refactor(core,chain)!: extract generic ChainQuery trait from CanonicalizationTask

Introduce a new `ChainQuery` trait in `bdk_core` that provides an
interface for query-based operations against blockchain data. This trait
enables sans-IO patterns for algorithms that need to interact with blockchain
oracles without directly performing I/O.

The `CanonicalizationTask` now implements this trait, making it more composable
and allowing the query pattern to be reused for other blockchain query operations.

- Add `ChainQuery` trait with associated types for Request, Response, Context, and Result
- Implement `ChainQuery` for `CanonicalizationTask` with `BlockId` as context

BREAKING CHANGE: `CanonicalizationTask::finish()` now requires a `BlockId` parameter

Co-Authored-By: Claude <noreply@anthropic.com>

Author: oleonardolima

crates/chain/src/canonical_task.rs

@@ -5,7 +5,7 @@ use alloc::boxed::Box;
 use alloc::collections::BTreeSet;
 use alloc::sync::Arc;
 use alloc::vec::Vec;
-use bdk_core::BlockId;
+use bdk_core::{BlockId, ChainQuery};
 use bitcoin::{Transaction, Txid};
 
 type CanonicalMap<A> = HashMap<Txid, (Arc<Transaction>, CanonicalReason<A>)>;
@@ -53,53 +53,13 @@ pub struct CanonicalizationTask<'g, A> {
     confirmed_anchors: HashMap<Txid, A>,
 }
 
-impl<'g, A: Anchor> CanonicalizationTask<'g, A> {
-    /// Creates a new canonicalization task.
-    pub fn new(tx_graph: &'g TxGraph<A>, params: CanonicalizationParams) -> Self {
-        let anchors = tx_graph.all_anchors();
-        let unprocessed_assumed_txs = Box::new(
-            params
-                .assume_canonical
-                .into_iter()
-                .rev()
-                .filter_map(|txid| Some((txid, tx_graph.get_tx(txid)?))),
-        );
-        let unprocessed_anchored_txs = Box::new(
-            tx_graph
-                .txids_by_descending_anchor_height()
-                .filter_map(|(_, txid)| Some((txid, tx_graph.get_tx(txid)?, anchors.get(&txid)?))),
-        );
-        let unprocessed_seen_txs = Box::new(
-            tx_graph
-                .txids_by_descending_last_seen()
-                .filter_map(|(last_seen, txid)| Some((txid, tx_graph.get_tx(txid)?, last_seen))),
-        );
+impl<'g, A: Anchor> ChainQuery for CanonicalizationTask<'g, A> {
+    type Request = CanonicalizationRequest<A>;
+    type Response = CanonicalizationResponse<A>;
+    type Context = BlockId;
+    type Result = CanonicalView<A>;
 
-        let mut task = Self {
-            tx_graph,
-
-            unprocessed_assumed_txs,
-            unprocessed_anchored_txs,
-            unprocessed_seen_txs,
-            unprocessed_leftover_txs: VecDeque::new(),
-
-            canonical: HashMap::new(),
-            not_canonical: HashSet::new(),
-
-            pending_anchor_checks: VecDeque::new(),
-
-            canonical_order: Vec::new(),
-            confirmed_anchors: HashMap::new(),
-        };
-
-        // process assumed transactions first (they don't need queries)
-        task.process_assumed_txs();
-
-        task
-    }
-
-    /// Returns the next query needed, if any.
-    pub fn next_query(&mut self) -> Option<CanonicalizationRequest<A>> {
+    fn next_query(&mut self) -> Option<Self::Request> {
         // Check if we have pending anchor checks
         if let Some((_, _, anchors)) = self.pending_anchor_checks.front() {
             return Some(CanonicalizationRequest {
@@ -111,8 +71,7 @@ impl<'g, A: Anchor> CanonicalizationTask<'g, A> {
         self.process_anchored_txs()
     }
 
-    /// Resolves a query with the given response.
-    pub fn resolve_query(&mut self, response: CanonicalizationResponse<A>) {
+    fn resolve_query(&mut self, response: Self::Response) {
         if let Some((txid, tx, anchors)) = self.pending_anchor_checks.pop_front() {
             match response {
                 Some(best_anchor) => {
@@ -138,13 +97,11 @@ impl<'g, A: Anchor> CanonicalizationTask<'g, A> {
         }
     }
 
-    /// Returns true if the canonicalization process is complete.
-    pub fn is_finished(&self) -> bool {
+    fn is_finished(&mut self) -> bool {
         self.pending_anchor_checks.is_empty() && self.unprocessed_anchored_txs.size_hint().0 == 0
     }
 
-    /// Completes the canonicalization and returns a CanonicalView.
-    pub fn finish(mut self, chain_tip: BlockId) -> CanonicalView<A> {
+    fn finish(mut self, context: Self::Context) -> Self::Result {
         // Process remaining transactions (seen and leftover)
         self.process_seen_txs();
         self.process_leftover_txs();
@@ -224,7 +181,53 @@ impl<'g, A: Anchor> CanonicalizationTask<'g, A> {
             }
         }
 
