From c1a89973f041a02aa3cb1c8ebd43db0a433dba2b Mon Sep 17 00:00:00 2001
From: Benjamin Wang <wachao@vmware.com>
Date: Tue, 6 Dec 2022 18:04:29 +0800
Subject: [PATCH] etcdserver: fix nil pointer panic for readonly txn

Backporting https://github.com/etcd-io/etcd/pull/14895

Signed-off-by: Benjamin Wang <wachao@vmware.com>
---
 server/etcdserver/util.go      |   6 +-
 server/etcdserver/util_test.go | 104 +++++++++++++++++++++++++++++++++
 2 files changed, 109 insertions(+), 1 deletion(-)

diff --git a/server/etcdserver/util.go b/server/etcdserver/util.go
index 6ad5f0f4c..b048b8641 100644
--- a/server/etcdserver/util.go
+++ b/server/etcdserver/util.go
@@ -140,7 +140,11 @@ func warnOfExpensiveReadOnlyTxnRequest(lg *zap.Logger, warningApplyDuration time
 		for _, r := range txnResponse.Responses {
 			switch op := r.Response.(type) {
 			case *pb.ResponseOp_ResponseRange:
-				resps = append(resps, fmt.Sprintf("range_response_count:%d", len(op.ResponseRange.Kvs)))
+				if op.ResponseRange != nil {
+					resps = append(resps, fmt.Sprintf("range_response_count:%d", len(op.ResponseRange.Kvs)))
+				} else {
+					resps = append(resps, "range_response:nil")
+				}
 			default:
 				// only range responses should be in a read only txn request
 			}
diff --git a/server/etcdserver/util_test.go b/server/etcdserver/util_test.go
index dd57c7e1d..97673427b 100644
--- a/server/etcdserver/util_test.go
+++ b/server/etcdserver/util_test.go
@@ -20,7 +20,9 @@ import (
 	"time"
 
 	"go.uber.org/zap"
+	"go.uber.org/zap/zaptest"
 
+	pb "go.etcd.io/etcd/api/v3/etcdserverpb"
 	"go.etcd.io/etcd/client/pkg/v3/types"
 	"go.etcd.io/etcd/raft/v3/raftpb"
 	"go.etcd.io/etcd/server/v3/etcdserver/api/membership"
@@ -110,3 +112,105 @@ type testStringerFunc func() string
 func (s testStringerFunc) String() string {
 	return s()
 }
+
+// TestWarnOfExpensiveReadOnlyTxnRequest verifies WarnOfExpensiveReadOnlyTxnRequest
+// never panic no matter what data the txnResponse contains.
+func TestWarnOfExpensiveReadOnlyTxnRequest(t *testing.T) {
+	testCases := []struct {
+		name    string
+		txnResp *pb.TxnResponse
+	}{
+		{
+			name: "all readonly responses",
+			txnResp: &pb.TxnResponse{
+				Responses: []*pb.ResponseOp{
+					{
+						Response: &pb.ResponseOp_ResponseRange{
+							ResponseRange: &pb.RangeResponse{},
+						},
+					},
+					{
+						Response: &pb.ResponseOp_ResponseRange{
+							ResponseRange: &pb.RangeResponse{},
+						},
+					},
+				},
+			},
+		},
+		{
+			name: "all readonly responses with partial nil responses",
+			txnResp: &pb.TxnResponse{
+				Responses: []*pb.ResponseOp{
+					{
+						Response: &pb.ResponseOp_ResponseRange{
+							ResponseRange: &pb.RangeResponse{},
+						},
+					},
+					{
+						Response: &pb.ResponseOp_ResponseRange{
+							ResponseRange: nil,
+						},
+					},
+				},
+			},
+		},
+		{
+			name: "all readonly responses with all nil responses",
+			txnResp: &pb.TxnResponse{
+				Responses: []*pb.ResponseOp{
+					{
+						Response: &pb.ResponseOp_ResponseRange{
+							ResponseRange: nil,
+						},
+					},
+					{
+						Response: &pb.ResponseOp_ResponseRange{
+							ResponseRange: nil,
+						},
+					},
+				},
+			},
+		},
+		{
+			name: "partial non readonly responses",
+			txnResp: &pb.TxnResponse{
+				Responses: []*pb.ResponseOp{
+					{
+						Response: &pb.ResponseOp_ResponseRange{
+							ResponseRange: nil,
+						},
+					},
+					{
+						Response: &pb.ResponseOp_ResponsePut{},
+					},
+					{
+						Response: &pb.ResponseOp_ResponseDeleteRange{},
+					},
+				},
+			},
+		},
+		{
+			name: "all non readonly responses",
+			txnResp: &pb.TxnResponse{
+				Responses: []*pb.ResponseOp{
+					{
+						Response: &pb.ResponseOp_ResponsePut{},
+					},
+					{
+						Response: &pb.ResponseOp_ResponseDeleteRange{},
+					},
+				},
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			lg := zaptest.NewLogger(t)
+			start := time.Now().Add(-1 * time.Second)
+			// WarnOfExpensiveReadOnlyTxnRequest shouldn't panic.
+			warnOfExpensiveReadOnlyTxnRequest(lg, 0, start, &pb.TxnRequest{}, tc.txnResp, nil)
+		})
+	}
+}