BufferStream example

    public function __construct(callable $source, array $options = [])
    {
        $this->source = $source;
        $this->size = $options['size'] ?? null;
        $this->metadata = $options['metadata'] ?? [];
        $this->buffer = new BufferStream();
    }

    public function __toString(): string
    {
        try {
            return Utils::copyToString($this);
        } catch (\Throwable $e) {
            if (\PHP_VERSION_ID >= 70400) {
                throw $e;
            }
            trigger_error(sprintf('%s::__toString exception: %s', self::class, (string) $e), E_USER_ERROR);