exforce_download() -- 对CI中force_download()增强后的函数(不依赖CI)

/**
 * Enhanced force_download, can accept file in server
 * @author Wilson Zeng
 * @param $filename | The name that will use as the download file's name by default
 * @param $data | Can be: [1]. a file real path; [2]. an string that contain the file's content
 * @param $is_file | To specify the type of the $data
 * @return Byte Stream
 */
function exforce_download($filename = '', $data = '', $is_file = FALSE)
{
        if ($filename == '' OR $data == '')
        {
                return FALSE;
        }
        
        if($is_file && !is_file($data)){
                return FALSE;
        }

        // Try to determine if the filename includes a file extension.
        // We need it in order to set the MIME type
        if (FALSE === strpos($filename, '.'))
        {
                return FALSE;
        }

        // Grab the file extension
        $x = explode('.', $filename);
        $extension = end($x);

        // Load the mime types
        /*zcs=Reduce Dependence
        if (defined('ENVIRONMENT') AND is_file(APPPATH.'config/'.ENVIRONMENT.'/mimes'.EXT))
        {
                include(APPPATH.'config/'.ENVIRONMENT.'/mimes'.EXT);
        }
        elseif (is_file(APPPATH.'config/mimes'.EXT))
        {
                include(APPPATH.'config/mimes'.EXT);
        }
        */
        $mimes = array(); //zcs=[NOTE] Here we just assign an empty array to reduce the dependence of the CI framework

        // Set a default mime if we can't find it
        if ( ! isset($mimes[$extension]))
        {
                $mime = 'application/octet-stream';
        }
        else
        {
                $mime = (is_array($mimes[$extension])) ? $mimes[$extension][0] : $mimes[$extension];
        }
        
        $size = 0;
        if($is_file){
                $size = filesize($data);
        }else{
                $size = strlen($data);
        }

        // Generate the server headers
        if (strpos($_SERVER['HTTP_USER_AGENT'], "MSIE") !== FALSE)
        {
                header('Content-Type: "'.$mime.'"');
                header('Content-Disposition: attachment; filename="'.$filename.'"');
                header('Expires: 0');
                header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
                header("Content-Transfer-Encoding: binary");
                header('Pragma: public');
                header("Content-Length: ".$size);
        }
        else
        {
                header('Content-Type: "'.$mime.'"');
                header('Content-Disposition: attachment; filename="'.$filename.'"');
                header("Content-Transfer-Encoding: binary");
                header('Expires: 0');
                header('Pragma: no-cache');
                header("Content-Length: ".$size);
        }
        
        if($is_file){
                $h_file = fopen($data, 'r');
                while(!feof($h_file)){
                        echo fread($h_file, 1048576);//1M
                }
                fclose($h_file);
        }else{
                exit($data);
        }
}