$Id: README.developer,v 1.62 2002/10/17 20:05:04 guy Exp $ This file is a HOWTO for Ethereal developers. It describes how to start coding a Ethereal protocol dissector and the use some of the important functions and variables. 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 Code style. 1.1.1 Portability. Ethereal runs on many platforms, and can be compiled with a number of different compilers; here are some rules for writing code that will work on multiple platforms. Don't use C++-style comments (comments beginning with "//" and running to the end of the line); Ethereal's dissectors are written in C, and thus run through C rather than C++ compilers, and not all C compilers support C++-style comments (GCC does, but IBM's C compiler for AIX, for example, doesn't do so by default). Don't use zero-length arrays; not all compilers support them. If an array would have no members, just leave it out. Don't use "inline"; not all compilers support it. If you want to have a function be an inline function if the compiler supports it, use G_INLINE_FUNC, which is declared by . This may not work with functions declared in header files; if it doesn't work, don't declare the function in a header file, even if this requires that you not make it inline on any platform. Don't use "long long"; use "gint64" or "guint64", and only do so if G_HAVE_GINT64 is defined. Make sure your code works even if G_HAVE_GINT64 isn't defined, even if that means treating 64-bit integral data types as opaque arrays of bytes on platforms where it's not defined. Also, don't assume you can use "%lld", "%llu", "%llx", or "%llo" to print 64-bit integral data types - not all platforms support "%ll" for printing them. Don't use "uint", "ulong" or "ushort"; they aren't defined on all platforms. If you want an "int-sized" unsigned quantity, use "uint"; if you want a 32-bit unsigned quantity, use "guint32"; and if you want a 16-bit unsigned quantity, use "guint16". Don't use "long" to mean "signed 32-bit integer", and don't use "unsigned long" to mean "unsigned 32-bit integer"; "long"s are 64 bits long on many platforms. Use "gint32" for signed 32-bit integers and use "guint32" for unsigned 32-bit integers. Don't use a label without a statement following it. For example, something such as if (...) { ... done: } will not work with all compilers - you have to do if (...) { ... done: ; } with some statement, even if it's a null statement, after the label. Don't use "bzero()", "bcopy()", or "bcmp()"; instead, use the ANSI C routines "memset()" (with zero as the second argument, so that it sets all the bytes to zero); "memcpy()" or "memmove()" (note that the first and second arguments to "memcpy()" are in the reverse order to the arguments to "bcopy()"; note also that "bcopy()" is typically guaranteed to work on overlapping memory regions, while "memcpy()" isn't, so if you may be copying from one region to a region that overlaps it, use "memmove()", not "memcpy()" - but "memcpy()" might be faster as a result of not guaranteeing correct operation on overlapping memory regions); and "memcmp()" (note that "memcmp()" returns 0, 1, or -1, doing an ordered comparison, rather than just returning 0 for "equal" and 1 for "not equal"). Not all platforms necessarily have "bzero()"/"bcopy()"/"bcmp()", and those that do might not declare them in the header file on which they're declared on your platform. Don't fetch data from packets by getting a pointer to data in the packet with "tvb_get_ptr()", casting that pointer to a pointer to a structure, and dereferencing that pointer. That point won't necessarily be aligned on the proper boundary, which can cause crashes on some platforms (even if it doesn't crash on an x86-based PC); furthermore, the data in a packet is not necessarily in the byte order of the machine on which Ethereal is running. Use the tvbuff routines to extract individual items from the packet, or use "proto_tree_add_item()" and let it extract the items for you. 1.1.2 Name convention. Ethereal uses the underscore_convention rather than the InterCapConvention for function names, so new code should probably use underscores rather than intercaps for functions and variable names. This is especially important if you are writing code that will be called from outside your code. We are just trying to keep thing consistent for other users. 1.2 Skeleton code. Ethereal requires certain things when setting up a protocol dissector. Below is skeleton code for a dissector that you can copy to a 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. Dissectors that use the dissector registration to tell a lower level dissector don't need to define a prototype in the .