Adapt Datetime parser to DST timezones (#1524)

When iOS device locale is set to location
which uses different timezeons depending on
daylight saving time (eg PST and PDT for
Los Angeles), then different `gmtoff` applied
by `strptime` for 'summer' and 'winter'
timestamps.

This results in the wrong translation of
datetime string into epoch.

Adapt code to iOS/MacOS behaviour, where
`timegm` updates an input parameter and
erases `gmtoff` value:
- remove logic to infer the offset using epoch
  datetime;
- store `gmtoff` value before calling `timegm`;
- offset result returned from `timegm` by
  saved `gmtoff`.

Relates-To: HERESDK-2568

Signed-off-by: Mykhailo Diachenko <[email protected]>

Author: diachenko-mischa

olp-cpp-sdk-authentication/src/AuthenticationClientUtils.cpp

@@ -98,7 +98,7 @@ constexpr auto kDate = "date";
 
 #ifdef _WIN32
 // Windows does not have ::strptime and ::timegm
-std::time_t DoParseTime(const std::string& value) {
+std::time_t ParseTime(const std::string& value) {
   std::tm tm = {};
   std::istringstream ss(value);
   ss >> std::get_time(&tm, "%a, %d %b %Y %H:%M:%S %z");
@@ -107,29 +107,22 @@ std::time_t DoParseTime(const std::string& value) {
 
 #else
 
-std::time_t DoParseTime(const std::string& value) {
+std::time_t ParseTime(const std::string& value) {
   std::tm tm = {};
   const auto format = "%a, %d %b %Y %H:%M:%S %Z";
   const auto parsed_until = ::strptime(value.c_str(), format, &tm);
   if (parsed_until != value.c_str() + value.size()) {
     OLP_SDK_LOG_WARNING(kLogTag, "Timestamp is not fully parsed" << value);
   }
-  return timegm(&tm);
+  // MacOS updates `tm_isdst`, `tm_zone` and `tm_gmtoff` fields in `timegm`
+  // call.
+  const auto gmtoff = tm.tm_gmtoff;
+  const auto local_time = timegm(&tm);
+  return local_time - gmtoff;
 }
 
 #endif
 
-std::time_t GmtEpochOffset() {
-  const auto epoch_as_date_time = "Thu, 1 Jan 1970 0:00:00 GMT";
-  return DoParseTime(epoch_as_date_time);
-}
-
-std::time_t ParseTime(const std::string& value) {
-  const auto time = DoParseTime(value);
-  const auto offset = GmtEpochOffset();
-  return time - offset;
-}
-
 boost::optional<std::time_t> GetTimestampFromHeaders(
     const olp::http::Headers& headers) {
   auto it =

olp-cpp-sdk-authentication/tests/AuthenticationClientTest.cpp

@@ -29,6 +29,8 @@
 
 namespace {
 constexpr auto kTime = "Fri, 29 May 2020 11:07:45 GMT";
+constexpr auto kEpochTime = "Thu, 1 Jan 1970 00:00:00 GMT";
+constexpr auto kSummerTime = "Tue, 18 Jun 2024 12:25:35 GMT";
 }  // namespace
 
 namespace auth = olp::authentication;
@@ -237,6 +239,16 @@ TEST(AuthenticationClientTest, TimeParsing) {
     SCOPED_TRACE("Parse time");
     EXPECT_EQ(auth::ParseTime(kTime), 1590750465);
   }
+
+  {
+    SCOPED_TRACE("Parse epoch time");
+    EXPECT_EQ(auth::ParseTime(kEpochTime), 0);
+  }
+
+  {
+    SCOPED_TRACE("Parse summer time");
+    EXPECT_EQ(auth::ParseTime(kSummerTime), 1718713535);
+  }
 }
 
 TEST(AuthenticationClientTest, GenerateAuthorizationHeader) {