TFTP协议实现

   依据TFTP协议的规定,实现通过TFTP来实现文件的传输功能。

TFTP Server：

实现功能：实现TFTP服务器，可以让用户下载文件

命令：  tftps rootdir（请求的文件路径）

实现思路：

监听69端口

接收到数据后，fork子进程服务该客户端

分析客户端的请求报文，检查是否有扩展参数

如果有扩展参数，则回应OACK，并等待客户端对OACK做回应

启动传输数据

文件传输结束后子进程退出

tftps.c


int main(int argc,char **argv)
{
    int server_sockfd,client_sockfd;
    int server_len,client_len;
    struct sockaddr_in server_address;
    struct sockaddr_in client_address;
    char recv_buf[516] = {};
    char send_buf[516] = {};
    char recv_cmd[4] = {};
    int byte;
    int n = 0;
    int pid,fd;

    server_sockfd = socket(AF_INET,SOCK_DGRAM,0);
    bzero(&server_address,sizeof(server_address));
    server_address.sin_family = AF_INET;
    server_address.sin_addr.s_addr = inet_addr("192.168.220.59");

//我的PC机IP地址
    server_address.sin_port = htons(69);
    server_len = sizeof(server_address);
    bind(server_sockfd,(struct sockaddr*)&server_address,server_len);

    if((byte = recvfrom(server_sockfd,recv_buf,516,0,(structsockaddr *)&client_address,sizeof(struct sockaddr))) == -1)
    {
        perror("recvfrom");
        exit(0);
    }

//创建一个进程来分析收到的报文信息
    if((pid = fork()) == 0)
    {
        if(recv_buf[1] == 1)  //为下载文件请求
        {
            printf("this is a read request:\n");
            if((fd = open(recv_buf[2],O_RDONLY)) < 0)
            {
                perror("open");
                exit(0);
            }


            while(1)
            {
                recvfrom(server_sockfd,recv_cmd,4,0,(struct sockaddr *)&client_address,sizeof(struct sockaddr));
                read(fd,send_buf+4,sizeof(send_buf+4));

//将文件内容读入数据区
                send_buf[1] = 3;

//构造报文
                if((byte = sendto(server_sockfd,send_buf,516,0,(struct sockaddr *)&client_address,sizeof(struct sockaddr))) == 516)
                {
                    sendto(server_sockfd,send_buf,4,0,(struct sockaddr *)&client_address,sizeof(struct sockaddr));
                    send_buf[3]++;
                }

//TFTP每次发送512个字节，附带四个字节的报文信息，小于516时就代表文件传输完毕
                else
                    exit(0);
            }
        }
        if (recv_buf[1] == 2) //为上传文件请求
        {
            printf("this is a write request:\n");
            if((fd = open(recv_buf[2],O_RDWR|O_CREAT)) < 0)
            {
                perror("open");
                exit(0);
            }
            while(1)
            {
                recvfrom(server_sockfd,recv_cmd,4,0,(struct sockaddr *)&client_address,sizeof(struct sockaddr));
                recvfrom(server_sockfd,recv_buf,512,0,(struct sockaddr *)&client_address,sizeof(struct sockaddr));
                write(fd,send_buf+4,sizeof(send_buf+4));
                send_buf[1] = 3;
                if((byte = sendto(server_sockfd,send_buf,516,0,(struct sockaddr *)&client_address,sizeof(struct sockaddr))) == 516)
                {
                    sendto(server_sockfd,send_buf,4,0,(struct sockaddr *)&client_address,sizeof(struct sockaddr));
                    send_buf[3]++;
                }
                else
                    exit(0);
            }
        }
        close(fd);
    }
    else
        return 0;
}
        
            


TFTP Client：

实现功能：通过tftp下载文件

命   令：tftpc ip file

实现思路：

构造请求报文，送至服务器

等待服务器回应

分析服务器回应

循环接收数据，直到接收到的数据包小于标准数据包

tftpc.c

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

int main(int argc,char **argv)
{
    int sockfd;
    struct sockaddr_in server;
    char read_cmd[100] = {};
    char buf[516]="";
    char *str;
    int addrlen = sizeof(server);
    int fd,rew,recv,read_num,send_num;
    int n = 0,num;
    char filename[100] = {};
    
    if(argc == 1)
    {
        printf("ERROR:please input a filename:\n");
        exit(0);
    }
    else if(argc == 2)
    {
        strcpy(filename,argv[1]);
    }
    bzero(&server, sizeof(struct sockaddr_in));
    server.sin_family = AF_INET;
    server.sin_port = htons(69);
    server.sin_addr.s_addr = inet_addr("192.168.220.59");
    
    printf("please input read?write:1 or 2: ");
    scanf("%d",&num);
    rew = sprintf(read_cmd,"%c%c%s%c%s%c",0,num,filename,0,"octet",0);
    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if(sockfd < 0)
    {
        perror("Invalid socket");
        exit(1);
    }

    sendto(sockfd, read_cmd, rew, 0, (struct sockaddr*)&server, sizeof(struct sockaddr));
    if((fd = open(filename, O_RDWR|O_CREAT))<0)    
    {        
        perror("open");
        exit(1);
    }

    if (num == 1)
    {
        num = 0;
        do{
            bzero(buf,sizeof(buf));
            recv = recvfrom(sockfd, buf, 516, 0, (struct sockaddr*)&server, &addrlen);    
            write(fd, buf+4, 512);
            if(n == 255)
            {
                num++;
                n = -1;
            }
            rew = sprintf(read_cmd,"%c%c%c%c",0,4,num,++n);
            sendto(sockfd, read_cmd, rew, 0, (struct sockaddr*)&server, sizeof(struct sockaddr));
        }while(recv == 516);
    }
    
    if( num == 2)
    {
        do{
            bzero(buf,sizeof(buf));
            recvfrom(sockfd, buf, 4, 0, (struct sockaddr*)&server, &addrlen);        
            buf[1] = 3;
            if((unsigned char)buf[3]==255)
            {
                buf[2]++;
            }
            buf[3]++;
            read_num = read(fd,buf+4,512);
            printf("%d\n",send_num);
            send_num = sendto(sockfd, buf, read_num+4, 0, (struct sockaddr*)&server, sizeof(struct sockaddr));
        }while(read_num==512);
    }                    
    close(fd);
    return 0;
}