Questions about SRB2's netcode

[Kaysakado]

(Can't be arsed to look through the source, and I want to see if something is possible before attempting it)

1. SRB2's netcode basically works by the client sending the button-press (and any relevant console commands) to the host, and then the host sending it to all the clients, right? (If the answer to this is no, ignore the rest of my post)

2. And so clag is caused because it takes time for the button-press to go to the host and back to the client, and the client doesn't actually move until they recieve the button-press they originally sent, right?

3. If so, would it be possible for a modified server-side EXE to stop a player from moving, for example, by ignoring the data sent by the client? If so, would this cause C-Fails?

4. In that case, what about even modifying the button-press sent back to the client so that they move differently? Would this cause c-fails?

Of course, I wouldn't use it for something like that, more like stuff like coloring names and muting people.

EDIT: Also, how does randomized stuff work? Does it come out differently for everyone and cause cfails, or is it just randomized server-side and sent out to all the clients?

 

[Oogaland]

1. SRB2's netcode basically works by the client sending the button-press (and any relevant console commands) to the host, and then the host sending it to all the clients, right? (If the answer to this is no, ignore the rest of my post)

It's not exactly the button-press that's sent, but that's broadly right.

2. And so clag is caused because it takes time for the button-press to go to the host and back to the client, and the client doesn't actually move until they recieve the button-press they originally sent, right?

Pretty much. Remember that everything is synchronised into tics, though.

3. If so, would it be possible for a modified server-side EXE to stop a player from moving, for example, by ignoring the data sent by the client? If so, would this cause C-Fails?

Should be okay, although I haven't checked in detail.

4. In that case, what about even modifying the button-press sent back to the client so that they move differently? Would this cause c-fails?

Ditto.

Of course, I wouldn't use it for something like that, more like stuff like coloring names and muting people.

You probably wouldn't want to do those things at such a low level.

EDIT: Also, how does randomized stuff work? Does it come out differently for everyone and cause cfails, or is it just randomized server-side and sent out to all the clients?

There's a table of 'random' numbers, and everyone agrees which one comes next.

 

[Kaysakado]

Of course, I wouldn't use it for something like that, more like stuff like coloring names and muting people.

You probably wouldn't want to do those things at such a low level.

What do you mean?

EDIT: Also, how does randomized stuff work? Does it come out differently for everyone and cause cfails, or is it just randomized server-side and sent out to all the clients?

There's a table of 'random' numbers, and everyone agrees which one comes next.

What do you mean?

 

[SSNTails]

Computers are not capable of generating truly random numbers.

 

[Oogaland]

Of course, I wouldn't use it for something like that, more like stuff like coloring names and muting people.

You probably wouldn't want to do those things at such a low level.

What do you mean?

Don't mix game logic in with the network logic. For example, muting should be handled by the code that currently handles chat, not the packet-processing stuff.

EDIT: Also, how does randomized stuff work? Does it come out differently for everyone and cause cfails, or is it just randomized server-side and sent out to all the clients?

There's a table of 'random' numbers, and everyone agrees which one comes next.

What do you mean?

static byte rndtable[256] =
{
	0,   8, 109, 220, 222, 241, 149, 107,  75, 248, 254, 140,  16,  66,
	74,  21, 211,  47,  80, 242, 154,  27, 205, 128, 161,  89,  77,  36,
	95, 110,  85,  48, 212, 140, 211, 249,  22,  79, 200,  50,  28, 188,
	52, 140, 202, 120,  68, 145,  62,  70, 184, 190,  91, 197, 152, 224,
	149, 104,  25, 178, 252, 182, 202, 182, 141, 197,   4,  81, 181, 242,
	145,  42,  39, 227, 156, 198, 225, 193, 219,  93, 122, 175, 249,   0,
	175, 143,  70, 239,  46, 246, 163,  53, 163, 109, 168, 135,   2, 235,
	25,  92,  20, 145, 138,  77,  69, 166,  78, 176, 173, 212, 166, 113,
	94, 161,  41,  50, 239,  49, 111, 164,  70,  60,   2,  37, 171,  75,
	136, 156,  11,  56,  42, 146, 138, 229,  73, 146,  77,  61,  98, 196,
	135, 106,  63, 197, 195,  86,  96, 203, 113, 101, 170, 247, 181, 113,
	80, 250, 108,   7, 255, 237, 129, 226,  79, 107, 112, 166, 103, 241,
	24, 223, 239, 120, 198,  58,  60,  82, 128,   3, 184,  66, 143, 224,
	145, 224,  81, 206, 163,  45,  63,  90, 168, 114,  59,  33, 159,  95,
	28, 139, 123,  98, 125, 196,  15,  70, 194, 253,  54,  14, 109, 226,
	71,  17, 161,  93, 186,  87, 244, 138,  20,  52, 123, 251,  26,  36,
	17,  46,  52, 231, 232,  76,  31, 221,  84,  37, 216, 165, 212, 106,
	197, 242,  98,  43,  39, 175, 254, 145, 190,  84, 118, 222, 187, 136,
	120, 163, 236, 249
};

If you just called rand() for things that affect gameplay, you would indeed get c-fails.

 

[Kaysakado]

Ah, I see.