UDP Networking Question

[stormforce02]

When someone sends you packets of data to the server, how can you differentiate whether it's the first time or not?

[Robin]

How do you mean that?

We might be able to help you better if you say what it is you want to achieve.

[stormforce02]

I want to create a new player when someone connects. Also, to extend my question, how do I differentiate between the different data being sent to the server? ie player position, name, etc.

[Charles Randall]

Generally it's up to you to decide what the data is, and how to interpret it. A common method to do this is to pack data descriptors in with the data. So you might have a set of flags that represent what the data is, and send a flag before the data. So your data might look like this:

Flag: Player Name
"Bob"
Flag: Player Position
x, y

[flashkot]

When you receive packet, you also get originating ip and port. You can create table players and add each sender to it using ip as a key. Then just check if record exists in table.

For storing data in packet: check out my post viewtopic.php?f=5&t=10363 may be it will be helpful

[stormforce02]

Don't quite get how setting up flags before data works. Can you give me some example code?

[flashkot]

I think his idea was to just use words to distinguish one data type from another.

In Lua socket you are sending and receiving strings. So, you should send your data like this:

Code: Select all

udp = socket.udp()

udp:send("Name:KrimsonKing")
udp:send("Position:37,16")

On server side, you receive and process this packets like this

Code: Select all

data, msg_or_ip, port_or_nil = udp:receivefrom()

if data:sub(1, 4) == "Name" then
    Player.Name = data:sub(6)
elseif data:sub(1, 8) == "Position" then
    Player.x, Player.y = data:match("^Position%:(%d+)%,(%d+)$")
    -- This values are still strings. So convert them to numbers
    Player.x = tonumber(Player.x)
    Player.y = tonumber(Player.y)
end

Quite simple, if you not going to send huge amount of data in one packet. (theoretically UDP packet can be almost 64k bytes long, but network hardware may limit this to something about 512 bytes or so. In real world big packets can be simply dropped)

You also should note, that it is not guaranteed what order of received packets will match their sending order (In this example you can receive Position packet and only then packet with Name)

[stormforce02]

Alright, sounds simple enough. One last thing. I've trying looking in many different places, and I can't seem to find and proper documentation on what things like (%d+)% is an %a and %b, etc are. If you can give me a link, or even briefly explain it to me, it'd be very helpful.

[Santos]

They're called patterns!

http://www.lua.org/manual/5.1/manual.html#5.4.1
http://www.lua.org/pil/20.2.html
http://lua-users.org/wiki/PatternsTutorial
http://www.wowpedia.org/Pattern_matching