lsn: add serde_as_u64 mod

libs/utils/src/lsn.rs

@@ -62,6 +62,49 @@ impl<'de> Deserialize<'de> for Lsn {
     }
 }
 
+/// Allows (de)serialization of an `Lsn` always as `u64`.
+///
+/// ### Example
+///
+/// ```rust
+/// # use serde::{Serialize, Deserialize};
+/// use utils::lsn::Lsn;
+///
+/// #[derive(Partialeq, Serialize, Deserialize)]
+/// struct Foo {
+///   #[serde(with = "utils::lsn::as_u64")]
+///   always_u64: Lsn,
+/// }
+///
+/// let orig = Foo { always_u64: Lsn(1234) };
+///
+/// let res = serde_json::to_string(&).unwrap();
+/// assert_eq!(res, r#"{"always_u64": 1234}"#);
+///
+/// let foo = serde_json::from_str::<Foo>(&res).unwrap();
+/// assert_eq!(res, orig);
+/// ```
+///
+pub mod serde_as_u64 {
+    use super::Lsn;
+
+    /// Serializes the Lsn as u64 disregarding the human readability of the format.
+    ///
+    /// Meant to be used via `#[serde(with = "...")]` or `#[serde(serialize_with = "...")]`.
+    pub fn serialize<S: serde::Serializer>(lsn: &Lsn, serializer: S) -> Result<S::Ok, S::Error> {
+        use serde::Serialize;
+        lsn.0.serialize(serializer)
+    }
+
+    /// Deserializes the Lsn as u64 disregarding the human readability of the format.
+    ///
+    /// Meant to be used via `#[serde(with = "...")]` or `#[serde(deserialize_with = "...")]`.
+    pub fn deserialize<'de, D: serde::Deserializer<'de>>(deserializer: D) -> Result<Lsn, D::Error> {
+        use serde::Deserialize;
+        u64::deserialize(deserializer).map(Lsn)
+    }
+}
+
 /// We tried to parse an LSN from a string, but failed
 #[derive(Debug, PartialEq, Eq, thiserror::Error)]
 #[error("LsnParseError")]