LWIP和FATFS 实现 FTP 服务端

目录

一、前言

二、LWIP 和 FTP 简介

1.LWIP

2.FTP

三、实现 FTP 服务端的主要步骤

1.初始化 LWIP

2.创建 FTP 服务器任务

3.处理客户端连接

4.实现 FTP 命令处理

5.文件系统操作

6.错误处理和日志记录

四、示例代码

1.创建FTP任务

2. FTP任务代码

3.处理交互数据

4.成功截图

五、总结

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一、前言

        在嵌入式系统开发中，有时候需要实现文件传输功能，而 FTP（File Transfer Protocol）是一种常用的文件传输协议。LWIP（Lightweight IP）是一个轻量级的 TCP/IP 协议栈，非常适合在资源受限的嵌入式系统中使用。本文将介绍如何使用 LWIP 实现一个简单的 FTP 服务端。

二、LWIP 和 FTP 简介

1.LWIP

        LWIP 是一个开源的轻量级 TCP/IP 协议栈，它具有占用内存少、可裁剪性强等特点，非常适合在嵌入式系统中使用。LWIP 支持多种网络接口，包括以太网、Wi-Fi 等，可以方便地与各种硬件平台进行集成。

2.FTP

        FTP 是一种用于在网络上进行文件传输的协议，它采用客户端 - 服务器模式。客户端通过向服务器发送命令来请求文件传输、目录列表等操作，服务器则根据客户端的请求进行相应的处理，并返回结果。FTP 支持两种传输模式：主动模式和被动模式。在主动模式下，服务器主动发起数据连接；在被动模式下，服务器等待客户端发起数据连接。

三、实现 FTP 服务端的主要步骤

1.初始化 LWIP

• 在嵌入式系统中，首先需要正确初始化 LWIP 协议栈。这包括配置网络接口、IP 地址、子网掩码、网关等网络参数。
• 确保网络硬件（如以太网控制器）正常工作，并与 LWIP 进行正确的交互。

2.创建 FTP 服务器任务

• 在应用程序中创建一个专门的任务来处理 FTP 服务端的功能。这个任务可以使用 LWIP 的 API 来监听特定端口（通常是 FTP 的默认端口 21），等待客户端的连接请求。
• 例如，可以使用 LWIP 的socket函数创建一个 TCP 套接字，并使用bind函数将其绑定到指定的端口，然后使用listen函数开始监听连接请求。

3.处理客户端连接

• 当有客户端连接请求到达时，接受这个连接并创建一个新的任务来处理与该客户端的通信。
• 对于每个客户端连接，可以使用 LWIP 的accept函数来接受连接，并为每个连接分配一个独立的任务或线程（取决于系统的支持）来处理后续的 FTP 命令和数据传输。

4.实现 FTP 命令处理

• 在处理客户端连接的任务中，实现对各种 FTP 命令的解析和处理。常见的 FTP 命令包括USER（用户登录）、PASS（密码验证）、CWD（改变目录）、LIST（列出目录）、RETR（下载文件）、STOR（上传文件）等。
• 根据接收到的命令，执行相应的操作，并向客户端发送适当的响应码和消息。例如，对于LIST命令，可以遍历当前目录下的文件和子目录，并将其列表发送给客户端。

5.文件系统操作

• 为了实现文件传输和目录操作，需要与嵌入式系统中的文件系统进行交互。这可能涉及到读取文件内容、写入文件、列出目录中的文件等操作。
• 可以使用现有的文件系统库（如 FatFs）来简化文件系统的操作，或者根据具体的存储设备（如内部 Flash、SD 卡等）实现自定义的文件系统操作函数。

6.错误处理和日志记录

• 在 FTP 服务端的实现中，需要考虑各种错误情况，如连接失败、文件不存在、权限不足等。对于这些错误情况，需要向客户端发送相应的错误响应码，并进行适当的日志记录，以便于调试和故障排除。
• 可以使用 LWIP 的错误处理机制和日志记录功能，或者在应用程序中实现自己的错误处理和日志记录机制。

