Update etcdserver to support DowngradeVersionTest request

Signed-off-by: Benjamin Wang <benjamin.ahrtr@gmail.com>

Author: ahrtr

server/etcdserver/api/v3rpc/maintenance.go

@@ -55,6 +55,7 @@ type Alarmer interface {
 
 type Downgrader interface {
 	Downgrade(ctx context.Context, dr *pb.DowngradeRequest) (*pb.DowngradeResponse, error)
+	DowngradeVersionTest(ctx context.Context, r *pb.DowngradeVersionTestRequest) (*pb.DowngradeVersionTestResponse, error)
 }
 
 type LeaderTransferrer interface {
@@ -296,6 +297,16 @@ func (ms *maintenanceServer) Downgrade(ctx context.Context, r *pb.DowngradeReque
 	return resp, nil
 }
 
+func (ms *maintenanceServer) DowngradeVersionTest(ctx context.Context, r *pb.DowngradeVersionTestRequest) (*pb.DowngradeVersionTestResponse, error) {
+	resp, err := ms.d.DowngradeVersionTest(ctx, r)
+	if err != nil {
+		return nil, togRPCError(err)
+	}
+	resp.Header = &pb.ResponseHeader{}
+	ms.hdr.fill(resp.Header)
+	return resp, nil
+}
+
 type authMaintenanceServer struct {
 	*maintenanceServer
 	*AuthAdmin
@@ -355,3 +366,11 @@ func (ams *authMaintenanceServer) Downgrade(ctx context.Context, r *pb.Downgrade
 
 	return ams.maintenanceServer.Downgrade(ctx, r)
 }
+
+func (ams *authMaintenanceServer) DowngradeVersionTest(ctx context.Context, r *pb.DowngradeVersionTestRequest) (*pb.DowngradeVersionTestResponse, error) {
+	if err := ams.isPermitted(ctx); err != nil {
+		return nil, togRPCError(err)
+	}
+
+	return ams.maintenanceServer.DowngradeVersionTest(ctx, r)
+}

server/etcdserver/server.go

@@ -2006,7 +2006,7 @@ func (s *EtcdServer) applyEntryNormal(e *raftpb.Entry, shouldApplyV3 membership.
 }
 
 func (s *EtcdServer) applyInternalRaftRequest(r *pb.InternalRaftRequest, shouldApplyV3 membership.ShouldApplyV3) *apply.Result {
-	if r.ClusterVersionSet == nil && r.ClusterMemberAttrSet == nil && r.DowngradeInfoSet == nil {
+	if r.ClusterVersionSet == nil && r.ClusterMemberAttrSet == nil && r.DowngradeInfoSet == nil && r.DowngradeVersionTest == nil {
 		if !shouldApplyV3 {
 			return nil
 		}
@@ -2029,6 +2029,10 @@ func (s *EtcdServer) applyInternalRaftRequest(r *pb.InternalRaftRequest, shouldA
 	case r.DowngradeInfoSet != nil:
 		op = "DowngradeInfoSet" // Implemented in 3.5.x
 		membershipApplier.DowngradeInfoSet(r.DowngradeInfoSet, shouldApplyV3)
+	case r.DowngradeVersionTest != nil:
+		op = "DowngradeVersionTest"
+		// do nothing, we are good as long as a WAL record
+		// has already been generated for this request.
 	default:
 		s.lg.Panic("not implemented apply", zap.Stringer("raft-request", r))
 		return nil

server/etcdserver/v3_server.go

@@ -1044,6 +1044,16 @@ func (s *EtcdServer) downgradeEnable(ctx context.Context, r *pb.DowngradeRequest
 	return &resp, nil
 }
 
+// DowngradeVersionTest is for test only! We intentionally send
+// a raft request so that a related WAL record can be generated.
+func (s *EtcdServer) DowngradeVersionTest(ctx context.Context, r *pb.DowngradeVersionTestRequest) (*pb.DowngradeVersionTestResponse, error) {
+	resp, err := s.raftRequest(ctx, pb.InternalRaftRequest{DowngradeVersionTest: r})
+	if err != nil {
+		return nil, err
+	}
+	return resp.(*pb.DowngradeVersionTestResponse), nil
+}
+
 func (s *EtcdServer) downgradeCancel(ctx context.Context) (*pb.DowngradeResponse, error) {
 	err := s.Version().DowngradeCancel(ctx)
 	if err != nil {