客户端登陆ftp服务器

流程

与ftp服务器建立连接
发送用户名和密码
使服务器进入被动模式

代码实现

#include <stdio.h>
#include <stdlib.h>
#include <winsock2.h>

int cmd_send(SOCKET sock, char *cmd)
{
    char readbuf[512];
    int i = 0, ret;
    send(sock, cmd, strlen(cmd), 0);
    while(1)
    {
        recv(sock, &readbuf[i], 1, 0);
        if(readbuf[i] == '\n')
        {
            readbuf[++i] = '\0';
            break;
        }
        i++;
    }
    sscanf(readbuf, "%d", &ret);
    printf("%s", readbuf);
    return ret;
}

SOCKET login_ftp(char *user, char *pwd, char *server_ip)
{
    char cmd[512] = {0};
    char readbuf[512] = {0};
    SOCKET sock_client = socket(PF_INET, SOCK_STREAM, 0);

    struct sockaddr_in server_addr;
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(21);
    server_addr.sin_addr.s_addr = inet_addr(server_ip);

    if(connect(sock_client, (SOCKADDR *)&server_addr, sizeof(server_addr)) < 0)
    {
        printf("connect error\n");
        return 0;
    }
    recv(sock_client, readbuf, sizeof(readbuf), 0);
    printf("%s", readbuf);
    sprintf(cmd, "USER %s\r\n", user);
    cmd_send(sock_client, cmd);
    sprintf(cmd, "PASS %s\r\n", pwd);
    cmd_send(sock_client, cmd);
    return sock_client;
}

int main()
{
    WSADATA wsaData;
    WSAStartup(MAKEWORD(2, 2), &wsaData);

    char user[255], pwd[255], server_ip[255];
    SOCKET sock_client;

    printf("welcom to ftp_client\n");
    printf("input ip: ");
    scanf("%s", server_ip);
    printf("input user: ");
    scanf("%s", user);
    printf("input password: ");
    scanf("%s", pwd);

    sock_client = login_ftp(user, pwd, server_ip);
    closesocket(sock_client);
    WSACleanup();

    return 0;
}

简单代码解释

cmd_send函数用来发送命令并返回响应码，打印ftp服务器返回的信息
login_ftp函数来登陆服务器并返回socket
USER指令用来输入用户名（anonymous用户名为匿名登陆）
PASS指令用来输入密码
strlen(cmd)那行画重点。。好像不能多传，传了会出错，有多少传多少，具体原因未知

一个星期了！！第七篇~~哎太困了写不下了今天