Add basic column family iterator support.

src/rocksdb.rs

@@ -106,6 +106,20 @@ impl DBIterator {
         }
     }
 
+    fn new_cf(db: &RocksDB, cf_name: &str, readopts: &ReadOptions) -> Result<DBIterator, String> {
+        let cf = db.cfs.get(cf_name);
+        if cf.is_none() {
+            return Err(format!("Invalid column family: {}", cf_name).to_string());
+        }
+        unsafe {
+            let iterator = rocksdb_ffi::rocksdb_create_iterator_cf(db.inner,
+                                                                   readopts.inner,
+                                                                   *cf.unwrap());
+            rocksdb_ffi::rocksdb_iter_seek_to_first(iterator);
+            Ok(DBIterator{ inner: iterator, direction: Direction::forward, just_seeked: true })
+        }
+    }
+
     pub fn from_start(&mut self) -> SubDBIterator {
         self.just_seeked = true;
         unsafe {
@@ -389,6 +403,11 @@ impl RocksDB {
         DBIterator::new(&self, &opts)
     }
 
+    pub fn iterator_cf(&self, cf: &str) -> Result<DBIterator, String> {
+        let opts = ReadOptions::new();
+        DBIterator::new_cf(&self, cf, &opts)
+    }
+
     pub fn snapshot(&self) -> Snapshot {
         Snapshot::new(self)
     }