diff --git a/examples/test/net_test.c b/examples/test/net_test.c
index c3867ecf4f..553305f4d0 100644
--- a/examples/test/net_test.c
+++ b/examples/test/net_test.c
@@ -14,41 +14,51 @@
 rt_thread_t udpecho_tid = RT_NULL;
 void udpecho_entry(void *parameter)
 {
-	struct netconn *conn;
-	struct netbuf *buf;
-	struct ip_addr *addr;
-	unsigned short port;
+    struct netconn *conn;
+    struct netbuf *buf;
+    struct ip_addr *addr;
+    unsigned short port;
 
-	conn = netconn_new(NETCONN_UDP);
-	netconn_bind(conn, IP_ADDR_ANY, 7);
+    conn = netconn_new(NETCONN_UDP);
+    if(conn == NULL)
+    {
+        rt_kprintf("no memory error\n");
+        return;
+    }
+    netconn_bind(conn, IP_ADDR_ANY, 7);
 
-	while(1)
-	{
+    while(1)
+    {
         /* received data to buffer */
 #if LWIP_VERSION_MINOR==3U 
-		buf = netconn_recv(conn);
+        buf = netconn_recv(conn);
 #else
-		netconn_recv(conn, &buf);
+        netconn_recv(conn, &buf);
 #endif
-		
-		addr = netbuf_fromaddr(buf);
-		port = netbuf_fromport(buf);
+        if(buf == NULL)	
+        {
+            break;
+        }
+        addr = netbuf_fromaddr(buf);
+        port = netbuf_fromport(buf);
 
-   		 /* send the data to buffer */
-		netconn_connect(conn, addr, port);
+        /* send the data to buffer */
+        netconn_connect(conn, addr, port);
 
-		/* reset address, and send to client */
+        /* reset address, and send to client */
 #if LWIP_VERSION_MINOR==3U 		
-		buf->addr = RT_NULL;
+        buf->addr = RT_NULL;
 #else
-		buf->addr = *IP_ADDR_ANY;
+        buf->addr = *IP_ADDR_ANY;
 #endif
 		
-		netconn_send(conn, buf);
+        netconn_send(conn, buf);
 		
-		/* release buffer */
-		netbuf_delete(buf);
-	}
+        /* release buffer */
+        netbuf_delete(buf);
+    }
+	
+    netconn_delete(conn);
 }
 /*
  * UDP socket echo server
@@ -58,57 +68,57 @@ void udpecho_entry(void *parameter)
 rt_thread_t udpecho_socket_tid = RT_NULL;
 void udpecho_socket_entry(void *parameter)
 {
-	int sock;
-	int bytes_read;
-	char *recv_data;
-	rt_uint32_t addr_len;
-	struct sockaddr_in server_addr, client_addr;
+    int sock;
+    int bytes_read;
+    char *recv_data;
+    rt_uint32_t addr_len;
+    struct sockaddr_in server_addr, client_addr;
 
-	/* allocate the data buffer */
-	recv_data = rt_malloc(UDP_SOCKET_BUFFER_SIZE);
-	if (recv_data == RT_NULL)
-	{
-		/* no memory yet */
-		rt_kprintf("no memory\n");
-		return;
-	}
-	/* create a UDP socket */
-	if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1)
-	{
-		rt_kprintf("create socket error\n");
-		goto _exit;
-	}
+    /* allocate the data buffer */
+    recv_data = rt_malloc(UDP_SOCKET_BUFFER_SIZE);
+    if (recv_data == RT_NULL)
+    {
+        /* no memory yet */
+        rt_kprintf("no memory\n");
+        return;
+    }
+    /* create a UDP socket */
+    if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1)
+    {
+        rt_kprintf("create socket error\n");
+        goto _exit;
+    }
 
-	/* initialize server address */
-	server_addr.sin_family = AF_INET;
-	server_addr.sin_port = htons(UDP_SOCKET_ECHO_PORT);
-	server_addr.sin_addr.s_addr = INADDR_ANY;
-	rt_memset(&(server_addr.sin_zero),0, sizeof(server_addr.sin_zero));
+    /* initialize server address */
+    server_addr.sin_family = AF_INET;
+    server_addr.sin_port = htons(UDP_SOCKET_ECHO_PORT);
+    server_addr.sin_addr.s_addr = INADDR_ANY;
+    rt_memset(&(server_addr.sin_zero),0, sizeof(server_addr.sin_zero));
 
