
1510 column. (Note that no blank separates the appended string from the
1511 string to which it is appended; if you want a blank there, you must add
1512 it yourself as part of the string being appended.)
1515 1.5.6 The col_append_fstr function.
1517 'col_append_fstr' is to 'col_add_fstr' as 'col_append_str' is to
1518 'col_add_str' - it takes, as arguments, the same arguments as
1519 'col_add_fstr', but the formatted string is appended to the end of the
1520 current value for the column, rather than replacing the value for that
1523 1.5.7 The col_append_sep_str and col_append_sep_fstr functions.
1525 In specific situations the developer knows that a column's value will be
1526 created in a stepwise manner, where the appended values are listed. Both
1527 'col_append_sep_str' and 'col_append_sep_fstr' functions will add an item
1528 separator between two consecutive items, and will not add the separator at the
1529 beginning of the column. The remainder of the work both functions do is
1530 identical to what 'col_append_str' and 'col_append_fstr' do.
1532 1.5.8 The col_set_fence and col_prepend_fence_fstr functions.
1534 Sometimes a dissector may be called multiple times for different PDUs in the
1535 same frame (for example in the case of SCTP chunk bundling: several upper
1536 layer data packets may be contained in one SCTP packet). If the upper layer
1537 dissector calls 'col_set_str()' or 'col_clear()' on the Info column when it
1538 begins dissecting each of those PDUs then when the frame is fully dissected
1539 the Info column would contain only the string from the last PDU in the frame.
1540 The 'col_set_fence' function erects a "fence" in the column that prevents
1541 subsequent 'col_...' calls from clearing the data currently in that column.
1542 For example, the SCTP dissector calls 'col_set_fence' on the Info column
1543 after it has called any subdissectors for that chunk so that subdissectors
1544 of any subsequent chunks may only append to the Info column.
1545 'col_prepend_fence_fstr' prepends data before a fence (moving it if
1546 necessary). It will create a fence at the end of the prepended data if the
1547 fence does not already exist.
1550 1.5.9 The col_set_time function.
1552 The 'col_set_time' function takes an nstime value as its third argument.
1553 This nstime value is a relative value and will be added as such to the
1554 column. The fourth argument is the filtername holding this value. This
1555 way, rightclicking on the column makes it possible to build a filter
1556 based on the time-value.
1560 nstime_delta(&ts, &pinfo->fd->abs_ts, &tcpd->ts_first);
1561 col_set_time(pinfo->cinfo, COL_REL_CONV_TIME, &ts, "tcp.time_relative");
1564 1.6 Constructing the protocol tree.
1566 The middle pane of the main window, and the topmost pane of a packet
1567 popup window, are constructed from the "protocol tree" for a packet.
1569 The protocol tree, or proto_tree, is a GNode, the N-way tree structure
1570 available within GLIB. Of course the protocol dissectors don't care
1571 what a proto_tree really is; they just pass the proto_tree pointer as an
1572 argument to the routines which allow them to add items and new branches
1575 When a packet is selected in the packet-list pane, or a packet popup
1576 window is created, a new logical protocol tree (proto_tree) is created.
1577 The pointer to the proto_tree (in this case, 'protocol tree'), is passed
1578 to the top-level protocol dissector, and then to all subsequent protocol
1579 dissectors for that packet, and then the GUI tree is drawn via
1582 The logical proto_tree needs to know detailed information about the protocols
1583 and fields about which information will be collected from the dissection
1584 routines. By strictly defining (or "typing") the data that can be attached to a
1585 proto tree, searching and filtering becomes possible. This means that for
1586 every protocol and field (which I also call "header fields", since they are
1587 fields in the protocol headers) which might be attached to a tree, some
1588 information is needed.
1590 Every dissector routine will need to register its protocols and fields
1591 with the central protocol routines (in proto.c). At first I thought I
1592 might keep all the protocol and field information about all the
1593 dissectors in one file, but decentralization seemed like a better idea.
1594 That one file would have gotten very large; one small change would have
1595 required a re-compilation of the entire file. Also, by allowing
1596 registration of protocols and fields at run-time, loadable modules of
1597 protocol dissectors (perhaps even user-supplied) is feasible.
1599 To do this, each protocol should have a register routine, which will be
1600 called when Wireshark starts. The code to call the register routines is
1601 generated automatically; to arrange that a protocol's register routine
1602 be called at startup:
1604 the file containing a dissector's "register" routine must be
1605 added to "DISSECTOR_SRC" in "epan/dissectors/Makefile.common"
1606 (and in "epan/CMakeLists.txt");
1608 the "register" routine must have a name of the form
1609 "proto_register_XXX";
1611 the "register" routine must take no argument, and return no
1614 the "register" routine's name must appear in the source file
1615 either at the beginning of the line, or preceded only by "void "
1616 at the beginning of the line (that would typically be the
1617 definition) - other white space shouldn't cause a problem, e.g.:
1619 void proto_register_XXX(void) {
1628 proto_register_XXX( void )
1635 and so on should work.
1637 For every protocol or field that a dissector wants to register, a variable of
1638 type int needs to be used to keep track of the protocol. The IDs are
1639 needed for establishing parent/child relationships between protocols and
1640 fields, as well as associating data with a particular field so that it
1641 can be stored in the logical tree and displayed in the GUI protocol
1644 Some dissectors will need to create branches within their tree to help
1645 organize header fields. These branches should be registered as header
1646 fields. Only true protocols should be registered as protocols. This is
1647 so that a display filter user interface knows how to distinguish
1648 protocols from fields.
1650 A protocol is registered with the name of the protocol and its
1653 Here is how the frame "protocol" is registered.
1657 proto_frame = proto_register_protocol (
1659 /* short name */ "Frame",
1660 /* abbrev */ "frame" );
1662 A header field is also registered with its name and abbreviation, but
1663 information about its data type is needed. It helps to look at
1664 the header_field_info struct to see what information is expected:
1666 struct header_field_info {
1671 const void *strings;
1679 A string representing the name of the field. This is the name
1680 that will appear in the graphical protocol tree. It must be a non-empty
1685 A string with an abbreviation of the field. We concatenate the
1686 abbreviation of the parent protocol with an abbreviation for the field,
1687 using a period as a separator. For example, the "src" field in an IP packet
1688 would have "ip.src" as an abbreviation. It is acceptable to have
1689 multiple levels of periods if, for example, you have fields in your
1690 protocol that are then subdivided into subfields. For example, TRMAC
1691 has multiple error fields, so the abbreviations follow this pattern:
1692 "trmac.errors.iso", "trmac.errors.noniso", etc.
1694 The abbreviation is the identifier used in a display filter. If it is
1695 an empty string then the field will not be filterable.
1699 The type of value this field holds. The current field types are:
1701 FT_NONE No field type. Used for fields that
1702 aren't given a value, and that can only
1703 be tested for presence or absence; a
1704 field that represents a data structure,
1705 with a subtree below it containing
1706 fields for the members of the structure,
1707 or that represents an array with a
1708 subtree below it containing fields for
1709 the members of the array, might be an
1711 FT_PROTOCOL Used for protocols which will be placing
1712 themselves as top-level items in the
1713 "Packet Details" pane of the UI.
1714 FT_BOOLEAN 0 means "false", any other value means
1716 FT_FRAMENUM A frame number; if this is used, the "Go
1717 To Corresponding Frame" menu item can
1719 FT_UINT8 An 8-bit unsigned integer.
1720 FT_UINT16 A 16-bit unsigned integer.
1721 FT_UINT24 A 24-bit unsigned integer.
1722 FT_UINT32 A 32-bit unsigned integer.
1723 FT_UINT64 A 64-bit unsigned integer.
1724 FT_INT8 An 8-bit signed integer.
1725 FT_INT16 A 16-bit signed integer.
1726 FT_INT24 A 24-bit signed integer.
1727 FT_INT32 A 32-bit signed integer.
1728 FT_INT64 A 64-bit signed integer.
1729 FT_FLOAT A single-precision floating point number.
1730 FT_DOUBLE A double-precision floating point number.
1731 FT_ABSOLUTE_TIME An absolute time from some fixed point in time,
1732 displayed as the date, followed by the time, as
1733 hours, minutes, and seconds with 9 digits after
1735 FT_RELATIVE_TIME Seconds (4 bytes) and nanoseconds (4 bytes)
1736 of time relative to an arbitrary time.
1737 displayed as seconds and 9 digits
1738 after the decimal point.
1739 FT_STRING A string of characters, not necessarily
1740 NULL-terminated, but possibly NULL-padded.
1741 This, and the other string-of-characters
1742 types, are to be used for text strings,
1743 not raw binary data.
1744 FT_STRINGZ A NULL-terminated string of characters.
1745 The string length is normally the length
1746 given in the proto_tree_add_item() call.
1747 However if the length given in the call
1748 is -1, then the length used is that
1749 returned by calling tvb_strsize().
1750 FT_UINT_STRING A counted string of characters, consisting
1751 of a count (represented as an integral value,
1752 of width given in the proto_tree_add_item()
1753 call) followed immediately by that number of
1755 FT_ETHER A six octet string displayed in
1756 Ethernet-address format.
1757 FT_BYTES A string of bytes with arbitrary values;
1758 used for raw binary data.
1759 FT_UINT_BYTES A counted string of bytes, consisting
1760 of a count (represented as an integral value,
1761 of width given in the proto_tree_add_item()
1762 call) followed immediately by that number of
1763 arbitrary values; used for raw binary data.
1764 FT_IPv4 A version 4 IP address (4 bytes) displayed
1765 in dotted-quad IP address format (4
1766 decimal numbers separated by dots).
1767 FT_IPv6 A version 6 IP address (16 bytes) displayed
1768 in standard IPv6 address format.
1769 FT_IPXNET An IPX address displayed in hex as a 6-byte
1770 network number followed by a 6-byte station
1772 FT_GUID A Globally Unique Identifier
1773 FT_OID An ASN.1 Object Identifier
1774 FT_EUI64 A EUI-64 Address
1776 Some of these field types are still not handled in the display filter
1777 routines, but the most common ones are. The FT_UINT* variables all
1778 represent unsigned integers, and the FT_INT* variables all represent
1779 signed integers; the number on the end represent how many bits are used
1780 to represent the number.
1782 Some constraints are imposed on the header fields depending on the type
1783 (e.g. FT_BYTES) of the field. Fields of type FT_ABSOLUTE_TIME must use
1784 'ABSOLUTE_TIME_{LOCAL,UTC,DOY_UTC}, NULL, 0x0' as values for the
1785 'display, 'strings', and 'bitmask' fields, and all other non-integral
1786 types (i.e.. types that are _not_ FT_INT* and FT_UINT*) must use
1787 'BASE_NONE, NULL, 0x0' as values for the 'display', 'strings', 'bitmask'
1788 fields. The reason is simply that the type itself implictly defines the
1789 nature of 'display', 'strings', 'bitmask'.
1793 The display field has a couple of overloaded uses. This is unfortunate,
1794 but since we're using C as an application programming language, this sometimes
1795 makes for cleaner programs. Right now I still think that overloading
1796 this variable was okay.
1798 For integer fields (FT_UINT* and FT_INT*), this variable represents the
1799 base in which you would like the value displayed. The acceptable bases
1809 BASE_DEC, BASE_HEX, and BASE_OCT are decimal, hexadecimal, and octal,
1810 respectively. BASE_DEC_HEX and BASE_HEX_DEC display value in two bases
1811 (the 1st representation followed by the 2nd in parenthesis).
1813 BASE_CUSTOM allows one to specify a callback function pointer that will
1814 format the value. The function pointer of the same type as defined by
1815 custom_fmt_func_t in epan/proto.h, specifically:
1817 void func(gchar *, guint32);
1819 The first argument is a pointer to a buffer of the ITEM_LABEL_LENGTH size
1820 and the second argument is the value to be formatted.
