Attribute Macro packet 

#[packet]

Attribute macro for protocol packet structs.

Generates Encode, Decode, EncodedSize implementations and a pub const PACKET_ID: i32 associated constant. The packet ID is NOT included in the wire format — it is only a declarative constant used by the packet registry for dispatch.

This replaces the need to manually derive all three traits on packet structs. Field attributes (#[field(varint)], etc.) work the same as with the individual derives.

Example

#[derive(Debug, Clone, PartialEq)]
#[packet(id = 0x00)]
pub struct HandshakePacket {
    #[field(varint)]
    pub protocol_version: i32,
    pub server_address: String,
    pub server_port: u16,
    #[field(varint)]
    pub next_state: i32,
}

assert_eq!(HandshakePacket::PACKET_ID, 0x00);