-	/* bind socket to server address */
-	if (bind(sock,(struct sockaddr *)&server_addr,
-			sizeof(struct sockaddr)) == -1)
-	{
-		/* bind failed */
-		rt_kprintf("bind error\n");
-		goto _exit;
-	}
+    /* bind socket to server address */
+    if (bind(sock,(struct sockaddr *)&server_addr,
+        sizeof(struct sockaddr)) == -1)
+    {
+        /* bind failed */
+        rt_kprintf("bind error\n");
+        goto _exit;
+    }
 
-	addr_len = sizeof(struct sockaddr);
-	while (1)
-	{
-		/* try to receive from UDP socket */
-		bytes_read = recvfrom(sock, recv_data, UDP_SOCKET_BUFFER_SIZE, 0,
-							 (struct sockaddr *)&client_addr, &addr_len);
-
-		/* send back */
-		sendto(sock, recv_data, bytes_read, 0,
-			(struct sockaddr *)&client_addr, addr_len);
-	}
+    addr_len = sizeof(struct sockaddr);
+    while (1)
+    {
+        /* try to receive from UDP socket */
+        bytes_read = recvfrom(sock, recv_data, UDP_SOCKET_BUFFER_SIZE, 0,
+            (struct sockaddr *)&client_addr, &addr_len);
+	    
+        /* send back */
+        sendto(sock, recv_data, bytes_read, 0,
+            (struct sockaddr *)&client_addr, addr_len);
+    }
 
 _exit:
-	rt_free(recv_data);
-	return;
+    rt_free(recv_data);
+    return;
 }
 
 /*
@@ -118,52 +128,62 @@ _exit:
 rt_thread_t tcpecho_tid = RT_NULL;
 void tcpecho_entry(void *parameter)
 {
-	struct netconn *conn, *newconn;
-	err_t err;
+    struct netconn *conn, *newconn;
+    err_t err;
 
-	/* Create a new connection identifier. */
-	conn = netconn_new(NETCONN_TCP);
+    /* Create a new connection identifier. */
+    conn = netconn_new(NETCONN_TCP);
+    if(conn == NULL)
+    {
+        rt_kprintf("no memory error\n");
+        return;
+    }
 
-	/* Bind connection to well known port number 7. */
-	netconn_bind(conn, NULL, TCP_ECHO_PORT);
+    /* Bind connection to well known port number 7. */
+    netconn_bind(conn, NULL, TCP_ECHO_PORT);
 
-	/* Tell connection to go into listening mode. */
-	netconn_listen(conn);
+    /* Tell connection to go into listening mode. */
+    netconn_listen(conn);
 
-	while(1)
-	{
-		/* Grab new connection. */
+    while(1)
+    {
+        /* Grab new connection. */
 #if LWIP_VERSION_MINOR==3U 
-		newconn = netconn_accept(conn);
-		if(newconn != NULL)
+        newconn = netconn_accept(conn);
+        if(newconn != NULL)
 #else
-		err = netconn_accept(conn, &newconn);
-		if(err == ERR_OK)
+        err = netconn_accept(conn, &newconn);
+        if(err == ERR_OK)
 #endif
-		/* Process the new connection. */
-		{
-			struct netbuf *buf;
-			void *data;
-			u16_t len;
+        /* Process the new connection. */
+        {
+            struct netbuf *buf;
+            void *data;
+            u16_t len;
 #if LWIP_VERSION_MINOR==3U
-			while((buf = netconn_recv(newconn)) != NULL)
+            while((buf = netconn_recv(newconn)) != NULL)
 #else
-			while((err = netconn_recv(newconn, &buf)) == ERR_OK)
+            while((err = netconn_recv(newconn, &buf)) == ERR_OK)
 #endif
-			{
-				do
-				{
-					netbuf_data(buf, &data, &len);
-					err = netconn_write(newconn, data, len, NETCONN_COPY);
-					if(err != ERR_OK){}
-				}
-				while(netbuf_next(buf) >= 0);
-				netbuf_delete(buf);
-			}
-			/* Close connection and discard connection identifier. */
-			netconn_delete(newconn);
-		}
-	}
+            {
+                do
+                {
+                    netbuf_data(buf, &data, &len);
+                    err = netconn_write(newconn, data, len, NETCONN_COPY);
+                    if(err != ERR_OK)
+                    {
+                        break;			    
+                    }
+                }while(netbuf_next(buf) >= 0);
+		    
+                netbuf_delete(buf);
+            }
+            /* Close connection and discard connection identifier. */
+            netconn_delete(newconn);
+        }
+    }
+	
+    netconn_delete(conn);
 }
 
