upstream_archive = $(OPK_SOURCE)-$(OPK_SOURCE_VERSION_UPSTREAM).tar.gz
upstream_url = http://www.libarchive.org/downloads/$(upstream_archive)
source_archive = ../$(OPK_SOURCE)-$(OPK_SOURCE_VERSION_UPSTREAM).orig.tar.gz

$(source_archive):
	wget -c '$(upstream_url)'
	printf '$(source_sha256sum)  $(upstream_archive)' | sha256sum -c -
	mv '$(upstream_archive)' '$@'

source: $(source_archive)