Snapshot manifest block added to prometheus (#232)

Co-authored-by: adria0.eth <5526331+adria0@users.noreply.github.com>

crates/ethcore/src/snapshot/service.rs

@@ -853,6 +853,13 @@ impl SnapshotService for Service {
         self.reader.read().as_ref().map(|r| r.manifest().clone())
     }
 
+    fn manifest_block(&self) -> Option<(u64, H256)> {
+        self.reader.read().as_ref().map(|reader| {
+            let manifest = reader.manifest();
+            (manifest.block_number, manifest.block_hash)
+        })
+    }
+
     fn supported_versions(&self) -> Option<(u64, u64)> {
         self.engine
             .snapshot_components()

crates/ethcore/src/snapshot/traits.rs

@@ -26,6 +26,9 @@ pub trait SnapshotService: Sync + Send {
     /// Query the most recent manifest data.
     fn manifest(&self) -> Option<ManifestData>;
 
+    /// Query the most recent snapshoted block number and hash.
+    fn manifest_block(&self) -> Option<(u64, H256)>;
+
     /// Get the supported range of snapshot version numbers.
     /// `None` indicates warp sync isn't supported by the consensus engine.
     fn supported_versions(&self) -> Option<(u64, u64)>;