Merge persisted updates if greater than given thresholds

lwk_test_util/src/lib.rs

@@ -253,6 +253,29 @@ pub fn update_v2_test_vector_after_many_transactions() -> Vec<u8> {
     include_bytes!("../test_data/update_v2_after_many_txs.bin").to_vec()
 }
 
+/// First of 3 consecutive updates for merge testing
+/// Contains initial wallet sync (tip only)
+pub fn update_merge_test_1() -> Vec<u8> {
+    include_bytes!("../test_data/merge_updates/update_merge_1.bin").to_vec()
+}
+
+/// Second of 3 consecutive updates for merge testing
+/// Contains wallet funding transaction
+pub fn update_merge_test_2() -> Vec<u8> {
+    include_bytes!("../test_data/merge_updates/update_merge_2.bin").to_vec()
+}
+
+/// Third of 3 consecutive updates for merge testing
+/// Contains spending transaction
+pub fn update_merge_test_3() -> Vec<u8> {
+    include_bytes!("../test_data/merge_updates/update_merge_3.bin").to_vec()
+}
+
+/// Descriptor used for the merge test updates
+pub fn update_merge_test_descriptor() -> String {
+    include_str!("../test_data/merge_updates/descriptor.txt").to_string()
+}
+
 pub fn update_test_vector_encrypted_bytes() -> Vec<u8> {
     Vec::<u8>::from_hex(include_str!(
         "../test_data/update_test_vector_encrypted.hex"

lwk_test_util/test_data/merge_updates/README.md

@@ -0,0 +1,34 @@
+# Merge Test Updates
+
+This directory contains 3 consecutive `Update` structs for a regtest wallet with descriptor:
+
+ct(slip77(e12440f9ab46536bee060598e3b6064c0c1fa46049731d614b5c973ed054b363),elwpkh(tpubD6NzVbkrYhZ4Y2AL6uijCXAKHRNLMt7rxWnZt3bjPuYv8ibEQvGmEhRPDqbLUX7a7yCwEyEgEV37gu2CUa3a6CCpjLfrv3Xks9pGitNtd7z/*))
+
+## Files
+
+- `update_merge_1.bin` - Initial wallet sync (tip only update)
+- `update_merge_2.bin` - Wallet funding transaction  
+- `update_merge_3.bin` - Spending transaction
+- `descriptor.txt` - The wallet descriptor used for these updates
+
+## Expected Wallet States
+
+When these updates are applied sequentially to a fresh wallet, the expected states are:
+
+### After Update 1
+- **Balance**: 0 L-BTC
+- **Transactions**: 0
+- **UTXOs**: 0
+- **Description**: Initial sync of an empty wallet, only updates the blockchain tip
+
+### After Update 2
+- **Balance**: 1,000,000
+- **Transactions**: 1
+- **UTXOs**: 1
+- **Description**: Wallet received funding transaction of 1,000,000 sats
+
+### After Update 3
+- **Balance**: 899,974 sats
+- **Transactions**: 2
+- **UTXOs**: 1 (change output)
+- **Description**: Wallet sent 100,000 sats to an external address with a fee of 26 sats

lwk_test_util/test_data/merge_updates/descriptor.txt

@@ -0,0 +1 @@
+ct(slip77(d48cc2f9c22d8afadf38f9656d6ebc2ad7773273f34cbf62e4b15f0e5fea46f2),elwpkh(tpubD6NzVbkrYhZ4X2UC8rSu2hqEuaZis6FakbAKRxjqMJLGWHyqLy4iKu41teNY4BuSkvgRhfG3Gi1LJnN4HzNkpuGxxRYYJYTVBow8xEs9MD2/*))

lwk_wollet/src/update.rs

@@ -173,6 +173,46 @@ impl Update {
             .map_err(|e| Error::Generic(e.to_string()))?;
         Self::deserialize_decrypted(&vec, desc)
     }
+
+    /// Merge another update into this one.
+    ///
+    /// This is used to squash multiple sequential updates into a single update.
+    ///
+    /// NOTE: it's caller responsibility to ensure that the following update is the next in sequence
+    /// and updates are not mixed up.
+    pub(crate) fn merge(&mut self, following: Update) {
+        // Merge new transactions: add new ones, replace existing ones
+        for (txid, tx) in following.new_txs.txs {
+            self.new_txs.txs.retain(|(t, _)| *t != txid);
+            self.new_txs.txs.push((txid, tx));
+        }
+        self.new_txs.unblinds.extend(following.new_txs.unblinds);
+
+        // Merge txid_height_new: union with override (later wins)
+        for (txid, height) in following.txid_height_new {
+            self.txid_height_new.retain(|(t, _)| *t != txid);
+            self.txid_height_new.push((txid, height));
+        }
+
+        // Remove deleted txids from txid_height_new
+        for txid in &following.txid_height_delete {
+            self.txid_height_new.retain(|(t, _)| t != txid);
+        }
+
+        // Merge deletes
+        self.txid_height_delete.extend(following.txid_height_delete);
+
+        // Merge timestamps and scripts
+        self.timestamps.extend(following.timestamps);
+        self.scripts_with_blinding_pubkey
+            .extend(following.scripts_with_blinding_pubkey);
+
+        // Update tip to other's tip
+        self.tip = following.tip;
+
+        // Update version to latest
+        self.version = following.version;
+    }
 }
 
 fn default_blockheader() -> BlockHeader {