feat: exported metrics for current finalized and safe block number (h…

…yperledger#7592)

* feat: exported metrics for current finalized and safe block number

Signed-off-by: Jones Ho <jones.ho@consensys.net>

* Update ethereum/core/src/main/java/org/hyperledger/besu/ethereum/chain/DefaultBlockchain.java

Co-authored-by: Fabio Di Fabio <fabio.difabio@consensys.net>
Signed-off-by: jonesho <81145364+jonesho@users.noreply.github.com>

* Update ethereum/core/src/main/java/org/hyperledger/besu/ethereum/chain/DefaultBlockchain.java

Co-authored-by: Fabio Di Fabio <fabio.difabio@consensys.net>
Signed-off-by: jonesho <81145364+jonesho@users.noreply.github.com>

* fix: spotless issue

Signed-off-by: Jones Ho <jones.ho@consensys.net>

---------

Signed-off-by: Jones Ho <jones.ho@consensys.net>
Signed-off-by: jonesho <81145364+jonesho@users.noreply.github.com>
Co-authored-by: Fabio Di Fabio <fabio.difabio@consensys.net>

ethereum/core/src/main/java/org/hyperledger/besu/ethereum/chain/DefaultBlockchain.java

@@ -122,6 +122,18 @@ private DefaultBlockchain(
         "The current height of the canonical chain",
         this::getChainHeadBlockNumber);
 
+    metricsSystem.createLongGauge(
+        BesuMetricCategory.ETHEREUM,
+        "blockchain_finalized_block",
+        "The current finalized block number",
+        this::getFinalizedBlockNumber);
+
+    metricsSystem.createLongGauge(
+        BesuMetricCategory.ETHEREUM,
+        "blockchain_safe_block",
+        "The current safe block number",
+        this::getSafeBlockNumber);
+
     metricsSystem.createGauge(
         BesuMetricCategory.BLOCKCHAIN,
         "difficulty_total",
@@ -759,6 +771,14 @@ public void setSafeBlock(final Hash blockHash) {
     updater.commit();
   }
 
+  private long getFinalizedBlockNumber() {
+    return this.getFinalized().flatMap(this::getBlockHeader).map(BlockHeader::getNumber).orElse(0L);
+  }
+
+  private long getSafeBlockNumber() {
+    return this.getSafeBlock().flatMap(this::getBlockHeader).map(BlockHeader::getNumber).orElse(0L);
+  }
+
   private void updateCacheForNewCanonicalHead(final Block block, final Difficulty uInt256) {
     chainHeader = block.getHeader();
     totalDifficulty = uInt256;