TFTP通信

1、下载

#include <myhead.h>

#define SER_PORT 69   //指定要将数据发给谁，填谁的端口号
#define SER_IP "192.168.101.50" //指定要将数据发给谁，填谁的IP

int do_download(int cfd,struct sockaddr_in sin);

int main(int argc, const char *argv[])
{
    //创建报式套接字 socket
    int cfd = socket(AF_INET, SOCK_DGRAM, 0); 
    if(cfd < 0)
    {   
        ERR_MSG("socket");    
        return -1; 
    }   
    printf("socket create success cfd=%d\n", cfd);

    //填充服务器的地址信息结构体，给sendto函数使用
    //真实的地址信息结构体根据地址族指定，AF_INET:man 7 IP
    struct sockaddr_in sin;
    sin.sin_family      = AF_INET;      //必须填AF_INET;
    sin.sin_port        = htons(SER_PORT);  
    sin.sin_addr.s_addr = inet_addr(SER_IP);

	char choose=0;
	while(1)
	{
		system("clear");
		printf("------------------------\n");
		printf("---------1、下载--------\n");
		printf("---------2、上传--------\n");
		printf("---------3、退出--------\n");
		printf("------------------------\n");
		printf("请输入:");
		scanf("%c",&choose);
		while(getchar()!=10);  //循环吸收垃圾字符，直到吸收到\n字符

		switch(choose)
		{
			case '1':
				do_download(cfd,sin);
				break;
			case '2':
				//do_upload();
				break;
			case '3':
				goto END;
				break;
			default:
				printf("输入错误，请重新输入\n");
				break;
		}

		printf("输入任意字符清屏：");
		while(getchar()!=10);
	}

#if 0
    char buf[128] = ""; /*{{{*/
    struct sockaddr_in rcvaddr;     //存储发送方的地址信息;
    socklen_t addrlen = sizeof(rcvaddr);

    while(1)
    {   
        bzero(buf, sizeof(buf));
        //发送数据----->从终端获取数据发送给指定端
        printf("请输入>>> ");
        fgets(buf, sizeof(buf), stdin);
        buf[strlen(buf)-1] = 0;

        if(sendto(cfd, buf, sizeof(buf), 0, (struct sockaddr*)&sin, sizeof(sin)) < 0)
        {
            ERR_MSG("sendto");
            return -1; 
        }
        printf("sendto success\n");

        //接收数据
        /*
        //在不考虑sendto回复信息的情况下可以使用
        //if(recvfrom(cfd, buf, sizeof(buf), 0, NULL, NULL) < 0)
        //if(recv(cfd, buf, sizeof(buf), 0) < 0)
        //if(read(cfd, buf, sizeof(buf)) < 0)
        */
        bzero(buf, sizeof(buf));    
        if(recvfrom(cfd, buf, sizeof(buf), 0, (struct sockaddr*)&rcvaddr, &addrlen) < 0)
        {
            ERR_MSG("recv");
            return -1; 
        }
        printf("[%s:%d] : %s\n", inet_ntoa(rcvaddr.sin_addr), ntohs(rcvaddr.sin_port), buf);

    }/*}}}*/
#endif
END:

    //关闭套接字
    close(cfd);


    return 0;
}

int do_download(int cfd, struct sockaddr_in sin)
{
    char filename[20] = "";
    char buf[516] = "";

    bzero(buf, sizeof(buf));
    printf("请输入要下载的文件名：");
    fgets(filename, sizeof(filename), stdin);
    filename[strlen(filename) - 1] = 0;

    //发送下载请求包
    int size = sprintf(buf, "%c%c%s%c%s%c", 0, 1, filename, 0, "octet", 0);
    if (sendto(cfd, buf, size, 0, (struct sockaddr *)&sin, sizeof(sin)) < 0)
    {
        perror("sendto");
        return -1;
    }

    int fd = -1, flag = 0;
    socklen_t addrlen = sizeof(sin);
    ssize_t res = 0;

    unsigned short num = 0; //记录数据包的编号

    //循环接收数据包，回复ACK
    while (1)
    {
        bzero(buf, sizeof(buf));
        res = recvfrom(cfd, buf, sizeof(buf), 0, (struct sockaddr *)&sin, &addrlen);
        if (res < 0)
        {
            perror("recvfrom");
            return -1;
        }
        if (3 == buf[1])
        {
            //判断收到的包是否出错
            if (htons(num + 1) == *(unsigned short *)(buf + 2))
            {
                num++;

                if (0 == flag)
                {
                    fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC, 0664);
                    if (fd < 0)
                    {
                        perror("open");
                        return -1;
                    }
                    flag = 1;
                }
                if (write(fd, buf + 4, res - 4) < 0)
                {
                    perror("write");
                    return -1;
                }

                //回复ACK,
                buf[1] = 4;
                if (sendto(cfd, buf, 4, 0, (struct sockaddr *)&sin, sizeof(sin)) < 0)
                {
                    perror("sendto");
                    return -1;
                }

                //判断数据包中下载的数据是否小于512,小于512默认传输完成
                if (res - 4 < 512)
                {
                    printf("%s 文件下载完毕\n", filename);
                    break;
                }
            }
        }
        else if (5 == buf[1])
        {
            fprintf(stderr, "错误码：%d 错误信息：%s\n", ntohs(*(unsigned short *)(buf + 2)), buf + 4);
            break;
        }
    }

    close(fd);
    return 0;
}

2、思维导图