---
-- Minimalistic DHCP6 (Dynamic Host Configuration Protocol for IPv6)
-- implementation supporting basic DHCP6 Solicit requests The library
-- is structured around the following classes:
-- * DHCP6.Option	- DHCP6 options encoders (for requests) and decoders
--                    (for responses)
-- * DHCP6.Request	- DHCP6 request encoder and decoder
-- * DHCP6.Response	- DHCP6 response encoder and decoder
-- * Helper 		- The helper class, primary script interface
--
-- The following sample code sends a DHCP6 Solicit request and returns a
-- response suitable for script output:
-- <code>
--   local helper = DHCP6.Helper:new("eth0")
--   local status, response = helper:solicit()
--   if ( status ) then
--      return stdnse.format_output(true, response)
--   end
-- </code>
--
-- @author "Patrik Karlsson <patrik@cqure.net>"
--
module(... or "dhcp6", package.seeall)

require 'bin'
require 'bit'
require 'ipOps'

DHCP6 = {}

-- DHCP6 request and response types
DHCP6.Type = {
	SOLICIT 	= 1,
	ADVERTISE	= 2,
	REQUEST 	= 3,
}

-- DHCP6 type as string
DHCP6.TypeStr = {
	[DHCP6.Type.SOLICIT] 	= "Solicit",
	[DHCP6.Type.ADVERTISE] 	= "Advertise",
	[DHCP6.Type.REQUEST] 	= "Request",
}

-- DHCP6 option types
DHCP6.OptionTypes = {
	OPTION_CLIENTID		= 0x01,
	OPTION_SERVERID		= 0x02,
	OPTION_IA_NA		= 0x03,
	OPTION_IAADDR		= 0x05,
	OPTION_ELAPSED_TIME = 0x08,
	OPTION_STATUS_CODE	= 0x0d,
	OPTION_DNS_SERVERS	= 0x17,
	OPTION_DOMAIN_LIST	= 0x18,
	OPTION_IA_PD		= 0x19,
	OPTION_SNTP_SERVERS	= 0x1f,
	OPTION_CLIENT_FQDN	= 0x27,
}

-- DHCP6 options
DHCP6.Option = {
	
	[DHCP6.OptionTypes.OPTION_ELAPSED_TIME] = {
		
		-- Create a new class instance
		-- @param time in ms since last request
		-- @return o new instance of class
		new = function(self, time)
			local o = {
				type = DHCP6.OptionTypes.OPTION_ELAPSED_TIME,
				time = time,
				-- in case no time was created, we need this to be able to
				-- calculate time since instantiation
				created = os.time(),
			}
			setmetatable(o, self)
			self.__index = self
			return o
		end,
		
		-- Converts option to a string
		-- @return str string containing the class instance as string
		__tostring = function(self)
			local data
			if ( self.time ) then
				data = bin.pack(">S", self.time)
			else
				data = bin.pack(">S", (os.time() - self.created) * 1000)
			end
			return bin.pack(">SP", self.type, data)
		end,
		
	},
	
	[DHCP6.OptionTypes.OPTION_CLIENTID] = {
		
		-- Create a new class instance
		-- @param mac string containing the mac address
		-- @param duid number the duid of the client
		-- @param hwtype number the hwtype of the client
		-- @param time number time since 2000-01-01 00:00:00
		-- @return o new instance of class
		new = function(self, mac, duid, hwtype, time)
			local o = {
				type = DHCP6.OptionTypes.OPTION_CLIENTID,
				duid = duid or 1,
				hwtype = hwtype or 1,
				time = time or os.time() - os.time({year=2000, day=1, month=1, hour=0, min=0, sec=0}),
				mac = mac,
			}
			setmetatable(o, self)
			self.__index = self
			return o
		end,
		
		-- Parse the data string and create an instance of the class
		-- @param data string containing the data as received over the socket
		-- @return opt new instance of option
		parse = function(data)
			local opt = DHCP6.Option[DHCP6.OptionTypes.OPTION_CLIENTID]:new()
			local pos
			pos, opt.duid = bin.unpack(">S", data, pos)
			if ( 1 ~= opt.duid ) then
				stdnse.print_debug("Unexpected DUID type (%d)", opt.duid)
				return
			end
			pos, opt.hwtype, opt.time, opt.mac = bin.unpack(">SIA" .. (#data - pos - 4 - 2 + 1), data, pos)
			opt.time = opt.time + os.time({year=2000, day=1, month=1, hour=0, min=0, sec=0})
			return opt
		end,
		
