feat: add implementation of ChannelPrimer to establish connection to …

…GFE and integrate into bigtable client

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/BigtableDataSettings.java

@@ -19,8 +19,10 @@
 import com.google.api.core.BetaApi;
 import com.google.api.gax.core.CredentialsProvider;
 import com.google.api.gax.core.NoCredentialsProvider;
+import com.google.api.gax.grpc.ChannelPrimer;
 import com.google.api.gax.grpc.InstantiatingGrpcChannelProvider;
 import com.google.api.gax.rpc.UnaryCallSettings;
+import com.google.cloud.bigtable.data.v2.internal.RefreshChannel;
 import com.google.cloud.bigtable.data.v2.models.Query;
 import com.google.cloud.bigtable.data.v2.models.Row;
 import com.google.cloud.bigtable.data.v2.stub.EnhancedBigtableStubSettings;
@@ -275,6 +277,21 @@ public CredentialsProvider getCredentialsProvider() {
       return stubSettings.getCredentialsProvider();
     }
 
+    /** Set to true to enable channels to periodically reconnect to GFE, false to disable */
+    @BetaApi("This API depends on experimental gRPC APIs")
+    public Builder setRefreshChannel(boolean isRefreshing) {
+      ChannelPrimer channelPrimer = null;
+      if (isRefreshing) {
+        channelPrimer = new RefreshChannel();
+      }
+      InstantiatingGrpcChannelProvider.Builder channelBuilder =
+          ((InstantiatingGrpcChannelProvider) stubSettings().getTransportChannelProvider())
+              .toBuilder()
+              .setChannelPrimer(channelPrimer);
+      stubSettings().setTransportChannelProvider(channelBuilder.build());
+      return this;
+    }
+
     /**
      * Returns the underlying settings for making RPC calls. The settings should be changed with
      * care.

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/internal/RefreshChannel.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2019 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.cloud.bigtable.data.v2.internal;
+
+import com.google.api.core.InternalApi;
+import com.google.api.gax.grpc.ChannelPrimer;
+import io.grpc.ConnectivityState;
+import io.grpc.ExperimentalApi;
+import io.grpc.ManagedChannel;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Establish a connection to the GFE on managedChannel
+ *
+ * <p>This class is considered an internal implementation detail and not meant to be used by
+ * applications.
+ */
+@ExperimentalApi("This API depends on gRPC experimental API")
+@InternalApi
+public class RefreshChannel implements ChannelPrimer {
+  @Override
+  public void primeChannel(ManagedChannel managedChannel) {
+    for (int i = 0; i < 10; i++) {
+      ConnectivityState connectivityState = managedChannel.getState(true);
+      if (connectivityState == ConnectivityState.READY) {
+        break;
+      }
+      try {
+        TimeUnit.SECONDS.sleep(1);
+      } catch (InterruptedException e) {
+        break;
+      }
+    }
+  }
+}