 /*
@@ -174,84 +194,83 @@ void tcpecho_entry(void *parameter)
 rt_thread_t tcpecho_socket_tid = RT_NULL;
 void tcpecho_socket_entry(void *parameter)
 {
-   char *recv_data;
-   rt_uint32_t sin_size;
-   int sock = -1, connected, bytes_received;
-   struct sockaddr_in server_addr, client_addr;
+    char *recv_data;
+    rt_uint32_t sin_size;
+    int sock = -1, connected, bytes_received;
+    struct sockaddr_in server_addr, client_addr;
 
-	recv_data = rt_malloc(TCP_SOCKET_BUFFER_SIZE);
-	if (recv_data == RT_NULL)
-	{
-		rt_kprintf("no memory\n");
-		return;
-	}
+    recv_data = rt_malloc(TCP_SOCKET_BUFFER_SIZE);
+    if (recv_data == RT_NULL)
+    {
+        rt_kprintf("no memory\n");
+        return;
+    }
 
-	/* create a TCP socket */
-	if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1)
-	{
-		rt_kprintf("create socket error\n");
-		goto _exit;
-	}
+    /* create a TCP socket */
+    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1)
+    {
+        rt_kprintf("create socket error\n");
+        goto _exit;
+    }
 
-	/* initialize server address */
-	server_addr.sin_family = AF_INET;
-	server_addr.sin_port = htons(TCP_SOCKET_ECHO_PORT);
-	server_addr.sin_addr.s_addr = INADDR_ANY;
-	rt_memset(&(server_addr.sin_zero),8, sizeof(server_addr.sin_zero));
+    /* initialize server address */
+    server_addr.sin_family = AF_INET;
+    server_addr.sin_port = htons(TCP_SOCKET_ECHO_PORT);
+    server_addr.sin_addr.s_addr = INADDR_ANY;
+    rt_memset(&(server_addr.sin_zero),8, sizeof(server_addr.sin_zero));
 
-	/* bind to server address */
-	if (bind(sock, (struct sockaddr *)&server_addr, sizeof(struct sockaddr)) == -1)
-	{
-		rt_kprintf("bind address failed\n");
-		goto _exit;
-   }
+    /* bind to server address */
+    if (bind(sock, (struct sockaddr *)&server_addr, sizeof(struct sockaddr)) == -1)
+    {
+        rt_kprintf("bind address failed\n");
+        goto _exit;
+    }
 
-	/* listen */
-	if (listen(sock, 5) == -1)
-	{
-		rt_kprintf("listen error\n");
-		goto _exit;
-	}
+    /* listen */
+    if (listen(sock, 5) == -1)
+    {
+        rt_kprintf("listen error\n");
+        goto _exit;
+    }
 
-	sin_size = sizeof(struct sockaddr_in);
-	while(1)
-	{
-		/* accept client connected */
-		connected = accept(sock, (struct sockaddr *)&client_addr, &sin_size);
-		if (connected > 0)
-		{
-			int timeout;
+    sin_size = sizeof(struct sockaddr_in);
+    while(1)
+    {
+        /* accept client connected */
+        connected = accept(sock, (struct sockaddr *)&client_addr, &sin_size);
+        if (connected > 0)
+        {
+            int timeout;
 			
-			/* set timeout option */
-			timeout = 5000; /* 5second */
-			setsockopt(connected, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout));
+            /* set timeout option */
+            timeout = 5000; /* 5second */
+            setsockopt(connected, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout));
 
-			/* handle this client */
-			while (1)
-			{
-				/* receive data from this connection */
-				bytes_received = recv(connected,recv_data, TCP_SOCKET_BUFFER_SIZE, 0);
-				if (bytes_received <= 0)
-				{
-					rt_kprintf("close client connection, errno: %d\n", 
-						rt_get_errno());
-					/* connection closed. */
-					lwip_close(connected);
-					break;
-				}
+            /* handle this client */
+            while (1)
+            {
+                /* receive data from this connection */
+                bytes_received = recv(connected,recv_data, TCP_SOCKET_BUFFER_SIZE, 0);
+                if (bytes_received <= 0)
+                {
+                    rt_kprintf("close client connection, errno: %d\n", rt_get_errno());
+                    /* connection closed. */
+                    lwip_close(connected);
+                    break;
+                }
 
