1 files changed, 126 insertions, 0 deletions
diff --git a/nselib/gps.lua b/nselib/gps.lua
new file mode 100644
index 0000000..a4528ce
--- /dev/null
+++ b/nselib/gps.lua
@@ -0,0 +1,126 @@
+local os = require "os"
+local stdnse = require "stdnse"
+local string = require "string"
+local unittest = require "unittest"
+_ENV = stdnse.module("gps", stdnse.seeall)
+
+---
+-- A smallish gps parsing module.
+-- Currently does GPRMC NMEA decoding
+--
+-- @author Patrik Karlsson <patrik@cqure.net>
+--
+--
+
+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 = 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("^%$GP([^,]*)")
+    if ( not(prefix) ) then
+      return false, "Not a NMEA sentence"
+    end
+
+    if ( NMEA[prefix] and NMEA[prefix].parse ) then
+      local e = NMEA[prefix].parse(str)
+      if (not(e)) then
+        return false, ("Failed to parse entry: %s"):format(str)
+      end
+      return true, e
+    else
+      local err = ("No parser for prefix: %s"):format(prefix)
+      stdnse.debug2("%s", err)
+      return false, err
+    end
+
+  end
+
+}
+
+Util = {
+
+  convertTime = function(date, time)
+    local d = {}
+    d.hour, d.min, d.sec = time:match("(..)(..)(..)")
+    d.day, d.month, d.year = date:match("(..)(..)(..)")
+    d.year = d.year + 2000
+    return os.time(d)
+  end
+}
+
+if not unittest.testing() then
+  return _ENV
+end
+
+test_suite = unittest.TestSuite:new()
+test_suite:add_test(unittest.is_true(NMEA.checksum("$GPGLL,5300.97914,N,00259.98174,E,125926,A*28")), "valid checksum")
+test_suite:add_test(unittest.is_false(NMEA.checksum("$XPGLL,5300.97914,N,00259.98174,E,125926,A*28")), "invalid checksum")
+return _ENV;