This file is a HOWTO for Wireshark developers interested in writing or working on Wireshark protocol dissectors. It describes expected code patterns and the use of some of the important functions and variables. This file is compiled to give in depth information on Wireshark. It is by no means all inclusive and complete. Please feel free to send remarks and patches to the developer mailing list. If you haven't read README.developer, read that first! 0. Prerequisites. Before starting to develop a new dissector, a "running" Wireshark build environment is required - there's no such thing as a standalone "dissector build toolkit". How to setup such an environment is platform dependent; detailed information about these steps can be found in the "Developer's Guide" (available from: https://www.wireshark.org) and in the INSTALL and README.md files of the sources root dir. 0.1. Dissector related README files. You'll find additional dissector related information in the following README files: - README.heuristic - what are heuristic dissectors and how to write them - README.plugins - how to "pluginize" a dissector - README.request_response_tracking - how to track req./resp. times and such - README.wmem - how to obtain "memory leak free" memory 0.2 Contributors James Coe <jammer[AT]cin.net> Gilbert Ramirez <gram[AT]alumni.rice.edu> Jeff Foster <jfoste[AT]woodward.com> Olivier Abad <oabad[AT]cybercable.fr> Laurent Deniel <laurent.deniel[AT]free.fr> Gerald Combs <gerald[AT]wireshark.org> Guy Harris <guy[AT]alum.mit.edu> Ulf Lamping <ulf.lamping[AT]web.de> Barbu Paul - Gheorghe <barbu.paul.gheorghe[AT]gmail.com> 1. Setting up your protocol dissector code. This section provides skeleton code for a protocol dissector. It also explains the basic functions needed to enter values in the traffic summary columns, add to the protocol tree, and work with registered header fields. 1.1 Skeleton code. Wireshark requires certain things when setting up a protocol dissector. We provide basic skeleton code for a dissector that you can copy to a new file and fill in. Your dissector should follow the naming convention of "packet-" followed by the abbreviated name for the protocol. It is recommended that where possible you keep to the IANA abbreviated name for the protocol, if there is one, or a commonly-used abbreviation for the protocol, if any. The skeleton code lives in the file "packet-PROTOABBREV.c" in the same source directory as this README. If instead of using the skeleton you base your dissector on an existing real dissector, please put a little note in the copyright header indicating which dissector you started with. Usually, you will put your newly created dissector file into the directory epan/dissectors/, just like all the other packet-*.c files already in there. Also, please add your dissector file to the corresponding makefiles, described in section "1.8 Editing CMakeLists.txt to add your dissector" below. Dissectors that use the dissector registration API to register with a lower level protocol (this is the vast majority) don't need to define a prototype in their .h file. For other dissectors the main dissector routine should have a prototype in a header file whose name is "packet-", followed by the abbreviated name for the protocol, followed by ".h"; any dissector file that calls your dissector should be changed to include that file. You may not need to include all the headers listed in the skeleton, and you may need to include additional headers. 1.2 Explanation of needed substitutions in code skeleton. In the skeleton sample code the following strings should be substituted with your information. YOUR_NAME Your name, of course. You do want credit, don't you? It's the only payment you will receive.... YOUR_EMAIL_ADDRESS Keep those cards and letters coming. PROTONAME The name of the protocol; this is displayed in the top-level protocol tree item for that protocol. PROTOSHORTNAME An abbreviated name for the protocol; this is displayed in the "Preferences" dialog box if your dissector has any preferences, in the dialog box of enabled protocols, and in the dialog box for filter fields when constructing a filter expression. PROTOABBREV A name for the protocol for use in filter expressions; it may contain only lower-case letters, digits, and hyphens, underscores, and periods. FIELDNAME The displayed name for the header field. FIELDABBREV The abbreviated name for the header field; it may contain only letters, digits, hyphens, underscores, and periods. FIELDTYPE FT_NONE, FT_BOOLEAN, FT_CHAR, FT_UINT8, FT_UINT16, FT_UINT24, FT_UINT32, FT_UINT40, FT_UINT48, FT_UINT56, FT_UINT64, FT_INT8, FT_INT16, FT_INT24, FT_INT32, FT_INT40, FT_INT48, FT_INT56, FT_INT64, FT_FLOAT, FT_DOUBLE, FT_ABSOLUTE_TIME, FT_RELATIVE_TIME, FT_STRING, FT_STRINGZ, FT_EUI64, FT_UINT_STRING, FT_ETHER, FT_BYTES, FT_UINT_BYTES, FT_IPv4, FT_IPv6, FT_IPXNET, FT_FRAMENUM, FT_PROTOCOL, FT_GUID, FT_OID, FT_REL_OID, FT_AX25, FT_VINES, FT_SYSTEM_ID, FT_FC, FT_FCWWN FIELDDISPLAY --For FT_UINT{8,16,24,32,40,48,56,64} and FT_INT{8,16,24,32,40,48,56,64): BASE_DEC, BASE_HEX, BASE_OCT, BASE_DEC_HEX, BASE_HEX_DEC, BASE_CUSTOM, or BASE_NONE, possibly ORed with BASE_RANGE_STRING, BASE_EXT_STRING, BASE_VAL64_STRING, BASE_ALLOW_ZERO, BASE_UNIT_STRING, BASE_SPECIAL_VALS or BASE_NO_DISPLAY_VALUE BASE_NONE may be used with a non-NULL FIELDCONVERT when the numeric value of the field itself is not of significance to the user (for example, the number is a generated field). When this is the case the numeric value is not shown to the user in the protocol decode nor is it used when preparing filters for the field in question. BASE_NO_DISPLAY_VALUE will just display the field name with no value. It is intended for byte arrays (FT_BYTES) or header fields above a subtree. The value will still be filterable, just not displayed. --For FT_UINT16: BASE_PT_UDP, BASE_PT_TCP, BASE_PT_DCCP or BASE_PT_SCTP --For FT_UINT24: BASE_OUI --For FT_CHAR: BASE_HEX, BASE_OCT, BASE_CUSTOM, or BASE_NONE, possibly ORed with BASE_RANGE_STRING, BASE_EXT_STRING or BASE_VAL64_STRING. BASE_NONE can be used in the same way as with FT_UINT8. --For FT_ABSOLUTE_TIME: ABSOLUTE_TIME_LOCAL, ABSOLUTE_TIME_UTC, or ABSOLUTE_TIME_DOY_UTC --For FT_BOOLEAN: if BITMASK is non-zero: Number of bits in the field containing the FT_BOOLEAN bitfield. otherwise: (must be) BASE_NONE --For FT_STRING, FT_STRINGZ and FT_UINT_STRING: STR_ASCII or STR_UNICODE --For FT_BYTES: SEP_DOT, SEP_DASH, SEP_COLON, or SEP_SPACE to provide a separator between bytes. BASE_NONE has no separator between bytes BASE_ALLOW_ZERO displays <none> instead of <MISSING> for zero sized byte array --For FT_IPv4: BASE_NETMASK - Used for IPv4 address that should never attempted to be resolved (like netmasks) otherwise: (must be) BASE_NONE --For all other types: BASE_NONE FIELDCONVERT VALS(x), VALS64(x), RVALS(x), TFS(x), CF_FUNC(x), NULL BITMASK Used to mask a field not 8-bit aligned or with a size other than a multiple of 8 bits FIELDDESCR A brief description of the field, or NULL. [Please do not use ""]. If, for example, PROTONAME is "Internet Bogosity Discovery Protocol", PROTOSHORTNAME would be "IBDP", and PROTOABBREV would be "ibdp". Try to conform with IANA names. 1.3 The dissector and the data it receives. 1.3.1 Header file. This is only needed if the dissector doesn't use self-registration to register itself with the lower level dissector, or if the protocol dissector wants/needs to expose code to other subdissectors. The dissector must be declared exactly as follows in the file packet-PROTOABBREV.h: int dissect_PROTOABBREV(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree); 1.3.2 Extracting data from packets. NOTE: See the file /epan/tvbuff.h for more details. The "tvb" argument to a dissector points to a buffer containing the raw data to be analyzed by the dissector; for example, for a protocol running atop UDP, it contains the UDP payload (but not the UDP header, or any protocol headers above it). A tvbuffer is an opaque data structure, the internal data structures are hidden and the data must be accessed via the tvbuffer accessors. The accessors are: Bit accessors for a maximum of 8-bits, 16-bits 32-bits and 64-bits: guint8 tvb_get_bits8(tvbuff_t *tvb, gint bit_offset, const gint no_of_bits); guint16 tvb_get_bits16(tvbuff_t *tvb, guint bit_offset, const gint no_of_bits, const guint encoding); guint32 tvb_get_bits32(tvbuff_t *tvb, guint bit_offset, const gint no_of_bits, const guint encoding); guint64 tvb_get_bits64(tvbuff_t *tvb, guint bit_offset, const gint no_of_bits, const guint encoding); Single-byte accessors for 8-bit unsigned integers (guint8) and 8-bit signed integers (gint8): guint8 tvb_get_guint8(tvbuff_t *tvb, const gint offset); gint8 tvb_get_gint8(tvbuff_t *tvb, const gint offset); Network-to-host-order accessors: 16-bit unsigned (guint16) and signed (gint16) integers: guint16 tvb_get_ntohs(tvbuff_t *tvb, const gint offset); gint16 tvb_get_ntohis(tvbuff_t *tvb, const gint offset); 24-bit unsigned and signed integers: guint32 tvb_get_ntoh24(tvbuff_t *tvb, const gint offset); gint32 tvb_get_ntohi24(tvbuff_t *tvb, const gint offset); 32-bit unsgined (guint32) and signed (gint32) integers: guint32 tvb_get_ntohl(tvbuff_t *tvb, const gint offset); gint32 tvb_get_ntohil(tvbuff_t *tvb, const gint offset); 40-bit unsigned and signed integers: guint64 tvb_get_ntoh40(tvbuff_t *tvb, const gint offset); gint64 tvb_get_ntohi40(tvbuff_t *tvb, const gint offset); 48-bit unsigned and signed integers: guint64 tvb_get_ntoh48(tvbuff_t *tvb, const gint offset); gint64 tvb_get_ntohi48(tvbuff_t *tvb, const gint offset); 56-bit unsigned and signed integers: guint64 tvb_get_ntoh56(tvbuff_t *tvb, const gint offset); gint64 tvb_get_ntohi56(tvbuff_t *tvb, const gint offset); 64-bit unsigned (guint64) and signed (gint64) integers: guint64 tvb_get_ntoh64(tvbuff_t *tvb, const gint offset); gint64 tvb_get_ntohi64(tvbuff_t *tvb, const gint offset); Single-precision and double-precision IEEE floating-point numbers: gfloat tvb_get_ntohieee_float(tvbuff_t *tvb, const gint offset); gdouble tvb_get_ntohieee_double(tvbuff_t *tvb, const gint offset); Little-Endian-to-host-order accessors: 16-bit unsigned (guint16) and signed (gint16) integers: guint16 tvb_get_letohs(tvbuff_t *tvb, const gint offset); gint16 tvb_get_letohis(tvbuff_t *tvb, const gint offset); 24-bit unsigned and signed integers: guint32 tvb_get_letoh24(tvbuff_t *tvb, const gint offset); gint32 tvb_get_letohi24(tvbuff_t *tvb, const gint offset); 32-bit unsigned (guint32) and signed (gint32) integers: guint32 tvb_get_letohl(tvbuff_t *tvb, const gint offset); gint32 tvb_get_letohil(tvbuff_t *tvb, const gint offset); 40-bit unsigned and signed integers: guint64 tvb_get_letoh40(tvbuff_t *tvb, const gint offset); gint64 tvb_get_letohi40(tvbuff_t *tvb, const gint offset); 48-bit unsigned and signed integers: guint64 tvb_get_letoh48(tvbuff_t *tvb, const gint offset); gint64 tvb_get_letohi48(tvbuff_t *tvb, const gint offset); 56-bit unsigned and signed integers: guint64 tvb_get_letoh56(tvbuff_t *tvb, const gint offset); gint64 tvb_get_letohi56(tvbuff_t *tvb, const gint offset); 64-bit unsigned (guint64) and signed (gint64) integers: guint64 tvb_get_letoh64(tvbuff_t *tvb, const gint offset); gint64 tvb_get_letohi64(tvbuff_t *tvb, const gint offset); Single-precision and double-precision IEEE floating-point numbers: gfloat tvb_get_letohieee_float(tvbuff_t *tvb, const gint offset); gdouble tvb_get_letohieee_double(tvbuff_t *tvb, const gint offset); Encoding-to_host-order accessors: 16-bit unsigned (guint16) and signed (gint16) integers: guint16 tvb_get_guint16(tvbuff_t *tvb, const gint offset, const guint encoding); gint16 tvb_get_gint16(tvbuff_t *tvb, const gint offset, const guint encoding); 24-bit unsigned and signed integers: guint32 tvb_get_guint24(tvbuff_t *tvb, const gint offset, const guint encoding); gint32 tvb_get_gint24(tvbuff_t *tvb, const gint offset, const guint encoding); 32-bit unsigned (guint32) and signed (gint32) integers: guint32 tvb_get_guint32(tvbuff_t *tvb, const gint offset, const guint encoding); gint32 tvb_get_gint32(tvbuff_t *tvb, const gint offset, const guint encoding); 40-bit unsigned and signed integers: guint64 tvb_get_guint40(tvbuff_t *tvb, const gint offset, const guint encoding); gint64 tvb_get_gint40(tvbuff_t *tvb, const gint offset, const guint encoding); 48-bit unsigned and signed integers: guint64 tvb_get_guint48(tvbuff_t *tvb, const gint offset, const guint encoding); gint64 tvb_get_gint48(tvbuff_t *tvb, const gint offset, const guint encoding); 56-bit unsigned and signed integers: guint64 tvb_get_guint56(tvbuff_t *tvb, const gint offset, const guint encoding); gint64 tvb_get_gint56(tvbuff_t *tvb, const gint offset, const guint encoding); 64-bit unsigned (guint64) and signed (gint64) integers: guint64 tvb_get_guint64(tvbuff_t *tvb, const gint offset, const guint encoding); gint64 tvb_get_gint64(tvbuff_t *tvb, const gint offset, const guint encoding); Single-precision and double-precision IEEE floating-point numbers: gfloat tvb_get_ieee_float(tvbuff_t *tvb, const gint offset, const guint encoding); gdouble tvb_get_ieee_double(tvbuff_t *tvb, const gint offset, const guint encoding); "encoding" should be ENC_BIG_ENDIAN for Network-to-host-order, ENC_LITTLE_ENDIAN for Little-Endian-to-host-order, or ENC_HOST_ENDIAN for host order. Accessors for IPv4 and IPv6 addresses: guint32 tvb_get_ipv4(tvbuff_t *tvb, const gint offset); void tvb_get_ipv6(tvbuff_t *tvb, const gint offset, ws_in6_addr *addr); NOTE: IPv4 addresses are not to be converted to host byte order before being passed to "proto_tree_add_ipv4()". You should use "tvb_get_ipv4()" to fetch them, not "tvb_get_ntohl()" *OR* "tvb_get_letohl()" - don't, for example, try to use "tvb_get_ntohl()", find that it gives you the wrong answer on the PC on which you're doing development, and try "tvb_get_letohl()" instead, as "tvb_get_letohl()" will give the wrong answer on big-endian machines. gchar *tvb_ip_to_str(tvbuff_t *tvb, const gint offset) gchar *tvb_ip6_to_str(tvbuff_t *tvb, const gint offset) Returns a null-terminated buffer containing a string with IPv4 or IPv6 Address from the specified tvbuff, starting at the specified offset. Accessors for GUID: void tvb_get_ntohguid(tvbuff_t *tvb, const gint offset, e_guid_t *guid); void tvb_get_letohguid(tvbuff_t *tvb, const gint offset, e_guid_t *guid); void tvb_get_guid(tvbuff_t *tvb, const gint offset, e_guid_t *guid, const guint encoding); String accessors: guint8 *tvb_get_string_enc(wmem_allocator_t *scope, tvbuff_t *tvb, const gint offset, const gint length, const guint encoding); Returns a null-terminated buffer allocated from the specified scope, containing data from the specified tvbuff, starting at the specified offset, and containing the specified length worth of characters. Reads data in the specified encoding and produces UTF-8 in the buffer. See below for a list of input encoding values. The buffer is allocated in the given wmem scope (see README.wmem for more information). guint8 *tvb_get_stringz_enc(wmem_allocator_t *scope, tvbuff_t *tvb, const gint offset, gint *lengthp, const guint encoding); Returns a null-terminated buffer allocated from the specified scope, containing data from the specified tvbuff, starting at the specified offset, and containing all characters from the tvbuff up to and including a terminating null character in the tvbuff. Reads data in the specified encoding and produces UTF-8 in the buffer. See below for a list of input encoding values. "*lengthp" will be set to the length of the string, including the terminating null. The buffer is allocated in the given wmem scope (see README.wmem for more information). const guint8 *tvb_get_const_stringz(tvbuff_t *tvb, const gint offset, gint *lengthp); Returns a null-terminated const buffer containing data from the specified tvbuff, starting at the specified offset, and containing all bytes from the tvbuff up to and including a terminating null character in the tvbuff. "*lengthp" will be set to the length of the string, including the terminating null. You do not need to free() this buffer; it will happen automatically once the next packet is dissected. This function is slightly more efficient than the others because it does not allocate memory and copy the string, but it does not do any mapping to UTF-8 or checks for valid octet sequences. gint tvb_get_nstringz(tvbuff_t *tvb, const gint offset, const guint bufsize, guint8* buffer); gint tvb_get_nstringz0(tvbuff_t *tvb, const gint offset, const guint bufsize, guint8* buffer); Copies bufsize bytes, including the terminating NULL, to buffer. If a NULL terminator is found before reaching bufsize, only the bytes up to and including the NULL are copied. Returns the number of bytes copied (not including terminating NULL), or -1 if the string was truncated in the buffer due to not having reached the terminating NULL. In this case, the resulting buffer is not NULL-terminated. tvb_get_nstringz0() works like tvb_get_nstringz(), but never returns -1 since the string is guaranteed to have a terminating NULL. If the string was truncated when copied into buffer, a NULL is placed at the end of buffer to terminate it. gchar *tvb_get_ts_23_038_7bits_string(wmem_allocator_t *scope, tvbuff_t *tvb, const gint bit_offset, gint no_of_chars); tvb_get_ts_23_038_7bits_string() returns a string of a given number of characters and encoded according to 3GPP TS 23.038 7 bits alphabet. The buffer is allocated in the given wmem scope (see README.wmem for more information). Byte Array Accessors: gchar *tvb_bytes_to_str(wmem_allocator_t *scope, tvbuff_t *tvb, const gint offset, const gint len); Formats a bunch of data from a tvbuff as bytes, returning a pointer to the string with the data formatted as two hex digits for each byte. The string pointed to is stored in an "wmem_alloc'd" buffer which will be freed depending on its scope (typically wmem_packet_scope which is freed after the frame). The formatted string will contain the hex digits for at most the first 16 bytes of the data. If len is greater than 16 bytes, a trailing "..." will be added to the string. gchar *tvb_bytes_to_str_punct(wmem_allocator_t *scope, tvbuff_t *tvb, const gint offset, const gint len, const gchar punct); This function is similar to tvb_bytes_to_str(...) except that 'punct' is inserted between the hex representation of each byte. GByteArray *tvb_get_string_bytes(tvbuff_t *tvb, const gint offset, const gint length, const guint encoding, GByteArray* bytes, gint *endoff) Given