socket访问ftp服务器

原理：ftp协议是基于tcpip协议，用socket实现tcpip协议发送ftp指令、内容

 

IP地址转换函数

inet_pton是一个IP地址转换函数，可以在将点分文本的IP地址转换为二进制网络字节序”的IP地址，而且inet_pton和inet_ntop这2个函数能够处理ipv4和ipv6。

 

strerror:

 C语言错误提示函数:strerror和errno 相关头文件: string.h errno.h 函数原型: char*strerror(interrnum); errnum是错误的编号,要通过“errno”来获得

 

 

 

代码实现功能：socket连接ftp服务器21端口，发送登录账号密码命令，登录成功

代码：

 

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

#define IPV4_PROTO     AF_INET
#define SOCKET_TYPE    SOCK_STREAM
#define protocol       IPPROTO
#define FTP_PORT       21
  

#define BUFF_LEN       4096

//return -1 connect failed -2 send failed  -3 recv failed 
//usage   pratise socket ftp
int main(int argc, char **argv)
{
    int sockFd = 0;
    int ret    = 0;

    char buf[BUFF_LEN]={0};
    struct sockaddr_in serverAddr;

    if(argc != 2)
    {
        return -1;
    }

    for(int i = 0; i < argc; i++)
    {
        printf("%s ", argv[i]);
    } 
    printf("\n");
    if( (sockFd = socket(AF_INET, SOCK_STREAM, 0)) < 0){
        printf("create socket error: %s(errno: %d)\n", strerror(errno),errno);
        exit(0);
    }

    memset(&serverAddr, 0, sizeof(serverAddr));
    serverAddr.sin_family = AF_INET;
    serverAddr.sin_port = htons(21);
    if( inet_pton(AF_INET, argv[1], &serverAddr.sin_addr) <= 0){
        printf("inet_pton error for %s\n",argv[1]);
        return -1;
    }

 
    if( connect(sockFd, (struct sockaddr*)&serverAddr, sizeof(serverAddr)) < 0)
    {
        printf("connect error: %s(errno: %d)\n",strerror(errno),errno);
        return -1;
    }
    if((ret = recv(sockFd, buf, BUFF_LEN,0)) == -1) 
    {
        perror("recv error");
        return -3;
    }
    buf[ret]  = '\0';
    printf("Received : %s ",buf);

    printf("send msg to server: \n");
    char user[] = "user ftpusr\r\n";
    char passwd[] = "pass 123456aB\r\n";
    if( send(sockFd, user, strlen(user), 0) < 0)
    {
        printf("send msg error: %s(errno: %d)\n", strerror(errno), errno);
        return -2;
    }
    printf("send : %s\n",user);
    if((ret = recv(sockFd, buf, BUFF_LEN,0)) == -1) 
    {
        perror("recv error");
        return -3;
    }
    buf[ret]  = '\0';
    printf("Received : %s ",buf);
    if( send(sockFd, passwd, strlen(passwd), 0) < 0)
    {
        printf("send msg error: %s(errno: %d)\n", strerror(errno), errno);
        return -2;
    }
    printf("send : %s\n",passwd);

    if((ret = recv(sockFd, buf, BUFF_LEN,0)) == -1) 
    {
        perror("recv error");
        return -3;
    }
    buf[ret]  = '\0';
    printf("Received : %s ",buf);
    
    close(sockFd);
    return 0;
}