Support for --pruning=auto.

util/src/journaldb/archivedb.rs

@@ -168,6 +168,8 @@ impl JournalDB for ArchiveDB {
 		Ok((inserts + deletes) as u32)
 	}
 
+	fn latest_era() -> Option<u64> { self.latest_era }
+
 	fn state(&self, id: &H256) -> Option<Bytes> {
 		self.backing.get_by_prefix(&id.bytes()[0..12]).and_then(|b| Some(b.to_vec()))
 	}

util/src/journaldb/earlymergedb.rs

@@ -333,6 +333,8 @@ impl JournalDB for EarlyMergeDB {
 		self.backing.get(&LATEST_ERA_KEY).expect("Low level database error").is_none()
 	}
 
+	fn latest_era() -> Option<u64> { self.latest_era }
+
 	fn mem_used(&self) -> usize {
 		self.overlay.mem_used() + match self.refs {
 			Some(ref c) => c.read().unwrap().heap_size_of_children(),

util/src/journaldb/overlayrecentdb.rs

@@ -213,6 +213,8 @@ impl JournalDB for OverlayRecentDB {
 		self.backing.get(&LATEST_ERA_KEY).expect("Low level database error").is_none()
 	}
 
+	fn latest_era() -> Option<u64> { self.latest_era }
+
 	fn commit(&mut self, now: u64, id: &H256, end: Option<(u64, H256)>) -> Result<u32, UtilError> {
 		// record new commit's details.
 		trace!("commit: #{} ({}), end era: {:?}", now, id, end);

util/src/journaldb/refcounteddb.rs

@@ -112,6 +112,8 @@ impl JournalDB for RefCountedDB {
 		self.latest_era.is_none()
 	}
 
+	fn latest_era() -> Option<u64> { self.latest_era }
+
 	fn commit(&mut self, now: u64, id: &H256, end: Option<(u64, H256)>) -> Result<u32, UtilError> {
 		// journal format:
 		// [era, 0] => [ id, [insert_0, ...], [remove_0, ...] ]
@@ -220,6 +222,25 @@ mod tests {
 		assert!(!jdb.exists(&h));
 	}
 
+	#[test]
+	fn latest_era_should_work() {
+		// history is 3
+		let mut jdb = RefCountedDB::new_temp();
+		assert_eq!(jdb.latest_era(), None);
+		let h = jdb.insert(b"foo");
+		jdb.commit(0, &b"0".sha3(), None).unwrap();
+		assert_eq!(jdb.latest_era(), Some(0));
+		jdb.remove(&h);
+		jdb.commit(1, &b"1".sha3(), None).unwrap();
+		assert_eq!(jdb.latest_era(), Some(1));
+		jdb.commit(2, &b"2".sha3(), None).unwrap();
+		assert_eq!(jdb.latest_era(), Some(2));
+		jdb.commit(3, &b"3".sha3(), Some((0, b"0".sha3()))).unwrap();
+		assert_eq!(jdb.latest_era(), Some(3));
+		jdb.commit(4, &b"4".sha3(), Some((1, b"1".sha3()))).unwrap();
+		assert_eq!(jdb.latest_era(), Some(4));
+	}
+
 	#[test]
 	fn complex() {
 		// history is 1

util/src/journaldb/traits.rs

@@ -31,6 +31,9 @@ pub trait JournalDB : HashDB + Send + Sync {
 	/// Check if this database has any commits
 	fn is_empty(&self) -> bool;
 
+	/// Get the latest era in the DB. None if there isn't yet any data in there.
+	fn latest_era() -> Option<u64> { self.latest_era }
+
 	/// Commit all recent insert operations and canonical historical commits' removals from the
 	/// old era to the backing database, reverting any non-canonical historical commit's inserts.
 	fn commit(&mut self, now: u64, id: &H256, end: Option<(u64, H256)>) -> Result<u32, UtilError>;