Program: 35203
Project: 35203
Buggy source:
public void handleKey(SelectionKey key){
  if (key.isValid() && key.isConnectable()) {
    PendingConnect data=(PendingConnect)key.attachment();
    Peer peer=data.peer;
    System.out.println("String_Node_Str" + peer.getHash());
    SocketChannel channel=(SocketChannel)key.channel();
    ConnectionHandler handler=new ConnectionHandler(peer,channel,key);
    try {
      if (channel.finishConnect()) {
        key.interestOps((key.interestOps() | SelectionKey.OP_READ) & ~SelectionKey.OP_CONNECT);
        key.attach(handler);
        peer.connectionOpened();
      }
 else {
        peer.destroy();
      }
    }
 catch (    Exception e) {
      Log.warn("String_Node_Str",channel.socket().getRemoteSocketAddress());
      peer.destroy();
    }
  }
 else   if (key.isValid() && key.isAcceptable()) {
    SocketChannel socketChannel=null;
    Peer peer=null;
    try {
      socketChannel=serverSocketChannel.accept();
      InetSocketAddress socketAddress=(InetSocketAddress)socketChannel.getRemoteAddress();
      if (!allowConnection(socketAddress)) {
        socketChannel.close();
        return;
      }
      socketChannel.configureBlocking(false);
      SelectionKey newKey=socketChannel.register(selector,SelectionKey.OP_READ);
      new Peer(network,Peer.IN,socketAddress);
      peersManager.addPeerToGroup(NetworkConstant.Network_Peer_In_Group,peer);
      ConnectionHandler handler=new ConnectionHandler(peer,socketChannel,newKey);
      newKey.attach(handler);
      peer.connectionOpened();
    }
 catch (    Exception e) {
      if (socketChannel != null) {
        Log.warn("String_Node_Str",socketChannel.socket().getRemoteSocketAddress());
        try {
          socketChannel.close();
        }
 catch (        IOException e1) {
          e1.printStackTrace();
        }
      }
      if (peer != null) {
        peer.destroy();
      }
    }
  }
 else {
    ConnectionHandler handler=(ConnectionHandler)key.attachment();
    if (handler != null) {
      ConnectionHandler.handleKey(key);
    }
  }
}

Fixed version (ground truth):
public void handleKey(SelectionKey key){
  if (key.isValid() && key.isConnectable()) {
    PendingConnect data=(PendingConnect)key.attachment();
    Peer peer=data.peer;
    System.out.println("String_Node_Str" + peer.getHash());
    SocketChannel channel=(SocketChannel)key.channel();
    ConnectionHandler handler=new ConnectionHandler(peer,channel,key);
    try {
      if (channel.finishConnect()) {
        key.interestOps((key.interestOps() | SelectionKey.OP_READ) & ~SelectionKey.OP_CONNECT);
        key.attach(handler);
        peer.connectionOpened();
      }
 else {
        peer.destroy();
      }
    }
 catch (    Exception e) {
      Log.warn("String_Node_Str",channel.socket().getRemoteSocketAddress());
      peer.destroy();
    }
  }
 else   if (key.isValid() && key.isAcceptable()) {
    SocketChannel socketChannel=null;
    Peer peer=null;
    try {
      socketChannel=serverSocketChannel.accept();
      InetSocketAddress socketAddress=(InetSocketAddress)socketChannel.getRemoteAddress();
      if (!allowConnection(socketAddress)) {
        socketChannel.close();
        return;
      }
      socketChannel.configureBlocking(false);
      SelectionKey newKey=socketChannel.register(selector,SelectionKey.OP_READ);
      new Peer(network,Peer.IN,socketAddress);
      peersManager.addPeerToGroup(NetworkConstant.NETWORK_PEER_IN_GROUP,peer);
      ConnectionHandler handler=new ConnectionHandler(peer,socketChannel,newKey);
      newKey.attach(handler);
      peer.connectionOpened();
    }
 catch (    Exception e) {
      if (socketChannel != null) {
        Log.warn("String_Node_Str",socketChannel.socket().getRemoteSocketAddress());
        try {
          socketChannel.close();
        }
 catch (        IOException e1) {
          e1.printStackTrace();
        }
      }
      if (peer != null) {
        peer.destroy();
      }
    }
  }
 else {
    ConnectionHandler handler=(ConnectionHandler)key.attachment();
    if (handler != null) {
      ConnectionHandler.handleKey(key);
    }
  }
}