code: protected EmbeddedChannel newContentCompressor(ChannelHandlerContext ctx, CharSequence contentEncoding)
              throws Http2Exception {
          if (GZIP.contentEqualsIgnoreCase(contentEncoding) || X_GZIP.contentEqualsIgnoreCase(contentEncoding)) {
              return newCompressionChannel(ctx, ZlibWrapper.GZIP);
          }
          if (DEFLATE.contentEqualsIgnoreCase(contentEncoding) || X_DEFLATE.contentEqualsIgnoreCase(contentEncoding)) {
              return newCompressionChannel(ctx, ZlibWrapper.ZLIB);
          }
          // 'identity' or unsupported
          return null;
      }
docs: Returns a new {@link EmbeddedChannel} that encodes the HTTP2 message content encoded in the specified
  {@code contentEncoding}.
  
  @param ctx the context.
  @param contentEncoding the value of the {@code content-encoding} header
  @return a new {@link ByteToMessageDecoder} if the specified encoding is supported. {@code null} otherwise
  (alternatively, you can throw a {@link Http2Exception} to block unknown encoding).
  @throws Http2Exception If the specified encoding is not not supported and warrants an exception