自己写的一个客户端下载文件程序

服务端：

/******************************************************
功能：可以从tftp服务器下载文件
命令格式：./tftp 192.168.221.x 文件名
时间：2012-04-25
******************************************************/
#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
#include<arpa/inet.h>
#include<netinet/in.h>
#include<sys/socket.h>
#include<string.h>
#include<errno.h>
#include <netdb.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>

int main(int argc, char *argv[])
{
    int fp;
    int sockfd = 0;
    int i=0,fd;
    unsigned short port = 69;
    struct sockaddr_in cliaddr;
    struct sockaddr_in recvddr;
    char buf[1024] = "";
    struct hostent *host;
    int ret;
    fp = open(argv[2],O_WRONLY|O_CREAT);    //创建打开文件
    if((host = gethostbyname(argv[1])) == NULL)        //从输入端获取IP
    {
        fprintf(stderr, "Gethostname error\n");
        exit(1);
    }
    if(argc < 1)
    {
        printf("You not input IP and filename!\n");
        exit(1);
    }
    bzero(&cliaddr, sizeof(cliaddr));
    cliaddr.sin_family = AF_INET;
    cliaddr.sin_port = htons(port);
    cliaddr.sin_addr = *((struct in_addr *)host->h_addr);

    if((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1)    //创建套接字
    {
        perror("socket error\n");
        exit(1);
    }
    ret = sprintf(buf, "%c%c%s%c%s%c", 0, 1,argv[2], 0, "octet", 0);    //传送命令，请求下载文件
    sendto(sockfd, buf, ret, 0, (struct sockaddr *)&cliaddr, sizeof(cliaddr));
    while(1)
    {
        char sendbuf[1024] = "";
        size_t len = 0;
        unsigned int recvddr_len = sizeof(struct sockaddr);
        bzero(&sendbuf, sizeof(sendbuf));
        bzero(&buf, sizeof(buf));
        len = recvfrom(sockfd, buf, sizeof(buf), 0, (struct sockaddr *)&recvddr, &recvddr_len) ;
        if(buf[1] == 5)
        {
            printf("%s\n",buf+4);
            unlink(argv[2]);    //如果服务器没有那个文件，防止创建空文件
            exit(1);
        }
        if(buf[1] == 3)
        {
            fd = sprintf(sendbuf, "%c%c%c%c", buf[0], buf[1]+1, buf[2], buf[3]);        //接到数据后发送ACK确认
            sendto(sockfd, sendbuf, fd, 0, (struct sockaddr *)&recvddr, sizeof(recvddr));
            if((unsigned short)(i+1) == ntohs(*(unsigned short*)(buf+2)))
            {
                write(fp, (buf+4), (len-4));    //这个地方很重要，大小一定要确定好
                i = ntohs(*(unsigned short*)(buf+2));
                printf("recv:%d\n",i);
            }

        }
        if(len < 516)
        {
            printf("Accept finished!\n");
            close(fp);
            close(sockfd);
            exit(1);
        }
    }
    return 0;
}

下载中：