package com.mattibal.meshnet;
import java.io.IOException;
import java.nio.BufferOverflowException;
import java.nio.BufferUnderflowException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.Random;
import com.mattibal.meshnet.Layer3Packet.InvalidPacketException;
public class Layer2Serial implements Layer3Base.ILayer2 {
private static final int MAX_FRAME_SIZE = 40;
private static final byte PREAMBLE = 0x7E;
private static final byte ESCAPE = 0x7D;
// Used to write to serial port
private SerialRXTXComm serial;
private Layer3Base layer3;
private ByteBuffer rxFrame = ByteBuffer.allocate(MAX_FRAME_SIZE);
private int myMacAddress;
public Layer2Serial(SerialRXTXComm serial, Layer3Base layer3){
this.serial = serial;
this.layer3 = layer3;
layer3.addLayer2Interface(this);
this.myMacAddress = new Random().nextInt(256);
}
private boolean isLastByteEscape = false;
private int currPayloadLength = 0;
/** Called when I receive a byte from the serial port */
public void onSerialByteReceived(byte byteValue){
if(byteValue == PREAMBLE){
rxFrame.position(0);
return;
}
if(byteValue == ESCAPE){
isLastByteEscape = true;
return;
}
if(isLastByteEscape){
byteValue = (byte) (byteValue ^ 0x20);
isLastByteEscape = false;
}
if(rxFrame.position()==0){
currPayloadLength = (int) byteValue & 0xff;
if(currPayloadLength > MAX_FRAME_SIZE-5){
return;
}
}
rxFrame.put(byteValue);
if(rxFrame.position() == currPayloadLength+5){
rxFrame.position(0);
try {
Frame frame = new Frame(rxFrame.array());
if(frame.getDestMac() == myMacAddress || frame.getDestMac() == 0){
layer3.onFrameReceived(ByteBuffer.wrap(frame.getPayload()), this, frame.getSrcMac());
}
} catch (InvalidPacketException e) {
e.printStackTrace();
}
rxFrame = ByteBuffer.allocate(MAX_FRAME_SIZE);
}
}
/**
* Send a frame to the serial port.
* @param bytesToSend
*/
@Override
public void sendLayer3Packet(byte[] bytesToSend, int destMacAddress) throws IOException{
Frame frame = new Frame((byte)myMacAddress, (byte)destMacAddress, bytesToSend);
byte[] notEscapedBytes = frame.getRawBytes();
serial.transmitByte(PREAMBLE);
for(byte b: notEscapedBytes){
if(b == PREAMBLE || b == ESCAPE){
serial.transmitByte(ESCAPE);
serial.transmitByte((byte)(b^0x20));
} else {
serial.transmitByte(b);
}
}
}
/**
* An instance of this class represent a frame of this specific layer2
*/
private static class Frame {
private final ByteBuffer bytes;
private final int totalLen;
private final int payloadLen;
protected Frame(byte srcMac, byte destMac, byte[] data){
payloadLen = data.length;
totalLen = payloadLen+5;
bytes = ByteBuffer.allocate(totalLen);
bytes.order(ByteOrder.LITTLE_ENDIAN);
bytes.put((byte)payloadLen);
bytes.put((byte)srcMac);
bytes.put((byte)destMac);
bytes.put(data);
byte[] crc = calculateCrc(bytes.array(), totalLen-2);
bytes.put(crc);
}
protected Frame(byte[] bytesArr) throws InvalidPacketException{
this.bytes=ByteBuffer.wrap(bytesArr);
bytes.order(ByteOrder.LITTLE_ENDIAN);
try {
payloadLen = (int) bytes.get();
totalLen = payloadLen+5;
// Test CRC and throw an exception if the frame is corrupted
byte[] readenCrc = new byte[2];
bytes.position(totalLen-2);
bytes.get(readenCrc, 0, 2);
byte[] calculatedCrc = calculateCrc(bytes.array(), totalLen-2);
if(readenCrc[0]!=calculatedCrc[0] || readenCrc[1]!=calculatedCrc[1]){
throw new InvalidPacketException();
