[#wsluarm]

// Attributes
:build_dir: ..

== Lua Support in Wireshark

[#wsluarm_intro]

=== Introduction

Lua is a powerful light-weight programming language designed for extending
applications. Wireshark contains an embedded Lua 5.2 interpreter which
can be used to write dissectors, taps, and capture file readers
and writers.

If Lua is enabled, Wireshark will first try to load a file named `init.lua`
from the global link:{wireshark-users-guide-url}ChPluginFolders.html[_plugins directory_].
and then from the user’s
link:{wireshark-users-guide-url}ChAppFilesConfigurationSection.html[_personal plugins directory_].
Then all files ending with _.lua_ are loaded from the global plugins
directory. Then all files ending with _.lua_ in the personal Lua plugin's
directory.

Whether or not Lua scripts are enabled can be controlled via the
_$$enable_lua$$_ variable. Lua scripts are enabled by
default. To disable Lua scripts, set the _$$enable_lua$$_ variable to _false_.
Wireshark 2.6 and earlier enabled or disabled Lua scripts using
the variable _$$disable_lua$$_ (deprecated). If both _$$enable_lua$$_ and
_$$disable_lua$$_ are present, _$$disable_lua$$_ is ignored.

.Example for init.lua
[source,lua]
----
-- Set enable_lua to false to disable Lua support.
enable_lua = true

if not enable_lua then
    return
end

-- If false and Wireshark was started as (setuid) root, then the user
-- will not be able to execute custom Lua scripts from the personal
-- configuration directory, the -Xlua_script command line option or
-- the Lua Evaluate menu option in the GUI.
-- Note: Not checked on Windows. running_superuser is always false.
run_user_scripts_when_superuser = true
----

The command line option _$$-X lua_script:$$++file.lua++_ can also be used to load
specific Lua scripts.

The Lua code is executed after all protocol dissectors are
initialized and before reading any file.

Wireshark for Windows uses a modified Lua runtime
(link:https://github.com/Lekensteyn/lua-unicode[lua-unicode]) to
support Unicode (UTF-8) filesystem paths. This brings consistency with other
platforms (for example, Linux and macOS).

[#wslua_menu_example]

=== Example: Creating a Menu with Lua

The code below adds a menu "Lua Dialog Test" under the Tools menu.
When selected, it opens a dialog prompting the user for input
and then opens a text window with the output.

[source,lua]
----

-- Define the menu entry's callback
local function dialog_menu()
    local function dialog_func(person,eyes,hair)
        local window = TextWindow.new("Person Info");
        local message = string.format("Person %s with %s eyes and %s hair.", person, eyes, hair);
        window:set(message);
    end

    new_dialog("Dialog Test",dialog_func,"A Person","Eyes","Hair")
end

-- Create the menu entry
register_menu("Lua Dialog Test",dialog_menu,MENU_TOOLS_UNSORTED)

-- Notify the user that the menu was created
if gui_enabled() then
   local splash = TextWindow.new("Hello!");
   splash:set("Wireshark has been enhanced with a useless feature.\n")
   splash:append("Go to 'Tools->Lua Dialog Test' and check it out!")
end

----

[#wslua_dissector_example]

=== Example: Dissector written in Lua

[source,lua]
----
local p_multi = Proto("multi", "MultiProto");

local vs_protos = {
        [2] = "mtp2",
        [3] = "mtp3",
        [4] = "alcap",
        [5] = "h248",
        [6] = "ranap",
        [7] = "rnsap",
        [8] = "nbap"
}

local f_proto = ProtoField.uint8("multi.protocol", "Protocol", base.DEC, vs_protos)
local f_dir = ProtoField.uint8("multi.direction", "Direction", base.DEC, { [1] = "incoming", [0] = "outgoing"})
local f_text = ProtoField.string("multi.text", "Text")

p_multi.fields = { f_proto, f_dir, f_text }

local data_dis = Dissector.get("data")

local protos = {
        [2] = Dissector.get("mtp2"),
        [3] = Dissector.get("mtp3"),
        [4] = Dissector.get("alcap"),
        [5] = Dissector.get("h248"),
        [6] = Dissector.get("ranap"),
        [7] = Dissector.get("rnsap"),
        [8] = Dissector.get("nbap"),
        [9] = Dissector.get("rrc"),
        [10] = DissectorTable.get("sctp.ppi"):get_dissector(3), -- m3ua
        [11] = DissectorTable.get("ip.proto"):get_dissector(132), -- sctp
}

function p_multi.dissector(buf, pkt, tree)

        local subtree = tree:add(p_multi, buf(0,2))
        subtree:add(f_proto, buf(0,1))
        subtree:add(f_dir, buf(1,1))

        local proto_id = buf(0,1):uint()

