raft: leader response to learner MsgReadIndex

Leader should check message sender after receiving MsgReadIndex, even
when raft quorum is 1. The message could be sent from learner node, and
leader should respond.

raft/raft_test.go

@@ -2416,6 +2416,57 @@ func TestReadOnlyOptionSafe(t *testing.T) {
 	}
 }
 
+func TestReadOnlyWithLearner(t *testing.T) {
+	a := newTestLearnerRaft(1, []uint64{1}, []uint64{2}, 10, 1, NewMemoryStorage())
+	b := newTestLearnerRaft(2, []uint64{1}, []uint64{2}, 10, 1, NewMemoryStorage())
+
+	nt := newNetwork(a, b)
+	setRandomizedElectionTimeout(b, b.electionTimeout+1)
+
+	for i := 0; i < b.electionTimeout; i++ {
+		b.tick()
+	}
+	nt.send(pb.Message{From: 1, To: 1, Type: pb.MsgHup})
+
+	if a.state != StateLeader {
+		t.Fatalf("state = %s, want %s", a.state, StateLeader)
+	}
+
+	tests := []struct {
+		sm        *raft
+		proposals int
+		wri       uint64
+		wctx      []byte
+	}{
+		{a, 10, 11, []byte("ctx1")},
+		{b, 10, 21, []byte("ctx2")},
+		{a, 10, 31, []byte("ctx3")},
+		{b, 10, 41, []byte("ctx4")},
+	}
+
+	for i, tt := range tests {
+		for j := 0; j < tt.proposals; j++ {
+			nt.send(pb.Message{From: 1, To: 1, Type: pb.MsgProp, Entries: []pb.Entry{{}}})
+		}
+
+		nt.send(pb.Message{From: tt.sm.id, To: tt.sm.id, Type: pb.MsgReadIndex, Entries: []pb.Entry{{Data: tt.wctx}}})
+
+		r := tt.sm
+		if len(r.readStates) == 0 {
+			t.Fatalf("#%d: len(readStates) = 0, want non-zero", i)
+		}
+		rs := r.readStates[0]
+		if rs.Index != tt.wri {
+			t.Errorf("#%d: readIndex = %d, want %d", i, rs.Index, tt.wri)
+		}
+
+		if !bytes.Equal(rs.RequestCtx, tt.wctx) {
+			t.Errorf("#%d: requestCtx = %v, want %v", i, rs.RequestCtx, tt.wctx)
+		}
+		r.readStates = nil
+	}
+}
+
 func TestReadOnlyOptionLease(t *testing.T) {
 	a := newTestRaft(1, []uint64{1, 2, 3}, 10, 1, NewMemoryStorage())
 	b := newTestRaft(2, []uint64{1, 2, 3}, 10, 1, NewMemoryStorage())