gps server record positions

gps/gpsServer.lua

@@ -6,6 +6,7 @@ local args       = { ... }
 local gps 			 = _G.gps
 local os         = _G.os
 local peripheral = _G.peripheral
+local term       = _G.term
 local turtle     = _G.turtle
 local vector     = _G.vector
 
@@ -65,6 +66,10 @@ local function server()
 	local modems = Config.load('gpsServer')
 	local computers = { }
 
+	if #modems == 0 then
+		error('Missing usr/config/gpsServer configuration file')
+	end
+
 	for k, modem in pairs(modems) do
 		Util.merge(modem, peripheral.wrap(k))
 		modem.open(gps.CHANNEL_GPS)
@@ -74,11 +79,12 @@ local function server()
 		local e, p1, p2, p3, p4, p5 = os.pullEvent( "modem_message" )
 		if e == "modem_message" then
 			-- We received a message from a modem
-			local sSide, channel, computerId, sMessage, distance = p1, p2, p3, p4, p5
+			local side, channel, computerId, sMessage, distance = p1, p2, p3, p4, p5
 			if channel == gps.CHANNEL_GPS and sMessage == "PING" then
 				-- We received a ping message on the GPS channel, send a response
+				local modem = modems[side]
+				if modem then
 					local computer = memoize(computers, computerId, function() return { } end)
-				local modem = modems[sSide]
 					table.insert(computer, {
 						position = vector.new(modem.x, modem.y, modem.z), distance = distance
 					})
@@ -100,6 +106,7 @@ local function server()
 			end
 		end
 	end
+end
 
 if args[1] == 'build' then
 	local y = tonumber(args[2] or 0)