		-- Converts option to a string
		-- @return str string containing the class instance as string
		__tostring = function(self)
			local data = bin.pack(">SSIA", self.duid, self.hwtype, self.time, self.mac)
			return bin.pack(">SP", self.type, data)
		end,	
	},
	
	[DHCP6.OptionTypes.OPTION_SERVERID] = {
		-- Create a new class instance
		-- @param mac string containing the mac address
		-- @param duid number the duid of the client
		-- @param hwtype number the hwtype of the client
		-- @param time number time since 2000-01-01 00:00:00
		-- @return o new instance of class
		new = function(...)	return DHCP6.Option[DHCP6.OptionTypes.OPTION_CLIENTID].new(...) end,
		
		-- Parse the data string and create an instance of the class
		-- @param data string containing the data as received over the socket
		-- @return opt new instance of option
		parse = function(...) return DHCP6.Option[DHCP6.OptionTypes.OPTION_CLIENTID].parse(...) end,

		-- Converts option to a string
		-- @return str string containing the class instance as string
		__tostring = function(...) return DHCP6.Option[DHCP6.OptionTypes.OPTION_CLIENTID].__tostring(...) end,
	},
	
	[DHCP6.OptionTypes.OPTION_STATUS_CODE] = {
		
		-- Create a new class instance
		-- @param code number containing the error code
		-- @param msg string containing the error message
		-- @return o new instance of class
		new = function(self, code, msg)
			local o = {
				type = DHCP6.OptionTypes.OPTION_STATUS_CODE,
				code = code,
				msg = msg,
			}
			setmetatable(o, self)
			self.__index = self
			return o
		end,

		-- Parse the data string and create an instance of the class
		-- @param data string containing the data as received over the socket
		-- @return opt new instance of option
		parse = function(data)
			local opt = DHCP6.Option[DHCP6.OptionTypes.OPTION_STATUS_CODE]:new()
			local pos
			
			pos, opt.code, opt.msg = bin.unpack(">SA" .. (#data - 2), data)
			return opt
		end,
		
	},
		
	[DHCP6.OptionTypes.OPTION_DNS_SERVERS] = {
		
		-- Create a new class instance
		-- @param servers table containing DNS servers
		-- @return o new instance of class
		new = function(self, servers)
			local o = {
				type = DHCP6.OptionTypes.OPTION_DNS_SERVERS,
				servers = servers or {},
			}
			setmetatable(o, self)
			self.__index = self
			return o
		end,

		-- Parse the data string and create an instance of the class
		-- @param data string containing the data as received over the socket
		-- @return opt new instance of option
		parse = function(data)
			local opt = DHCP6.Option[DHCP6.OptionTypes.OPTION_DNS_SERVERS]:new()
			local pos, count = 1, #data/16
			
			for i=1,count do
				local srv
				pos, srv = bin.unpack(">B16", data, pos)
				table.insert(opt.servers, srv)
			end
			return opt
		end,
		
		-- Converts option to a string
		-- @return str string containing the class instance as string
		__tostring = function(self)
			local len = #self.servers * 16
			local data= bin.pack(">SS", self.type, self.len)
			for _, ipv6 in ipairs(self.servers) do
				data = data .. ipOps.ip_to_str(ipv6)
			end
			return data
		end
	},
	
	[DHCP6.OptionTypes.OPTION_DOMAIN_LIST] = {
	
		-- Create a new class instance
		-- @param domain table containing the search domains
		-- @return o new instance of class
		new = function(self, domains)
			local o = {
				type = DHCP6.OptionTypes.OPTION_DOMAIN_LIST,
				domains = domains or {},
			}
			setmetatable(o, self)
			self.__index = self
			return o
		end,

