Minor clean-ups in DateTime and changelog (#224)

## Description

This PR is a follow-up to #223 and cleans up the code a little, adding
test assertions and a missing changelog message.

Author: sgoll

CHANGELOG.md

@@ -7,13 +7,18 @@ adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+### Added
+
+- Add `ua::ServerStatusDataType` with `ua::ServerState` and `ua::BuildInfo`.
+- Add methods `ua::DateTime::try_from_unix_timestamp_nanos()` and `as_unix_timestamp_nanos()` that
+  work independently of the `time` feature.
+
 ## [0.8.4] - 2025-04-30
 
 ### Added
 
 - Add `ua::Guid`.
-- Add `ua::EnumDefinition` with `ua::EnumField`.
-- Add `ua::ServerStatusDataType` with `ua::ServerState` and `ua::BuildInfo`.
+- Add `ua::EnumDefinition` and `ua::EnumField`.
 
 ## [0.8.3] - 2025-03-27
 

src/ua/data_types/date_time.rs

@@ -1,51 +1,62 @@
-crate::data_type!(DateTime);
+use open62541_sys::{UA_DATETIME_UNIX_EPOCH, UA_DATETIME_USEC};
 
-impl DateTime {
-    /// Returns the UNIX timestamp with nanosecond precision.
-    #[must_use]
-    pub fn as_unix_timestamp_nanos(&self) -> i128 {
-        use open62541_sys::{UA_DATETIME_UNIX_EPOCH, UA_DATETIME_USEC};
+use crate::Error;
 
-        // OPC UA encodes `DateTime` as Windows file time: a 64-bit value that represents the number
-        // of 100-nanosecond intervals that have elapsed since 12:00 A.M. January 1, 1601 (UTC).
-        let ua_ticks = i128::from(self.0);
-        let unix_ticks = ua_ticks - i128::from(UA_DATETIME_UNIX_EPOCH);
-        unix_ticks * i128::from(1000 / UA_DATETIME_USEC)
-    }
+crate::data_type!(DateTime);
 
+impl DateTime {
     /// Creates [`DateTime`] from a UNIX timestamp with nanosecond precision.
     ///
+    /// /// # Examples
+    ///
+    /// ```
+    /// use open62541::ua;
+    ///
+    /// // Unix timestamp (1707482096 seconds) corresponding to 9th February 2024, 12:34:56 UTC.
+    /// let dt = ua::DateTime::try_from_unix_timestamp_nanos(1_707_482_096_000_000_000).unwrap();
+    ///
+    /// assert_eq!(format!("{dt:?}"), "\"2024-02-09T12:34:56Z\"");
+    /// ```
+    ///
     /// # Errors
     ///
     /// The UNIX timestamp must be valid and in range of the 64-bit representation of [`DateTime`].
-    pub fn try_from_unix_timestamp_nanos(unix_timestamp_nanos: i128) -> Result<Self, crate::Error> {
-        use open62541_sys::{UA_DATETIME_UNIX_EPOCH, UA_DATETIME_USEC};
-
+    pub fn try_from_unix_timestamp_nanos(unix_timestamp_nanos: i128) -> Result<Self, Error> {
         // OPC UA encodes `DateTime` as Windows file time: a 64-bit value that represents the number
         // of 100-nanosecond intervals that have elapsed since 12:00 A.M. January 1, 1601 (UTC).
-        let ticks_unix = unix_timestamp_nanos / i128::from(1000 / UA_DATETIME_USEC);
-        let ticks_ua = ticks_unix + i128::from(UA_DATETIME_UNIX_EPOCH);
+        let unix_ticks = unix_timestamp_nanos / i128::from(1000 / UA_DATETIME_USEC);
+        let ua_ticks = unix_ticks + i128::from(UA_DATETIME_UNIX_EPOCH);
 
-        i64::try_from(ticks_ua)
-            // Explicit module path to avoid linter errors when feature is not enable by `#[cfg()]`.
-            .map_err(|_| crate::Error::internal("DateTime should be in range"))
+        i64::try_from(ua_ticks)
+            .map_err(|_| Error::internal("DateTime should be in range"))
             .map(Self)
     }
+
+    /// Returns the UNIX timestamp with nanosecond precision.
+    #[must_use]
+    pub fn as_unix_timestamp_nanos(&self) -> i128 {
+        // OPC UA encodes `DateTime` as Windows file time: a 64-bit value that represents the number
+        // of 100-nanosecond intervals that have elapsed since 12:00 A.M. January 1, 1601 (UTC).
+        let ua_ticks = i128::from(self.0);
+        let unix_ticks = ua_ticks - i128::from(UA_DATETIME_UNIX_EPOCH);
+
+        unix_ticks * i128::from(1000 / UA_DATETIME_USEC)
+    }
 }
 
 #[cfg(feature = "time")]
 impl DateTime {
-    // TODO (breaking change): Return time::UtcDateTime instead of time::OffsetDateTime.
+    // TODO (breaking change): Return `time::UtcDateTime` instead of `time::OffsetDateTime`.
     #[must_use]
     pub fn to_utc(&self) -> Option<time::OffsetDateTime> {
         time::OffsetDateTime::from_unix_timestamp_nanos(self.as_unix_timestamp_nanos()).ok()
     }
 }
 
+// TODO (breaking change): Upgrade `time` (0.3.38), add conversion from `time::UtcDateTime`.
 #[cfg(feature = "time")]
 impl TryFrom<time::OffsetDateTime> for DateTime {
-    // Explicit module path to avoid linter errors when feature is not enable by `#[cfg()]`.
-    type Error = crate::Error;
+    type Error = Error;
 
     /// Creates [`DateTime`] from [`time::OffsetDateTime`].
     ///
@@ -56,6 +67,8 @@ impl TryFrom<time::OffsetDateTime> for DateTime {
     /// use time::macros::datetime;
     ///
     /// let dt: ua::DateTime = datetime!(2024-02-09 12:34:56 UTC).try_into().unwrap();
+    ///
+    /// assert_eq!(format!("{dt:?}"), "\"2024-02-09T12:34:56Z\"");
     /// ```
     ///
     /// # Errors