content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you 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
   *
   *      http://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 org.apache.bookkeeper.clients.utils;
  
  import com.google.common.util.concurrent.FutureCallback;
  import com.google.common.util.concurrent.Futures;
  import com.google.common.util.concurrent.ListenableFuture;
  import io.grpc.Status;
  import io.grpc.StatusException;
  import io.grpc.StatusRuntimeException;
  import java.util.Iterator;
  import java.util.concurrent.CompletableFuture;
  import java.util.concurrent.ScheduledExecutorService;
  import java.util.concurrent.TimeUnit;
  import java.util.function.BiConsumer;
  import lombok.extern.slf4j.Slf4j;
  import org.apache.bookkeeper.clients.impl.channel.StorageServerChannel;
  import org.apache.bookkeeper.clients.impl.container.StorageContainerChannel;
  import org.apache.bookkeeper.common.concurrent.FutureUtils;
  import org.apache.bookkeeper.common.util.Backoff.Policy;
  
  /**
   * A process for processing rpc request on storage container channel.
   */
  @Slf4j
  public abstract class ListenableFutureRpcProcessor<RequestT, ResponseT, ResultT>
      implements BiConsumer<StorageServerChannel, Throwable>,
      FutureCallback<ResponseT>,
      Runnable {
  
      private final StorageContainerChannel scChannel;
      private final Iterator<Long> backoffs;
      private final ScheduledExecutorService executor;
      private final CompletableFuture<ResultT> resultFuture;
  
      private CompletableFuture<StorageServerChannel> serverChannelFuture = null;
  
      protected ListenableFutureRpcProcessor(StorageContainerChannel channel,
                                             ScheduledExecutorService executor,
                                             Policy backoffPolicy) {
          this.scChannel = channel;
          this.backoffs = backoffPolicy.toBackoffs().iterator();
          this.resultFuture = FutureUtils.createFuture();
          this.executor = executor;
      }
  
      /**
       * Create the rpc request for the processor.
       *
       * @return the created rpc request.
       */
      protected abstract RequestT createRequest();
  
      /**
       * Get the RPC service from the server channel.
       *
       * @return rpc service.
       */
      protected abstract ListenableFuture<ResponseT> sendRPC(StorageServerChannel rsChannel, RequestT requestT);
  
      /**
       * Process the response and convert it back to a result.
       *
       * @param response response
       * @return the converted result.
       */
      protected abstract ResultT processResponse(ResponseT response) throws Exception;
  
      public CompletableFuture<ResultT> process() {
          serverChannelFuture = scChannel.getStorageContainerChannelFuture();
          serverChannelFuture.whenCompleteAsync(this, executor);
          return resultFuture;
      }
  
      @Override
      public void run() {
          process();
      }
  
      /**
       * Logic on handling channel exceptions.
       *
       * @param storageServerChannel server channel
       * @param cause                exception on establishing channel.
       */
      @Override
      public void accept(StorageServerChannel storageServerChannel, Throwable cause) {
          if (null != cause) {
              // The `StorageContainerChannel` already retry on failures related to server channel,
              // So we don't need to retry here if failed to retrieve a channel to the server
              // that hosts this storage container.
              resultFuture.completeExceptionally(cause);
              return;
          }
  
          sendRpcToServerChannel(storageServerChannel);
      }
  
      private void sendRpcToServerChannel(StorageServerChannel rsChannel) {
          RequestT request;
          try {
              request = createRequest();
          } catch (Exception e) {
              // fail to create request
              resultFuture.completeExceptionally(e);
              return;
          }
  
          Futures.addCallback(
              sendRPC(rsChannel, request),
              this,
              executor);
      }
  
      @Override
      public void onSuccess(ResponseT result) {
          try {
              resultFuture.complete(processResponse(result));
          } catch (Exception e) {
              resultFuture.completeExceptionally(e);
          }
      }
  
      @Override
      public void onFailure(Throwable t) {
          Status status = null;
          if (t instanceof StatusRuntimeException) {
              status = ((StatusRuntimeException) t).getStatus();
          } else if (t instanceof StatusException) {
              status = ((StatusException) t).getStatus();
          }
  
          if (Status.NOT_FOUND == status) {
              // `NOT_FOUND` means storage container is not found. that means:
              //
              // - the container is moved to a different server
              // - the container is not assigned to any servers yet
              // - the container is assigned, but it is still starting up and not ready for serving
              //
              // at either case, we need to reset the storage server channel, so next retry can attempt to re-locate
              // the storage container again
              scChannel.resetStorageServerChannelFuture(serverChannelFuture);
          }
  
          if (shouldRetryOn(status) && backoffs.hasNext()) {
              long backoffMs = backoffs.next();
              executor.schedule(this, backoffMs, TimeUnit.MILLISECONDS);
          } else {
              resultFuture.completeExceptionally(t);
          }
      }
  
      protected boolean shouldRetryOn(Status statusCode) {
          return Status.NOT_FOUND == statusCode;
      }
  }
  