Program: 5627
Project: 5627
Buggy source:
public void handlePacket(IPv6Packet packet){
  TCPPacket tcpPacket=(TCPPacket)packet.getIPPayload();
  TCPConnection connection=findConnection(packet,tcpPacket);
  if (connection == null) {
    connection=findListenConnection(packet,tcpPacket);
    if (connection == null) {
      System.out.println("String_Node_Str");
    }
 else {
      if (tcpPacket.isSyn()) {
        TCPPacket tcpReply=createAck(tcpPacket,TCPPacket.SYN);
        TCPConnection tc=new TCPConnection(ipStack,packet.netInterface);
        tc.externalIP=packet.sourceAddress;
        tc.externalPort=tcpPacket.sourcePort;
        tc.localIP=ipStack.myIPAddress;
        tc.localPort=tcpPacket.destinationPort;
        tc.state=TCPConnection.SYN_RECEIVED;
        tc.receiveNext=tcpPacket.seqNo + 1;
        tc.sentUnack=tc.sendNext=tcpReply.seqNo=(int)(System.currentTimeMillis() * 7);
        addConnection(tc);
        connection.newConnection(tc);
        tcpReply.ackNo=tc.receiveNext;
        tc.send(tcpReply);
        tc.sentUnack=tc.sendNext=tc.sendNext + 1;
        tc.serverConnection=connection;
      }
    }
  }
 else {
switch (connection.state) {
case TCPConnection.SYN_RECEIVED:
      if (tcpPacket.isAck()) {
        System.out.println("String_Node_Str");
        connection.state=TCPConnection.ESTABLISHED;
        connection.receive(tcpPacket);
synchronized (connection) {
          connection.notify();
        }
      }
    break;
case TCPConnection.ESTABLISHED:
  if (tcpPacket.isFin()) {
    connection.state=TCPConnection.CLOSE_WAIT;
  }
connection.receive(tcpPacket);
break;
case TCPConnection.LAST_ACK:
if (tcpPacket.isAck()) {
connection.state=TCPConnection.CLOSED;
}
break;
case TCPConnection.FIN_WAIT_1:
if (tcpPacket.isAck()) {
connection.state=TCPConnection.FIN_WAIT_2;
connection.receive(tcpPacket);
}
if (tcpPacket.isFin()) {
connection.state=TCPConnection.TIME_WAIT;
connection.lastSendTime=System.currentTimeMillis();
connection.receiveNext++;
connection.sendAck(tcpPacket);
}
break;
case TCPConnection.FIN_WAIT_2:
if (tcpPacket.isFin()) {
System.out.println("String_Node_Str");
connection.state=TCPConnection.TIME_WAIT;
connection.lastSendTime=System.currentTimeMillis();
connection.receiveNext++;
connection.sendAck(tcpPacket);
}
break;
case TCPConnection.CLOSE_WAIT:
break;
}
}
}

Fixed version (ground truth):
public void handlePacket(IPv6Packet packet){
  TCPPacket tcpPacket=(TCPPacket)packet.getIPPayload();
  TCPConnection connection=findConnection(packet,tcpPacket);
  if (connection == null) {
    connection=findListenConnection(packet,tcpPacket);
    if (connection == null) {
      System.out.println("String_Node_Str");
    }
 else {
      if (tcpPacket.isSyn()) {
        TCPPacket tcpReply=createAck(tcpPacket,TCPPacket.SYN);
        TCPConnection tc=new TCPConnection(ipStack,packet.netInterface);
        tc.externalIP=packet.sourceAddress;
        tc.externalPort=tcpPacket.sourcePort;
        tc.localIP=ipStack.myIPAddress;
        tc.localPort=tcpPacket.destinationPort;
        tc.state=TCPConnection.SYN_RECEIVED;
        tc.receiveNext=tcpPacket.seqNo + 1;
        tc.sentUnack=tc.sendNext=tcpReply.seqNo=(int)(System.currentTimeMillis() * 7);
        addConnection(tc);
        connection.newConnection(tc);
        tcpReply.ackNo=tc.receiveNext;
        try {
          tc.send(tcpReply);
        }
 catch (        IOException e) {
          e.printStackTrace();
        }
        tc.sentUnack=tc.sendNext=tc.sendNext + 1;
        tc.serverConnection=connection;
      }
 else {
        System.out.println("String_Node_Str");
      }
    }
  }
 else {
switch (connection.state) {
case TCPConnection.SYN_RECEIVED:
      if (tcpPacket.isAck()) {
        System.out.println("String_Node_Str" + connection.pos);
        connection.state=TCPConnection.ESTABLISHED;
        connection.receive(tcpPacket);
synchronized (connection) {
          connection.notify();
        }
      }
    break;
case TCPConnection.ESTABLISHED:
  if (tcpPacket.isFin()) {
    connection.state=TCPConnection.CLOSE_WAIT;
  }
connection.receive(tcpPacket);
break;
case TCPConnection.LAST_ACK:
if (tcpPacket.isAck()) {
System.out.println("String_Node_Str" + connection.pos);
connection.state=TCPConnection.CLOSED;
}
break;
case TCPConnection.FIN_WAIT_1:
if (tcpPacket.isAck()) {
connection.state=TCPConnection.FIN_WAIT_2;
connection.receive(tcpPacket);
}
if (tcpPacket.isFin()) {
connection.state=TCPConnection.TIME_WAIT;
connection.lastSendTime=System.currentTimeMillis();
connection.receiveNext++;
connection.sendAck(tcpPacket);
}
break;
case TCPConnection.FIN_WAIT_2:
if (tcpPacket.isFin()) {
System.out.println("String_Node_Str" + connection.pos);
connection.state=TCPConnection.TIME_WAIT;
connection.lastSendTime=System.currentTimeMillis();
connection.receiveNext++;
connection.sendAck(tcpPacket);
}
break;
case TCPConnection.CLOSE_WAIT:
break;
}
}
}