class FileBinaryMimeTypeGuesser

MimeTypeTest.php in drupal/core/vendor/symfony/http-foundation/Symfony/Component/HttpFoundation/Tests/File/MimeType/MimeTypeTest.php

class FileBinaryMimeTypeGuesser implements MimeTypeGuesserInterface {
  private $cmd;

  /**
   * Constructor.
   *
   * The $cmd pattern must contain a "%s" string that will be replaced
   * with the file name to guess.
   *
   * The command output must start with the mime type of the file.
   *
   * @param string $cmd The command to run to get the mime type of a file
   */
  public function __construct($cmd = 'file -b --mime %s 2>/dev/null') {
    $this->cmd = $cmd;
  }

  /**
   * Returns whether this guesser is supported on the current OS
   *
   * @return Boolean
   */
  public static function isSupported() {
    return !defined('PHP_WINDOWS_VERSION_BUILD');
  }

  /**
   * {@inheritdoc}
   */
  public function guess($path) {
    if (!is_file($path)) {
      throw new FileNotFoundException($path);
    }
    if (!is_readable($path)) {
      throw new AccessDeniedException($path);
    }
    if (!self::isSupported()) {
      return null;
    }
    ob_start();

    // need to use --mime instead of -i. see #6641
    passthru(sprintf($this->cmd, escapeshellarg($path)), $return);
    if ($return > 0) {
      ob_end_clean();
      return null;
    }
    $type = trim(ob_get_clean());
    if (!preg_match('#^([a-z0-9\\-]+/[a-z0-9\\-]+)#i', $type, $match)) {

      // it's not a type, but an error message
      return null;
    }
    return $match[1];
  }

}