Fix ClassCastException in DebugMetrics nested structures [#7383]

CHANGELOG.md

@@ -1,5 +1,13 @@
 # Changelog
 
+## [Unreleased]
+
+### Fixed
+- **DebugMetrics**: Fixed a `ClassCastException` occurring in `DebugMetrics` when handling nested metric structures. Previously, `Double` values within these structures were incorrectly cast to `Map` objects, leading to errors. This update allows for proper handling of both direct values and nested structures at the same level. Issue# [#7383]
+
+### Tests
+- Added a comprehensive test case to reproduce the bug and verify the fix for the `ClassCastException` in `DebugMetrics`. This ensures that complex, dynamically nested metric structures can be handled without errors.
+
 ## Next release
 
 ### Upcoming Breaking Changes
@@ -17,6 +25,7 @@
 - Correctly release txpool save and restore lock in case of exceptions [#7473](https://github.com/hyperledger/besu/pull/7473)
 - Fix for `eth_gasPrice` could not retrieve block error [#7482](https://github.com/hyperledger/besu/pull/7482)
 
+
 ## 24.8.0
 
 ### Upcoming Breaking Changes

ethereum/api/src/main/java/org/hyperledger/besu/ethereum/api/jsonrpc/internal/methods/DebugMetrics.java

@@ -71,7 +71,26 @@ private void addLabelledObservation(
   @SuppressWarnings("unchecked")
   private Map<String, Object> getNextMapLevel(
       final Map<String, Object> current, final String name) {
+    // Use compute to either return the existing map or create a new one
     return (Map<String, Object>)
-        current.computeIfAbsent(name, key -> new HashMap<String, Object>());
+        current.compute(
+            name,
+            (k, v) -> {
+              if (v instanceof Map) {
+                // If the value is already a Map, return it as is
+                return v;
+              } else {
+                // If the value is not a Map, create a new Map
+                Map<String, Object> newMap = new HashMap<>();
+                if (v != null) {
+                  // If v is not null and not a Map, we store it as a leaf value
+                  // If the original value was not null, store it under the "value" key
+                  // This handles cases where a metric value (e.g., Double) was previously stored
+                  // directly
+                  newMap.put("value", v);
+                }
+                return newMap;
+              }
+            });
   }
 }

ethereum/api/src/test/java/org/hyperledger/besu/ethereum/api/jsonrpc/internal/methods/DebugMetricsTest.java

@@ -16,6 +16,7 @@
 
 import static java.util.Arrays.asList;
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.hyperledger.besu.metrics.BesuMetricCategory.BLOCKCHAIN;
 import static org.hyperledger.besu.metrics.BesuMetricCategory.PEERS;
 import static org.hyperledger.besu.metrics.BesuMetricCategory.RPC;
 import static org.mockito.Mockito.mock;
@@ -28,6 +29,7 @@
 import org.hyperledger.besu.metrics.Observation;
 
 import java.util.Collections;
+import java.util.List;
 import java.util.stream.Stream;
 
 import com.google.common.collect.ImmutableMap;
@@ -84,6 +86,36 @@ public void shouldNestObservationsByLabel() {
                     ImmutableMap.of("label2B", "value3")))));
   }
 
+  @Test
+  public void shouldHandleDoubleValuesInNestedStructureWithoutClassCastException() {
+    // Tests fix for issue# 7383: debug_metrics method error
+    when(metricsSystem.streamObservations())
+        .thenReturn(
+            Stream.of(
+                // This creates a double value for "a"
+                new Observation(BLOCKCHAIN, "nested_metric", 1.0, List.of("a")),
+                // This attempts to create a nested structure under "a", which was previously a
+                // double
+                new Observation(BLOCKCHAIN, "nested_metric", 2.0, asList("a", "b")),
+                // This adds another level of nesting
+                new Observation(BLOCKCHAIN, "nested_metric", 3.0, asList("a", "b", "c"))));
+
+    assertResponse(
+        ImmutableMap.of(
+            BLOCKCHAIN.getName(),
+            ImmutableMap.of(
+                "nested_metric",
+                ImmutableMap.of(
+                    "a",
+                    ImmutableMap.of(
+                        "value",
+                        1.0,
+                        "b",
+                        ImmutableMap.of(
+                            "value", 2.0,
+                            "c", 3.0))))));
+  }
+
   private void assertResponse(final ImmutableMap<String, Object> expectedResponse) {
     final JsonRpcSuccessResponse response = (JsonRpcSuccessResponse) method.response(REQUEST);
     assertThat(response.getResult()).isEqualTo(expectedResponse);