四、示例代码

        本文对lwip的移植代码不做示例，以单片机网络可以正常访问ip可以ping通后为基础。以ucosIII系统为例，创建的FTP服务代码是一个独立的任务，如果是freertos系统的话把时间调度那句代码替换一下就行了。

1.创建FTP任务

//FTP任务
#define FTP_TASK_PRIO 		9
//任务堆栈大小
#define FTP_STK_SIZE		1024	
//任务控制块
OS_TCB FTPTaskTCB;
//任务堆栈
CPU_STK FTP_TASK_STK[FTP_STK_SIZE];
//任务函数
void ftpd_thread(void *pdata); //创建FTP线程
//返回值:0 FTP创建成功
//		其他 FTP创建失败
u8 FTP_demo_init(void)
{OS_ERR err;CPU_SR_ALLOC();OS_CRITICAL_ENTER();//进入临界区//创建FTP任务OSTaskCreate((OS_TCB 	* )&FTPTaskTCB,		(CPU_CHAR	* )"FTP task", 		(OS_TASK_PTR )ftpd_thread, 			(void		* )0,					(OS_PRIO	  )FTP_TASK_PRIO,     (CPU_STK   * )&FTP_TASK_STK[0],	(CPU_STK_SIZE)FTP_STK_SIZE/10,	(CPU_STK_SIZE)FTP_STK_SIZE,		(OS_MSG_QTY  )0,					(OS_TICK	  )0,					(void   	* )0,					(OS_OPT      )OS_OPT_TASK_STK_CHK|OS_OPT_TASK_STK_CLR,(OS_ERR 	* )&err);OS_CRITICAL_EXIT();	//退出临界区return err;
}

注意任务堆栈大小，堆栈设置太小的话，有的时候会发生内存溢出导致程序崩溃，或者socked不能创建等问题。

2. FTP任务代码

void ftpd_thread(void *par)
{OS_ERR err;int numbytes;int sockfd, maxfdp1;struct sockaddr_in local;fd_set readfds, tmpfds;struct conn *conn;u32 addr_len = sizeof(struct sockaddr);#if 0char *ftp_buf = (char *) malloc(FTP_BUFFER_SIZE);	
#endifprintf("Mount OK\n\r");local.sin_port = htons(FTP_CMD_PORT);local.sin_family = PF_INET;local.sin_addr.s_addr = INADDR_ANY;FD_ZERO(&readfds);FD_ZERO(&tmpfds);sockfd = socket(AF_INET, SOCK_STREAM, 0);if (sockfd < 0) {printf("ERROR: Create socket\r\n");return;}printf("SUCCESS: Create socket\r\n");if (bind(sockfd, (struct sockaddr *) &local, addr_len) < 0) {printf("ERROR: Bind socket\r\n");}printf("SUCCESS: Bind socket\r\n");if (listen(sockfd, FTP_MAX_CONNECTION) < 0) {printf("ERROR: Listen %d socket connections\r\n", FTP_MAX_CONNECTION);}printf("SUCCESS: Listen socket\r\n");FD_SET(sockfd, &readfds);for (;;) {/* get maximum fd */maxfdp1 = sockfd + 1;conn = conn_list;while (conn != NULL) {if (maxfdp1 < conn->sockfd + 1)maxfdp1 = conn->sockfd + 1;FD_SET(conn->sockfd, &readfds);conn = conn->next;}tmpfds = readfds;if (select(maxfdp1, &tmpfds, 0, 0, 0) == 0)continue;if (FD_ISSET(sockfd, &tmpfds)) {int com_socket;struct sockaddr_in remote;com_socket = accept(sockfd, (struct sockaddr *) &remote, (socklen_t *) & addr_len);if (com_socket == -1) {printf("Error on accept()\nContinuing...\r\n");continue;} else {printf("Got connection from %s\r\n", inet_ntoa(remote.sin_addr));send(com_socket, FTP_WELCOME_MSG, strlen(FTP_WELCOME_MSG), 0);FD_SET(com_socket, &readfds);/* new conn */if(conn!=NULL){destroy_conn(conn);conn=NULL;}conn = alloc_new_conn();if (conn != NULL) {strcpy(conn->currentdir, FTP_SRV_ROOT);conn->sockfd = com_socket;conn->remote = remote;}}}{struct conn *next;conn = conn_list;while (conn != NULL) {next = conn->next;if (FD_ISSET(conn->sockfd, &tmpfds)) {numbytes = recv(conn->sockfd, ftp_buf, FTP_BUFFER_SIZE, 0);if (numbytes == 0 || numbytes == -1) {printf("Client %s disconnected\r\n", inet_ntoa(conn->remote.sin_addr));FD_CLR(conn->sockfd, &readfds);if(conn!=NULL){close(conn->sockfd);destroy_conn(conn);conn=NULL;}if(sockfd_ft!=-1){closesocket(sockfd_ft);sockfd_ft=-1;}} else {ftp_buf[numbytes] = 0;if (ftp_process_request(conn, ftp_buf) == -1) {printf("Client %s disconnected\r\n", inet_ntoa(conn->remote.sin_addr));if(conn!=NULL){close(conn->sockfd);destroy_conn(conn);conn=NULL;}if(sockfd_ft!=-1){closesocket(sockfd_ft);sockfd_ft=-1;}}OSTimeDlyHMSM(0,0,0,1,OS_OPT_TIME_HMSM_STRICT,&err); //延时1ms}}conn = next;}}}
}static struct conn *alloc_new_conn(void)
{struct conn *conn;conn = (struct conn *) mymalloc(SRAMEX,sizeof(struct conn));conn->next = conn_list;conn->offset = 0;conn_list = conn;/*    printf("Alloc addr: %p\r\n", conn); */return conn;
}static void destroy_conn(struct conn *conn)
{struct conn *list;if (conn_list == conn) {conn_list = conn_list->next;conn->next = NULL;} else {list = conn_list;while (list->next != conn)list = list->next;list->next = conn->next;conn->next = NULL;}myfree(SRAMEX,conn);
}

