tapping with stats_tree

Let's suppose that you want to write a tap only to keep counters, and you
don't want to get involved with GUI programming or maybe you'd like to make
it a plugin. A stats_tree might be the way to go. The stats_tree module takes
care of the representation (GUI for Wireshark and text for TShark) of the
tap data. So there's very little code to write to make a tap listener usable
from both Wireshark and TShark.

First, you should add the TAP to the dissector in question as described in
README.tapping .

Once the dissector in question is "tapped" you have to write the stats tree
code which is made of three parts:

The init callback routine:
   which will be executed before any packet is passed to the tap. Here you
   should create the "static" nodes of your tree. As well as initialize your
   data.

The (per)packet callback routine:
   As the tap_packet callback is going to be called for every packet, it
   should be used to increment the counters.

The cleanup callback:
   It is called at the destruction of the stats_tree and might be used to
   free ....

Other than that the stats_tree should be registered.

If you want to make it a plugin, stats_tree_register() should be called by
plugin_register_tap_listener() read README.plugins for other information
regarding Wireshark plugins.

If you want it as part of the dissector stats_tree_register() can be called
either by proto_register_xxx() or if you prefer by proto_reg_handoff_xxx().


A small example of a very basic stats_tree plugin follows.

----- example stats_tree plugin ------
/* udpterm_stats_tree.c
 * A small example of stats_tree plugin that counts udp packets by termination
 * 2005, Luis E. G. Ontanon
 *
 * Wireshark - Network traffic analyzer
 * By Gerald Combs <gerald@wireshark.org>
 * Copyright 1998 Gerald Combs
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 */

#include "config.h"

#include <gmodule.h>

#include <epan/stats_tree.h>
#include <epan/dissectors/udp.h>

static int st_udp_term;
static gchar* st_str_udp_term = "UDP terminations";

/* this one initializes the tree, creating the root nodes */
extern void udp_term_stats_tree_init(stats_tree* st) {
	/* we create a node under which we'll add every termination */
	st_udp_term = stats_tree_create_node(st, st_str_udp_term, 0, TRUE);
}

/* this one will be called with every udp packet */
extern int udp_term_stats_tree_packet(stats_tree *st, /* st as it was passed to us */
                                      packet_info *pinfo,  /* we'll fetch the addresses from here */
                                      epan_dissect_t *edt _U_, /* unused */
                                      const void *p) /* we'll use this to fetch the ports */
{
	static guint8 str[128];
	e_udphdr* udphdr = (e_udphdr*) p;

	/* we increment by one (tick) the root node */
	tick_stat_node(st, st_str_udp_term, 0, FALSE);

	/* we then tick a node for this src_addr:src_port
	   if the node doesn't exists it will be created */
	g_snprintf(str, sizeof(str),"%s:%u",address_to_str(&pinfo->net_src),udphdr->sport);
	tick_stat_node(st, str, st_udp_term, FALSE);

	/* same thing for dst */
	g_snprintf(str, sizeof(str),"%s:%u",address_to_str(&pinfo->net_dst),udphdr->dport);
	tick_stat_node(st, str, st_udp_term, FALSE);

	return 1;
}

WS_DLL_PUBLIC_DEF const gchar version[] = "0.0";

WS_DLL_PUBLIC_DEF void plugin_register_tap_listener(void) {

    stats_tree_register_plugin("udp", /* the proto we are going to "tap" */
                               "udp_terms", /* the abbreviation for this tree (to be used as -z udp_terms,tree) */
                               st_str_udp_term, /* the name of the menu and window (use "/" for sub menus)*/
                               0, /* tap listener flags for per-packet callback */
                               udp_term_stats_tree_packet, /* the per packet callback */
                               udp_term_stats_tree_init, /* the init callback */
                               NULL ); /* the cleanup callback (in this case there isn't) */

}

----- END ------

the stats_tree API
==================
 every stats_tree callback has a stats_tree* parameter (st), stats_tree is an obscure
 data structure which should be passed to the api functions.

