packet

package main

import (
	pk "github.com/VacPlusPlus/go-mc/net/packet"
)

func main() {
	var length pk.VarInt
	var data []pk.String

	var p pk.Packet // = conn.ReadPacket()
	if err := p.Scan(

		&length, // decode length first
		pk.Ary{ // then decode Ary according to length
			Len: &length,
			Ary: &data,
		},
	); err != nil {
		panic(err)
	}
}

Output:

package main

import (
	pk "github.com/VacPlusPlus/go-mc/net/packet"
)

func main() {
	data := []pk.Int{0, 1, 2, 3, 4, 5, 6}
	// Len is completely ignored by WriteTo method.
	// The length is inferred from the length of Ary.
	pk.Marshal(
		0x00,
		// It's important to remember that
		// typically the responsibility of
		// sending the length field
		// is on you.
		pk.VarInt(len(data)),
		pk.Ary{
			Len: len(data), // this line can be removed
			Ary: data,
		},
	)
}

Output:

package main

import (
	"fmt"

	pk "github.com/VacPlusPlus/go-mc/net/packet"
)

func main() {
	var has pk.Boolean

	var data pk.String
	p1 := pk.Packet{Data: []byte{
		0x01,                  // pk.Boolean(true)
		4, 'T', 'n', 'z', 'e', // pk.String
	}}
	if err := p1.Scan(
		&has,
		pk.Opt{
			Has: &has, Field: &data,
		},
	); err != nil {
		panic(err)
	}
	fmt.Println(data)

	var data2 pk.String = "WILL NOT BE READ, WILL NOT BE COVERED"
	p2 := pk.Packet{Data: []byte{
		0x00, // pk.Boolean(false)
		// empty
	}}
	if err := p2.Scan(
		&has,
		pk.Opt{
			Has: &has, Field: &data2,
		},
	); err != nil {
		panic(err)
	}
	fmt.Println(data2)

}

Output:

Tnze
WILL NOT BE READ, WILL NOT BE COVERED

package main

import (
	"fmt"

	pk "github.com/VacPlusPlus/go-mc/net/packet"
)

func main() {
	// As an example, we define this packet as this:
	// +------+-----------------+----------------------------------+
	// | Name | Type            | Notes                            |
	// +------+-----------------+----------------------------------+
	// | Flag | Unsigned Byte   | Odd if the following is present. |
	// +------+-----------------+----------------------------------+
	// | User | Optional String | The player's name.               |
	// +------+-----------------+----------------------------------+
	// So we need a function to decide if the User field is present.
	var flag pk.Byte
	var data pk.String
	p := pk.Packet{Data: []byte{
		0b_0010_0011,          // pk.Byte(flag)
		4, 'T', 'n', 'z', 'e', // pk.String
	}}
	if err := p.Scan(
		&flag,
		pk.Opt{
			Has: func() bool {
				return flag&1 != 0
			},
			Field: &data,
		},
	); err != nil {
		panic(err)
	}
	fmt.Println(data)

}

Output:

Tnze

package main

import (
	"fmt"

	_ "embed"
	pk "github.com/VacPlusPlus/go-mc/net/packet"
)

//go:embed joingame_test.bin
var testJoinGameData []byte

func main() {
	p := pk.Packet{ID: 0x24, Data: testJoinGameData}
	var (
		EID            pk.Int
		Hardcore       pk.Boolean
		Gamemode       pk.UnsignedByte
		PreGamemode    pk.Byte
		WorldCount     pk.VarInt
		WorldNames     = make([]pk.Identifier, 0) // This cannot replace with "var WorldNames []pk.Identifier" because "nil" has no type information
		DimensionCodec struct {
			DimensionType interface{} `nbt:"minecraft:dimension_type"`
			WorldgenBiome interface{} `nbt:"minecraft:worldgen/biome"`
		}
		Dimension                 interface{}
		WorldName                 pk.Identifier
		HashedSeed                pk.Long
		MaxPlayers                pk.VarInt
		ViewDistance              pk.VarInt
		RDI, ERS, IsDebug, IsFlat pk.Boolean
	)
	err := p.Scan(
		&EID,
		&Hardcore,
		&Gamemode,
		&PreGamemode,
		&WorldCount,
		pk.Ary{
			Len: &WorldCount,
			Ary: &WorldNames,
		},
		pk.NBT(&DimensionCodec),
		pk.NBT(&Dimension),
		&WorldName,
		&HashedSeed,
		&MaxPlayers,
		&ViewDistance,
		&RDI, &ERS, &IsDebug, &IsFlat,
	)
	fmt.Print(err)
}

Output:

<nil>

package main

import (
	pk "github.com/VacPlusPlus/go-mc/net/packet"
)

func main() {
	// When you need to read an "Optional Array of X":
	var has pk.Boolean
	var arylen pk.Int
	var ary []pk.String

	var p pk.Packet // = conn.ReadPacket()
	if err := p.Scan(
		&has,
		pk.Opt{
			Has: &has,
			Field: pk.Tuple{
				&arylen,
				pk.Ary{
					Len: &arylen,
					Ary: &ary,
				},
			},
		},
	); err != nil {
		panic(err)
	}
}

Output: