<?php
class Util_Utils_Download {
    
    /**
     * 获取浏览器附件信息
     * 
     * @param string $saveName
     * @return string
     */
    public static function getBrowserAttachmentInfo($saveName)
    {
        // 浏览器
        $ua = $_SERVER['HTTP_USER_AGENT'];
        $encoded_saveName = urlencode($saveName);
        $encoded_saveName = str_replace("+", "%20", $encoded_saveName);
        // IE
        if(stripos($ua, "MSIE"))
        {
            $headerDownLoadInfo = 'Content-Disposition: attachment;filename="' . $encoded_saveName . '.expand"';
        }
        // FF
        else if((stripos($ua, "Firefox")) || (stripos($ua, "Opera")))
        {
            $firefoxPos = stripos($ua,"Firefox");
            if($firefoxPos)
            {
                //FF版本
               $firefoxVer = intval(substr($ua, $firefoxPos+8, 3));
               if($firefoxVer >= 8)
               {
                   $headerDownLoadInfo = 'Content-Disposition: attachment; filename="' . $saveName . '.expand"';
               }
               else
               {
                  $headerDownLoadInfo = 'Content-Disposition: attachment; filename*="utf8\'\'' . $saveName . '.expand"'; 
               }
            }
            else
            {
                $headerDownLoadInfo = 'Content-Disposition: attachment; filename*="utf8\'\'' . $saveName . '.expand"';
            }
        }
        //other
        else
        {
            $headerDownLoadInfo = 'Content-Disposition: attachment; filename="' . $saveName . '.expand"';
        }
        return $headerDownLoadInfo;
    }
    
    /**
     * 断点下载
     * 
     * @param string $file
     * @return string
     */
    public static function rangeDownload($file) 
    {
        $fp = @fopen($file, 'rb');
     
        $size   = filesize($file); // File size
        $length = $size;           // Content length
        $start  = 0;               // Start byte
        $end    = $size - 1;       // End byte
        // Now that we've gotten so far without errors we send the accept range header
        /* At the moment we only support single ranges.
         * Multiple ranges requires some more work to ensure it works correctly
         * and comply with the spesifications: http://www.w3.org/Protocols/rfc2616/rfc2616-sec19.html#sec19.2
         *
         * Multirange support annouces itself with:
         * header('Accept-Ranges: bytes');
         *
         * Multirange content must be sent with multipart/byteranges mediatype,
         * (mediatype = mimetype)
         * as well as a boundry header to indicate the various chunks of data.
         */
        header("Accept-Ranges: 0-$length");
        // header('Accept-Ranges: bytes');
        // multipart/byteranges
        // http://www.w3.org/Protocols/rfc2616/rfc2616-sec19.html#sec19.2
        if (isset($_SERVER['HTTP_RANGE'])) {
     
            $c_start = $start;
            $c_end   = $end;
            // Extract the range string
            list(, $range) = explode('=', $_SERVER['HTTP_RANGE'], 2);
            // Make sure the client hasn't sent us a multibyte range
            if (strpos($range, ',') !== false) {
     
                // (?) Shoud this be issued here, or should the first
                // range be used? Or should the header be ignored and
                // we output the whole content?
                header('HTTP/1.1 416 Requested Range Not Satisfiable');
                header("Content-Range: bytes $start-$end/$size");
                // (?) Echo some info to the client?
                exit;
            }
            // If the range starts with an '-' we start from the beginning
            // If not, we forward the file pointer
            // And make sure to get the end byte if spesified
            if ($range0 == '-') {
     
                // The n-number of the last bytes is requested
                $c_start = $size - substr($range, 1);
            }
            else {
     
                $range  = explode('-', $range);
                $c_start = $range[0];
                $c_end   = (isset($range[1]) && is_numeric($range[1])) ? $range[1] : $size;
            }
            /* Check the range and make sure it's treated according to the specs.
             * http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html
             */
            // End bytes can not be larger than $end.
            $c_end = ($c_end > $end) ? $end : $c_end;
            // Validate the requested range and return an error if it's not correct.
            if ($c_start > $c_end || $c_start > $size - 1 || $c_end >= $size) {
     
                header('HTTP/1.1 416 Requested Range Not Satisfiable');
                header("Content-Range: bytes $start-$end/$size");
                // (?) Echo some info to the client?
                exit;
            }
            $start  = $c_start;
            $end    = $c_end;
            $length = $end - $start + 1; // Calculate new content length
            fseek($fp, $start);
            header('HTTP/1.1 206 Partial Content');
        }
        // Notify the client the byte range we'll be outputting
        header("Content-Range: bytes $start-$end/$size");
        header("Content-Length: $length");
     
        // Start buffered download
        $buffer = 1024 * 8;
        while(!feof($fp) && ($p = ftell($fp)) <= $end) {
     
            if ($p + $buffer > $end) {
     
                // In case we're only outputtin a chunk, make sure we don't
                // read past the length
                $buffer = $end - $p + 1;
            }
            set_time_limit(0); // Reset time limit for big files
            echo fread($fp, $buffer);
            flush(); // Free up memory. Otherwise large files will trigger PHP's memory limit.
        }
        fclose($fp);
    }

}