ParagonIE\Halite\File::checksumData PHP Method

    protected static function checksumData(StreamInterface $fileStream, Key $key = null, bool $raw = false) : string
    {
        $config = self::getConfig(Halite::HALITE_VERSION_FILE, 'checksum');
        // 1. Initialize the hash context
        if ($key instanceof AuthenticationKey) {
            // AuthenticationKey is for HMAC, but we can use it for keyed hashes too
            $state = \Sodium\crypto_generichash_init($key->getRawKeyMaterial(), $config->HASH_LEN);
        } elseif ($config->CHECKSUM_PUBKEY && $key instanceof SignaturePublicKey) {
            // In version 2, we use the public key as a hash key
            $state = \Sodium\crypto_generichash_init($key->getRawKeyMaterial(), $config->HASH_LEN);
        } elseif (isset($key)) {
            throw new InvalidKey('Argument 2: Expected an instance of AuthenticationKey or SignaturePublicKey');
        } else {
            $state = \Sodium\crypto_generichash_init('', $config->HASH_LEN);
        }
        // 2. Calculate the hash
        $size = $fileStream->getSize();
        while ($fileStream->remainingBytes() > 0) {
            // Don't go past the file size even if $config->BUFFER is not an even multiple of it:
            if ($fileStream->getPos() + $config->BUFFER > $size) {
                $amount_to_read = $size - $fileStream->getPos();
            } else {
                $amount_to_read = $config->BUFFER;
            }
            $read = $fileStream->readBytes($amount_to_read);
            \Sodium\crypto_generichash_update($state, $read);
        }
        // 3. Do we want a raw checksum?
        if ($raw) {
            return \Sodium\crypto_generichash_final($state, $config->HASH_LEN);
        }
        return \Sodium\bin2hex(\Sodium\crypto_generichash_final($state, $config->HASH_LEN));
    }