PHP开发的二手回收网站提供密码找回功能

<?php
session_start();

// 连接数据库
$conn = new mysqli("localhost", "root", "password", "database_name");

if ($conn->connect_error) {
    die("数据库连接失败: " . $conn->connect_error);
}

// 用户注册
if (isset($_POST['register'])) {
    $username = $_POST['username'];
    $password = $_POST['password'];
    
    // 插入用户信息到数据库
    $sql = "INSERT INTO users (username, password) VALUES ('$username', '$password')";
    if ($conn->query($sql) === TRUE) {
        echo "注册成功";
    } else {
        echo "注册失败: " . $conn->error;
    }
}

// 用户登录
if (isset($_POST['login'])) {
    $username = $_POST['username'];
    $password = $_POST['password'];
    
    // 查询数据库，验证用户名和密码
    $sql = "SELECT * FROM users WHERE username='$username' AND password='$password'";
    $result = $conn->query($sql);
    
    if ($result->num_rows > 0) {
        $_SESSION['username'] = $username;
        echo "登录成功";
    } else {
        echo "用户名或密码错误";
    }
}
?>

<?php
// 密码找回
if (isset($_POST['forgot_password'])) {
    $username = $_POST['username'];
    
    // 查询数据库，验证用户名
    $sql = "SELECT * FROM users WHERE username='$username'";
    $result = $conn->query($sql);
    
    if ($result->num_rows > 0) {
        // 生成一个随机的密码
        $new_password = generateRandomString(8);
        
        // 更新用户密码
        $sql = "UPDATE users SET password='$new_password' WHERE username='$username'";
        if ($conn->query($sql) === TRUE) {
            echo "新密码已发送至您的注册邮箱";
        } else {
            echo "密码重置失败: " . $conn->error;
        }
    } else {
        echo "用户名不存在";
    }
}

// 生成随机字符串
function generateRandomString($length) {
    $characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
    $randomString = '';
    
    for ($i = 0; $i < $length; $i++) {
        $randomString .= $characters[rand(0, strlen($characters) - 1)];
    }
    
    return $randomString;
}
?>