linux c ftp下载

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

#define SERVER "ftp.example.com"
#define USER "username"
#define PASS "password"
#define REMOTE_FILE "/path/to/remote/file.txt"
#define LOCAL_FILE "local_file.txt"

void ftp_send_command(int sockfd, const char *command) {
    send(sockfd, command, strlen(command), 0);
    printf("%s\n", command);
}

int main() {
    int sockfd;
    struct sockaddr_in server_addr;
    FILE *local_file;

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

    // 设置服务器地址
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(21); // FTP 控制端口
    inet_pton(AF_INET, SERVER, &server_addr.sin_addr);

    // 连接服务器
    if (connect(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
        perror("connect");
        close(sockfd);
        exit(EXIT_FAILURE);
    }

    // 读取欢迎信息
    char buffer[1024];
    recv(sockfd, buffer, sizeof(buffer), 0);
    printf("%s", buffer);

    // 登录
    ftp_send_command(sockfd, USER);
    ftp_send_command(sockfd, PASS);

    // 切换到被动模式
    ftp_send_command(sockfd, "PASV\r\n");

    // 解析被动模式的端口
    int pasv_port;
    sscanf(buffer, "227 Entering Passive Mode (%*d,%*d,%*d,%*d,%d,%d)",
           &pasv_port >> 8, &pasv_port & 0xFF);

    // 创建数据连接
    int data_sockfd;
    struct sockaddr_in data_addr;
    if ((data_sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        perror("socket");
        close(sockfd);
        exit(EXIT_FAILURE);
    }

    memset(&data_addr, 0, sizeof(data_addr));
    data_addr.sin_family = AF_INET;
    data_addr.sin_port = htons(pasv_port);
    inet_pton(AF_INET, SERVER, &data_addr.sin_addr);

    if (connect(data_sockfd, (struct sockaddr *)&data_addr, sizeof(data_addr)) < 0) {
        perror("connect");
        close(sockfd);
        close(data_sockfd);
        exit(EXIT_FAILURE);
    }

    // 下载文件
    ftp_send_command(sockfd, "RETR ");
    strcat(buffer, REMOTE_FILE);
    strcat(buffer, "\r\n");
    send(sockfd, buffer, strlen(buffer), 0);

    local_file = fopen(LOCAL_FILE, "wb");
    if (!local_file) {
        perror("fopen");
        close(sockfd);
        close(data_sockfd);
        exit(EXIT_FAILURE);
    }

    while (recv(data_sockfd, buffer, sizeof(buffer), 0) > 0) {
        fwrite(buffer, 1, strlen(buffer), local_file);
    }

    fclose(local_file);
    close(data_sockfd);

    // 登出
    ftp_send_command(sockfd, "QUIT\r\n");

    close(sockfd);
    return 0;
}