基于UDP的TFTP文件传输

#include <myhead.h>
#define SER_PORT 69
#define SER_IP "192.168.125.64"
int main(int argc, const char *argv[])
{
	//以写的形式打开要写入的文件
	int fd=-1;
	if((fd=open("./5.png",O_WRONLY|O_CREAT|O_TRUNC,0664))==-1)
	{
		perror("open error");
		return -1;
	}
	//创建用于通信的套接字文件描述符
	int cfd = socket(AF_INET,SOCK_DGRAM,0);
	if(cfd==-1)
	{
		perror("socket error");
		return -1;
	}
	//填充服务器的地址信息结构体
	struct sockaddr_in sin;
	sin.sin_family = AF_INET;
	sin.sin_port= htons(SER_PORT);
	sin.sin_addr.s_addr = inet_addr(SER_IP);
	socklen_t socklen = sizeof(sin);
//向服务器发送下载请求
	short str=0;
	char buf[516]="";
	//组装请求数据
	short *p1 = (short *)buf;
	*p1 =htons(1);
	char *p2 = buf+2;
	strcpy(p2,"5.png");
	char *p3=p2+strlen(p2)+1;
	strcpy(p3,"octet");
	int len =4+strlen(p2)+strlen(p3);
	//向服务器发送请求
	sendto(cfd,buf,len,0,(struct sockaddr*)&sin,sizeof(sin));
	while(1)
	{
		bzero(buf,sizeof(buf));
		//向后移动指针，读取数据
		lseek(cfd,4,SEEK_SET);
		int res=recvfrom(cfd,buf,sizeof(buf),0,(struct sockaddr*)&sin,&socklen);
		char *sbuf=buf+4;
		write(fd,sbuf,res-4);
		printf("%d\n",res);
		//判断是否拷贝完成
		if(res<516)
		{
			break;
		}
		bzero(buf,sizeof(buf));
		short *p1 = (short *)buf;
		*p1 =htons(4);
		short *p2 = (short *)(buf+2);
		str++;
		*p2=htons(str);
		printf("%d\n",str);
		len =4;
		//发送ACK,继续拷贝
		sendto(cfd,buf,len,0,(struct sockaddr*)&sin,sizeof(sin));
	}
	//关闭套接字
	close(cfd);
	//关闭文件指针
	close(fd);
	return 0;
}