Mobile server

ar2rsawseen · June 2012

Hello all,
I'm quite new to networking and wanted to explore the dark waters with Gideros. So I wanted to create simple server app, to which other could connect. Probably similar to Gideros Player.

So I tried this piece of code

-- load namespace
local socket = require("socket")
local ip, t = socket.dns.toip("localhost")
-- create a TCP socket and bind it to the local host, at any port
local server = assert(socket.bind(ip, 53883))
-- find out which port the OS chose for us
local ip, port = server:getsockname()
-- print a message informing what's up
print("Please telnet to "..ip.." on port " .. port)
print("After connecting, you have 10s to enter a line to be echoed")
-- loop forever waiting for clients
while 1 do
  -- wait for a connection from any client
  local client = server:accept()
  -- make sure we don't block waiting for this client's line
  client:settimeout(10)
  -- receive the line
  local line, err = client:receive()
  -- if there was no error, send it back to the client
  if not err then client:send(line .. "\n") end
  -- done with client, close the object
  client:close()
end

Which allows me to connect to localhost through putty on same port, but then after some time it says server has stopped unexpectedly. And when I check Gideros player it's simply hangs (Not responding).

I'm probably doing something completely wrong using while loop. So how does one can create a server app?

ar2rsawseen · June 2012

If you'll wonder about the purpose, then I want to create a real time game, that can be simply played between two phones in LAN, without any third parity server.

Is it even possible?
That app should both listen and send data

ar2rsawseen · June 2012

Ok, it's probably due to my slow machine, tried on PC and it works ok.

But still interested from point of efficiency, is it ok for app to be a server?

ar2rsawseen · June 2012

This is how far I got and it works great.

-- load namespace
local socket = require("socket")
local ip, t = socket.dns.toip("localhost")
-- create a TCP socket and bind it to the local host, at any port
local server = assert(socket.bind(ip, 53882))
-- find out which port the OS chose for us
local ip, port = server:getsockname()
-- print a message informing what's up
print("Please telnet to "..ip.." on port " .. port)
print("After connecting, you have 10s to enter a line to be echoed")
-- loop forever waiting for clients
local clients = {}
local maxClients = 2
local writeClient = {}
 
while 1 do
	local ready, none, erra = socket.select(clients, writeClient, 10)
	if err == nil then
		for i = 1, maxClients do
			local client = clients[i]
			if client == nil then
				-- wait for a connection from any client
				client = server:accept()
				-- make sure we don't block waiting for this client's line
				server:settimeout(1)
				if client then
					clients[i] = client
				end
			end
		end
		for i = 1, #ready do
			local client = ready[i]
			-- receive the line
			local line, err = client:receive()
			-- if there was no error, send it back to the client
			if not err then 
				if line == "exit" then
					-- done with client, close the object
					client:close()
					clients[i] = nil
				elseif line == "whoami" then
					client:send(client:getpeername().."\r\n")
				elseif line == "howdidigethere" then
					client:send(client:getsockname().."\r\n")
				elseif line == "whattimeisit" then
					client:send(socket.gettime().."\r\n")
				else
					client:send("Unknown command: "..line.." \r\n")
				end
			end
		end
	end
end

Will keep updating snippet and probably someday create a tutorial

atilim · June 2012

<:-P I'll learn a lot from your tutorial.

ar2rsawseen · June 2012

Ok created some sort of device discovery using udp broadcasting (255.255.255.255), which works great between two pc's in Gideros player.
But once I try it on Android's Gideros player, it does not receive any broadcasted packages. I can send messages directly to Android using it's IP, but not broadcast.

Another interesting thing, that to get PC's IP address I simply use

socket.dns.toip(socket.dns.gethostname())

But on Android it returns 127.0.0.1, so I have to manually set up current Android's IP to bind socket to, to make it work.

Is there any other way to get current device's IP address?

Did a lot of reading, and many says that both problems are because of multiple interfaces, and that currently used interface to connect to LAN is not default.

