accept only the expected UTC timezones in date parsing

HTTP/1.1 hardcodes GMT (RFC 7231 §7.1.1.1) and what is good enough for the
internet must be good enough for us™ as we reuse the implementation
internally to parse (most) dates we encounter in various places like the
Release files with their Date and Valid-Until header fields.

Implementing a fully timezone aware parser just feels too hard for no
effective benefit as it would take 5+ years (= until LTS's are out of
fashion) until a repository could use non-UTC dates and expect it to
work. Not counting non-apt implementations which might or might not
only want to encounter UTC here as well.

As a bonus, this eliminates the use of an instance of setlocale in
libapt.

Closes: 819697
(cherry picked from commit 9febc2b238e1e322dce1f94ecbed46d595893b52)

1 files changed, 2 insertions, 2 deletions

diff --git a/test/integration/test-apt-update-ims b/test/integration/test-apt-update-ims
index 5a44911a6..88f479465 100755
--- a/test/integration/test-apt-update-ims
+++ b/test/integration/test-apt-update-ims
@@ -97,9 +97,9 @@ runtest 'warning'
 
 # make the release file old
 find aptarchive -name '*Release' -exec sed -i \
-	-e "s#^Date: .*\$#Date: $(date -d '-2 weeks' '+%a, %d %b %Y %H:%M:%S %Z')#" \
+	-e "s#^Date: .*\$#Date: $(date -ud '-2 weeks' '+%a, %d %b %Y %H:%M:%S %Z')#" \
 	-e '/^Valid-Until: / d' -e "/^Date: / a\
-Valid-Until: $(date -d '-1 weeks' '+%a, %d %b %Y %H:%M:%S %Z')" '{}' \;
+Valid-Until: $(date -ud '-1 weeks' '+%a, %d %b %Y %H:%M:%S %Z')" '{}' \;
 signreleasefiles
 logcurrentarchivedirectory