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 below, and you may need to include additional headers. For example, the code inside #ifdef NEED_SNPRINTF_H ... #endif is needed only if you are using the "snprintf()" function. The "$Id: README.developer,v 1.62 2002/10/17 20:05:04 guy Exp $" in the comment will be updated by CVS when the file is checked in; it will allow the RCS "ident" command to report which version of the file is currently checked out. ------------------------------------Cut here------------------------------------ /* packet-PROTOABBREV.c * Routines for PROTONAME dissection * Copyright 2000, YOUR_NAME * * $Id: README.developer,v 1.62 2002/10/17 20:05:04 guy Exp $ * * Ethereal - Network traffic analyzer * By Gerald Combs * Copyright 1998 Gerald Combs * * Copied from WHATEVER_FILE_YOU_USED (where "WHATEVER_FILE_YOU_USED" * is a dissector file; if you just copied this from README.developer, * don't bother with the "Copied from" - you don't even need to put * in a "Copied from" if you copied an existing dissector, especially * if the bulk of the code in the new dissector is your code) * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; either version 2 * of the License, or (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ #ifdef HAVE_CONFIG_H # include "config.h" #endif #include #include #include #include #ifdef NEED_SNPRINTF_H # include "snprintf.h" #endif #include #include "packet-PROTOABBREV.h" /* Initialize the protocol and registered fields */ static int proto_PROTOABBREV = -1; static int hf_PROTOABBREV_FIELDABBREV = -1; /* Initialize the subtree pointers */ static gint ett_PROTOABBREV = -1; /* Code to actually dissect the packets */ static void dissect_PROTOABBREV(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree) { /* Set up structures needed to add the protocol subtree and manage it */ proto_item *ti; proto_tree *PROTOABBREV_tree; /* Make entries in Protocol column and Info column on summary display */ if (check_col(pinfo->cinfo, COL_PROTOCOL)) col_set_str(pinfo->cinfo, COL_PROTOCOL, "PROTOABBREV"); /* This field shows up as the "Info" column in the display; you should make it, if possible, summarize what's in the packet, so that a user looking at the list of packets can tell what type of packet it is. See section 1.5 for more information. If you are setting it to a constant string, use "col_set_str()", as it's more efficient than the other "col_set_XXX()" calls. If you're setting it to a string you've constructed, or will be appending to the column later, use "col_add_str()". "col_add_fstr()" can be used instead of "col_add_str()"; it takes "printf()"-like arguments. Don't use "col_add_fstr()" with a format string of "%s" - just use "col_add_str()" or "col_set_str()", as it's more efficient than "col_add_fstr()". If you will be fetching any data from the packet before filling in the Info column, clear that column first, in case the calls to fetch data from the packet throw an exception because they're fetching data past the end of the packet, so that the Info column doesn't have data left over from the previous dissector; do if (check_col(pinfo->cinfo, COL_INFO)) col_clear(pinfo->cinfo, COL_INFO); */ if (check_col(pinfo->cinfo, COL_INFO)) col_set_str(pinfo->cinfo, COL_INFO, "XXX Request"); /* In the interest of speed, if "tree" is NULL, don't do any work not necessary to generate protocol tree items. */ if (tree) { /* NOTE: The offset and length values in the call to "proto_tree_add_item()" define what data bytes to highlight in the hex display window when the line in the protocol tree display corresponding to that item is selected. Supplying a length of -1 is the way to highlight all data from the offset to the end of the packet. */ /* create display subtree for the protocol */ ti = proto_tree_add_item(tree, proto_PROTOABBREV, tvb, 0, -1, FALSE); PROTOABBREV_tree = proto_item_add_subtree(ti, ett_PROTOABBREV); /* add an item to the subtree, see section 1.6 for more information */ proto_tree_add_item(PROTOABBREV_tree, hf_PROTOABBREV_FIELDABBREV, tvb, offset, len, FALSE) /* Continue adding tree items to process the packet here */ } /* If this protocol has a sub-dissector call it here, see section 1.8 */ } /* Register the protocol with Ethereal */ /* this format is require because a script is used to build the C function that calls all the protocol registration. */ void proto_register_PROTOABBREV(void) { /* Setup list of header fields See Section 1.6.1 for details*/ static hf_register_info hf[] = { { &hf_PROTOABBREV_FIELDABBREV, { "FIELDNAME", "PROTOABBREV.FIELDABBREV", FIELDTYPE, FIELDBASE, FIELDCONVERT, BITMASK, "FIELDDESCR" } }, }; /* Setup protocol subtree array */ static gint *ett[] = { &ett_PROTOABBREV, }; /* Register the protocol name and description */ proto_PROTOABBREV = proto_register_protocol("PROTONAME", "PROTOSHORTNAME", "PROTOABBREV"); /* Required function calls to register the header fields and subtrees used */ proto_register_field_array(proto_PROTOABBREV, hf, array_length(hf)); proto_register_subtree_array(ett, array_length(ett)); } /* If this dissector uses sub-dissector registration add a registration routine. This format is required because a script is used to find these routines and create the code that calls these routines. */ void proto_reg_handoff_PROTOABBREV(void) { dissector_handle_t PROTOABBREV_handle; PROTOABBREV_handle = create_dissector_handle(dissect_PROTOABBREV, proto_PROTOABBREV); dissector_add("PARENT_SUBFIELD", ID_VALUE, PROTOABBREV_handle); } ------------------------------------Cut here------------------------------------ 1.3 Explanation of needed substitutions in code skeleton. In the above code block 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. WHATEVER_FILE_YOU_USED Add this line if you are using another file as a starting point. 