		-- Parse the data string and create an instance of the class
		-- @param data string containing the data as received over the socket
		-- @return opt new instance of option
		parse = function(data)
			local opt = DHCP6.Option[DHCP6.OptionTypes.OPTION_DOMAIN_LIST]:new()
			local pos = 1
			
			repeat
				local domain = {}
				repeat
					local part
					pos, part = bin.unpack("p", data, pos)
					if ( part ~= "" ) then
						table.insert(domain, part)
					end
				until( part == "" )
				table.insert(opt.domains, stdnse.strjoin(".", domain))
			until( pos > #data )
			return opt
		end,

		
	},
	
	[DHCP6.OptionTypes.OPTION_IA_PD] = {
		
		-- Create a new class instance
		-- @param iad number containing iad
		-- @param t1 number containing t1
		-- @param t2 number containing t2
		-- @param option string containing any options
		-- @return o new instance of class
		new = function(self, iaid, t1, t2, options)
			local o = {
				type = DHCP6.OptionTypes.OPTION_IA_PD,
				iaid = iaid,
				t1 = t1 or 0,
				t2 = t2 or 0,
				options = options or "",
			}
			setmetatable(o, self)
			self.__index = self
			return o
		end,
		
		-- Converts option to a string
		-- @return str string containing the class instance as string
		__tostring = function(self)
			local data = bin.pack(">IIIA", self.iaid, self.t1, self.t2, self.options)
			return bin.pack(">SP", self.type, data)
		end,
		
	},
	
	[DHCP6.OptionTypes.OPTION_IA_NA] = {
		
		-- Create a new class instance
		-- @param iad number containing iad
		-- @param t1 number containing t1
		-- @param t2 number containing t2
		-- @param option table containing any options
		-- @return o new instance of class
		new = function(self, iaid, t1, t2, options)
			local o = {
				type = DHCP6.OptionTypes.OPTION_IA_NA,
				iaid = iaid,
				t1 = t1 or 0,
				t2 = t2 or 0,
				options = options or {},
			}
			setmetatable(o, self)
			self.__index = self
			return o
		end,
		
		-- Parse the data string and create an instance of the class
		-- @param data string containing the data as received over the socket
		-- @return opt new instance of option
		parse = function(data)
			local opt = DHCP6.Option[DHCP6.OptionTypes.OPTION_IA_NA]:new()
			local pos
			
			pos, opt.iaid, opt.t1, opt.t2 = bin.unpack(">III", data)
			
			-- do we have any options
			while ( pos < #data ) do
				local typ, len, ipv6, pref_lt, valid_lt, options
				pos, typ, len = bin.unpack(">SS", data, pos)
				
				if ( 5 == DHCP6.OptionTypes.OPTION_IAADDR ) then
					local addr = { type = DHCP6.OptionTypes.OPTION_IAADDR }
					pos, addr.ipv6, addr.pref_lt, addr.valid_lt = bin.unpack(">A16II", data, pos)
					table.insert(opt.options, addr)
				else
					pos = pos + len
				end
			end	
			return opt
		end,
		
		-- Converts option to a string
		-- @return str string containing the class instance as string
		__tostring = function(self)
			local data = bin.pack(">III", self.iaid, self.t1, self.t2)

			-- TODO: we don't cover self.options here, we should probably add that
			return bin.pack(">SP", self.type, data)
		end,	
	},
	
	[DHCP6.OptionTypes.OPTION_SNTP_SERVERS] = {

		-- Create a new class instance
		-- @param servers table containing the NTP servers
		-- @return o new instance of class
		new = function(self, servers)
			local o = {
				type = DHCP6.OptionTypes.OPTION_SNTP_SERVERS,
				servers = servers or {},
			}
				setmetatable(o, self)
			self.__index = self
			return o
		end,
		
		-- Parse the data string and create an instance of the class
		-- @param data string containing the data as received over the socket
		-- @return opt new instance of option
		parse = function(data)
			local opt = DHCP6.Option[DHCP6.OptionTypes.OPTION_SNTP_SERVERS]:new()
			local pos, server = 1

			repeat
				pos, server = bin.unpack(">B16", data, pos)
				table.insert( opt.servers, ipOps.bin_to_ip(server) )
			until( pos > #data )
			return opt
		end,
	},
			