-				/* send data to client */
-				send(connected, recv_data, bytes_received, 0);
-			}
-		}
-   }
+                /* send data to client */
+                send(connected, recv_data, bytes_received, 0);
+            }
+        }
+    }
 
 _exit:
-	/* close socket */
-	if (sock != -1) lwip_close(sock);
-	rt_free(recv_data);
+    /* close socket */
+    if (sock != -1) lwip_close(sock);
+    rt_free(recv_data);
 
-	return ;
+    return;
 }
 
 /*
@@ -261,40 +280,56 @@ _exit:
 /* network test utilities entry */
 void net_test(void)
 {
-	/* start UDP echo server */
-	if (udpecho_tid == RT_NULL)
-	{
-		udpecho_tid = rt_thread_create("uecho",
-									udpecho_entry, RT_NULL,
-									512, RT_THREAD_PRIORITY_MAX/2, 5);
-		if (udpecho_tid != RT_NULL)
-			rt_thread_startup(udpecho_tid);
-	}
-	if (udpecho_socket_tid == RT_NULL)
-	{
-		udpecho_socket_tid = rt_thread_create("uecho_s",
-									udpecho_socket_entry, RT_NULL,
-									512, RT_THREAD_PRIORITY_MAX/2 + 1, 5);
-		if (udpecho_socket_tid != RT_NULL)
-			rt_thread_startup(udpecho_socket_tid);
-	}
+    /* start UDP echo server */
+    if (udpecho_tid == RT_NULL)
+    {
+        udpecho_tid = rt_thread_create("uecho",
+                                       udpecho_entry,
+                                       RT_NULL, 
+                                       512, 
+                                       RT_THREAD_PRIORITY_MAX/2, 5);
+        if (udpecho_tid != RT_NULL)
+        {
+            rt_thread_startup(udpecho_tid);
+        }
+    }
 
-	if (tcpecho_tid == RT_NULL)
-	{
-		tcpecho_tid = rt_thread_create("techo",
-									tcpecho_entry, RT_NULL,
-									512, RT_THREAD_PRIORITY_MAX/2 + 2, 5);
-		if (tcpecho_tid != RT_NULL)
-			rt_thread_startup(tcpecho_tid);
-	}
-	if (tcpecho_socket_tid == RT_NULL)
-	{
-		tcpecho_socket_tid = rt_thread_create("techo_s",
-									tcpecho_socket_entry, RT_NULL,
-									512, RT_THREAD_PRIORITY_MAX/2 + 3, 5);
-		if (tcpecho_socket_tid != RT_NULL)
-			rt_thread_startup(tcpecho_socket_tid);
-	}
+    if (udpecho_socket_tid == RT_NULL)
+    {
+        udpecho_socket_tid = rt_thread_create("uecho_s",
+                                              udpecho_socket_entry,
+                                              RT_NULL,
+                                              512, 
+                                              RT_THREAD_PRIORITY_MAX/2 + 1, 5);
+        if (udpecho_socket_tid != RT_NULL)
+        {
+            rt_thread_startup(udpecho_socket_tid);
+        }
+    }
+
+    if (tcpecho_tid == RT_NULL)
+    {
+        tcpecho_tid = rt_thread_create("techo",
+                                       tcpecho_entry, 
+                                       RT_NULL,
+                                       512, 
+                                       RT_THREAD_PRIORITY_MAX/2 + 2, 5);
+        if (tcpecho_tid != RT_NULL)
+        {
+            rt_thread_startup(tcpecho_tid);
+        }
+    }
+	
+    if (tcpecho_socket_tid == RT_NULL)
+    {
+        tcpecho_socket_tid = rt_thread_create("techo_s",
+                                              tcpecho_socket_entry, 
+                                              RT_NULL,
+                                              512, 
+                                              RT_THREAD_PRIORITY_MAX/2 + 3, 5);
+    if (tcpecho_socket_tid != RT_NULL)
+    {
+        rt_thread_startup(tcpecho_socket_tid);
+    }
 }
 FINSH_FUNCTION_EXPORT(net_test, network test);
-