fix(cbf): distinguish UnknownHash from real fetch errors in fee estimation

Only treat FetchBlockError::UnknownHash as an expected graceful break
when walking past Kyoto's known header range. Other fetch errors
(SendError, RecvError) now log at error level since they indicate actual
communication failures rather than expected boundary conditions.

Author: febyeji

src/chain/cbf.rs

@@ -14,6 +14,7 @@ use std::time::{Duration, Instant, SystemTime, UNIX_EPOCH};
 use bdk_chain::{BlockId, ConfirmationBlockTime, TxUpdate};
 use bdk_wallet::{KeychainKind, Update};
 use bip157::chain::{BlockHeaderChanges, ChainState};
+use bip157::error::FetchBlockError;
 use bip157::{
 	BlockHash, Builder, Client, Event, HeaderCheckpoint, Info, Node as CbfNode, Requester,
 	SyncUpdate, TrustedPeer, Warning,
@@ -989,54 +990,65 @@ impl CbfChainSource {
 			// On later iterations we may walk past Kyoto's known header range and
 			// hit `UnknownHash`; in that case we use whatever blocks we already
 			// have rather than failing the whole fee update.
-			let indexed_block =
-				match tokio::time::timeout(remaining_timeout, requester.get_block(current_hash))
-					.await
-				{
-					Ok(Ok(indexed_block)) => indexed_block,
-					Ok(Err(e)) if idx == 0 => {
-						log_debug!(
-							self.logger,
-							"Cached CBF tip {} was unavailable during fee estimation, \
+			let indexed_block = match tokio::time::timeout(
+				remaining_timeout,
+				requester.get_block(current_hash),
+			)
+			.await
+			{
+				Ok(Ok(indexed_block)) => indexed_block,
+				Ok(Err(e)) if idx == 0 => {
+					log_debug!(
+						self.logger,
+						"Cached CBF tip {} was unavailable during fee estimation, \
 							 likely due to initial sync or a reorg: {:?}",
-							current_hash,
-							e
-						);
-						*self.latest_tip.lock().unwrap() = None;
-						return Ok(None);
-					},
-					Ok(Err(e)) => {
-						log_debug!(
+						current_hash,
+						e
+					);
+					*self.latest_tip.lock().unwrap() = None;
+					return Ok(None);
+				},
+				Ok(Err(FetchBlockError::UnknownHash)) => {
+					log_debug!(
 							self.logger,
-							"CBF could not serve block {} during fee estimation after {} successful fetches: {:?}",
+							"CBF walked past known header range at {} during fee estimation after {} successful fetches.",
 							current_hash,
 							block_fee_rates.len(),
-							e
 						);
-						break;
-					},
-					Err(e) if idx == 0 => {
-						log_debug!(
+					break;
+				},
+				Ok(Err(e)) => {
+					log_error!(
 							self.logger,
-							"Timed out fetching cached CBF tip {} during fee estimation, \
-							 likely due to initial sync or a reorg: {}",
+							"Failed to fetch block {} during fee estimation after {} successful fetches: {:?}",
 							current_hash,
+							block_fee_rates.len(),
 							e
 						);
-						*self.latest_tip.lock().unwrap() = None;
-						return Ok(None);
-					},
-					Err(e) => {
-						log_debug!(
+					break;
+				},
+				Err(e) if idx == 0 => {
+					log_debug!(
+						self.logger,
+						"Timed out fetching cached CBF tip {} during fee estimation, \
+							 likely due to initial sync or a reorg: {}",
+						current_hash,
+						e
+					);
+					*self.latest_tip.lock().unwrap() = None;
+					return Ok(None);
+				},
+				Err(e) => {
+					log_debug!(
 							self.logger,
 							"Timed out fetching block {} during fee estimation after {} successful fetches: {}",
 							current_hash,
 							block_fee_rates.len(),
 							e
 						);
-						break;
-					},
-				};
+					break;
+				},
+			};
 
 			let height = indexed_block.height;
 			let block = &indexed_block.block;