}
} catch(Exception e){
throw new InvalidPacketException();
}
}
public byte[] getRawBytes(){
return bytes.array();
}
public byte[] getPayload(){
byte[] payload = new byte[payloadLen];
bytes.position(3);
bytes.get(payload);
return payload;
}
public int getSrcMac(){
return (int)bytes.get(1) & 0xff;
}
public int getDestMac(){
return (int)bytes.get(2) & 0xff;
}
}
// CRC16 CCITT CALCULATION
private static final int crc_ccitt_table[] = { 0x0000, 0x1189, 0x2312, 0x329b,
0x4624, 0x57ad, 0x6536, 0x74bf, 0x8c48, 0x9dc1, 0xaf5a, 0xbed3,
0xca6c, 0xdbe5, 0xe97e, 0xf8f7, 0x1081, 0x0108, 0x3393, 0x221a,
0x56a5, 0x472c, 0x75b7, 0x643e, 0x9cc9, 0x8d40, 0xbfdb, 0xae52,
0xdaed, 0xcb64, 0xf9ff, 0xe876, 0x2102, 0x308b, 0x0210, 0x1399,
0x6726, 0x76af, 0x4434, 0x55bd, 0xad4a, 0xbcc3, 0x8e58, 0x9fd1,
0xeb6e, 0xfae7, 0xc87c, 0xd9f5, 0x3183, 0x200a, 0x1291, 0x0318,
0x77a7, 0x662e, 0x54b5, 0x453c, 0xbdcb, 0xac42, 0x9ed9, 0x8f50,
0xfbef, 0xea66, 0xd8fd, 0xc974, 0x4204, 0x538d, 0x6116, 0x709f,
0x0420, 0x15a9, 0x2732, 0x36bb, 0xce4c, 0xdfc5, 0xed5e, 0xfcd7,
0x8868, 0x99e1, 0xab7a, 0xbaf3, 0x5285, 0x430c, 0x7197, 0x601e,
0x14a1, 0x0528, 0x37b3, 0x263a, 0xdecd, 0xcf44, 0xfddf, 0xec56,
0x98e9, 0x8960, 0xbbfb, 0xaa72, 0x6306, 0x728f, 0x4014, 0x519d,
0x2522, 0x34ab, 0x0630, 0x17b9, 0xef4e, 0xfec7, 0xcc5c, 0xddd5,
0xa96a, 0xb8e3, 0x8a78, 0x9bf1, 0x7387, 0x620e, 0x5095, 0x411c,
0x35a3, 0x242a, 0x16b1, 0x0738, 0xffcf, 0xee46, 0xdcdd, 0xcd54,
0xb9eb, 0xa862, 0x9af9, 0x8b70, 0x8408, 0x9581, 0xa71a, 0xb693,
0xc22c, 0xd3a5, 0xe13e, 0xf0b7, 0x0840, 0x19c9, 0x2b52, 0x3adb,
0x4e64, 0x5fed, 0x6d76, 0x7cff, 0x9489, 0x8500, 0xb79b, 0xa612,
0xd2ad, 0xc324, 0xf1bf, 0xe036, 0x18c1, 0x0948, 0x3bd3, 0x2a5a,
0x5ee5, 0x4f6c, 0x7df7, 0x6c7e, 0xa50a, 0xb483, 0x8618, 0x9791,
0xe32e, 0xf2a7, 0xc03c, 0xd1b5, 0x2942, 0x38cb, 0x0a50, 0x1bd9,
0x6f66, 0x7eef, 0x4c74, 0x5dfd, 0xb58b, 0xa402, 0x9699, 0x8710,
0xf3af, 0xe226, 0xd0bd, 0xc134, 0x39c3, 0x284a, 0x1ad1, 0x0b58,
0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c, 0xc60c, 0xd785, 0xe51e, 0xf497,
0x8028, 0x91a1, 0xa33a, 0xb2b3, 0x4a44, 0x5bcd, 0x6956, 0x78df,
0x0c60, 0x1de9, 0x2f72, 0x3efb, 0xd68d, 0xc704, 0xf59f, 0xe416,
0x90a9, 0x8120, 0xb3bb, 0xa232, 0x5ac5, 0x4b4c, 0x79d7, 0x685e,
0x1ce1, 0x0d68, 0x3ff3, 0x2e7a, 0xe70e, 0xf687, 0xc41c, 0xd595,
0xa12a, 0xb0a3, 0x8238, 0x93b1, 0x6b46, 0x7acf, 0x4854, 0x59dd,
0x2d62, 0x3ceb, 0x0e70, 0x1ff9, 0xf78f, 0xe606, 0xd49d, 0xc514,
0xb1ab, 0xa022, 0x92b9, 0x8330, 0x7bc7, 0x6a4e, 0x58d5, 0x495c,
0x3de3, 0x2c6a, 0x1ef1, 0x0f78 };
private static byte[] calculateCrc(byte[] data, int len) {
/*int crc = 0xffff;
for (int i = 0; i < data.length; i++) {
crc = (crc >> 8) ^ crc_ccitt_table[((crc ^ data[i]) & 0xff)];
crc = crc & 0xffff;
}
crc ^= 0xffff;
crc = crc & 0xffff;
byte[] outbytes = {(byte) crc, (byte) (crc >> 8) };
return outbytes;*/
short x = 0;
int pos = 0;
while((len--)!=0){
x = crc_xmodem_update(x, data[pos]);
pos++;
}
ByteBuffer buf = ByteBuffer.allocate(2);
buf.order(ByteOrder.LITTLE_ENDIAN);
buf.putShort(x);
return buf.array();
}
private static short crc_xmodem_update (short crc, byte data){
int i;
short dataExpanded = (short) (data & 0xff);
crc = (short) (crc ^ (dataExpanded << 8));
for (i=0; i<8; i++)
{
if ((crc & 0x8000) != 0){
crc = (short)((crc << 1) ^ 0x1021);
} else {
crc <<= 1;
}
}
return crc;
}
}