local bit = require "bit" local os = require "os" local package = require "package" local stdnse = require "stdnse" local string = require "string" _ENV = stdnse.module("gps", stdnse.seeall) --- -- A smallish gps parsing module. -- Currently does GPRMC NMEA decoding -- -- @author "Patrik Karlsson " -- -- NMEA = { -- Parser for the RMC sentence RMC = { parse = function(str) local time, status, latitude, ns_indicator, longitude, ew_indicator, speed, course, date, variation, ew_variation, checksum = str:match("^%$GPRMC,([^,]*),([^,]*),([^,]*),([^,]*),([^,]*),([^,]*),([^,]*),([^,]*),([^,]*),([^,]*),([^%*]*)(.*)$") if ( not(latitude) or not(longitude) ) then return end local deg, min = latitude:match("^(..)(.*)$") if ( not(deg) or not(min) ) then return end latitude = tonumber(deg) + (tonumber(min)/60) deg, min = longitude:match("^(..)(.*)$") if ( not(deg) or not(min) ) then return end longitude = tonumber(deg) + (tonumber(min)/60) if ( ew_indicator == 'W' ) then longitude = -longitude end if ( ns_indicator == 'S' ) then latitude = -latitude end return { time = time, status = status, latitude = latitude, longitude = longitude, speed = speed, course = course, date = date, variation = variation, ew_variation = ew_variation } end, }, -- Calculates an verifies the message checksum -- -- @param str containing the GPS sentence -- @return status true on success, false if the checksum does not match -- @return err string if status is false checksum = function(str) local val = 0 for c in str:sub(2,-4):gmatch(".") do val = bit.bxor(val, string.byte(c)) end if ( str:sub(-2):upper() ~= stdnse.tohex(string.char(val)):upper() ) then return false, ("Failed to verify checksum (got: %s; expected: %s)"):format(stdnse.tohex(string.char(val)), str:sub(-2)) end return true end, -- Parses a GPS sentence using the appropriate parser -- -- @param str containing the GPS sentence -- @return entry table containing the parsed response or -- err string if status is false -- @return status true on success, false on failure parse = function(str) local status, err = NMEA.checksum(str) if ( not(status) ) then return false, err end local prefix = str:match("^%$GP([^,]*)") if ( not(prefix) ) then return false, "Not a NMEA sentence" end if ( NMEA[prefix] and NMEA[prefix].parse ) then local e = NMEA[prefix].parse(str) if (not(e)) then return false, ("Failed to parse entry: %s"):format(str) end return true, e else local err = ("No parser for prefix: %s"):format(prefix) stdnse.print_debug(2, err) return false, err end end } Util = { convertTime = function(date, time) local d = {} d.hour, d.min, d.sec = time:match("(..)(..)(..)") d.day, d.month, d.year = date:match("(..)(..)(..)") d.year = d.year + 2000 return os.time(d) end } return _ENV;