Linux应用——FTP服务器的实现

FTP介绍

文件传输协议（File Transfer Protocol，FTP）是用于在网络上进行文件传输的一套标准协议，它工作在 OSI 模型的第七层， TCP 模型的第四层， 即应用层， 使用 TCP 传输而不是 UDP， 客户在和服务器建立连接前要经过一个“三次握手”的过程， 保证客户与服务器之间的连接是可靠的， 而且是面向连接， 为数据传输提供可靠保证。

FTP允许用户以文件操作的方式（如文件的增、删、改、查、传送等）与另一主机相互通信。

本文实现基本的文件传输（上传文件，下载文件，查看文件列表）。

程序设计架构

...待补充

规定的协议（宏定义和函数声明）

通信消息体

#define NAMESIZE 255
#define BUFFSIZE 1024
typedef struct{
　　int type;    /* 消息标志，通信双方根据标志，执行不同的操作 */
　　char file_name[NAMESIZE];    /* 文件名 */
 　　long file_size;    /* 文件大小，long类型，与系统函数表示文件大小的结构体保持一致 */
　　char file_data[BUFFSIZE];    /* 一次传输的数据大小，文件太大就多传几次拼接 */
}MSG;

消息体msg.type的值

#define LIST 1　　/* 查看文件列表请求 */
#define DOWNLOAD 2　　/* 下载文件请求 */
#define UPLOAD 3　　/* 上传文件请求 */
#define QUIT 4　　/* 退出连接请求 */
#define SUCCESS 5 /* 成功标志 */
#define FAIL 6 /* 失败标志 */
#define CONTINUE 7 /* 当传输较大文件时，可能分多次传输，当还需要传输时，标志置为CONTINUE */
#define END 8 /* 当传输文件时，表示这是最后一段数据 */

其他内容

/* server */
#define DIR_PATH "public_dir" /* server保存文件的目录 */
#define SERVER_PORT 5001 /* ftp端口 */
#define BACKLOG 10 /* 最大accept pendding */

/* client */
#define DOWNLOAD_DIR "download" /* 用户下载文件保存的位置 */
#define UPLOAD_DIR "upload" /* 用户上传文件，从该目录选择文件上传 */

函数的声明

server.h

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

#define DIR_PATH "public_dir"
#define SERVER_PORT 5001
#define BACKLOG 10 /* 最大accept pendding */
#define NAMESIZE 255 /* equals dirent.h lib */
#define BUFFSIZE 1024
typedef struct{
    int type;
    char file_name[NAMESIZE];
    long file_size;
    char file_data[BUFFSIZE];
}MSG;

typedef struct{
    int fd;
    struct sockaddr_in cin;
}Cli_info;

#define LIST 1
#define DOWNLOAD 2
#define UPLOAD 3
#define QUIT 4

#define SUCCESS 5 /* server - ok */
#define FAIL 6 /* server - faile */
#define CONTINUE 7 /* server - send not end and continue */
#define END 8 /* server - send end */

int sock_init(); /* 封装一下 socket, bind, listen操作，返回一个socket fd */
void *handle_client(void *arg);  /* 子线程执行函数 */
int do_list(int cli_fd, MSG *msg); /* 客户端请求查看文件列表时，执行 */
int do_download(int cli_fd, MSG *msg); /* 客户端下载文件时，执行 */
int do_upload(int cli_fd, MSG *msg); /* 客户端请求上传文件时，执行 */
int do_send_errmsg(int cli_fd, MSG *msg); /* 客户端类型错误时，执行 */
void print_ctime(); /* 打印当前时间，记录客户端操作时间 */

 

client.h

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

#define DOWNLOAD_DIR "download" /* user download dir */
#define UPLOAD_DIR "upload" /* user upload dir */
#define NAMESIZE 255 /* file name size, equals dirent.h */
#define BUFFSIZE 1024
#define LIST 1
#define DOWNLOAD 2
#define UPLOAD 3
#define QUIT 4
#define SUCCESS 5
#define FAIL 6
#define CONTINUE 7
#define END 8

typedef struct{
    int type;
    char file_name[NAMESIZE];
    long file_size;
    char file_data[BUFFSIZE];
}MSG;

int sock_init(); /* 封装一下 socket, bind, accept */
void do_print_cmd_list(); /* 显示指令集合 */
int do_print_file_list(int sockfd, MSG *msg); /* 请求查看文件列表 */
int do_download(int sockfd, MSG *msg); /* 下载文件 */
int do_upload(int sockfd, MSG *msg); /* 上传文件 */
int do_quit(int sockfd, MSG *msg); /* 退出，通知server，关闭相关资源 */

