网络编程0810作业-洪庆乐

C语言编程实现TFTP网络通信

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

//打印错误新的宏函数
#define ERR_MSG(msg)  do{\
    fprintf(stderr, " __%d__ ", __LINE__);\
    perror(msg);\
}while(0)

int main(int argc, const char *argv[])
{

	if(argc < 2)
	{
		fprintf(stderr, "请输入IP\n");
		return -1;
	}
	/*
	//将获取到的端口号字符串，转换成整形
	int port = atoi(argv[2]);
	if(port < 1024 || port > 49151)
	{
		fprintf(stderr, "port %d input error!! 1024~49151\n", port);
		return -1;
	}
	*/

	//创建报式套接字
	int sfd = socket(AF_INET, SOCK_DGRAM, 0);
	if(sfd < 0)
	{
		ERR_MSG("socket");
		return -1;                                                               
	}
                 

	//组一个请求包发送给服务器
	char filename[10] = "";
	char buf[516] = "";
	printf("请输入你要下载的文件名:");
	scanf("%s",filename);
	
	char* ptr = buf;
	short int* pa = (short int *)ptr;
	*pa = htons(1);         						//将操作码存入

	char* pb = ptr + 2;
	strcpy(pb,filename);   							//将文件名存入

	char* pc = pb+strlen(pb); 
	*pc = '\0';

	char* pd = pc + 1;
	strcpy(pd,"octet");    							//将模式存入

	size_t size = 2+strlen(pb)+1+strlen("octet")+1;        //求出请求包的长度	

	//填充服务器的IP地址以及端口号 -->因为客户端要主动发送数据包给服务器
	struct sockaddr_in sin;
	sin.sin_family      = AF_INET;
	sin.sin_port        = htons(69);
	sin.sin_addr.s_addr = inet_addr(argv[1]);                                  

	//发送请求包
	sendto(sfd,buf,size,0,(struct sockaddr*)&sin,sizeof(sin));


	struct sockaddr_in rcv_addrmsg;     //存储接收到的数据包来自哪里
	socklen_t addrlen = sizeof(rcv_addrmsg);


	//打开一个要存的文件
	int fd = open("./copy.png",O_RDWR|O_TRUNC|O_CREAT,0777);
	if(fd < 0)
	{
		ERR_MSG("open");
		return -1;
	}
	printf("打开成功\n");

	unsigned char ack[4];    //ACK包
	unsigned short code = 0; //操作码
	unsigned short newnum = 0;  //块编号 或者 错误码

	//数据的长度以512Byte传输
	char text[512] = {0}; //文件内容 或 错误信息
	int oldnum = 0;
	//主要功能代码
	while(1)
	{
		bzero(buf,sizeof(buf));
		bzero(text,sizeof(text));
		ssize_t res;
		//接收服务器发来的数据包
		res = recvfrom(sfd, buf, sizeof(buf), 0, (struct sockaddr*)&rcv_addrmsg, &addrlen);
		if(res < 0)
		{
			ERR_MSG("recvfrom");
			return -1;
		}
		printf("%ld接收成功\n",res);

		//解析操作码
		code = ntohs(*(unsigned short *)buf);
		//解析块编号 或者 错误码
		newnum = ntohs(*(unsigned short *)(buf + 2));


		//判断操作码和块编号
		if(code == 3 && newnum == (oldnum + 1))
		{
			char* a = buf + 4;
			if(res < 516)
			{
				write(fd,buf+4,res - 4);
				printf("传输完成\n");
				break;
			}
			else if(res == 516)
			{
				write(fd,buf+4,512);
			}

			//组建新的ack包
			*(unsigned short *)ack = htons(4);
			*(unsigned short *)(ack + 2) = htons(newnum);

			//向服务器发送ack包
			if(sendto(sfd, ack, 4, 0, (struct sockaddr*)&rcv_addrmsg, sizeof(rcv_addrmsg)) < 0)
			{                                                                               
				ERR_MSG("sendto");
				return -1;
			}
			printf("sendto success\n");
			oldnum++;
		}
		else if(code == 5)
		{
			printf("发生错误[%s]\n",text);
			return -1;
		}
	
	}
    printf("下载完成\n");
	close(sfd);
	return 0;
}