$_SERVER['HTTP_RANGE'] returns Null every time?

问题

In the given code only else condition is running every time. I have used pdf.js library and trying to break the pdf in chunks. I user this code on server side but it seems like only else condition is running and perhaps isset($_SERVER['HTTP_RANGE'] returns null. So the pdf gets loaded in the first go itself .

if(isset($_SERVER['HTTP_RANGE']))  { 

$fp = @fopen($filepath, 'rb');
$size   = filesize($filepath); // File size
$length = $size;           // Content length
$start  = 0;               // Start byte
$end    = $size - 1;       // End byte
header("Accept-Ranges: 0-$length");
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) {

                header('HTTP/1.1 416 Requested Range Not Satisfiable');
                header("Content-Range: bytes $start-$end/$size");
                // (?) Echo some info to the client?
                exit;
        }
        if ($range == '-') {

                // 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;
        }
        $c_end = ($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);

}
else {

    header("Content-Length: ".filesize($filepath));
    header("X-Sendfile: $filepath");
    readfile($filepath);
}

回答1:

Author of http://pdf.yt/ was kind enough to publish source code -- old version of which was written in PHP and it's powered by PDF.js. See https://github.com/joepie91/pdfy/blob/master/public_html/modules/download.php for complete solution. Pretty much it's your code above with proper HTTP headers (e.g. "Accept-Ranges: bytes") and few workarounds.

来源：https://stackoverflow.com/questions/35337958/serverhttp-range-returns-null-every-time

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