improve robustness in natpmp code a bit

include/libtorrent/natpmp.hpp

@@ -133,7 +133,7 @@ private:
 	log_callback_t m_log_callback;
 
 	std::vector<mapping_t> m_mappings;
-	
+
 	// the endpoint to the nat router
 	udp::endpoint m_nat_endpoint;
 
@@ -145,7 +145,7 @@ private:
 	// current retry count
 	int m_retry_count;
 
-	// used to receive responses in	
+	// used to receive responses in
 	char m_response_buffer[16];
 
 	// router external IP address
@@ -153,7 +153,7 @@ private:
 
 	// the endpoint we received the message from
 	udp::endpoint m_remote;
-	
+
 	// the udp socket used to communicate
 	// with the NAT router
 	udp::socket m_socket;
@@ -167,7 +167,7 @@ private:
 
 	// the mapping index that will expire next
 	int m_next_refresh;
-	
+
 	bool m_disabled;
 
 	bool m_abort;

src/natpmp.cpp

@@ -127,7 +127,8 @@ void natpmp::start()
 #if defined TORRENT_ASIO_DEBUGGING
 	add_outstanding_async("natpmp::on_reply");
 #endif
-	m_socket.async_receive_from(boost::asio::buffer(&m_response_buffer, 16)
+	m_socket.async_receive_from(boost::asio::buffer(&m_response_buffer[0]
+		, sizeof(m_response_buffer))
 		, m_remote, boost::bind(&natpmp::on_reply, self(), _1, _2));
 	send_get_ip_address_request(l);
 
@@ -433,10 +434,11 @@ void natpmp::on_reply(error_code const& e
 #endif
 	// make a copy of the response packet buffer
 	// to avoid overwriting it in the next receive call
-	char msg_buf[16];
+	char msg_buf[sizeof(m_response_buffer)];
 	memcpy(msg_buf, m_response_buffer, bytes_transferred);
 
-	m_socket.async_receive_from(boost::asio::buffer(&m_response_buffer, 16)
+	m_socket.async_receive_from(boost::asio::buffer(&m_response_buffer[0]
+		, sizeof(m_response_buffer))
 		, m_remote, boost::bind(&natpmp::on_reply, self(), _1, _2));
 
 	// simulate packet loss
@@ -485,7 +487,7 @@ void natpmp::on_reply(error_code const& e
 
 	}
 
-	if (bytes_transferred < 16)
+	if (bytes_transferred != 16)
 	{
 		char msg[200];
 		snprintf(msg, sizeof(msg), "received packet of invalid size: %d", int(bytes_transferred));