Send NSPanels the POSIX TZ rule for the manager's timezone

docker/MQTTManager/include/mqtt_manager_config/mqtt_manager_config.cpp

@@ -17,6 +17,7 @@
 #include <exception>
 #include <fmt/core.h>
 #include <fstream>
+#include <iterator>
 #include <mutex>
 #include <nlohmann/detail/conversions/to_json.hpp>
 #include <nlohmann/detail/exceptions.hpp>
@@ -42,6 +43,12 @@ void MqttManagerConfig::load() {
   boost::algorithm::trim(timezone_str);
   MqttManagerConfig::timezone = timezone_str;
   SPDLOG_INFO("Read timezone {} from /etc/timezone.", timezone_str);
+  MqttManagerConfig::timezone_posix_rule = MqttManagerConfig::read_posix_tz_rule(fmt::format("/usr/share/zoneinfo/{}", timezone_str));
+  if (MqttManagerConfig::timezone_posix_rule.empty()) {
+    SPDLOG_WARN("Could not read a POSIX TZ rule for timezone {}. NSPanels will show the time sent by the manager.", timezone_str);
+  } else {
+    SPDLOG_INFO("Using POSIX TZ rule {} for timezone {}.", MqttManagerConfig::timezone_posix_rule, timezone_str);
+  }
 
   SPDLOG_DEBUG("Clearing config values cache.");
   MqttManagerConfig::_settings_values_cache.clear();
@@ -529,6 +536,30 @@ std::expected<std::string, bool> MqttManagerConfig::get_us_horizontal_mirrored_t
   return MqttManagerConfig::_md5_checksum_us_horizontal_mirrored_tft4;
 }
 
+std::string MqttManagerConfig::read_posix_tz_rule(const std::string &tzif_path) {
+  try {
+    std::ifstream file(tzif_path, std::ios::in | std::ios::binary);
+    if (!file) {
+      return "";
+    }
+    std::string content((std::istreambuf_iterator<char>(file)), std::istreambuf_iterator<char>());
+
+    // Version 2 and later files end with the rule between two newlines (RFC 8536, section 3.3).
+    // Version 1 files have a zero version byte and no rule.
+    if (content.size() < 5 || content.compare(0, 4, "TZif") != 0 || content[4] < '2' || content.back() != '\n') {
+      return "";
+    }
+    size_t rule_start = content.rfind('\n', content.size() - 2);
+    if (rule_start == std::string::npos) {
+      return "";
+    }
+    return content.substr(rule_start + 1, content.size() - rule_start - 2);
+  } catch (std::exception &ex) {
+    SPDLOG_WARN("Caught exception while reading POSIX TZ rule from '{}': {}", tzif_path, ex.what());
+    return "";
+  }
+}
+
 // TESTING
 #if defined(TEST_MODE) && TEST_MODE == 1
 #include <gtest/gtest.h>

docker/MQTTManager/include/mqtt_manager_config/mqtt_manager_config.hpp

@@ -88,6 +88,15 @@ class MqttManagerConfig {
   static void populate_default_and_clean();
 
   static inline std::string timezone;
+  // POSIX TZ rule for timezone, read from its tzdata file. Empty if it could not be read.
+  static inline std::string timezone_posix_rule;
+
+  /**
+   * Read the POSIX TZ rule from the end of a tzdata (TZif) file, ex. "CET-1CEST,M3.5.0,M10.5.0/3".
+   * @param tzif_path: Path of the file, ex. /usr/share/zoneinfo/Europe/Stockholm.
+   * @return The rule, or empty if the file is missing, not version 2 or later, or has no rule.
+   */
+  static std::string read_posix_tz_rule(const std::string &tzif_path);
 
   template <typename T>
   static T get_setting_with_default(MQTT_MANAGER_SETTING key);

docker/MQTTManager/include/nspanel/nspanel.cpp

@@ -299,6 +299,7 @@ void NSPanel::send_config() {
   config.set_screensaver_dim_level(std::stoi(this->_get_nspanel_setting_with_default("screensaver_dim_level", MqttManagerConfig::get_setting_with_default<std::string>(MQTT_MANAGER_SETTING::SCREENSAVER_DIM_LEVEL))));
   config.set_screensaver_activation_timeout(std::stoi(this->_get_nspanel_setting_with_default("screensaver_activation_timeout", MqttManagerConfig::get_setting_with_default<std::string>(MQTT_MANAGER_SETTING::SCREENSAVER_ACTIVATION_TIMEOUT))));
   config.set_clock_us_style(MqttManagerConfig::get_setting_with_default<bool>(MQTT_MANAGER_SETTING::CLOCK_US_STYLE));
+  config.set_tz_posix(MqttManagerConfig::timezone_posix_rule);
   config.set_use_fahrenheit(MqttManagerConfig::get_setting_with_default<bool>(MQTT_MANAGER_SETTING::USE_FAHRENHEIT));
   config.set_is_us_panel(this->_get_nspanel_setting_with_default("is_us_panel", "False").compare("True") == 0);
   config.set_reverse_relays(this->_get_nspanel_setting_with_default("reverse_relays", "False").compare("True") == 0);

docker/MQTTManager/tests/nspanel_test.cpp

@@ -206,6 +206,30 @@ TEST_F(NSPanelTest, panel_settings_are_sent_in_the_config) {
   EXPECT_FALSE(config->show_screensaver_outside_temperature());
 }
 
