improve download of dcs.db

avoid unnecessary downloads and rebuilds
improve handling of download errors
make 'make load' work

src/gen/Makefile.am

@@ -28,17 +28,32 @@ fixup-local: fixup.remove fixup.reorder fixup.out
 
 load-local: dcs.db.refresh dcs.db
 
+dcs.db.tstamp:
+	touch dcs.db.tstamp
+
 dcs.db.refresh:
-	touch dcs.db.refresh
+	-rm  dcs.db.tstamp
+
+.PHONY: dcs.db.refresh
+
+# note on the diff/rm/ln logic below:
+# if the dcs.db has not changed, we do not want to rebuild, so we
+# do not want to change its timestamp.
 
-dcs.db:	dcs.db.refresh
-	curl -H 'Content-Type: application/json' \
+dcs.db:	dcs.db.tstamp
+	curl -f -H 'Content-Type: application/json' \
 		-d '{"profile":"", "uri":"/ds/classifier/get/account/'$(DCS_ACCOUNT)'", "token":"'$(DCS_KEY)'"}'	\
 		'https://dcs.netbiscuits.net/ds/classifier/get/account/'$(DCS_ACCOUNT) \
 		> dcs.db.tmp
-	if [[ -f dcs.db ]] ; then	\
+
+	test -s dcs.db.tmp
+
+	if test -f dcs.db ; then	\
 		if ! diff --brief dcs.db dcs.db.tmp >/dev/null ; then	\
 			mv -f dcs.db.tmp dcs.db ;			\
+		else 							\
+			rm dcs.db.tstamp ;				\
+			ln dcs.db dcs.db.tstamp	;			\
 		fi ;							\
 	else								\
 		mv -f dcs.db.tmp dcs.db ;				\
@@ -51,4 +66,5 @@ CLEANFILES = \
 	fixup.remove \
 	fixup.reorder \
 	fixup.out \
-	dcs.db
\ No newline at end of file
+	dcs.db \
+	dcs.db.tstamp