public void askUpstreamForElement() {
        if (!askedUpstreamForElement) {
            askedUpstreamForElement = true;
            assert upstream != null;
            upstream.request(1);
        }
    }
Returns a new {@link DecodedStreamMessage} with the specified {@link HttpDecoder},
{@link ByteBufAllocator} and {@code byteBufConverter}.
core/src/main/java/com/linecorp/armeria/internal/common/stream/DecodedStreamMessage.java