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, 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 should contain only lower-case letters, digits, and hyphens. FIELDNAME The displayed name for the header field. FIELDABBREV The abbreviated name for the header field. (NO SPACES) FIELDTYPE FT_NONE, FT_BOOLEAN, FT_UINT8, FT_UINT16, FT_UINT24, FT_UINT32, FT_UINT64, FT_INT8, FT_INT16, FT_INT24, FT_INT32, FT_INT64, FT_FLOAT, FT_DOUBLE, FT_ABSOLUTE_TIME, FT_RELATIVE_TIME, FT_STRING, FT_STRINGZ, FT_UINT_STRING, FT_ETHER, FT_BYTES, FT_IPv4, FT_IPv6, FT_IPXNET FIELDBASE BASE_NONE, BASE_DEC, BASE_HEX, BASE_OCT, BASE_BIN FIELDCONVERT VALS(x), TFS(x), NULL BITMASK Usually 0x0 unless using the TFS(x) field conversion. FIELDDESCR A brief description of the field. PARENT_SUBFIELD Lower level protocol field used for lookup, i.e. "tcp.port" ID_VALUE Lower level protocol field value that identifies this protocol For example the TCP or UDP port number If, for example, PROTONAME is "Internet Bogosity Discovery Protocol", PROTOSHORTNAME would be "IBDP", and PROTOABBREV would be "ibdp". Try to conform with IANA names. 1.4 The dissector and the data it receives. 1.4.1 Header file. This is only needed if the dissector doesn't use self-registration to register itself with the lower level dissector. The dissector has the following header that must be placed into packet-PROTOABBREV.h. void dissect_PROTOABBREV(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree); 1.4.2 Extracting data from packets. NOTE: See the README.tvbuff 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 a opaque data structure, the internal data structures are hidden and the data must be access via the tvbuffer accessors. The accessors are: Single-byte accessor: guint8 tvb_get_guint8(tvbuff_t*, gint offset); Network-to-host-order access for 16-bit integers (guint16), 32-bit integers (guint32), and 24-bit integers: guint16 tvb_get_ntohs(tvbuff_t*, gint offset); guint32 tvb_get_ntohl(tvbuff_t*, gint offset); guint32 tvb_get_ntoh24(tvbuff_t*, gint offset); Network-to-host-order access for single-precision and double-precision IEEE floating-point numbers: gfloat tvb_get_ntohieee_float(tvbuff_t*, gint offset); gdouble tvb_get_ntohieee_double(tvbuff_t*, gint offset); Little-Endian-to-host-order access for 16-bit integers (guint16), 32-bit integers (guint32), and 24-bit integers: guint16 tvb_get_letohs(tvbuff_t*, gint offset); guint32 tvb_get_letohl(tvbuff_t*, gint offset); guint32 tvb_get_letoh24(tvbuff_t*, gint offset); Little-Endian-to-host-order access for single-precision and double-precision IEEE floating-point numbers: gfloat tvb_get_letohieee_float(tvbuff_t*, gint offset); gdouble tvb_get_letohieee_double(tvbuff_t*, gint offset); NOTE: IPv4 addresses are not to be converted to host byte order before being passed to "proto_tree_add_ipv4()". You should use "tvb_memcpy()" 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. Copying memory: guint8* tvb_memcpy(tvbuff_t*, guint8* target, gint offset, gint length); guint8* tvb_memdup(tvbuff_t*, gint offset, gint length); Pointer-retrieval: /* WARNING! This function is possibly expensive, temporarily allocating * another copy of the packet data. Furthermore, 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. */ guint8* tvb_get_ptr(tvbuff_t*, gint offset, gint length); The reason that tvb_get_ptr() have to allocate a copy of its data only occurs with TVBUFF_COMPOSITES, data that spans multiple tvbuffers. If the user request a pointer to a range of bytes that spans the member tvbuffs that make up the TVBUFF_COMPOSITE, the data will have to be copied to another memory region to assure that all the bytes are contiguous. 1.5 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. A value for a column should only be added if the user specified that it be displayed; to check whether a given column is to be displayed, call 'col_info' with the COL_ value for that field as an argument - it will return TRUE if the column is to be displayed and FALSE if it is not to be displayed. 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. 1.5.1 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": if (check_col(pinfo->cinfo, COL_PROTOCOL)) col_set_str(pinfo->cinfo, COL_PROTOCOL, "PROTOABBREV"); 1.5.2 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. 1.5.3 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 " request, 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: if (check_col(pinfo->cinfo, COL_INFO)) 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. 