 创建一个 TCP 服务器套接字，并监听 FTP 端口（默认端口为 21）,有数据传给服务器端以后，通过ftp_process_request函数做处理。

3.处理交互数据

static int ftp_process_request(struct conn *conn, char *buf)
{OS_ERR err;FRESULT rc;FIL file;ftp_cmd_user cmd;int num_bytes;char *spare_buf;char *msgsend;spare_buf=(char *) mymalloc(SRAMEX,256);msgsend=(char *) mymalloc(SRAMEX,256);memset(msgsend,0,256);memset(spare_buf,0,256);struct timeval tv;fd_set readfds;char *sbuf;char *parameter_ptr, *ptr;struct sockaddr_in pasvremote, local;u32 addr_len = sizeof(struct sockaddr_in);int ret = 0;		int led_r = 0, led_w = 0;	sbuf = (char *) mymalloc(SRAMEX,FTP_BUFFER_SIZE);if (sbuf == NULL) {printf("ERROR: mymalloc for conn\r\n");return -1;}/* printf("SUCCESS: mymalloc for conn\r\n"); */tv.tv_sec = 3;tv.tv_usec = 0;/* remove \r\n */ptr = buf;while (*ptr) {if (*ptr == '\r' || *ptr == '\n')*ptr = 0;ptr++;}parameter_ptr = strchr(buf, ' ');if (parameter_ptr != NULL)parameter_ptr++;/* debug: */printf("%s requested \"%s\"\r\n", inet_ntoa(conn->remote.sin_addr), buf);cmd = (ftp_cmd_user) do_parse_command(buf);
#if 0if (cmd > CMD_PASS && conn->status != LOGGED_STAT) {do_send_reply(conn->sockfd, "550 Permission denied.\r\n");myfree(SRAMEX,sbuf);return 0;}
#endifswitch (cmd) {case CMD_USER:
#if 0printf("%s sent login \"%s\"\r\n", inet_ntoa(conn->remote.sin_addr), parameter_ptr);/* login correct */if (strcmp(parameter_ptr, FTP_USER) == 0) {do_send_reply(conn->sockfd, "331 Password required for \"%s\"\r\n", parameter_ptr);conn->status = USER_STAT;} else {/* incorrect login */do_send_reply(conn->sockfd, "530 Login incorrect. Bye.\r\n");ret = -1;}
#endifsprintf(msgsend,"331 Password required for \"%s\"\r\n", parameter_ptr);do_send_reply_me(conn->sockfd,msgsend);		//do_send_reply(conn->sockfd, "331 Password required for \"%s\"\r\n", parameter_ptr);break;case CMD_PASS:
#if 0printf("%s sent password \"%s\"\r\n", inet_ntoa(conn->remote.sin_addr), parameter_ptr);/* password correct */if (strcmp(parameter_ptr, FTP_PASSWORD) == 0) {do_send_reply(conn->sockfd, "230 User logged in\r\n");conn->status = LOGGED_STAT;printf("%s Password correct\r\n", inet_ntoa(conn->remote.sin_addr));} else {/* incorrect password */do_send_reply(conn->sockfd, "530 Login or Password incorrect. Bye!\r\n");conn->status = ANON_STAT;ret = -1;}
#endifsprintf(msgsend,"230 Password OK. Current directory is %s\r\n", FTP_SRV_ROOT);do_send_reply_me(conn->sockfd,msgsend);			//do_send_reply(conn->sockfd, "230 Password OK. Current directory is %s\r\n", FTP_SRV_ROOT);break;case CMD_LIST:sprintf(msgsend,"150 Opening Binary mode connection for file list.\r\n");do_send_reply_me(conn->sockfd,msgsend);			//do_send_reply(conn->sockfd, "150 Opening Binary mode connection for file list.