1 files changed, 163 insertions, 0 deletions
diff --git a/internal/packet/packet.go b/internal/packet/packet.go
new file mode 100644
index 0000000..21ba0cc
--- /dev/null
+++ b/internal/packet/packet.go
@@ -0,0 +1,163 @@
+package packet
+
+import (
+	"encoding/binary"
+	"encoding/json"
+	"fmt"
+	"io"
+
+	"github.com/vmihailenco/msgpack/v5"
+
+	"github.com/kyren223/eko/pkg/assert"
+)
+
+type Encoding uint8
+
+func (e Encoding) String() string {
+	switch e {
+	case EncodingJson:
+		return "EncodingJson"
+	case EncodingMsgPack:
+		return "EncodingMsgPack"
+	case EncodingUnused1:
+		return "EncodingUnused1"
+	case EncodingUnused2:
+		return "EncodingUnused2"
+	default:
+		return fmt.Sprintf("EncodingInvalid(%v)", e)
+	}
+}
+
+func (e Encoding) IsSupported() bool {
+	switch e {
+	case EncodingJson, EncodingMsgPack:
+		return true
+	default:
+		return false
+	}
+}
+
+const (
+	EncodingJson Encoding = iota
+	EncodingMsgPack
+	EncodingUnused1
+	EncodingUnused2
+)
+
+type PacketType uint8
+
+func (t PacketType) String() string {
+	switch t {
+	case TypeEko:
+		return "PacketTypeEko"
+	case TypeError:
+		return "PacketTypeError"
+	default:
+		return fmt.Sprintf("PacketTypeInvalid(%v)", t)
+	}
+}
+
+func (e PacketType) IsSupported() bool {
+	switch e {
+	case TypeEko, TypeError:
+		return true
+	default:
+		return false
+	}
+}
+
+const (
+	TypeEko PacketType = iota
+	TypeError
+)
+
+const (
+	VERSION          = 1
+	PACKET_MAX_SIZE  = ^uint16(0)
+	PAYLOAD_MAX_SIZE = PACKET_MAX_SIZE - HEADER_SIZE
+	HEADER_SIZE      = 4
+	VERSION_OFFSET   = 0
+	TYPE_OFFSET      = 1
+	ENCODING_OFFSET  = 1
+	LENGTH_OFFSET    = 2
+)
+
+type PacketEncoder interface {
+	io.Reader
+	Encoding() Encoding
+	Type() PacketType
+}
+
+// The following diagram shows the packet structure:
+//
+//	 0                   1                   2                   3
+//	 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+//	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//	|    Version    |En.|    Type   |         Payload Length        |
+//	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//	|              Payload... Payload Length bytes ...              |
+//	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+type Packet struct {
+	data []byte
+}
+
+func NewPacket(encoder PacketEncoder) Packet {
+	data := make([]byte, PACKET_MAX_SIZE)
+
+	n, err := encoder.Read(data[HEADER_SIZE:])
+	assert.NoError(err, "packet encoder should never error when reading")
+
+	binary.BigEndian.PutUint16(data[LENGTH_OFFSET:], uint16(n))
+
+	data[VERSION_OFFSET] = VERSION
+
+	packetType, encoding := byte(encoder.Type()), byte(encoder.Encoding())
+	assert.Assert(packetType <= 63, "packet type exceeded allowed size type=%v", packetType)
+	assert.Assert(encoding <= 3, "encoding exceeded allowed permutations encoding=%v", encoding)
+	data[TYPE_OFFSET] = packetType | encoding<<6
+
+	return Packet{data[:HEADER_SIZE+n]}
+}
+
+func (p Packet) Version() uint8 {
+	return p.data[VERSION_OFFSET]
+}
+
+func (p Packet) Type() PacketType {
+	return PacketType(p.data[TYPE_OFFSET] & 63) // 2^6-1
+}
+
+func (p Packet) Encoding() Encoding {
+	return Encoding(p.data[ENCODING_OFFSET] >> 6)
+}
+
+func (p Packet) PayloadLength() uint16 {
+	return binary.BigEndian.Uint16(p.data[LENGTH_OFFSET:])
+}
+
+// The payload data, caller must not modify the returned slice, even temporarily
+func (p Packet) Payload() []byte {
+	return p.data[HEADER_SIZE:]
+}
+
+func (p Packet) DecodePayload(v *TypedMessage) error {
+	if p.Type() != (*v).Type() {
+		return fmt.Errorf("", p.Type(), (*v).Type())
+	}
+	switch p.Encoding() {
+	case EncodingJson:
+		return json.Unmarshal(p.Payload(), v)
+	case EncodingMsgPack:
+		return msgpack.Unmarshal(p.Payload(), v)
+	case EncodingUnused1:
+		fallthrough
+	case EncodingUnused2:
+		return fmt.Errorf("unsupported encoding: ", p.Encoding().String())
+	default:
+		assert.Unreachable("encoding from packet should always be valid encoding=%v", p.Encoding())
+	}
+}
+
+func (p Packet) Into(writer io.Writer) (int, error) {
+	return writer.Write(p.data[:len(p.data)])
+}