+TEST_F(NSPanelTest, timezone_rule_is_sent_in_the_config) {
+  std::string previous_rule = MqttManagerConfig::timezone_posix_rule;
+  OnExit restore_rule{[&] { MqttManagerConfig::timezone_posix_rule = previous_rule; }};
+  MqttManagerConfig::timezone_posix_rule = "CET-1CEST,M3.5.0,M10.5.0/3";
+
+  load_panel();
+
+  auto config = last_published_config();
+  ASSERT_TRUE(config.has_value());
+  EXPECT_EQ(config->tz_posix(), "CET-1CEST,M3.5.0,M10.5.0/3");
+}
+
+TEST_F(NSPanelTest, unknown_timezone_rule_is_sent_empty) {
+  std::string previous_rule = MqttManagerConfig::timezone_posix_rule;
+  OnExit restore_rule{[&] { MqttManagerConfig::timezone_posix_rule = previous_rule; }};
+  MqttManagerConfig::timezone_posix_rule = "";
+
+  load_panel();
+
+  auto config = last_published_config();
+  ASSERT_TRUE(config.has_value());
+  EXPECT_EQ(config->tz_posix(), "");
+}
+
 TEST_F(NSPanelTest, temperature_calibration_is_sent_in_tenths_of_a_degree) {
   set_panel_setting("temperature_calibration", "-1.5"); // Django stores str(float(...)).
 

docker/MQTTManager/tests/posix_tz_rule_test.cpp

@@ -0,0 +1,71 @@
+#include <filesystem>
+#include <fstream>
+#include <gtest/gtest.h>
+#include <mqtt_manager_config/mqtt_manager_config.hpp>
+#include <string>
+
+namespace {
+
+// A tzdata file of the given version: the header, a stand-in for the binary data (which can hold
+// newlines), then, from version 2, the rule between two newlines.
+std::string tzif(char version, const std::string &rule) {
+  std::string content = std::string("TZif") + version + std::string(15, '\0') + "\x01\n\x02\n\x03";
+  if (version != '\0') {
+    content += "\n" + rule + "\n";
+  }
+  return content;
+}
+
+class PosixTzRuleTest : public ::testing::Test {
+protected:
+  void SetUp() override {
+    path = std::filesystem::temp_directory_path() / "nspm_posix_tz_rule_test";
+  }
+
+  void TearDown() override {
+    std::filesystem::remove(path);
+  }
+
+  std::string read(const std::string &content) {
+    std::ofstream(path, std::ios::binary) << content;
+    return MqttManagerConfig::read_posix_tz_rule(path);
+  }
+
+  std::filesystem::path path;
+};
+
+} // namespace
+
+TEST_F(PosixTzRuleTest, reads_the_rule_from_a_version_2_file) {
+  EXPECT_EQ(read(tzif('2', "CET-1CEST,M3.5.0,M10.5.0/3")), "CET-1CEST,M3.5.0,M10.5.0/3");
+}
+
+TEST_F(PosixTzRuleTest, reads_the_rule_from_a_version_3_file) {
+  EXPECT_EQ(read(tzif('3', "IST-2IDT,M3.4.4/26,M10.5.0")), "IST-2IDT,M3.4.4/26,M10.5.0");
+}
+
+TEST_F(PosixTzRuleTest, version_1_file_has_no_rule) {
+  EXPECT_EQ(read(tzif('\0', "")), "");
+}
+
+TEST_F(PosixTzRuleTest, empty_rule_is_empty) {
+  EXPECT_EQ(read(tzif('2', "")), "");
+}
+
+TEST_F(PosixTzRuleTest, file_that_is_not_tzdata_has_no_rule) {
+  EXPECT_EQ(read("Europe/Stockholm\n"), "");
+  EXPECT_EQ(read(""), "");
+}
+
+TEST_F(PosixTzRuleTest, missing_file_has_no_rule) {
+  EXPECT_EQ(MqttManagerConfig::read_posix_tz_rule("/nonexistent/zoneinfo/Europe/Stockholm"), "");
+}
+
+// Against the real tzdata the manager image ships, if this one has it too.
+TEST(PosixTzRuleSystemTest, reads_the_rule_from_installed_tzdata) {
+  const std::string utc = "/usr/share/zoneinfo/UTC";
+  if (!std::filesystem::exists(utc)) {
+    GTEST_SKIP() << "No tzdata installed at " << utc;
+  }
+  EXPECT_EQ(MqttManagerConfig::read_posix_tz_rule(utc), "UTC0");
+}

docker/protobuf/protobuf_nspanel.proto

@@ -89,6 +89,10 @@ message NSPanelConfig {
     string rtttl = 2; // Melody in RTTTL format, ex. "touch:d=32,o=6,b=190:g6,16p,32c7"
   }
   repeated Sound sounds = 45;
+
+  // POSIX TZ rule for the manager's timezone, ex. "CET-1CEST,M3.5.0,M10.5.0/3", for setenv("TZ", ...) and tzset().
+  // Empty if the manager could not work it out, in which case show the time from the manager's status/time topic.
+  string tz_posix = 46;
 }
 
 enum NSPanelWarningLevel {