php下载文件，PHP下载文件源码

<?php
function downFile($fileName, $fancyName='', $forceDownload=true, $speedLimit=0, $contentType='')
{
    if (!is_readable($fileName))
    {
        header("HTTP/1.1 404 Not Found");
        return false;
    }
 
    $fileStat=stat($fileName);
    $lastModified=$fileStat['mtime'];
 
    $md5=md5($fileStat['mtime'] .'='. $fileStat['ino'] .'='. $fileStat['size']);
    $etag='"' . $md5 . '-' . crc32($md5) . '"';
 
    header('Last-Modified: ' . gmdate("D, d M Y H:i:s", $lastModified) . ' GMT');
    header("ETag: $etag");
 
    if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) && strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) >=$lastModified)
    {
        header("HTTP/1.1 304 Not Modified");
        return true;
    }
 
    if (isset($_SERVER['HTTP_IF_UNMODIFIED_SINCE']) && strtotime($_SERVER['HTTP_IF_UNMODIFIED_SINCE']) < $lastModified)
    {
        header("HTTP/1.1 304 Not Modified");
        return true;
    }
 
    if (isset($_SERVER['HTTP_IF_NONE_MATCH']) &&  $_SERVER['HTTP_IF_NONE_MATCH']==$etag)
    {
        header("HTTP/1.1 304 Not Modified");
        return true;
    }
 
    if ($fancyName=='')
    {
        $fancyName=basename($fileName);
    }
 
    if ($contentType=='')
    {
        $contentType='application/octet-stream';
    }
 
    $fileSize=$fileStat['size'];
 
    $contentLength=$fileSize;
    $isPartial=false;
 
    if (isset($_SERVER['HTTP_RANGE']))
    {
        if (preg_match('/^bytes=(\d*)-(\d*)$/', $_SERVER['HTTP_RANGE'], $matches))
        {
            $startPos=$matches[1];
            $endPos=$matches[2];
 
            if ($startPos=='' && $endPos=='')
            {
                return false;
            }
 
            if ($startPos=='')
            {
                $startPos=$fileSize - $endPos;
                $endPos=$fileSize - 1;
            }
            else if ($endPos=='')
            {
                $endPos=$fileSize - 1;
            }
 
            $startPos=$startPos < 0 ? 0 : $startPos;
            $endPos=$endPos > $fileSize - 1 ? $fileSize - 1 : $endPos;
 
            $length=$endPos - $startPos + 1;
 
            if ($length < 0)
            {
                return false;
            }
 
            $contentLength=$length;
            $isPartial=true;
        }
    }
 
    // send headers
    if ($isPartial)
    {
        header('HTTP/1.1 206 Partial Content');
        header("Content-Range: bytes $startPos-$endPos/$fileSize");
 
    }
    else
    {
        header("HTTP/1.1 200 OK");
        $startPos=0;
        $endPos=$contentLength - 1;
    }
 
    header('Pragma: cache');
    header('Cache-Control: public, must-revalidate, max-age=0');
    header('Accept-Ranges: bytes');
    header('Content-type: ' . $contentType);
    header('Content-Length: ' . $contentLength);
 
    if ($forceDownload)
    {
        header('Content-Disposition: attachment; filename="' . rawurlencode($fancyName). '"');
    }
 
    header("Content-Transfer-Encoding: binary");
 
    $bufferSize=2048;
 
    if ($speedLimit !=0)
    {
        $packetTime=floor($bufferSize * 1000000 / $speedLimit);
    }
 
    $bytesSent=0;
    $fp=fopen($fileName, "rb");
    fseek($fp, $startPos);
    while ($bytesSent < $contentLength && !feof($fp) && connection_status()==0 )
    {
        if ($speedLimit !=0)
        {
            list($usec, $sec)=explode(" ", microtime());
            $outputTimeStart=((float)$usec + (float)$sec);
        }
 
        $readBufferSize=$contentLength - $bytesSent < $bufferSize ? $contentLength - $bytesSent : $bufferSize;
        $buffer=fread($fp, $readBufferSize);
 
        echo $buffer;
 
        ob_flush();
        flush();
 
        $bytesSent +=$readBufferSize;
 
        if ($speedLimit !=0)
        {
            list($usec, $sec)=explode(" ", microtime());
            $outputTimeEnd=((float)$usec + (float)$sec);
 
            $useTime=((float) $outputTimeEnd - (float) $outputTimeStart) * 1000000;
            $sleepTime=round($packetTime - $useTime);
            if ($sleepTime > 0)
            {
                usleep($sleepTime);
            }
        }
    }
    return true;
}
?>

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