Prevent watching unsuppoted channels

include/grpc/grpc.h

@@ -178,6 +178,9 @@ GRPCAPI void grpc_channel_watch_connectivity_state(
     grpc_channel *channel, grpc_connectivity_state last_observed_state,
     gpr_timespec deadline, grpc_completion_queue *cq, void *tag);
 
+/** Check whether a grpc channel support connectivity watcher */
+GRPCAPI int grpc_channel_support_connectivity_watcher(grpc_channel *channel);
+
 /** Create a call given a grpc_channel, in order to call 'method'. All
     completions are sent to 'completion_queue'. 'method' and 'host' need only
     live through the invocation of this function.

src/core/ext/filters/client_channel/channel_connectivity.c

@@ -191,6 +191,12 @@ static void watcher_timer_init(grpc_exec_ctx *exec_ctx, void *arg,
   gpr_free(wa);
 }
 
+int grpc_channel_support_connectivity_watcher(grpc_channel *channel) {
+  grpc_channel_element *client_channel_elem =
+      grpc_channel_stack_last_element(grpc_channel_get_channel_stack(channel));
+  return client_channel_elem->filter != &grpc_client_channel_filter ? 0 : 1;
+}
+
 void grpc_channel_watch_connectivity_state(
     grpc_channel *channel, grpc_connectivity_state last_observed_state,
     gpr_timespec deadline, grpc_completion_queue *cq, void *tag) {

src/cpp/client/channel_cc.cc

@@ -101,7 +101,7 @@ Channel::Channel(const grpc::string& host, grpc_channel* channel)
       host_(host),
       c_channel_(channel) {
   g_gli_initializer.summon();
-  if (host != "inproc") {
+  if (grpc_channel_support_connectivity_watcher(channel)) {
     connectivity_watcher_->StartWatching();
   }
 }