 

程序的实现

server.c

#include "server.h"
int main(int argc, char **argv)
{
    int server_fd = sock_init();
    if(server_fd < 0)
    {
        perror("sock init");
        exit(1);
    }

    socklen_t len = sizeof(struct sockaddr_in);
    Cli_info *cli_info;
    pthread_t tid;
    while(1)
    {
        cli_info = (Cli_info*)malloc(sizeof(Cli_info));
        bzero(&cli_info->cin, sizeof(struct sockaddr_in));
        printf("main thread: wait client connected...\n");
        cli_info->fd = accept(server_fd, 
                (struct sockaddr*)&cli_info->cin,
                &len);
        if(cli_info->fd < 0)
        {
            perror("accept");
            continue;
        }
        pthread_create(&tid, NULL, handle_client, (void *)cli_info);
    }
    
    close(server_fd);
    printf("server exit, bye.");
    return 0;
}

int sock_init()
{
    int fd = socket(AF_INET, SOCK_STREAM, 0);
    if(fd < 0)
    {
        perror("socket");
        return -1;
    }

    struct sockaddr_in sin;
    bzero(&sin, sizeof(sin));
    sin.sin_family = AF_INET;
    sin.sin_addr.s_addr = INADDR_ANY;
    sin.sin_port = htons(SERVER_PORT);

    int b_reuse = 1;
    setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &b_reuse, sizeof(b_reuse));
    
    if(bind(fd, (struct sockaddr*)&sin, sizeof(sin)) < 0)
    {
        perror("bind");
        return -2;
    }

    if(listen(fd, BACKLOG) < 0)
    {
        perror("listen");
        return -3;
    }

    return fd;
}


void *handle_client(void *arg)
{
    pthread_detach(pthread_self());
    
    Cli_info *cli_info = (Cli_info*)arg;
    int cli_fd = cli_info->fd;/*获取fd*/
    char ip_addr[64];
    /* 获取ip addr */
    inet_ntop(AF_INET, 
            (void *)&cli_info->cin.sin_addr.s_addr, ip_addr, 
            sizeof(ip_addr));
    free(cli_info); /* 及时销毁 */
    
    printf("Client(%s) connected. time:\t", ip_addr);
    print_ctime();

    int ret = -1;
    MSG msg;
    while(1)
    {
        bzero(&msg, sizeof(MSG));
        ret = recv(cli_fd, &msg, sizeof(MSG), 0);
        if(ret < 0)
        {
            perror("recv");
            continue;
        }

        if(ret == 0 || msg.type == QUIT)
        {
            printf("Client(%s) quit, time:", ip_addr);
            print_ctime();
            close(cli_fd);
            break;
        }
         
        switch(msg.type)
        {
            case LIST:
                do_list(cli_fd, &msg);
                break;
            case DOWNLOAD:
                do_download(cli_fd, &msg);
                break;
            case UPLOAD:
                do_upload(cli_fd, &msg);
                break;
            default:
                do_send_errmsg(cli_fd, &msg);
                break;
        }

        pthread_testcancel();
    }
    pthread_exit(0);
}

/* 循环读文件 name + size， 发送 */
int do_list(int cli_fd, MSG *msg)
{
    int ret = -1;

    DIR *dir = opendir(DIR_PATH);
    struct dirent *dirp;
    FILE *fp;
    char file_path[255];
    if(dir == NULL)
    {
        perror("opendir");
        return -1;
    }

    while((dirp = readdir(dir)) != NULL)
    {
        /* 小数点(.)开头是隐藏文件，跳过 */
        if(!strncmp(dirp->d_name, ".", 1))
            continue;
        bzero(file_path, sizeof(file_path));
        bzero(msg, sizeof(MSG));

        /* get & set msg->file_size*/
        sprintf(file_path, "%s/%s", DIR_PATH, dirp->d_name);
        fp = fopen(file_path, "r");
        fseek(fp, 0, SEEK_END);    
        msg->file_size = ftell(fp);
        fclose(fp);

        /* set msg->type: CONTINUE */
        msg->type = CONTINUE;

