rich-indexer: Record tip metrics (#5078)

### Related changes

- In RichIndexer, record tip in ckb_metrics

### Check List <!--REMOVE the items that are not applicable-->

Tests <!-- At least one of them must be included. -->

- Unit test
- Integration test
- Manual test (add detailed scripts or steps below)
- No code

Side effects

- None

Author: eval-exec

Cargo.lock

@@ -19,6 +19,7 @@ ckb-indexer-sync.workspace = true
 ckb-jsonrpc-types.workspace = true
 ckb-notify.workspace = true
 ckb-types.workspace = true
+ckb-metrics.workspace = true
 futures.workspace = true
 log.workspace = true
 sql-builder.workspace = true

util/rich-indexer/Cargo.toml

@@ -39,6 +39,20 @@ pub(crate) struct RichIndexer {
     request_limit: usize,
 }
 
+fn set_indexer_tip_metric(block_number: BlockNumber) {
+    let Ok(block_number) = i64::try_from(block_number) else {
+        log::warn!(
+            "skip updating ckb_indexer_tip: block number {} exceeds i64::MAX",
+            block_number
+        );
+        return;
+    };
+
+    if let Some(metrics) = ckb_metrics::handle() {
+        metrics.ckb_indexer_tip.set(block_number);
+    }
+}
+
 impl RichIndexer {
     /// Construct new Rich Indexer instance
     pub fn new(
@@ -74,13 +88,27 @@ impl IndexerSync for RichIndexer {
     /// Appends a new block to the indexer
     fn append(&self, block: &BlockView) -> Result<(), Error> {
         let future = self.async_rich_indexer.append(block);
-        self.async_runtime.block_on(future)
+        let append_ret = self.async_runtime.block_on(future);
+
+        if append_ret.is_ok() {
+            set_indexer_tip_metric(block.number());
+        }
+
+        append_ret
     }
 
     /// Rollback the indexer to a previous state
     fn rollback(&self) -> Result<(), Error> {
         let future = self.async_rich_indexer.rollback();
-        self.async_runtime.block_on(future)
+        let rollback_ret = self.async_runtime.block_on(future);
+
+        if rollback_ret.is_ok()
+            && let Some((number, _)) = self.tip().ok().flatten()
+        {
+            set_indexer_tip_metric(number);
+        }
+
+        rollback_ret
     }
 
     /// Return identity