\r\n");do_full_list(conn->currentdir, conn->pasv_sockfd);close(conn->pasv_sockfd);conn->pasv_active = 0;sprintf(msgsend,"226 Transfer complete.\r\n");do_send_reply_me(conn->sockfd,msgsend);		//do_send_reply(conn->sockfd, "226 Transfer complete.\r\n");break;case CMD_NLST:sprintf(msgsend,"150 Opening Binary mode connection for file list.\r\n");do_send_reply_me(conn->sockfd,msgsend);		//do_send_reply(conn->sockfd, "150 Opening Binary mode connection for file list.\r\n");do_simple_list(conn->currentdir, conn->pasv_sockfd);close(conn->pasv_sockfd);conn->pasv_active = 0;sprintf(msgsend,"226 Transfer complete.\r\n");do_send_reply_me(conn->sockfd,msgsend);			//do_send_reply(conn->sockfd, "226 Transfer complete.\r\n");break;case CMD_TYPE:if (strcmp(parameter_ptr, "I") == 0) {sprintf(msgsend,"200 Type set to binary.\r\n");do_send_reply_me(conn->sockfd,msgsend);		//do_send_reply(conn->sockfd, "200 Type set to binary.\r\n");} else {sprintf(msgsend,"200 Switching to ASCII mode.\r\n");do_send_reply_me(conn->sockfd,msgsend);		// do_send_reply(conn->sockfd, "200 Type set to ascii.\r\n");}break;case CMD_RETR:strcpy(spare_buf, buf + 5);do_full_path(conn, parameter_ptr, spare_buf, 256);num_bytes = do_get_filesize(spare_buf);if (num_bytes == -1) {sprintf(msgsend,"550 \"%s\" : not a regular file\r\n", spare_buf);do_send_reply_me(conn->sockfd,msgsend);		//do_send_reply(conn->sockfd, "550 \"%s\" : not a regular file\r\n", spare_buf);conn->offset = 0;break;}rc = f_open(&file, spare_buf, FA_READ);if (rc != FR_OK) {printf("ERROR: open file %s for reading\r\n", spare_buf);break;}if (conn->offset > 0 && conn->offset < num_bytes) {f_lseek(&file, conn->offset);sprintf(msgsend,"150 Opening binary mode data connection for partial \"%s\" (%d/%d bytes).\r\n",spare_buf, num_bytes - conn->offset, num_bytes);do_send_reply_me(conn->sockfd,msgsend);	//do_send_reply(conn->sockfd, "150 Opening binary mode data connection for partial \"%s\" (%d/%d bytes).\r\n",//  spare_buf, num_bytes - conn->offset, num_bytes);} else {sprintf(msgsend,"150 Opening binary mode data connection for \"%s\" (%d bytes).\r\n", spare_buf, num_bytes);do_send_reply_me(conn->sockfd,msgsend);	//do_send_reply(conn->sockfd, "150 Opening binary mode data connection for \"%s\" (%d bytes).\r\n", spare_buf, num_bytes);}led_r = 0;do {f_read(&file, sbuf, FTP_BUFFER_SIZE, (unsigned *) &num_bytes);if (num_bytes > 0) {send(conn->pasv_sockfd, sbuf, num_bytes, 0);if (led_r++ % 50 == 0) {//led_toggle(LED2);}}OSTimeDlyHMSM(0,0,0,1,OS_OPT_TIME_HMSM_STRICT,&err); //延时1ms} while (num_bytes > 0);sprintf(msgsend,"226 Finished.\r\n");do_send_reply_me(conn->sockfd,msgsend);	//do_send_reply(conn->sockfd, "226 Finished.