-        CanonicalView::new(chain_tip, view_order, view_txs, view_spends)
+        CanonicalView::new(context, view_order, view_txs, view_spends)
+    }
+}
+
+impl<'g, A: Anchor> CanonicalizationTask<'g, A> {
+    /// Creates a new canonicalization task.
+    pub fn new(tx_graph: &'g TxGraph<A>, params: CanonicalizationParams) -> Self {
+        let anchors = tx_graph.all_anchors();
+        let unprocessed_assumed_txs = Box::new(
+            params
+                .assume_canonical
+                .into_iter()
+                .rev()
+                .filter_map(|txid| Some((txid, tx_graph.get_tx(txid)?))),
+        );
+        let unprocessed_anchored_txs = Box::new(
+            tx_graph
+                .txids_by_descending_anchor_height()
+                .filter_map(|(_, txid)| Some((txid, tx_graph.get_tx(txid)?, anchors.get(&txid)?))),
+        );
+        let unprocessed_seen_txs = Box::new(
+            tx_graph
+                .txids_by_descending_last_seen()
+                .filter_map(|(last_seen, txid)| Some((txid, tx_graph.get_tx(txid)?, last_seen))),
+        );
+
+        let mut task = Self {
+            tx_graph,
+
+            unprocessed_assumed_txs,
+            unprocessed_anchored_txs,
+            unprocessed_seen_txs,
+            unprocessed_leftover_txs: VecDeque::new(),
+
+            canonical: HashMap::new(),
+            not_canonical: HashSet::new(),
+
+            pending_anchor_checks: VecDeque::new(),
+
+            canonical_order: Vec::new(),
+            confirmed_anchors: HashMap::new(),
+        };
+
+        // process assumed transactions first (they don't need queries)
+        task.process_assumed_txs();
+
+        task
     }
 
     fn is_canonicalized(&self, txid: Txid) -> bool {

crates/chain/src/local_chain.rs

@@ -7,7 +7,7 @@ use core::ops::RangeBounds;
 use crate::canonical_task::CanonicalizationTask;
 use crate::collections::BTreeMap;
 use crate::{Anchor, BlockId, CanonicalView, ChainOracle, Merge};
-use bdk_core::ToBlockHash;
+use bdk_core::{ChainQuery, ToBlockHash};
 pub use bdk_core::{CheckPoint, CheckPointIter};
 use bitcoin::block::Header;
 use bitcoin::BlockHash;

crates/core/src/chain_query.rs

@@ -0,0 +1,65 @@
+//! Generic trait for query-based operations that require external blockchain data.
+//!
+//! The [`ChainQuery`] trait provides a standardized interface for implementing
+//! algorithms that need to make queries to blockchain sources and process responses
+//! in a sans-IO manner.
+
+/// A trait for types that perform query-based operations against blockchain data.
+///
+/// This trait enables types to request blockchain information via queries and process
+/// responses in a decoupled, sans-IO manner. It's particularly useful for algorithms
+/// that need to interact with blockchain oracles, chain sources, or other blockchain
+/// data providers without directly performing I/O.
+///
+/// # Type Parameters
+///
+/// * `Request` - The type of query request that can be made
+/// * `Response` - The type of response expected for queries
+/// * `Context` - The type of context needed for finalization (e.g., `BlockId` for chain tip)
+/// * `Result` - The final result type produced when the query process is complete
+pub trait ChainQuery {
+    /// The type of query request that can be made.
+    type Request;
+
+    /// The type of response expected for queries.
+    type Response;
+
+    /// The type of context needed for finalization.
+    ///
+    /// This could be `BlockId` for algorithms needing chain tip information,
+    /// `()` for algorithms that don't need additional context, or any other
+    /// type specific to the implementation's needs.
+    type Context;
+
+    /// The final result type produced when the query process is complete.
+    type Result;
+
+    /// Returns the next query needed, if any.
+    ///
+    /// This method should return `Some(request)` if more information is needed,
+    /// or `None` if no more queries are required.
+    fn next_query(&mut self) -> Option<Self::Request>;
+
+    /// Resolves a query with the given response.
+    ///
+    /// This method processes the response to a previous query request and updates
+    /// the internal state accordingly.
+    fn resolve_query(&mut self, response: Self::Response);
+
+    /// Returns true if the query process is complete and ready to finish.
+    ///
+    /// The default implementation returns `true` when there are no more queries needed.
+    /// Implementors can override this for more specific behavior if needed.
+    fn is_finished(&mut self) -> bool {
+        self.next_query().is_none()
+    }
+
+    /// Completes the query process and returns the final result.
+    ///
+    /// This method should be called when `is_finished` returns `true`.
+    /// It consumes `self` and produces the final result.
+    ///
+    /// The `context` parameter provides implementation-specific context
+    /// needed for finalization.
+    fn finish(self, context: Self::Context) -> Self::Result;
+}

crates/core/src/lib.rs

@@ -72,3 +72,6 @@ mod merge;
 pub use merge::*;
 
 pub mod spk_client;
+
+mod chain_query;
+pub use chain_query::*;