c - 使用C语言中的套接字向FTP服务器发送命令

Question

我是套接字编程新手。我想登录我的 ftp 服务器。我可以成功建立连接，但无法发送用户和密码的其他命令。

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

int main(int argc, char *argv[])
{
    argv[0]="2";
    argv[1]="00.00.00.0000"; //my ip

    int sockfd = 0, n = 0;
    char recvBuff[1024];
    struct sockaddr_in serv_addr;
    char message[100]="USER <a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="5e382a2e2b2d3b2c1e3a31333f3730703d3133" rel="noreferrer noopener nofollow">[email protected]</a>";

    argc=2;

    if(argc != 2)
    {
        printf("\n Usage: %s <ip of server> \n",argv[0]);
        return 1;
    }

    memset(recvBuff, '0',sizeof(recvBuff));
    if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        printf("\n Error : Could not create socket \n");
        return 1;
    }

    memset(&serv_addr, '0', sizeof(serv_addr));

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(21);


    serv_addr.sin_addr.s_addr = inet_addr(argv[1]);

    if( connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
    {
        printf("\n Error : Connect Failed \n");
        return 1;
    }

    if( send(sockfd , message , strlen(message) , 0) < 0)
    {
        perror("send failed");
        return 1;
    }


    while ( (n = read(sockfd, recvBuff, sizeof(recvBuff)-1)) > 0)
    {
        recvBuff[n] = 0;
        if(fputs(recvBuff, stdout) == EOF)
        {
            printf("\n Error : Fputs error\n");
            return 0;
        }
    }

    if(n < 0)
    {
        printf("\n Read error \n");
        return 0;
    } 

    return 0;
}

我得到这个:

220---------- Welcome to Pure-FTPd [privsep] [TLS] ----------
220-You are user number 1 of 50 allowed.
220-Local time is now 22:05. Server port: 21.
220 You will be disconnected after 15 minutes of inactivity.

为什么建立连接后无法向服务器发送命令？

Answer 1

您需要使用 CRLF 终止每个 FTP 命令。您的 USER 命令中缺少此内容。远程服务器在收到换行符之前不会处理该命令。

来源:RFC 959