Port over the index 0 -> 1 code that lived in the old rpc setQueryMeta function. (#13561)

agent/consul/watch/server_local.go

@@ -135,6 +135,16 @@ func ServerLocalBlockingQuery[ResultType any, StoreType StateStore](
 		ws.Add(state.AbandonCh())
 
 		index, result, err := query(ws, state)
+		// Always set a non-zero index. Generally we expect the index
+		// to be set to Raft index which can never be 0. If the query
+		// returned no results we expect it to be set to the max index of the table,
+		// however we can't guarantee this always happens.
+		// To prevent a client from accidentally performing many non-blocking queries
+		// (which causes lots of unnecessary load), we always set a default value of 1.
+		// This is sufficient to prevent the unnecessary load in most cases.
+		if index < 1 {
+			index = 1
+		}
 
 		switch {
 		case errors.Is(err, ErrorNotFound):

agent/consul/watch/server_local_test.go

@@ -103,6 +103,34 @@ func TestServerLocalBlockingQuery_NonBlocking(t *testing.T) {
 	require.Equal(t, &testResult{value: "foo"}, result)
 }
 
+func TestServerLocalBlockingQuery_Index0(t *testing.T) {
+	abandonCh := make(chan struct{})
+	t.Cleanup(func() { close(abandonCh) })
+
+	store := NewMockStateStore(t)
+	store.On("AbandonCh").
+		Return(closeChan(abandonCh)).
+		Once()
+
+	provider := newMockStoreProvider(t)
+	provider.On("getStore").Return(store).Once()
+	provider.On("query", mock.Anything, store).
+		// the index 0 returned here should get translated to 1 by ServerLocalBlockingQuery
+		Return(uint64(0), &testResult{value: "foo"}, nil).
+		Once()
+
+	idx, result, err := ServerLocalBlockingQuery(
+		context.Background(),
+		provider.getStore,
+		0,
+		true,
+		provider.query,
+	)
+	require.NoError(t, err)
+	require.EqualValues(t, 1, idx)
+	require.Equal(t, &testResult{value: "foo"}, result)
+}
+
 func TestServerLocalBlockingQuery_NotFound(t *testing.T) {
 	abandonCh := make(chan struct{})
 	t.Cleanup(func() { close(abandonCh) })
@@ -387,8 +415,10 @@ func TestServerLocalNotify_internal(t *testing.T) {
 	provider.On("query", mock.Anything, store).
 		Return(uint64(0), nilResult, fmt.Errorf("injected error")).
 		Times(3)
+	// we should only notify the first time as the index of 1 wont exceed the min index
+	// after the second two queries.
 	provider.On("notify", ctx, "test", nilResult, fmt.Errorf("injected error")).
-		Times(3)
+		Once()
 	provider.On("query", mock.Anything, store).
 		Return(uint64(7), &testResult{value: "foo"}, nil).
 		Once()