bugfix. handle recv after disconnect.

libp2p/UDP.h

@@ -203,7 +203,10 @@ void UDPSocket<Handler, MaxDatagramSize>::doRead()
 	auto self(UDPSocket<Handler, MaxDatagramSize>::shared_from_this());
 	m_socket.async_receive_from(boost::asio::buffer(m_recvData), m_recvEndpoint, [this, self](boost::system::error_code _ec, size_t _len)
 	{
-		if (_ec)
+		// ASIO Safety: It is possible that ASIO will call lambda w/o an error
+		// and after the socket has been disconnected. Checking m_closed
+		// guarantees that m_host will not be called after disconnect().
+		if (_ec || m_closed)
 			return disconnectWithError(_ec);
 
 		assert(_len);
@@ -222,7 +225,7 @@ void UDPSocket<Handler, MaxDatagramSize>::doWrite()
 	auto self(UDPSocket<Handler, MaxDatagramSize>::shared_from_this());
 	m_socket.async_send_to(boost::asio::buffer(datagram.data), datagram.endpoint(), [this, self](boost::system::error_code _ec, std::size_t)
 	{
-		if (_ec)
+		if (_ec || m_closed)
 			return disconnectWithError(_ec);
 		else
 		{