CODEWITHSUNDEEP
javasocketsnio
connergdavis
connergdavis

Reputation: 303

Java NIO server how to read variable-len packets w/out any header

I'm learning to make Minecraft servers similar to Bukkit for fun. I've dealt with NIO before but not very much and not in a practical way. I'm encountering an issue right now where Minecraft has many variable-length packets and since there's not any sort of consistent "header" for these packets of data, NIO is doing this weird thing where it fragments packets because the data isn't always sent immediately in full.

I learned recently that this is a thing from this thread: Java: reading variable-size packets using NIO I'd rather not use Netty/MINA/etc. because I'd like to learn this all myself as I'm doing this for the education and not with the intention of making it some huge project.

So my question is, how exactly do I go about preventing this sort of fragmenting of packets? I tried using Nagle's algorithm in java.net.Socket#setTcpNoDelay(boolean on) but oddly enough, all this does is make it so that every single time the packet is sent, it's fragmented, whereas when I don't have it enabled, the first packet always comes through OK, and then the following packets become fragmented.

I followed the Rox Java NIO Tutorial pretty closely so I know this code should work, but that tutorial only went as far as echoing a string message back to peers, not complicated bytestreams.

Here's my code. For some context, I'm using Executor#execute(Runnable) to create the two threads. Since I'm still learning about threads and concurrency and trying to piece them together with networking, any feedback on that would be very appreciated as well!!

ServerSocketManager ServerDataManager

Thanks a lot, I know this is quite a bit of stuff to take in, so I can't thank you enough for taking the time to read & respond!!

Upvotes: 0

Views: 990

Answers (1)

xaxxon
xaxxon

Reputation: 19751

TCP is ALWAYS a stream of bytes. You don't get to control when you get them or how many you get. It can come in at any time with any amount. That's why protocols exist.

Headers are a common part of a protocol to tell you how much data you need to read before you have the whole message.

So the short answer here is: You can't.

Everything you're saying you don't want to do -- that's what you have to do.

Upvotes: 4

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