Удаление многоугольника из Google Maps DrawingManager V3

И вот PHP-версия вычисления ETag:

function calculate_aws_etag($filename, $chunksize) {
    /*
    DESCRIPTION:
    - calculate Amazon AWS ETag used on the S3 service
    INPUT:
    - $filename : path to file to check
    - $chunksize : chunk size in Megabytes
    OUTPUT:
    - ETag (string)
    */
    $chunkbytes = $chunksize*1024*1024;
    if (filesize($filename) < $chunkbytes) {
        return md5_file($filename);
    } else {
        $md5s = array();
        $handle = fopen($filename, 'rb');
        if ($handle === false) {
            return false;
        }
        while (!feof($handle)) {
            $buffer = fread($handle, $chunkbytes);
            $md5s[] = md5($buffer);
            unset($buffer);
        }
        fclose($handle);

        $concat = '';
        foreach ($md5s as $indx => $md5) {
            $concat .= hex2bin($md5);
        }
        return md5($concat) .'-'. count($md5s);
    }
}

$etag = calculate_aws_etag('path/to/myfile.ext', 8);

И вот расширенная версия, которая может проверять ожидаемый ETag - и даже догадываться о chunksize, если вы этого не знаете !

function calculate_etag($filename, $chunksize, $expected = false) {
    /*
    DESCRIPTION:
    - calculate Amazon AWS ETag used on the S3 service
    INPUT:
    - $filename : path to file to check
    - $chunksize : chunk size in Megabytes
    - $expected : verify calculated etag against this specified etag and return true or false instead
        - if you make chunksize negative (eg. -8 instead of 8) the function will guess the chunksize by checking all possible sizes given the number of parts mentioned in $expected
    OUTPUT:
    - ETag (string)
    - or boolean true|false if $expected is set
    */
    if ($chunksize < 0) {
        $do_guess = true;
        $chunksize = 0 - $chunksize;
    } else {
        $do_guess = false;
    }

    $chunkbytes = $chunksize*1024*1024;
    $filesize = filesize($filename);
    if ($filesize < $chunkbytes && (!$expected || !preg_match("/^\\w{32}-\\w+$/", $expected))) {
        $return = md5_file($filename);
        if ($expected) {
            $expected = strtolower($expected);
            return ($expected === $return ? true : false);
        } else {
            return $return;
        }
    } else {
        $md5s = array();
        $handle = fopen($filename, 'rb');
        if ($handle === false) {
            return false;
        }
        while (!feof($handle)) {
            $buffer = fread($handle, $chunkbytes);
            $md5s[] = md5($buffer);
            unset($buffer);
        }
        fclose($handle);

        $concat = '';
        foreach ($md5s as $indx => $md5) {
            $concat .= hex2bin($md5);
        }
        $return = md5($concat) .'-'. count($md5s);
        if ($expected) {
            $expected = strtolower($expected);
            $matches = ($expected === $return ? true : false);
            if ($matches || $do_guess == false || strlen($expected) == 32) {
                return $matches;
            } else {
                // Guess the chunk size
                preg_match("/-(\\d+)$/", $expected, $match);
                $parts = $match[1];
                $min_chunk = ceil($filesize / $parts /1024/1024);
                $max_chunk =  floor($filesize / ($parts-1) /1024/1024);
                $found_match = false;
                for ($i = $min_chunk; $i <= $max_chunk; $i++) {
                    if (calculate_aws_etag($filename, $i) === $expected) {
                        $found_match = true;
                        break;
                    }
                }
                return $found_match;
            }
        } else {
            return $return;
        }
    }
}