My packets are not sending properly from client to server -- they are staying on the client side. I checked the packet handler with World.isRemote, and it was always called on the client side. If you could help that'd be great.

 

Packet class: http://pastebin.com/suiV6Xx5 Packet handler Class: http://pastebin.com/Wn3YnuRV

Just to be sure, when isRemote is true then the code is running on the client. I'm writing it, because in your code you're sending packet client -> server. But in the incoming packet code is:

                        if(!world.isRemote){
                                PacketDispatcher.sendPacketToServer(packet);
                        }

~ On a server side if it is a server side you resend same packet to a server?

 

I compared it to mine packet handling and I can't see anything bad (I'm using getEffectiveSide but world object should carry same information).

You can take a look (it's functional code):

https://github.com/mnn/jaffas/blob/b6b35d87e3a00b2fa36baf297569982a38fd5250/src/minecraft/monnef/jaffas/food/common/SpawnStonePacketUtils.java

https://github.com/mnn/jaffas/blob/b6b35d87e3a00b2fa36baf297569982a38fd5250/src/minecraft/monnef/jaffas/food/common/PacketHandler.java

When I added that code to the packet handler it created an infinite loop, which resulted in a stack overflow.

That code snippet is from your packet handler. If you're talking about my code than you're doing something wrong.

 

My handler uses 2 types of packets and each type is strictly either client->server or server->client, so it's not possible to loop infinitely (one is request for update from client, second is update packet for client. on a second one client does not respond, so there can't be a loop).

Okay, thanks. I got it working.