Go\Instrument\ClassLoading\SourceTransformingLoader::filter PHP Method

    public function filter($in, $out, &$consumed, $closing)
    {
        while ($bucket = stream_bucket_make_writeable($in)) {
            $this->data .= $bucket->data;
        }
        if ($closing || feof($this->stream)) {
            $consumed = strlen($this->data);
            // $this->stream contains pointer to the source
            $metadata = new StreamMetaData($this->stream, $this->data);
            self::transformCode($metadata);
            $bucket = stream_bucket_new($this->stream, $metadata->source);
            stream_bucket_append($out, $bucket);
            return PSFS_PASS_ON;
        }
        return PSFS_FEED_ME;
    }