a tvbuff, an offset into the tvbuff, and a length that starts at that offset (which may be -1 for "all the way to the end of the tvbuff"), fetch the hex-decoded byte values of the tvbuff into the passed-in 'bytes' array, based on the passed-in encoding. In other words, convert from a hex-ascii string in tvbuff, into the supplied GByteArray. gchar *tvb_bcd_dig_to_wmem_packet_str(tvbuff_t *tvb, const gint offset, const gint len, dgt_set_t *dgt, gboolean skip_first); Given a tvbuff, an offset into the tvbuff, and a length that starts at that offset (which may be -1 for "all the way to the end of the tvbuff"), fetch BCD encoded digits from a tvbuff starting from either the low or high half byte, formatting the digits according to an input digit set, if NUll a default digit set of 0-9 returning "?" for overdecadic digits will be used. A pointer to the packet scope allocated string will be returned. Note: a tvbuff content of 0xf is considered a 'filler' and will end the conversion. Copying memory: void* tvb_memcpy(tvbuff_t *tvb, void* target, const gint offset, size_t length); Copies into the specified target the specified length's worth of data from the specified tvbuff, starting at the specified offset. void *tvb_memdup(wmem_allocator_t *scope, tvbuff_t *tvb, const gint offset, size_t length); Returns a buffer containing a copy of the given TVB bytes. The buffer is allocated in the given wmem scope (see README.wmem for more information). Pointer-retrieval: /* WARNING! Don't use this function. There is almost always a better way. * It's dangerous because once this pointer is given to the user, there's * no guarantee that the user will honor the 'length' and not overstep the * boundaries of the buffer. Also see the warning in the Portability section. */ const guint8* tvb_get_ptr(tvbuff_t *tvb, const gint offset, const gint length); Length query: Get amount of captured data in the buffer (which is *NOT* necessarily the length of the packet). You probably want tvb_reported_length instead: guint tvb_captured_length(const tvbuff_t *tvb); Get reported length of buffer: guint tvb_reported_length(const tvbuff_t *tvb); 1.4 Functions to handle columns in the traffic summary window. The topmost pane of the main window is a list of the packets in the capture, possibly filtered by a display filter. Each line corresponds to a packet, and has one or more columns, as configured by the user. Many of the columns are handled by code outside individual dissectors; most dissectors need only specify the value to put in the "Protocol" and "Info" columns. Columns are specified by COL_ values; the COL_ value for the "Protocol" field, typically giving an abbreviated name for the protocol (but not the all-lower-case abbreviation used elsewhere) is COL_PROTOCOL, and the COL_ value for the "Info" field, giving a summary of the contents of the packet for that protocol, is COL_INFO. The value for a column can be specified with one of several functions, all of which take the 'fd' argument to the dissector as their first argument, and the COL_ value for the column as their second argument. 1.4.1 The col_set_str function. 'col_set_str' takes a string as its third argument, and sets the value for the column to that value. It assumes that the pointer passed to it points to a string constant or a static "const" array, not to a variable, as it doesn't copy the string, it merely saves the pointer value; the argument can itself be a variable, as long as it always points to a string constant or a static "const" array. It is more efficient than 'col_add_str' or 'col_add_fstr'; however, if the dissector will be using 'col_append_str' or 'col_append_fstr" to append more information to the column, the string will have to be copied anyway, so it's best to use 'col_add_str' rather than 'col_set_str' in that case. For example, to set the "Protocol" column to "PROTOABBREV": col_set_str(pinfo->cinfo, COL_PROTOCOL, "PROTOABBREV"); 1.4.2 The col_add_str function. 'col_add_str' takes a string as its third argument, and sets the value for the column to that value. It takes the same arguments as 'col_set_str', but copies the string, so that if the string is, for example, an automatic variable that won't remain in scope when the dissector returns, it's safe to use. 1.4.3 The col_add_fstr function. 'col_add_fstr' takes a 'printf'-style format string as its third argument, and 'printf'-style arguments corresponding to '%' format items in that string as its subsequent arguments. For example, to set the "Info" field to "<XXX> request, <N> bytes", where "reqtype" is a string containing the type of the request in the packet and "n" is an unsigned integer containing the number of bytes in the request: col_add_fstr(pinfo->cinfo, COL_INFO, "%s request, %u bytes", reqtype, n); Don't use 'col_add_fstr' with a format argument of just "%s" - 'col_add_str', or possibly even 'col_set_str' if the string that matches the "%s" is a static constant string, will do the same job more efficiently. 1.4.4 The col_clear function. If the Info column will be filled with information from the packet, that means that some data will be fetched from the packet before the Info column is filled in. If the packet is so small that the data in question cannot be fetched, the routines to fetch the data will throw an exception (see the comment at the beginning about tvbuffers improving the handling of short packets - the tvbuffers keep track of how much data is in the packet, and throw an exception on an attempt to fetch data past the end of the packet, so that the dissector won't process bogus data), causing the Info column not to be filled in. This means that the Info column will have data for the previous protocol, which would be confusing if, for example, the Protocol column had data for this protocol. Therefore, before a dissector fetches any data whatsoever from the packet (unless it's a heuristic dissector fetching data to determine whether the packet is one that it should dissect, in which case it should check, before fetching the data, whether there's any data to fetch; if there isn't, it should return FALSE), it should set the Protocol column and the Info column. If the Protocol column will ultimately be set to, for example, a value containing a protocol version number, with the version number being a field in the packet, the dissector should, before fetching the version number field or any other field from the packet, set it to a value without a version number, using 'col_set_str', and should later set it to a value with the version number after it's fetched the version number. If the Info column will ultimately be set to a value containing information from the packet, the dissector should, before fetching any fields from the packet, clear the column using 'col_clear' (which is more efficient than clearing it by calling 'col_set_str' or 'col_add_str' with a null string), and should later set it to the real string after it's fetched the data to use when doing that. 1.4.5 The col_append_str function. Sometimes the value of a column, especially the "Info" column, can't be conveniently constructed at a single point in the dissection process; for example, it might contain small bits of information from many of the fields in the packet. 'col_append_str' takes, as arguments, the same arguments as 'col_add_str', but the string is appended to the end of the current value for the column, rather than replacing the value for that column. (Note that no blank separates the appended string from the string to which it is appended; if you want a blank there, you must add it yourself as part of the string being appended.) 1.4.6 The col_append_fstr function. 'col_append_fstr' is to 'col_add_fstr' as 'col_append_str' is to 'col_add_str' - it takes, as arguments, the same arguments as 'col_add_fstr', but the formatted string is appended to the end of the current value for the column, rather than replacing the value for that column. 1.4.7 The col_append_sep_str and col_append_sep_fstr functions. In specific situations the developer knows that a column's value will be created in a stepwise manner, where the appended values are listed. Both 'col_append_sep_str' and 'col_append_sep_fstr' functions will add an item separator between two consecutive items, and will not add the separator at the beginning of the column. The remainder of the work both functions do is identical to what 'col_append_str' and 'col_append_fstr' do. 1.4.8 The col_set_fence and col_prepend_fence_fstr functions. Sometimes a dissector may be called multiple times for different PDUs in the same frame (for example in the case of SCTP chunk bundling: several upper layer data packets may be contained in one SCTP packet). If the upper layer dissector calls 'col_set_str()' or 'col_clear()' on the Info column when it begins dissecting each of those PDUs then when the frame is fully dissected the Info column would contain only the string from the last PDU in the frame. The 'col_set_fence' function erects a "fence" in the column that prevents subsequent 'col_...' calls from clearing the data currently in that column. For example, the SCTP dissector calls 'col_set_fence' on the Info column after it has called any subdissectors for that chunk so that subdissectors of any subsequent chunks may only append to the Info column. 'col_prepend_fence_fstr' prepends data before a fence (moving it if necessary). It will create a fence at the end of the prepended data if the fence does not already exist. 1.4.9 The col_set_time function. The 'col_set_time' function takes an nstime value as its third argument. This nstime value is a relative value and will be added as such to the column. The fourth argument is the filtername holding this value. This way, rightclicking on the column makes it possible to build a filter based on the time-value. For example: col_set_time(pinfo->cinfo, COL_REL_TIME, &ts, "s4607.ploc.time"); 1.5 Constructing the protocol tree. The middle pane of the main window, and the topmost pane of a packet popup window, are constructed from the "protocol tree" for a packet. The protocol tree, or proto_tree, is a GNode, the N-way tree structure available within GLIB. Of course the protocol dissectors don't care what a proto_tree really is; they just pass the proto_tree pointer as an argument to the routines which allow them to add items and new branches to the tree. When a packet is selected in the packet-list pane, or a packet popup window is created, a new logical protocol tree (proto_tree) is created. The pointer to the proto_tree (in this case, 'protocol tree'), is passed to the top-level protocol dissector, and then to all subsequent protocol dissectors for that packet, and then the GUI tree is drawn via proto_tree_draw(). The logical proto_tree needs to know detailed information about the protocols and fields about which information will be collected from the dissection routines. By strictly defining (or "typing") the data that can be attached to a proto tree, searching and filtering becomes possible. This means that for every protocol and field (which I also call "header fields", since they are fields in the protocol headers) which might be attached to a tree, some information is needed. Every dissector routine will need to register its protocols and fields with the central protocol routines (in proto.c). At first I thought I might keep all the protocol and field information about all the dissectors in one file, but decentralization seemed like a better idea. That one file would have gotten very large; one small change would have required a re-compilation of the entire file. Also, by allowing registration of protocols and fields at run-time, loadable modules of protocol dissectors (perhaps even user-supplied) is feasible. To do this, each protocol should have a register routine, which will be called when Wireshark starts. The code to call the register routines is generated automatically; to arrange that a protocol's register routine be called at startup: the file containing a dissector's "register" routine must be added to "DISSECTOR_SRC" in "epan/dissectors/CMakeLists.txt"; the "register" routine must have a name of the form "proto_register_XXX"; the "register" routine must take no argument, and return no value; the "register" routine's name must appear in the source file either at the beginning of the line, or preceded only by "void " at the beginning of the line (that would typically be the definition) - other white space shouldn't cause a problem, e.g.: void proto_register_XXX(void) { ... } and void proto_register_XXX( void ) { ... } and so on should work. For every protocol or field that a dissector wants to register, a variable of type int needs to be used to keep track of the protocol. The IDs are needed for establishing parent/child relationships between protocols and fields, as well as associating data with a particular field so that it can be stored in the logical tree and displayed in the GUI protocol tree. Some dissectors will need to create branches within their tree to help organize header fields. These branches should be registered as header fields. Only true protocols should be registered as protocols. This is so that a display filter user interface knows how to distinguish protocols from fields. A protocol is registered with the name of the protocol and its abbreviation. Here is how the frame "protocol" is registered. int proto_frame; proto_frame = proto_register_protocol ( /* name */ "Frame", /* short name */ "Frame", /* abbrev */ "frame" ); A header field is also registered with its name and abbreviation, but information about its data type is needed. It helps to look at the header_field_info struct to see what information is expected: struct header_field_info { const char *name; const char *abbrev; enum ftenum type; int display; const void *strings; guint64 bitmask; const char *blurb; ..... }; name (FIELDNAME) ---------------- A string representing the name of the field. This is the name that will appear in the graphical protocol tree. It must be a non-empty string. abbrev (FIELDABBREV) -------------------- A string with an abbreviation of the field. The abbreviation should start with the abbreviation of the parent protocol followed by a period as a separator. For example, the "src" field in an IP packet would have "ip.src" as an abbreviation. It is acceptable to have multiple levels of periods if, for example, you have fields in your protocol that are then subdivided into subfields. For example, TRMAC has multiple error fields, so the abbreviations follow this pattern: "trmac.errors.iso", "trmac.errors.noniso", etc. The abbreviation is the identifier used in a display filter. As such it cannot be an empty string. type (FIELDTYPE) ---------------- The type of value this field holds. The current field types are: FT_NONE No field type. Used for fields that aren't given a value, and that can only be tested for presence or absence; a field that represents a data structure, with a subtree below it containing fields for the members of the structure, or that represents an array with a subtree below it containing fields for the members of the array, might be an FT_NONE field. FT_PROTOCOL Used for protocols which will be placing themselves as top-level items in the "Packet Details" pane of the UI. FT_BOOLEAN 0 means "false", any other value means "true". FT_FRAMENUM A frame number; if this is used, the "Go To Corresponding Frame" menu item can work on that field. FT_CHAR An 8-bit ASCII character. It's treated similarly to an FT_UINT8, but is displayed as a C-style character constant. FT_UINT8 An 8-bit unsigned integer. FT_UINT16 A 16-bit unsigned integer. FT_UINT24 A 24-bit unsigned integer. FT_UINT32 A 32-bit unsigned integer. FT_UINT40 A 40-bit unsigned integer. FT_UINT48 A 48-bit unsigned integer. FT_UINT56 A 56-bit unsigned integer. FT_UINT64 A 64-bit unsigned integer. FT_INT8 An 8-bit signed integer. FT_INT16 A 16-bit signed integer. FT_INT24 A 24-bit signed integer. FT_INT32 A 32-bit signed integer. FT_INT40 A 40-bit signed integer. FT_INT48 A 48-bit signed integer. FT_INT56 A 56-bit signed integer. FT_INT64 A 64-bit signed integer. FT_FLOAT A single-precision floating point number. FT_DOUBLE A double-precision floating point number. FT_ABSOLUTE_TIME An absolute time from some fixed point in time, displayed as the date, followed by the time, as hours, minutes, and seconds with 9 digits after the decimal point. FT_RELATIVE_TIME Seconds (4 bytes) and nanoseconds (4 bytes) of time relative to an arbitrary time. displayed as seconds and 9 digits after the decimal point. FT_STRING A string of characters, not necessarily NULL-terminated, but possibly NULL-padded. This, and the other string-of-characters types, are to be used for text strings, not raw binary data. FT_STRINGZ A NULL-terminated string of characters. The string length is normally the length given in the proto_tree_add_item() call. However if the length given in the call is -1, then the length used is that returned by calling tvb_strsize(). FT_UINT_STRING A counted string of characters, consisting of a count (represented as an integral value, of width given in the proto_tree_add_item() call) followed immediately by that number of characters. FT_ETHER A six octet string displayed in Ethernet-address format. FT_BYTES A string of bytes with arbitrary values; used for raw binary data. FT_UINT_BYTES A counted string of bytes, consisting of a count (represented as an integral value, of width given in the proto_tree_add_item() call) followed immediately by that number of arbitrary values; used for raw binary data. FT_IPv4 A version 4 IP address (4 bytes) displayed in dotted-quad IP address format (4 decimal numbers separated by dots). FT_IPv6 A version 6 IP address (16 bytes) displayed in standard IPv6 address format. FT_IPXNET An IPX address displayed in hex as a 6-byte network number followed by a 6-byte station address. FT_GUID A Globally Unique Identifier FT_OID An ASN.1 Object Identifier FT_REL_OID An ASN.1 Relative Object Identifier FT_EUI64 A EUI-64 Address FT_AX25 A AX-25 Address FT_VINES A Vines Address FT_SYSTEM_ID An OSI System-ID FT_FCWWN A Fibre Channel WWN Address Some of these field types are still not handled in the display filter routines, but the most common ones are. The FT_UINT* variables all represent unsigned integers, and the FT_INT* variables all represent signed integers; the number on the end represent how many bits are used to represent the number. Some constraints are imposed on the header fields