\r\n");f_close(&file);close(conn->pasv_sockfd);break;case CMD_STOR:do_full_path(conn, parameter_ptr, spare_buf, 256);rc = f_open(&file, spare_buf, FA_WRITE | FA_OPEN_ALWAYS);if (rc != FR_OK) {sprintf(msgsend,"550 Cannot open \"%s\" for writing.\r\n", spare_buf);do_send_reply_me(conn->sockfd,msgsend);	//do_send_reply(conn->sockfd, "550 Cannot open \"%s\" for writing.\r\n", spare_buf);break;}sprintf(msgsend,"150 Opening binary mode data connection for \"%s\".\r\n", spare_buf);do_send_reply_me(conn->sockfd,msgsend);	//do_send_reply(conn->sockfd, "150 Opening binary mode data connection for \"%s\".\r\n", spare_buf);FD_ZERO(&readfds);FD_SET(conn->pasv_sockfd, &readfds);printf("Waiting %d seconds for data...\r\n", tv.tv_sec);led_w = 0;while (select(conn->pasv_sockfd + 1, &readfds, 0, 0, &tv) > 0) {if ((num_bytes = recv(conn->pasv_sockfd, sbuf, FTP_BUFFER_SIZE, 0)) > 0) {unsigned bw;f_write(&file, sbuf, num_bytes, &bw);if (led_w++ % 50 == 0) {//led_toggle(LED1);}} else if (num_bytes == 0) {f_close(&file);//do_send_reply(conn->sockfd, "226 Finished.\r\n");sprintf(msgsend,"226 Finished.\r\n");do_send_reply_me(conn->sockfd,msgsend);			break;} else if (num_bytes == -1) {f_close(&file);ret = -1;break;}}close(conn->pasv_sockfd);break;case CMD_SIZE:do_full_path(conn, parameter_ptr, spare_buf, 256);num_bytes = do_get_filesize(spare_buf);if (num_bytes == -1) {sprintf(msgsend,"550 \"%s\" : not a regular file\r\n", spare_buf);do_send_reply_me(conn->sockfd,msgsend);//do_send_reply(conn->sockfd, "550 \"%s\" : not a regular file\r\n", spare_buf);} else {//do_send_reply(conn->sockfd, "213 %d\r\n", num_bytes);sprintf(msgsend,"213 %d\r\n", num_bytes);do_send_reply_me(conn->sockfd,msgsend);}break;case CMD_MDTM:sprintf(msgsend,"550 \"/\" : not a regular file\r\n");do_send_reply_me(conn->sockfd,msgsend);//do_send_reply(conn->sockfd, "550 \"/\" : not a regular file\r\n");break;case CMD_SYST:sprintf(msgsend,"215 UNIX Type: L8\r\n");do_send_reply_me(conn->sockfd,msgsend);//do_send_reply(conn->sockfd, "215 UNIX Type: L8\r\n");break;case CMD_PWD:sprintf(msgsend,"257 \"%s\" is current directory.\r\n", conn->currentdir);			//do_send_reply(conn->sockfd, "257 \"%s\" is current directory.\r\n", conn->currentdir);do_send_reply_me(conn->sockfd,msgsend);	break;case CMD_CWD:do_full_path(conn, parameter_ptr, spare_buf, 256);sprintf(msgsend,"250 Changed to directory \"%s\"\r\n", spare_buf);	//do_send_reply(conn->sockfd, "250 Changed to directory \"%s\"\r\n", spare_buf);do_send_reply_me(conn->sockfd,msgsend);memset(conn->currentdir,0,256);strcpy(conn->currentdir, spare_buf);//printf("CWD: Changed to directory %s\r\n", spare_buf);break;case CMD_CDUP://sprintf(spare_buf, "%s/%s", conn->currentdir, "..");sprintf(spare_buf, "%s", conn->currentdir);do_step_down(spare_buf);memset(conn->currentdir,0,256);	