diff --git a/.github/workflows/go.yml b/.github/workflows/go.yml
index 89b0ded..1a2fe57 100644
--- a/.github/workflows/go.yml
+++ b/.github/workflows/go.yml
@@ -10,7 +10,7 @@ jobs:
     - name: Setup Go
       uses: actions/setup-go@v1
       with:
-        go-version: 1.18
+        go-version: 1.19
       id: go
 
     - name: Check out code into the Go module directory
diff --git a/bot/mcbot.go b/bot/mcbot.go
index 22dff86..2411d40 100644
--- a/bot/mcbot.go
+++ b/bot/mcbot.go
@@ -6,10 +6,7 @@ package bot
 
 import (
 	"context"
-	"encoding/base64"
-	"encoding/pem"
 	"errors"
-	"io"
 	"net"
 	"strconv"
 
@@ -79,22 +76,20 @@ func (c *Client) join(ctx context.Context, d *mcnet.Dialer, addr string) error {
 	}
 	// Login Start
 	c.KeyPair, err = user.GetOrFetchKeyPair(c.Auth.AsTk)
-	HasSignature := err == nil
+	KeyPair := pk.OptionEncoder[user.KeyPairResp]{
+		Has: err == nil,
+		Val: c.KeyPair,
+	}
 	c.UUID, err = uuid.Parse(c.Auth.UUID)
-	HasPlayerUUID := err == nil
+	PlayerUUID := pk.Option[pk.UUID, *pk.UUID]{
+		Has: err == nil,
+		Val: pk.UUID(c.UUID),
+	}
 	err = c.Conn.WritePacket(pk.Marshal(
 		packetid.LoginStart,
 		pk.String(c.Auth.Name),
-		pk.Boolean(HasSignature),
-		pk.Opt{
-			Has:   HasSignature,
-			Field: keyPair(c.KeyPair),
-		},
-		pk.Boolean(HasPlayerUUID),
-		pk.Opt{
-			Has:   HasPlayerUUID,
-			Field: pk.UUID(c.UUID),
-		},
+		KeyPair,
+		PlayerUUID,
 	))
 	if err != nil {
 		return LoginErr{"login start", err}
@@ -148,9 +143,10 @@ func (c *Client) join(ctx context.Context, d *mcnet.Dialer, addr string) error {
 				return LoginErr{"Login Plugin", err}
 			}
 
-			handler, ok := c.LoginPlugin[string(channel)]
-			if ok {
-				data, err = handler(data)
+			var PluginMessageData pk.Option[pk.PluginMessageData, *pk.PluginMessageData]
+			if handler, ok := c.LoginPlugin[string(channel)]; ok {
+				PluginMessageData.Has = true
+				PluginMessageData.Val, err = handler(data)
 				if err != nil {
 					return LoginErr{"Login Plugin", err}
 				}
@@ -158,8 +154,7 @@ func (c *Client) join(ctx context.Context, d *mcnet.Dialer, addr string) error {
 
 			if err := c.Conn.WritePacket(pk.Marshal(
 				packetid.LoginPluginResponse,
-				msgid, pk.Boolean(ok),
-				pk.Opt{Has: ok, Field: data},
+				msgid, PluginMessageData,
 			)); err != nil {
 				return LoginErr{"login Plugin", err}
 			}
@@ -167,24 +162,6 @@ func (c *Client) join(ctx context.Context, d *mcnet.Dialer, addr string) error {
 	}
 }
 
-type keyPair user.KeyPairResp
-
-func (k keyPair) WriteTo(w io.Writer) (int64, error) {
-	block, _ := pem.Decode([]byte(k.KeyPair.PublicKey))
-	if block == nil {
-		return 0, errors.New("pem decode error: no data is found")
-	}
-	signature, err := base64.StdEncoding.DecodeString(k.PublicKeySignature)
-	if err != nil {
-		return 0, err
-	}
-	return pk.Tuple{
-		pk.Long(k.ExpiresAt.UnixMilli()),
-		pk.ByteArray(block.Bytes),
-		pk.ByteArray(signature),
-	}.WriteTo(w)
-}
-
 type LoginErr struct {
 	Stage string
 	Err   error
diff --git a/chat/message.go b/chat/message.go
index 2195900..f8cab08 100644
--- a/chat/message.go
+++ b/chat/message.go
@@ -11,6 +11,7 @@
 package chat
 
 import (
+	"bytes"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -113,6 +114,7 @@ func (m Message) MarshalJSON() ([]byte, error) {
 
