@Override
    public HttpData finish() {
        if (decoder.finish()) {
            return fetchDecoderOutput();
        } else {
            return HttpData.empty();
        }
    }
Skeletal {@link StreamDecoder} implementation. Netty implementation used to allow
for incremental decoding using an {@link EmbeddedChannel}.
core/src/main/java/com/linecorp/armeria/common/encoding/AbstractStreamDecoder.java