}
	
	
DHCP6.Request = {
	
	-- Create a new class instance
	-- @param msgtype number containing the message type
	-- @param xid number containing the transaction id
	-- @param opts table containing any request options
	-- @return o new instance of class
	new = function(self, msgtype, xid, opts)
		local o = {
			type = msgtype,
			xid = xid or math.random(1048575),
			opts = opts or {}
		}
		setmetatable(o, self)
		self.__index = self
		return o
	end,
	
	-- Adds a new DHCP6 option to the request
	-- @param opt instance of object to add to the request
	addOption = function(self, opt)
		table.insert(self.opts, opt)
	end,
	
	-- Converts option to a string
	-- @return str string containing the class instance as string
	__tostring = function(self)
		local tmp = bit.lshift(self.type, 24) + self.xid
		local data = ""

		for _, opt in ipairs(self.opts) do
			data = data .. tostring(opt)
		end
		return bin.pack(">IA", tmp, data)
	end,

}

-- The Response class handles responses from the server
DHCP6.Response = {
		
		-- Creates a new instance of the response class
		-- @param msgtype number containing the type of DHCP6 message
		-- @param xid number containing the transaction ID
		new = function(self, msgtype, xid, opts)
			local o = {
				msgtype = msgtype,
				xid = xid,
				opts = opts or {},
			}
			setmetatable(o, self)
			self.__index = self
			return o
		end,
		
		-- Parse the data string and create an instance of the class
		-- @param data string containing the data as received over the socket
		-- @return opt new instance of option
		parse = function(data)
			local resp = DHCP6.Response:new()
			local pos, tmp = bin.unpack(">I", data)

			resp.msgtype = bit.band(tmp, 0xFF000000)
			resp.msgtype = bit.rshift(resp.msgtype, 24)			
			resp.xid = bit.band(tmp, 0x00FFFFFF)
			while( pos < #data ) do
				local opt = {}
				pos, opt.type, opt.data = bin.unpack(">SP", data, pos)
				if ( DHCP6.Option[opt.type] and DHCP6.Option[opt.type].parse ) then
					local opt_parsed = DHCP6.Option[opt.type].parse(opt.data)
					if ( not(opt_parsed) ) then
						table.insert(resp.opts, { type = opt.type, raw = opt.data })
					else
						table.insert(resp.opts, { type = opt.type, resp = opt_parsed })
					end
				else
					stdnse.print_debug(2, "No option decoder for type: %d; len: %d", opt.type, #(opt.data or ""))
					table.insert(resp.opts, { type = opt.type, raw = opt.data })
				end
			end
			return resp
		end
		
}

-- Table of option to string converters
-- Each option should have it's own function to convert an instance of option
-- to a printable string.
--
-- TODO: These functions could eventually be moved to a method in it's
-- respective class.
OptionToString = {
	
	[DHCP6.OptionTypes.OPTION_CLIENTID] = function(opt)
		local HWTYPE_ETHER = 1
		if ( HWTYPE_ETHER == opt.hwtype ) then
			local mac = stdnse.tohex(opt.mac):upper()
			mac = mac:gsub("..", "%1:"):sub(1, -2)
			local tm = os.date("%Y-%m-%d %H:%M:%S", opt.time)
			return "Client identifier", ("MAC: %s; Time: %s"):format(mac, tm)
		end
	end,
	
	[DHCP6.OptionTypes.OPTION_SERVERID] = function(opt)
		local topic, str = OptionToString[DHCP6.OptionTypes.OPTION_CLIENTID](opt)
		return "Server identifier", str
	end,
	
	[DHCP6.OptionTypes.OPTION_IA_NA] = function(opt)
		if ( opt.options and 1 == #opt.options ) then
			local ipv6 = opt.options[1].ipv6
			ipv6 = select(2, bin.unpack("B" .. #ipv6, ipv6))
			ipv6 = ipOps.bin_to_ip(ipv6)
			return "Non-temporary Address", ipv6
		end
	end,
	