stats_tree_register(tapname, abbr, name, flags, packet_cb, init_cb, cleanup_cb);
 registers a new stats tree

stats_tree_register_plugin(tapname, abbr, name, flags, packet_cb, init_cb, cleanup_cb);
 registers a new stats tree from a plugin

stats_tree_parent_id_by_name( st, parent_name)
  returns the id of a candidate parent node given its name


Node functions
==============

All the functions that operate on nodes return a parent_id

stats_tree_create_node(st, name, parent_id, with_children)
  Creates a node in the tree (to be used in the in init_cb)
    name: the name of the new node
    parent_id: the id of the parent_node (NULL for root)
    with_children: TRUE if this node will have "dynamically created" children
                   (i.e. it will be a candidate parent)


stats_tree_create_node_by_pname(st, name, parent_name, with_children);
  As before but creates a node using its parent's name


stats_tree_create_range_node(st, name, parent_id, ...)
stats_tree_create_range_node_string(st, name, parent_id, num_str_ranges, str_ranges)
stats_tree_range_node_with_pname(st, name, parent_name, ...)
  Creates a node in the tree, that will contain a ranges list.
    example:
       stats_tree_create_range_node(st,name,parent_id,
				"-99","100-199","200-299","300-399","400-", NULL);

stats_tree_tick_range( st, name,  parent_id, value_in_range);
stats_tree_tick_range_by_pname(st,name,parent_name,value_in_range)
   Increases by one the ranged node and the sub node to whose range the value belongs


stats_tree_create_pivot(st, name, parent_id);
stats_tree_create_pivot_by_pname(st, name, parent_name);
  Creates a "pivot node"

stats_tree_tick_pivot(st, pivot_id, pivoted_string);
 Each time a pivot node will be ticked it will get increased, and, it will
 increase (or create) the children named as pivoted_string


the following will either increase or create a node (with value 1) when called

tick_stat_node(st,name,parent_id,with_children)
increases by one a stat_node

increase_stat_node(st,name,parent_id,with_children,value)
increases by value a stat_node

set_stat_node(st,name,parent_id,with_children,value)
sets the value of a stat_node

zero_stat_node(st,name,parent_id,with_children)
resets to zero a stat_node

Averages work by tracking both the number of items added to node (the ticking
action) and the value of each item added to the node. This is done
automatically for ranged nodes; for other node types you need to call one of
the functions below to associate item values with each tick.

avg_stat_node_add_value_notick(st,name,parent_id,with_children,value)
avg_stat_node_add_value(st,name,parent_id,with_children,value)

The difference between the above functions is whether the item count is
increased or not. To properly compute the average you need to either call
avg_stat_node_add_value or avg_stat_node_add_value_notick combined
tick_stat_node. The later sequence allows for plug-ins which are compatible
with older Wireshark versions which ignores avg_stat_node_add_value because
it does not understand the command. This would result in 0 counts for all
nodes. It is preferred to use avg_stat_node_add_value if you are not writing
a plug-in.

avg_stat_node_add_value is used the same way as tick_stat_node with the
exception that you now specify an additional value associated with the tick.

Do not mix increase_stat_node, set_stat_node or zero_stat_node
with avg_stat_node_add_value as this will lead to incorrect results for the
average value.

stats_tree now also support setting flags per node to control the behaviour
of these nodes. This can be done using the stat_node_set_flags and
stat_node_clear_flags functions. Currently these flags are defined:

	ST_FLG_DEF_NOEXPAND: By default the top-level nodes in a tree are
			automatically expanded in the GUI. Setting this flag on
			such a node	prevents the node from automatically expanding.
	ST_FLG_SORT_TOP: Nodes with this flag is sorted separately from nodes
			without this flag (in effect partitioning tree into a top and
			bottom half. Each half is sorted normally. Top always appear
			first :)

You can find more examples of these in $srcdir/plugins/epan/stats_tree/pinfo_stats_tree.c

Luis E. G. Ontanon.
