Add configuration of keepalive on Android

Author: Mitch528

android/src/main/java/com/reactnativegrpc/GrpcModule.java

@@ -15,6 +15,7 @@
 
 import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.TimeUnit;
 
 import io.grpc.CallOptions;
 import io.grpc.ClientCall;
@@ -33,6 +34,10 @@ public class GrpcModule extends ReactContextBaseJavaModule {
   private boolean withCompression = false;
   private String compressorName = "";
   private Integer responseSizeLimit = null;
+  private boolean keepAliveEnabled = false;
+  private Integer keepAliveTime;
+  private Integer keepAliveTimeout;
+
   private ManagedChannel managedChannel = null;
 
   public GrpcModule(ReactApplicationContext context) {
@@ -76,6 +81,12 @@ public void setResponseSizeLimit(int limit) {
     this.responseSizeLimit = limit;
   }
 
+  public void setKeepalive(boolean enabled, int time, int timeout) {
+    this.keepAliveEnabled = enabled;
+    this.keepAliveTime = time;
+    this.keepAliveTimeout = timeout;
+  }
+
   @ReactMethod
   public void unaryCall(int id, String path, ReadableMap obj, ReadableMap headers, final Promise promise) {
     ClientCall call = this.startGrpcCall(id, path, MethodDescriptor.MethodType.UNARY, headers);
@@ -300,6 +311,13 @@ private ManagedChannel getManagedChannel() {
       channelBuilder = channelBuilder.usePlaintext();
     }
 
+    if (this.keepAliveEnabled) {
+      channelBuilder = channelBuilder
+        .keepAliveWithoutCalls(true)
+        .keepAliveTime(keepAliveTime, TimeUnit.SECONDS)
+        .keepAliveTimeout(keepAliveTime, TimeUnit.SECONDS);
+    }
+
     managedChannel = channelBuilder.build();
     return managedChannel;
   }