1.5.4 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. 1.5.5 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.) 1.5.6 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. 1.6 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 the 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 Ethereal 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_SOURCES" in "Makefile.am"; 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'd 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 the 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 { char *name; char *abbrev; enum ftenum type; int display; void *strings; guint bitmask; char *blurb; int id; /* calculated */ int parent; int bitshift; /* calculated */ }; name ---- A string representing the name of the field. This is the name that will appear in the graphical protocol tree. abbrev ------ A string with an abbreviation of the field. We concatenate the abbreviation of the parent protocol with an abbreviation for the field, using a period as a separator. For example, the "src" field in an IP packet would have "ip.addr" 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. type ---- 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_BOOLEAN 0 means "false", any other value means "true". 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_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_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 Seconds (4 bytes) and nanoseconds (4 bytes) of time displayed as month name, month day, year, hours, minutes, and seconds with 9 digits after the decimal point. FT_RELATIVE_TIME Seconds (4 bytes) and nanoseconds (4 bytes) of time displayed as seconds and 9 digits after the decimal point. FT_STRING A string of characters, not necessarily NUL-terminated, but possibly NUL-padded. This, and the other string-of-characters types, are to be used for text strings, not raw binary data. FT_STRINGZ A NUL-terminated string of characters. FT_UINT_STRING A counted string of characters, consisting of a count (represented as an integral value) followed immediately by the specified 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_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. 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. display ------- The display field has a couple of overloaded uses. This is unfortunate, but since we're 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_BIN BASE_DEC, BASE_HEX, and BASE_OCT are decimal, hexadecimal, and octal, respectively. BASE_BIN is reserved for binary, although it's currently treated as decimal - if you want decimal, use BASE_DEC, not BASE_BIN. For FT_BOOLEAN fields that are also bitfields, 'display' is used to tell the proto_tree how wide the parent bitfield is. With integers this is not needed since the type of integer itself (FT_UINT8, FT_UINT16, FT_UINT24, FT_UINT32, etc.) tells the proto_tree how wide the parent bitfield is. Additionally, BASE_NONE is used for 'display' as a NULL-value. That is, for non-integers 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. strings ------- 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)'. (Note: before Ethereal 0.7.6, we had separate field types like FT_VALS_UINT8 which denoted the use of value_strings. Now, the non-NULLness of the pointer lets the proto_tree know that a value_string is meant for this field). If the field has a numeric rather than an enumerated type, the 'strings' field would be set to NULL. 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. (This struct is new as of Ethereal 0.7.6). 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. 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. If the field is not a bitfield, then bitmask should be set to 0. blurb ----- This is a string giving a proper description of the field. It should be at least one grammatically complete sentence. 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. 1.6.1 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" }}, { &hf_field_b, { "Field B", "proto.field_b", FT_UINT16, BASE_DEC, VALS(vs), 0x0, "Field B represents Bananas" }} }; 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 Ethereal support them. Just omit the "hf" array, and the "proto_register_field_array()" call, entirely. 1.6.2 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_tree_add_XXX() 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. 