upstream_ver = $$(printf '%s\n' '$(OPK_SOURCE_VERSION_UPSTREAM)' | \
	sed 's/^\([0-9a-z.~-][0-9a-z.~-]*\)+sip[1-9][0-9]*.*$$/\1/')
upstream_url = http://zlib.net/zlib-$(upstream_ver).tar.gz
source_archive = ../zlib-$(OPK_SOURCE_VERSION_UPSTREAM).orig.tar.gz

$(source_archive):
	wget -O - "$(upstream_url)" | tar -xz
	rm -f "zlib-$(upstream_ver)"/doc/rfc*.txt
	tar -czf '$(source_archive)' "zlib-$(upstream_ver)"
	rm -Rf src
	mv "zlib-$(upstream_ver)" src

source: $(source_archive)