depending on the type (e.g. FT_BYTES) of the field. Fields of type FT_ABSOLUTE_TIME must use 'ABSOLUTE_TIME_{LOCAL,UTC,DOY_UTC}, NULL, 0x0' as values for the 'display, 'strings', and 'bitmask' fields, and all other non-integral types (i.e.. types that are _not_ FT_INT* and FT_UINT*) must use 'BASE_NONE, NULL, 0x0' as values for the 'display', 'strings', 'bitmask' fields. The reason is simply that the type itself implicitly defines the nature of 'display', 'strings', 'bitmask'. display (FIELDDISPLAY) ---------------------- The display field has a couple of overloaded uses. This is unfortunate, but since we're using C as an application programming language, this sometimes makes for cleaner programs. Right now I still think that overloading this variable was okay. For integer fields (FT_UINT* and FT_INT*), this variable represents the base in which you would like the value displayed. The acceptable bases are: BASE_DEC, BASE_HEX, BASE_OCT, BASE_DEC_HEX, BASE_HEX_DEC, BASE_CUSTOM BASE_DEC, BASE_HEX, and BASE_OCT are decimal, hexadecimal, and octal, respectively. BASE_DEC_HEX and BASE_HEX_DEC display value in two bases (the 1st representation followed by the 2nd in parenthesis). BASE_CUSTOM allows one to specify a callback function pointer that will format the value. For 32-bit and smaller values, custom_fmt_func_t can be used to declare the callback function pointer. Specifically, this is defined as: void func(gchar *, guint32); For values larger than 32-bits, custom_fmt_func_64_t can be used to declare the callback function pointer. Specifically, this is defined as: void func(gchar *, guint64); The first argument is a pointer to a buffer of the ITEM_LABEL_LENGTH size and the second argument is the value to be formatted. Both custom_fmt_func_t and custom_fmt_func_64_t are defined in epan/proto.h. For FT_UINT16 'display' can be used to select a transport layer protocol using one of BASE_PT_UDP, BASE_PT_TCP, BASE_PT_DCCP or BASE_PT_SCTP. If transport name resolution is enabled the port field label is displayed in decimal and as a well-known service name (if one is available). For FT_BOOLEAN fields that are also bitfields (i.e., 'bitmask' is non-zero), 'display' is used specify a "field-width" (i.e., tell the proto_tree how wide the parent bitfield is). (If the FT_BOOLEAN 'bitmask' is zero, then 'display' must be BASE_NONE). For integer fields a "field-width" is not needed since the type of integer itself (FT_UINT8, FT_UINT16, FT_UINT24, FT_UINT32, FT_UINT40, FT_UINT48, FT_UINT56, FT_UINT64, etc) tells the proto_tree how wide the parent bitfield is. The same is true of FT_CHAR, as it's an 8-bit character. For FT_ABSOLUTE_TIME fields, 'display' is used to indicate whether the time is to be displayed as a time in the time zone for the machine on which Wireshark/TShark is running or as UTC and, for UTC, whether the date should be displayed as "{monthname} {day_of_month}, {year}" or as "{year/day_of_year}". Additionally, BASE_NONE is used for 'display' as a NULL-value. That is, for non-integers other than FT_ABSOLUTE_TIME fields, and non-bitfield FT_BOOLEANs, you'll want to use BASE_NONE in the 'display' field. You may not use BASE_NONE for integers. It is possible that in the future we will record the endianness of integers. If so, it is likely that we'll use a bitmask on the display field so that integers would be represented as BEND|BASE_DEC or LEND|BASE_HEX. But that has not happened yet; note that there are protocols for which no endianness is specified, such as the X11 protocol and the DCE RPC protocol, so it would not be possible to record the endianness of all integral fields. strings (FIELDCONVERT) ---------------------- -- value_string Some integer fields, of type FT_UINT*, need labels to represent the true value of a field. You could think of those fields as having an enumerated data type, rather than an integral data type. A 'value_string' structure is a way to map values to strings. typedef struct _value_string { guint32 value; gchar *strptr; } value_string; For fields of that type, you would declare an array of "value_string"s: static const value_string valstringname[] = { { INTVAL1, "Descriptive String 1" }, { INTVAL2, "Descriptive String 2" }, { 0, NULL } }; (the last entry in the array must have a NULL 'strptr' value, to indicate the end of the array). The 'strings' field would be set to 'VALS(valstringname)'. If the field has a numeric rather than an enumerated type, the 'strings' field would be set to NULL. If BASE_SPECIAL_VALS is also applied to the display bitmask, then if the numeric value of a field doesn't match any values in the value_string then just the numeric value is displayed (i.e. no "Unknown"). This is intended for use when the value_string only gives special names for certain field values and values not in the value_string are expected. -- Extended value strings You can also use an extended version of the value_string for faster lookups. It requires a value_string array as input. If all of a contiguous range of values from min to max are present in the array in ascending order the value will be used as a direct index into a value_string array. If the values in the array are not contiguous (ie: there are "gaps"), but are in ascending order a binary search will be used. Note: "gaps" in a value_string array can be filled with "empty" entries eg: {value, "Unknown"} so that direct access to the array is is possible. Note: the value_string array values are *unsigned*; IOW: -1 is greater than 0. So: { -2, -1, 1, 2 }; wrong: linear search will be used (note gap) { 1, 2, -2, -1 }; correct: binary search will be used As a special case: { -2, -1, 0, 1, 2 }; OK: direct(indexed) access will be used (note no gap) The init macro (see below) will perform a check on the value string the first time it is used to determine which search algorithm fits and fall back to a linear search if the value_string does not meet the criteria above. Use this macro to initialize the extended value_string at compile time: static value_string_ext valstringname_ext = VALUE_STRING_EXT_INIT(valstringname); Extended value strings can be created at run time by calling value_string_ext_new(<ptr to value_string array>, <total number of entries in the value_string_array>, /* include {0, NULL} entry */ <value_string_name>); For hf[] array FT_(U)INT* fields that need a 'valstringname_ext' struct, the 'strings' field would be set to '&valstringname_ext'. Furthermore, the 'display' field must be ORed with 'BASE_EXT_STRING' (e.g. BASE_DEC|BASE_EXT_STRING). -- val64_string val64_strings are like value_strings, except that the integer type used is a guint64 (instead of guint32). Instead of using the VALS() macro for the 'strings' field in the header_field_info struct array, 'VALS64()' is used. BASE_SPECIAL_VALS can also be used for val64_string. -- val64_string_ext val64_string_ext is like value_string_ext, except that the integer type used is a guint64 (instead of guint32). Use this macro to initialize the extended val64_string at compile time: static val64_string_ext val64stringname_ext = VAL64_STRING_EXT_INIT(val64stringname); Extended val64 strings can be created at run time by calling val64_string_ext_new(<ptr to val64_string array>, <total number of entries in the val64_string_array>, /* include {0, NULL} entry */ <val64_string_name>); For hf[] array FT_(U)INT* fields that need a 'val64stringname_ext' struct, the 'strings' field would be set to '&val64stringname_ext'. Furthermore, the 'display' field must be ORed with both 'BASE_EXT_STRING' and 'BASE_VAL64_STRING' (e.g. BASE_DEC|BASE_EXT_STRING|BASE_VAL64_STRING). -- Unit string Some integer fields, of type FT_UINT* and float fields, of type FT_FLOAT or FT_DOUBLE, need units of measurement to help convey the field value. A 'unit_name_string' structure is a way to add a unit suffix to a field. typedef struct unit_name_string { char *singular; /* name to use for 1 unit */ char *plural; /* name to use for < 1 or > 1 units */ } unit_name_string; For fields with that unit name, you would declare a "unit_name_string": static const unit_name_string unitname[] = { "single item name" , "multiple item name" }; (the second entry can be NULL if there is no plural form of the unit name. This is typically the case when abbreviations are used instead of full words.) There are several "common" unit name structures already defined in epan/unit_strings.h. Dissector authors may choose to add the unit name structure there rather than locally in a dissector. For hf[] array FT_(U)INT*, FT_FlOAT and FT_DOUBLE fields that need a 'unit_name_string' struct, the 'strings' field would be set to '&units_second_seconds'. Furthermore, the 'display' field must be ORed with 'BASE_UNIT_STRING' (e.g. BASE_DEC|BASE_UNIT_STRING). -- Ranges If the field has a numeric type that might logically fit in ranges of values one can use a range_string struct. Thus a 'range_string' structure is a way to map ranges to strings. typedef struct _range_string { guint32 value_min; guint32 value_max; const gchar *strptr; } range_string; For fields of that type, you would declare an array of "range_string"s: static const range_string rvalstringname[] = { { INTVAL_MIN1, INTVALMAX1, "Descriptive String 1" }, { INTVAL_MIN2, INTVALMAX2, "Descriptive String 2" }, { 0, 0, NULL } }; If INTVAL_MIN equals INTVAL_MAX for a given entry the range_string behavior collapses to the one of value_string. For FT_(U)INT* fields that need a 'range_string' struct, the 'strings' field would be set to 'RVALS(rvalstringname)'. Furthermore, 'display' field must be ORed with 'BASE_RANGE_STRING' (e.g. BASE_DEC|BASE_RANGE_STRING). -- Booleans FT_BOOLEANs have a default map of 0 = "False", 1 (or anything else) = "True". Sometimes it is useful to change the labels for boolean values (e.g., to "Yes"/"No", "Fast"/"Slow", etc.). For these mappings, a struct called true_false_string is used. typedef struct true_false_string { char *true_string; char *false_string; } true_false_string; For Boolean fields for which "False" and "True" aren't the desired labels, you would declare a "true_false_string"s: static const true_false_string boolstringname = { "String for True", "String for False" }; Its two fields are pointers to the string representing truth, and the string representing falsehood. For FT_BOOLEAN fields that need a 'true_false_string' struct, the 'strings' field would be set to 'TFS(&boolstringname)'. If the Boolean field is to be displayed as "False" or "True", the 'strings' field would be set to NULL. Wireshark predefines a whole range of ready made "true_false_string"s in tfs.h, included via packet.h. -- Custom Custom fields (BASE_CUSTOM) should use CF_FUNC(&custom_format_func) for the 'strings' field. -- Note to plugin authors Data cannot get exported from DLLs. For this reason plugin authors cannot use existing fieldconvert strings (e.g. from existing dissectors or those from epan/unit_strings.h). Plugins must define value_strings, unit_name_strings, range_strings and true_false_strings locally. bitmask (BITMASK) ----------------- If the field is a bitfield, then the bitmask is the mask which will leave only the bits needed to make the field when ANDed with a value. The proto_tree routines will calculate 'bitshift' automatically from 'bitmask', by finding the rightmost set bit in the bitmask. This shift is applied before applying string mapping functions or filtering. If the field is not a bitfield, then bitmask should be set to 0. blurb (FIELDDESCR) ------------------ This is a string giving a proper description of the field. It should be at least one grammatically complete sentence, or NULL in which case the name field is used. (Please do not use ""). It is meant to provide a more detailed description of the field than the name alone provides. This information will be used in the man page, and in a future GUI display-filter creation tool. We might also add tooltips to the labels in the GUI protocol tree, in which case the blurb would be used as the tooltip text. 1.5.1 Field Registration. Protocol registration is handled by creating an instance of the header_field_info struct (or an array of such structs), and calling the registration function along with the registration ID of the protocol that is the parent of the fields. Here is a complete example: static int proto_eg = -1; static int hf_field_a = -1; static int hf_field_b = -1; static hf_register_info hf[] = { { &hf_field_a, { "Field A", "proto.field_a", FT_UINT8, BASE_HEX, NULL, 0xf0, "Field A represents Apples", HFILL }}, { &hf_field_b, { "Field B", "proto.field_b", FT_UINT16, BASE_DEC, VALS(vs), 0x0, "Field B represents Bananas", HFILL }} }; proto_eg = proto_register_protocol("Example Protocol", "PROTO", "proto"); proto_register_field_array(proto_eg, hf, array_length(hf)); Be sure that your array of hf_register_info structs is declared 'static', since the proto_register_field_array() function does not create a copy of the information in the array... it uses that static copy of the information that the compiler created inside your array. Here's the layout of the hf_register_info struct: typedef struct hf_register_info { int *p_id; /* pointer to parent variable */ header_field_info hfinfo; } hf_register_info; Also be sure to use the handy array_length() macro found in packet.h to have the compiler compute the array length for you at compile time. If you don't have any fields to register, do *NOT* create a zero-length "hf" array; not all compilers used to compile Wireshark support them. Just omit the "hf" array, and the "proto_register_field_array()" call, entirely. It is OK to have header fields with a different format be registered with the same abbreviation. For instance, the following is valid: static hf_register_info hf[] = { { &hf_field_8bit, /* 8-bit version of proto.field */ { "Field (8 bit)", "proto.field", FT_UINT8, BASE_DEC, NULL, 0x00, "Field represents FOO", HFILL }}, { &hf_field_32bit, /* 32-bit version of proto.field */ { "Field (32 bit)", "proto.field", FT_UINT32, BASE_DEC, NULL, 0x00, "Field represents FOO", HFILL }} }; This way a filter expression can match a header field, irrespective of the representation of it in the specific protocol context. This is interesting for protocols with variable-width header fields. Note that the formats used must all belong to the same group as defined below: - FT_INT8, FT_INT16, FT_INT24 and FT_INT32 - FT_CHAR, FT_UINT8, FT_UINT16, FT_UINT24, FT_UINT32, FT_IPXNET and FT_FRAMENUM - FT_INT40, FT_INT48, FT_INT56 and FT_INT64 - FT_UINT40, FT_UINT48, FT_UINT56, FT_UINT64 and FT_EUI64 - FT_ABSOLUTE_TIME and FT_RELATIVE_TIME - FT_STRING, FT_STRINGZ, FT_UINT_STRING and FT_STRINGZPAD - FT_FLOAT and FT_DOUBLE - FT_BYTES, FT_UINT_BYTES, FT_ETHER, FT_AX25, FT_VINES and FT_FCWWN - FT_OID, FT_REL_OID and FT_SYSTEM_ID Any field not in a grouping above should *NOT* be used in duplicate field abbreviations. The current code does not prevent it, but someday in the future it might. The HFILL macro at the end of the struct will set reasonable default values for internally used fields. 1.5.2 Adding Items and Values to the Protocol Tree. A protocol item is added to an existing protocol tree with one of a handful of proto_XXX_DO_YYY() functions. Subtrees can be made with the proto_item_add_subtree() function: item = proto_tree_add_item(....); new_tree = proto_item_add_subtree(item, tree_type); This will add a subtree under the item in question; a subtree can be created under an item made by any of the "proto_tree_add_XXX" functions, so that the tree can be given an arbitrary depth. Subtree types are integers, assigned by "proto_register_subtree_array()". To register subtree types, pass an array of pointers to "gint" variables to hold the subtree type values to "proto_register_subtree_array()": static gint ett_eg = -1; static gint ett_field_a = -1; static gint *ett[] = { &ett_eg, &ett_field_a }; proto_register_subtree_array(ett, array_length(ett)); in your "register" routine, just as you register the protocol and the fields for that protocol. The ett_ variables identify particular type of subtree so that if you expand one of them, Wireshark keeps track of that and, when you click on another packet, it automatically opens all subtrees of that type. If you close one of them, all subtrees of that type will be closed when you move to another packet. There are several functions that the programmer can use to add either protocol or field labels to the proto_tree: proto_item* proto_tree_add_item(tree, id, tvb, start, length, encoding); proto_item* proto_tree_add_item_ret_int(tree, id, tvb, start, length, encoding, *retval); proto_item* proto_tree_add_item_ret_uint(tree, id, tvb, start, length, encoding, *retval); proto_item* proto_tree_add_item_ret_uint64(tree, id, tvb, start, length, encoding, *retval); proto_item* proto_tree_add_item_ret_boolean(tree, id, tvb, start, length, encoding, *retval); proto_item* proto_tree_add_subtree(tree, tvb, start, length, idx, tree_item, text); proto_item* proto_tree_add_subtree_format(tree, tvb, start, length, idx, tree_item, format, ...); proto_item* proto_tree_add_none_format(tree, id, tvb, start, length, format, ...); proto_item* proto_tree_add_protocol_format(tree, id, tvb, start, length, format, ...); proto_item * proto_tree_add_bytes(tree, id, tvb, start, length, start_ptr); proto_item * proto_tree_add_bytes_item(tree, id, tvb, start, length, encoding, retval, endoff, err); proto_item * proto_tree_add_bytes_format(tree, id, tvb, start, length, start_ptr, format, ...); proto_item * proto_tree_add_bytes_format_value(tree, id, tvb, start, length, start_ptr, format, ...); proto_item * proto_tree_add_bytes_with_length(tree, id, tvb, start, tvb_length, start_ptr, ptr_length); proto_item * proto_tree_add_time(tree, id, tvb, start, length, value_ptr); proto_item * proto_tree_add_time_item(tree, id, tvb, start, length, encoding, retval, endoff, err); proto_item * proto_tree_add_time_format(tree, id, tvb, start, length, value_ptr, format, ...); proto_item * proto_tree_add_time_format_value(tree, id, tvb, start, length, value_ptr, format, ...); proto_item * proto_tree_add_ipxnet(tree, id, tvb, start, length, value); proto_item * proto_tree_add_ipxnet_format(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_ipxnet_format_value(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_ipv4(tree, id, tvb, start, length, value); proto_item * proto_tree_add_ipv4_format(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_ipv4_format_value(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_ipv6(tree, id, tvb, start, length, value_ptr); proto_item * proto_tree_add_ipv6_format(tree, id, tvb, start, length, value_ptr, format, ...); proto_item * proto_tree_add_ipv6_format_value(tree, id, tvb, start, length, value_ptr, format, ...); proto_item * proto_tree_add_ether(tree, id, tvb, start, length, value_ptr); proto_item * proto_tree_add_ether_format(tree, id, tvb, start, length, value_ptr, format, ...); proto_item * proto_tree_add_ether_format_value(tree, id, tvb, start, length, value_ptr, format, ...); proto_item * proto_tree_add_guid(tree, id, tvb, start, length, value_ptr); proto_item * proto_tree_add_guid_format(tree, id, tvb, start, length, value_ptr, format, ...); proto_item * proto_tree_add_guid_format_value(tree, id, tvb, start, length, value_ptr, format, ...); proto_item * proto_tree_add_oid(tree, id, tvb, start, length, value_ptr); proto_item * proto_tree_add_oid_format(tree, id, tvb, start, length, value_ptr, format, ...); proto_item * proto_tree_add_oid_format_value(tree, id, tvb, start, length, value_ptr, format, ...); proto_item * proto_tree_add_string(tree, id, tvb, start, length, value_ptr); proto_item * proto_tree_add_string_format(tree, id, tvb, start, length, value_ptr, format, ...); proto_item * proto_tree_add_string_format_value(tree, id, tvb, start, length, value_ptr, format, ...); proto_item * proto_tree_add_boolean(tree, id, tvb, start, length, value); proto_item * proto_tree_add_boolean_format(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_boolean_format_value(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_float(tree, id, tvb, start, length, value); proto_item * proto_tree_add_float_format(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_float_format_value(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_double(tree, id, tvb, start, length, value); proto_item * proto_tree_add_double_format(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_double_format_value(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_uint(tree, id, tvb, start, length, value); proto_item * proto_tree_add_uint_format(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_uint_format_value(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_uint64(tree, id, tvb, start, length, value); proto_item * proto_tree_add_uint64_format(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_uint64_format_value(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_int(tree, id, tvb, start, length, value); proto_item * proto_tree_add_int_format(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_int_format_value(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_int64(tree, id, tvb, start, length, value); proto_item * proto_tree_add_int64_format(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_int64_format_value(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_eui64(tree, id, tvb, start, length, value); proto_item * proto_tree_add_eui64_format(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_eui64_format_value(tree, id, tvb, start, length, value, format, ...); proto_item * proto_tree_add_checksum(proto_tree *tree, tvbuff_t *tvb, const guint offset, const int hf_checksum, const int hf_checksum_status, struct expert_field* bad_checksum_expert, packet_info *pinfo, guint32 computed_checksum, const guint encoding, const guint flags); proto_item * proto_tree_add_bitmask(tree, tvb, start, header, ett, fields, encoding); proto_item * proto_tree_add_bitmask_len(tree, tvb, start, len, header, ett, fields, encoding); proto_item * proto_tree_add_bitmask_text(tree, tvb, offset, len, name, fallback, ett, fields, encoding, flags); proto_item * proto_tree_add_bitmask_with_flags(tree, tvb, offset, hf_hdr, ett, fields, encoding, flags); proto_item* proto_tree_add_bits_item(tree, id, tvb, bit_offset, no_of_bits, encoding); proto_item * proto_tree_add_split_bits_item_ret_val(tree, hf_index, tvb, bit_offset, crumb_spec, return_value); void proto_tree_add_split_bits_crumb(tree, hf_index, tvb, bit_offset, crumb_spec, crumb_index); proto_item * proto_tree_add_bits_ret_val(tree, id, tvb, bit_offset, no_of_bits, return_value, encoding); proto_item * proto_tree_add_uint_bits_format_value(tree, id, tvb, bit_offset, no_of_bits, value, format, ...); proto_item * proto_tree_add_boolean_bits_format_value(tree, id, tvb, bit_offset, no_of_bits, value, format, ...); proto_item * proto_tree_add_int_bits_format_value(tree, id, tvb, bit_offset, no_of_bits, value, format, ...); proto_item * proto_tree_add_float_bits_format_value(tree, id, tvb, bit_offset, no_of_bits, value, format, ...); proto_item * proto_tree_add_ts_23_038_7bits_item(tree, hf_index, tvb, bit_offset, no_of_chars); The 'tree' argument is the tree to which the item is to be added. The 'tvb' argument is the tvbuff from which the item's value is being extracted; the 'start' argument is the offset from the beginning of that tvbuff of the item being added, and the 'length' argument is the length, in bytes, of the item, bit_offset is the offset in bits and no_of_bits is the length in bits. The length of some items cannot be determined until the item has been dissected; to add such an item, add it with a length of -1, and, when the dissection is complete, set the length with 'proto_item_set_len()': void proto_item_set_len(ti, length); The "ti" argument is the value returned by the call that added the item to the tree, and the "length" argument is the length of the item. proto_tree_add_item() --------------------- proto_tree_add_item is used when you wish to do no special formatting. The item added to the GUI tree will contain the name (as passed in the proto_register_*() function) and a value. The value will be fetched from the tvbuff by proto_tree_add_item(), based on the type of the field and the encoding of the value as specified by the "encoding" argument. For FT_NONE, FT_BYTES, FT_ETHER, FT_IPv6, FT_IPXNET, FT_OID, FT_REL_OID, FT_AX25, FT_VINES, FT_SYSTEM_ID, FT_FCWWN fields, and 'protocol' fields the encoding is not relevant; the 'encoding' argument should be ENC_NA (Not Applicable). For FT_UINT_BYTES fields, the byte order of the count must be specified as well as the 'encoding' for bytes which should be ENC_NA, i.e. ENC_LITTLE_ENDIAN|ENC_NA For integral, floating-point, Boolean, FT_GUID, and FT_EUI64 fields, the encoding specifies the byte order of the value; the 'encoding' argument should be ENC_LITTLE_ENDIAN if the value is little-endian and ENC_BIG_ENDIAN if it is big-endian. For FT_IPv4 fields, the encoding also specifies the byte order of the value. In almost all cases, the encoding is in network byte order, hence big-endian, but in at least one protocol dissected by Wireshark, at least one IPv4 address is byte-swapped, so it's in little-endian order. For string fields, the encoding specifies the character set used for the string and the way individual code points in that character set are encoded. For FT_UINT_STRING fields, the byte order of the count must be specified; for UCS-2 and UTF-16, the byte order of the encoding must be specified (for counted UCS-2 and UTF-16 strings, the byte order of the count and the 16-bit values in the string must be the same). In other cases, ENC_NA should be used. The character encodings that are currently supported are: ENC_ASCII - ASCII (currently treated as UTF-8; in the future, all bytes with the 8th bit set will be treated as errors) ENC_UTF_8 - UTF-8-encoded Unicode ENC_UTF_16 - UTF-16-encoded Unicode, with surrogate pairs ENC_UCS_2 - UCS-2-encoded subset of Unicode, with no surrogate pairs and thus no code points above 0xFFFF ENC_UCS_4 - UCS-4-encoded Unicode ENC_WINDOWS_1250 - Windows-1250 code page ENC_ISO_8859_1 - ISO 8859-1 ENC_ISO_8859_2 - ISO 8859-2 ENC_ISO_8859_3 - ISO 8859-3 ENC_ISO_8859_4 - ISO 8859-4 ENC_ISO_8859_5 - ISO 8859-5 ENC_ISO_8859_6 - ISO 8859-6 ENC_ISO_8859_7 - ISO 8859-7 ENC_ISO_8859_8 - ISO 8859-8 ENC_ISO_8859_9 - ISO 8859-9 ENC_ISO_8859_10 - ISO 8859-10 ENC_ISO_8859_11 - ISO 8859-11 ENC_ISO_8859_13 - ISO 8859-13 ENC_ISO_8859_14 - ISO 8859-14 ENC_ISO_8859_15 - ISO 8859-15 ENC_ISO_8859_16 - ISO 8859-16 ENC_WINDOWS_1250 - Windows-1250 ENC_3GPP_TS_23_038_7BITS - GSM 7 bits alphabet as described in 3GPP TS 23.038 ENC_EBCDIC - EBCDIC ENC_MAC_ROMAN - MAC ROMAN ENC_CP437 - DOS CP437 ENC_ASCII_7BITS - 7 bits ASCII ENC_T61 - ITU T.61 Other encodings will be added in the future. For FT_ABSOLUTE_TIME fields, the encoding specifies the form in which the time stamp is specified, as well as its byte order. The time stamp encodings that are currently supported are: ENC_TIME_SECS_NSECS - 8, 12, or 16 bytes. For 8 bytes, the first 4 bytes are seconds and the next 4 bytes are nanoseconds; for 12 bytes, the first 8 bytes are seconds and the next 4 bytes are nanoseconds; for 16 bytes, the first 8 bytes are seconds and the next 8 bytes are nanoseconds. The seconds are seconds since the UN*X epoch (1970-01-01 00:00:00 UTC). (I.e., a UN*X struct timespec with a 4-byte or 8-byte time_t or a structure with an 8-byte time_t and an 8-byte nanoseconds field.) ENC_TIME_NTP - 8 bytes; the first 4 bytes are seconds since the NTP epoch (1900-01-01 00:00:00 GMT) and the next 4 bytes are 1/2^32's of a second since that second. (I.e., a 64-bit count of 1/2^32's of a second since the NTP epoch, with the upper 32 bits first and the lower 32 bits second, even when little-endian.) ENC_TIME_TOD - 8 bytes, as a count of microseconds since the System/3x0 and z/Architecture epoch (1900-01-01 00:00:00 GMT). ENC_TIME_RTPS - 8 bytes; the first 4 bytes are seconds since the UN*X epoch and the next 4 bytes are are 1/2^32's of a second since that second. (I.e., it's the offspring of a mating between UN*X time and NTP time.) It's used by the Object Management Group's Real-Time Publish-Subscribe Wire Protocol for the Data Distribution Service. ENC_TIME_SECS_USECS - 8 bytes; the first 4 bytes are seconds since the UN*X epoch and the next 4 bytes are microseconds since that second. (I.e., a UN*X struct timeval with a 4-byte time_t.) ENC_TIME_SECS - 4 to 8 bytes, representing a value in seconds since the UN*X epoch. ENC_TIME_MSECS - 6 to 8 bytes, representing a value in milliseconds since the UN*X epoch. ENC_TIME_SECS_NTP - 4 bytes, representing a count of seconds since the NTP epoch. (I.e., seconds since the NTP epoch.) ENC_TIME_RFC_3971 - 8 bytes, representing a count of 1/64ths of a second since the UN*X epoch; see section 5.3.1 "Timestamp Option" in RFC 3971. ENC_TIME_MSEC_NTP - 4-8 bytes, representing a count of milliseconds since the NTP epoch. (I.e., milliseconds since the NTP epoch.) For FT_RELATIVE_TIME fields, the encoding specifies the form in which the time stamp is specified, as well as its byte order. The time stamp encodings that are currently supported are: ENC_TIME_SECS_NSECS - 8, 12, or 16 bytes. For 8 bytes, the first 4 bytes are seconds and the next 4 bytes are nanoseconds; for 12 bytes, the first 8 bytes are seconds and the next 4 bytes are nanoseconds; for 16 bytes, the first 8 bytes are seconds and the next 8 bytes are nanoseconds. ENC_TIME_SECS_USECS - 8 bytes; the first 4 bytes are seconds and the next 4 bytes are microseconds. ENC_TIME_SECS - 4 to 8 bytes, representing a value in seconds. ENC_TIME_MSECS - 6 to 8 bytes, representing a value in milliseconds. For other types, there is no support for proto_tree_add_item(). Now that definitions of fields have detailed information about bitfield fields, you can use proto_tree_add_item() with no extra processing to add bitfield values to your tree. Here's an example. Take the Format Identifier (FID) field in the Transmission Header (TH) portion of the SNA protocol. The FID is the high nibble of the first byte of the TH. The FID would be registered like this: name = "Format Identifier" abbrev = "sna.th.fid" type = FT_UINT8 display = BASE_HEX strings = sna_th_fid_vals bitmask = 0xf0 The bitmask contains the value which would leave only the FID if bitwise-ANDed against the parent field, the first byte of the TH. The code to add the FID to the tree would be; proto_tree_add_item(bf_tree, hf_sna_th_fid, tvb, offset, 1, ENC_BIG_ENDIAN); The definition of the field already has the information about bitmasking and bitshifting, so it does the work of masking and shifting for us! This also means that you no longer have to create value_string structs with the values bitshifted. The value_string for FID looks like this, even though the FID value is actually contained in the high nibble. (You'd expect the values to be 0x0, 0x10, 0x20, etc.) /* Format Identifier */ static const value_string sna_th_fid_vals[] = { { 0x0, "SNA device <--> Non-SNA Device" }, { 0x1, "Subarea Node <--> Subarea Node" }, { 0x2, "Subarea Node <--> PU2" }, { 0x3, "Subarea Node or SNA host <--> Subarea Node" }, { 0x4, "?" }, { 0x5, "?" }, { 0xf, "Adjacent Subarea Nodes" }, { 0, NULL } }; The final implication of this is that display filters work the way you'd naturally expect them to. You'd type "sna.th.fid == 0xf" to find Adjacent Subarea Nodes. The user does not have to shift the value of the FID to the high nibble of the byte ("sna.th.fid == 0xf0") as was necessary in the past. proto_tree_add_item_ret_XXX() ------------------------------ proto_tree_add_item_ret_XXX is used when you want the displayed value returned for futher processing only integer and unsigned integer types up to 32 bits are supported usage of proper FT_ is checked. proto_tree_add_XXX_item() --------------------- proto_tree_add_XXX_item is used when you wish to do no special formatting, but also either wish for the retrieved value from the tvbuff to be handed back (to avoid doing tvb_get_...), and/or wish to have the value be decoded from the tvbuff in a string-encoded format. The item added to the GUI tree will contain the name (as passed in the proto_register_*() function) and a value. The value will be fetched from the tvbuff, based on the type of the XXX name and the encoding of the value as specified by the "encoding" argument. This function retrieves the value even if the passed-in tree param is NULL, so that it can be used by dissectors at all times to both get the value and set the tree item to it. Like other proto_tree_add functions, if there is a tree and the value cannot be decoded from the tvbuff, then an expert info error is reported. For string encoding, this means that a failure to decode the hex value from the string results in an expert info error being added to the tree. For string-decoding, the passed-in encoding argument needs to specify the string encoding (e.g., ENC_ASCII, ENC_UTF_8) as well as the format. For some XXX types, the format is constrained - for example for the encoding format for proto_tree_add_time_item() can only be one of the ENC_ISO_8601_* ones or ENC_RFC_822 or ENC_RFC_1123. For proto_tree_add_bytes_item() it can only be ENC_STR_HEX bit-or'ed with one or more of the ENC_SEP_* separator types. proto_tree_add_protocol_format() -------------------------------- proto_tree_add_protocol_format is used to add the top-level item for the protocol when the dissector routine wants complete control over how the field and value will be represented on the GUI tree. The ID value for the protocol is passed in as the "id" argument; the rest of the arguments are a "printf"-style format and any arguments for that format. The caller must include the name of the protocol in the format; it is not added automatically as in proto_tree_add_item(). proto_tree_add_none_format() ---------------------------- proto_tree_add_none_format is used to add an item of type FT_NONE. The caller must include the name of the field in the format; it is not added automatically as in proto_tree_add_item(). proto_tree_add_bytes() proto_tree_add_time() proto_tree_add_ipxnet() proto_tree_add_ipv4() proto_tree_add_ipv6() proto_tree_add_ether() proto_tree_add_string() proto_tree_add_boolean() proto_tree_add_float() proto_tree_add_double() proto_tree_add_uint() proto_tree_add_uint64() proto_tree_add_int() proto_tree_add_int64() proto_tree_add_guid() proto_tree_add_oid() proto_tree_add_eui64() ------------------------ These routines are used to add items to the protocol tree if either: the value of the item to be added isn't just extracted from the packet data, but is computed from data in the packet; the value was fetched into a variable. The 'value' argument has the value to be added to the tree. NOTE: in all cases where the 'value' argument is a pointer, a copy is made of the object pointed to; if you have dynamically allocated a buffer for the object, that buffer will not be freed when the protocol tree is freed - you must free the buffer yourself when you don't need it any more. For proto_tree_add_bytes(), the 'value_ptr' argument is a pointer to a sequence of bytes. proto_tree_add_bytes_with_length() is similar to proto_tree_add_bytes, except that the length is not derived from the tvb length. Instead, the displayed data size is controlled by 'ptr_length'. For proto_tree_add_bytes_format() and proto_tree_add_bytes_format_value(), the 'value_ptr' argument is a pointer to a sequence of bytes or NULL if the bytes should be taken from the given TVB using the given offset and length. For proto_tree_add_time(), the 'value_ptr' argument is a pointer to an "nstime_t", which is a structure containing the time to be added; it has 'secs' and 'nsecs' members, giving the integral part and the fractional part of a time in units of seconds, with 'nsecs' being the number of nanoseconds. For absolute times, "secs" is a UNIX-style seconds since January 1, 1970, 00:00:00 GMT value. For proto_tree_add_ipxnet(), the 'value' argument is a 32-bit IPX network address. For proto_tree_add_ipv4(), the 'value' argument is a 32-bit IPv4 address, in network byte order. For proto_tree_add_ipv6(), the 'value_ptr' argument is a pointer to a 128-bit IPv6 address. For proto_tree_add_ether(), the 'value_ptr' argument is a pointer to a 48-bit MAC address. For proto_tree_add_string(), the 'value_ptr' argument is a pointer to a text string; this string must be NULL terminated even if the string in the TVB is not (as may be the case with FT_STRINGs). For proto_tree_add_boolean(), the 'value' argument is a 32-bit integer. It is masked and shifted as defined by the field info after which zero means "false", and non-zero means "true". For proto_tree_add_float(), the 'value' argument is a 'float' in the host's floating-point format. For proto_tree_add_double(), the 'value' argument is a 'double' in the host's floating-point format. For proto_tree_add_uint(), the 'value' argument is a 32-bit unsigned integer value, in