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 com.datastax.dse.driver.internal.core.cql.reactive;
  
  import java.util.Objects;
  import org.reactivestreams.Publisher;
  import org.reactivestreams.Subscriber;
  
  /**
   * A {@link Publisher} that immediately signals the error passed at instantiation to all its
   * subscribers.
   */
  public class FailedPublisher<ElementT> implements Publisher<ElementT> {
  
    protected final Throwable error;
  
    public FailedPublisher(Throwable error) {
      this.error = error;
    }
  
    @Override
    public void subscribe(Subscriber<? super ElementT> subscriber) {
      Objects.requireNonNull(subscriber, "Subscriber cannot be null");
      // Per rule 1.9, we need to call onSubscribe before any other signal. Pass a dummy
      // subscription since we know it will never be used.
      subscriber.onSubscribe(EmptySubscription.INSTANCE);
      // Signal the error to the subscriber right away. This is safe to do because per rule 2.10,
      // a Subscriber MUST be prepared to receive an onError signal without a preceding
      // Subscription.request(long n) call.
      // Also, per rule 2.13: onError MUST return normally except when any provided parameter
      // is null (which is not the case here); so we don't need care about catching errors here.
      subscriber.onError(error);
    }
  }
  