        local dissector = protos[proto_id]

        if dissector ~= nil then
                -- Dissector was found, invoke subdissector with a new Tvb,
                -- created from the current buffer (skipping first two bytes).
                dissector:call(buf(2):tvb(), pkt, tree)
        elseif proto_id < 2 then
                subtree:add(f_text, buf(2))
                -- pkt.cols.info:set(buf(2, buf:len() - 3):string())
        else
                -- fallback dissector that just shows the raw data.
                data_dis:call(buf(2):tvb(), pkt, tree)
        end

end

local wtap_encap_table = DissectorTable.get("wtap_encap")
local udp_encap_table = DissectorTable.get("udp.port")

wtap_encap_table:add(wtap.USER15, p_multi)
wtap_encap_table:add(wtap.USER12, p_multi)
udp_encap_table:add(7555, p_multi)
----

[#wslua_tap_example]

=== Example: Listener written in Lua

[source,lua]
----
-- This program will register a menu that will open a window with a count of occurrences
-- of every address in the capture

local function menuable_tap()
	-- Declare the window we will use
	local tw = TextWindow.new("Address Counter")

	-- This will contain a hash of counters of appearances of a certain address
	local ips = {}

	-- this is our tap
	local tap = Listener.new();

	local function remove()
		-- this way we remove the listener that otherwise will remain running indefinitely
		tap:remove();
	end

	-- we tell the window to call the remove() function when closed
	tw:set_atclose(remove)

	-- this function will be called once for each packet
	function tap.packet(pinfo,tvb)
		local src = ips[tostring(pinfo.src)] or 0
		local dst = ips[tostring(pinfo.dst)] or 0

		ips[tostring(pinfo.src)] = src + 1
		ips[tostring(pinfo.dst)] = dst + 1
	end

	-- this function will be called once every few seconds to update our window
	function tap.draw(t)
		tw:clear()
		for ip,num in pairs(ips) do
			tw:append(ip .. "\t" .. num .. "\n");
		end
	end

	-- this function will be called whenever a reset is needed
	-- e.g. when reloading the capture file
	function tap.reset()
		tw:clear()
		ips = {}
	end

	-- Ensure that all existing packets are processed.
	retap_packets()
end

-- using this function we register our function
-- to be called when the user selects the Tools->Test->Packets menu
register_menu("Test/Packets", menuable_tap, MENU_TOOLS_UNSORTED)
----

[#wsluarm_modules]

== Wireshark’s Lua API Reference Manual

This Part of the User Guide describes the Wireshark specific functions in the embedded Lua.

Classes group certain functionality, the following notational conventions are
used:

* _Class.function()_ represents a class method (named _function_) on class
  _Class_, taking no arguments.

* _Class.function(a)_ represents a class method taking one argument.

* _Class.function(...)_ represents a class method taking a variable number of
  arguments.

* _class:method()_ represents an instance method (named _method_) on an instance
  of class _Class_, taking no arguments. Note the lowercase notation in the
  documentation to clarify an instance.

* _class.prop_ represents a property _prop_ on the instance of class _Class_.

Trying to access a non-existing property, function or method currently gives an
error, but do not rely on it as the behavior may change in the future.


include::{build_dir}/wsluarm_src/wslua_utility.adoc[]
include::{build_dir}/wsluarm_src/wslua_gui.adoc[]
include::{build_dir}/wsluarm_src/wslua_proto.adoc[]
include::{build_dir}/wsluarm_src/wslua_field.adoc[]
include::{build_dir}/wsluarm_src/wslua_pinfo.adoc[]
include::{build_dir}/wsluarm_src/wslua_tvb.adoc[]
include::{build_dir}/wsluarm_src/wslua_tree.adoc[]
include::{build_dir}/wsluarm_src/wslua_listener.adoc[]
include::{build_dir}/wsluarm_src/wslua_dumper.adoc[]
include::{build_dir}/wsluarm_src/wslua_wtap.adoc[]
include::{build_dir}/wsluarm_src/wslua_file.adoc[]
include::{build_dir}/wsluarm_src/wslua_dir.adoc[]
include::{build_dir}/wsluarm_src/wslua_int64.adoc[]
include::{build_dir}/wsluarm_src/wslua_struct.adoc[]

[#lua_module_PCRE2]

=== PCRE2 Regular Expressions

Lua has its own native _pattern_ syntax in the string library, but sometimes a
real regex engine is more useful. Wireshark comes with Perl Compatible Regular
Expressions version 2 (PCRE2). This engine is exposed into Wireshark’s Lua engine through the
well-known Lrexlib library. The module is loaded in the global environment using
the "rex_pcre2" table. The manual is available at https://rrthomas.github.io/lrexlib/manual.html.
