简单文件传输协议

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,则使用临死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)

6.小于512Byte的数据意味着传输结束

示例代码

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

void sys_err(const char *str)
{
     perror(str);
     exit(1);
}

int main(int argc,char *argv[])
 {
     int skfd = socket(AF_INET,SOCK_DGRAM,0);
     int fd = open("a.txt",O_WRONLY|O_CREAT|O_TRUNC,0664);
     unsigned char cmd[512] = "";
     int len = sprintf(cmd,"%c%c%s%c%s%c",0,1,"a.txt",0,"octet",0);//下载文件请求报文
     

     struct sockaddr_in ser_addr,from_addr;
     socklen_t from_len = sizeof(from_addr);
     bzero(&ser_addr,sizeof(ser_addr));
     ser_addr.sin_family = AF_INET;
     ser_addr.sin_port  = htons(69);//69端口为tftp服务器端口
     ser_addr.sin_addr.s_addr = inet_addr("192.168.10.59");

     sendto(skfd,cmd,len,0,(struct sockaddr *)&ser_addr,sizeof(ser_addr));
     int pack_num = 0;
     while(1)
    {
         unsigned char buf[1600] = "";
         int size = recvfrom(skfd,buf,sizeof(buf),0,(struct sockaddr *)&from_addr,&from_len);
         if(buf[1] == 5){ //5位错误码
             printf("err\n");
             break;
         }else if(buf[1] == 3){ //3为数据包
             int num = ntohs(*(unsigned short *)(buf+2));
             if(pack_num +1 == num){ //是否为想要的数据包避免数据重复接受
                     pack_num = num;
                     write(fd,buf+4,size-4);
           }
             buf[1] = 4;
             sendto(skfd,buf,4,0,(struct sockaddr *)&from_addr,sizeof(from_addr)); //发送回应报文
             if(size < 516)
                     break;
             }
     }
     close(skfd);
     close(fd);
     return 0;
}