1822 For FT_BOOLEAN fields that are also bitfields (i.e. 'bitmask' is non-zero),
1823 'display' is used to tell the proto_tree how wide the parent bitfield is.
1824 With integers this is not needed since the type of integer itself
1825 (FT_UINT8, FT_UINT16, FT_UINT24, FT_UINT32, etc.) tells the proto_tree how
1826 wide the parent bitfield is.
1828 For FT_ABSOLUTE_TIME fields, 'display' is used to indicate whether the
1829 time is to be displayed as a time in the time zone for the machine on
1830 which Wireshark/TShark is running or as UTC and, for UTC, whether the
1831 date should be displayed as "{monthname}, {month} {day_of_month},
1832 {year}" or as "{year/day_of_year}".
1834 Additionally, BASE_NONE is used for 'display' as a NULL-value. That is, for
1835 non-integers other than FT_ABSOLUTE_TIME fields, and non-bitfield
1836 FT_BOOLEANs, you'll want to use BASE_NONE in the 'display' field. You may
1837 not use BASE_NONE for integers.
1839 It is possible that in the future we will record the endianness of
1840 integers. If so, it is likely that we'll use a bitmask on the display field
1841 so that integers would be represented as BEND|BASE_DEC or LEND|BASE_HEX.
1842 But that has not happened yet; note that there are protocols for which
1843 no endianness is specified, such as the X11 protocol and the DCE RPC
1844 protocol, so it would not be possible to record the endianness of all
1850 Some integer fields, of type FT_UINT*, need labels to represent the true
1851 value of a field. You could think of those fields as having an
1852 enumerated data type, rather than an integral data type.
1854 A 'value_string' structure is a way to map values to strings.
1856 typedef struct _value_string {
1861 For fields of that type, you would declare an array of "value_string"s:
1863 static const value_string valstringname[] = {
1864 { INTVAL1, "Descriptive String 1" },
1865 { INTVAL2, "Descriptive String 2" },
1869 (the last entry in the array must have a NULL 'strptr' value, to
1870 indicate the end of the array). The 'strings' field would be set to
1871 'VALS(valstringname)'.
1873 If the field has a numeric rather than an enumerated type, the 'strings'
1874 field would be set to NULL.
1876 -- Extended value strings
1877 You can also use an extended version of the value_string for faster lookups.
1878 It requires a value_string as input.
1879 If all of a contiguous range of values from min to max are present in the array
1880 the value will be used as as a direct index into a value_string array.
1882 If the values in the array are not contiguous (ie: there are "gaps"), but are
1883 in ascending order a binary search will be used.
1885 Note: "gaps" in a value_string array can be filled with "empty" entries eg:
1886 {value, "Unknown"} so that direct access to the array is is possible.
1888 The init macro (see below) will perform a check on the value string the first
1889 time it is used to determine which search algorithm fits and fall back to a
1890 linear search if the value_string does not meet the criteria above.
1892 Use this macro to initialize the extended value_string at compile time:
1894 static value_string_ext valstringname_ext = VALUE_STRING_EXT_INIT(valstringname);
1896 Extended value strings can be created at run time by calling
1897 value_string_ext_new(<ptr to value_string array>,
1898 <total number of entries in the value_string_array>, /* include {0, NULL} entry */
1899 <value_string_name>);
1901 For hf[] array FT_(U)INT* fields that need a 'valstringname_ext' struct, the
1902 'strings' field would be set to '&valstringname_ext)'. Furthermore, 'display'
1903 field must be ORed with 'BASE_EXT_STRING' (e.g. BASE_DEC|BASE_EXT_STRING).
1907 If the field has a numeric type that might logically fit in ranges of values
1908 one can use a range_string struct.
1910 Thus a 'range_string' structure is a way to map ranges to strings.
1912 typedef struct _range_string {
1915 const gchar *strptr;
1918 For fields of that type, you would declare an array of "range_string"s:
1920 static const range_string rvalstringname[] = {
1921 { INTVAL_MIN1, INTVALMAX1, "Descriptive String 1" },
1922 { INTVAL_MIN2, INTVALMAX2, "Descriptive String 2" },
1926 If INTVAL_MIN equals INTVAL_MAX for a given entry the range_string
1927 behavior collapses to the one of value_string.
1928 For FT_(U)INT* fields that need a 'range_string' struct, the 'strings' field
1929 would be set to 'RVALS(rvalstringname)'. Furthermore, 'display' field must be
1930 ORed with 'BASE_RANGE_STRING' (e.g. BASE_DEC|BASE_RANGE_STRING).
1933 FT_BOOLEANs have a default map of 0 = "False", 1 (or anything else) = "True".
1934 Sometimes it is useful to change the labels for boolean values (e.g.,
1935 to "Yes"/"No", "Fast"/"Slow", etc.). For these mappings, a struct called
1936 true_false_string is used.
1938 typedef struct true_false_string {
1941 } true_false_string;
1943 For Boolean fields for which "False" and "True" aren't the desired
1944 labels, you would declare a "true_false_string"s:
1946 static const true_false_string boolstringname = {
1951 Its two fields are pointers to the string representing truth, and the
1952 string representing falsehood. For FT_BOOLEAN fields that need a
1953 'true_false_string' struct, the 'strings' field would be set to
1954 'TFS(&boolstringname)'.
1956 If the Boolean field is to be displayed as "False" or "True", the
1957 'strings' field would be set to NULL.
1959 Wireshark predefines a whole range of ready made "true_false_string"s
1960 in tfs.h, included via packet.h.
1964 If the field is a bitfield, then the bitmask is the mask which will
1965 leave only the bits needed to make the field when ANDed with a value.
1966 The proto_tree routines will calculate 'bitshift' automatically
1967 from 'bitmask', by finding the rightmost set bit in the bitmask.
1968 This shift is applied before applying string mapping functions or
1970 If the field is not a bitfield, then bitmask should be set to 0.
1974 This is a string giving a proper description of the field. It should be
1975 at least one grammatically complete sentence, or NULL in which case the
1976 name field is used. (Please do not use "").
1977 It is meant to provide a more detailed description of the field than the
1978 name alone provides. This information will be used in the man page, and
1979 in a future GUI display-filter creation tool. We might also add tooltips
1980 to the labels in the GUI protocol tree, in which case the blurb would
1981 be used as the tooltip text.
1984 1.6.1 Field Registration.
1986 Protocol registration is handled by creating an instance of the
1987 header_field_info struct (or an array of such structs), and
1988 calling the registration function along with the registration ID of
1989 the protocol that is the parent of the fields. Here is a complete example:
1991 static int proto_eg = -1;
1992 static int hf_field_a = -1;
1993 static int hf_field_b = -1;
1995 static hf_register_info hf[] = {
1998 { "Field A", "proto.field_a", FT_UINT8, BASE_HEX, NULL,
1999 0xf0, "Field A represents Apples", HFILL }},
2002 { "Field B", "proto.field_b", FT_UINT16, BASE_DEC, VALS(vs),
2003 0x0, "Field B represents Bananas", HFILL }}
2006 proto_eg = proto_register_protocol("Example Protocol",
2008 proto_register_field_array(proto_eg, hf, array_length(hf));
2010 Be sure that your array of hf_register_info structs is declared 'static',
2011 since the proto_register_field_array() function does not create a copy
2012 of the information in the array... it uses that static copy of the
2013 information that the compiler created inside your array. Here's the
2014 layout of the hf_register_info struct:
2016 typedef struct hf_register_info {
2017 int *p_id; /* pointer to parent variable */
2018 header_field_info hfinfo;
2021 Also be sure to use the handy array_length() macro found in packet.h
2022 to have the compiler compute the array length for you at compile time.
2024 If you don't have any fields to register, do *NOT* create a zero-length
2025 "hf" array; not all compilers used to compile Wireshark support them.
2026 Just omit the "hf" array, and the "proto_register_field_array()" call,
2029 It is OK to have header fields with a different format be registered with
2030 the same abbreviation. For instance, the following is valid:
2032 static hf_register_info hf[] = {
2034 { &hf_field_8bit, /* 8-bit version of proto.field */
2035 { "Field (8 bit)", "proto.field", FT_UINT8, BASE_DEC, NULL,
2036 0x00, "Field represents FOO", HFILL }},
2038 { &hf_field_32bit, /* 32-bit version of proto.field */
2039 { "Field (32 bit)", "proto.field", FT_UINT32, BASE_DEC, NULL,
2040 0x00, "Field represents FOO", HFILL }}
2043 This way a filter expression can match a header field, irrespective of the
2044 representation of it in the specific protocol context. This is interesting
2045 for protocols with variable-width header fields.
2047 The HFILL macro at the end of the struct will set reasonable default values
2048 for internally used fields.
2050 1.6.2 Adding Items and Values to the Protocol Tree.
2052 A protocol item is added to an existing protocol tree with one of a
2053 handful of proto_XXX_DO_YYY() functions.
2055 Remember that it only makes sense to add items to a protocol tree if its
2056 proto_tree pointer is not null. Should you add an item to a NULL tree, then
2057 the proto_XXX_DO_YYY() function will immediately return. The cost of this
2058 function call can be avoided by checking for the tree pointer.
2060 Subtrees can be made with the proto_item_add_subtree() function:
2062 item = proto_tree_add_item(....);
2063 new_tree = proto_item_add_subtree(item, tree_type);
2065 This will add a subtree under the item in question; a subtree can be
2066 created under an item made by any of the "proto_tree_add_XXX" functions,
2067 so that the tree can be given an arbitrary depth.
2069 Subtree types are integers, assigned by
2070 "proto_register_subtree_array()". To register subtree types, pass an
2071 array of pointers to "gint" variables to hold the subtree type values to
2072 "proto_register_subtree_array()":
2074 static gint ett_eg = -1;
2075 static gint ett_field_a = -1;
2077 static gint *ett[] = {
2082 proto_register_subtree_array(ett, array_length(ett));
2084 in your "register" routine, just as you register the protocol and the
2085 fields for that protocol.
2087 The ett_ variables identify particular type of subtree so that if you expand
2088 one of them, Wireshark keeps track of that and, when you click on
2089 another packet, it automatically opens all subtrees of that type.
2090 If you close one of them, all subtrees of that type will be closed when
2091 you move to another packet.
