linux c实现ftp

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>

#define SERVER_IP "127.0.0.1"
#define SERVER_PORT 21

int main() {
    int sockfd;
    struct sockaddr_in serv_addr;
    socklen_t length;

    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        perror("socket");
        exit(1);
    }

    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(SERVER_PORT);

    if (inet_pton(AF_INET, SERVER_IP, &serv_addr.sin_addr) <= 0) {
        perror("inet_pton");
        exit(1);
    }

    if (connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
        perror("connect");
        exit(1);
    }

    char buffer[1024];
    ssize_t n = read(sockfd, buffer, sizeof(buffer) - 1);
    printf("Server response: %s
", buffer);

    // 发送USER命令
    const char *user_cmd = "USER username\r
";
    write(sockfd, user_cmd, strlen(user_cmd));

    // 接收响应...
    n = read(sockfd, buffer, sizeof(buffer) - 1);
    printf("Server response: %s
", buffer);

    // ...发送更多命令，处理数据连接等

    close(sockfd);
    return 0;
}