	[DHCP6.OptionTypes.OPTION_DNS_SERVERS] = function(opt)
		local servers = {}
		for _, srv in ipairs(opt.servers) do
			local ipv6 = ipOps.bin_to_ip(srv)
			table.insert(servers, ipv6)
		end
		return "DNS Servers", stdnse.strjoin(",", servers)
	end,
	
	[DHCP6.OptionTypes.OPTION_DOMAIN_LIST] = function(opt)
		return "Domain Search", stdnse.strjoin(", ", opt.domains)
	end,
	
	[DHCP6.OptionTypes.OPTION_STATUS_CODE] = function(opt)
		return "Error", ("Code: %d; Message: %s"):format(opt.code, opt.msg)
	end,
	
	[DHCP6.OptionTypes.OPTION_SNTP_SERVERS] = function(opt)
		return "NTP Servers", stdnse.strjoin(", ", opt.servers)
	end,
}

-- The Helper class serves as the main interface to scripts
Helper = {
	
	-- Creates a new Helper class instance
	-- @param iface string containing the interface name
	-- @param options table containing any options, currently
	--        <code>timeout</code> - socket timeout in ms
	-- @return o new instance of Helper
	new = function(self, iface, options)
		local o = {
			iface = iface,
			options = options or {},
		}
		setmetatable(o, self)
		self.__index = self
		
		local info, err = nmap.get_interface_info(iface)
		-- if we faile to get interface info, don't return a helper
		-- this is true on OS X for interfaces like: p2p0 and vboxnet0
		if ( not(info) and err ) then
			return
		end
		o.mac = info.mac
		o.socket = nmap.new_socket("udp")
		o.socket:bind(nil, 546)
		o.socket:set_timeout(o.options.timeout or 5000)
		return o
	end,
	
	-- Sends a DHCP6 Solicit message to the server, essentiall requesting a new
	-- IPv6 non-temporary address
	-- @return table of results suitable for use with 
	--         <code>stdnse.format_output</code>
	solicit = function(self)
		local req = DHCP6.Request:new( DHCP6.Type.SOLICIT )
		local option = DHCP6.Option
		req:addOption(option[DHCP6.OptionTypes.OPTION_ELAPSED_TIME]:new())
		req:addOption(option[DHCP6.OptionTypes.OPTION_CLIENTID]:new(self.mac))
		
		local iaid = select(2, bin.unpack(">I", self.mac:sub(3)))
		req:addOption(option[DHCP6.OptionTypes.OPTION_IA_NA]:new(iaid, 3600, 5400))

		self.host, self.port = { ip = "ff02::1:2" }, { number = 547, protocol = "udp"}
		local status, err = self.socket:sendto( self.host, self.port, tostring(req) )
		if ( not(status) ) then
			self.host.ip = ("%s%%%s"):format(self.host.ip, self.iface)
			status, err = self.socket:sendto( self.host, self.port, tostring(req) )
			if ( not(status) ) then
				return false, "Failed to send DHCP6 request to server"
			end
		end

		local resp, retries = {}, 3
		repeat
			retries = retries - 1
			local status, data = self.socket:receive()
			if ( not(status) ) then
				return false, "Failed to receive DHCP6 request from server"
			end

			resp = DHCP6.Response.parse(data)		
			if ( not(resp) ) then
				return false, "Failed to decode DHCP6 response from server"
			end
		until( req.xid == resp.xid or retries == 0 )

		if ( req.xid ~= resp.xid ) then
			return false, "Failed to receive DHCP6 response from server"
		end

		local result, result_options = {}, { name = "Options" }
		local resptype = DHCP6.TypeStr[resp.msgtype] or ("Unknown (%d)"):format(resp.msgtype)
		
		table.insert(result, ("Message type: %s"):format(resptype))
		table.insert(result, ("Transaction id: %d"):format(resp.xid))

		for _, opt in ipairs(resp.opts or {}) do
			if ( OptionToString[opt.type] ) then
				local topic, str = OptionToString[opt.type](opt.resp)
				if ( topic and str ) then
					table.insert(result_options, ("%s: %s"):format(topic, str))
				end
			else
				stdnse.print_debug(2, "No decoder for option type: %d", opt.type)
			end
		end
		table.insert(result, result_options)
		return true, result
	end,	
}