        /* set set->file_name */
        strcpy(msg->file_name, dirp->d_name);
        ret = send(cli_fd, msg, sizeof(MSG), 0);
    }

    bzero(msg, sizeof(MSG));
    msg->type = END;
    send(cli_fd, msg, sizeof(MSG), 0);
    return 0;
}

int do_download(int cli_fd, MSG *msg)
{
    int ret = -1;
    char file_path[255];
    char *buff;
    bzero(msg->file_data, sizeof(msg->file_data));
    /* 1. check file exist */
    sprintf(file_path, "%s/%s", DIR_PATH, msg->file_name);
    FILE *fp= fopen(file_path, "r");
    if(fp == NULL)
    {
        msg->type = FAIL;
        strcpy(msg->file_data, "file not exist.");
        send(cli_fd, msg, sizeof(MSG), 0);
        return -1;
    }
    fseek(fp, 0, SEEK_END);
    msg->file_size = ftell(fp);
    if(msg->file_size < 1)
    {
        msg->type = FAIL;
        strcpy(msg->file_data, "file is empty.");
        send(cli_fd, msg, sizeof(msg), 0);
        return -2;
    }

    rewind(fp);
    msg->type = CONTINUE;
    while(1)
    {
        ret = fread(msg->file_data, BUFFSIZE, 1, fp);
        send(cli_fd, msg, sizeof(MSG), 0);
        if(ret <= 0)
            break;
    }
    msg->type = END;
    send(cli_fd, msg, sizeof(msg), 0);

    printf("client download file: %s\t - ", msg->file_name);
    print_ctime();
    fclose(fp);
    return 0;
}

int do_upload(int cli_fd, MSG *msg)
{
    int ret = -1;
    char file_path[255];
    sprintf(file_path, "%s/%s", DIR_PATH, msg->file_name);
    FILE *fp = fopen(file_path, "a");/* append模式 */
    while(1)
    {
        ret = recv(cli_fd, msg, sizeof(MSG), 0);
        if(ret <= 0)/*意外错误*/
        {
            perror("upload recv error");
            fclose(fp);
            return -1;
        }

        if(msg->type != CONTINUE)
            break;
        fwrite(msg->file_data, strlen(msg->file_data), 1, fp );
    }

    fclose(fp);
    printf("client upload file: %s\t - ",msg->file_name);
    print_ctime();
    return 0;
}

int do_send_errmsg(int cli_fd, MSG *msg)
{
    printf("do_send error msg\n");
    return 0;
}


/* 打印当前的格式化时间 */
void print_ctime()
{
    time_t t;
    struct tm *tp;

    time(&t);
    tp = localtime(&t);

    printf("%d-%d-%d %d:%d:%d\n",
        tp->tm_year + 1900,
        tp->tm_mon+1,
        tp->tm_mday, 
        tp->tm_hour, 
        tp->tm_min,
        tp->tm_sec);
}

client.c

#include "client.h"
int main(int argc, char **argv)
{
    if(check_arg(argc, argv) < 0)/* check usage right */
        exit(1);

    int sockfd = sock_init(argv[1], argv[2]); 
    if(sockfd < 0)
    {
        perror("sock_init");
        exit(1);
    }

    MSG msg;
    char cmd = 0;
    do_print_cmd_list();
    while(1)
    {
        printf("Please input cmd: ");
        scanf("%c", &cmd);
        getchar();
        switch(cmd)
        {
            case 'q':
                do_quit(sockfd, &msg); /* 通知server, client exit */
                goto exit;
                break;
            case 'h':
                do_print_cmd_list();
                break;
            case 'l':
                do_print_file_list(sockfd, &msg);
                break;
            case 'd':
                do_download(sockfd, &msg);
                break;
            case 'u':
                do_upload(sockfd, &msg);
                break;
            default:
                printf("cmd illegal, please try again.\n");
                break;
        }
    }

exit:
    close(sockfd);
    exit(0);
}

/* 检查启动参数，ip port */
int check_arg(int argc, char **argv)
{
    if(argc != 3)
    {
        printf("Usage:./client [ip addr] [port]\n");
        printf("ip addr format: xxx.xxx.xxx.xxx\n");
        printf("port limit 5000~10000\n");
        return -1;
    }
     /*
     * if ip illegal ...return -2;
     * if port illegal ...return -3;
     * FIXME
     * */
    return 0;
}

int sock_init(char *ip, char *port)
{
    int fd = socket(AF_INET, SOCK_STREAM, 0);
    if(fd < 0)
    {
        perror("socket");
            return -1;
    }

