clientv3: ignore sort-ascend-key option

clientv3/op.go

@@ -193,6 +193,14 @@ func WithRev(rev int64) OpOption { return func(op *Op) { op.rev = rev } }
 // 'order' can be either 'SortNone', 'SortAscend', 'SortDescend'.
 func WithSort(target SortTarget, order SortOrder) OpOption {
 	return func(op *Op) {
+		if target == SortByKey && order == SortAscend {
+			// If order != SortNone, server fetches the entire key-space,
+			// and then applies the sort and limit, if provided.
+			// Since current mvcc.Range implementation returns results
+			// sorted by keys in lexiographically ascending order,
+			// client should ignore SortOrder if the target is SortByKey.
+			order = SortNone
+		}
 		op.sort = &SortOption{target, order}
 	}
 }

clientv3/op_test.go

@@ -0,0 +1,38 @@
+// Copyright 2016 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package clientv3
+
+import (
+	"reflect"
+	"testing"
+
+	pb "github.com/coreos/etcd/etcdserver/etcdserverpb"
+)
+
+// TestOpWithSort tests if WithSort(ASCEND, KEY) and WithLimit are specified,
+// RangeRequest ignores the SortOption to avoid unnecessarily fetching
+// the entire key-space.
+func TestOpWithSort(t *testing.T) {
+	opReq := OpGet("foo", WithSort(SortByKey, SortAscend), WithLimit(10)).toRequestOp().Request
+	q, ok := opReq.(*pb.RequestOp_RequestRange)
+	if !ok {
+		t.Fatalf("expected range request, got %v", reflect.TypeOf(opReq))
+	}
+	req := q.RequestRange
+	wreq := &pb.RangeRequest{Key: []byte("foo"), SortOrder: pb.RangeRequest_NONE, Limit: 10}
+	if !reflect.DeepEqual(req, wreq) {
+		t.Fatalf("expected %+v, got %+v", wreq, req)
+	}
+}