Improper State Changing when Crouching with a item in Offhand

[smell-of-curry]

Currently when you whole a shield (or any other item) in your offhand, then crouch. Once you uncrouch and check your inventory you will notice that you are no longer able to remove the shield from your offhand slot.

[Happy2018new]

This is because gophertunnel not really store blockingTick when marshal a shield item stack / item instance.
In the other words, gophertunnel always read this field and discard it, and always write 0 when encoding.

Therefore, to fix this (shield problem), you can store BlockingTick into protocol.ItemStack like this.

Then, read/write blocking tick by using this new field.

By the way, I don't know why gophertunnel not store this field, so I'm not sure if I need to open a Pull Request to fix this.

[Happy2018new]

Or this code can also solve this issue, although it is ugly.

			if p, ok := pk.(*packet.InventoryContent); ok {
				if p.WindowID == protocol.WindowIDOffHand && len(p.Content) == 1 {
					newerPacket := packet.InventoryContent{
						WindowID:    p.WindowID,
						Content:     make([]protocol.ItemInstance, 1),
						Container:   protocol.FullContainerName{},
						StorageItem: protocol.ItemInstance{},
					}
					newerPacket.Content[0].Stack = p.Content[0].Stack
					newerPacket.Content[0].Stack.NBTData = map[string]any{"Happy2018new": "ANYTHING"}
					conn.WritePacket(&newerPacket)
				}
			}

[JAMadison]

Confirming fix and providing implementation details

I've implemented and tested the fix suggested by @Happy2018new - it completely resolves the shield stuck issue.

Here are the minimal changes needed:

minecraft/protocol/item.go - Add to ItemStack struct:
// BlockingTick is the tick at which a shield started blocking.
BlockingTick int64

minecraft/protocol/reader.go - In both ItemInstance and Item methods, replace:
var blockingTick int64
bufReader.Int64(&blockingTick)
with:
bufReader.Int64(&x.BlockingTick)

minecraft/protocol/writer.go - In both ItemInstance and Item methods, replace:
var blockingTick int64
bufWriter.Int64(&blockingTick)
with:
bufWriter.Int64(&x.BlockingTick)

Tested with gophertunnel v1.52.2 on a proxy setup - shields now properly preserve their blocking state through inventory updates.