功能介绍：
均有服务器和客户端代码，基于TCP写的。
在同一路径下，将客户端可执行代码复制到其他的路径下，接下来再不同的路径下运行服务器和客户端。相当于另外一台电脑在访问服务器。
客户端和服务器链接成功后出现以下提示：四个功能
list//列出服务器所在目录下的文件名(除目录不显示)
put filename//上传一个文件
get filename//重服务器所在路径下载文件
quit//退出(可只退出客户端，服务器等待下一个客户端链接)

server.c

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

void list_server(int acceptfd,char *buf,int size);
int main(int argc, char const *argv[])
{
    if (argc != 2)
    {
        printf("please input %s <port>\n", argv[0]);
        return -1;
    }
    int sockfd, acceptfd;
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0)
    {
        perror("socket err.");
        return -1;
    }
    struct sockaddr_in serveraddr, caddr;
    serveraddr.sin_family = AF_INET;
    serveraddr.sin_port = htons(atoi(argv[1]));
    // serveraddr.sin_addr.s_addr=inet_addr(argv[1]);

    //自动获取ip
    //serveraddr.sin_addr.s_addr=htonl(INADDR_ANY);
    // serveraddr.sin_addr.s_addr=INADDR_ANY; //0.0.0.0
    serveraddr.sin_addr.s_addr = inet_addr("0.0.0.0");

    socklen_t len = sizeof(caddr);

    if (bind(sockfd, (struct sockaddr *)&serveraddr, sizeof(serveraddr)) < 0)
    {
        perror("bind err.");
        return -1;
    }

    if (listen(sockfd, 5) < 0)
    {
        perror("listen err.");
        return -1;
    }
    while (1)
    {
        acceptfd = accept(sockfd, (struct sockaddr *)&caddr, &len);
        if (acceptfd < 0)
        {
            perror("accept err.");
            return -1;
        }
        printf("client:ip=%s  port=%d\n",
               inet_ntoa(caddr.sin_addr), ntohs(caddr.sin_port));
        int recvbyte;
        char buf[128];
        while(1)
        {
            recvbyte=recv(acceptfd,buf,sizeof(buf),0);
            if(recvbyte < 0)
            {
                perror("recv err.");
                return -1;
            }else if(recvbyte==0)
            {
                printf("client exit.\n");
                break;
            }else 
            {
                if(strncmp(buf,"list",4)==0)
                {
                    list_server(acceptfd,buf,sizeof(buf));
                }
            }
        }

        close(acceptfd);
    }
    close(sockfd);
    return 0;
}

//list - 功能：把当前路径下的普通文件，将名字发给链接的客户端
void list_server(int acceptfd,char *buf,int size)
{
    struct dirent *file=NULL;
    struct stat st;
     //1.打开当前目录
     DIR *dir=opendir("./");
     //2.读目录中的文件，判断是否是普通文件，是将文件名发给客户端
     while( (file=readdir(dir))!=NULL)
     {
         //判断文件类型
         stat(file->d_name,&st);
         if(S_ISREG(st.st_mode))
         {
             strcpy(buf,file->d_name);
             send(acceptfd,buf,size,0);
         }
     }
    strcpy(buf,"list ok");
    send(acceptfd,buf,size,0);
}

client.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <sys/wait.h>
void list_client(int sockfd, char *buf, int size);
void show(void);
int main(int argc, char const *argv[])
{
    if (argc != 3)
    {
        printf("please input %s <ip> <port>\n", argv[0]);
        return -1;
    }
    //1.创建套接子
    int sockfd;
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0)
    {
        perror("socket error.");
        return -1;
    }
    printf("sockfd=%d\n", sockfd);
    //填充ipv4的通信结构体  服务器的ip和端口
    struct sockaddr_in serveraddr;
    serveraddr.sin_family = AF_INET;
    serveraddr.sin_port = htons(atoi(argv[2]));
    serveraddr.sin_addr.s_addr = inet_addr(argv[1]);

    //2.请求链接服务器
    if (connect(sockfd, (struct sockaddr *)&serveraddr, sizeof(serveraddr)) < 0)
    {
        perror("connect error.");
        return -1;
    }

    //5.循环发送消息  通信
    char buf[128];
    while (1)
    {
        show();
        printf("please input chose:");
        fgets(buf, sizeof(buf), stdin);
        if (buf[strlen(buf) - 1] == '\n')
            ;
        buf[strlen(buf) - 1] = '\0';
        send(sockfd, buf, sizeof(buf), 0);
        if (strncmp(buf, "list", 4) == 0)
        {
            list_client(sockfd, buf, sizeof(buf));
        }
        close(sockfd);
        return 0;
    }
}
void list_client(int sockfd, char *buf, int size)
{
    int recvbyte;
    while (1)
    {
        recvbyte = recv(sockfd, buf, size, 0);
        if (recvbyte < 0)
        {
            perror("recv err");
            return;
        }
        if (strncmp(buf, "list ok", 7) == 0)
            break;
        printf("%s\n", buf);
    }
}
void show(void)
{
    printf("---------------list------------------\n");
    printf("------------put filename------------------\n");
    printf("------------get filename---------------\n");
    printf("---------------quit------------------\n");
}