1、UDP下载

#include<myhead.h>

#define ERR_MSG(msg)  do{\
    fprintf(stderr, "__%d__:", __LINE__); \
    perror(msg);\
}while(0)

#define SER_PORT 8888               //端口号，范围1024~49151
#define SET_IP  "192.168.114.85"   //本机IP，ifconfig

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_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
	struct sockaddr_in sin;
	sin.sin_family    = 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':
				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);
	}
END:
	//关闭套接字
	
	close(cfd);
	return 0;
}

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

	printf("请输入要下载的文件名>>>");
	scanf("%s",filename);
	while(getchar()!=10)
	unsigned short* ptr1 = (unsigned short*)buf;
	*ptr1 = htons(1);

	char* ptr2 = buf+2;
	strcpy(ptr2,filename);

	char* ptr4 = ptr2+strlen(filename)+1;

	strcpy(ptr4,"octet");

	int size = 2+strlen(ptr2)+1+strlen(ptr4)+1;

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

	printf("sendto download request success\n");

	while(1)
   	{
		//接收数据 recvfrom,接收地址信息
		//组ACK包
		//发送ACK sendto
		//判断数据是否小于512个字节，若小于则下载完成
	}

	return 0;
}

2、思维导图