2093 There are several functions that the programmer can use to add either
2094 protocol or field labels to the proto_tree:
2097 proto_tree_add_item(tree, id, tvb, start, length, encoding);
2100 proto_tree_add_none_format(tree, id, tvb, start, length, format, ...);
2103 proto_tree_add_protocol_format(tree, id, tvb, start, length,
2107 proto_tree_add_bytes(tree, id, tvb, start, length, start_ptr);
2110 proto_tree_add_bytes_format(tree, id, tvb, start, length, start_ptr,
2114 proto_tree_add_bytes_format_value(tree, id, tvb, start, length,
2115 start_ptr, format, ...);
2118 proto_tree_add_time(tree, id, tvb, start, length, value_ptr);
2121 proto_tree_add_time_format(tree, id, tvb, start, length, value_ptr,
2125 proto_tree_add_time_format_value(tree, id, tvb, start, length,
2126 value_ptr, format, ...);
2129 proto_tree_add_ipxnet(tree, id, tvb, start, length, value);
2132 proto_tree_add_ipxnet_format(tree, id, tvb, start, length, value,
2136 proto_tree_add_ipxnet_format_value(tree, id, tvb, start, length,
2137 value, format, ...);
2140 proto_tree_add_ipv4(tree, id, tvb, start, length, value);
2143 proto_tree_add_ipv4_format(tree, id, tvb, start, length, value,
2147 proto_tree_add_ipv4_format_value(tree, id, tvb, start, length,
2148 value, format, ...);
2151 proto_tree_add_ipv6(tree, id, tvb, start, length, value_ptr);
2154 proto_tree_add_ipv6_format(tree, id, tvb, start, length, value_ptr,
2158 proto_tree_add_ipv6_format_value(tree, id, tvb, start, length,
2159 value_ptr, format, ...);
2162 proto_tree_add_ether(tree, id, tvb, start, length, value_ptr);
2165 proto_tree_add_ether_format(tree, id, tvb, start, length, value_ptr,
2169 proto_tree_add_ether_format_value(tree, id, tvb, start, length,
2170 value_ptr, format, ...);
2173 proto_tree_add_string(tree, id, tvb, start, length, value_ptr);
2176 proto_tree_add_string_format(tree, id, tvb, start, length, value_ptr,
2180 proto_tree_add_string_format_value(tree, id, tvb, start, length,
2181 value_ptr, format, ...);
2184 proto_tree_add_boolean(tree, id, tvb, start, length, value);
2187 proto_tree_add_boolean_format(tree, id, tvb, start, length, value,
2191 proto_tree_add_boolean_format_value(tree, id, tvb, start, length,
2192 value, format, ...);
2195 proto_tree_add_float(tree, id, tvb, start, length, value);
2198 proto_tree_add_float_format(tree, id, tvb, start, length, value,
2202 proto_tree_add_float_format_value(tree, id, tvb, start, length,
2203 value, format, ...);
2206 proto_tree_add_double(tree, id, tvb, start, length, value);
2209 proto_tree_add_double_format(tree, id, tvb, start, length, value,
2213 proto_tree_add_double_format_value(tree, id, tvb, start, length,
2214 value, format, ...);
2217 proto_tree_add_uint(tree, id, tvb, start, length, value);
2220 proto_tree_add_uint_format(tree, id, tvb, start, length, value,
2224 proto_tree_add_uint_format_value(tree, id, tvb, start, length,
2225 value, format, ...);
2228 proto_tree_add_uint64(tree, id, tvb, start, length, value);
2231 proto_tree_add_uint64_format(tree, id, tvb, start, length, value,
2235 proto_tree_add_uint64_format_value(tree, id, tvb, start, length,
2236 value, format, ...);
2239 proto_tree_add_int(tree, id, tvb, start, length, value);
2242 proto_tree_add_int_format(tree, id, tvb, start, length, value,
2246 proto_tree_add_int_format_value(tree, id, tvb, start, length,
2247 value, format, ...);
2250 proto_tree_add_int64(tree, id, tvb, start, length, value);
2253 proto_tree_add_int64_format(tree, id, tvb, start, length, value,
2257 proto_tree_add_int64_format_value(tree, id, tvb, start, length,
2258 value, format, ...);
2261 proto_tree_add_text(tree, tvb, start, length, format, ...);
2264 proto_tree_add_text_valist(tree, tvb, start, length, format, ap);
2267 proto_tree_add_guid(tree, id, tvb, start, length, value_ptr);
2270 proto_tree_add_guid_format(tree, id, tvb, start, length, value_ptr,
2274 proto_tree_add_guid_format_value(tree, id, tvb, start, length,
2275 value_ptr, format, ...);
2278 proto_tree_add_oid(tree, id, tvb, start, length, value_ptr);
2281 proto_tree_add_oid_format(tree, id, tvb, start, length, value_ptr,
2285 proto_tree_add_eui64(tree, id, tvb, start, length, value);
2288 proto_tree_add_eui64_format(tree, id, tvb, start, length, value,
2292 proto_tree_add_eui64_format_value(tree, id, tvb, start, length,
2293 value, format, ...);
2296 proto_tree_add_oid_format_value(tree, id, tvb, start, length,
2297 value_ptr, format, ...);
2300 proto_tree_add_bits_item(tree, id, tvb, bit_offset, no_of_bits,
2304 proto_tree_add_bits_ret_val(tree, id, tvb, bit_offset, no_of_bits,
2305 return_value, little_endian);
2308 proto_tree_add_bitmask(tree, tvb, start, header, ett, fields,
2312 proto_tree_add_bitmask_text(tree, tvb, offset, len, name, fallback,
2313 ett, fields, little_endian, flags);
2315 The 'tree' argument is the tree to which the item is to be added. The
2316 'tvb' argument is the tvbuff from which the item's value is being
2317 extracted; the 'start' argument is the offset from the beginning of that
2318 tvbuff of the item being added, and the 'length' argument is the length,
2319 in bytes, of the item, bit_offset is the offset in bits and no_of_bits
2320 is the length in bits.
2322 The length of some items cannot be determined until the item has been
2323 dissected; to add such an item, add it with a length of -1, and, when the
2324 dissection is complete, set the length with 'proto_item_set_len()':
2327 proto_item_set_len(ti, length);
2329 The "ti" argument is the value returned by the call that added the item
2330 to the tree, and the "length" argument is the length of the item.
2332 proto_tree_add_item()
2333 ---------------------
2334 proto_tree_add_item is used when you wish to do no special formatting.
2335 The item added to the GUI tree will contain the name (as passed in the
2336 proto_register_*() function) and a value. The value will be fetched
2337 from the tvbuff by proto_tree_add_item(), based on the type of the field
2338 and the encoding of the value as specified by the "encoding" argument.
2340 For FT_NONE, FT_BYTES, FT_ETHER, FT_IPv6, FT_IPXNET, FT_OID fields,
2341 and 'protocol' fields the encoding is not relevant; the 'encoding'
2342 argument should be ENC_NA (Not Applicable).
2344 For integral, floating-point, Boolean, FT_GUID, and FT_EUI64 fields,
2345 the encoding specifies the byte order of the value; the 'encoding'
2346 argument should be is ENC_LITTLE_ENDIAN if the value is little-endian
2347 and ENC_BIG_ENDIAN if it is big-endian.
2349 For FT_IPv4 fields, the encoding also specifies the byte order of the
2350 value. In almost all cases, the encoding is in network byte order,
2351 hence big-endian, but in at least one protocol dissected by Wireshark,
2352 at least one IPv4 address is byte-swapped, so it's in little-endian
2355 For string fields, the encoding specifies the character set used for the
2356 string and the way individual code points in that character set are
2357 encoded. For FT_UINT_STRING fields, the byte order of the count must be
2358 specified; when support for UTF-16 encoding is added, the byte order of
2359 the encoding will also have to be specified. In other cases, ENC_NA
2360 should be used. The character encodings that are currently
2364 ENC_ASCII - ASCII (currently treated as UTF-8; in the future,
2365 all bytes with the 8th bit set will be treated as
2369 Other encodings will be added in the future.
2371 For FT_ABSOLUTE_TIME fields, the encoding specifies the form in which
2372 the time stamp is specified, as well as its byte order. The time stamp
2373 encodings that are currently supported are:
2375 ENC_TIME_TIMESPEC - seconds (4 bytes) and nanoseconds (4 bytes)
2376 of time since January 1, 1970, midnight UTC.
2378 ENC_TIME_NTP - an NTP timestamp, represented as a 64-bit
2379 unsigned fixed-point number, in seconds relative to 0h
2380 on 1 January 1900. The integer part is in the first 32
2381 bits and the fraction part in the last 32 bits.
2383 For other types, there is no support for proto_tree_add_item().
2385 Now that definitions of fields have detailed information about bitfield
2386 fields, you can use proto_tree_add_item() with no extra processing to
2387 add bitfield values to your tree. Here's an example. Take the Format
2388 Identifier (FID) field in the Transmission Header (TH) portion of the SNA
2389 protocol. The FID is the high nibble of the first byte of the TH. The
2390 FID would be registered like this:
2392 name = "Format Identifier"
2393 abbrev = "sna.th.fid"
2396 strings = sna_th_fid_vals
2399 The bitmask contains the value which would leave only the FID if bitwise-ANDed
2400 against the parent field, the first byte of the TH.
2402 The code to add the FID to the tree would be;
2404 proto_tree_add_item(bf_tree, hf_sna_th_fid, tvb, offset, 1,
2407 The definition of the field already has the information about bitmasking
2408 and bitshifting, so it does the work of masking and shifting for us!
2409 This also means that you no longer have to create value_string structs
2410 with the values bitshifted. The value_string for FID looks like this,
2411 even though the FID value is actually contained in the high nibble.
2412 (You'd expect the values to be 0x0, 0x10, 0x20, etc.)
2414 /* Format Identifier */
2415 static const value_string sna_th_fid_vals[] = {
2416 { 0x0, "SNA device <--> Non-SNA Device" },
2417 { 0x1, "Subarea Node <--> Subarea Node" },
2418 { 0x2, "Subarea Node <--> PU2" },
2419 { 0x3, "Subarea Node or SNA host <--> Subarea Node" },
2422 { 0xf, "Adjacent Subarea Nodes" },
2426 The final implication of this is that display filters work the way you'd
2427 naturally expect them to. You'd type "sna.th.fid == 0xf" to find Adjacent
2428 Subarea Nodes. The user does not have to shift the value of the FID to
2429 the high nibble of the byte ("sna.th.fid == 0xf0") as was necessary
2432 proto_tree_add_protocol_format()
2433 --------------------------------
2434 proto_tree_add_protocol_format is used to add the top-level item for the
2435 protocol when the dissector routine wants complete control over how the
2436 field and value will be represented on the GUI tree. The ID value for
2437 the protocol is passed in as the "id" argument; the rest of the
2438 arguments are a "printf"-style format and any arguments for that format.
2439 The caller must include the name of the protocol in the format; it is
2440 not added automatically as in proto_tree_add_item().
2442 proto_tree_add_none_format()
2443 ----------------------------
2444 proto_tree_add_none_format is used to add an item of type FT_NONE.
2445 The caller must include the name of the field in the format; it is
2446 not added automatically as in proto_tree_add_item().
2448 proto_tree_add_bytes()
2449 proto_tree_add_time()
2450 proto_tree_add_ipxnet()
2451 proto_tree_add_ipv4()
2452 proto_tree_add_ipv6()
2453 proto_tree_add_ether()
2454 proto_tree_add_string()
2455 proto_tree_add_boolean()
2456 proto_tree_add_float()
2457 proto_tree_add_double()
2458 proto_tree_add_uint()
2459 proto_tree_add_uint64()
2460 proto_tree_add_int()
2461 proto_tree_add_int64()
2462 proto_tree_add_guid()
2463 proto_tree_add_oid()
2464 proto_tree_add_eui64()
2465 ------------------------
2466 These routines are used to add items to the protocol tree if either:
2468 the value of the item to be added isn't just extracted from the
2469 packet data, but is computed from data in the packet;
2471 the value was fetched into a variable.
2473 The 'value' argument has the value to be added to the tree.
2475 NOTE: in all cases where the 'value' argument is a pointer, a copy is
2476 made of the object pointed to; if you have dynamically allocated a
2477 buffer for the object, that buffer will not be freed when the protocol
2478 tree is freed - you must free the buffer yourself when you don't need it
2481 For proto_tree_add_bytes(), the 'value_ptr' argument is a pointer to a
2484 For proto_tree_add_bytes_format() and proto_tree_add_bytes_format_value(), the
2485 'value_ptr' argument is a pointer to a sequence of bytes or NULL if the bytes
2486 should be taken from the given TVB using the given offset and length.
2488 For proto_tree_add_time(), the 'value_ptr' argument is a pointer to an
2489 "nstime_t", which is a structure containing the time to be added; it has
2490 'secs' and 'nsecs' members, giving the integral part and the fractional
2491 part of a time in units of seconds, with 'nsecs' being the number of
2492 nanoseconds. For absolute times, "secs" is a UNIX-style seconds since
2493 January 1, 1970, 00:00:00 GMT value.
2495 For proto_tree_add_ipxnet(), the 'value' argument is a 32-bit IPX
2498 For proto_tree_add_ipv4(), the 'value' argument is a 32-bit IPv4
2499 address, in network byte order.
2501 For proto_tree_add_ipv6(), the 'value_ptr' argument is a pointer to a
2502 128-bit IPv6 address.
