Wireshark · Ethereal-dev: [ethereal-dev] A developer HOWTO

[James Coe <jammer@xxxxxxx>]

Got to looking at the notes I took while developing the SRVLOC dissector
and thought it would be nice to have a devloper HOWTO for Ethereal.
Here's what I've put together so far. Let me know what you guys think.

Jamie Coe.


This file is a HOWTO for Ethereal developers. It describes how to start coding
a protocol dissector and the use some of the important functions and variables 
in Ethereal.

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.

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
abbreviated name for the protocol. It is recommended that where possible you
keep to the IANA abbreviated name for the protocol.

/* Recommended includes for Ethereal protocol dissectors */
#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

#include <stdio.h>
#include <stdlib.h>

#ifdef HAVE_SYS_TYPES_H
# include <sys/types.h>
#endif

#ifdef HAVE_NETINET_IN_H
# include <netinet/in.h>
#endif

#ifdef NEED_SNPRINTF_H
# ifdef HAVE_STDARG_H
#  include <stdarg.h>
# else
#  include <varargs.h>
# endif
# include "snprintf.h"
#endif

#include <string.h>
#include <glib.h>
#include "packet.h"
#include "packet-ipv6.h"


/* Initialize the protocol and registered fields */
int proto_PROTOABBREV = -1;
int hf_PROTOABBREV_FIELDABBREV = -1;

/* Initialize the subtree pointers */
static gint ett_PROTOABBREV = -1;


/* Code to actually dissect the packets */
void
dissect_PROTOABBREV(cont u_char *pd, int offset, frame_data *fd, proto_tree *tree)
{

/* Set up structures we will need 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(fd, COL_PROTOCOL)) 
	col_add_str(fd, COL_PROTOCOL, "PROTOABBREV");
    
	if (check_col(fd, COL_INFO)) 
	col_add_str(fd, COL_INFO, "PROTONAME");

	if (tree) {
		ti = proto_tree_add_item(tree, proto_PROTOABBREV, offset, END_OF_FRAME, NULL);
	        PROTOABBREV_tree = proto_item_add_subtree(ti, ett_PROTOABBREV);

/* Code to process the packet goes here */


	};
};

/* Register the protocol with Ethereal */
proto_register_srvloc(void)
{                 

/* Setup list of header fields */
	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_srvloc = proto_register_protocol("PROTONAME", "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));
};

1.2 Explanation of needed substituions in code skeleton.

In the above code block the following strings should be substituted with
your information.

PROTONAME	The name of the protocol.
PROTOABBREV	An abbreviated name for the protocol. (NO SPACES) (rec. 
		a-z, 0-9 only and try to conform with IANA names)
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_INT_8, FT_INT_16, FT_INT_24, FT_INT_32, 
		FT_DOUBLE, FT_ABSOLUTE_TIME, FT_RELATIVE_TIME, FT_STRING,
		FT_ETHER, FT_BYTES, FT_IPv4, FT_IPv6, FT_IPXNET,
		FT_TEXT_ONLY
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.

1.3 Explanation of FIELDTYPE, FIELDBASE, FIELDCONVERT 

1.3.1 FIELDBASE

The FIELDTYPE values are described as follows:

FT_NONE			No field type. Used for protocol labels.
FT_BOOLEAN		TRUE and FALSE from glib.h
FT_UINT8		An 8 bit unsigned integer.
FT_UINT16		A 16 bit unsigned integer.
FT_UINT24		A 32 bit unsigned integer displayed as 3 hex-digits.
FT_UINT32		A 32 bit unsigned integer.
FT_INT8			An 8 bit signed integer.
FT_INT16		A 16 bit signed integer.
FT_INT24		A 32 bit signed integer displayed as 3 hex-digits.
FT_INT32		A 32 bit signed integer.
FT_DOUBLE		A floating point number.
FT_ABSOLUTE_TIME	Seconds (4 bytes) and microseconds (4 bytes) of time 
			displayed as month name, month day, year, hours,
			minutes, and seconds with 4 digits after the decimal
			point.
FT_RELATIVE_TIME	Seconds (4 bytes) and microseconds (4 bytes) of time 
			displayed as seconds and 6 digits after the decimal
			point.
FT_STRING		A string of characters.
FT_ETHER		A six octet string of hexadecimal bytes displayed in
			Ethernet address format.
FT_BYTES		A string of bytes.
FT_IPv4			A version 4 IP address (4 bytes)  displayed as 4 
			dot seperated decimal numbers.
FT_IPv6			A version 6 IP address (16 bytes).
FT_IPXNET		An IPX address displayed in hex as a 6-byte network 
			number followed by a 6 byte station address. 
FT_TEXT_ONLY		A reserved, non-filterable type for converting old
			style trees. You shouldn't be using this.

1.3.2 FIELDCONVERT

NULL is used when no value to string conversions are desired.

The VALS (x) field conversion changes an integer to a string for display. In
order to use it you must have defined a value_string array. The x in VALS(x) 
is replaced with the name of the value_string you wish to use (i.e.
VALS(valstringname)). The value string array is created as follows and an 
integer corresponding to the descriptive string is substituted for INTVALy.

static const value_string valstringname[] = {
	{ INTVAL1, "Descriptive String 1" }, 
	{ INTVAL2, "Descriptive String 2" }, 
};

The TFS(x) field conversion changes an FT_BOOLEAN field in conjunction with a
BITMASK to a string for display. In order to use it you must create the
structure shown below. The x in TFS(x) is replaced with the pointer name of
the true_false_string you wish to use (i.e. TFS(&boolstringname)). The
string corresponding to True or False is displayed according to the valuse
of the bit selected by the bitmask.

static const true_false_string boolstringname = {
  "String for True",
  "String for False"
};

1.4 The dissector and the data it receives.

1.4.1 The dissector has the following header which must be placed into
packet.h.

void
dissect_PROTOABBREV(const u_char *pd, int offset, frame_data *fd, proto_tree *tree); 

1.5 Functions to handle columns in the traffic summary window.

check_col
col_add_str

1.5.1 The check_col function.

1.5.2 The col_add_str function.

1.6 Functions to add to the protocol dissection window.

The functions shown below are necessary to add data to the protocol dissection
tree and their use is detailed in the sections that follow.

proto_item_add_subtree
proto_tree_add_item
proto_tree_add_item_format
proto_tree_add_text
proto_tree_add_text_format

1.5.1 The proto_item_add_subtree function.

1.6.2 The proto_tree_add_item function.

1.6.3 The proto_tree_add_item_format function.

1.6.4 The proto_tree_add_text function.

1.6.5 The proto_tree_add_text_format function.

1.7 Editing Makefile.am to add your dissector.

1.8 Using the CVS source code tree.

1.9 Submitting code for your new dissector.

2. Advanced dissector topics.

2.1 ?? 

2.2 Following "conversations."

In ethereal a conversation is ...

2.2.1 The conversation_init function.

2.2.2 The conversation_new function.

2.2.3 The find_conversation function.

2.2 ??

3.0 Plugins

4.0 Extending Wiretap.

5.0 Adding new capabilities.




James Coe <jammer@xxxxxxx>