Warn when the user's configured lookahead limit is ignored

zebrad/src/components/sync.rs

@@ -188,13 +188,21 @@ where
         );
         // We apply a timeout to the verifier to avoid hangs due to missing earlier blocks.
         let verifier = Timeout::new(verifier, BLOCK_VERIFY_TIMEOUT);
+        // Warn the user if we're ignoring their configured lookahead limit
+        let lookahead_limit = if config.sync.lookahead_limit < MIN_LOOKAHEAD_LIMIT {
+            tracing::warn!(config_lookahead_limit = ?config.sync.lookahead_limit, ?MIN_LOOKAHEAD_LIMIT,
+                          "configured lookahead limit too low: using minimum lookahead limit");
+            MIN_LOOKAHEAD_LIMIT
+        } else {
+            config.sync.lookahead_limit
+        };
         Self {
             tip_network,
             state,
             downloads: Box::pin(Downloads::new(block_network, verifier)),
             prospective_tips: HashSet::new(),
             genesis_hash: genesis_hash(config.network.network),
-            lookahead_limit: std::cmp::max(config.sync.lookahead_limit, MIN_LOOKAHEAD_LIMIT),
+            lookahead_limit,
         }
     }