2504 For proto_tree_add_ether(), the 'value_ptr' argument is a pointer to a
2507 For proto_tree_add_string(), the 'value_ptr' argument is a pointer to a
2510 For proto_tree_add_boolean(), the 'value' argument is a 32-bit integer.
2511 It is masked and shifted as defined by the field info after which zero
2512 means "false", and non-zero means "true".
2514 For proto_tree_add_float(), the 'value' argument is a 'float' in the
2515 host's floating-point format.
2517 For proto_tree_add_double(), the 'value' argument is a 'double' in the
2518 host's floating-point format.
2520 For proto_tree_add_uint(), the 'value' argument is a 32-bit unsigned
2521 integer value, in host byte order. (This routine cannot be used to add
2524 For proto_tree_add_uint64(), the 'value' argument is a 64-bit unsigned
2525 integer value, in host byte order.
2527 For proto_tree_add_int(), the 'value' argument is a 32-bit signed
2528 integer value, in host byte order. (This routine cannot be used to add
2531 For proto_tree_add_int64(), the 'value' argument is a 64-bit signed
2532 integer value, in host byte order.
2534 For proto_tree_add_guid(), the 'value_ptr' argument is a pointer to an
2537 For proto_tree_add_oid(), the 'value_ptr' argument is a pointer to an
2538 ASN.1 Object Identifier.
2540 For proto_tree_add_eui64(), the 'value' argument is a 64-bit integer
2543 proto_tree_add_bytes_format()
2544 proto_tree_add_time_format()
2545 proto_tree_add_ipxnet_format()
2546 proto_tree_add_ipv4_format()
2547 proto_tree_add_ipv6_format()
2548 proto_tree_add_ether_format()
2549 proto_tree_add_string_format()
2550 proto_tree_add_boolean_format()
2551 proto_tree_add_float_format()
2552 proto_tree_add_double_format()
2553 proto_tree_add_uint_format()
2554 proto_tree_add_uint64_format()
2555 proto_tree_add_int_format()
2556 proto_tree_add_int64_format()
2557 proto_tree_add_guid_format()
2558 proto_tree_add_oid_format()
2559 proto_tree_add_eui64_format()
2560 ----------------------------
2561 These routines are used to add items to the protocol tree when the
2562 dissector routine wants complete control over how the field and value
2563 will be represented on the GUI tree. The argument giving the value is
2564 the same as the corresponding proto_tree_add_XXX() function; the rest of
2565 the arguments are a "printf"-style format and any arguments for that
2566 format. The caller must include the name of the field in the format; it
2567 is not added automatically as in the proto_tree_add_XXX() functions.
2569 proto_tree_add_bytes_format_value()
2570 proto_tree_add_time_format_value()
2571 proto_tree_add_ipxnet_format_value()
2572 proto_tree_add_ipv4_format_value()
2573 proto_tree_add_ipv6_format_value()
2574 proto_tree_add_ether_format_value()
2575 proto_tree_add_string_format_value()
2576 proto_tree_add_boolean_format_value()
2577 proto_tree_add_float_format_value()
2578 proto_tree_add_double_format_value()
2579 proto_tree_add_uint_format_value()
2580 proto_tree_add_uint64_format_value()
2581 proto_tree_add_int_format_value()
2582 proto_tree_add_int64_format_value()
2583 proto_tree_add_guid_format_value()
2584 proto_tree_add_oid_format_value()
2585 proto_tree_add_eui64_format_value()
2586 ------------------------------------
2588 These routines are used to add items to the protocol tree when the
2589 dissector routine wants complete control over how the value will be
2590 represented on the GUI tree. The argument giving the value is the same
2591 as the corresponding proto_tree_add_XXX() function; the rest of the
2592 arguments are a "printf"-style format and any arguments for that format.
2593 With these routines, unlike the proto_tree_add_XXX_format() routines,
2594 the name of the field is added automatically as in the
2595 proto_tree_add_XXX() functions; only the value is added with the format.
2597 proto_tree_add_text()
2598 ---------------------
2599 proto_tree_add_text() is used to add a label to the GUI tree. It will
2600 contain no value, so it is not searchable in the display filter process.
2601 This function was needed in the transition from the old-style proto_tree
2602 to this new-style proto_tree so that Wireshark would still decode all
2603 protocols w/o being able to filter on all protocols and fields.
2604 Otherwise we would have had to cripple Wireshark's functionality while we
2605 converted all the old-style proto_tree calls to the new-style proto_tree
2606 calls. In other words, you should not use this in new code unless you've got
2607 a specific reason (see below).
2609 This can also be used for items with subtrees, which may not have values
2610 themselves - the items in the subtree are the ones with values.
2612 For a subtree, the label on the subtree might reflect some of the items
2613 in the subtree. This means the label can't be set until at least some
2614 of the items in the subtree have been dissected. To do this, use
2615 'proto_item_set_text()' or 'proto_item_append_text()':
2618 proto_item_set_text(proto_item *ti, ...);
2621 proto_item_append_text(proto_item *ti, ...);
2623 'proto_item_set_text()' takes as an argument the value returned by
2624 'proto_tree_add_text()', a 'printf'-style format string, and a set of
2625 arguments corresponding to '%' format items in that string, and replaces
2626 the text for the item created by 'proto_tree_add_text()' with the result
2627 of applying the arguments to the format string.
2629 'proto_item_append_text()' is similar, but it appends to the text for
2630 the item the result of applying the arguments to the format string.
2632 For example, early in the dissection, one might do:
2634 ti = proto_tree_add_text(tree, tvb, offset, length, <label>);
2638 proto_item_set_text(ti, "%s: %s", type, value);
2640 after the "type" and "value" fields have been extracted and dissected.
2641 <label> would be a label giving what information about the subtree is
2642 available without dissecting any of the data in the subtree.
2644 Note that an exception might be thrown when trying to extract the values of
2645 the items used to set the label, if not all the bytes of the item are
2646 available. Thus, one should create the item with text that is as
2647 meaningful as possible, and set it or append additional information to
2648 it as the values needed to supply that information are extracted.
2650 proto_tree_add_text_valist()
2651 ----------------------------
2652 This is like proto_tree_add_text(), but takes, as the last argument, a
2653 'va_list'; it is used to allow routines that take a printf-like
2654 variable-length list of arguments to add a text item to the protocol
2657 proto_tree_add_bits_item()
2658 --------------------------
2659 Adds a number of bits to the protocol tree which does not have to be byte
2660 aligned. The offset and length is in bits.
2663 ..10 1010 10.. .... "value" (formatted as FT_ indicates).
2665 proto_tree_add_bits_ret_val()
2666 -----------------------------
2667 Works in the same way but also returns the value of the read bits.
2669 proto_tree_add_bitmask() and proto_tree_add_bitmask_text()
2670 ----------------------------------------------------------
2671 This function provides an easy to use and convenient helper function
2672 to manage many types of common bitmasks that occur in protocols.
2674 This function will dissect a 1/2/3/4 byte large bitmask into its individual
2676 header is an integer type and must be of type FT_[U]INT{8|16|24|32} and
2677 represents the entire width of the bitmask.
2679 'header' and 'ett' are the hf fields and ett field respectively to create an
2680 expansion that covers the 1-4 bytes of the bitmask.
2682 'fields' is a NULL terminated array of pointers to hf fields representing
2683 the individual subfields of the bitmask. These fields must either be integers
2684 of the same byte width as 'header' or of the type FT_BOOLEAN.
2685 Each of the entries in 'fields' will be dissected as an item under the
2686 'header' expansion and also IF the field is a boolean and IF it is set to 1,
2687 then the name of that boolean field will be printed on the 'header' expansion
2688 line. For integer type subfields that have a value_string defined, the
2689 matched string from that value_string will be printed on the expansion line
2692 Example: (from the SCSI dissector)
2693 static int hf_scsi_inq_peripheral = -1;
2694 static int hf_scsi_inq_qualifier = -1;
2695 static int hf_scsi_inq_devtype = -1;
2697 static gint ett_scsi_inq_peripheral = -1;
2699 static const int *peripheral_fields[] = {
2700 &hf_scsi_inq_qualifier,
2701 &hf_scsi_inq_devtype,
2705 /* Qualifier and DeviceType */
2706 proto_tree_add_bitmask(tree, tvb, offset, hf_scsi_inq_peripheral,
2707 ett_scsi_inq_peripheral, peripheral_fields, FALSE);
2710 { &hf_scsi_inq_peripheral,
2711 {"Peripheral", "scsi.inquiry.preipheral", FT_UINT8, BASE_HEX,
2712 NULL, 0, NULL, HFILL}},
2713 { &hf_scsi_inq_qualifier,
2714 {"Qualifier", "scsi.inquiry.qualifier", FT_UINT8, BASE_HEX,
2715 VALS (scsi_qualifier_val), 0xE0, NULL, HFILL}},
2716 { &hf_scsi_inq_devtype,
2717 {"Device Type", "scsi.inquiry.devtype", FT_UINT8, BASE_HEX,
2718 VALS (scsi_devtype_val), SCSI_DEV_BITS, NULL, HFILL}},
2721 Which provides very pretty dissection of this one byte bitmask.
2723 Peripheral: 0x05, Qualifier: Device type is connected to logical unit, Device Type: CD-ROM
2724 000. .... = Qualifier: Device type is connected to logical unit (0x00)
2725 ...0 0101 = Device Type: CD-ROM (0x05)
2727 The proto_tree_add_bitmask_text() function is an extended version of
2728 the proto_tree_add_bitmask() function. In addition, it allows to:
2729 - Provide a leading text (e.g. "Flags: ") that will appear before
2730 the comma-separated list of field values
2731 - Provide a fallback text (e.g. "None") that will be appended if
2732 no fields warranted a change to the top-level title.
2733 - Using flags, specify which fields will affect the top-level title.
2735 There are the following flags defined:
2737 BMT_NO_APPEND - the title is taken "as-is" from the 'name' argument.
2738 BMT_NO_INT - only boolean flags are added to the title.
2739 BMT_NO_FALSE - boolean flags are only added to the title if they are set.
2740 BMT_NO_TFS - only add flag name to the title, do not use true_false_string
2742 The proto_tree_add_bitmask() behavior can be obtained by providing
2743 both 'name' and 'fallback' arguments as NULL, and a flags of
2744 (BMT_NO_FALSE|BMT_NO_TFS).
2746 PROTO_ITEM_SET_GENERATED()
2747 --------------------------
2748 PROTO_ITEM_SET_GENERATED is used to mark fields as not being read from the
2749 captured data directly, but inferred from one or more values.
2751 One of the primary uses of this is the presentation of verification of
2752 checksums. Every IP packet has a checksum line, which can present the result
2753 of the checksum verification, if enabled in the preferences. The result is
2754 presented as a subtree, where the result is enclosed in square brackets
2755 indicating a generated field.
2757 Header checksum: 0x3d42 [correct]
2761 PROTO_ITEM_SET_HIDDEN()
2762 -----------------------
2763 PROTO_ITEM_SET_HIDDEN is used to hide fields, which have already been added
2764 to the tree, from being visible in the displayed tree.
2766 NOTE that creating hidden fields is actually quite a bad idea from a UI design
2767 perspective because the user (someone who did not write nor has ever seen the
2768 code) has no way of knowing that hidden fields are there to be filtered on
2769 thus defeating the whole purpose of putting them there. A Better Way might
2770 be to add the fields (that might otherwise be hidden) to a subtree where they
2771 won't be seen unless the user opens the subtree--but they can be found if the
2774 One use for hidden fields (which would be better implemented using visible
2775 fields in a subtree) follows: The caller may want a value to be
2776 included in a tree so that the packet can be filtered on this field, but
2777 the representation of that field in the tree is not appropriate. An
2778 example is the token-ring routing information field (RIF). The best way
2779 to show the RIF in a GUI is by a sequence of ring and bridge numbers.