 // UnmarshalJSON decode json to Message
 func (m *Message) UnmarshalJSON(raw []byte) (err error) {
+	raw = bytes.TrimSpace(raw)
 	if len(raw) == 0 {
 		return io.EOF
 	}
diff --git a/go.mod b/go.mod
index f1c4a5d..e3cc9ba 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module github.com/Tnze/go-mc
 
-go 1.18
+go 1.19
 
 require (
 	github.com/google/uuid v1.1.1
diff --git a/net/packet/types.go b/net/packet/types.go
index 4d522f1..37eb68f 100644
--- a/net/packet/types.go
+++ b/net/packet/types.go
@@ -479,8 +479,8 @@ func (u *UUID) ReadFrom(r io.Reader) (n int64, err error) {
 	return int64(nn), err
 }
 
-func (p *PluginMessageData) WriteTo(w io.Writer) (n int64, err error) {
-	nn, err := w.Write(*p)
+func (p PluginMessageData) WriteTo(w io.Writer) (n int64, err error) {
+	nn, err := w.Write(p)
 	return int64(nn), err
 }
 
diff --git a/net/packet/util.go b/net/packet/util.go
index 2ef0d17..e0c7bc2 100644
--- a/net/packet/util.go
+++ b/net/packet/util.go
@@ -7,6 +7,12 @@ import (
 	"reflect"
 )
 
+var (
+	_ Field = (*Option[VarInt, *VarInt])(nil)
+	_ Field = (*Ary[VarInt])(nil)
+	_ Field = Tuple(nil)
+)
+
 // Ary is used to send or receive the packet field like "Array of X"
 // which has a count must be known from the context.
 //
@@ -19,16 +25,16 @@ import (
 // So it's allowed to directly set an integer type Len, but not a pointer.
 //
 // Note that Ary DO read or write the Len. You aren't need to do so by your self.
-type Ary[T VarInt | VarLong | Byte | UnsignedByte | Short | UnsignedShort | Int | Long] struct {
+type Ary[LEN VarInt | VarLong | Byte | UnsignedByte | Short | UnsignedShort | Int | Long] struct {
 	Ary interface{} // Slice or Pointer of Slice of FieldEncoder, FieldDecoder or both (Field)
 }
 
-func (a Ary[T]) WriteTo(w io.Writer) (n int64, err error) {
+func (a Ary[LEN]) WriteTo(w io.Writer) (n int64, err error) {
 	array := reflect.ValueOf(a.Ary)
 	for array.Kind() == reflect.Ptr {
 		array = array.Elem()
 	}
-	Len := T(array.Len())
+	Len := LEN(array.Len())
 	if nn, err := any(&Len).(FieldEncoder).WriteTo(w); err != nil {
 		return n, err
 	} else {
@@ -45,8 +51,8 @@ func (a Ary[T]) WriteTo(w io.Writer) (n int64, err error) {
 	return n, nil
 }
 
-func (a Ary[T]) ReadFrom(r io.Reader) (n int64, err error) {
-	var Len T
+func (a Ary[LEN]) ReadFrom(r io.Reader) (n int64, err error) {
+	var Len LEN
 	if nn, err := any(&Len).(FieldDecoder).ReadFrom(r); err != nil {
 		return nn, err
 	} else {
@@ -80,6 +86,12 @@ func Array(ary any) Field {
 	return Ary[VarInt]{Ary: ary}
 }
 
+// Opt is a optional [Field] which sending/receiving or not is depending on its Has field.
+// When calling `WriteTo()` or `ReadFrom()`, if Has is true, the Field's `WriteTo` or `ReadFrom()` is called.
+// Otherwise, it does nothing and return 0 and nil.
+//
+// The different between [Opt] and [Option] is that [Opt] does NOT read or write the Has field for you.
+// Which should be cared.
 type Opt struct {
 	Has   any // Pointer of bool, or `func() bool`
 	Field any // FieldEncoder, FieldDecoder, `func() FieldEncoder`, `func() FieldDecoder` or `func() Field`
@@ -133,7 +145,99 @@ func (o Opt) ReadFrom(r io.Reader) (int64, error) {
 	return 0, nil
 }
 