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, little_endian); proto_item* proto_tree_add_item_hidden(tree, id, tvb, start, length, little_endian); 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_hidden(tree, id, tvb, start, length, start_ptr); proto_item * proto_tree_add_bytes_format(tree, id, tvb, start, length, start_ptr, format, ...); proto_item * proto_tree_add_time(tree, id, tvb, start, length, value_ptr); proto_item * proto_tree_add_time_hidden(tree, id, tvb, start, length, value_ptr); proto_item * proto_tree_add_time_format(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_hidden(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_ipv4(tree, id, tvb, start, length, value); proto_item * proto_tree_add_ipv4_hidden(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_ipv6(tree, id, tvb, start, length, value_ptr); proto_item * proto_tree_add_ipv6_hidden(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_ether(tree, id, tvb, start, length, value_ptr); proto_item * proto_tree_add_ether_hidden(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_string(tree, id, tvb, start, length, value_ptr); proto_item * proto_tree_add_string_hidden(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_boolean(tree, id, tvb, start, length, value); proto_item * proto_tree_add_boolean_hidden(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_float(tree, id, tvb, start, length, value); proto_item * proto_tree_add_float_hidden(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_double(tree, id, tvb, start, length, value); proto_item * proto_tree_add_double_hidden(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_uint(tree, id, tvb, start, length, value); proto_item * proto_tree_add_uint_hidden(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_int(tree, id, tvb, start, length, value); proto_item * proto_tree_add_int_hidden(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_text(tree, tvb, start, length, format, ...); proto_item* proto_tree_add_text_valist(tree, tvb, start, length, format, ap); 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. 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, for integral and Boolean fields, the byte order of the value; the byte order is specified by the 'little_endian' argument, which is TRUE if the value is little-endian and FALSE if it is big-endian. 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 Identifer (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 Identifer" 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, TRUE); 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 crate 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, "Adjaced 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 before Ethereal 0.7.6. proto_tree_add_item_hidden() ---------------------------- proto_tree_add_item_hidden is used to add fields and values to a tree, but not show them on a GUI tree. 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_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_tree_add_item_hidden(tree, hf_tr_rif_ring, ..., FALSE); } for(i = 0; i < num_rings - 1; i++) { proto_tree_add_item_hidden(tree, hf_tr_rif_bridge, ..., FALSE); } 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_tree_add_protocol_format() ---------------------------- proto_tree_add_protocol_format is used to add the top-level item for the protocol when the dissector routines 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_int() ---------------------------- 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. For proto_tree_add_bytes(), the 'value_ptr' argument is a pointer to a sequence of bytes. 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. For proto_tree_add_boolean(), the 'value' argument is a 32-bit integer; 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; they can only be added with proto_tree_add_item().) 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; they can only be added with proto_tree_add_item().) proto_tree_add_bytes_hidden() proto_tree_add_time_hidden() proto_tree_add_ipxnet_hidden() proto_tree_add_ipv4_hidden() proto_tree_add_ipv6_hidden() proto_tree_add_ether_hidden() proto_tree_add_string_hidden() proto_tree_add_boolean_hidden() proto_tree_add_float_hidden() proto_tree_add_double_hidden() proto_tree_add_uint_hidden() proto_tree_add_int_hidden() ---------------------------- These routines add fields and values to a tree, but don't show them in the GUI tree. They are used for the same reason that proto_tree_add_item() is used. 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_int_format() ---------------------------- These routines are used to add items to the protocol tree when the dissector routines 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_text() --------------------- proto_tree_add_text() is used to add a label to the GUI tree. It will contain no value, so it is not searchable in the display filter process. This function was needed in the transition from the old-style proto_tree to this new-style proto_tree so that Ethereal would still decode all protocols w/o being able to filter on all protocols and fields. Otherwise we would have had to cripple Ethereal's functionality while we converted all the old-style proto_tree calls to the new-style proto_tree calls. This can also 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 value returned by 'proto_tree_add_text()', 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_text()' 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: ti = proto_tree_add_text(tree, tvb, offset, length,