2780 Rings are 3-digit hex numbers, and bridges are single hex digits:
2782 RIF: 001-A-013-9-C0F-B-555
2784 In the case of RIF, the programmer should use a field with no value and
2785 use proto_tree_add_none_format() to build the above representation. The
2786 programmer can then add the ring and bridge values, one-by-one, with
2787 proto_tree_add_item() and hide them with PROTO_ITEM_SET_HIDDEN() so that the
2788 user can then filter on or search for a particular ring or bridge. Here's a
2789 skeleton of how the programmer might code this.
2792 rif = create_rif_string(...);
2794 proto_tree_add_none_format(tree, hf_tr_rif_label, ..., "RIF: %s", rif);
2796 for(i = 0; i < num_rings; i++) {
2799 pi = proto_tree_add_item(tree, hf_tr_rif_ring, ...,
2801 PROTO_ITEM_SET_HIDDEN(pi);
2803 for(i = 0; i < num_rings - 1; i++) {
2806 pi = proto_tree_add_item(tree, hf_tr_rif_bridge, ...,
2808 PROTO_ITEM_SET_HIDDEN(pi);
2811 The logical tree has these items:
2813 hf_tr_rif_label, text="RIF: 001-A-013-9-C0F-B-555", value = NONE
2814 hf_tr_rif_ring, hidden, value=0x001
2815 hf_tr_rif_bridge, hidden, value=0xA
2816 hf_tr_rif_ring, hidden, value=0x013
2817 hf_tr_rif_bridge, hidden, value=0x9
2818 hf_tr_rif_ring, hidden, value=0xC0F
2819 hf_tr_rif_bridge, hidden, value=0xB
2820 hf_tr_rif_ring, hidden, value=0x555
2822 GUI or print code will not display the hidden fields, but a display
2823 filter or "packet grep" routine will still see the values. The possible
2824 filter is then possible:
2826 tr.rif_ring eq 0x013
2830 PROTO_ITEM_SET_URL is used to mark fields as containing a URL. This can only
2831 be done with fields of type FT_STRING(Z). If these fields are presented they
2832 are underlined, as could be done in a browser. These fields are sensitive to
2833 clicks as well, launching the configured browser with this URL as parameter.
2835 1.7 Utility routines.
2837 1.7.1 match_strval, match_strval_ext, val_to_str and val_to_str_ext.
2839 A dissector may need to convert a value to a string, using a
2840 'value_string' structure, by hand, rather than by declaring a field with
2841 an associated 'value_string' structure; this might be used, for example,
2842 to generate a COL_INFO line for a frame.
2844 'match_strval()' will do that:
2847 match_strval(guint32 val, const value_string *vs)
2849 It will look up the value 'val' in the 'value_string' table pointed to
2850 by 'vs', and return either the corresponding string, or NULL if the
2851 value could not be found in the table. Note that, unless 'val' is
2852 guaranteed to be a value in the 'value_string' table ("guaranteed" as in
2853 "the code has already checked that it's one of those values" or "the
2854 table handles all possible values of the size of 'val'", not "the
2855 protocol spec says it has to be" - protocol specs do not prevent invalid
2856 packets from being put onto a network or into a purported packet capture
2857 file), you must check whether 'match_strval()' returns NULL, and arrange
2858 that its return value not be dereferenced if it's NULL. 'val_to_str()'
2859 can be used to generate a string for values not found in the table:
2862 val_to_str(guint32 val, const value_string *vs, const char *fmt)
2864 If the value 'val' is found in the 'value_string' table pointed to by
2865 'vs', 'val_to_str' will return the corresponding string; otherwise, it
2866 will use 'fmt' as an 'sprintf'-style format, with 'val' as an argument,
2867 to generate a string, and will return a pointer to that string.
2868 You can use it in a call to generate a COL_INFO line for a frame such as
2870 col_add_fstr(COL_INFO, ", %s", val_to_str(val, table, "Unknown %d"));
2872 The match_strval_ext and val_to_str_ext functions are "extended" versions
2873 of match_strval and val_to_str. They should be used for large value-string
2874 arrays which contain many entries. They implement value to string conversions
2875 which will do either a direct access or a binary search of the
2876 value string array if possible. See "Extended Value Strings" under
2877 section 1.6 "Constructing the protocol tree" for more information.
2879 See epan/value_string.h for detailed information on the various value_string
2883 1.7.2 match_strrval and rval_to_str.
2885 A dissector may need to convert a range of values to a string, using a
2886 'range_string' structure.
2888 'match_strrval()' will do that:
2891 match_strrval(guint32 val, const range_string *rs)
2893 It will look up the value 'val' in the 'range_string' table pointed to
2894 by 'rs', and return either the corresponding string, or NULL if the
2895 value could not be found in the table. Please note that its base
2896 behavior is inherited from match_strval().
2898 'rval_to_str()' can be used to generate a string for values not found in
2902 rval_to_str(guint32 val, const range_string *rs, const char *fmt)
2904 If the value 'val' is found in the 'range_string' table pointed to by
2905 'rs', 'rval_to_str' will return the corresponding string; otherwise, it
2906 will use 'fmt' as an 'sprintf'-style format, with 'val' as an argument,
2907 to generate a string, and will return a pointer to that string. Please
2908 note that its base behavior is inherited from match_strval().
2910 1.8 Calling Other Dissectors.
2912 As each dissector completes its portion of the protocol analysis, it
2913 is expected to create a new tvbuff of type TVBUFF_SUBSET which
2914 contains the payload portion of the protocol (that is, the bytes
2915 that are relevant to the next dissector).
2917 The syntax for creating a new TVBUFF_SUBSET is:
2919 next_tvb = tvb_new_subset(tvb, offset, length, reported_length)
2922 tvb is the tvbuff that the dissector has been working on. It
2923 can be a tvbuff of any type.
2925 next_tvb is the new TVBUFF_SUBSET.
2927 offset is the byte offset of 'tvb' at which the new tvbuff
2928 should start. The first byte is the 0th byte.
2930 length is the number of bytes in the new TVBUFF_SUBSET. A length
2931 argument of -1 says to use as many bytes as are available in
2934 reported_length is the number of bytes that the current protocol
2935 says should be in the payload. A reported_length of -1 says that
2936 the protocol doesn't say anything about the size of its payload.
2939 An example from packet-ipx.c -
2942 dissect_ipx(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
2945 int reported_length, available_length;
2948 /* Make the next tvbuff */
2950 /* IPX does have a length value in the header, so calculate report_length */
2951 Set this to -1 if there isn't any length information in the protocol
2953 reported_length = ipx_length - IPX_HEADER_LEN;
2955 /* Calculate the available data in the packet,
2956 set this to -1 to use all the data in the tv_buffer
2958 available_length = tvb_length(tvb) - IPX_HEADER_LEN;
2960 /* Create the tvbuffer for the next dissector */
2961 next_tvb = tvb_new_subset(tvb, IPX_HEADER_LEN,
2962 MIN(available_length, reported_length),
2965 /* call the next dissector */
2966 dissector_next( next_tvb, pinfo, tree);
2969 1.9 Editing Makefile.common and CMakeLists.txt to add your dissector.
2971 To arrange that your dissector will be built as part of Wireshark, you
2972 must add the name of the source file for your dissector to the
2973 'DISSECTOR_SRC' macro in the 'Makefile.common' file in the 'epan/dissectors'
2974 directory. (Note that this is for modern versions of UNIX, so there
2975 is no 14-character limitation on file names, and for modern versions of
2976 Windows, so there is no 8.3-character limitation on file names.)
2978 If your dissector also has its own header file or files, you must add
2979 them to the 'DISSECTOR_INCLUDES' macro in the 'Makefile.common' file in
2980 the 'epan/dissectors' directory, so that it's included when release source
2981 tarballs are built (otherwise, the source in the release tarballs won't
2984 In addition to the above, you should add your dissector source file name
2985 to the DISSECTOR_SRC section of epan/CMakeLists.txt
2988 1.10 Using the SVN source code tree.
2990 See <http://www.wireshark.org/develop.html>
2993 1.10a Using git with the SVN source code tree.
2995 Install git and the git-svn package.
2996 Run "mkdir git; cd git; git svn clone <svn-url>", e.g. if you are using
2997 the anonymous svn tree, run
2998 "git svn clone http://anonsvn.wireshark.org/wireshark/trunk/"
3000 After that, a typical workflow may look like this (from "man git-svn"):
3002 # Clone a repo (like git clone):
3003 git svn clone http://svn.example.com/project/trunk
3004 # Enter the newly cloned directory:
3006 # You should be on master branch, double-check with ´git branch´
3008 # Do some work and commit locally to git:
3010 # Something is committed to SVN, rebase your local changes against the
3011 # latest changes in SVN:
3013 # Now commit your changes (that were committed previously using git) to SVN
3014 # as well as automatically updating your working HEAD:
3016 # Append svn:ignore settings to the default git exclude file:
3017 git svn show-ignore >> .git/info/exclude
3020 1.11 Submitting code for your new dissector.
3022 - VERIFY that your dissector code does not use prohibited or deprecated APIs
3024 perl <wireshark_root>/tools/checkAPIs.pl <source-filename(s)>
3026 - TEST YOUR DISSECTOR BEFORE SUBMITTING IT.
3027 Use fuzz-test.sh and/or randpkt against your dissector. These are
3028 described at <http://wiki.wireshark.org/FuzzTesting>.
3030 - Subscribe to <mailto:wireshark-dev[AT]wireshark.org> by sending an email to
3031 <mailto:wireshark-dev-request[AT]wireshark.org?body="help"> or visiting
3032 <http://www.wireshark.org/lists/>.
3034 - 'svn add' all the files of your new dissector.
3036 - 'svn diff' the workspace and save the result to a file.
3038 - Edit the diff file - remove any changes unrelated to your new dissector,
3039 e.g. changes in config.nmake
3041 - Submit a bug report to the Wireshark bug database, found at
3042 <http://bugs.wireshark.org>, qualified as an enhancement and attach your
3043 diff file there. Set the review request flag to '?' so it will pop up in
3044 the patch review list.
3046 - Create a Wiki page on the protocol at <http://wiki.wireshark.org>.
3047 A template is provided so it is easy to setup in a consistent style.
3048 See: <http://wiki.wireshark.org/HowToEdit>
3049 and <http://wiki.wireshark.org/ProtocolReference>
3051 - If possible, add sample capture files to the sample captures page at
3052 <http://wiki.wireshark.org/SampleCaptures>. These files are used by
3053 the automated build system for fuzz testing.
3055 - If you find that you are contributing a lot to wireshark on an ongoing
3056 basis you can request to become a committer which will allow you to
3057 commit files to subversion directly.
3059 2. Advanced dissector topics.
3063 Some of the advanced features are being worked on constantly. When using them
3064 it is wise to check the relevant header and source files for additional details.
3066 2.2 Following "conversations".
3068 In wireshark a conversation is defined as a series of data packets between two
3069 address:port combinations. A conversation is not sensitive to the direction of
3070 the packet. The same conversation will be returned for a packet bound from
3071 ServerA:1000 to ClientA:2000 and the packet from ClientA:2000 to ServerA:1000.
3073 2.2.1 Conversation Routines
3075 There are six routines that you will use to work with a conversation:
3076 conversation_new, find_conversation, conversation_add_proto_data,
3077 conversation_get_proto_data, conversation_delete_proto_data,
3078 and conversation_set_dissector.
3081 2.2.1.1 The conversation_init function.
3083 This is an internal routine for the conversation code. As such you
3084 will not have to call this routine. Just be aware that this routine is
3085 called at the start of each capture and before the packets are filtered
3086 with a display filter. The routine will destroy all stored
3087 conversations. This routine does NOT clean up any data pointers that are
3088 passed in the conversation_add_proto_data 'data' variable. You are
3089 responsible for this clean up if you pass a malloc'ed pointer
3092 See item 2.2.1.5 for more information about use of the 'data' pointer.
3095 2.2.1.2 The conversation_new function.
