9.12 TFTP通信

客户端设计（仅供参考）：

下载本质：读取服务器发送的数据包，写入到本地文件
上传本质：读取本地文件内容，发送给服务器。
1、建立菜单选项，上传和下载。
2、上传功能函数：
1、只读打开本地文件
2、发送上传请求数据包
3、接收服务器应答并回复ACK包
3、1如果接收的是ACK确认包，将包修改为数据包填充本地文件内容并发送给服务器
3、2如果是错误包，上传结束，检查网络。
3、下载功能函数
1、发送下载请求包
2、循环接收服务器数据包
2.1判断收到的包如果是数据包并且块编号正确，就写入客户端文件，然后回复ACK确认包
2.2如果包的长度小于512+2+2，说明接收完毕
2.3如果是错误包。输出对应错误信息并停止接收。

TFTP下载模型：

TFTP上传模型

TFTP通信过程总结

1、服务器在69号端口等待客户端的请求
2、服务器若批准此请求,则使用临时端口与客户端进行通信
3、每个数据包的编号都有变化（从1开始）
4、每个数据包都要得到ACK的确认如果出现超时,则需要重新发送最后的包（数据或
ACK）
5、数据的长度以512Byte传输
6、小于512Byte的数据意味着传输结束

do_upload（上传文件）

void do_upload(int sockfd,struct sockaddr_in sin,const char *filename){
	char text[1024] = "";
	int text_len;
	socklen_t sinlen = sizeof(sin);
	int fd;
	int flags = 0;
	int num = 0;
	ssize_t bytes;
	text_len = sprintf(text,"%c%c%s%c%s%c",0,2,filename,0,"octet",0);
	if(sendto(sockfd,text,text_len,0,(struct sockaddr *)&sin,sinlen)<0){
		perror("sendto");
		exit(1);
	}
	while(1){
		if((bytes = recvfrom(sockfd,text,sizeof(text),0,(struct sockaddr *)&sin,&sinlen))<0){
			perror("recvfrom");
			exit(1);
		}
		printf("接收操作码：%d,块编号：%hd\n",text[1],ntohs(*(short *)(text+2)));

		if(text[1] == 5){
			printf("差错码是：%d,差错信息error:%s\n",ntohs(*(short *)(text+2)),text+4);
			return ;
		}
		else if(text[1] == 4){
			if(flags == 0){
				if((fd = open(filename,O_RDONLY))<0){
					perror("open");
					exit(1);
				}
				flags = 1;
				printf("文件打开成功:%d\n",fd);
			}
			int len = read(fd,text+4,512);
			if (len < 0) { //检查 read 函数的返回值
                perror("read");
                exit(1);
            }
		//	printf("%s\n",text+4);
			if(len == 0){
				break;
			}
			text[1] = 3;
			*(short *)(text+2) = htons(++num);
			printf("发送操作码：%d,块编号：%hd\n",text[1],ntohs(*(short *)(text+2)));
			if(sendto(sockfd,text,len+4,0,(struct sockaddr *)&sin,sinlen)<0){
				perror("sendto");
				exit(1);
			}
		}
	}
}

do_download（下载文件）

void do_download(int sockfd,struct sockaddr_in sin,const char *filename){
	char text[1024] = "";
	int text_len;
	socklen_t sinlen = sizeof(sin);
	int fd;
	int flags = 0;
	int num = 0;
	ssize_t bytes;
	
	text_len = sprintf(text,"%c%c%s%c%s%c",0,1,filename,0,"octet",0);
	if(sendto(sockfd,text,text_len,0,(struct sockaddr *)&sin,sinlen)<0){
		perror("sendto");
		exit(1);
	}
	while(1){
		if((bytes = recvfrom(sockfd,text,sizeof(text),0,(struct sockaddr *)&sin,&sinlen))<0){
			perror("recvfrom");
			exit(1);
		}
		printf("操作码:%d,块编号:%hd\n",text[1],ntohs(*(short *)(text+2)));

		if(text[1] == 5){
			printf("错误码是：%d,错误信息error：%s\n",ntohs(*(short *)(text+2)),text+4);
			return;
		}
		else if(text[1]==3){
			if(flags==0){
				if((fd = open(filename,O_WRONLY|O_CREAT|O_TRUNC,0664))<0){
					perror("open");
					exit(1);
				}
				flags = 1;
			}
			if((num+1 == ntohs(*(short *)(text+2))) && (bytes == 516)){
				num = ntohs(*(short *)(text+2));
				if(write(fd,text+4,bytes-4)<0){
					perror("write");
					exit(1);
				}
				text[1] = 4;
				if(sendto(sockfd,text,4,0,(struct sockaddr *)&sin,sinlen)<0){
					perror("sendto");
					exit(1);
				}
			}
			else if((num+1 == ntohs(*(short *)(text+2)))&&(bytes<516)){
				if(write(fd,text+4,bytes-4)<0){
					perror("write");
					exit(1);
				}
				text[1]=4;
				if(sendto(sockfd,text,4,0,(struct sockaddr *)&sin,sinlen)<0){
					perror("sendto");
					exit(1);
				}
				printf("文件下载完毕\n");
				return;
			}
		}
	}
	close(fd);
}