host byte order. (This routine cannot be used to add 64-bit integers.) For proto_tree_add_uint64(), the 'value' argument is a 64-bit unsigned integer value, in host byte order. For proto_tree_add_int(), the 'value' argument is a 32-bit signed integer value, in host byte order. (This routine cannot be used to add 64-bit integers.) For proto_tree_add_int64(), the 'value' argument is a 64-bit signed integer value, in host byte order. For proto_tree_add_guid(), the 'value_ptr' argument is a pointer to an e_guid_t structure. For proto_tree_add_oid(), the 'value_ptr' argument is a pointer to an ASN.1 Object Identifier. For proto_tree_add_eui64(), the 'value' argument is a 64-bit integer value proto_tree_add_bytes_format() proto_tree_add_time_format() proto_tree_add_ipxnet_format() proto_tree_add_ipv4_format() proto_tree_add_ipv6_format() proto_tree_add_ether_format() proto_tree_add_string_format() proto_tree_add_boolean_format() proto_tree_add_float_format() proto_tree_add_double_format() proto_tree_add_uint_format() proto_tree_add_uint64_format() proto_tree_add_int_format() proto_tree_add_int64_format() proto_tree_add_guid_format() proto_tree_add_oid_format() proto_tree_add_eui64_format() ---------------------------- These routines are used to add items to the protocol tree when the dissector routine wants complete control over how the field and value will be represented on the GUI tree. The argument giving the value is the same as the corresponding proto_tree_add_XXX() function; the rest of the arguments are a "printf"-style format and any arguments for that format. The caller must include the name of the field in the format; it is not added automatically as in the proto_tree_add_XXX() functions. proto_tree_add_bytes_format_value() proto_tree_add_time_format_value() proto_tree_add_ipxnet_format_value() proto_tree_add_ipv4_format_value() proto_tree_add_ipv6_format_value() proto_tree_add_ether_format_value() proto_tree_add_string_format_value() proto_tree_add_boolean_format_value() proto_tree_add_float_format_value() proto_tree_add_double_format_value() proto_tree_add_uint_format_value() proto_tree_add_uint64_format_value() proto_tree_add_int_format_value() proto_tree_add_int64_format_value() proto_tree_add_guid_format_value() proto_tree_add_oid_format_value() proto_tree_add_eui64_format_value() ------------------------------------ These routines are used to add items to the protocol tree when the dissector routine wants complete control over how the value will be represented on the GUI tree. The argument giving the value is the same as the corresponding proto_tree_add_XXX() function; the rest of the arguments are a "printf"-style format and any arguments for that format. With these routines, unlike the proto_tree_add_XXX_format() routines, the name of the field is added automatically as in the proto_tree_add_XXX() functions; only the value is added with the format. One use case for this would be to add a unit of measurement string to the value of the field, however using BASE_UNIT_STRING in the hf_ definition is now preferred. proto_tree_add_checksum() ---------------------------- proto_tree_add_checksum is used to add a checksum field. The hf field provided must be the correct size of the checksum (FT_UINT, FT_UINT16, FT_UINT32, etc). Additional parameters are there to provide "status" and expert info depending on whether the checksum matches the provided value. The "status" and expert info can be used in cases except where PROTO_CHECKSUM_NO_FLAGS is used. proto_tree_add_subtree() --------------------- proto_tree_add_subtree() is used to add a label to the GUI tree and create a subtree for other fields. It will contain no value, so it is not searchable in the display filter process. This should only be used for items with subtrees, which may not have values themselves - the items in the subtree are the ones with values. For a subtree, the label on the subtree might reflect some of the items in the subtree. This means the label can't be set until at least some of the items in the subtree have been dissected. To do this, use 'proto_item_set_text()' or 'proto_item_append_text()': void proto_item_set_text(proto_item *ti, ...); void proto_item_append_text(proto_item *ti, ...); 'proto_item_set_text()' takes as an argument the proto_item value returned by one of the parameters in 'proto_tree_add_subtree()', a 'printf'-style format string, and a set of arguments corresponding to '%' format items in that string, and replaces the text for the item created by 'proto_tree_add_subtree()' with the result of applying the arguments to the format string. 'proto_item_append_text()' is similar, but it appends to the text for the item the result of applying the arguments to the format string. For example, early in the dissection, one might do: subtree = proto_tree_add_subtree(tree, tvb, offset, length, ett, &ti, <label>); and later do proto_item_set_text(ti, "%s: %s", type, value); after the "type" and "value" fields have been extracted and dissected. <label> would be a label giving what information about the subtree is available without dissecting any of the data in the subtree. Note that an exception might be thrown when trying to extract the values of the items used to set the label, if not all the bytes of the item are available. Thus, one should create the item with text that is as meaningful as possible, and set it or append additional information to it as the values needed to supply that information are extracted. proto_tree_add_subtree_format() ---------------------------- This is like proto_tree_add_subtree(), but uses printf-style arguments to create the label; it is used to allow routines that take a printf-like variable-length list of arguments to add a text item to the protocol tree. proto_tree_add_bits_item() -------------------------- Adds a number of bits to the protocol tree which does not have to be byte aligned. The offset and length is in bits. Output format: ..10 1010 10.. .... "value" (formatted as FT_ indicates). proto_tree_add_bits_ret_val() ----------------------------- Works in the same way but also returns the value of the read bits. proto_tree_add_split_bits_item_ret_val() ----------------------------------- Similar, but is used for items that are made of 2 or more smaller sets of bits (crumbs) which are not contiguous, but are concatenated to form the actual value. The size of the crumbs and the order of assembly are specified in an array of crumb_spec structures. proto_tree_add_split_bits_crumb() --------------------------------- Helper function for the above, to add text for each crumb as it is encountered. proto_tree_add_ts_23_038_7bits_item() ------------------------------------- Adds a string of a given number of characters and encoded according to 3GPP TS 23.038 7 bits alphabet. proto_tree_add_bitmask() et al. ------------------------------- These functions provide easy to use and convenient dissection of many types of common bitmasks into individual fields. header is an integer type and must be of type FT_[U]INT{8|16|24|32||40|48|56|64} and represents the entire dissectable width of the bitmask. 'header' and 'ett' are the hf fields and ett field respectively to create an expansion that covers the bytes of the bitmask. 'fields' is a NULL terminated array of pointers to hf fields representing the individual subfields of the bitmask. These fields must either be integers (usually of the same byte width as 'header') or of the type FT_BOOLEAN. Each of the entries in 'fields' will be dissected as an item under the 'header' expansion and also IF the field is a boolean and IF it is set to 1, then the name of that boolean field will be printed on the 'header' expansion line. For integer type subfields that have a value_string defined, the matched string from that value_string will be printed on the expansion line as well. Example: (from the SCSI dissector) static int hf_scsi_inq_peripheral = -1; static int hf_scsi_inq_qualifier = -1; static int hf_scsi_inq_devtype = -1; ... static gint ett_scsi_inq_peripheral = -1; ... static const int *peripheral_fields[] = { &hf_scsi_inq_qualifier, &hf_scsi_inq_devtype, NULL }; ... /* Qualifier and DeviceType */ proto_tree_add_bitmask(tree, tvb, offset, hf_scsi_inq_peripheral, ett_scsi_inq_peripheral, peripheral_fields, ENC_BIG_ENDIAN); offset+=1; ... { &hf_scsi_inq_peripheral, {"Peripheral", "scsi.inquiry.peripheral", FT_UINT8, BASE_HEX, NULL, 0, NULL, HFILL}}, { &hf_scsi_inq_qualifier, {"Qualifier", "scsi.inquiry.qualifier", FT_UINT8, BASE_HEX, VALS (scsi_qualifier_val), 0xE0, NULL, HFILL}}, { &hf_scsi_inq_devtype, {"Device Type", "scsi.inquiry.devtype", FT_UINT8, BASE_HEX, VALS (scsi_devtype_val), SCSI_DEV_BITS, NULL, HFILL}}, ... Which provides very pretty dissection of this one byte bitmask. Peripheral: 0x05, Qualifier: Device type is connected to logical unit, Device Type: CD-ROM 000. .... = Qualifier: Device type is connected to logical unit (0x00) ...0 0101 = Device Type: CD-ROM (0x05) The proto_tree_add_bitmask_text() function is an extended version of the proto_tree_add_bitmask() function. In addition, it allows to: - Provide a leading text (e.g. "Flags: ") that will appear before the comma-separated list of field values - Provide a fallback text (e.g. "None") that will be appended if no fields warranted a change to the top-level title. - Using flags, specify which fields will affect the top-level title. There are the following flags defined: BMT_NO_APPEND - the title is taken "as-is" from the 'name' argument. BMT_NO_INT - only boolean flags are added to the title. BMT_NO_FALSE - boolean flags are only added to the title if they are set. BMT_NO_TFS - only add flag name to the title, do not use true_false_string The proto_tree_add_bitmask_with_flags() function is an extended version of the proto_tree_add_bitmask() function. It allows using flags to specify which fields will affect the top-level title. The flags are the same BMT_NO_* flags as used in the proto_tree_add_bitmask_text() function. The proto_tree_add_bitmask() behavior can be obtained by providing both 'name' and 'fallback' arguments as NULL, and a flags of (BMT_NO_FALSE|BMT_NO_TFS). The proto_tree_add_bitmask_len() function is intended for protocols where bitmask length is permitted to vary, so a length is specified explicitly along with the bitmask value. USB Video "bmControl" and "bControlSize" fields follow this pattern. The primary intent of this is "forward compatibility," enabling an interpreter coded for version M of a structure to comprehend fields in version N of the structure, where N > M and bControlSize increases from version M to version N. proto_tree_add_bitmask_len() is an extended version of proto_tree_add_bitmask() that uses an explicitly specified (rather than inferred) length to control dissection. Because of this, it may encounter two cases that proto_tree_add_bitmask() and proto_tree_add_bitmask_text() may not: - A length that exceeds that of the 'header' and bitmask subfields. In this case the least-significant bytes of the bitmask are dissected. An expert warning is generated in this case, because the dissection code likely needs to be updated for a new revision of the protocol. - A length that is shorter than that of the 'header' and bitmask subfields. In this case, subfields whose data is fully present are dissected, and other subfields are not. No warning is generated in this case, because the dissection code is likely for a later revision of the protocol than the packet it was called to interpret. PROTO_ITEM_SET_GENERATED() -------------------------- PROTO_ITEM_SET_GENERATED is used to mark fields as not being read from the captured data directly, but inferred from one or more values. One of the primary uses of this is the presentation of verification of checksums. Every IP packet has a checksum line, which can present the result of the checksum verification, if enabled in the preferences. The result is presented as a subtree, where the result is enclosed in square brackets indicating a generated field. Header checksum: 0x3d42 [correct] [Checksum Status: Good (1)] PROTO_ITEM_SET_HIDDEN() ----------------------- PROTO_ITEM_SET_HIDDEN is used to hide fields, which have already been added to the tree, from being visible in the displayed tree. NOTE that creating hidden fields is actually quite a bad idea from a UI design perspective because the user (someone who did not write nor has ever seen the code) has no way of knowing that hidden fields are there to be filtered on thus defeating the whole purpose of putting them there. A Better Way might be to add the fields (that might otherwise be hidden) to a subtree where they won't be seen unless the user opens the subtree--but they can be found if the user wants. One use for hidden fields (which would be better implemented using visible fields in a subtree) follows: The caller may want a value to be included in a tree so that the packet can be filtered on this field, but the representation of that field in the tree is not appropriate. An example is the token-ring routing information field (RIF). The best way to show the RIF in a GUI is by a sequence of ring and bridge numbers. Rings are 3-digit hex numbers, and bridges are single hex digits: RIF: 001-A-013-9-C0F-B-555 In the case of RIF, the programmer should use a field with no value and use proto_tree_add_none_format() to build the above representation. The programmer can then add the ring and bridge values, one-by-one, with proto_tree_add_item() and hide them with PROTO_ITEM_SET_HIDDEN() so that the user can then filter on or search for a particular ring or bridge. Here's a skeleton of how the programmer might code this. char *rif; rif = create_rif_string(...); proto_tree_add_none_format(tree, hf_tr_rif_label, ..., "RIF: %s", rif); for(i = 0; i < num_rings; i++) { proto_item *pi; pi = proto_tree_add_item(tree, hf_tr_rif_ring, ..., ENC_BIG_ENDIAN); PROTO_ITEM_SET_HIDDEN(pi); } for(i = 0; i < num_rings - 1; i++) { proto_item *pi; pi = proto_tree_add_item(tree, hf_tr_rif_bridge, ..., ENC_BIG_ENDIAN); PROTO_ITEM_SET_HIDDEN(pi); } The logical tree has these items: hf_tr_rif_label, text="RIF: 001-A-013-9-C0F-B-555", value = NONE hf_tr_rif_ring, hidden, value=0x001 hf_tr_rif_bridge, hidden, value=0xA hf_tr_rif_ring, hidden, value=0x013 hf_tr_rif_bridge, hidden, value=0x9 hf_tr_rif_ring, hidden, value=0xC0F hf_tr_rif_bridge, hidden, value=0xB hf_tr_rif_ring, hidden, value=0x555 GUI or print code will not display the hidden fields, but a display filter or "packet grep" routine will still see the values. The possible filter is then possible: tr.rif_ring eq 0x013 PROTO_ITEM_SET_URL ------------------ PROTO_ITEM_SET_URL is used to mark fields as containing a URL. This can only be done with fields of type FT_STRING(Z). If these fields are presented they are underlined, as could be done in a browser. These fields are sensitive to clicks as well, launching the configured browser with this URL as parameter. 1.6 Utility routines. 1.6.1 val_to_str, val_to_str_const, try_val_to_str and try_val_to_str_idx A dissector may need to convert a value to a string, using a 'value_string' structure, by hand, rather than by declaring a field with an associated 'value_string' structure; this might be used, for example, to generate a COL_INFO line for a frame. val_to_str() handles the most common case: const gchar* val_to_str(guint32 val, const value_string *vs, const char *fmt) If the value 'val' is found in the 'value_string' table pointed to by 'vs', 'val_to_str' will return the corresponding string; otherwise, it will use 'fmt' as an 'sprintf'-style format, with 'val' as an argument, to generate a string, and will return a pointer to that string. You can use it in a call to generate a COL_INFO line for a frame such as col_add_fstr(COL_INFO, ", %s", val_to_str(val, table, "Unknown %d")); If you don't need to display 'val' in your fmt string, you can use val_to_str_const() which just takes a string constant instead and returns it unmodified when 'val' isn't found. If you need to handle the failure case in some custom way, try_val_to_str() will return NULL if val isn't found: const gchar* try_val_to_str(guint32 val, const value_string *vs) Note that, you must check whether 'try_val_to_str()' returns NULL, and arrange that its return value not be dereferenced if it's NULL. 'try_val_to_str_idx()' behaves similarly, except it also returns an index into the value_string array, or -1 if 'val' was not found. The *_ext functions are "extended" versions of those already described. They should be used for large value-string arrays which contain many entries. They implement value to string conversions which will do either a direct access or a binary search of the value string array if possible. See "Extended Value Strings" under section 1.6 "Constructing the protocol tree" for more information. See epan/value_string.h for detailed information on the various value_string functions. To handle 64-bit values, there are an equivalent set of functions. These are: const gchar * val64_to_str(const guint64 val, const val64_string *vs, const char *fmt) const gchar * val64_to_str_const(const guint64 val, const val64_string *vs, const char *unknown_str); const gchar * try_val64_to_str(const guint64 val, const val64_string *vs); const gchar * try_val64_to_str_idx(const guint64 val, const val64_string *vs, gint *idx); 1.6.2 rval_to_str, try_rval_to_str and try_rval_to_str_idx A dissector may need to convert a range of values to a string, using a 'range_string' structure. Most of the same functions exist as with regular value_strings (see section 1.6.1) except with the names 'rval' instead of 'val'. 