3097 This routine will create a new conversation based upon two address/port
3098 pairs. If you want to associate with the conversation a pointer to a
3099 private data structure you must use the conversation_add_proto_data
3100 function. The ptype variable is used to differentiate between
3101 conversations over different protocols, i.e. TCP and UDP. The options
3102 variable is used to define a conversation that will accept any destination
3103 address and/or port. Set options = 0 if the destination port and address
3104 are know when conversation_new is called. See section 2.4 for more
3105 information on usage of the options parameter.
3107 The conversation_new prototype:
3108 conversation_t *conversation_new(guint32 setup_frame, address *addr1,
3109 address *addr2, port_type ptype, guint32 port1, guint32 port2,
3113 guint32 setup_frame = The lowest numbered frame for this conversation
3114 address* addr1 = first data packet address
3115 address* addr2 = second data packet address
3116 port_type ptype = port type, this is defined in packet.h
3117 guint32 port1 = first data packet port
3118 guint32 port2 = second data packet port
3119 guint options = conversation options, NO_ADDR2 and/or NO_PORT2
3121 setup_frame indicates the first frame for this conversation, and is used to
3122 distinguish multiple conversations with the same addr1/port1 and addr2/port2
3123 pair that occur within the same capture session.
3125 "addr1" and "port1" are the first address/port pair; "addr2" and "port2"
3126 are the second address/port pair. A conversation doesn't have source
3127 and destination address/port pairs - packets in a conversation go in
3128 both directions - so "addr1"/"port1" may be the source or destination
3129 address/port pair; "addr2"/"port2" would be the other pair.
3131 If NO_ADDR2 is specified, the conversation is set up so that a
3132 conversation lookup will match only the "addr1" address; if NO_PORT2 is
3133 specified, the conversation is set up so that a conversation lookup will
3134 match only the "port1" port; if both are specified, i.e.
3135 NO_ADDR2|NO_PORT2, the conversation is set up so that the lookup will
3136 match only the "addr1"/"port1" address/port pair. This can be used if a
3137 packet indicates that, later in the capture, a conversation will be
3138 created using certain addresses and ports, in the case where the packet
3139 doesn't specify the addresses and ports of both sides.
3141 2.2.1.3 The find_conversation function.
3143 Call this routine to look up a conversation. If no conversation is found,
3144 the routine will return a NULL value.
3146 The find_conversation prototype:
3148 conversation_t *find_conversation(guint32 frame_num, address *addr_a,
3149 address *addr_b, port_type ptype, guint32 port_a, guint32 port_b,
3153 guint32 frame_num = a frame number to match
3154 address* addr_a = first address
3155 address* addr_b = second address
3156 port_type ptype = port type
3157 guint32 port_a = first data packet port
3158 guint32 port_b = second data packet port
3159 guint options = conversation options, NO_ADDR_B and/or NO_PORT_B
3161 frame_num is a frame number to match. The conversation returned is where
3162 (frame_num >= conversation->setup_frame
3163 && frame_num < conversation->next->setup_frame)
3164 Suppose there are a total of 3 conversations (A, B, and C) that match
3165 addr_a/port_a and addr_b/port_b, where the setup_frame used in
3166 conversation_new() for A, B and C are 10, 50, and 100 respectively. The
3167 frame_num passed in find_conversation is compared to the setup_frame of each
3168 conversation. So if (frame_num >= 10 && frame_num < 50), conversation A is
3169 returned. If (frame_num >= 50 && frame_num < 100), conversation B is returned.
3170 If (frame_num >= 100) conversation C is returned.
3172 "addr_a" and "port_a" are the first address/port pair; "addr_b" and
3173 "port_b" are the second address/port pair. Again, as a conversation
3174 doesn't have source and destination address/port pairs, so
3175 "addr_a"/"port_a" may be the source or destination address/port pair;
3176 "addr_b"/"port_b" would be the other pair. The search will match the
3177 "a" address/port pair against both the "1" and "2" address/port pairs,
3178 and match the "b" address/port pair against both the "2" and "1"
3179 address/port pairs; you don't have to worry about which side the "a" or
3180 "b" pairs correspond to.
3182 If the NO_ADDR_B flag was specified to "find_conversation()", the
3183 "addr_b" address will be treated as matching any "wildcarded" address;
3184 if the NO_PORT_B flag was specified, the "port_b" port will be treated
3185 as matching any "wildcarded" port. If both flags are specified, i.e.
3186 NO_ADDR_B|NO_PORT_B, the "addr_b" address will be treated as matching
3187 any "wildcarded" address and the "port_b" port will be treated as
3188 matching any "wildcarded" port.
3191 2.2.1.4 The find_or_create_conversation function.
3193 This convenience function will create find an existing conversation (by calling
3194 find_conversation()) and, if a conversation does not already exist, create a
3195 new conversation by calling conversation_new().
3197 The find_or_create_conversation prototype:
3199 extern conversation_t *find_or_create_conversation(packet_info *pinfo);
3202 packet_info *pinfo = the packet_info structure
3204 The frame number and the addresses necessary for find_conversation() and
3205 conversation_new() are taken from the pinfo structure (as is commonly done)
3206 and no 'options' are used.
3209 2.2.1.5 The conversation_add_proto_data function.
3211 Once you have created a conversation with conversation_new, you can
3212 associate data with it using this function.
3214 The conversation_add_proto_data prototype:
3216 void conversation_add_proto_data(conversation_t *conv, int proto,
3220 conversation_t *conv = the conversation in question
3221 int proto = registered protocol number
3222 void *data = dissector data structure
3224 "conversation" is the value returned by conversation_new. "proto" is a
3225 unique protocol number created with proto_register_protocol. Protocols
3226 are typically registered in the proto_register_XXXX section of your
3227 dissector. "data" is a pointer to the data you wish to associate with the
3228 conversation. "data" usually points to "se_alloc'd" memory; the
3229 memory will be automatically freed each time a new dissection begins
3230 and thus need not be managed (freed) by the dissector.
3231 Using the protocol number allows several dissectors to
3232 associate data with a given conversation.
3235 2.2.1.6 The conversation_get_proto_data function.
3237 After you have located a conversation with find_conversation, you can use
3238 this function to retrieve any data associated with it.
3240 The conversation_get_proto_data prototype:
3242 void *conversation_get_proto_data(conversation_t *conv, int proto);
3245 conversation_t *conv = the conversation in question
3246 int proto = registered protocol number
3248 "conversation" is the conversation created with conversation_new. "proto"
3249 is a unique protocol number created with proto_register_protocol,
3250 typically in the proto_register_XXXX portion of a dissector. The function
3251 returns a pointer to the data requested, or NULL if no data was found.
3254 2.2.1.7 The conversation_delete_proto_data function.
3256 After you are finished with a conversation, you can remove your association
3257 with this function. Please note that ONLY the conversation entry is
3258 removed. If you have allocated any memory for your data (other than with se_alloc),
3259 you must free it as well.
3261 The conversation_delete_proto_data prototype:
3263 void conversation_delete_proto_data(conversation_t *conv, int proto);
3266 conversation_t *conv = the conversation in question
3267 int proto = registered protocol number
3269 "conversation" is the conversation created with conversation_new. "proto"
3270 is a unique protocol number created with proto_register_protocol,
3271 typically in the proto_register_XXXX portion of a dissector.
3273 2.2.1.8 The conversation_set_dissector function
3275 This function sets the protocol dissector to be invoked whenever
3276 conversation parameters (addresses, port_types, ports, etc) are matched
3277 during the dissection of a packet.
3279 The conversation_set_dissector prototype:
3281 void conversation_set_dissector(conversation_t *conversation, const dissector_handle_t handle);
3284 conversation_t *conv = the conversation in question
3285 const dissector_handle_t handle = the dissector handle.
3288 2.2.2 Using timestamps relative to the conversation
3290 There is a framework to calculate timestamps relative to the start of the
3291 conversation. First of all the timestamp of the first packet that has been
3292 seen in the conversation must be kept in the protocol data to be able
3293 to calculate the timestamp of the current packet relative to the start
3294 of the conversation. The timestamp of the last packet that was seen in the
3295 conversation should also be kept in the protocol data. This way the
3296 delta time between the current packet and the previous packet in the
3297 conversation can be calculated.
3299 So add the following items to the struct that is used for the protocol data:
3304 The ts_prev value should only be set during the first run through the
3305 packets (ie pinfo->fd->flags.visited is false).
3307 Next step is to use the per-packet information (described in section 2.5)
3308 to keep the calculated delta timestamp, as it can only be calculated
3309 on the first run through the packets. This is because a packet can be
3310 selected in random order once the whole file has been read.
3312 After calculating the conversation timestamps, it is time to put them in
3313 the appropriate columns with the function 'col_set_time' (described in
3314 section 1.5.9). There are two columns for conversation timestamps:
3316 COL_REL_CONV_TIME, /* Relative time to beginning of conversation */
3317 COL_DELTA_CONV_TIME,/* Delta time to last frame in conversation */
3319 Last but not least, there MUST be a preference in each dissector that
3320 uses conversation timestamps that makes it possible to enable and
3321 disable the calculation of conversation timestamps. The main argument
3322 for this is that a higher level conversation is able to overwrite
3323 the values of lower level conversations in these two columns. Being
3324 able to actively select which protocols may overwrite the conversation
3325 timestamp columns gives the user the power to control these columns.
3326 (A second reason is that conversation timestamps use the per-packet
3327 data structure which uses additional memory, which should be avoided
3328 if these timestamps are not needed)
3330 Have a look at the differences to packet-tcp.[ch] in SVN 22966 and
3331 SVN 23058 to see the implementation of conversation timestamps for
3335 2.2.3 The example conversation code using se_alloc'd memory.
3337 For a conversation between two IP addresses and ports you can use this as an
3338 example. This example uses se_alloc() to allocate memory and stores the data
3339 pointer in the conversation 'data' variable.
3341 /************************ Global values ************************/
3343 /* define your structure here */
3348 /* Registered protocol number */
3349 static int my_proto = -1;
3351 /********************* in the dissector routine *********************/
3353 /* the local variables in the dissector */
3355 conversation_t *conversation;
3356 my_entry_t *data_ptr;
3359 /* look up the conversation */
3361 conversation = find_conversation(pinfo->fd->num, &pinfo->src, &pinfo->dst,
3362 pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
3364 /* if conversation found get the data pointer that you stored */
3366 data_ptr = (my_entry_t*)conversation_get_proto_data(conversation, my_proto);
3369 /* new conversation create local data structure */
3371 data_ptr = se_alloc(sizeof(my_entry_t));
3373 /*** add your code here to setup the new data structure ***/
3375 /* create the conversation with your data pointer */
3377 conversation = conversation_new(pinfo->fd->num, &pinfo->src, &pinfo->dst, pinfo->ptype,
3378 pinfo->srcport, pinfo->destport, 0);
3379 conversation_add_proto_data(conversation, my_proto, (void *)data_ptr);
3382 /* at this point the conversation data is ready */
3384 /***************** in the protocol register routine *****************/
3386 my_proto = proto_register_protocol("My Protocol", "My Protocol", "my_proto");
3389 2.2.4 An example conversation code that starts at a specific frame number.
3391 Sometimes a dissector has determined that a new conversation is needed that
3392 starts at a specific frame number, when a capture session encompasses multiple
3393 conversation that reuse the same src/dest ip/port pairs. You can use the
3394 conversation->setup_frame returned by find_conversation with
3395 pinfo->fd->num to determine whether or not there already exists a conversation
3396 that starts at the specific frame number.
3398 /* in the dissector routine */
3400 conversation = find_conversation(pinfo->fd->num, &pinfo->src, &pinfo->dst,
3401 pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
3402 if (conversation == NULL || (conversation->setup_frame != pinfo->fd->num)) {
3403 /* It's not part of any conversation or the returned
3404 * conversation->setup_frame doesn't match the current frame
3407 conversation = conversation_new(pinfo->fd->num, &pinfo->src,
3408 &pinfo->dst, pinfo->ptype, pinfo->srcport, pinfo->destport,
3413 2.2.5 The example conversation code using conversation index field.