strcpy(conn->currentdir, spare_buf);sprintf(msgsend,"250 Changed to directory \"%s\"\r\n", spare_buf); //printf("path: %s\r\n", conn->currentdir);//do_send_reply(conn->sockfd, "250 Changed to directory \"%s\"\r\n", spare_buf);do_send_reply_me(conn->sockfd,msgsend);printf("CDUP: Changed to directory %s\r\n", spare_buf);break;case CMD_PORT:{int portcom[6];num_bytes = 0;portcom[num_bytes++] = atoi(strtok(parameter_ptr, ".,;()"));for (; num_bytes < 6; num_bytes++) {portcom[num_bytes] = atoi(strtok(0, ".,;()"));}sprintf(spare_buf, "%d.%d.%d.%d", portcom[0], portcom[1], portcom[2], portcom[3]);FD_ZERO(&readfds);if ((conn->pasv_sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {sprintf(msgsend,"425 Can't open data connection.\r\n");do_send_reply_me(conn->sockfd,msgsend);			//do_send_reply(conn->sockfd, "425 Can't open data connection.\r\n");close(conn->pasv_sockfd);conn->pasv_active = 0;break;}local.sin_port = htons(FTP_DATA_PORT);local.sin_addr.s_addr = INADDR_ANY;local.sin_family = PF_INET;if (bind(conn->pasv_sockfd, (struct sockaddr *) &local, addr_len) < 0) {printf("ERROR: Bind socket\r\n");}printf("SUCCESS: Bind socket to %d port\r\n", FTP_DATA_PORT);pasvremote.sin_addr.s_addr = ((u32) portcom[3] << 24) | ((u32) portcom[2] << 16) | ((u32) portcom[1] << 8) | ((u32) portcom[0]);pasvremote.sin_port = htons(portcom[4] * 256 + portcom[5]);pasvremote.sin_family = PF_INET;if (connect(conn->pasv_sockfd, (struct sockaddr *) &pasvremote, addr_len) == -1) {pasvremote.sin_addr = conn->remote.sin_addr;if (connect(conn->pasv_sockfd, (struct sockaddr *) &pasvremote, addr_len) == -1) {//do_send_reply(conn->sockfd, "425 Can't open data connection.\r\n");sprintf(msgsend,"425 Can't open data connection.\r\n");do_send_reply_me(conn->sockfd,msgsend);			close(conn->pasv_sockfd);break;}}conn->pasv_active = 1;conn->pasv_port = portcom[4] * 256 + portcom[5];printf("Connected to Data(PORT) %s @ %d\r\n", spare_buf, portcom[4] * 256 + portcom[5]);sprintf(msgsend,"200 Port Command Successful.\r\n");do_send_reply_me(conn->sockfd,msgsend);	//do_send_reply(conn->sockfd, "200 Port Command Successful.\r\n");}break;case CMD_REST:if (atoi(parameter_ptr) >= 0) {conn->offset = atoi(parameter_ptr);//do_send_reply(conn->sockfd, "350 Send RETR or STOR to start transfert.\r\n");sprintf(msgsend,"350 Send RETR or STOR to start transfert.\r\n");do_send_reply_me(conn->sockfd,msgsend);	}break;case CMD_MKD:do_full_path(conn, parameter_ptr, spare_buf, 256);if (f_mkdir(spare_buf)) {sprintf(msgsend,"550 File \"%s\" exists.\r\n", spare_buf);do_send_reply_me(conn->sockfd,msgsend);//do_send_reply(conn->sockfd, "550 File \"%s\" exists.