-type Tuple []interface{} // FieldEncoder, FieldDecoder or both (Field)
+type fieldPointer[T any] interface {
+	*T
+	FieldDecoder
+}
+
+// Option is a helper type for encoding/decoding these kind of packet:
+//
+//	+-----------+------------+----------------------------------------- +
+//	| Name      | Type       | Notes                                    |
+//	+-----------+------------+------------------------------------------+
+//	| Has Value | Boolean    | Whether or not the Value should be sent. |
+//	+-----------+------------+------------------------------------------+
+//	| Value     | Optional T | Only exist when Has Value is true.       |
+//	+-----------+------------+------------------------------------------+
+//
+// # Usage
+//
+// `Option[T]` implements [FieldEncoder] and `*Option[T]` implements [FieldDecoder].
+// That is, you can call `WriteTo()` and `ReadFrom()` methods on it.
+//
+//	var optStr Option[String]
+//	n, err := optStr.ReadFrom(r)
+//	if err != nil {
+//		// ...
+//	}
+//	if optStr.Has {
+//		fmt.Println(optStr.Val)
+//	}
+//
+// # Notes
+//
+// Currently we have to repeat T in the type arguments.
+//
+//	var opt Option[String, *String]
+//
+// Constraint type will inference makes it less awkward in the future.
+// See: https://github.com/golang/go/issues/54469
+type Option[T FieldEncoder, P fieldPointer[T]] struct {
+	Has Boolean
+	Val T
+}
+
+func (o Option[T, P]) WriteTo(w io.Writer) (n int64, err error) {
+	n1, err := o.Has.WriteTo(w)
+	if err != nil || !o.Has {
+		return n1, err
+	}
+	n2, err := o.Val.WriteTo(w)
+	return n1 + n2, err
+}
+
+func (o *Option[T, P]) ReadFrom(r io.Reader) (n int64, err error) {
+	n1, err := o.Has.ReadFrom(r)
+	if err != nil || !o.Has {
+		return n1, err
+	}
+	n2, err := P(&o.Val).ReadFrom(r)
+	return n1 + n2, err
+}
+
+// OptionDecoder is basiclly same with [Option], but support [FieldDecoder] only.
+// This allowed wrapping a [FieldDecoder] type (which isn't a [FieldEncoder]) to an Option.
+type OptionDecoder[T any, P fieldPointer[T]] struct {
+	Has Boolean
+	Val T
+}
+
+func (o *OptionDecoder[T, P]) ReadFrom(r io.Reader) (n int64, err error) {
+	n1, err := o.Has.ReadFrom(r)
+	if err != nil || !o.Has {
+		return n1, err
+	}
+	n2, err := P(&o.Val).ReadFrom(r)
+	return n1 + n2, err
+}
+
+// OptionEncoder is basiclly same with [Option], but support [FieldEncoder] only.
+// This allowed wrapping a [FieldEncoder] type (which isn't a [FieldDecoder]) to an Option.
+type OptionEncoder[T FieldEncoder] struct {
+	Has Boolean
+	Val T
+}
+
+func (o OptionEncoder[T]) WriteTo(w io.Writer) (n int64, err error) {
+	n1, err := o.Has.WriteTo(w)
+	if err != nil || !o.Has {
+		return n1, err
+	}
+	n2, err := o.Val.WriteTo(w)
+	return n1 + n2, err
+}
+
+type Tuple []any // FieldEncoder, FieldDecoder or both (Field)
 
 // WriteTo write Tuple to io.Writer, panic when any of filed don't implement FieldEncoder
 func (t Tuple) WriteTo(w io.Writer) (n int64, err error) {
diff --git a/net/packet/util_test.go b/net/packet/util_test.go
index dc147bf..101d3f1 100644
--- a/net/packet/util_test.go
+++ b/net/packet/util_test.go
@@ -138,16 +138,16 @@ func ExampleOpt_ReadFrom() {
 	// WILL NOT BE READ, WILL NOT BE COVERED
 }
 