1.7 Calling Other Dissectors. As each dissector completes its portion of the protocol analysis, it is expected to create a new tvbuff of type TVBUFF_SUBSET which contains the payload portion of the protocol (that is, the bytes that are relevant to the next dissector). To create a new TVBUFF_SUBSET that begins at a specified offset in a parent tvbuff, and runs to the end of the parent tvbuff, the routine tvbuff_new_subset_remaining() is used: next_tvb = tvb_new_subset_remaining(tvb, offset); Where: tvb is the tvbuff that the dissector has been working on. It can be a tvbuff of any type. next_tvb is the new TVBUFF_SUBSET. offset is the byte offset of 'tvb' at which the new tvbuff should start. The first byte is the 0th byte. To create a new TVBUFF_SUBSET that begins at a specified offset in a parent tvbuff, with a specified number of bytes in the payload, the routine tvbuff_new_subset_length() is used: next_tvb = tvb_new_subset_length(tvb, offset, reported_length); Where: tvb is the tvbuff that the dissector has been working on. It can be a tvbuff of any type. next_tvb is the new TVBUFF_SUBSET. offset is the byte offset of 'tvb' at which the new tvbuff should start. The first byte is the 0th byte. reported_length is the number of bytes that the current protocol says should be in the payload. In the few cases where the number of bytes available in the new subset must be explicitly specified, rather than being calculated based on the number of bytes in the payload, the routine tvb_new_subset_length_caplen() is used: next_tvb = tvb_new_subset_length_caplen(tvb, offset, length, reported_length); Where: tvb is the tvbuff that the dissector has been working on. It can be a tvbuff of any type. next_tvb is the new TVBUFF_SUBSET. offset is the byte offset of 'tvb' at which the new tvbuff should start. The first byte is the 0th byte. length is the number of bytes in the new TVBUFF_SUBSET. A length argument of -1 says to use as many bytes as are available in 'tvb'. reported_length is the number of bytes that the current protocol says should be in the payload. A reported_length of -1 says that the protocol doesn't say anything about the size of its payload. To call a dissector you need to get the handle of the dissector using find_dissector(), passing it the string name of the dissector. The setting of the handle is usually done once at startup during the proto_reg_handoff function within the calling dissector. 1.7.1 Dissector Tables Another way to call a subdissector is to setup a dissector table. A dissector table is a list of subdissectors grouped by a common identifier (integer or string) in a dissector. Subdissectors will register themselves with the dissector table using their unique identifier using one of the following APIs: void dissector_add_uint(const char *abbrev, const guint32 pattern, dissector_handle_t handle); void dissector_add_uint_range(const char *abbrev, struct epan_range *range, dissector_handle_t handle); void dissector_add_string(const char *name, const gchar *pattern, dissector_handle_t handle); void dissector_add_for_decode_as(const char *name, dissector_handle_t handle); dissector_add_for_decode_as doesn't add a unique identifier in the dissector table, but it lets the user add it from the command line or, in Wireshark, through the "Decode As" UI. Then when the dissector hits the common identifier field, it will useone of the following APIs to invoke the subdissector: int dissector_try_uint(dissector_table_t sub_dissectors, const guint32 uint_val, tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree); int dissector_try_uint_new(dissector_table_t sub_dissectors, const guint32 uint_val, tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, const gboolean add_proto_name, void *data); int dissector_try_string(dissector_table_t sub_dissectors, const gchar *string, tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data); These pass a subset of the remaining packet (typically the rest of the packet) for the dissector table to determine which subdissector is called. This allows dissection of a packet to be expanded outside of dissector without having to modify the dissector directly. 1.8 Editing CMakeLists.txt to add your dissector. To arrange that your dissector will be built as part of Wireshark, you must add the name of the source file for your dissector to the DISSECTOR_SRC section of epan/dissectors/CMakeLists.txt 1.9 Using the git source code tree. See <https://www.wireshark.org/develop.html> 1.10 Submitting code for your new dissector. - VERIFY that your dissector code does not use prohibited or deprecated APIs as follows: perl <wireshark_root>/tools/checkAPIs.pl <source-filename(s)> - VERIFY that your dissector code does not contain any header field related problems: perl <wireshark_root>/tools/checkhf.pl <source-filename(s)> - VERIFY that your dissector code does not contain any display filter related problems: perl <wireshark_root>/tools/checkfiltername.pl <source-filename(s)> - CHECK your dissector with CppCheck (http://cppcheck.sourceforge.net/) using Wireshark's customized configuration. This is particularly important on Windows, since Microsoft's compiler warnings are quite thin: ./tools/cppcheck/cppcheck.sh <source-filename(s)> - TEST YOUR DISSECTOR BEFORE SUBMITTING IT. Use fuzz-test.sh and/or randpkt against your dissector. These are described at <https://wiki.wireshark.org/FuzzTesting>. - Subscribe to <mailto:wireshark-dev[AT]wireshark.org> by sending an email to <mailto:wireshark-dev-request[AT]wireshark.org?body="help"> or visiting <https://www.wireshark.org/lists/>. - 'git diff' to verify all your changes look good. - 'git add' all the files you changed. - 'git commit' to commit (locally) your changes. First line of commit message should be a summary of the changes followed by an empty line and a more verbose description. - 'git push origin HEAD:refs/for/master' to push the changes to Gerrit. (If you previously ran 'git config --add remote.origin.push HEAD:refs/for/master' then only 'git push' is needed.) - Create a Wiki page on the protocol at <https://wiki.wireshark.org>. A template is provided so it is easy to setup in a consistent style. See: <https://wiki.wireshark.org/HowToEdit> and <https://wiki.wireshark.org/ProtocolReference> - If possible, add sample capture files to the sample captures page at <https://wiki.wireshark.org/SampleCaptures>. These files are used by the automated build system for fuzz testing. - If you don't think the wiki is the right place for your sample capture, submit a bug report to the Wireshark bug database, found at <https://bugs.wireshark.org>, qualified as an enhancement and attach your sample capture there. Normally a new dissector won't be accepted without a sample capture! If you open a bug be sure to cross-link your Gerrit change and bug. 2. Advanced dissector topics. 2.1 Introduction. Some of the advanced features are being worked on constantly. When using them it is wise to check the relevant header and source files for additional details. 2.2 Following "conversations". In wireshark a conversation is defined as a series of data packets between two address:port combinations. A conversation is not sensitive to the direction of the packet. The same conversation will be returned for a packet bound from ServerA:1000 to ClientA:2000 and the packet from ClientA:2000 to ServerA:1000. 2.2.1 Conversation Routines There are seven routines that you will use to work with a conversation: conversation_new, find_conversation, find_or_create_conversation, conversation_add_proto_data, conversation_get_proto_data, conversation_delete_proto_data, and conversation_set_dissector. 2.2.1.1 The conversation_init function. This is an internal routine for the conversation code. As such you will not have to call this routine. Just be aware that this routine is called at the start of each capture and before the packets are filtered with a display filter. The routine will destroy all stored conversations. This routine does NOT clean up any data pointers that are passed in the conversation_add_proto_data 'data' variable. You are responsible for this clean up if you pass a malloc'ed pointer in this variable. See item 2.2.1.5 for more information about use of the 'data' pointer. 2.2.1.2 The conversation_new function. This routine will create a new conversation based upon two address/port pairs. If you want to associate with the conversation a pointer to a private data structure you must use the conversation_add_proto_data function. The ptype variable is used to differentiate between conversations over different protocols, i.e. TCP and UDP. The options variable is used to define a conversation that will accept any destination address and/or port. Set options = 0 if the destination port and address are know when conversation_new is called. See section 2.4 for more information on usage of the options parameter. The conversation_new prototype: conversation_t *conversation_new(guint32 setup_frame, address *addr1, address *addr2, port_type ptype, guint32 port1, guint32 port2, guint options); Where: guint32 setup_frame = The lowest numbered frame for this conversation address* addr1 = first data packet address address* addr2 = second data packet address port_type ptype = port type, this is defined in packet.h guint32 port1 = first data packet port guint32 port2 = second data packet port guint options = conversation options, NO_ADDR2 and/or NO_PORT2 setup_frame indicates the first frame for this conversation, and is used to distinguish multiple conversations with the same addr1/port1 and addr2/port2 pair that occur within the same capture session. "addr1" and "port1" are the first address/port pair; "addr2" and "port2" are the second address/port pair. A conversation doesn't have source and destination address/port pairs - packets in a conversation go in both directions - so "addr1"/"port1" may be the source or destination address/port pair; "addr2"/"port2" would be the other pair. If NO_ADDR2 is specified, the conversation is set up so that a conversation lookup will match only the "addr1" address; if NO_PORT2 is specified, the conversation is set up so that a conversation lookup will match only the "port1" port; if both are specified, i.e. NO_ADDR2|NO_PORT2, the conversation is set up so that the lookup will match only the "addr1"/"port1" address/port pair. This can be used if a packet indicates that, later in the capture, a conversation will be created using certain addresses and ports, in the case where the packet doesn't specify the addresses and ports of both sides. 2.2.1.3 The find_conversation function. Call this routine to look up a conversation. If no conversation is found, the routine will return a NULL value. The find_conversation prototype: conversation_t *find_conversation(guint32 frame_num, address *addr_a, address *addr_b, port_type ptype, guint32 port_a, guint32 port_b, guint options); Where: guint32 frame_num = a frame number to match address* addr_a = first address address* addr_b = second address port_type ptype = port type guint32 port_a = first data packet port guint32 port_b = second data packet port guint options = conversation options, NO_ADDR_B and/or NO_PORT_B frame_num is a frame number to match. The conversation returned is where (frame_num >= conversation->setup_frame && frame_num < conversation->next->setup_frame) Suppose there are a total of 3 conversations (A, B, and C) that match addr_a/port_a and addr_b/port_b, where the setup_frame used in conversation_new() for A, B and C are 10, 50, and 100 respectively. The frame_num passed in find_conversation is compared to the setup_frame of each conversation. So if (frame_num >= 10 && frame_num < 50), conversation A is returned. If (frame_num >= 50 && frame_num < 100), conversation B is returned. If (frame_num >= 100) conversation C is returned. "addr_a" and "port_a" are the first address/port pair; "addr_b" and "port_b" are the second address/port pair. Again, as a conversation doesn't have source and destination address/port pairs, so "addr_a"/"port_a" may be the source or destination address/port pair; "addr_b"/"port_b" would be the other pair. The search will match the "a" address/port pair against both the "1" and "2" address/port pairs, and match the "b" address/port pair against both the "2" and "1" address/port pairs; you don't have to worry about which side the "a" or "b" pairs correspond to. If the NO_ADDR_B flag was specified to "find_conversation()", the "addr_b" address will be treated as matching any "wildcarded" address; if the NO_PORT_B flag was specified, the "port_b" port will be treated as matching any "wildcarded" port. If both flags are specified, i.e. NO_ADDR_B|NO_PORT_B, the "addr_b" address will be treated as matching any "wildcarded" address and the "port_b" port will be treated as matching any "wildcarded" port. 2.2.1.4 The find_conversation_pinfo function. This convenience function will find an existing conversation (by calling find_conversation()) The find_conversation_pinfo prototype: extern conversation_t *find_conversation_pinfo(packet_info *pinfo); Where: packet_info *pinfo = the packet_info structure The frame number and the addresses necessary for find_conversation() are taken from the pinfo structure (as is commonly done). 2.2.1.5 The find_or_create_conversation function. This convenience function will find an existing conversation (by calling find_conversation()) and, if a conversation does not already exist, create a new conversation by calling conversation_new(). The find_or_create_conversation prototype: extern conversation_t *find_or_create_conversation(packet_info *pinfo); Where: packet_info *pinfo = the packet_info structure The frame number and the addresses necessary for find_conversation() and conversation_new() are taken from the pinfo structure (as is commonly done) and no 'options' are used. 2.2.1.6 The conversation_add_proto_data function. Once you have created a conversation with conversation_new, you can associate data with it using this function. The conversation_add_proto_data prototype: void conversation_add_proto_data(conversation_t *conv, int proto, void *proto_data); Where: conversation_t *conv = the conversation in question int proto = registered protocol number void *data = dissector data structure "conversation" is the value returned by conversation_new. "proto" is a unique protocol number created with proto_register_protocol. Protocols are typically registered in the proto_register_XXXX section of your dissector. "data" is a pointer to the data you wish to associate with the conversation. "data" usually points to "wmem_alloc'd" memory; the memory will be automatically freed each time a new dissection begins and thus need not be managed (freed) by the dissector. Using the protocol number allows several dissectors to associate data with a given conversation. 2.2.1.7 The conversation_get_proto_data function. After you have located a conversation with find_conversation, you can use this function to retrieve any data associated with it. The conversation_get_proto_data prototype: void *conversation_get_proto_data(conversation_t *conv, int proto); Where: conversation_t *conv = the conversation in question int proto = registered protocol number "conversation" is the conversation created with conversation_new. "proto" is a unique protocol number created with proto_register_protocol, typically in the proto_register_XXXX portion of a dissector. The function returns a pointer to the data requested, or NULL if no data was found. 2.2.1.8 The conversation_delete_proto_data function. After you are finished with a conversation, you can remove your association with this function. Please note that ONLY the conversation entry is removed. If you have allocated any memory for your data (other than with wmem_alloc), you must free it as well. The conversation_delete_proto_data prototype: void conversation_delete_proto_data(conversation_t *conv, int proto); Where: conversation_t *conv = the conversation in question int proto = registered protocol number "conversation" is the conversation created with conversation_new. "proto" is a unique protocol number created with proto_register_protocol, typically in the proto_register_XXXX portion of a dissector. 2.2.1.9 The conversation_set_dissector function This function sets the protocol dissector to be invoked whenever conversation parameters (addresses, port_types, ports, etc) are matched during the dissection of a packet. The conversation_set_dissector prototype: void conversation_set_dissector(conversation_t *conversation, const dissector_handle_t handle); Where: conversation_t *conv = the conversation in question const dissector_handle_t handle = the dissector handle. 2.2.2 Using timestamps relative to the conversation There is a framework to calculate timestamps relative to the start of the conversation. First of all the timestamp of the first packet that has been seen in the conversation must be kept in the protocol data to be able to calculate the timestamp of the current packet relative to the start of the conversation. The timestamp of the last packet that was seen in the conversation should also be kept in the protocol data. This way the delta time between the current packet and the previous packet in the conversation can be calculated. So add the following items to the struct that is used for the protocol data: nstime_t ts_first; nstime_t ts_prev; The ts_prev value should only be set during the first run through the packets (ie PINFO_FD_VISITED(pinfo) is false). Next step is to use the per-packet information (described in section 2.5) to keep the calculated delta timestamp, as it can only be calculated on the first run through the packets. This is because a packet can be selected in random order once the whole file has been read. After calculating the conversation timestamps, it is time to put them in the appropriate columns with the function 'col_set_time' (described in section 1.5.9). The column used for relative timestamps is: COL_REL_TIME, /* Delta time to last frame in conversation */ Last but not least, there MUST be a preference in each dissector that uses conversation timestamps that makes it possible to enable and disable the calculation of conversation timestamps. The main argument for this is that a higher level conversation is able to overwrite the values of lower level conversations in these two columns. Being able to actively select which protocols may overwrite the conversation timestamp columns gives the user the power to control these columns. (A second reason is that conversation timestamps use the per-packet data structure which uses additional memory, which should be avoided if these timestamps are not needed) Have a look at the differences to packet-tcp.[ch] in SVN 22966 and SVN 23058 to see the implementation of conversation timestamps for the tcp-dissector. 