\r\n", spare_buf);} else {sprintf(msgsend,"257 directory \"%s\" was successfully created.\r\n", spare_buf);do_send_reply_me(conn->sockfd,msgsend);//do_send_reply(conn->sockfd, "257 directory \"%s\" was successfully created.\r\n", spare_buf);}break;case CMD_DELE:do_full_path(conn, parameter_ptr, spare_buf, 256);if (f_unlink(spare_buf) == FR_OK){sprintf(msgsend,"250 file \"%s\" was successfully deleted.\r\n", spare_buf);do_send_reply_me(conn->sockfd,msgsend);//do_send_reply(conn->sockfd, "250 file \"%s\" was successfully deleted.\r\n", spare_buf);}else {sprintf(msgsend,"550 Not such file or directory: %s.\r\n", spare_buf);do_send_reply_me(conn->sockfd,msgsend);//do_send_reply(conn->sockfd, "550 Not such file or directory: %s.\r\n", spare_buf);}break;case CMD_RMD:do_full_path(conn, parameter_ptr, spare_buf, 256);if (f_unlink(spare_buf)) {sprintf(msgsend,"550 Directory \"%s\" doesn't exist.\r\n", spare_buf);do_send_reply_me(conn->sockfd,msgsend);//do_send_reply(conn->sockfd, "550 Directory \"%s\" doesn't exist.\r\n", spare_buf);} else {sprintf(msgsend,"257 directory \"%s\" was successfully deleted.\r\n", spare_buf);do_send_reply_me(conn->sockfd,msgsend);//do_send_reply(conn->sockfd, "257 directory \"%s\" was successfully deleted.\r\n", spare_buf);}break;#if 1case CMD_PASV:do {int dig1, dig2;extern struct ip_addr my_ipaddr;unsigned char optval = 1;if(FTP_PASSV_PORT!=1499&&FTP_PASSV_PORT<=10000){FTP_PASSV_PORT=FTP_PASSV_PORT+1;}else if(FTP_PASSV_PORT==1499){FTP_PASSV_PORT=FTP_PASSV_PORT+2;}else{FTP_PASSV_PORT=1025;}conn->pasv_port = FTP_PASSV_PORT;conn->pasv_active = 1;local.sin_port = htons(conn->pasv_port);local.sin_addr.s_addr = INADDR_ANY;local.sin_family = PF_INET;dig1 = (int) (conn->pasv_port / 256);dig2 = conn->pasv_port % 256;FD_ZERO(&readfds);sockfd_ft = socket(PF_INET, SOCK_STREAM, 0);if (sockfd_ft  == -1) {sprintf(msgsend,"425 Can't open data connection.\r\n");do_send_reply_me(conn->sockfd,msgsend);		//do_send_reply(conn->sockfd, "425 Can't open data connection.\r\n");printf("Can't make passive TCP socket\r\n");ret = 1;break;}if (bind(sockfd_ft, (struct sockaddr *) &local, addr_len) == -1) {sprintf(msgsend,"425 Can't open data connection.\r\n");do_send_reply_me(conn->sockfd,msgsend);			//do_send_reply(conn->sockfd, "425 Can't open data connection.\r\n");printf("Can't bind passive socket\r\n");ret = 3;break;		}if (listen(sockfd_ft, 1) == -1) {sprintf(msgsend,"425 Can't open data connection.\r\n");do_send_reply_me(conn->sockfd,msgsend);			//do_send_reply(conn->sockfd, "425 Can't open data connection.