[ENet-discuss] A query about channels

[M. Rijks]

Isn't it better to serialize the struct somehow? There are a few  
reasons I'd do this:

1. Structs can't contain strings (or other data types) that have  
arbitrary length, and maxing them out towards some convenient maximum  
is expensive in terms of message size.
2. You can remain forward/backward compatibility of structs between  
versions of your games, by ignoring missing or unknown data.
3. You do not have to send all struct data if you don't need to.

A practical example is a session information message - I'd like it to  
contain - or not - a session ID, sesion name, session owner name,  
maximum amount of players, current amount of players, map data,  
session settings, et cetera. But not necessarily all.

I'm not at home in C++ far enough to know if struct fields can be  
accessed by index somehow, but it would be easy to decompose a message  
- one byte to identify the struct, followed by a stream of fields each  
started with the index of the field in the struct (assuming 255  
members max) by which you can look up its size in the struct, and then  
know how many bytes this field should take from the message.

Would really make it easy to serialize just about any struct. Speaking  
of which, when receiving any kind of struct (serialized or not) it  
does seem to make sense to check the incoming struct size and see if  
it matches your own, or you may crash your server. I'm thinking about  
malevolent players intercepting packages, changing the size and then  
reapplying the CRC to pass it under ENet's radar.


Quoting Jay Sprenkle <jsprenkle at gmail.com>:

> A great way to do this. There are plenty of other ways. Just identify the
> data in any way you like so you can classify it on the receiver.
>
> 2010/1/17 Thorbjørn Lindeijer <bjorn at lindeijer.nl>
>
>> On Sun, Jan 17, 2010 at 19:50, Alex Milstead <alex.milstead at gatech.edu>
>> wrote:
>> > Also, Jay you mentioned earlier that it was easy to do simple data-type
>> > checking on the receiving end. I'm a bit of a fledgling network
>> programmer
>> > -- I'm still definitely becoming more acquainted the vast amount of
>> > unfamiliar programming techniques in this particular arena. The only
>> > surefire type-checking system I know about in programming is in java
>> (=/),
>> > with it's "instanceof" operator. As far as I know this type of mechanism,
>> or
>> > anything similar, doesn't really exist in C/C++. So my next question is,
>> if
>> > we're sending binary data along and receiving it as binary data, what's
>> the
>> > most efficient way of type-checking the probable struct being piped
>> through?
>>
>> You give it a number which designates its type. You'd usually prepend
>> such a number to each of your messages, so that you know how to
>> interpret them on the other end.
>>
>>
> Cause united breaks guitars
> http://www.youtube.com/watch?v=5YGc4zOqozo
>