运行结果

完整代码

#include <myhead.h>
#define SERPORT 69
#define SERIP "192.168.11.1"

void do_download(int sockfd,struct sockaddr_in sin,const char *filename);
void do_upload(int sockfd,struct sockaddr_in sin,const char *filename);

int main(int argc, const char *argv[])
{
    //1.创建用于通信的套接字文件描述符
    int clienfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (clienfd == -1) {
        perror("socket");
        return -1;
    }
    //2.填充服务器的地址信息结构体
    struct sockaddr_in sin = {
        .sin_family = AF_INET,
        .sin_port = htons(SERPORT),
        .sin_addr.s_addr = inet_addr(SERIP)
    };
    //3.菜单栏选择
    int choice;
    char filename[100];
    while (1) { //3.菜单栏
        printf("请选择操作：\n");
        printf("1.上传文件\n");
        printf("2.下载文件\n");
        printf("3.退出\n");
        scanf("%d", &choice);
        bzero(filename, sizeof(filename));
        if (choice == 1) {
            printf("请输入要上传的文件名：");
            scanf("%s", filename);
            do_upload(clienfd, sin, filename);
        } else if (choice == 2) {
            printf("请输入要下载的文件名：");
            scanf("%s", filename);
            do_download(clienfd, sin, filename);
        } else if (choice == 3) {
            break;
        } else {
            printf("无效选项，请重新选择。\n");
        }
    }
    close(clienfd);
    return 0;
}

void do_download(int sockfd,struct sockaddr_in sin,const char *filename){
	char text[1024] = "";
	int text_len;
	socklen_t sinlen = sizeof(sin);
	int fd;
	int flags = 0;
	int num = 0;
	ssize_t bytes;
	
	text_len = sprintf(text,"%c%c%s%c%s%c",0,1,filename,0,"octet",0);
	if(sendto(sockfd,text,text_len,0,(struct sockaddr *)&sin,sinlen)<0){
		perror("sendto");
		exit(1);
	}
	while(1){
		if((bytes = recvfrom(sockfd,text,sizeof(text),0,(struct sockaddr *)&sin,&sinlen))<0){
			perror("recvfrom");
			exit(1);
		}
		printf("操作码:%d,块编号:%hd\n",text[1],ntohs(*(short *)(text+2)));

		if(text[1] == 5){
			printf("错误码是：%d,错误信息error：%s\n",ntohs(*(short *)(text+2)),text+4);
			return;
		}
		else if(text[1]==3){
			if(flags==0){
				if((fd = open(filename,O_WRONLY|O_CREAT|O_TRUNC,0664))<0){
					perror("open");
					exit(1);
				}
				flags = 1;
			}
			if((num+1 == ntohs(*(short *)(text+2))) && (bytes == 516)){
				num = ntohs(*(short *)(text+2));
				if(write(fd,text+4,bytes-4)<0){
					perror("write");
					exit(1);
				}
				text[1] = 4;
				if(sendto(sockfd,text,4,0,(struct sockaddr *)&sin,sinlen)<0){
					perror("sendto");
					exit(1);
				}
			}
			else if((num+1 == ntohs(*(short *)(text+2)))&&(bytes<516)){
				if(write(fd,text+4,bytes-4)<0){
					perror("write");
					exit(1);
				}
				text[1]=4;
				if(sendto(sockfd,text,4,0,(struct sockaddr *)&sin,sinlen)<0){
					perror("sendto");
					exit(1);
				}
				printf("文件下载完毕\n");
				return;
			}
		}
	}
	close(fd);
}

void do_upload(int sockfd,struct sockaddr_in sin,const char *filename){
	char text[1024] = "";
	int text_len;
	socklen_t sinlen = sizeof(sin);
	int fd;
	int flags = 0;
	int num = 0;
	ssize_t bytes;
	text_len = sprintf(text,"%c%c%s%c%s%c",0,2,filename,0,"octet",0);
	if(sendto(sockfd,text,text_len,0,(struct sockaddr *)&sin,sinlen)<0){
		perror("sendto");
		exit(1);
	}
	while(1){
		if((bytes = recvfrom(sockfd,text,sizeof(text),0,(struct sockaddr *)&sin,&sinlen))<0){
			perror("recvfrom");
			exit(1);
		}
		printf("接收操作码：%d,块编号：%hd\n",text[1],ntohs(*(short *)(text+2)));

		if(text[1] == 5){
			printf("差错码是：%d,差错信息error:%s\n",ntohs(*(short *)(text+2)),text+4);
			return ;
		}
		else if(text[1] == 4){
			if(flags == 0){
				if((fd = open(filename,O_RDONLY))<0){
					perror("open");
					exit(1);
				}
				flags = 1;
				printf("文件打开成功:%d\n",fd);
			}
			int len = read(fd,text+4,512);
			if (len < 0) { //检查 read 函数的返回值
                perror("read");
                exit(1);
            }
		//	printf("%s\n",text+4);
			if(len == 0){
				break;
			}
			text[1] = 3;
			*(short *)(text+2) = htons(++num);
			printf("发送操作码：%d,块编号：%hd\n",text[1],ntohs(*(short *)(text+2)));
			if(sendto(sockfd,text,len+4,0,(struct sockaddr *)&sin,sinlen)<0){
				perror("sendto");
				exit(1);
			}
		}
	}
}