Accept the 'z' and 'Z' timezone in timestamp_from_string.

The 'z' (or 'Z') timezone denotes UTC+00:00.
Fixes scylladb#4641.

Signed-off-by: Kamil Braun <kbraun@scylladb.com>

tests/types_test.cc

@@ -248,6 +248,8 @@ void test_timestamp_like_string_conversions(data_type timestamp_type) {
     BOOST_REQUIRE(timestamp_type->equal(timestamp_type->from_string("2015-07-02 23:00-0100"), timestamp_type->decompose(tp)));
     BOOST_REQUIRE(timestamp_type->equal(timestamp_type->from_string("2015-07-03T00:00+0000"), timestamp_type->decompose(tp)));
     BOOST_REQUIRE(timestamp_type->equal(timestamp_type->from_string("2015-07-03T01:00:00+0000"), timestamp_type->decompose(tp + 1h)));
+    BOOST_REQUIRE(timestamp_type->equal(timestamp_type->from_string("2015-07-03t00:00:00z"), timestamp_type->decompose(tp)));
+    BOOST_REQUIRE(timestamp_type->equal(timestamp_type->from_string("2015-07-03T00:00:00Z"), timestamp_type->decompose(tp)));
     BOOST_REQUIRE(timestamp_type->equal(timestamp_type->from_string("2015-07-03T00:00:00.123+0000"), timestamp_type->decompose(tp + 123ms)));
     BOOST_REQUIRE(timestamp_type->equal(timestamp_type->from_string("2015-07-03T12:30:00+1230"), timestamp_type->decompose(tp)));
     BOOST_REQUIRE(timestamp_type->equal(timestamp_type->from_string("2015-07-02T23:00-0100"), timestamp_type->decompose(tp)));

types.cc

@@ -830,7 +830,7 @@ class timestamp_type_impl : public simple_type_impl<db_clock::time_point> {
                 auto t2 = local_tz::utc_to_local(t - tz_offset);
                 auto dst_offset = t2 - t;
                 t -= tz_offset + dst_offset;
-            } else {
+            } else if (tz != "z") {
                 throw marshal_exception(sprint("Unable to parse timezone '%s'", tz));
             }
             return (t - boost::posix_time::from_time_t(0)).total_milliseconds();