3415 Sometimes the conversation isn't enough to define a unique data storage
3416 value for the network traffic. For example if you are storing information
3417 about requests carried in a conversation, the request may have an
3418 identifier that is used to define the request. In this case the
3419 conversation and the identifier are required to find the data storage
3420 pointer. You can use the conversation data structure index value to
3421 uniquely define the conversation.
3423 See packet-afs.c for an example of how to use the conversation index. In
3424 this dissector multiple requests are sent in the same conversation. To store
3425 information for each request the dissector has an internal hash table based
3426 upon the conversation index and values inside the request packets.
3429 /* in the dissector routine */
3431 /* to find a request value, first lookup conversation to get index */
3432 /* then used the conversation index, and request data to find data */
3433 /* in the local hash table */
3435 conversation = find_or_create_conversation(pinfo);
3437 request_key.conversation = conversation->index;
3438 request_key.service = pntohs(&rxh->serviceId);
3439 request_key.callnumber = pntohl(&rxh->callNumber);
3441 request_val = (struct afs_request_val *)g_hash_table_lookup(
3442 afs_request_hash, &request_key);
3444 /* only allocate a new hash element when it's a request */
3446 if (!request_val && !reply)
3448 new_request_key = se_alloc(sizeof(struct afs_request_key));
3449 *new_request_key = request_key;
3451 request_val = se_alloc(sizeof(struct afs_request_val));
3452 request_val -> opcode = pntohl(&afsh->opcode);
3453 opcode = request_val->opcode;
3455 g_hash_table_insert(afs_request_hash, new_request_key,
3461 2.3 Dynamic conversation dissector registration.
3464 NOTE: This sections assumes that all information is available to
3465 create a complete conversation, source port/address and
3466 destination port/address. If either the destination port or
3467 address is know, see section 2.4 Dynamic server port dissector
3470 For protocols that negotiate a secondary port connection, for example
3471 packet-msproxy.c, a conversation can install a dissector to handle
3472 the secondary protocol dissection. After the conversation is created
3473 for the negotiated ports use the conversation_set_dissector to define
3474 the dissection routine.
3475 Before we create these conversations or assign a dissector to them we should
3476 first check that the conversation does not already exist and if it exists
3477 whether it is registered to our protocol or not.
3478 We should do this because it is uncommon but it does happen that multiple
3479 different protocols can use the same socketpair during different stages of
3480 an application cycle. By keeping track of the frame number a conversation
3481 was started in wireshark can still tell these different protocols apart.
3483 The second argument to conversation_set_dissector is a dissector handle,
3484 which is created with a call to create_dissector_handle or
3487 create_dissector_handle takes as arguments a pointer to the dissector
3488 function and a protocol ID as returned by proto_register_protocol;
3489 register_dissector takes as arguments a string giving a name for the
3490 dissector, a pointer to the dissector function, and a protocol ID.
3492 The protocol ID is the ID for the protocol dissected by the function.
3493 The function will not be called if the protocol has been disabled by the
3494 user; instead, the data for the protocol will be dissected as raw data.
3498 /* the handle for the dynamic dissector *
3499 static dissector_handle_t sub_dissector_handle;
3501 /* prototype for the dynamic dissector */
3502 static void sub_dissector(tvbuff_t *tvb, packet_info *pinfo,
3505 /* in the main protocol dissector, where the next dissector is setup */
3507 /* if conversation has a data field, create it and load structure */
3509 /* First check if a conversation already exists for this
3512 conversation = find_conversation(pinfo->fd->num,
3513 &pinfo->src, &pinfo->dst, protocol,
3514 src_port, dst_port, 0);
3516 /* If there is no such conversation, or if there is one but for
3517 someone else's protocol then we just create a new conversation
3518 and assign our protocol to it.
3520 if ( (conversation == NULL) ||
3521 (conversation->dissector_handle != sub_dissector_handle) ) {
3522 new_conv_info = se_alloc(sizeof(struct _new_conv_info));
3523 new_conv_info->data1 = value1;
3525 /* create the conversation for the dynamic port */
3526 conversation = conversation_new(pinfo->fd->num,
3527 &pinfo->src, &pinfo->dst, protocol,
3528 src_port, dst_port, new_conv_info, 0);
3530 /* set the dissector for the new conversation */
3531 conversation_set_dissector(conversation, sub_dissector_handle);
3536 proto_register_PROTOABBREV(void)
3540 sub_dissector_handle = create_dissector_handle(sub_dissector,
3546 2.4 Dynamic server port dissector registration.
3548 NOTE: While this example used both NO_ADDR2 and NO_PORT2 to create a
3549 conversation with only one port and address set, this isn't a
3550 requirement. Either the second port or the second address can be set
3551 when the conversation is created.
3553 For protocols that define a server address and port for a secondary
3554 protocol, a conversation can be used to link a protocol dissector to
3555 the server port and address. The key is to create the new
3556 conversation with the second address and port set to the "accept
3559 Some server applications can use the same port for different protocols during
3560 different stages of a transaction. For example it might initially use SNMP
3561 to perform some discovery and later switch to use TFTP using the same port.
3562 In order to handle this properly we must first check whether such a
3563 conversation already exists or not and if it exists we also check whether the
3564 registered dissector_handle for that conversation is "our" dissector or not.
3565 If not we create a new conversation on top of the previous one and set this new
3566 conversation to use our protocol.
3567 Since wireshark keeps track of the frame number where a conversation started
3568 wireshark will still be able to keep the packets apart even though they do use
3569 the same socketpair.
3570 (See packet-tftp.c and packet-snmp.c for examples of this)
3572 There are two support routines that will allow the second port and/or
3573 address to be set later.
3575 conversation_set_port2( conversation_t *conv, guint32 port);
3576 conversation_set_addr2( conversation_t *conv, address addr);
3578 These routines will change the second address or port for the
3579 conversation. So, the server port conversation will be converted into a
3580 more complete conversation definition. Don't use these routines if you
3581 want to create a conversation between the server and client and retain the
3582 server port definition, you must create a new conversation.
3587 /* the handle for the dynamic dissector *
3588 static dissector_handle_t sub_dissector_handle;
3592 /* in the main protocol dissector, where the next dissector is setup */
3594 /* if conversation has a data field, create it and load structure */
3596 new_conv_info = se_alloc(sizeof(struct _new_conv_info));
3597 new_conv_info->data1 = value1;
3599 /* create the conversation for the dynamic server address and port */
3600 /* NOTE: The second address and port values don't matter because the */
3601 /* NO_ADDR2 and NO_PORT2 options are set. */
3603 /* First check if a conversation already exists for this
3606 conversation = find_conversation(pinfo->fd->num,
3607 &server_src_addr, 0, protocol,
3608 server_src_port, 0, NO_ADDR2 | NO_PORT_B);
3609 /* If there is no such conversation, or if there is one but for
3610 someone else's protocol then we just create a new conversation
3611 and assign our protocol to it.
3613 if ( (conversation == NULL) ||
3614 (conversation->dissector_handle != sub_dissector_handle) ) {
3615 conversation = conversation_new(pinfo->fd->num,
3616 &server_src_addr, 0, protocol,
3617 server_src_port, 0, new_conv_info, NO_ADDR2 | NO_PORT2);
3619 /* set the dissector for the new conversation */
3620 conversation_set_dissector(conversation, sub_dissector_handle);
3623 2.5 Per-packet information.
3625 Information can be stored for each data packet that is processed by the
3626 dissector. The information is added with the p_add_proto_data function and
3627 retrieved with the p_get_proto_data function. The data pointers passed into
3628 the p_add_proto_data are not managed by the proto_data routines. If you use
3629 malloc or any other dynamic memory allocation scheme, you must release the
3630 data when it isn't required.
3633 p_add_proto_data(frame_data *fd, int proto, void *proto_data)
3635 p_get_proto_data(frame_data *fd, int proto)
3638 fd - The fd pointer in the pinfo structure, pinfo->fd
3639 proto - Protocol id returned by the proto_register_protocol call
3640 during initialization
3641 proto_data - pointer to the dissector data.
3644 2.6 User Preferences.
3646 If the dissector has user options, there is support for adding these preferences
3647 to a configuration dialog.
3649 You must register the module with the preferences routine with -
3651 module_t *prefs_register_protocol(proto_id, void (*apply_cb)(void))
3653 module_t *prefs_register_protocol_subtree(const char *subtree, int id,
3654 void (*apply_cb)(void));
3657 Where: proto_id - the value returned by "proto_register_protocol()" when
3658 the protocol was registered.
3659 apply_cb - Callback routine that is called when preferences are
3660 applied. It may be NULL, which inhibits the callback.
3661 subtree - grouping preferences tree node name (several protocols can
3662 be grouped under one preferences subtree)
3664 Then you can register the fields that can be configured by the user with these
3667 /* Register a preference with an unsigned integral value. */
3668 void prefs_register_uint_preference(module_t *module, const char *name,
3669 const char *title, const char *description, guint base, guint *var);
3671 /* Register a preference with an Boolean value. */
3672 void prefs_register_bool_preference(module_t *module, const char *name,
3673 const char *title, const char *description, gboolean *var);
3675 /* Register a preference with an enumerated value. */
3676 void prefs_register_enum_preference(module_t *module, const char *name,
3677 const char *title, const char *description, gint *var,
3678 const enum_val_t *enumvals, gboolean radio_buttons)
3680 /* Register a preference with a character-string value. */
3681 void prefs_register_string_preference(module_t *module, const char *name,
3682 const char *title, const char *description, char **var)
3684 /* Register a preference with a range of unsigned integers (e.g.,
3687 void prefs_register_range_preference(module_t *module, const char *name,
3688 const char *title, const char *description, range_t *var,
3691 Where: module - Returned by the prefs_register_protocol routine
3692 name - This is appended to the name of the protocol, with a
3693 "." between them, to construct a name that identifies
3694 the field in the preference file; the name itself
3695 should not include the protocol name, as the name in
3696 the preference file will already have it. Make sure that
3697 only lower-case ASCII letters, numbers, underscores and
3698 dots appear in the preference name.
3699 title - Field title in the preferences dialog
3700 description - Comments added to the preference file above the
3701 preference value and shown as tooltip in the GUI, or NULL
3702 var - pointer to the storage location that is updated when the
3703 field is changed in the preference dialog box. Note that
3704 with string preferences the given pointer is overwritten
3705 with a pointer to a new copy of the string during the
3706 preference registration. The passed-in string may be
3707 freed, but you must keep another pointer to the string
3708 in order to free it.
3709 base - Base that the unsigned integer is expected to be in,
3711 enumvals - an array of enum_val_t structures. This must be
3712 NULL-terminated; the members of that structure are:
3714 a short name, to be used with the "-o" flag - it
3715 should not contain spaces or upper-case letters,
3716 so that it's easier to put in a command line;
3718 a description, which is used in the GUI (and
3719 which, for compatibility reasons, is currently
3720 what's written to the preferences file) - it can
3721 contain spaces, capital letters, punctuation,
3724 the numerical value corresponding to that name
3726 radio_buttons - TRUE if the field is to be displayed in the
3727 preferences dialog as a set of radio buttons,
3728 FALSE if it is to be displayed as an option
3730 max_value - The maximum allowed value for a range (0 is the minimum).
3732 An example from packet-beep.c -
3734 proto_beep = proto_register_protocol("Blocks Extensible Exchange Protocol",
3739 /* Register our configuration options for BEEP, particularly our port */
3741 beep_module = prefs_register_protocol(proto_beep, proto_reg_handoff_beep);
3743 prefs_register_uint_preference(beep_module, "tcp.port", "BEEP TCP Port",
3744 "Set the port for BEEP messages (if other"
3745 " than the default of 10288)",
3746 10, &global_beep_tcp_port);
3748 prefs_register_bool_preference(beep_module, "strict_header_terminator",
3749 "BEEP Header Requires CRLF",
3750 "Specifies that BEEP requires CRLF as a "
3751 "terminator, and not just CR or LF",
3752 &global_beep_strict_term);
3754 This will create preferences "beep.tcp.port" and
3755 "beep.strict_header_terminator", the first of which is an unsigned
3756 integer and the second of which is a Boolean.
