improve and add comments in examples/network/ including tcpserver.c

tcpclient.c udpserver.c and udpclient.c
Formatting
Co-authored-by: Man, Jianting (Meco) <920369182@qq.com>

examples/network/tcpclient.c

@@ -1,10 +1,11 @@
 /*
- * Copyright (c) 2006-2021, RT-Thread Development Team
+ * Copyright (c) 2006-2022, RT-Thread Development Team
  *
  * SPDX-License-Identifier: Apache-2.0
  *
  * Change Logs:
  * Date           Author       Notes
+ * 2022-01-24     ChungHsuan   improve code comments
  */
 
 #include <rtthread.h>
@@ -16,7 +17,7 @@
 #include <sys/time.h>
 #include <sys/select.h>
 #endif
-#include <sys/socket.h> /* 使用BSD socket，需要包含socket.h头文件 */
+#include <sys/socket.h> /* socket.h header file is needed when using BSD socket */ /* 使用BSD socket，需要包含socket.h头文件 */
 #include "netdb.h"
 
 #define DEBUG_TCP_CLIENT
@@ -35,8 +36,11 @@ static int started = 0;
 static int is_running = 0;
 static char url[256];
 static int port = 8080;
-static const char send_data[] = "This is TCP Client from RT-Thread."; /* 发送用到的数据 */
+static const char send_data[] = "This is TCP Client from RT-Thread."; /* The message be sent */ /* 发送用到的数据 */
 
+/**
+* @brief  This function is for creating a tcp client on RT-Thread
+*/
 static void tcpclient(void *arg)
 {
     int ret;
@@ -48,7 +52,7 @@ static void tcpclient(void *arg)
 
     struct timeval timeout;
     fd_set readset;
-
+    /* Get host address by parameter url(Domain name resolution if input domain) */
     /* 通过函数入口参数url获得host地址（如果是域名，会做域名解析） */
     host = gethostbyname(url);
     if (host == RT_NULL)
@@ -56,7 +60,7 @@ static void tcpclient(void *arg)
         LOG_E("Get host by name failed!");
         return;
     }
-
+    /* Allocate space for recv_data */
     /* 分配用于存放接收数据的缓冲 */
     recv_data = rt_malloc(BUFSZ);
     if (recv_data == RT_NULL)
@@ -64,24 +68,26 @@ static void tcpclient(void *arg)
         LOG_E("No memory");
         return;
     }
-
+    /* Create a socket and set it to SOCK_STREAM(TCP) */
     /* 创建一个socket，类型是SOCKET_STREAM，TCP类型 */
     if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1)
     {
+        /* Failed on creatinf socket */
         /* 创建socket失败 */
         LOG_E("Create socket error");
         goto __exit;
     }
-
+    /* Initialize server side address */
     /* 初始化预连接的服务端地址 */
     server_addr.sin_family = AF_INET;
     server_addr.sin_port = htons(port);
     server_addr.sin_addr = *((struct in_addr *)host->h_addr);
     rt_memset(&(server_addr.sin_zero), 0, sizeof(server_addr.sin_zero));
-
+    /* Connect to server */
     /* 连接到服务端 */
     if (connect(sock, (struct sockaddr *)&server_addr, sizeof(struct sockaddr)) == -1)
     {
+        /*Failed on connecting to server*/
         /* 连接失败 */
         LOG_E("Connect fail!");
         goto __exit;
@@ -101,49 +107,56 @@ static void tcpclient(void *arg)
         /* Wait for read */
         if (select(sock + 1, &readset, RT_NULL, RT_NULL, &timeout) == 0)
             continue;
-
+        /* Receive the maximum size 1024 bytes from socket */
         /* 从sock连接中接收最大BUFSZ - 1字节数据 */
         bytes_received = recv(sock, recv_data, BUFSZ - 1, 0);
         if (bytes_received < 0)
         {
+            /* Receive failed and close the connection */
             /* 接收失败，关闭这个连接 */
             LOG_E("Received error, close the socket.");
             goto __exit;
         }
         else if (bytes_received == 0)
         {
+            /* Print warning message when recv function return 0 */
             /* 打印recv函数返回值为0的警告信息 */
             LOG_W("Received warning, recv function return 0.");
             continue;
         }
         else
         {
+            /* Receive data sucessfully and append '\0' at the end of message */
             /* 有接收到数据，把末端清零 */
             recv_data[bytes_received] = '\0';
 
             if (rt_strcmp(recv_data, "q") == 0 || rt_strcmp(recv_data, "Q") == 0)
             {
+                /* If the first letter is 'q' or 'Q', close the connection */
                 /* 如果是首字母是q或Q，关闭这个连接 */
                 LOG_I("Got a 'q' or 'Q', close the socket.");
                 goto __exit;
             }
             else
             {
+                /* Show the message in terminal */
                 /* 在控制终端显示收到的数据 */
                 LOG_D("Received data = %s", recv_data);
             }
         }
-
+        /* Send message to connected socket */
         /* 发送数据到sock连接 */
         ret = send(sock, send_data, rt_strlen(send_data), 0);
         if (ret < 0)
         {
+            /* Send failed, close the connection */
             /* 发送失败，关闭这个连接 */
             LOG_I("send error, close the socket.");
             goto __exit;
         }
         else if (ret == 0)
         {
+            /* Print warning message when send function return 0 */
             /* 打印send函数返回值为0的警告信息 */
             LOG_W("Send warning, send function return 0.");
         }
@@ -165,6 +178,9 @@ __exit:
     return;
 }
 
+/**
+* @brief    The usage description of tcp client on rt-Thread
+*/
 static void usage(void)
 {
     rt_kprintf("Usage: tcpclient -h <host> -p <port>\n");
@@ -178,6 +194,9 @@ static void usage(void)
     rt_kprintf("  --help       Print help information\n");
 }
 
+/**
+* @brief    This function is for testing tcp client on rt-Thread
+*/
 static void tcpclient_test(int argc, char** argv)
 {
     rt_thread_t tid;