\r\n");printf("Can't listen passive socket\r\n");ret = 4;break;}sprintf(msgsend,"227 Entering passive mode (%d,%d,%d,%d,%d,%d)\r\n",sys_save_dat.lan_devive_ip[0],sys_save_dat.lan_devive_ip[1],sys_save_dat.lan_devive_ip[2],sys_save_dat.lan_devive_ip[3],dig1, dig2);do_send_reply_me(conn->sockfd,msgsend);	FD_SET(sockfd_ft, &readfds);select(sockfd_ft + 1, &readfds, 0, 0, &tv);if (FD_ISSET(sockfd_ft, &readfds)) {conn->pasv_sockfd = accept(sockfd_ft, (struct sockaddr *) &pasvremote, (socklen_t *) & addr_len);if (conn->pasv_sockfd < 0) {printf("Can't accept socket\r\n");sprintf(msgsend,"425 Can't open data connection.\r\n");do_send_reply_me(conn->sockfd,msgsend);		//do_send_reply(conn->sockfd, "425 Can't open data connection.\r\n");ret = 5;break;} else {printf("Got Data(PASV) connection from %s\r\n", inet_ntoa(pasvremote.sin_addr));conn->pasv_active = 1;if(sockfd_ft!=-1){closesocket(sockfd_ft);sockfd_ft=-1;}}} else {ret = 6;break;}} while (0);if (ret) {if(sockfd_ft!=-1){closesocket(sockfd_ft);sockfd_ft=-1;}printf("Select err\r\n");close(conn->pasv_sockfd);conn->pasv_active = 0;ret = 0;}break;
#endifcase CMD_FEAT:sprintf(msgsend,"211 No-features\r\n");do_send_reply_me(conn->sockfd,msgsend);				//do_send_reply(conn->sockfd, "211 No-features\r\n");break;case CMD_QUIT:sprintf(msgsend,"221 Adios!\r\n");do_send_reply_me(conn->sockfd,msgsend);				//do_send_reply(conn->sockfd, "221 Adios!\r\n");ret = -1;		break;default:sprintf(msgsend,"502 Not Implemented yet.\r\n");do_send_reply_me(conn->sockfd,msgsend);				//do_send_reply(conn->sockfd, "502 Not Implemented yet.\r\n");break;}if (sbuf) {myfree(SRAMEX,sbuf);}if (spare_buf) {myfree(SRAMEX,spare_buf);}if (msgsend) {myfree(SRAMEX,msgsend);}return ret;
}/*目录处理*/
int do_step_down(char *path)
{int len, i;int flag;len = strlen(path);if(len==1){path[0]='/';path[1]=0;}else if(len>1){for(i=len-2;i>=0;i--){if(path[i]=='/'){flag=i;break;}}for(i=len-1;i>=flag;i--){if(i!=0){path[i]=0;}}}return 0;
}int do_full_path(struct conn *conn, char *path, char *new_path, size_t size)
{int len = strlen(path);if(path[0]=='.'&&path[1]==0x00){sprintf(new_path,"%s", conn->currentdir);}else if(path[0]!='/'){if(path[len-1]!='/'){if(conn->currentdir[2]==0){sprintf(new_path, "%s%s",conn->currentdir,path);}else{sprintf(new_path, "%s/%s",conn->currentdir,path);}}else{sprintf(new_path, "/%s",path);}}else{sprintf(new_path, "%s",path);}return 0;
}

关键点在于 USER（用户登录）、PASS（密码验证）、CWD（改变目录）、LIST（列出目录）、RETR（下载文件）、STOR（上传文件）这几个命令的解析，尤其是CWD，不同FTP客户端软件会发送不同的CWD命令，有的发送命令前面带/，有的不带/，要根据实际客户端做好解析，不然不能进入正确的目录，PASV命令被动连接会创建一个UDP，如果分配的堆栈不足或者lwip设置的udp连接数和内存过少，会导致PASV的UDP失败，导致不能正常运行。

4.成功截图

（1）XFTP8通讯

（2）MobaXterm通讯

两种客户端CWD发送的地址不同（带不带/），上面代码已经通过目录解析适配了。

五、总结

        本文介绍了如何使用 LWIP 实现一个简单的 FTP 服务端。通过本文的介绍，你可以了解到 LWIP 和 FTP 的基本概念，以及如何使用 LWIP 实现 FTP 服务端的步骤。在实际应用中，你可以根据自己的需求对 FTP 服务端进行扩展和优化，以满足不同的应用场景。