---
-- Username/password database library.
--
-- The <code>usernames</code> and <code>passwords</code> functions return
-- multiple values for use with exception handling via
-- <code>nmap.new_try</code>. The first value is the Boolean success
-- indicator, the second value is the closure.
--
-- The closures can take an argument of <code>"reset"</code> to rewind the list
-- to the beginning.
--
-- To avoid taking a long time against slow services, the closures will
-- stop returning values (start returning <code>nil</code>) after a
-- certain time. The time depends on the timing template level, and is
-- * <code>-T3</code> or less: 10 minutes
-- * <code>-T4</code>: 5 minutes
-- * <code>-T5</code>: 3 minutes
-- Time limits are increased by 50% if a custom username or password
-- database is used with the <code>userdb</code> or <code>passdb</code>
-- script arguments. You can control the time limit directly with the
-- <code>unpwdb.timelimit</code> script argument. Use
-- <code>unpwdb.timelimit=0</code> to disable the time limit.
--
-- You can select your own username and/or password database to read from with
-- the script arguments <code>userdb</code> and <code>passdb</code>,
-- respectively.  Comments are allowed in these files, prefixed with
-- <code>"#!comment:"</code>.  Comments cannot be on the same line as a
-- username or password because this leaves too much ambiguity, e.g. does the
-- password in <code>"mypass  #!comment: blah"</code> contain a space, two
-- spaces, or do they just separate the password from the comment?
--
-- @usage
-- require("unpwdb")
--
-- local usernames, passwords
-- local try = nmap.new_try()
--
-- usernames = try(unpwdb.usernames())
-- passwords = try(unpwdb.passwords())
--
-- for password in passwords do
--   for username in usernames do
--     -- Do something with username and password.
--   end
--   usernames("reset")
-- end
--
-- @usage
-- nmap --script-args userdb=/tmp/user.lst
-- nmap --script-args unpwdb.timelimit=10m
--
-- @args userdb The filename of an alternate username database.
-- @args passdb The filename of an alternate password database.
-- @args unpwdb.userlimit The maximum number of usernames
-- <code>usernames</code> will return (default unlimited).
-- @args unpwdb.passlimit The maximum number of passwords
-- <code>passwords</code> will return (default unlimited).
-- @args unpwdb.timelimit The maximum amount of time that any iterator will run
-- before stopping. The value is in seconds by default and you can follow it
-- with <code>ms</code>, <code>s</code>, <code>m</code>, or <code>h</code> for
-- milliseconds, seconds, minutes, or hours. For example,
-- <code>unpwdb.timelimit=30m</code> or <code>unpwdb.timelimit=.5h</code> for
-- 30 minutes. The default depends on the timing template level (see the module
-- description). Use the value <code>0</code> to disable the time limit.
-- @author Kris Katterjohn 06/2008
-- @copyright Same as Nmap--See http://nmap.org/book/man-legal.html

module(... or "unpwdb", package.seeall)

local usertable = {}
local passtable = {}

local customdata = false

-- So I don't have to type as much :)
local args = nmap.registry.args

local userfile = function()
	if args.userdb then
		customdata = true
		return args.userdb
	end

	return nmap.fetchfile("nselib/data/usernames.lst")
end

local passfile = function()
	if args.passdb then
		customdata = true
		return args.passdb
	end

	return nmap.fetchfile("nselib/data/passwords.lst")
end

local filltable = function(filename, table)
	if #table ~= 0 then
		return true
	end

	local file = io.open(filename, "r")

	if not file then
		return false
	end

	for l in file:lines() do
		-- Comments takes up a whole line
		if not l:match("#!comment:") then
			table[#table + 1] = l
		end
	end

	file:close()

	return true
end

local closure = function(table)
	local i = 1

	return function(cmd)
		if cmd == "reset" then
			i = 1
			return
		end
		local elem = table[i]
		if elem then i = i + 1 end
		return elem
	end
end

