Add client abridged protocol

wrappers/packetack/client_abridged.go

@@ -0,0 +1,119 @@
+package packetack
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net"
+
+	"go.uber.org/zap"
+
+	"github.com/9seconds/mtg/conntypes"
+	"github.com/9seconds/mtg/utils"
+)
+
+const (
+	clientAbridgedSmallPacketLength = 0x7f
+	clientAbridgedQuickAckLength    = 0x80
+	clientAbridgedLargePacketLength = 16777216 // 256 ^ 3
+)
+
+type wrapperClientAbridged struct {
+	parent conntypes.StreamReadWriteCloser
+}
+
+func (w *wrapperClientAbridged) Read(acks *conntypes.ConnectionAcks) (conntypes.Packet, error) {
+	buf := bytes.Buffer{}
+
+	if _, err := io.CopyN(&buf, w.parent, 1); err != nil {
+		return nil, fmt.Errorf("cannot read message length: %w", err)
+	}
+	msgLength := uint32(buf.Bytes()[0])
+	buf.Reset()
+
+	if msgLength >= clientAbridgedQuickAckLength {
+		acks.Quick = true
+		msgLength -= clientAbridgedQuickAckLength
+	}
+
+	if msgLength == clientAbridgedSmallPacketLength {
+		if _, err := io.CopyN(&buf, w.parent, 3); err != nil {
+			return nil, fmt.Errorf("cannot read correct message length: %w", err)
+		}
+		number := utils.Uint24{}
+		copy(number[:], buf.Bytes())
+		msgLength = utils.FromUint24(number)
+	}
+	msgLength *= 4
+
+	buf.Reset()
+	if _, err := io.CopyN(&buf, w.parent, int64(msgLength)); err != nil {
+		return nil, fmt.Errorf("cannot read message: %w", err)
+	}
+
+	return conntypes.Packet(buf.Bytes()), nil
+}
+
+func (w *wrapperClientAbridged) Write(packet conntypes.Packet, acks *conntypes.ConnectionAcks) error {
+	if len(packet)%4 != 0 {
+		return fmt.Errorf("incorrect packet length %d", len(packet))
+	}
+
+	if acks.Simple {
+		if _, err := w.parent.Write(utils.ReverseBytes(packet)); err != nil {
+			return fmt.Errorf("cannot send a simpleacked packet: %w", err)
+		}
+		return nil
+	}
+
+	packetLength := len(packet) / 4
+	switch {
+	case packetLength < clientAbridgedSmallPacketLength:
+		data := append([]byte{byte(packetLength)}, packet...)
+		if _, err := w.parent.Write(data); err != nil {
+			return fmt.Errorf("cannot send small packet: %w", err)
+		}
+		return nil
+
+	case packetLength < clientAbridgedLargePacketLength:
+		length24 := utils.ToUint24(uint32(packetLength))
+		buf := bytes.Buffer{}
+
+		buf.WriteByte(byte(clientAbridgedSmallPacketLength))
+		buf.Write(length24[:])
+		buf.Write(packet)
+
+		if _, err := w.parent.Write(buf.Bytes()); err != nil {
+			return fmt.Errorf("cannot send large packet: %w", err)
+		}
+		return nil
+	}
+
+	return fmt.Errorf("packet is too big: %d", len(packet))
+}
+
+func (w *wrapperClientAbridged) Close() error {
+	return w.parent.Close()
+}
+
+func (w *wrapperClientAbridged) Conn() net.Conn {
+	return w.parent.Conn()
+}
+
+func (w *wrapperClientAbridged) LocalAddr() *net.TCPAddr {
+	return w.parent.LocalAddr()
+}
+
+func (w *wrapperClientAbridged) RemoteAddr() *net.TCPAddr {
+	return w.parent.RemoteAddr()
+}
+
+func (w *wrapperClientAbridged) Logger() *zap.SugaredLogger {
+	return w.parent.Logger().Named("client-abridged")
+}
+
+func NewClientAbridged(parent conntypes.StreamReadWriteCloser) conntypes.PacketAckFullReadWriteCloser {
+	return &wrapperClientAbridged{
+		parent: parent,
+	}
+}