Merge pull request #22407 from markdroth/xds_wfr

Use wait_for_ready for xds calls.

src/core/ext/filters/client_channel/lb_policy/xds/xds.cc

@@ -920,12 +920,14 @@ void XdsLb::UpdateXdsPickerLocked() {
   // If we are in fallback mode, don't generate an xds picker from localities.
   if (fallback_policy_ != nullptr) return;
   if (current_priority_ == UINT32_MAX) {
-    grpc_error* error = grpc_error_set_int(
-        GRPC_ERROR_CREATE_FROM_STATIC_STRING("no ready locality map"),
-        GRPC_ERROR_INT_GRPC_STATUS, GRPC_STATUS_UNAVAILABLE);
-    channel_control_helper()->UpdateState(
-        GRPC_CHANNEL_TRANSIENT_FAILURE,
-        absl::make_unique<TransientFailurePicker>(error));
+    if (fallback_policy_ == nullptr) {
+      grpc_error* error = grpc_error_set_int(
+          GRPC_ERROR_CREATE_FROM_STATIC_STRING("no ready locality map"),
+          GRPC_ERROR_INT_GRPC_STATUS, GRPC_STATUS_UNAVAILABLE);
+      channel_control_helper()->UpdateState(
+          GRPC_CHANNEL_TRANSIENT_FAILURE,
+          absl::make_unique<TransientFailurePicker>(error));
+    }
     return;
   }
   priorities_[current_priority_]->UpdateXdsPickerLocked();
@@ -1022,7 +1024,7 @@ XdsLb::LocalityMap::LocalityMap(RefCountedPtr<XdsLb> xds_policy,
       &on_failover_timer_);
   failover_timer_callback_pending_ = true;
   // This is the first locality map ever created, report CONNECTING.
-  if (priority_ == 0) {
+  if (priority_ == 0 && xds_policy_->fallback_policy_ == nullptr) {
     xds_policy_->channel_control_helper()->UpdateState(
         GRPC_CHANNEL_CONNECTING,
         absl::make_unique<QueuePicker>(

src/core/ext/filters/client_channel/xds/xds_client.cc

@@ -704,7 +704,8 @@ XdsClient::ChannelState::AdsCallState::AdsCallState(
   grpc_op* op = ops;
   op->op = GRPC_OP_SEND_INITIAL_METADATA;
   op->data.send_initial_metadata.count = 0;
-  op->flags = 0;
+  op->flags = GRPC_INITIAL_METADATA_WAIT_FOR_READY |
+              GRPC_INITIAL_METADATA_WAIT_FOR_READY_EXPLICITLY_SET;
   op->reserved = nullptr;
   op++;
   call_error = grpc_call_start_batch_and_execute(call_, ops, (size_t)(op - ops),
@@ -1520,7 +1521,8 @@ XdsClient::ChannelState::LrsCallState::LrsCallState(
   grpc_op* op = ops;
   op->op = GRPC_OP_SEND_INITIAL_METADATA;
   op->data.send_initial_metadata.count = 0;
-  op->flags = 0;
+  op->flags = GRPC_INITIAL_METADATA_WAIT_FOR_READY |
+              GRPC_INITIAL_METADATA_WAIT_FOR_READY_EXPLICITLY_SET;
   op->reserved = nullptr;
   op++;
   // Op: send request message.

test/cpp/end2end/xds_end2end_test.cc

@@ -3108,7 +3108,7 @@ TEST_P(FallbackTest, FallbackModeIsExitedWhenBalancerSaysToDropAllCalls) {
 }
 
 // Tests that fallback mode is exited if the child policy becomes ready.
-TEST_P(FallbackTest, FallbackModeIsExitedAfterChildRready) {
+TEST_P(FallbackTest, FallbackModeIsExitedAfterChildReady) {
   // Return an unreachable balancer and one fallback backend.
   SetNextResolution({backends_[0]->port()});
   SetNextResolutionForLbChannel({g_port_saver->GetPort()});