--- Returns the suggested number of seconds to attempt a brute force attack,
-- based on the <code>unpwdb.timelimit</code> script argument, Nmap's timing
-- values (<code>-T4</code> etc.) and whether or not a user-defined list is
-- used.
--
-- You can use the script argument <code>notimelimit</code> to make this
-- function return <code>nil</code>, which means the brute-force should run
-- until the list is empty. If <code>notimelimit</code> is not used, be sure to
-- still check for <code>nil</code> return values on the above two functions in
-- case you finish before the time limit is up.
timelimit = function()
   -- If we're reading from a user-defined username or password list,
   -- we'll give them a timeout 1.5x the default.  If the "notimelimit"
   -- script argument is used, we return nil.
	local t = nmap.timing_level()

	-- Easy enough
	if args.notimelimit then
		return nil
	end
	if args["unpwdb.timelimit"] then
		local limit, err = stdnse.parse_timespec(args["unpwdb.timelimit"])
		if not limit then
			error(err)
		end
		return limit
	end

	if t <= 3 then
		return (customdata and 900) or 600
	elseif t == 4 then
		return (customdata and 450) or 300
	elseif t == 5 then
		return (customdata and 270) or 180
	end
end

--- Returns a function closure which returns a new username with every call
-- until the username list is exhausted (in which case it returns
-- <code>nil</code>).
-- @return boolean Status.
-- @return function The usernames iterator.
local usernames_raw = function()
	local path = userfile()

	if not path then
		return false, "Cannot find username list"
	end

	if not filltable(path, usertable) then
		return false, "Error parsing username list"
	end

	return true, closure(usertable)
end

--- Returns a function closure which returns a new password with every call
-- until the password list is exhausted (in which case it returns
-- <code>nil</code>).
-- @return boolean Status.
-- @return function The passwords iterator.
local passwords_raw = function()
	local path = passfile()

	if not path then
		return false, "Cannot find password list"
	end

	if not filltable(path, passtable) then
		return false, "Error parsing password list"
	end

	return true, closure(passtable)
end

--- Wraps time and count limits around an iterator. When either limit expires,
-- starts returning <code>nil</code>. Calling the iterator with an argument of
-- "reset" resets the count.
-- @param time_limit Time limit in seconds. Use 0 or <code>nil</code> for no limit.
-- @param count_limit Count limit in seconds. Use 0 or <code>nil</code> for no limit.
-- @return boolean Status.
-- @return function The wrapped iterator.
local limited_iterator = function(iterator, time_limit, count_limit)
	local start, count, elem

	time_limit = (time_limit and time_limit > 0) and time_limit
	count_limit = (count_limit and count_limit > 0) and count_limit

	start = os.time()
	count = 0
	return function(cmd)
		if cmd == "reset" then
			count = 0
		else
			count = count + 1
		end
		if count_limit and count > count_limit then
			return
		end
		if time_limit and os.time() - start >= time_limit then
			return
		end
		return iterator(cmd)
	end
end

--- Returns a function closure which returns a new password with every call
-- until the username list is exhausted or either limit expires (in which cases
-- it returns <code>nil</code>).
-- @param time_limit Time limit in seconds. Use 0 for no limit.
-- @param count_limit Count limit in seconds. Use 0 for no limit.
-- @return boolean Status.
-- @return function The usernames iterator.
usernames = function(time_limit, count_limit)
	local status, iterator

	status, iterator = usernames_raw()
	if not status then
		return false, iterator
	end

	time_limit = time_limit or timelimit()
	if not count_limit and args["unpwdb.userlimit"] then
		count_limit = tonumber(args["unpwdb.userlimit"])
	end

	return true, limited_iterator(iterator, time_limit, count_limit)
end

--- Returns a function closure which returns a new password with every call
-- until the password list is exhausted or either limit expires (in which cases
-- it returns <code>nil</code>).
-- @param time_limit Time limit in seconds. Use 0 for no limit.
-- @param count_limit Count limit in seconds. Use 0 for no limit.
-- @return boolean Status.
-- @return function The passwords iterator.
passwords = function(time_limit, count_limit)
	local status, iterator

	status, iterator = passwords_raw()
	if not status then
		return false, iterator
	end

	time_limit = time_limit or timelimit()
	if not count_limit and args["unpwdb.passlimit"] then
		count_limit = tonumber(args["unpwdb.passlimit"])
	end

	return true, limited_iterator(iterator, time_limit, count_limit)
end