+// 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.
 func ExampleOpt_ReadFrom_func() {
-	// 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{
@@ -188,3 +188,38 @@ func ExampleTuple_ReadFrom() {
 		panic(err)
 	}
 }
+
+// As an example, we define this packet as this:
+// +------+-----------------+-----------------------------------+
+// | Name | Type            | Notes                             |
+// +------+-----------------+-----------------------------------+
+// | Has  | Boolean         | True 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.
+func ExampleOption_ReadFrom_func() {
+	p1 := pk.Packet{Data: []byte{
+		0x01,                  // pk.Boolean(true)
+		4, 'T', 'n', 'z', 'e', // pk.String("Tnze")
+	}}
+	p2 := pk.Packet{Data: []byte{
+		0x00, // pk.Boolean(false)
+		// empty
+	}}
+
+	var User1, User2 pk.Option[pk.String, *pk.String]
+	if err := p1.Scan(&User1); err != nil {
+		panic(err)
+	}
+	if err := p2.Scan(&User2); err != nil {
+		panic(err)
+	}
+
+	fmt.Println(User1.Has, User1.Val)
+	fmt.Println(User2.Has, User2.Val)
+
+	// Output:
+	// true Tnze
+	// false
+}
diff --git a/server/auth/pubkey.go b/server/auth/pubkey.go
index 0001b8c..15824fc 100644
--- a/server/auth/pubkey.go
+++ b/server/auth/pubkey.go
@@ -17,7 +17,7 @@ type PublicKey struct {
 	Signature []byte
 }
 
-func (p *PublicKey) WriteTo(w io.Writer) (n int64, err error) {
+func (p PublicKey) WriteTo(w io.Writer) (n int64, err error) {
 	pubKeyEncoded, err := x509.MarshalPKIXPublicKey(p.PubKey)
 	if err != nil {
 		return 0, err
diff --git a/server/client.go b/server/client.go
index 8ae1e9e..244d8bd 100644
--- a/server/client.go
+++ b/server/client.go
@@ -4,6 +4,7 @@ import (
 	"container/list"
 	"strconv"
 	"sync"
+	"sync/atomic"
 
 	pk "github.com/Tnze/go-mc/net/packet"
 )
@@ -28,21 +29,27 @@ func (s WritePacketError) Unwrap() error {
 	return s.Err
 }
 
-type PacketQueue struct {
-	queue  *list.List
-	closed bool
-	cond   sync.Cond
+type PacketQueue interface {
+	Push(packet pk.Packet)
+	Pull() (packet pk.Packet, ok bool)
+	Close()
 }
 
-func NewPacketQueue() (p *PacketQueue) {
-	p = &PacketQueue{
+func NewPacketQueue() (p PacketQueue) {
+	p = &LinkedListPacketQueue{
 		queue: list.New(),
 		cond:  sync.Cond{L: new(sync.Mutex)},
 	}
 	return p
 }
 
-func (p *PacketQueue) Push(packet pk.Packet) {
+type LinkedListPacketQueue struct {
+	queue  *list.List
+	closed bool
+	cond   sync.Cond
+}
+
+func (p *LinkedListPacketQueue) Push(packet pk.Packet) {
 	p.cond.L.Lock()
 	if !p.closed {
 		p.queue.PushBack(packet)
@@ -51,7 +58,7 @@ func (p *PacketQueue) Push(packet pk.Packet) {
 	p.cond.L.Unlock()
 }
 
-func (p *PacketQueue) Pull() (packet pk.Packet, ok bool) {
+func (p *LinkedListPacketQueue) Pull() (packet pk.Packet, ok bool) {
 	p.cond.L.Lock()
 	defer p.cond.L.Unlock()
 	for p.queue.Front() == nil && !p.closed {
@@ -65,9 +72,36 @@ func (p *PacketQueue) Pull() (packet pk.Packet, ok bool) {
 	return
 }
 
-func (p *PacketQueue) Close() {
+func (p *LinkedListPacketQueue) Close() {
 	p.cond.L.Lock()
 	p.closed = true
 	p.cond.Broadcast()
 	p.cond.L.Unlock()
 }
+
+type ChannelPacketQueue struct {
+	c      chan pk.Packet
+	closed atomic.Bool
+}
+
+func (c ChannelPacketQueue) Push(packet pk.Packet) {
+	if c.closed.Load() {
+		return
+	}
+	select {
+	case c.c <- packet:
+	default:
+		c.closed.Store(true)
+	}
+}
+
+func (c ChannelPacketQueue) Pull() (packet pk.Packet, ok bool) {
+	if !c.closed.Load() {
+		packet, ok = <-c.c
+	}
+	return
+}
+
+func (c ChannelPacketQueue) Close() {
+	c.closed.Store(true)
+}
diff --git a/server/keepalive.go b/server/keepalive.go
index 826f629..861c18b 100644
--- a/server/keepalive.go
+++ b/server/keepalive.go
@@ -118,7 +118,6 @@ func (k *KeepAlive) tickPlayer(c KeepAliveClient) {
 	elem, ok := k.listIndex[c]
 	if !ok {
 		panic(errors.New("keepalive: fail to tick player: client not found"))
-		return
 	}
 	if elem.Prev() == nil {
 		if !k.waitTimer.Stop() {
@@ -156,7 +155,6 @@ func keepAliveSetTimer(l *list.List, timer *time.Timer, interval time.Duration)
 		}
 	}
 	timer.Reset(interval)
-	return
 }
 
