tighter moss KV store iterator handling

index/store/moss/iterator.go

@@ -23,15 +23,15 @@ type Iterator struct {
 	iter  moss.Iterator
 	start []byte
 	end   []byte
-	done  bool
 	k     []byte
 	v     []byte
+	err   error
 }
 
 func (x *Iterator) Seek(seekToKey []byte) {
-	x.done = true
 	x.k = nil
 	x.v = nil
+	x.err = moss.ErrIteratorDone
 
 	if bytes.Compare(seekToKey, x.start) < 0 {
 		seekToKey = x.start
@@ -51,31 +51,21 @@ func (x *Iterator) Seek(seekToKey []byte) {
 
 	x.iter = iter
 
-	x.checkDone()
+	x.current()
 }
 
 func (x *Iterator) Next() {
-	if x.done {
-		return
-	}
+	_ = x.iter.Next()
 
-	err := x.iter.Next()
-	if err != nil {
-		x.done = true
-		x.k = nil
-		x.v = nil
-		return
-	}
-
-	x.checkDone()
+	x.k, x.v, x.err = x.iter.Current()
 }
 
 func (x *Iterator) Current() ([]byte, []byte, bool) {
-	return x.k, x.v, !x.done
+	return x.k, x.v, x.err == nil
 }
 
 func (x *Iterator) Key() []byte {
-	if x.done {
+	if x.err != nil {
 		return nil
 	}
 
@@ -83,7 +73,7 @@ func (x *Iterator) Key() []byte {
 }
 
 func (x *Iterator) Value() []byte {
-	if x.done {
+	if x.err != nil {
 		return nil
 	}
 
@@ -91,7 +81,7 @@ func (x *Iterator) Value() []byte {
 }
 
 func (x *Iterator) Valid() bool {
-	return !x.done
+	return x.err == nil
 }
 
 func (x *Iterator) Close() error {
@@ -104,23 +94,13 @@ func (x *Iterator) Close() error {
 		x.iter = nil
 	}
 
-	x.done = true
 	x.k = nil
 	x.v = nil
+	x.err = moss.ErrIteratorDone
 
 	return err
 }
 
-func (x *Iterator) checkDone() {
-	k, v, err := x.iter.Current()
-	if err != nil {
-		x.done = true
-		x.k = nil
-		x.v = nil
-		return
-	}
-
-	x.done = false
-	x.k = k
-	x.v = v
+func (x *Iterator) current() {
+	x.k, x.v, x.err = x.iter.Current()
 }

index/store/moss/reader.go

@@ -57,7 +57,7 @@ func (r *Reader) PrefixIterator(k []byte) store.KVIterator {
 		end:   kEnd,
 	}
 
-	rv.checkDone()
+	rv.current()
 
 	return rv
 }
@@ -76,7 +76,7 @@ func (r *Reader) RangeIterator(start, end []byte) store.KVIterator {
 		end:   end,
 	}
 
-	rv.checkDone()
+	rv.current()
 
 	return rv
 }