问PHP -包含二进制数据的Pack数组

EN

<?php
class Codec
{
    /**
     * Pack metadata along with binary data
     *
     * @param $meta
     * @param $data
     * @return false|string
     */
    public static function encode($meta, $data)
    {
        $meta = base64_encode($meta);

        //determine length of metadata
        $metaLength = strlen($meta);

        //The first part of the message is the metadata length
        $output = pack('VA*', $metaLength, $meta);

        //Length and metadata are set, now include the binary data
        $output .= $data;

        return $output;
    }

    /**
     * Unpack data encoded via the encode function.
     * Returns an array with "meta" and "data" elaments
     *
     * @param $content
     * @return array
     */
    public static function decode($content)
    {
        //Get the length of the metadata content
        $metaLength = unpack('V', $content)[1];

        //Slice out the metatdata, offset 4 to account for the length bytes
        $metaPacked = substr($content, 4, $metaLength);

        //Unpack and base64 decode the metadata
        $meta = unpack('A*', $metaPacked)[1];
        $meta = base64_decode($meta);

        //The binary data is everything after the metadata
        $data = substr($content, $metaLength+4);

        return [
            'meta' => $meta,
            'data' => $data
        ];
    }
}

//Load contents of a binary file
$imageFilePath = 'path_to_image.png';
$data = file_get_contents($imageFilePath);

//Arbitrary metadata - could be anything, let's use JSON
$meta = [
    'filename' => 'foo.png',
    'uid' => 12345,
    'md5' => md5_file($imageFilePath)
];

$metaJson = json_encode($meta);

//Encode the message, you can then send this to the receiver
$payload = Codec::encode($metaJson, $data);

//Receiver decodes the message
$result = Codec::decode($payload);

//Decode our JSON string
$resultMeta = json_decode($result['meta'], true);


echo 'Filename: '.$resultMeta['filename'].PHP_EOL;
echo 'UID: '.$resultMeta['uid'].PHP_EOL;

//We included an MD5 hash of the file, so we can verify here
if($resultMeta['md5'] != md5($result['data']))
{
    echo 'MD5 mismatch!';
}