2.2.3 The example conversation code using wmem_file_scope memory. For a conversation between two IP addresses and ports you can use this as an example. This example uses wmem_alloc() with wmem_file_scope() to allocate memory and stores the data pointer in the conversation 'data' variable. /************************ Global values ************************/ /* define your structure here */ typedef struct { } my_entry_t; /* Registered protocol number */ static int my_proto = -1; /********************* in the dissector routine *********************/ /* the local variables in the dissector */ conversation_t *conversation; my_entry_t *data_ptr; /* look up the conversation */ conversation = find_conversation(pinfo->num, &pinfo->src, &pinfo->dst, pinfo->ptype, pinfo->srcport, pinfo->destport, 0); /* if conversation found get the data pointer that you stored */ if (conversation) data_ptr = (my_entry_t*)conversation_get_proto_data(conversation, my_proto); else { /* new conversation create local data structure */ data_ptr = wmem_alloc(wmem_file_scope(), sizeof(my_entry_t)); /*** add your code here to setup the new data structure ***/ /* create the conversation with your data pointer */ conversation = conversation_new(pinfo->num, &pinfo->src, &pinfo->dst, pinfo->ptype, pinfo->srcport, pinfo->destport, 0); conversation_add_proto_data(conversation, my_proto, (void *)data_ptr); } /* at this point the conversation data is ready */ /***************** in the protocol register routine *****************/ my_proto = proto_register_protocol("My Protocol", "My Protocol", "my_proto"); 2.2.4 An example conversation code that starts at a specific frame number. Sometimes a dissector has determined that a new conversation is needed that starts at a specific frame number, when a capture session encompasses multiple conversation that reuse the same src/dest ip/port pairs. You can use the conversation->setup_frame returned by find_conversation with pinfo->num to determine whether or not there already exists a conversation that starts at the specific frame number. /* in the dissector routine */ conversation = find_conversation(pinfo->num, &pinfo->src, &pinfo->dst, pinfo->ptype, pinfo->srcport, pinfo->destport, 0); if (conversation == NULL || (conversation->setup_frame != pinfo->num)) { /* It's not part of any conversation or the returned * conversation->setup_frame doesn't match the current frame * create a new one. */ conversation = conversation_new(pinfo->num, &pinfo->src, &pinfo->dst, pinfo->ptype, pinfo->srcport, pinfo->destport, NULL, 0); } 2.2.5 The example conversation code using conversation index field. Sometimes the conversation isn't enough to define a unique data storage value for the network traffic. For example if you are storing information about requests carried in a conversation, the request may have an identifier that is used to define the request. In this case the conversation and the identifier are required to find the data storage pointer. You can use the conversation data structure index value to uniquely define the conversation. See packet-afs.c for an example of how to use the conversation index. In this dissector multiple requests are sent in the same conversation. To store information for each request the dissector has an internal hash table based upon the conversation index and values inside the request packets. /* in the dissector routine */ /* to find a request value, first lookup conversation to get index */ /* then used the conversation index, and request data to find data */ /* in the local hash table */ conversation = find_or_create_conversation(pinfo); request_key.conversation = conversation->index; request_key.service = pntoh16(&rxh->serviceId); request_key.callnumber = pntoh32(&rxh->callNumber); request_val = (struct afs_request_val *)g_hash_table_lookup( afs_request_hash, &request_key); /* only allocate a new hash element when it's a request */ opcode = 0; if (!request_val && !reply) { new_request_key = wmem_alloc(wmem_file_scope(), sizeof(struct afs_request_key)); *new_request_key = request_key; request_val = wmem_alloc(wmem_file_scope(), sizeof(struct afs_request_val)); request_val -> opcode = pntoh32(&afsh->opcode); opcode = request_val->opcode; g_hash_table_insert(afs_request_hash, new_request_key, request_val); } 2.3 Dynamic conversation dissector registration. NOTE: This sections assumes that all information is available to create a complete conversation, source port/address and destination port/address. If either the destination port or address is known, see section 2.4 Dynamic server port dissector registration. For protocols that negotiate a secondary port connection, for example packet-msproxy.c, a conversation can install a dissector to handle the secondary protocol dissection. After the conversation is created for the negotiated ports use the conversation_set_dissector to define the dissection routine. Before we create these conversations or assign a dissector to them we should first check that the conversation does not already exist and if it exists whether it is registered to our protocol or not. We should do this because it is uncommon but it does happen that multiple different protocols can use the same socketpair during different stages of an application cycle. By keeping track of the frame number a conversation was started in wireshark can still tell these different protocols apart. The second argument to conversation_set_dissector is a dissector handle, which is created with a call to create_dissector_handle or register_dissector. create_dissector_handle takes as arguments a pointer to the dissector function and a protocol ID as returned by proto_register_protocol; register_dissector takes as arguments a string giving a name for the dissector, a pointer to the dissector function, and a protocol ID. The protocol ID is the ID for the protocol dissected by the function. The function will not be called if the protocol has been disabled by the user; instead, the data for the protocol will be dissected as raw data. An example - /* the handle for the dynamic dissector * static dissector_handle_t sub_dissector_handle; /* prototype for the dynamic dissector */ static void sub_dissector(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree); /* in the main protocol dissector, where the next dissector is setup */ /* if conversation has a data field, create it and load structure */ /* First check if a conversation already exists for this socketpair */ conversation = find_conversation(pinfo->num, &pinfo->src, &pinfo->dst, protocol, src_port, dst_port, 0); /* If there is no such conversation, or if there is one but for someone else's protocol then we just create a new conversation and assign our protocol to it. */ if ( (conversation == NULL) || (conversation->dissector_handle != sub_dissector_handle) ) { new_conv_info = wmem_alloc(wmem_file_scope(), sizeof(struct _new_conv_info)); new_conv_info->data1 = value1; /* create the conversation for the dynamic port */ conversation = conversation_new(pinfo->num, &pinfo->src, &pinfo->dst, protocol, src_port, dst_port, new_conv_info, 0); /* set the dissector for the new conversation */ conversation_set_dissector(conversation, sub_dissector_handle); } ... void proto_register_PROTOABBREV(void) { ... sub_dissector_handle = create_dissector_handle(sub_dissector, proto); ... } 2.4 Dynamic server port dissector registration. NOTE: While this example used both NO_ADDR2 and NO_PORT2 to create a conversation with only one port and address set, this isn't a requirement. Either the second port or the second address can be set when the conversation is created. For protocols that define a server address and port for a secondary protocol, a conversation can be used to link a protocol dissector to the server port and address. The key is to create the new conversation with the second address and port set to the "accept any" values. Some server applications can use the same port for different protocols during different stages of a transaction. For example it might initially use SNMP to perform some discovery and later switch to use TFTP using the same port. In order to handle this properly we must first check whether such a conversation already exists or not and if it exists we also check whether the registered dissector_handle for that conversation is "our" dissector or not. If not we create a new conversation on top of the previous one and set this new conversation to use our protocol. Since wireshark keeps track of the frame number where a conversation started wireshark will still be able to keep the packets apart even though they do use the same socketpair. (See packet-tftp.c and packet-snmp.c for examples of this) There are two support routines that will allow the second port and/or address to be set later. conversation_set_port2( conversation_t *conv, guint32 port); conversation_set_addr2( conversation_t *conv, address addr); These routines will change the second address or port for the conversation. So, the server port conversation will be converted into a more complete conversation definition. Don't use these routines if you want to create a conversation between the server and client and retain the server port definition, you must create a new conversation. An example - /* the handle for the dynamic dissector * static dissector_handle_t sub_dissector_handle; ... /* in the main protocol dissector, where the next dissector is setup */ /* if conversation has a data field, create it and load structure */ new_conv_info = wmem_alloc(wmem_file_scope(), sizeof(struct _new_conv_info)); new_conv_info->data1 = value1; /* create the conversation for the dynamic server address and port */ /* NOTE: The second address and port values don't matter because the */ /* NO_ADDR2 and NO_PORT2 options are set. */ /* First check if a conversation already exists for this IP/protocol/port */ conversation = find_conversation(pinfo->num, &server_src_addr, 0, protocol, server_src_port, 0, NO_ADDR2 | NO_PORT_B); /* If there is no such conversation, or if there is one but for someone else's protocol then we just create a new conversation and assign our protocol to it. */ if ( (conversation == NULL) || (conversation->dissector_handle != sub_dissector_handle) ) { conversation = conversation_new(pinfo->num, &server_src_addr, 0, protocol, server_src_port, 0, new_conv_info, NO_ADDR2 | NO_PORT2); /* set the dissector for the new conversation */ conversation_set_dissector(conversation, sub_dissector_handle); } 2.5 Per-packet information. Information can be stored for each data packet that is processed by the dissector. The information is added with the p_add_proto_data function and retrieved with the p_get_proto_data function. The data pointers passed into the p_add_proto_data are not managed by the proto_data routines, however the data pointer memory scope must match that of the scope parameter. The two most common use cases for p_add_proto_data/p_get_proto_data are for persistent data about the packet for the lifetime of the capture (file scope) and to exchange data between dissectors across a single packet (packet scope). It is also used to provide packet data for Decode As dialog (packet scope). These functions are delcared in <epan/proto_data.h>. void p_add_proto_data(wmem_allocator_t *scope, packet_info *pinfo, int proto, guint32 key, void *proto_data) void * p_get_proto_data(wmem_allocator_t *scope, packet_info *pinfo, int proto, guint32 key) Where: scope - Lifetime of the data to be stored, typically wmem_file_scope() or pinfo->pool (packet scope). Must match scope of data allocated. pinfo - The packet info pointer. proto - Protocol id returned by the proto_register_protocol call during initialization key - key associated with 'proto_data' proto_data - pointer to the dissector data. 2.6 User Preferences. If the dissector has user options, there is support for adding these preferences to a configuration dialog. You must register the module with the preferences routine with - module_t *prefs_register_protocol(proto_id, void (*apply_cb)(void)) or module_t *prefs_register_protocol_subtree(const char *subtree, int id, void (*apply_cb)(void)); Where: proto_id - the value returned by "proto_register_protocol()" when the protocol was registered. apply_cb - Callback routine that is called when preferences are applied. It may be NULL, which inhibits the callback. subtree - grouping preferences tree node name (several protocols can be grouped under one preferences subtree) Then you can register the fields that can be configured by the user with these routines - /* Register a preference with an unsigned integral value. */ void prefs_register_uint_preference(module_t *module, const char *name, const char *title, const char *description, guint base, guint *var); /* Register a preference with an Boolean value. */ void prefs_register_bool_preference(module_t *module, const char *name, const char *title, const char *description, gboolean *var); /* Register a preference with an enumerated value. */ void prefs_register_enum_preference(module_t *module, const char *name, const char *title, const char *description, gint *var, const enum_val_t *enumvals, gboolean radio_buttons) /* Register a preference with a character-string value. */ void prefs_register_string_preference(module_t *module, const char *name, const char *title, const char *description, char **var) /* Register a preference with a file name (string) value. * File name preferences are basically like string preferences * except that the GUI gives the user the ability to browse for the * file. Set for_writing TRUE to show a Save dialog instead of normal Open. */ void prefs_register_filename_preference(module_t *module, const char *name, const char *title, const char *description, char **var, gboolean for_writing) /* Register a preference with a range of unsigned integers (e.g., * "1-20,30-40"). */ void prefs_register_range_preference(module_t *module, const char *name, const char *title, const char *description, range_t *var, guint32 max_value) Where: module - Returned by the prefs_register_protocol routine name - This is appended to the name of the protocol, with a "." between them, to construct a name that identifies the field in the preference file; the name itself should not include the protocol name, as the name in the preference file will already have it. Make sure that only lower-case ASCII letters, numbers, underscores and dots appear in the preference name. title - Field title in the preferences dialog description - Comments added to the preference file above the preference value and shown as tooltip in the GUI, or NULL var - pointer to the storage location that is updated when the field is changed in the preference dialog box. Note that with string preferences the given pointer is overwritten with a pointer to a new copy of the string during the preference registration. The passed-in string may be freed, but you must keep another pointer to the string in order to free it. base - Base that the unsigned integer is expected to be in, see strtoul(3). enumvals - an array of enum_val_t structures. This must be NULL-terminated; the members of that structure are: a short name, to be used with the "-o" flag - it should not contain spaces or upper-case letters, so that it's easier to put in a command line; a description, which is used in the GUI (and which, for compatibility reasons, is currently what's written to the preferences file) - it can contain spaces, capital letters, punctuation, etc.; the numerical value corresponding to that name and description radio_buttons - TRUE if the field is to be displayed in the preferences dialog as a set of radio buttons, FALSE if it is to be displayed as an option menu max_value - The maximum allowed value for a range (0 is the minimum). These functions are declared in <epan/prefs.h>. An example from packet-rtpproxy.c - proto_rtpproxy = proto_register_protocol ( "Sippy RTPproxy Protocol", "RTPproxy", "rtpproxy"); ... rtpproxy_module = prefs_register_protocol(proto_rtpproxy, proto_reg_handoff_rtpproxy); prefs_register_bool_preference(rtpproxy_module, "establish_conversation", "Establish Media Conversation", "Specifies that RTP/RTCP/T.38/MSRP/etc streams are decoded based " "upon port numbers found in RTPproxy answers", &rtpproxy_establish_conversation); prefs_register_uint_preference(rtpproxy_module, "reply.timeout", "RTPproxy reply timeout", /* Title */ "Maximum timeout value in waiting for reply from RTPProxy (in milliseconds).", /* Descr */ 10, &rtpproxy_timeout); This will create preferences "rtpproxy.establish_conversation" and "rtpproxy.reply.timeout", the first of which is an Boolean and the second of which is a unsigned integer. Note that a warning will pop up if you've saved such preference to the preference file and you subsequently take the code out. The way to make a preference obsolete is to register it as such: /* Register a preference that used to be supported but no longer is. */ void prefs_register_obsolete_preference(module_t *module, const char *name); 2.7 Reassembly/desegmentation for protocols running atop TCP. There are two main ways of reassembling a Protocol Data Unit (PDU) which spans across multiple TCP segments. The first approach is simpler, but assumes you are running atop of TCP when this occurs (but your dissector might run atop of UDP, too, for example), and that your PDUs consist of a fixed amount of data that includes enough information to determine the PDU length, possibly followed by additional data. The second method is more generic but requires more code and is less efficient. 2.7.1 Using tcp_dissect_pdus(). For the first method, you register two different dissection methods, one for the TCP case, and one for the other cases. It is a good idea to also have a dissect_PROTO_common function which will parse the generic content that you can find in all PDUs which is called from dissect_PROTO_tcp when the reassembly is complete and from dissect_PROTO_udp (or dissect_PROTO_other). To register the distinct dissector functions, consider the following example, stolen from packet-dns.c: #include "packet-tcp.h" dissector_handle_t hartip_tcp_handle; dissector_handle_t hartip_udp_handle; hartip_tcp_handle = create_dissector_handle(dissect_hartip_tcp, proto_hartip); hartip_udp_handle = create_dissector_handle(dissect_hartip_udp, proto_hartip); dissector_add_uint("udp.port", HARTIP_PORT, hartip_udp_handle); dissector_add_uint_with_preference("tcp.port", HARTIP_PORT, hartip_tcp_handle); The dissect_hartip_udp function does very little work and calls dissect_hartip_common, while dissect_hartip_tcp calls tcp_dissect_pdus with a reference to a callback which will be called with reassembled data: static int dissect_hartip_tcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data) { if (!tvb_bytes_exist(tvb, 0, HARTIP_HEADER_LENGTH)) return 0; tcp_dissect_pdus(tvb, pinfo, tree, hartip_desegment, HARTIP_HEADER_LENGTH, get_dissect_hartip_len, dissect_hartip_pdu, data); return tvb_reported_length(tvb); } (The dissect_hartip_pdu function acts similarly to dissect_hartip_udp.) The arguments to tcp_dissect_pdus are: the tvbuff pointer, packet_info pointer, and proto_tree pointer passed to the dissector; a gboolean flag indicating whether desegmentation is enabled for your protocol; the number of bytes of PDU data required to determine the length of the PDU; a routine that takes as arguments a packet_info pointer, a tvbuff pointer and an offset value representing the offset into the tvbuff at which a PDU begins, and a void pointer for user data, and should return the total length of the PDU in bytes (or 0 if more bytes are needed to determine the message length). The routine must not throw exceptions (it is guaranteed that the number of bytes specified by the previous argument to tcp_dissect_pdus is available, but more data might not be available, so don't refer to any data past that); a new_dissector_t routine to dissect the pdu that's passed a tvbuff pointer, packet_info pointer, proto_tree pointer and a void pointer for user data, with the tvbuff containing a possibly-reassembled PDU. (The "reported_length" of the tvbuff will be the length of the PDU); a void pointer to user data that is passed to the length-determining routine, and the dissector routine referenced in the previous parameter. 