Close BaseEndpointChannel once

Closing the bluetoth socket and streams more than once is wasteful and error prone.

PiperOrigin-RevId: 549964135

connections/implementation/base_endpoint_channel.cc

@@ -265,6 +265,11 @@ void BaseEndpointChannel::Close() {
   {
     // In case channel is paused, resume it first thing.
     MutexLock lock(&is_paused_mutex_);
+    if (is_closed_) {
+      NEARBY_LOGS(VERBOSE) << "EndpointChannel already closed";
+      return;
+    }
+    is_closed_ = true;
     UnblockPausedWriter();
   }
   CloseIo();

connections/implementation/base_endpoint_channel.h

@@ -130,6 +130,7 @@ class BaseEndpointChannel : public EndpointChannel {
   ConditionVariable is_paused_cond_{&is_paused_mutex_};
   // If true, writes should block until this has been set to false.
   bool is_paused_ ABSL_GUARDED_BY(is_paused_mutex_) = false;
+  bool is_closed_ ABSL_GUARDED_BY(is_paused_mutex_) = false;
 
   // The medium technology information of this endpoint channel.
   location::nearby::proto::connections::ConnectionTechnology technology_;