So broadcasting goes to default interface and IP address returned for default interface.

Still don't know if it's true, but is there any option to change interface on device (I always thought that my Android has only WiFi) and is there a way to get list of all device interfaces?

And another question if someone might know, is there a way to identify clients, right now I'm implementing my own protocol, but maybe there is easier way?

ar2rsawseen · June 2012

Ok resolved detecting IP address problem, not an elegant solution, but it works:
http://stackoverflow.com/questions/7046291/get-ip-address-in-lua

local function getIP()
	local s = socket.udp()
	s:setpeername("74.125.115.104",80)
	local ip, _ = s:getsockname()
	return ip
end

ar2rsawseen · June 2012

Resolved device discovery using multicast

Although, I don't know why, my PC does not want to bind socket to multicast address, simply says: Cannot assign requested address

But at least between devices it works

And also found out better docs for Lua Sockets
https://github.com/sam-github/luasocket/tree/unstable/doc

A lot of undocumented features are there, for example, multicast

ar2rsawseen · June 2012

Current result:

It now seems obvious, that another thread is needed.

Right now I'm using Timer, which at least does not block UI completely (like loop), but still it's too slow

Any hacks for separate thread?

ar2rsawseen · June 2012

It must be magic, but every time I write here, I get back to the project and resolve the question I posted here. That's why I'm kind of talking to myself here, and will continue to do it

But well, it seems that by setting timeout to 0, then sockets are completely not blocking UI.

Result is much better:

atilim · June 2012

looks great! I'm enjoying this thread a lot.

atilim · June 2012

@ar2rsawseen also did you try copas? http://keplerproject.github.com/copas/

ar2rsawseen · June 2012

No, haven't tried it. Right now I'm ok on my own

Well actually, I came to an idea to develop a little LuaSocket framework for Gideros, let's call it "Unite" for now.
It would allow to create servers on mobile phone, discover other phones, allow other phones to join the server and then call Gideros functions on other devices through network.

The video that was posted before will be an example app for this framework. First version will be far from production version, and I'll need you guys to test it too, because as I said I have little knowledge of networking, all I did was through experiments, what works and what is not. So I'm more than sure I didn't cover all scenarios.

Hopefully I'll be done by the weekend and then post you guys to try it out.

ar2rsawseen · June 2012

But all in all, yeah a lot of new stuff, for example, you can't send tcp message, without new line symbol in the end of message. (Took me couple of hours to figure out)

and a lot of this kind of stuff

Mells · June 2012

@ar2rsawseen I totally don't understand how you do this but I can see how this would be useful., nice work.

ar2rsawseen · June 2012

Well I'll also try to post a more detail tutorial on how things work.
Examples for both tcp (server/client) udp (server/client), udp(broadcast/multicast)
That should clear up some things

I probably haven't mentioned, but that's actually my homework for Networking course in University. Build your own communication protocol on top of tcp or udp and create an application using it. (Bonus points if it's a mobile application)

So this was a no brainer, where and how I should create it

Michal · June 2012

But all in all, yeah a lot of new stuff, for example, you can't send tcp message, without new line symbol in the end of message. (Took me couple of hours to figure out)

I think you are wrong here. Sending out is not buffered by LuaSocket, you can verify this with some network sniffer (like wireshark).
But if you are reading data with receive('*l'), then the client waits for the new line. You should then use receive('*a') or receive(8192) (or any other burref size).

BTW, your example would work faster if you used UDP instead of TCP. You can check this out: https://love2d.org/forums/viewtopic.php?f=3&t=3289&start=10#p33373

ar2rsawseen · June 2012

Finally someone who understands something.

Thank you.

Well I agree UDP works faster, right now I'm struggling with optimizing TCP, to catch up with UDP speed. I just can't believe that difference is so huge, I must be simply doing something wrong with TCP.

But as I understood, then you can't rely on UDP to deliver the packages, if for example one of the devices looses the connection, and then establishes it again. TCP however would still deliver them. Am I right?

