rdpgw/protocol/common.go

package protocol

import (
	"bytes"
	"encoding/binary"
	"errors"
	"github.com/bolkedebruin/rdpgw/transport"
	"io"
	"log"
	"net"
)

type RedirectFlags struct {
	Clipboard  bool
	Port       bool
	Drive      bool
	Printer    bool
	Pnp        bool
	DisableAll bool
	EnableAll  bool
}

type SessionInfo struct {
	// The connection-id (RDG-ConnID) as reported by the client
	ConnId           string
	// The underlying incoming transport being either websocket or legacy http
	// in case of websocket TransportOut will equal TransportIn
	TransportIn      transport.Transport
	// The underlying outgoing transport being either websocket or legacy http
	// in case of websocket TransportOut will equal TransportOut
	TransportOut     transport.Transport
	// The remote desktop server (rdp, vnc etc) the clients intends to connect to
	RemoteServer	 string
	// The obtained client ip address
	ClientIp		 string
}

// readMessage parses and defragments a packet from a Transport. It returns
// at most the bytes that have been reported by the packet
func readMessage(in transport.Transport) (pt int, n int, msg []byte, err error) {
	fragment := false
	index := 0
	buf := make([]byte, 4096)

	for {
		size, pkt, err := in.ReadPacket()
		if err != nil {
			return 0, 0, []byte{0, 0}, err
		}

		// check for fragments
		var pt uint16
		var sz uint32
		var msg []byte

		if !fragment {
			pt, sz, msg, err = readHeader(pkt[:size])
			if err != nil {
				fragment = true
				index = copy(buf, pkt[:size])
				continue
			}
			index = 0
		} else {
			fragment = false
			pt, sz, msg, err = readHeader(append(buf[:index], pkt[:size]...))
			// header is corrupted even after defragmenting
			if err != nil {
				return 0, 0, []byte{0, 0}, err
			}
		}
		if !fragment {
			return int(pt), int(sz), msg, nil
		}
	}
}

// createPacket wraps the data into the protocol packet
func createPacket(pktType uint16, data []byte) (packet []byte) {
	size := len(data) + 8
	buf := new(bytes.Buffer)

	binary.Write(buf, binary.LittleEndian, uint16(pktType))
	binary.Write(buf, binary.LittleEndian, uint16(0)) // reserved
	binary.Write(buf, binary.LittleEndian, uint32(size))
	buf.Write(data)

	return buf.Bytes()
}

// readHeader parses a packet and verifies its reported size
func readHeader(data []byte) (packetType uint16, size uint32, packet []byte, err error) {
	// header needs to be 8 min
	if len(data) < 8 {
		return 0, 0, nil, errors.New("header too short, fragment likely")
	}
	r := bytes.NewReader(data)
	binary.Read(r, binary.LittleEndian, &packetType)
	r.Seek(4, io.SeekStart)
	binary.Read(r, binary.LittleEndian, &size)
	if len(data) < int(size) {
		return packetType, size, data[8:], errors.New("data incomplete, fragment received")
	}
	return packetType, size, data[8:size], nil
}

// forwards data from a Connection to Transport and wraps it in the rdpgw protocol
func forward(in net.Conn, out transport.Transport) {
	defer in.Close()

	b1 := new(bytes.Buffer)
	buf := make([]byte, 4086)

	for {
		n, err := in.Read(buf)
		if err != nil {
			log.Printf("Error reading from local conn %s", err)
			break
		}
		binary.Write(b1, binary.LittleEndian, uint16(n))
		b1.Write(buf[:n])
		out.WritePacket(createPacket(PKT_TYPE_DATA, b1.Bytes()))
		b1.Reset()
	}
}

// receive data received from the gateway client, unwrap and forward the remote desktop server
func receive(data []byte, out net.Conn) {
	buf := bytes.NewReader(data)

	var cblen uint16
	binary.Read(buf, binary.LittleEndian, &cblen)
	pkt := make([]byte, cblen)
	binary.Read(buf, binary.LittleEndian, &pkt)

	out.Write(pkt)
}