feat: add DBIterator

db/src/diskdb.rs

@@ -103,6 +103,15 @@ impl KeyValueDB for RocksDB {
         .map(|v| v.and_then(|vi| vi.get(range.start..range.end).map(|slice| slice.to_vec())))
         .map_err(Into::into)
     }
+
+    fn iter(&self, col: Col, key: &[u8]) -> Option<DBIterator> {
+        self.cf_handle(col).expect("invalid col").map(|cf| {
+            self.inner
+                .db
+                .iterator_cf(cf, IteratorMode::From(key, Direction::Forward))
+                .expect("invalid iterator")
+        })
+    }
 }
 
 #[cfg(test)]

db/src/kvdb.rs

@@ -1,13 +1,14 @@
 use crate::batch::{Batch, Col};
 use bincode::Error as BcError;
 use failure::Fail;
-use rocksdb::Error as RdbError;
+use rocksdb::{DBIterator as RdbIterator, Error as RdbError};
 use std::error::Error as StdError;
 use std::ops::Range;
 use std::result;
 
 pub type Error = ErrorKind;
 pub type Result<T> = result::Result<T, Error>;
+pub type DBIterator<'a> = RdbIterator<'a>;
 
 #[derive(Clone, Debug, PartialEq, Eq, Fail)]
 pub enum ErrorKind {
@@ -36,4 +37,9 @@ pub trait KeyValueDB: Sync + Send {
     fn batch(&self) -> Batch {
         Batch::new()
     }
+    /// returns an iterator over a column, starts from a key in forward direction.
+    /// TODO use Rocksdb's DBIterator as a temp soluction, refactor it to associated type, same as Batch
+    fn iter(&self, col: Col, key: &[u8]) -> Option<DBIterator> {
+        None
+    }
 }

shared/src/cachedb.rs

@@ -1,5 +1,5 @@
 use ckb_db::batch::{Batch, Col, Operation};
-use ckb_db::kvdb::{KeyValueDB, Result};
+use ckb_db::kvdb::{DBIterator, KeyValueDB, Result};
 use ckb_util::RwLock;
 use fnv::FnvHashMap;
 use lru_cache::LruCache;
@@ -72,4 +72,8 @@ where
         }
         self.db.partial_read(col, key, range)
     }
+
+    fn iter(&self, col: Col, key: &[u8]) -> Option<DBIterator> {
+        self.db.iter(col, key)
+    }
 }