mtg/wrappers/mtproto_abridged.go

package wrappers

import (
	"bytes"
	"io"
	"net"

	"github.com/juju/errors"
	"go.uber.org/zap"

	"github.com/9seconds/mtg/mtproto"
	"github.com/9seconds/mtg/utils"
)

const (
	mtprotoAbridgedSmallPacketLength = 0x7f
	mtprotoAbridgedQuickAckLength    = 0x80
	mtprotoAbridgedLargePacketLength = 16777216 // 256 ^ 3
)

// MTProtoAbridged presents abridged connection between client and
// middle proxy.
type MTProtoAbridged struct {
	conn   StreamReadWriteCloser
	opts   *mtproto.ConnectionOpts
	logger *zap.SugaredLogger

	readCounter  uint32
	writeCounter uint32
}

func (m *MTProtoAbridged) Read() ([]byte, error) {
	defer func() {
		m.readCounter++
	}()

	m.logger.Debugw("Read packet",
		"simple_ack", m.opts.ReadHacks.SimpleAck,
		"quick_ack", m.opts.ReadHacks.QuickAck,
		"counter", m.readCounter,
	)

	buf := &bytes.Buffer{}
	buf.Grow(3)

	if _, err := io.CopyN(buf, m.conn, 1); err != nil {
		return nil, errors.Annotate(err, "Cannot read message length")
	}
	msgLength := uint32(buf.Bytes()[0])
	buf.Reset()

	m.logger.Debugw("Packet first byte",
		"byte", msgLength,
		"counter", m.readCounter,
		"simple_ack", m.opts.ReadHacks.SimpleAck,
		"quick_ack", m.opts.ReadHacks.QuickAck,
	)

	if msgLength >= mtprotoAbridgedQuickAckLength {
		m.opts.ReadHacks.QuickAck = true
		msgLength -= mtprotoAbridgedQuickAckLength
	}

	if msgLength == mtprotoAbridgedSmallPacketLength {
		if _, err := io.CopyN(buf, m.conn, 3); err != nil {
			return nil, errors.Annotate(err, "Cannot read the correct message length")
		}
		number := utils.Uint24{}
		copy(number[:], buf.Bytes())
		msgLength = utils.FromUint24(number)
	}
	msgLength *= 4

	m.logger.Debugw("Packet length",
		"length", msgLength,
		"simple_ack", m.opts.ReadHacks.SimpleAck,
		"quick_ack", m.opts.ReadHacks.QuickAck,
		"counter", m.readCounter,
	)

	buf.Reset()
	buf.Grow(int(msgLength))
	if _, err := io.CopyN(buf, m.conn, int64(msgLength)); err != nil {
		return nil, errors.Annotate(err, "Cannot read message")
	}

	return buf.Bytes(), nil
}

func (m *MTProtoAbridged) Write(p []byte) (int, error) {
	defer func() {
		m.writeCounter++
	}()

	m.logger.Debugw("Write packet",
		"length", len(p),
		"simple_ack", m.opts.WriteHacks.SimpleAck,
		"quick_ack", m.opts.WriteHacks.QuickAck,
		"counter", m.writeCounter,
	)

	if len(p)%4 != 0 {
		return 0, errors.Errorf("Incorrect packet length %d", len(p))
	}

	if m.opts.WriteHacks.SimpleAck {
		return m.conn.Write(utils.ReverseBytes(p))
	}

	packetLength := len(p) / 4
	switch {
	case packetLength < mtprotoAbridgedSmallPacketLength:
		newData := append([]byte{byte(packetLength)}, p...)
		return m.conn.Write(newData)

	case packetLength < mtprotoAbridgedLargePacketLength:
		length24 := utils.ToUint24(uint32(packetLength))

		buf := &bytes.Buffer{}
		buf.Grow(1 + 3 + len(p))

		buf.WriteByte(byte(mtprotoAbridgedSmallPacketLength))
		buf.Write(length24[:])
		buf.Write(p)

		return m.conn.Write(buf.Bytes())
	}

	return 0, errors.Errorf("Packet is too big %d", len(p))
}

// Logger returns an instance of the logger for this wrapper.
func (m *MTProtoAbridged) Logger() *zap.SugaredLogger {
	return m.logger
}

// LocalAddr returns local address of the underlying net.Conn.
func (m *MTProtoAbridged) LocalAddr() *net.TCPAddr {
	return m.conn.LocalAddr()
}

// RemoteAddr returns remote address of the underlying net.Conn.
func (m *MTProtoAbridged) RemoteAddr() *net.TCPAddr {
	return m.conn.RemoteAddr()
}

// Close closes underlying net.Conn instance.
func (m *MTProtoAbridged) Close() error {
	return m.conn.Close()
}

// NewMTProtoAbridged creates new wrapper for abridged client connection.
func NewMTProtoAbridged(conn StreamReadWriteCloser, opts *mtproto.ConnectionOpts) PacketReadWriteCloser {
	return &MTProtoAbridged{
		conn:   conn,
		opts:   opts,
		logger: conn.Logger().Named("mtproto-abridged"),
	}
}