How to safely separate packet data?

debugcn Published at Dev

Ladas125

I am creating a multiplayer game and not sure how should I separate packet data.

My packet structure looks like this (it is one string): id (separator) content

And the content sometimes also has multiple separators (to send more data in one packet)

But if my game had a chat (or any other user input), user could type the separator string and break the server. How can I prevent that?

Is there any other more safe way of sending network data than PrintWriter to the socket output stream?

Alec Teal

There are 3 solutions:

Termination character - strings often end with a literal 0 (a byte of value 0) - this isn't a character so you can tell when the string ends because it reads for example Alec0 where the 0 is a literal 0 not the letter. Because it doesn't map to a letter you KNOW that it ends the string. You could employ the same thing
A start character (not a good solution) suppose we start data with 0 instead (this works for streams) then you can processes 0msg0other as g must be the last of message because 0 starts a new incoming bit of data. Then the stream ends so the last bit must be other
The most common for protocols where the messages are defined (as for games) is so common it even has a name, https://en.wikipedia.org/wiki/Type-length-value - type length value (encoding).
Basically you say "the first 4 bytes are an integer denoted the message type" then the next 4 bytes is the length of the payload (the value) for example: 0x1 0x4 Alec denotes
- message type: 1
- length: 4
- data: Alec