fix(esplora): revert back to using a for loop in chain_update

..to preserve the original control flow. In case of error we want
to return the last local hash that is tried for equality with the
remote hash. To do so we store a copy of the current local hash
on each iteration.

Author: ValuedMammal

crates/esplora/src/async_ext.rs

@@ -224,31 +224,35 @@ async fn chain_update<S: Sleeper>(
     local_tip: &CheckPoint,
     anchors: &BTreeSet<(ConfirmationBlockTime, Txid)>,
 ) -> Result<CheckPoint, Error> {
-    let mut cp = local_tip.clone();
+    let mut point_of_agreement = None;
+    let mut local_cp_hash = local_tip.hash();
     let mut conflicts = vec![];
 
-    let mut tip = loop {
-        let remote_hash = match fetch_block(client, latest_blocks, cp.height()).await? {
+    for local_cp in local_tip.iter() {
+        let remote_hash = match fetch_block(client, latest_blocks, local_cp.height()).await? {
             Some(hash) => hash,
             None => continue,
         };
-        if remote_hash == cp.hash() {
-            break cp;
+        if remote_hash == local_cp.hash() {
+            point_of_agreement = Some(local_cp);
+            break;
         }
-        // it is not strictly necessary to include all the conflicted heights (we do need the
+        local_cp_hash = local_cp.hash();
+        // It is not strictly necessary to include all the conflicted heights (we do need the
         // first one) but it seems prudent to make sure the updated chain's heights are a
         // superset of the existing chain after update.
         conflicts.push(BlockId {
-            height: cp.height(),
+            height: local_cp.height(),
             hash: remote_hash,
         });
-        cp = match cp.prev() {
-            Some(prev) => prev,
-            None => {
-                return Err(Box::new(esplora_client::Error::HeaderHashNotFound(
-                    cp.hash(),
-                )));
-            }
+    }
+
+    let mut tip = match point_of_agreement {
+        Some(tip) => tip,
+        None => {
+            return Err(Box::new(esplora_client::Error::HeaderHashNotFound(
+                local_cp_hash,
+            )));
         }
     };
 

crates/esplora/src/blocking_ext.rs

@@ -209,31 +209,35 @@ fn chain_update(
     local_tip: &CheckPoint,
     anchors: &BTreeSet<(ConfirmationBlockTime, Txid)>,
 ) -> Result<CheckPoint, Error> {
-    let mut cp = local_tip.clone();
+    let mut point_of_agreement = None;
+    let mut local_cp_hash = local_tip.hash();
     let mut conflicts = vec![];
 
-    let mut tip = loop {
-        let remote_hash = match fetch_block(client, latest_blocks, cp.height())? {
+    for local_cp in local_tip.iter() {
+        let remote_hash = match fetch_block(client, latest_blocks, local_cp.height())? {
             Some(hash) => hash,
             None => continue,
         };
-        if remote_hash == cp.hash() {
-            break cp;
+        if remote_hash == local_cp.hash() {
+            point_of_agreement = Some(local_cp);
+            break;
         }
-        // it is not strictly necessary to include all the conflicted heights (we do need the
+        local_cp_hash = local_cp.hash();
+        // It is not strictly necessary to include all the conflicted heights (we do need the
         // first one) but it seems prudent to make sure the updated chain's heights are a
         // superset of the existing chain after update.
         conflicts.push(BlockId {
-            height: cp.height(),
+            height: local_cp.height(),
             hash: remote_hash,
         });
-        cp = match cp.prev() {
-            Some(prev) => prev,
-            None => {
-                return Err(Box::new(esplora_client::Error::HeaderHashNotFound(
-                    cp.hash(),
-                )));
-            }
+    }
+
+    let mut tip = match point_of_agreement {
+        Some(tip) => tip,
+        None => {
+            return Err(Box::new(esplora_client::Error::HeaderHashNotFound(
+                local_cp_hash,
+            )));
         }
     };