Only enforce successful fee rate cache updates on mainnet

This behavior mirrors what we do in the Esplora case: we only enforce
successful fee rate updates on mainnet. On regtest/signet/testnet we
will just skip (i.e. return `Ok(())`) if we fail to retrieve the updates
(e.g., when bitcoind's `estimatesmartfee` isn't sufficiently populated)
and will either keep previously-retrieved values or worst case fallback
to the fallback defaults.

Author: tnull

src/chain/mod.rs

@@ -841,34 +841,32 @@ impl ChainSource {
 			Self::BitcoindRpc {
 				bitcoind_rpc_client,
 				fee_estimator,
+				config,
 				kv_store,
 				logger,
 				node_metrics,
 				..
 			} => {
 				macro_rules! get_fee_rate_update {
 					($estimation_fut: expr) => {{
-						tokio::time::timeout(
+						let update_res = tokio::time::timeout(
 							Duration::from_secs(FEE_RATE_CACHE_UPDATE_TIMEOUT_SECS),
 							$estimation_fut,
 						)
 						.await
 						.map_err(|e| {
 							log_error!(logger, "Updating fee rate estimates timed out: {}", e);
 							Error::FeerateEstimationUpdateTimeout
-						})?
-						.map_err(|e| {
-							log_error!(logger, "Failed to retrieve fee rate estimates: {}", e);
-							Error::FeerateEstimationUpdateFailed
-						})?
+						})?;
+						update_res
 					}};
 				}
 				let confirmation_targets = get_all_conf_targets();
 
 				let mut new_fee_rate_cache = HashMap::with_capacity(10);
 				let now = Instant::now();
 				for target in confirmation_targets {
-					let fee_rate = match target {
+					let fee_rate_update_res = match target {
 						ConfirmationTarget::Lightning(
 							LdkConfirmationTarget::MinAllowedAnchorChannelRemoteFee,
 						) => {
@@ -903,6 +901,24 @@ impl ChainSource {
 						},
 					};
 
+					let fee_rate = match (fee_rate_update_res, config.network) {
+						(Ok(rate), _) => rate,
+						(Err(e), Network::Bitcoin) => {
+							// Strictly fail on mainnet.
+							log_error!(logger, "Failed to retrieve fee rate estimates: {}", e);
+							return Err(Error::FeerateEstimationUpdateFailed);
+						},
+						(Err(e), _) => {
+							// On regtest/testnet/signet we just skip, which will have us falling back to defaults.
+							log_error!(
+								logger,
+								"Failed to retrieve fee rate estimates: {}. Falling back to defaults.",
+								e,
+							);
+							return Ok(());
+						},
+					};
+
 					// LDK 0.0.118 introduced changes to the `ConfirmationTarget` semantics that
 					// require some post-estimation adjustments to the fee rates, which we do here.
 					let adjusted_fee_rate = apply_post_estimation_adjustments(target, fee_rate);