linux c smtp

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

void send_email(const char *smtp_server, int smtp_port, const char *from, const char *to, const char *subject, const char *body) {
    int sockfd;
    struct sockaddr_in server_addr;
    char buffer[1024];
    FILE *fp;

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

    // 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(smtp_port);
    inet_pton(AF_INET, smtp_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);
        return;
    }

    // 读取SMTP服务器响应
    while (fgets(buffer, sizeof(buffer), stdin) != NULL) {
        write(sockfd, buffer, strlen(buffer));
        if (strstr(buffer, "220 ") != NULL) break;
    }

    // 发送HELO命令
    sprintf(buffer, "HELO localhost\r\n");
    write(sockfd, buffer, strlen(buffer));

    // 发送MAIL FROM命令
    sprintf(buffer, "MAIL FROM:<%s>\r\n", from);
    write(sockfd, buffer, strlen(buffer));

    // 发送RCPT TO命令
    sprintf(buffer, "RCPT TO:<%s>\r\n", to);
    write(sockfd, buffer, strlen(buffer));

    // 发送DATA命令
    write(sockfd, "DATA\r\n", 6);

    // 发送邮件内容
    fprintf(fp = fopen("email.txt", "w"), "From: %s\r\nTo: %s\r\nSubject: %s\r\n\r\n%s\r\n.\r\n", from, to, subject, body);
    fclose(fp);
    fp = fopen("email.txt", "r");
    while (fgets(buffer, sizeof(buffer), fp) != NULL) {
        write(sockfd, buffer, strlen(buffer));
    }
    fclose(fp);

    // 发送QUIT命令
    write(sockfd, "QUIT\r\n", 6);

    close(sockfd);
}

int main() {
    send_email("smtp.example.com", 25, "sender@example.com", "recipient@example.com", "Test Subject", "This is a test email.");
    return 0;
}