    struct sockaddr_in sin;
    bzero(&sin, sizeof(sin));
    sin.sin_family = AF_INET;
    sin.sin_addr.s_addr = inet_addr(ip);
    sin.sin_port = htons(atoi(port));

    if(connect(fd, (struct sockaddr*)&sin, sizeof(sin)) < 0)
    {
        perror("connect");
        return -2;
    }
    
    return fd;
}

void do_print_cmd_list()
{
    printf("\n*************************************\n");
    printf("************** cmd list **************\n");
    printf("*** h: view help *********************\n");
    printf("*** l: print server file list ********\n");
    printf("*** d: download file *****************\n");
    printf("*** u: upload file *******************\n");
    printf("*** q: quit client *******************\n");
    printf("**************************************\n");
}

int do_print_file_list(int sockfd, MSG *msg)
{
    int ret = -1;
    printf("wait get file list...\n");
    msg->type = LIST;
    ret = send(sockfd, msg, sizeof(MSG), 0);
    if(ret <= 0)
    {
        perror("send list request error");
        return -1;
    }

    printf("*************** file list ********************\n");
    printf("no\tfile name\t\tfile size\n");
    int i = 1;
    while(1)
    {
        ret = recv(sockfd, msg, sizeof(MSG), 0);
        if(ret <= 0)
        {
            perror("recv list error");
            break;
        }

        /* server 不想继续 */
        if(msg->type != CONTINUE)
            break;

        printf("%4d: %10s\t\t%10ld\n", 
                i++,
                msg->file_name,
                msg->file_size);
    }
    printf("************** file list end ******************\n");
}
int do_download(int sockfd, MSG *msg)
{
    int ret = -1;
    bzero(msg, sizeof(MSG));
    printf("Please input file_name: ");
    fflush(stdout);
    scanf("%s", msg->file_name);
    getchar();

    /* 1. send request get file size */
    msg->type = DOWNLOAD;
    ret = send(sockfd, msg, sizeof(MSG), 0);
    if(ret <= 0)
    {
        perror("send request get file size error");
        return -1;
    }
    
    char file_path[255];
    sprintf(file_path, "%s/%s", DOWNLOAD_DIR, msg->file_name);
    FILE *fp = fopen(file_path, "a");/* append模式 */
    while(1)
    {
        ret = recv(sockfd, msg, sizeof(MSG), 0);
        if(ret <= 0)/* 意外错误 */
        {
            perror("recv: download error");
            return -2;
        }
        if(msg->type != CONTINUE) /* 正常结束 */
        {
            break;
        }
        fwrite(msg->file_data, strlen(msg->file_data), 1, fp);
    }

    printf("download file: %s ok!\n", msg->file_name);
    fclose(fp);
    return 0;
}


int do_upload(int sockfd, MSG *msg)
{
    int ret = -1;
    bzero(msg, sizeof(MSG));
    printf("Please input file name to upload: ");
    scanf("%s", msg->file_name);
    getchar();
    char file_path[255];
    sprintf(file_path, "%s/%s", UPLOAD_DIR, msg->file_name);
    FILE *fp = fopen(file_path, "r");
    if(fp == NULL)
    {
        perror("fopen");
        return -1;
    }
    fseek(fp, 0, SEEK_END);
    msg->file_size = ftell(fp);
    if(msg->file_size < 1)
    {
        printf("file is empty, can't upload.");
        return -2;
    }

    /* upload预请求(让server跳转到do_upload) */
    msg->type = UPLOAD;
    ret = send(sockfd, msg, sizeof(MSG), 0);
    if(ret <= 0)
    {
        perror("send request error");
        return -3;
    }
    /* upload */
    rewind(fp);
    while(1)
    {
        bzero(msg->file_data, BUFFSIZE);
        msg->type = CONTINUE;
        ret = fread(msg->file_data, BUFFSIZE, 1, fp);
        send(sockfd, msg, sizeof(MSG), 0);
        if(ret <= 0)
            break;
    }
    /* 通知server结束upload */
    bzero(msg->file_data, BUFFSIZE);
    msg->type = END;
    send(sockfd, msg, sizeof(MSG), 0);
    printf("upload file: %s ok.\n", msg->file_name);
    return 0;
}


int do_quit(int sockfd, MSG *msg)
{
　　/* !FIXME 可能还需要补充的其它结束操作 */
    printf("do quit\n");
    return 0;
}

---

END