fix: truncate milliseconds to i64 before serializing

time/src/serde/timestamp/milliseconds_i64.rs

@@ -0,0 +1,64 @@
+//! Treat an [`OffsetDateTime`] as a [Unix timestamp] with milliseconds for
+//! the purposes of serde.
+//!
+//! Use this module in combination with serde's [`#[with]`][with] attribute.
+//!
+//! When deserializing, the offset is assumed to be UTC.
+//!
+//! [Unix timestamp]: https://en.wikipedia.org/wiki/Unix_time
+//! [with]: https://serde.rs/field-attrs.html#with
+
+use num_conv::Truncate;
+use serde::{de, Deserialize, Deserializer, Serialize, Serializer};
+
+use crate::OffsetDateTime;
+
+/// Serialize an `OffsetDateTime` as its Unix timestamp with milliseconds
+pub fn serialize<S: Serializer>(
+    datetime: &OffsetDateTime,
+    serializer: S,
+) -> Result<S::Ok, S::Error> {
+    let timestamp = (datetime.unix_timestamp_nanos() / 1_000_000).truncate::<i64>();
+    timestamp.serialize(serializer)
+}
+
+/// Deserialize an `OffsetDateTime` from its Unix timestamp with milliseconds
+pub fn deserialize<'a, D: Deserializer<'a>>(deserializer: D) -> Result<OffsetDateTime, D::Error> {
+    let value: i128 = <_>::deserialize(deserializer)?;
+    OffsetDateTime::from_unix_timestamp_nanos(value * 1_000_000)
+        .map_err(|err| de::Error::invalid_value(de::Unexpected::Signed(err.value), &err))
+}
+
+/// Treat an `Option<OffsetDateTime>` as a [Unix timestamp] with milliseconds
+/// for the purposes of serde.
+///
+/// Use this module in combination with serde's [`#[with]`][with] attribute.
+///
+/// When deserializing, the offset is assumed to be UTC.
+///
+/// [Unix timestamp]: https://en.wikipedia.org/wiki/Unix_time
+/// [with]: https://serde.rs/field-attrs.html#with
+pub mod option {
+    #[allow(clippy::wildcard_imports)]
+    use super::*;
+
+    /// Serialize an `Option<OffsetDateTime>` as its Unix timestamp with milliseconds
+    pub fn serialize<S: Serializer>(
+        option: &Option<OffsetDateTime>,
+        serializer: S,
+    ) -> Result<S::Ok, S::Error> {
+        option
+            .map(|timestamp| (timestamp.unix_timestamp_nanos() / 1_000_000).truncate::<i64>())
+            .serialize(serializer)
+    }
+
+    /// Deserialize an `Option<OffsetDateTime>` from its Unix timestamp with milliseconds
+    pub fn deserialize<'a, D: Deserializer<'a>>(
+        deserializer: D,
+    ) -> Result<Option<OffsetDateTime>, D::Error> {
+        Option::deserialize(deserializer)?
+            .map(|value: i128| OffsetDateTime::from_unix_timestamp_nanos(value * 1_000_000))
+            .transpose()
+            .map_err(|err| de::Error::invalid_value(de::Unexpected::Signed(err.value), &err))
+    }
+}

time/src/serde/timestamp/mod.rs

@@ -9,6 +9,7 @@
 
 pub mod microseconds;
 pub mod milliseconds;
+pub mod milliseconds_i64;
 pub mod nanoseconds;
 
 use serde::{de, Deserialize, Deserializer, Serialize, Serializer};