Meaning how much can I rely on UDP?

Michal · June 2012

If you have followed the link I gave you, you should also read some previous messages on that forum. In short: for 99,9% you can rely on UDP, and on top of the UDP you can send/receive PING packets to discover closed connections. Download the archive MultiCircles.zip and read MultiCircles/UDPIPE.txt

ar2rsawseen · June 2012

I completely agree that if everyone is connected udp is as almost as reliable as tcp, but my question was about situation, when device looses connection and reconnects.

Well, although I managed to get almost as same speed as with udp (by changing, reading/listening order), I guess, I could leave it as an option, what to use udp of tcp

Michal · June 2012

FYI: UDP is connectionless protocol: you send out a packet, and it either gets delivered or not (and that is why it is faster than TCP). With TCP, every packet delivered has to be ACKnowledged, which causes delays.
Other use of UDP is hole punching: connecting two devices which are behind a NAT. TCP would not work, UDP usually would work.

ar2rsawseen · June 2012

So I added a project for anyone who wants to test. Consider it version 0.1.
You need to start project simultaneously on multiple devices (or PC and device, also with some PC's, depending on configuration, firewall, etc discovering might not work).

Then select one of them as server, and on other devices select option to join.

Then there will be list of servers, to which you can join, then on server device you need to accept this device. Then on clients device a button draw will appear, when you accept all clients you want, you may start drawing together

You can check the code and comments right now, if you want to know more.
File Unite.lua contains the Server and Client classes,
new_server.lua is the scene for servers
join_server.lua is the scene for clients
and in draw.lua is the scene of drawing, where it does not matter anymore whether you are server or client, you simply call functions on all other devices and that's it.

So tell me what you think and if it even works on your devices in your LAN.

techdojo · June 2012

Amazing - didn't work from PC to device (at work - not surprising), however @Scouser and I both linked our ZTE-Blades and it just worked!!!

I was going to try linking my iPod to my Blade but the player on my iPod is out of date and doesn't have the socket module in it

yvz5 · June 2012

great job!

i was looking to find a way to stream pc's sound output to my mobile. for example, i wanna watch a movie but its quite late at home and i wanna lay on my bed but i dont have a headset with a long cable. so a server app runs on pc and handles the sound output and sends it throughout tcp or udp protocol to the client(my mobile). but it was soooooo dificult to do it on my symbian phone.

techdojo · June 2012

Talk about an over engineered solution

Interesting idea (and potentially useful for other apps), but wouldn't getting some kind of audio extension cable be easier?

Michal · June 2012

great job!

i was looking to find a way to stream pc's sound output to my mobile. for example, i wanna watch a movie but its quite late at home and i wanna lay on my bed but i dont have a headset with a long cable. so a server app runs on pc and handles the sound output and sends it throughout tcp or udp protocol to the client(my mobile). but it was soooooo dificult to do it on my symbian phone.

You should look for UPNP server (or a stand-alone external disk with such a server) and a UPNP player for your phone. Works for me.

yvz5 · June 2012

Talk about an over engineered solution
Interesting idea (and potentially useful for other apps), but wouldn't getting some kind of audio extension cable be easier?

it would be easier, but where is the innovation part ? :P

You should look for UPNP server (or a stand-alone external disk with such a server) and a UPNP player for your phone. Works for me.

i ll give it a try

techdojo · June 2012

it would be easier, but where is the innovation part ? :P

Fair point - can't argue with that

TokyoDan · October 2012

I did the same thing back in June. I made an AI server that acts as the 2nd player in my game. The game was created in Corona (sorry. I want to port it to Gideros as I'm sick of Corona) but the server part is pure Lua with LuaSocket. The server will handle multiple clients playing completely separate games.

TokyoDan · October 2012

I forgot to mention that the server is not a compiled standalone app. It is just a Lua script that runs in the iLuaBox app.

ar2rsawseen · October 2012

Wow, that is awesome. I imagine how well it could be used for application testing.
Is there any intention of sharing the code on specific license?

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