3758 Note that a warning will pop up if you've saved such preference to the
3759 preference file and you subsequently take the code out. The way to make
3760 a preference obsolete is to register it as such:
3762 /* Register a preference that used to be supported but no longer is. */
3763 void prefs_register_obsolete_preference(module_t *module,
3766 2.7 Reassembly/desegmentation for protocols running atop TCP.
3768 There are two main ways of reassembling a Protocol Data Unit (PDU) which
3769 spans across multiple TCP segments. The first approach is simpler, but
3770 assumes you are running atop of TCP when this occurs (but your dissector
3771 might run atop of UDP, too, for example), and that your PDUs consist of a
3772 fixed amount of data that includes enough information to determine the PDU
3773 length, possibly followed by additional data. The second method is more
3774 generic but requires more code and is less efficient.
3776 2.7.1 Using tcp_dissect_pdus().
3778 For the first method, you register two different dissection methods, one
3779 for the TCP case, and one for the other cases. It is a good idea to
3780 also have a dissect_PROTO_common function which will parse the generic
3781 content that you can find in all PDUs which is called from
3782 dissect_PROTO_tcp when the reassembly is complete and from
3783 dissect_PROTO_udp (or dissect_PROTO_other).
3785 To register the distinct dissector functions, consider the following
3786 example, stolen from packet-dns.c:
3788 dissector_handle_t dns_udp_handle;
3789 dissector_handle_t dns_tcp_handle;
3790 dissector_handle_t mdns_udp_handle;
3792 dns_udp_handle = create_dissector_handle(dissect_dns_udp,
3794 dns_tcp_handle = create_dissector_handle(dissect_dns_tcp,
3796 mdns_udp_handle = create_dissector_handle(dissect_mdns_udp,
3799 dissector_add_uint("udp.port", UDP_PORT_DNS, dns_udp_handle);
3800 dissector_add_uint("tcp.port", TCP_PORT_DNS, dns_tcp_handle);
3801 dissector_add_uint("udp.port", UDP_PORT_MDNS, mdns_udp_handle);
3802 dissector_add_uint("tcp.port", TCP_PORT_MDNS, dns_tcp_handle);
3804 The dissect_dns_udp function does very little work and calls
3805 dissect_dns_common, while dissect_dns_tcp calls tcp_dissect_pdus with a
3806 reference to a callback which will be called with reassembled data:
3809 dissect_dns_tcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
3811 tcp_dissect_pdus(tvb, pinfo, tree, dns_desegment, 2,
3812 get_dns_pdu_len, dissect_dns_tcp_pdu);
3815 (The dissect_dns_tcp_pdu function acts similarly to dissect_dns_udp.)
3816 The arguments to tcp_dissect_pdus are:
3818 the tvbuff pointer, packet_info pointer, and proto_tree pointer
3819 passed to the dissector;
3821 a gboolean flag indicating whether desegmentation is enabled for
3824 the number of bytes of PDU data required to determine the length
3827 a routine that takes as arguments a packet_info pointer, a tvbuff
3828 pointer and an offset value representing the offset into the tvbuff
3829 at which a PDU begins and should return - *without* throwing an
3830 exception (it is guaranteed that the number of bytes specified by the
3831 previous argument to tcp_dissect_pdus is available, but more data
3832 might not be available, so don't refer to any data past that) - the
3833 total length of the PDU, in bytes;
3835 a routine that's passed a tvbuff pointer, packet_info pointer,
3836 and proto_tree pointer, with the tvbuff containing a
3837 possibly-reassembled PDU, and that should dissect that PDU.
3839 2.7.2 Modifying the pinfo struct.
3841 The second reassembly mode is preferred when the dissector cannot determine
3842 how many bytes it will need to read in order to determine the size of a PDU.
3843 It may also be useful if your dissector needs to support reassembly from
3844 protocols other than TCP.
3846 Your dissect_PROTO will initially be passed a tvbuff containing the payload of
3847 the first packet. It should dissect as much data as it can, noting that it may
3848 contain more than one complete PDU. If the end of the provided tvbuff coincides
3849 with the end of a PDU then all is well and your dissector can just return as
3850 normal. (If it is a new-style dissector, it should return the number of bytes
3851 successfully processed.)
3853 If the dissector discovers that the end of the tvbuff does /not/ coincide with
3854 the end of a PDU, (ie, there is half of a PDU at the end of the tvbuff), it can
3855 indicate this to the parent dissector, by updating the pinfo struct. The
3856 desegment_offset field is the offset in the tvbuff at which the dissector will
3857 continue processing when next called. The desegment_len field should contain
3858 the estimated number of additional bytes required for completing the PDU. Next
3859 time your dissect_PROTO is called, it will be passed a tvbuff composed of the
3860 end of the data from the previous tvbuff together with desegment_len more bytes.
3862 If the dissector cannot tell how many more bytes it will need, it should set
3863 desegment_len=DESEGMENT_ONE_MORE_SEGMENT; it will then be called again as soon
3864 as any more data becomes available. Dissectors should set the desegment_len to a
3865 reasonable value when possible rather than always setting
3866 DESEGMENT_ONE_MORE_SEGMENT as it will generally be more efficient. Also, you
3867 *must not* set desegment_len=1 in this case, in the hope that you can change
3868 your mind later: once you return a positive value from desegment_len, your PDU
3869 boundary is set in stone.
3871 static hf_register_info hf[] = {
3873 {"C String", "c.string", FT_STRING, BASE_NONE, NULL, 0x0,
3879 * Dissect a buffer containing ASCII C strings.
3881 * @param tvb The buffer to dissect.
3882 * @param pinfo Packet Info.
3883 * @param tree The protocol tree.
3885 static void dissect_cstr(tvbuff_t * tvb, packet_info * pinfo, proto_tree * tree)
3888 while(offset < tvb_reported_length(tvb)) {
3889 gint available = tvb_reported_length_remaining(tvb, offset);
3890 gint len = tvb_strnlen(tvb, offset, available);
3893 /* we ran out of data: ask for more */
3894 pinfo->desegment_offset = offset;
3895 pinfo->desegment_len = DESEGMENT_ONE_MORE_SEGMENT;
3899 col_set_str(pinfo->cinfo, COL_INFO, "C String");
3901 len += 1; /* Add one for the '\0' */
3904 proto_tree_add_item(tree, hf_cstring, tvb, offset, len,
3907 offset += (guint)len;
3910 /* if we get here, then the end of the tvb coincided with the end of a
3911 string. Happy days. */
3914 This simple dissector will repeatedly return DESEGMENT_ONE_MORE_SEGMENT
3915 requesting more data until the tvbuff contains a complete C string. The C string
3916 will then be added to the protocol tree. Note that there may be more
3917 than one complete C string in the tvbuff, so the dissection is done in a
3922 The ptvcursor API allows a simpler approach to writing dissectors for
3923 simple protocols. The ptvcursor API works best for protocols whose fields
3924 are static and whose format does not depend on the value of other fields.
3925 However, even if only a portion of your protocol is statically defined,
3926 then that portion could make use of ptvcursors.
3928 The ptvcursor API lets you extract data from a tvbuff, and add it to a
3929 protocol tree in one step. It also keeps track of the position in the
3930 tvbuff so that you can extract data again without having to compute any
3931 offsets --- hence the "cursor" name of the API.
3933 The three steps for a simple protocol are:
3934 1. Create a new ptvcursor with ptvcursor_new()
3935 2. Add fields with multiple calls of ptvcursor_add()
3936 3. Delete the ptvcursor with ptvcursor_free()
3938 ptvcursor offers the possibility to add subtrees in the tree as well. It can be
3939 done in very simple steps :
3940 1. Create a new subtree with ptvcursor_push_subtree(). The old subtree is
3941 pushed in a stack and the new subtree will be used by ptvcursor.
3942 2. Add fields with multiple calls of ptvcursor_add(). The fields will be
3943 added in the new subtree created at the previous step.
3944 3. Pop the previous subtree with ptvcursor_pop_subtree(). The previous
3945 subtree is again used by ptvcursor.
3946 Note that at the end of the parsing of a packet you must have popped each
3947 subtree you pushed. If it's not the case, the dissector will generate an error.
3949 To use the ptvcursor API, include the "ptvcursor.h" file. The PGM dissector
3950 is an example of how to use it. You don't need to look at it as a guide;
3951 instead, the API description here should be good enough.
3953 2.8.1 ptvcursor API.
3956 ptvcursor_new(proto_tree* tree, tvbuff_t* tvb, gint offset)
3957 This creates a new ptvcursor_t object for iterating over a tvbuff.
3958 You must call this and use this ptvcursor_t object so you can use the
3962 ptvcursor_add(ptvcursor_t* ptvc, int hf, gint length, const guint encoding)
3963 This will extract 'length' bytes from the tvbuff and place it in
3964 the proto_tree as field 'hf', which is a registered header_field. The
3965 pointer to the proto_item that is created is passed back to you. Internally,
3966 the ptvcursor advances its cursor so the next call to ptvcursor_add
3967 starts where this call finished. The 'encoding' parameter is relevant for
3968 certain type of fields (See above under proto_tree_add_item()).
3971 ptvcursor_add_no_advance(ptvcursor_t* ptvc, int hf, gint length, const guint encoding)
3972 Like ptvcursor_add, but does not advance the internal cursor.
3975 ptvcursor_advance(ptvcursor_t* ptvc, gint length)
3976 Advances the internal cursor without adding anything to the proto_tree.
3979 ptvcursor_free(ptvcursor_t* ptvc)
3980 Frees the memory associated with the ptvcursor. You must call this
3981 after your dissection with the ptvcursor API is completed.
3985 ptvcursor_push_subtree(ptvcursor_t* ptvc, proto_item* it, gint ett_subtree)
3986 Pushes the current subtree in the tree stack of the cursor, creates a new
3987 one and sets this one as the working tree.
3990 ptvcursor_pop_subtree(ptvcursor_t* ptvc);
3991 Pops a subtree in the tree stack of the cursor
3994 ptvcursor_add_with_subtree(ptvcursor_t* ptvc, int hfindex, gint length,
3995 const guint encoding, gint ett_subtree);
3996 Adds an item to the tree and creates a subtree.
3997 If the length is unknown, length may be defined as SUBTREE_UNDEFINED_LENGTH.
3998 In this case, at the next pop, the item length will be equal to the advancement
3999 of the cursor since the creation of the subtree.
4002 ptvcursor_add_text_with_subtree(ptvcursor_t* ptvc, gint length,
4003 gint ett_subtree, const char* format, ...);
4004 Add a text node to the tree and create a subtree.
4005 If the length is unknown, length may be defined as SUBTREE_UNDEFINED_LENGTH.
4006 In this case, at the next pop, the item length will be equal to the advancement
4007 of the cursor since the creation of the subtree.
4009 2.8.2 Miscellaneous functions.
4012 ptvcursor_tvbuff(ptvcursor_t* ptvc)
4013 Returns the tvbuff associated with the ptvcursor.
4016 ptvcursor_current_offset(ptvcursor_t* ptvc)
4017 Returns the current offset.
4020 ptvcursor_tree(ptvcursor_t* ptvc)
4021 Returns the proto_tree associated with the ptvcursor.
4024 ptvcursor_set_tree(ptvcursor_t* ptvc, proto_tree *tree)
4025 Sets a new proto_tree for the ptvcursor.
4028 ptvcursor_set_subtree(ptvcursor_t* ptvc, proto_item* it, gint ett_subtree);
4029 Creates a subtree and adds it to the cursor as the working tree but does
4030 not save the old working tree.