diff --git a/packet.go b/packet.go
new file mode 100644
index 0000000..060362a
--- /dev/null
+++ b/packet.go
@@ -0,0 +1,56 @@
+package main
+
+const (
+	packetFlagControl     = 1
+	packetFlagResend      = 2
+	packetFlagCompression = 4
+	packetFlagConnless    = 8
+)
+
+type PacketFlags struct {
+	connless    bool
+	compression bool
+	resend      bool
+	control     bool
+}
+
+type PacketHeader struct {
+	flags     PacketFlags
+	ack       int
+	numChunks int
+	token     [4]byte
+}
+
+func (header *PacketHeader) unpack(packet []byte) {
+	header.flags.unpack(packet)
+	header.ack = (int(packet[0]&0x3) << 8) | int(packet[1])
+	header.numChunks = int(packet[2])
+	copy(header.token[:], packet[3:7])
+}
+
+func (flags *PacketFlags) unpack(packetHeaderRaw []byte) {
+	flagBits := packetHeaderRaw[0] >> 2
+	flags.control = (flagBits & packetFlagControl) != 0
+	flags.resend = (flagBits & packetFlagResend) != 0
+	flags.compression = (flagBits & packetFlagCompression) != 0
+	flags.connless = (flagBits & packetFlagConnless) != 0
+}
+
+func (flags *PacketFlags) pack() []byte {
+	data := 0
+
+	if flags.control {
+		data |= packetFlagControl
+	}
+	if flags.resend {
+		data |= packetFlagResend
+	}
+	if flags.compression {
+		data |= packetFlagCompression
+	}
+	if flags.connless {
+		data |= packetFlagConnless
+	}
+
+	return []byte{byte(data)}
+}
diff --git a/packet_test.go b/packet_test.go
new file mode 100644
index 0000000..c6e50dc
--- /dev/null
+++ b/packet_test.go
@@ -0,0 +1,172 @@
+package main
+
+import (
+	"reflect"
+	"slices"
+	"testing"
+)
+
+// pack
+
+func TestPackFlagsUnset(t *testing.T) {
+	flags := PacketFlags{
+		connless:    false,
+		compression: false,
+		resend:      false,
+		control:     false,
+	}
+
+	got := flags.pack()
+	want := []byte{0b0000}
+
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("got %v, wanted %v", got, want)
+	}
+}
+
+func TestPackFlagsCompressionSet(t *testing.T) {
+	flags := PacketFlags{
+		connless:    false,
+		compression: true,
+		resend:      false,
+		control:     false,
+	}
+
+	got := flags.pack()
+	want := []byte{0b0100}
+
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("got %v, wanted %v", got, want)
+	}
+}
+
+func TestPackFlagsAllSet(t *testing.T) {
+	flags := PacketFlags{
+		connless:    true,
+		compression: true,
+		resend:      true,
+		control:     true,
+	}
+
+	got := flags.pack()
+	want := []byte{0b1111}
+
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("got %v, wanted %v", got, want)
+	}
+}
+
+// unpack
+
+func TestUnpackFlagsAllSet(t *testing.T) {
+	got := PacketFlags{}
+	want := PacketFlags{
+		connless:    true,
+		compression: true,
+		resend:      true,
+		control:     true,
+	}
+
+	got.unpack([]byte{0b00111100})
+
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("got %v, wanted %v", got, want)
+	}
+}
+
+func TestUnpackFlagsControlSet(t *testing.T) {
+	got := PacketFlags{}
+	want := PacketFlags{
+		connless:    false,
+		compression: false,
+		resend:      false,
+		control:     true,
+	}
+
+	got.unpack([]byte{0b00000100})
+
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("got %v, wanted %v", got, want)
+	}
+}
+
+func TestUnpackFlagsUnset(t *testing.T) {
+	got := PacketFlags{}
+	want := PacketFlags{
+		connless:    false,
+		compression: false,
+		resend:      false,
+		control:     false,
+	}
+
+	got.unpack([]byte{0b00000000})
+
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("got %v, wanted %v", got, want)
+	}
+}
+
+// packet header unpack
+
+func TestUnpackCloseWithReason(t *testing.T) {
+	got := PacketHeader{}
+	want := PacketHeader{
+		flags: PacketFlags{
+			connless:    false,
+			compression: false,
+			resend:      false,
+			control:     true,
+		},
+		ack:       10,
+		numChunks: 0,
+		token:     [4]byte{0xcf, 0x2e, 0xde, 0x1d},
+	}
+
+	got.unpack(slices.Concat([]byte{0x04, 0x0a, 0x00, 0xcf, 0x2e, 0xde, 0x1d, 0x04}, []byte("shutdown"), []byte{0x00}))
+
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("got %v, wanted %v", got, want)
+	}
+}
+
+func TestUnpackHeaderFlagsControlSet(t *testing.T) {
+	got := PacketHeader{}
+	want := PacketHeader{
+		flags: PacketFlags{
+			connless:    false,
+			compression: false,
+			resend:      false,
+			control:     true,
+		},
+		ack:       0,
+		numChunks: 0,
+		token:     [4]byte{0xff, 0xff, 0xff, 0xff},
+	}
+
+	got.unpack([]byte{0b00000100, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff})
+
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("got %v, wanted %v", got, want)
+	}
+}
+
+func TestUnpackHeaderFlagsAllSet(t *testing.T) {
+	got := PacketHeader{}
+	want := PacketHeader{
+		flags: PacketFlags{
+			connless:    true,
+			compression: true,
+			resend:      true,
+			control:     true,
+		},
+		ack:       0,
+		numChunks: 0,
+		token:     [4]byte{0xff, 0xff, 0xff, 0xff},
+	}
+
+	got.unpack([]byte{0b00111100, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff})
+
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("got %v, wanted %v", got, want)
+	}
+}
diff --git a/teeworlds.go b/teeworlds.go
index efe33c2..b6ea3ba 100644
--- a/teeworlds.go
+++ b/teeworlds.go
@@ -1,4 +1,4 @@
-package teeworlds
+package main
 
 import (
 	"bufio"
diff --git a/teeworlds_test.go b/teeworlds_test.go
index f0e9727..a501db9 100644
--- a/teeworlds_test.go
+++ b/teeworlds_test.go
@@ -1,4 +1,4 @@
-package teeworlds
+package main
 
 import (
 	"testing"