/** Decompression **/
byte[] brotliCompressedData = ...; // arbritary data source
byte[] uncompressedData = Brotli.DecompressBuffer(brotliCompressedData, 0, brotliCompressedData.Length /**, customDictionary **/);

/** Compression **/
byte[] uncompressedData = ...; // arbritary data source

// By default, brotli uses a quality value of 11 and window size of 22 if the parameters are omitted.
byte[] compressedData = Brotli.CompressBuffer(uncompressedData, 0, uncompressedData.Length /**, quality, windowSize, customDictionary **/);

/** Decompression **/
using (var ms = new MemoryStream())
using (var bs = new BrotliStream(compressedStream, CompressionMode.Decompress))
{
    bs.CopyTo(ms);
}

/** Compression **/
using (var fs = File.OpenRead(filePath))
using (var ms = new MemoryStream())
{
    using (var bs = new BrotliStream(ms, CompressionMode.Compress))
    {
        // By default, BrotliSharpLib uses a quality value of 1 and window size of 22 if the methods are not called.
        /** bs.SetQuality(quality); **/
        /** bs.SetWindow(windowSize); **/
        /** bs.SetCustomDictionary(customDict); **/
        fs.CopyTo(bs);
    }

    byte[] compressed = ms.ToArray();
}

static class HttpClientEx
{
    private class BrotliCompressionHandler : DelegatingHandler
    {
        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            request.Headers.AcceptEncoding.Add(new StringWithQualityHeaderValue("br"));
            var response = await base.SendAsync(request, cancellationToken);
            IEnumerable<string> ce;
            if (response.Content.Headers.TryGetValues("Content-Encoding", out ce) && ce.First() == "br")
            {
                var buffer = await response.Content.ReadAsByteArrayAsync();
                response.Content = new ByteArrayContent(Brotli.DecompressBuffer(buffer, 0, buffer.Length));
            }
            return response;
        }
    }

    public static HttpClient Create()
    {
        var handler = new HttpClientHandler();
        if (handler.SupportsAutomaticDecompression)
            handler.AutomaticDecompression = System.Net.DecompressionMethods.Deflate | System.Net.DecompressionMethods.GZip;
        return HttpClientFactory.Create(handler, new BrotliCompressionHandler());
    }
}