 type keepAliveItem struct {
diff --git a/server/login.go b/server/login.go
index a256a62..acd0cf3 100644
--- a/server/login.go
+++ b/server/login.go
@@ -64,21 +64,13 @@ func (d *MojangLoginHandler) AcceptLogin(conn *net.Conn, protocol int32) (name s
 	}
 
 	var (
-		hasPubKey   pk.Boolean
-		pubKey      auth.PublicKey
-		hasUUID     pk.Boolean
-		profileUUID pk.UUID // ignored
+		pubKey      pk.Option[auth.PublicKey, *auth.PublicKey]
+		profileUUID pk.Option[pk.UUID, *pk.UUID] // ignored
 	)
 	err = p.Scan(
 		(*pk.String)(&name), // decode username as pk.String
-		&hasPubKey, pk.Opt{
-			Has:   &hasPubKey,
-			Field: &pubKey,
-		},
-		&hasUUID, pk.Opt{
-			Has:   &hasUUID,
-			Field: &profileUUID,
-		},
+		&pubKey,
+		&profileUUID,
 	)
 	if err != nil {
 		return
@@ -86,12 +78,12 @@ func (d *MojangLoginHandler) AcceptLogin(conn *net.Conn, protocol int32) (name s
 
 	// auth
 	if d.OnlineMode {
-		if hasPubKey {
-			if !pubKey.Verify() {
+		if pubKey.Has {
+			if !pubKey.Val.Verify() {
 				err = LoginFailErr{reason: chat.TranslateMsg("multiplayer.disconnect.invalid_public_key_signature")}
 				return
 			}
-			profilePubKey = &pubKey
+			profilePubKey = &pubKey.Val
 		} else if d.EnforceSecureProfile {
 			err = LoginFailErr{reason: chat.TranslateMsg("multiplayer.disconnect.missing_public_key")}
 			return
@@ -99,7 +91,7 @@ func (d *MojangLoginHandler) AcceptLogin(conn *net.Conn, protocol int32) (name s
 
 		var resp *auth.Resp
 		// Auth, Encrypt
-		resp, err = auth.Encrypt(conn, name, pubKey.PubKey)
+		resp, err = auth.Encrypt(conn, name, pubKey.Val.PubKey)
 		if err != nil {
 			return
 		}
diff --git a/yggdrasil/user/user.go b/yggdrasil/user/user.go
index e86b204..b062ea2 100644
--- a/yggdrasil/user/user.go
+++ b/yggdrasil/user/user.go
@@ -1,10 +1,16 @@
 package user
 
 import (
+	"encoding/base64"
 	"encoding/json"
+	"encoding/pem"
+	"errors"
 	"fmt"
+	"io"
 	"net/http"
 	"time"
+
+	pk "github.com/Tnze/go-mc/net/packet"
 )
 
 var ServicesURL = "https://api.minecraftservices.com"
@@ -21,6 +27,22 @@ type KeyPairResp struct {
 	RefreshedAfter     time.Time `json:"refreshedAfter"`
 }
 
+func (k KeyPairResp) WriteTo(w io.Writer) (int64, error) {
+	block, _ := pem.Decode([]byte(k.KeyPair.PublicKey))
+	if block == nil {
+		return 0, errors.New("pem decode error: no data is found")
+	}
+	signature, err := base64.StdEncoding.DecodeString(k.PublicKeySignature)
+	if err != nil {
+		return 0, err
+	}
+	return pk.Tuple{
+		pk.Long(k.ExpiresAt.UnixMilli()),
+		pk.ByteArray(block.Bytes),
+		pk.ByteArray(signature),
+	}.WriteTo(w)
+}
+
 func GetOrFetchKeyPair(accessToken string) (KeyPairResp, error) {
 	return fetchKeyPair(accessToken) // TODO: cache
 }