etcdserver: use prev-value for ignore_value writes

etcdserver/apply.go

@@ -161,7 +161,7 @@ func (a *applierV3backend) Put(txnID int64, p *pb.PutRequest) (*pb.PutResponse,
 	)
 
 	var rr *mvcc.RangeResult
-	if p.PrevKv {
+	if p.PrevKv || p.IgnoreValue {
 		if txnID != noTxn {
 			rr, err = a.s.KV().TxnRange(txnID, p.Key, nil, mvcc.RangeOptions{})
 			if err != nil {
@@ -175,6 +175,14 @@ func (a *applierV3backend) Put(txnID int64, p *pb.PutRequest) (*pb.PutResponse,
 		}
 	}
 
+	if p.IgnoreValue {
+		if rr == nil || len(rr.KVs) == 0 {
+			// ignore_value flag expects previous key-value pair
+			return nil, ErrKeyNotFound
+		}
+		p.Value = rr.KVs[0].Value
+	}
+
 	if txnID != noTxn {
 		rev, err = a.s.KV().TxnPut(txnID, p.Key, p.Value, lease.LeaseID(p.Lease))
 		if err != nil {
@@ -190,7 +198,7 @@ func (a *applierV3backend) Put(txnID int64, p *pb.PutRequest) (*pb.PutResponse,
 		rev = a.s.KV().Put(p.Key, p.Value, leaseID)
 	}
 	resp.Header.Revision = rev
-	if rr != nil && len(rr.KVs) != 0 {
+	if p.PrevKv && rr != nil && len(rr.KVs) != 0 {
 		resp.PrevKv = &rr.KVs[0]
 	}
 	return resp, nil
@@ -364,7 +372,7 @@ func (a *applierV3backend) Txn(rt *pb.TxnRequest) (*pb.TxnResponse, error) {
 		reqs = rt.Failure
 	}
 
-	if err := a.checkRequestLeases(reqs); err != nil {
+	if err := a.checkRequestPut(reqs); err != nil {
 		return nil, err
 	}
 	if err := a.checkRequestRange(reqs); err != nil {
@@ -749,14 +757,27 @@ func (s *kvSortByValue) Less(i, j int) bool {
 	return bytes.Compare(s.kvs[i].Value, s.kvs[j].Value) < 0
 }
 
-func (a *applierV3backend) checkRequestLeases(reqs []*pb.RequestOp) error {
+func (a *applierV3backend) checkRequestPut(reqs []*pb.RequestOp) error {
 	for _, requ := range reqs {
 		tv, ok := requ.Request.(*pb.RequestOp_RequestPut)
 		if !ok {
 			continue
 		}
 		preq := tv.RequestPut
-		if preq == nil || lease.LeaseID(preq.Lease) == lease.NoLease {
+		if preq == nil {
+			continue
+		}
+		if preq.IgnoreValue {
+			// expects previous key-value, error if not exist
+			rr, err := a.s.KV().Range(preq.Key, nil, mvcc.RangeOptions{})
+			if err != nil {
+				return err
+			}
+			if rr == nil || len(rr.KVs) == 0 {
+				return ErrKeyNotFound
+			}
+		}
+		if lease.LeaseID(preq.Lease) == lease.NoLease {
 			continue
 		}
 		if l := a.s.lessor.Lookup(lease.LeaseID(preq.Lease)); l == nil {

etcdserver/errors.go

@@ -34,6 +34,7 @@ var (
 	ErrInvalidAuthToken           = errors.New("etcdserver: invalid auth token")
 	ErrTooManyRequests            = errors.New("etcdserver: too many requests")
 	ErrUnhealthy                  = errors.New("etcdserver: unhealthy cluster")
+	ErrKeyNotFound                = errors.New("etcdserver: key not found")
 )
 
 type DiscoveryError struct {