Staying on a server for more than 24 hours crashes everyone

AgentK brings up a good point. We have to resend the data every time a player respawns or moves in/out of view. Not sure to what extent the client caches that data, but we shouldn't need to be resending it so often.

AgentK but they want user skin changes to be real time. Client side caching will make that not possible.

• EDIT -
  I was /partially/ wrong. Read this tweet for a more clear statement.
  https://twitter.com/Dinnerbone/status/422752438031241216

Actually, Anthony, as it is now, the vanilla server caches it from /hasJoined and resends the SAME (guaranteed by the client) data every time that the player object is spawned. This includes traveling out of view and traveling to other dimensions. Skins changes are not in realtime.

Since this is intentional to avoid the server faking or withholding a player's skin I'd suggest a non-avoidable kick somewhere around 24 hours after the player has joined the server.

Amaranth: Why on earth is it fair to punish a player (kicking them) for playing the game as intended?

They've stated they don't want the server to be able to screw with the skin in any way so what other option is there?

Skins should not have an expiry time. There's no way (as far as I'm aware) to give skins an expiry time and have them served server side.

Not only does this new method (server sending skins in player spawn packets) use magnitudes more data (skin data must be resent every respawn, move in/out of view, etc), but it also causes issues for players and could possibly let servers hold back skin changes.

You bring up the server being able to hold back a skin update (currently for up to 24 hours) and in the same comment suggest the solution to this problem is to not have an expiry?

Amaranth: The other option is to not serve skins from the server.... there's no way to let the server serve skins without somehow being able to tamper with them and use magnitudes more data than if Mojang just served the skins themselves. For example, right now, I can give my player with a skin a different name or even holdback a skin change for 24 hours. Neither of those would be possible if Mojang kept serving skins themselves.

MonsieurApple: Look a little closer at what Amaranth just said... The real reason for this change is so that servers can't provide /fake/ skins. Basically saying that they don't want serves having skinned NPCs or players posing as mojangstas. It has nothing to do with what players want obviously since the response is to kick players. I know first hand that players get a good laugh when killing the Notch NPC.

• EDIT -
  Oh, and it's an additional slap to servers for the increased bandwidth, however marginal it may be.

Anthony: If the real reason Mojang wants this is to prevent fake Notch NPCs, all they need to send with the player spawn packet is some sort of session ID. The client requests the skin using that session ID to see if Notch has actually joined the server. If it doesn't work out, the client falls back to a Steve skin.

Anthony: In addition, the current system does not prevent me from setting my user's skin to Notch then changing my overhead name to Notch (as far as I'm aware).

I'm a bit curious, if the reason for the change is to prevent NPC characters, is this tweet incorrect? https://twitter.com/_grum/status/454353805011079169

Also, an expire time only poses to prevent servers from serving old skins, rather than skins for incorrect players. This doesn't seem like it's a big enough deal to crash clients or force a disconnect after a certain time period.

The client verifies the skin blob exists, that it is signed and the signature is correct, that the blob hasn't expired, and that the UUID and name in the blob match what is in the packet. You couldn't pretend to be Notch unless he was on your server.

Amaranth: From what I originally saw only the UUIDs were verified to match. However, I suppose this could have changed when Grum decided to push an update today.

Easily fixed by kicking the player after 23h59m 🙂

This is a joke right?

@Grum That is not an acceptable response.

In the following situation:

• Fully vanilla server

• No server administrators present (gee, maybe they're sleeping?)

An unprivileged client is able to mount a Layer 7 denial of service attack on other players simply by being on a server for a day. Staying on a server for 24 hours is, although uncommon, a perfectly valid action by a player, and should not be arbitrarily prohibited. I highly suggest you come up with a more robust solution than that.

EDIT: This also gives server owners a "<strike>crash command</strike>" "nonstandard kick command" (a pattern Mojang has fixed in the past) - simply copy one of the skin data files to another folder and send it to anyone you don't like. Boom, repeated client <strike>crashes</strike> disconnects.

For all those worrying about NPCs no longer working (like Anthony), I'll quote fullwall (Lead developer of CitizensNPCs)

[22:13:48] <fullwall> mcmonkey: I have personally tested 1.7.7r2 with Citizens
[22:13:54] <fullwall> and it works.
...
[22:17:43] <mcmonkey> fullwall: Is it possible for NPCs to have skins in 1.7.7r2?
[22:17:52] <fullwall> mcmonkey: no, they have steve skins

So NPCs will still work, they just can't be skinned... so we're not /completely/ ruined. Disguising fun is gone though D:

Another side effect of this is it breaks things like https://miners-movies.com/ which is a really cool project that allows replaying of minecraft games. It's a shame to see cool projects like this and Citizens being negatively effected by these random restrictions. Officially supported or not, these projects are cool and represent the creative spirit that minecraft is supposed to be about (at least I thought) and skin can be served in a way that doesn't kill or maim projects like these.

This bug has literally halted production on a large server network due to release within the week.

Currently Grum plans to have clients kicked after 23 hours, 59 minutes.

This means that if the clients/server timestamps are more than 1 minute off. Players are still going to crash.
This would have to change to 23 hours, 30 minutes to be on the safe side.

And this does still not cover the common case where players modify their computers date/time.

That's just not acceptable at all. We need a legitimate fix, or just rollback the update and force a downgrade on minecraft as a whole until the idea is more thoroughly thought out and bug tested. Bug testing this stuff live and then throwing patches on it, does not make people happy. If anything it makes them more frustrated.

https://miners-movies.com/ programmer here. I'm affected by this as 1.8 will probably prevent my service from showing you recordings using the vanilla Minecraft client, therefore totally ruining the experience. I also suggest removing the timestamp that prevents using the skin after 24h.

According to Grum, old skins won't be deleted ever once uploaded to the server. So the combination of UUID and skin can be frozen in time without becoming invalid. Ignoring the expiration date would then only allow server owners to assign you a previous skin you used (if you have ever joined the server using that skin or acquired the hasJoined texture blob in any other way). It won't allow server owners to assign you skins you never used. On the other hand it would also allow server owners to spawn NPCs of players, provided they have their texture blob. Which might or might not be something mojang wants to prevent. :-\
Another solution (in my case) might be to have a Minecraft Client option that toggles whether the client checks the timestamp or not (Somewhere next to the "Allow colors in chat" maybe? "Show expired skins" (any other suggestion?)).

@mcmonkey, it only works like that in 1.7. In 1.8, spawning NPC won't be possible any longer unless you have the non-expired texture blob. If you spawn NPCs with an expire texture blob, all clients that receive the SpawnPlayer packet will disconnect.