code: private byte[] fetchDecoderOutput() {
          final CompositeByteBuf decoded = Unpooled.compositeBuffer();
          for (;;) {
              final ByteBuf buf = decoder.readInbound();
              if (buf == null) {
                  break;
              }
              if (!buf.isReadable()) {
                  buf.release();
                  continue;
              }
              decoded.addComponent(true, buf);
          }
          final byte[] ret = ByteBufUtil.getBytes(decoded);
          decoded.release();
          return ret;
      }
docs: Mostly copied from netty's HttpContentDecoder.