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Upload File : current_dir [ Writeable ] document_root [ Writeable ]

<?php
/**
 * File Security Utilities
 * Prevents path traversal and unauthorized file access
 */

/**
 * Validate and sanitize file path to prevent path traversal
 * 
 * @param string $file_path The file path to validate
 * @param array $allowed_directories Whitelist of allowed base directories
 * @return string|false Returns normalized absolute path if valid, false otherwise
 */
function validateFilePath($file_path, $allowed_directories = null) {
    if (empty($file_path)) {
        return false;
    }
    
    // Default allowed directories
    if ($allowed_directories === null) {
        $allowed_directories = [
            $_SERVER['DOCUMENT_ROOT'] . '/audio_files',
            $_SERVER['DOCUMENT_ROOT'] . '/uploads',
        ];
    }
    
    // If it's already an absolute path
    if (strpos($file_path, '/') === 0 || strpos($file_path, $_SERVER['DOCUMENT_ROOT']) === 0) {
        // Ensure it's within DOCUMENT_ROOT
        if (strpos($file_path, $_SERVER['DOCUMENT_ROOT']) !== 0) {
            $file_path = $_SERVER['DOCUMENT_ROOT'] . $file_path;
        }
    } else {
        // Relative path - make it absolute
        $file_path = $_SERVER['DOCUMENT_ROOT'] . '/' . ltrim($file_path, '/');
    }
    
    // Normalize path (remove double slashes, resolve .. and .)
    $file_path = str_replace('//', '/', $file_path);
    $real_path = realpath($file_path);
    
    // realpath() returns false if path doesn't exist or contains traversal
    if ($real_path === false) {
        return false;
    }
    
    // Ensure the resolved path is within DOCUMENT_ROOT
    $doc_root = realpath($_SERVER['DOCUMENT_ROOT']);
    if (strpos($real_path, $doc_root) !== 0) {
        // Path is outside DOCUMENT_ROOT - security violation
        error_log("SECURITY: Path traversal attempt detected: " . $file_path);
        return false;
    }
    
    // Check if path is within allowed directories
    $is_allowed = false;
    foreach ($allowed_directories as $allowed_dir) {
        $allowed_real = realpath($allowed_dir);
        if ($allowed_real && strpos($real_path, $allowed_real) === 0) {
            $is_allowed = true;
            break;
        }
    }
    
    if (!$is_allowed) {
        error_log("SECURITY: File access outside allowed directories: " . $real_path);
        return false;
    }
    
    // Verify file exists
    if (!file_exists($real_path)) {
        return false;
    }
    
    return $real_path;
}

/**
 * Validate audio URL from database
 * Ensures URL is either a valid external URL or a safe local path
 * 
 * @param string $audio_url The audio URL to validate
 * @return array Returns ['type' => 'local'|'external'|'invalid', 'path' => string|null, 'url' => string|null]
 */
function validateAudioUrl($audio_url) {
    if (empty($audio_url)) {
        return ['type' => 'invalid', 'path' => null, 'url' => null];
    }
    
    // Check if it's an external URL
    if (strpos($audio_url, 'http://') === 0 || strpos($audio_url, 'https://') === 0) {
        // Validate URL format
        if (filter_var($audio_url, FILTER_VALIDATE_URL)) {
            return ['type' => 'external', 'path' => null, 'url' => $audio_url];
        } else {
            return ['type' => 'invalid', 'path' => null, 'url' => null];
        }
    }
    
    // It's a local path - validate it
    $allowed_dirs = [
        $_SERVER['DOCUMENT_ROOT'] . '/audio_files',
        $_SERVER['DOCUMENT_ROOT'] . '/uploads',
    ];
    
    $valid_path = validateFilePath($audio_url, $allowed_dirs);
    
    if ($valid_path) {
        return ['type' => 'local', 'path' => $valid_path, 'url' => null];
    } else {
        return ['type' => 'invalid', 'path' => null, 'url' => null];
    }
}

/**
 * Sanitize filename for download headers
 * 
 * @param string $filename The filename to sanitize
 * @return string Sanitized filename
 */
function sanitizeDownloadFilename($filename) {
    // Remove or replace invalid characters
    $filename = preg_replace('/[^a-zA-Z0-9\s\-_\.]/', '', $filename);
    $filename = preg_replace('/\s+/', '_', $filename);
    $filename = trim($filename, '._-');
    
    // Limit length
    if (strlen($filename) > 100) {
        $filename = substr($filename, 0, 100);
    }
    
    return $filename;
}
?>