网络编程 day30

基于ftp的服务器下载

#include
#include
#include
#include
#include
#include

#define ERR_MSG(msg) do{\
	fprintf(stderr, "\nline:%d: %s %s ", __LINE__, __FILE__, __func__);\
	perror("socket");\
}while(0)

#define IP "192.168.2.89"  //ifconfig出来的本机ip
#define PORT 69            //1024~49151,网络字节序
#define CLI_PORT 8888
#define CLI_IP "192.168.2.11"

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

	//填充服务器的地址信息结构体，给sendto函数使用
	//sendto函数中，想发给谁，就填谁的地址信息
	struct sockaddr_in sin;
	sin.sin_family      = AF_INET;     //必须填AF_INET;
	sin.sin_port        = htons(PORT); //1024~49151,网络字节序
	sin.sin_addr.s_addr = inet_addr(IP);

	printf("输入要下载的文件名>>");
	char filename[20] = "";
	scanf("%s",filename);
	getchar();
	//组下载请求包
	char buf[516] = "";

	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)
	{
		ERR_MSG("sendto");
		return -1;
	}
	printf("send success __%d__\n",__LINE__);

	//打开文件,用于存储数据
	int fd = -1;
	socklen_t addrlen = sizeof(sin);
	ssize_t res = 0;
	unsigned short int num = 0;

	//接收
	struct sockaddr_in addr;
	socklen_t addrlen = sizeof(addr);
	while(1)
	{
		bzero(buf,sizeof(buf));
		if(recvfrom(cfd, buf, sizeof(buf), 0, (struct sockaddr*)&addr, &addrlen) < 0)
		{
			ERR_MSG("recvfrom");
			return -1;
		}
		
		//判断是错误包还是数据包
		if(3 == buf[1])
		{
			if(fd < 0)
			{
				fd = open(filename, O_WRONLY|O_CREAT|O_TRUNC, 0664);
				if(fd < 0)
				{
					ERR_MSG("open");
					return -1;
				}
			}
			//判断服务器发送过来的数据包是否是需要的数据包，防止重复收包
			if(htons(num+1) == *(unsigned short*)(buf+2))
			{
				num++;

				//将数据存储到文件中，注意最后一次的数据长度小于512
				if(write(fd, buf+4, res-4) < 0)
				{
					ERR_MSG("write");
					return -1;
				}

				//回复ACK包，由于数据包的前四个字节与ACK包只有操作码不一致
				//所以只需要修改操作码为4即可
				buf[1] = 4;
				if(sendto(cfd, buf, 4, 0, (struct sockaddr*)&sin, sizeof(sin)) < 0)
				{
					ERR_MSG("sendto");
					return -1;
				}

				//若数据小于512，跳出循环
				if(res-2-2<512)
				{
					printf("下载完毕\n");
					break;
				}
			}
		}
		else if(5 == buf[1])    //错误包
		{
			printf("download failed:%s\n", buf+4);
			break;
		}
	}
	close(fd);

	//关闭套接字
	close(cfd);				
	return 0;	
}