inflatestream.php

См. документацию.

<?php
 
namespace Bitrix\Main\Web\Http;
 
class InflateStream extends Stream
{
    public function __construct($stream, $mode = 'r+')
    {
        parent::__construct($stream, $mode);
 
        // ZLIB or GZIP: use window=$W+32 for automatic header detection, so that both the formats can be recognized and decompressed; window=15+32=47 is the safer choice.
        stream_filter_append($this->resource, 'zlib.inflate', STREAM_FILTER_WRITE, ['window' => 47]);
    }
}