2.7.2 Modifying the pinfo struct. The second reassembly mode is preferred when the dissector cannot determine how many bytes it will need to read in order to determine the size of a PDU. It may also be useful if your dissector needs to support reassembly from protocols other than TCP. Your dissect_PROTO will initially be passed a tvbuff containing the payload of the first packet. It should dissect as much data as it can, noting that it may contain more than one complete PDU. If the end of the provided tvbuff coincides with the end of a PDU then all is well and your dissector can just return as normal. (If it is a new-style dissector, it should return the number of bytes successfully processed.) If the dissector discovers that the end of the tvbuff does /not/ coincide with the end of a PDU, (ie, there is half of a PDU at the end of the tvbuff), it can indicate this to the parent dissector, by updating the pinfo struct. The desegment_offset field is the offset in the tvbuff at which the dissector will continue processing when next called. The desegment_len field should contain the estimated number of additional bytes required for completing the PDU. Next time your dissect_PROTO is called, it will be passed a tvbuff composed of the end of the data from the previous tvbuff together with desegment_len more bytes. If the dissector cannot tell how many more bytes it will need, it should set desegment_len=DESEGMENT_ONE_MORE_SEGMENT; it will then be called again as soon as any more data becomes available. Dissectors should set the desegment_len to a reasonable value when possible rather than always setting DESEGMENT_ONE_MORE_SEGMENT as it will generally be more efficient. Also, you *must not* set desegment_len=1 in this case, in the hope that you can change your mind later: once you return a positive value from desegment_len, your PDU boundary is set in stone. static hf_register_info hf[] = { {&hf_cstring, {"C String", "c.string", FT_STRING, BASE_NONE, NULL, 0x0, NULL, HFILL} } }; /** * Dissect a buffer containing ASCII C strings. * * @param tvb The buffer to dissect. * @param pinfo Packet Info. * @param tree The protocol tree. * @param data Optional data parameter given by parent dissector. **/ static int dissect_cstr(tvbuff_t * tvb, packet_info * pinfo, proto_tree * tree, void *data _U_) { guint offset = 0; while(offset < tvb_reported_length(tvb)) { gint available = tvb_reported_length_remaining(tvb, offset); gint len = tvb_strnlen(tvb, offset, available); if( -1 == len ) { /* we ran out of data: ask for more */ pinfo->desegment_offset = offset; pinfo->desegment_len = DESEGMENT_ONE_MORE_SEGMENT; return (offset + available); } col_set_str(pinfo->cinfo, COL_INFO, "C String"); len += 1; /* Add one for the '\0' */ if (tree) { proto_tree_add_item(tree, hf_cstring, tvb, offset, len, ENC_ASCII|ENC_NA); } offset += (guint)len; } /* if we get here, then the end of the tvb coincided with the end of a string. Happy days. */ return tvb_captured_length(tvb); } This simple dissector will repeatedly return DESEGMENT_ONE_MORE_SEGMENT requesting more data until the tvbuff contains a complete C string. The C string will then be added to the protocol tree. Note that there may be more than one complete C string in the tvbuff, so the dissection is done in a loop. 2.8 Using udp_dissect_pdus(). As noted in section 2.7.1, TCP has an API to dissect its PDU that can handle a PDU spread across multiple packets or multiple PDUs spread across a single packet. This section describes a similar mechanism for UDP, but is only applicable for one or more PDUs in a single packet. If a protocol runs on top of TCP as well as UDP, a common PDU dissection function can be created for both. To register the distinct dissector functions, consider the following example using UDP and TCP dissection, stolen from packet-dnp.c: #include "packet-tcp.h" #include "packet-udp.h" dissector_handle_t dnp3_tcp_handle; dissector_handle_t dnp3_udp_handle; dnp3_tcp_handle = create_dissector_handle(dissect_dnp3_tcp, proto_dnp3); dnp3_udp_handle = create_dissector_handle(dissect_dnp3_udp, proto_dnp3); dissector_add_uint("tcp.port", TCP_PORT_DNP, dnp3_tcp_handle); dissector_add_uint("udp.port", UDP_PORT_DNP, dnp3_udp_handle); Both dissect_dnp3_tcp and dissect_dnp3_udp call tcp_dissect_pdus and udp_dissect_pdus respectively, with a reference to the same callbacks which are called to handle PDU data. static int dissect_dnp3_udp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data) { return udp_dissect_pdus(tvb, pinfo, tree, DNP_HDR_LEN, dnp3_udp_check_header, get_dnp3_message_len, dissect_dnp3_message, data); } static int dissect_dnp3_tcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data) { if (!check_dnp3_header(tvb, FALSE)) { return 0; } tcp_dissect_pdus(tvb, pinfo, tree, TRUE, DNP_HDR_LEN, get_dnp3_message_len, dissect_dnp3_message, data); return tvb_captured_length(tvb); } (udp_dissect_pdus has an option of a heuristic check function within it while tcp_dissect_pdus does not, so it's done outside) The arguments to udp_dissect_pdus are: the tvbuff pointer, packet_info pointer, and proto_tree pointer passed to the dissector; the number of bytes of PDU data required to determine the length of the PDU; an optional routine (passing NULL is okay) that takes as arguments a packet_info pointer, a tvbuff pointer and an offset value representing the offset into the tvbuff at which a PDU begins, and a void pointer for user data, and should return TRUE if the packet belongs to the dissector. The routine must not throw exceptions (it is guaranteed that the number of bytes specified by the previous argument to udp_dissect_pdus is available, but more data might not be available, so don't refer to any data past that); a routine that takes as arguments a packet_info pointer, a tvbuff pointer and an offset value representing the offset into the tvbuff at which a PDU begins, and a void pointer for user data, and should return the total length of the PDU in bytes. If return value is 0, it's treated the same as a failed heuristic. The routine must not throw exceptions (it is guaranteed that the number of bytes specified by the previous argument to tcp_dissect_pdus is available, but more data might not be available, so don't refer to any data past that); a new_dissector_t routine to dissect the pdu that's passed a tvbuff pointer, packet_info pointer, proto_tree pointer and a void pointer for user data, with the tvbuff containing a possibly-reassembled PDU. (The "reported_length" of the tvbuff will be the length of the PDU); a void pointer to user data that is passed to the length-determining routine, and the dissector routine referenced in the previous parameter. 2.9 PINOs (Protocols in name only) For the typical dissector there is a 1-1 relationship between it and it's protocol. However, there are times when a protocol needs multiple "names" because it has multiple dissection functions going into the same dissector table. The muliple names removes confusion when picking dissection through Decode As functionality. Once the "main" protocol name has been created through proto_register_protocol, additional "pinos" can be created with proto_register_protocol_in_name_only. These pinos have all of the naming conventions of a protocol, but are stored separately as to remove confusion from real protocols. "pinos" the main protocol's properties for things like enable/disable. i.e. If the "main" protocol has been disabled, all of its pinos will be disabled as well. Pinos should not have any fields registered with them or heuristic tables associated with them. Another use case for pinos is when a protocol contains a TLV design and it wants to create a dissector table to handle dissection of the "V". Dissector tables require a "protocol", but the dissection functions for that table typically aren't a protocol. In this case proto_register_protocol_in_name_only creates the necessary placeholder for the dissector table. In addition, because a dissector table exists, "V"s of the TLVs can be dissected outside of the original dissector file. 2.10 Creating Decode As functionality. While the Decode As functionality is available through the GUI, the underlying functionality is controlled by dissectors themselves. To create Decode As functionality for a dissector, two things are required: 1. A dissector table 2. A series of structures to assist the GUI in how to present the dissector table data. Consider the following example using IP dissection, stolen from packet-ip.c: static build_valid_func ip_da_build_value[1] = {ip_value}; static decode_as_value_t ip_da_values = {ip_prompt, 1, ip_da_build_value}; static decode_as_t ip_da = {"ip", "Network", "ip.proto", 1, 0, &ip_da_values, NULL, NULL, decode_as_default_populate_list, decode_as_default_reset, decode_as_default_change, NULL}; ... ip_dissector_table = register_dissector_table("ip.proto", "IP protocol", ip_proto, FT_UINT8, BASE_DEC); ... register_decode_as(&ip_da); ip_da_build_value contains all of the function pointers (typically just 1) that can be used to retrieve the value(s) that go into the dissector table. This is usually data saved by the dissector during packet dissector with an API like p_add_proto_data and retrieved in the "value" function with p_get_proto_data. ip_da_values contains all of the function pointers (typically just 1) that provide the text explaining the name and use of the value field that will be passed to the dissector table to change the dissection output. ip_da pulls everything together including the dissector (protocol) name, the "layer type" of the dissector, the dissector table name, the function pointer values as well as handlers for populating, applying and reseting the changes to the dissector table through Decode As GUI functionality. For dissector tables that are an integer or string type, the provided "default" handling functions shown in the example should suffice. All entries into a dissector table that use Decode As must have a unique protocol ID. If a protocol wants multiple entries into a dissector table, a pino should be used (see section 2.9) 2.11 ptvcursors. The ptvcursor API allows a simpler approach to writing dissectors for simple protocols. The ptvcursor API works best for protocols whose fields are static and whose format does not depend on the value of other fields. However, even if only a portion of your protocol is statically defined, then that portion could make use of ptvcursors. The ptvcursor API lets you extract data from a tvbuff, and add it to a protocol tree in one step. It also keeps track of the position in the tvbuff so that you can extract data again without having to compute any offsets --- hence the "cursor" name of the API. The three steps for a simple protocol are: 1. Create a new ptvcursor with ptvcursor_new() 2. Add fields with multiple calls of ptvcursor_add() 3. Delete the ptvcursor with ptvcursor_free() ptvcursor offers the possibility to add subtrees in the tree as well. It can be done in very simple steps : 1. Create a new subtree with ptvcursor_push_subtree(). The old subtree is pushed in a stack and the new subtree will be used by ptvcursor. 2. Add fields with multiple calls of ptvcursor_add(). The fields will be added in the new subtree created at the previous step. 3. Pop the previous subtree with ptvcursor_pop_subtree(). The previous subtree is again used by ptvcursor. Note that at the end of the parsing of a packet you must have popped each subtree you pushed. If it's not the case, the dissector will generate an error. To use the ptvcursor API, include the "ptvcursor.h" file. The PGM dissector is an example of how to use it. You don't need to look at it as a guide; instead, the API description here should be good enough. 2.11.1 ptvcursor API. ptvcursor_t* ptvcursor_new(proto_tree* tree, tvbuff_t* tvb, gint offset) This creates a new ptvcursor_t object for iterating over a tvbuff. You must call this and use this ptvcursor_t object so you can use the ptvcursor API. proto_item* ptvcursor_add(ptvcursor_t* ptvc, int hf, gint length, const guint encoding) This will extract 'length' bytes from the tvbuff and place it in the proto_tree as field 'hf', which is a registered header_field. The pointer to the proto_item that is created is passed back to you. Internally, the ptvcursor advances its cursor so the next call to ptvcursor_add starts where this call finished. The 'encoding' parameter is relevant for certain type of fields (See above under proto_tree_add_item()). proto_item* ptvcursor_add_ret_uint(ptvcursor_t* ptvc, int hf, gint length, const guint encoding, guint32 *retval); Like ptvcursor_add, but returns uint value retreived proto_item* ptvcursor_add_ret_int(ptvcursor_t* ptvc, int hf, gint length, const guint encoding, gint32 *retval); Like ptvcursor_add, but returns int value retreived proto_item* ptvcursor_add_ret_string(ptvcursor_t* ptvc, int hf, gint length, const guint encoding, wmem_allocator_t *scope, const guint8 **retval); Like ptvcursor_add, but returns string retreived proto_item* ptvcursor_add_ret_boolean(ptvcursor_t* ptvc, int hf, gint length, const guint encoding, gboolean *retval); Like ptvcursor_add, but returns boolean value retreived proto_item* ptvcursor_add_no_advance(ptvcursor_t* ptvc, int hf, gint length, const guint encoding) Like ptvcursor_add, but does not advance the internal cursor. void ptvcursor_advance(ptvcursor_t* ptvc, gint length) Advances the internal cursor without adding anything to the proto_tree. void ptvcursor_free(ptvcursor_t* ptvc) Frees the memory associated with the ptvcursor. You must call this after your dissection with the ptvcursor API is completed. proto_tree* ptvcursor_push_subtree(ptvcursor_t* ptvc, proto_item* it, gint ett_subtree) Pushes the current subtree in the tree stack of the cursor, creates a new one and sets this one as the working tree. void ptvcursor_pop_subtree(ptvcursor_t* ptvc); Pops a subtree in the tree stack of the cursor proto_tree* ptvcursor_add_with_subtree(ptvcursor_t* ptvc, int hfindex, gint length, const guint encoding, gint ett_subtree); Adds an item to the tree and creates a subtree. If the length is unknown, length may be defined as SUBTREE_UNDEFINED_LENGTH. In this case, at the next pop, the item length will be equal to the advancement of the cursor since the creation of the subtree. proto_tree* ptvcursor_add_text_with_subtree(ptvcursor_t* ptvc, gint length, gint ett_subtree, const char* format, ...); Add a text node to the tree and create a subtree. If the length is unknown, length may be defined as SUBTREE_UNDEFINED_LENGTH. In this case, at the next pop, the item length will be equal to the advancement of the cursor since the creation of the subtree. 2.11.2 Miscellaneous functions. tvbuff_t* ptvcursor_tvbuff(ptvcursor_t* ptvc) Returns the tvbuff associated with the ptvcursor. gint ptvcursor_current_offset(ptvcursor_t* ptvc) Returns the current offset. proto_tree* ptvcursor_tree(ptvcursor_t* ptvc) Returns the proto_tree associated with the ptvcursor. void ptvcursor_set_tree(ptvcursor_t* ptvc, proto_tree *tree) Sets a new proto_tree for the ptvcursor. proto_tree* ptvcursor_set_subtree(ptvcursor_t* ptvc, proto_item* it, gint ett_subtree); Creates a subtree and adds it to the cursor as the working tree but does not save the old working tree. 2.12 Optimizations A protocol dissector may be called in 2 different ways - with, or without a non-null "tree" argument. If the proto_tree argument is null, Wireshark does not need to use the protocol tree information from your dissector, and therefore is passing the dissector a null "tree" argument so that it doesn't need to do work necessary to build the protocol tree. In the interest of speed, if "tree" is NULL, avoid building a protocol tree and adding stuff to it, or even looking at any packet data needed only if you're building the protocol tree, if possible. Note, however, that you must fill in column information, create conversations, reassemble packets, do calls to "expert" functions, build any other persistent state needed for dissection, and call subdissectors regardless of whether "tree" is NULL or not. This might be inconvenient to do without doing most of the dissection work; the routines for adding items to the protocol tree can be passed a null protocol tree pointer, in which case they'll return a null item pointer, and "proto_item_add_subtree()" returns a null tree pointer if passed a null item pointer, so, if you're careful not to dereference any null tree or item pointers, you can accomplish this by doing all the dissection work. This might not be as efficient as skipping that work if you're not building a protocol tree, but if the code would have a lot of tests whether "tree" is null if you skipped that work, you might still be better off just doing all that work regardless of whether "tree" is null or not. Note also that there is no guarantee, the first time the dissector is called, whether "tree" will be null or not; your dissector must work correctly, building or updating whatever state information is necessary, in either case. /* * Editor modelines - https://www.wireshark.org/tools/modelines.html * * Local variables: * c-basic-offset: 4 * tab-width: 8 * indent-tabs-mode: nil * End: * * vi: set shiftwidth=4 tabstop=8 expandtab: * :indentSize=4:tabSize=8:noTabs=true: */