Let's consider the class net.minecraft.network.NetHandlerPlayServer

The method processUseEntity handles interactions with entities:

 

public void processUseEntity(C02PacketUseEntity packetIn)
{
    WorldServer worldserver = this.serverController.worldServerForDimension(this.playerEntity.dimension);
    Entity entity = packetIn.getEntityFromWorld(worldserver);
    this.playerEntity.markPlayerActive();

    if (entity != null)
    {
        boolean flag = this.playerEntity.canEntityBeSeen(entity);
        double d0 = 36.0D;

        if (!flag)
        {
            d0 = 9.0D;
        }

        if (this.playerEntity.getDistanceSqToEntity(entity) < d0)
        {
            if (packetIn.getAction() == C02PacketUseEntity.Action.INTERACT)
            {
                this.playerEntity.interactWith(entity);
            }
            else if (packetIn.getAction() == C02PacketUseEntity.Action.ATTACK)
            {
                if (entity instanceof EntityItem || entity instanceof EntityXPOrb || entity instanceof EntityArrow || entity == this.playerEntity)
                {
                    this.kickPlayerFromServer("Attempting to attack an invalid entity");
                    this.serverController.logWarning("Player " + this.playerEntity.getCommandSenderName() + " tried to attack an invalid entity");
                    return;
                }

                this.playerEntity.attackTargetEntityWithCurrentItem(entity);
            }
        }
    }
}

 

Why does it allow to attack within 6 blocks?

What is going to break in the game if I skip attacks with distance more than 2 or something like that?

26 minutes ago, ZhabaKlava said:

Why does it allow to attack within 6 blocks?

Because the player's reach is 5 blocks and this method allows anything within less than 6 blocks to be attacked.

 

26 minutes ago, ZhabaKlava said:

What is going to break in the game if I skip attacks with distance more than 2 or something like that?

The combat will break completely because the player won't be able to attack anything that isn't extremely close to them. And it won't prevent the "kill aura" anyway.

 

As a side note - what version of the game are you talking about? This method is different in the latest version. In fact since it doesn't check the thread the packet is received on I suspect this is 1.7 or earlier but I might be incorrect.

But using legal mouse clicks it is not possible to attack even within 4 blocks, is it?
The code is from 1.7.10 but I guess this behavior hasn't changed in further versions.

10 minutes ago, ZhabaKlava said:

it is not possible to attack even within 4 blocks, is it?

It is possible to attack up to the block reach distance in creative mode. Which is 6 blocks.

 

10 minutes ago, ZhabaKlava said:

The code is from 1.7.10

1.7.10 is no longer supported on these forums.

27 minutes ago, V0idWa1k3r said:

It is possible to attack up to the block reach distance in creative mode. Which is 6 blocks. 

Yeah, but what about survival. You can't attack within 4 blocks which is block reach distance in survival mode.

 

EDIT:

I see it is possible within less than 4. But the code doesn't check if you are in creative mode, so you can attack within less than 6 blocks while being in survival mode using cheats.

Edited October 21, 20186 yr by ZhabaKlava

1 hour ago, ZhabaKlava said:

I see it is possible within less than 4. But the code doesn't check if you are in creative mode, so you can attack within less than 6 blocks while being in survival mode using cheats.

This is so if you are lagging and the entity you're trying to attack has moved away from you before you have noticed it.