Merge ValuedMammal/bdk-kyoto#48: feat(builder): use wallet lookahead …

…for recovery

7cfb3f5 feat(builder): use wallet lookahead for recovery (Rob N)

Pull request description:

  i think this should resolve the recovery issue. developers should be specifying the lookahead if more than 25 scripts were used per keychain, so we just take that lookahead here.

  cc @ValuedMammal

ACKs for top commit:
  ValuedMammal:
    ACK 7cfb3f5

Tree-SHA512: d7402c027fa2a9ed3b68cd564ff42aaa8494e125d3e810747eea8da86180bb18c4505826104772c76de95c46683ffa2fa55f1d0aec6fc64fe55b14bc49f8f2d0

examples/wallet.rs

@@ -30,12 +30,14 @@ async fn main() -> anyhow::Result<()> {
 
     let mut wallet = Wallet::create(desc, change_desc)
         .network(Network::Signet)
+        .lookahead(30)
         .create_wallet_no_persist()?;
 
     // The light client builder handles the logic of inserting the SPKs
     let (node, mut client) = LightClientBuilder::new(&wallet)
         .scan_after(170_000)
         .peers(peers)
+        .use_lookahead_scripts()
         .build()
         .unwrap();
 

src/builder.rs

@@ -57,7 +57,7 @@ use kyoto::{
 
 use crate::Client;
 
-const TARGET_INDEX: u32 = 20;
+const PEEK_INDEX: u32 = 20;
 const RECOMMENDED_PEERS: u8 = 2;
 
 #[derive(Debug)]
@@ -69,6 +69,7 @@ pub struct LightClientBuilder<'a> {
     birthday_height: Option<u32>,
     data_dir: Option<PathBuf>,
     timeout: Option<Duration>,
+    lookahead: bool,
 }
 
 impl<'a> LightClientBuilder<'a> {
@@ -81,6 +82,7 @@ impl<'a> LightClientBuilder<'a> {
             birthday_height: None,
             data_dir: None,
             timeout: None,
+            lookahead: false,
         }
     }
     /// Add peers to connect to over the P2P network.
@@ -109,6 +111,14 @@ impl<'a> LightClientBuilder<'a> {
         self
     }
 
+    /// Use all the scripts up to the wallet's lookahead parameter. Only to be used during wallet recovery,
+    /// when we do not have any knowledge of the scripts used in the wallet yet. For more information on the wallet lookahead,
+    /// see [`KeychainTxOutIndex`](bdk_wallet::chain::indexer::keychain_txout::KeychainTxOutIndex).
+    pub fn use_lookahead_scripts(mut self) -> Self {
+        self.lookahead = true;
+        self
+    }
+
     /// Configure the duration of time a remote node has to respond to a message.
     pub fn timeout_duration(mut self, timeout: Duration) -> Self {
         self.timeout = Some(timeout);
@@ -193,15 +203,20 @@ impl<'a> LightClientBuilder<'a> {
         node_builder =
             node_builder.num_required_peers(self.connections.unwrap_or(RECOMMENDED_PEERS));
         let mut spks: HashSet<ScriptBuf> = HashSet::new();
-        // Reveal 20 scripts ahead of the last revealed index so we don't miss any transactions.
         for keychain in [KeychainKind::External, KeychainKind::Internal] {
-            for index in 0..=self
+            // The user may choose to recover a wallet with lookahead scripts
+            // or use the last revealed index plus some padding to find new transactions
+            let last_revealed = self
                 .wallet
                 .spk_index()
                 .last_revealed_index(keychain)
-                .unwrap_or(0)
-                + TARGET_INDEX
-            {
+                .unwrap_or(0);
+            let lookahead_index = if self.lookahead {
+                last_revealed + self.wallet.spk_index().lookahead()
+            } else {
+                last_revealed + PEEK_INDEX
+            };
+            for index in 0..=lookahead_index {
                 spks.insert(self.wallet.peek_address(keychain, index).script_pubkey());
             }
         }