feat(chain): Add SyncRequestExt::check_unconfirmed_statuses

This is a convenience method for adding unconfirmed txs alongside their
associated spks the the sync request. This way, we will be able to
detect evictions of these transactions from the mempool.

crates/chain/src/indexer/keychain_txout.rs

@@ -7,11 +7,13 @@ use crate::{
     spk_client::{FullScanRequestBuilder, SyncRequestBuilder},
     spk_iter::BIP32_MAX_INDEX,
     spk_txout::SpkTxOutIndex,
-    DescriptorExt, DescriptorId, Indexed, Indexer, KeychainIndexed, SpkIterator,
+    Anchor, CanonicalIter, CanonicalReason, ChainOracle, DescriptorExt, DescriptorId, Indexed,
+    Indexer, KeychainIndexed, SpkIterator,
 };
 use alloc::{borrow::ToOwned, vec::Vec};
 use bitcoin::{Amount, OutPoint, ScriptBuf, SignedAmount, Transaction, TxOut, Txid};
 use core::{
+    convert::Infallible,
     fmt::Debug,
     ops::{Bound, RangeBounds},
 };
@@ -879,6 +881,20 @@ pub trait SyncRequestBuilderExt<K> {
 
     /// Add [`Script`](bitcoin::Script)s that are revealed by the `indexer` but currently unused.
     fn unused_spks_from_indexer(self, indexer: &KeychainTxOutIndex<K>) -> Self;
+
+    /// Add unconfirmed txids and their associated spks.
+    ///
+    /// We expect that the chain source should include these txids in their spk histories. If not,
+    /// the transaction has been evicted for some reason and we will inform the receiving
+    /// structures in the response.
+    fn check_unconfirmed_statuses<A, C>(
+        self,
+        indexer: &KeychainTxOutIndex<K>,
+        canonical_iter: CanonicalIter<A, C>,
+    ) -> Self
+    where
+        A: Anchor,
+        C: ChainOracle<Error = Infallible>;
 }
 
 impl<K: Clone + Ord + core::fmt::Debug> SyncRequestBuilderExt<K> for SyncRequestBuilder<(K, u32)> {
@@ -892,6 +908,29 @@ impl<K: Clone + Ord + core::fmt::Debug> SyncRequestBuilderExt<K> for SyncRequest
     fn unused_spks_from_indexer(self, indexer: &KeychainTxOutIndex<K>) -> Self {
         self.spks_with_indexes(indexer.unused_spks())
     }
+
+    fn check_unconfirmed_statuses<A, C>(
+        self,
+        indexer: &KeychainTxOutIndex<K>,
+        canonical_iter: CanonicalIter<A, C>,
+    ) -> Self
+    where
+        A: Anchor,
+        C: ChainOracle<Error = Infallible>,
+    {
+        self.expected_txs(
+            canonical_iter
+                .map(|res| res.expect("infallible"))
+                .filter(|(_, _, reason)| matches!(reason, CanonicalReason::ObservedIn { .. }))
+                .flat_map(|(txid, tx, _)| {
+                    indexer
+                        .inner
+                        .relevant_spks_of_tx(tx.as_ref())
+                        .into_iter()
+                        .map(move |spk| (txid, spk))
+                }),
+        )
+    }
 }
 
 /// Trait to extend [`FullScanRequestBuilder`].

crates/chain/src/indexer/spk_txout.rs

@@ -3,7 +3,7 @@
 use core::ops::RangeBounds;
 
 use crate::{
-    collections::{hash_map::Entry, BTreeMap, BTreeSet, HashMap},
+    collections::{hash_map::Entry, BTreeMap, BTreeSet, HashMap, HashSet},
     Indexer,
 };
 use bitcoin::{Amount, OutPoint, ScriptBuf, SignedAmount, Transaction, TxOut, Txid};
@@ -334,4 +334,21 @@ impl<I: Clone + Ord + core::fmt::Debug> SpkTxOutIndex<I> {
             .any(|output| self.spk_indices.contains_key(&output.script_pubkey));
         input_matches || output_matches
     }
+
+    /// Find relevant script pubkeys associated with a transaction.
+    ///
+    /// The script pubkeys of the transaction's outputs and previous outputs as scanned.
+    pub fn relevant_spks_of_tx(&self, tx: &Transaction) -> HashSet<ScriptBuf> {
+        let spks_from_inputs = tx.input.iter().filter_map(|txin| {
+            self.txouts
+                .get(&txin.previous_output)
+                .map(|(_, prev_txo)| prev_txo.script_pubkey.clone())
+        });
+        let spks_from_outputs = tx
+            .output
+            .iter()
+            .filter(|txout| self.spk_indices.contains_key(&txout.script_pubkey))
+            .map(|txo| txo.script_pubkey.clone());
+        spks_from_inputs.chain(spks_from_outputs).collect()
+    }
 }