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)
@@ -74,27 +79,29 @@ 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 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
-				})
-				if #computer == 4 then
-					local pt = GPS.trilaterate(computer)
-					if pt then
-						positions[computerId] = pt
-						term.clear()
-						for k,v in pairs(positions) do
-							Util.print('ID: %d: %s %s %s', k, v.x, v.y, v.z)
+				local modem = modems[side]
+				if modem then
+					local computer = memoize(computers, computerId, function() return { } end)
+					table.insert(computer, {
+						position = vector.new(modem.x, modem.y, modem.z), distance = distance
+					})
+					if #computer == 4 then
+						local pt = GPS.trilaterate(computer)
+						if pt then
+							positions[computerId] = pt
+							term.clear()
+							for k,v in pairs(positions) do
+								Util.print('ID: %d: %s %s %s', k, v.x, v.y, v.z)
+							end
 						end
+						computers[computerId] = nil
+					end
+					for _, modem in pairs(modems) do
+						modem.transmit( computerId, gps.CHANNEL_GPS, { modem.x, modem.y, modem.z })
 					end
-					computers[computerId] = nil
-				end
-				for _, modem in pairs(modems) do
-					modem.transmit( computerId, gps.CHANNEL_GPS, { modem.x, modem.y, modem.z })
 				end
 			end
 		end