feat(core): Introduce MissingMarker

Marks a transaction as missing from the mempool and the latest timestamp
of when it was missing.

Author: evanlinjin

crates/core/src/lib.rs

@@ -71,4 +71,7 @@ pub use tx_update::*;
 mod merge;
 pub use merge::*;
 
+mod missing_marker;
+pub use missing_marker::*;
+
 pub mod spk_client;

crates/core/src/missing_marker.rs

@@ -0,0 +1,23 @@
+use bitcoin::Txid;
+
+/// Marks a transaction as missing from the mempool.
+#[derive(Debug, Clone, PartialEq, Eq, Copy, PartialOrd, Ord, core::hash::Hash)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+pub struct MissingMarker {
+    /// The txid of the transaction being marked.
+    pub txid: Txid,
+    /// The latest timestamp of when the transaction is missing from the mempool.
+    pub last_missing: u64,
+}
+
+impl From<(Txid, u64)> for MissingMarker {
+    fn from((txid, last_missing): (Txid, u64)) -> Self {
+        Self { txid, last_missing }
+    }
+}
+
+impl From<MissingMarker> for (Txid, u64) {
+    fn from(marker: MissingMarker) -> Self {
+        (marker.txid, marker.last_missing)
+    }
+}