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JDBC Driver for Google Cloud Spanner
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/*
 * Copyright 2015, Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *    * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *    * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *
 *    * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package nl.topicus.jdbc.shaded.io.grpc.stub;

import nl.topicus.jdbc.shaded.com.google.nl.topicus.jdbc.shaded.com.on.base.Preconditions;
import nl.topicus.jdbc.shaded.io.grpc.ExperimentalApi;
import java.util.Iterator;

/**
 * Utility functions for working with {@link StreamObserver} and it's nl.topicus.jdbc.shaded.com.on subclasses like
 * {@link CallStreamObserver}.
 */
@ExperimentalApi
public final class StreamObservers {
  /**
   * Copy the values of an {@link Iterator} to the target {@link CallStreamObserver} while properly
   * accounting for outbound flow-control.
   *
   * For clients this method is safe to call inside {@link ClientResponseObserver#beforeStart},
   * on servers it is safe to call inside the service method implementation.
   * 
   *
   * @param source of values expressed as an {@link Iterator}.
   * @param target {@link CallStreamObserver} which accepts values from the source.
   */
  public static  void copyWithFlowControl(final Iterator source,
      final CallStreamObserver target) {
    Preconditions.checkNotNull(source, "source");
    Preconditions.checkNotNull(target, "target");
    target.setOnReadyHandler(new Runnable() {
      @Override
      public void run() {
        while (target.isReady() && source.hasNext()) {
          target.onNext(source.next());
        }
        if (!source.hasNext()) {
          target.onCompleted();
        }
      }
    });
  }

  /**
   * Copy the values of an {@link Iterable} to the target {@link CallStreamObserver} while properly
   * accounting for outbound flow-control.
   *
   * For clients this method is safe to call inside {@link ClientResponseObserver#beforeStart},
   * on servers it is safe to call inside the service method implementation.
   * 
   *
   * @param source of values expressed as an {@link Iterable}.
   * @param target {@link CallStreamObserver} which accepts values from the source.
   */
  public static  void copyWithFlowControl(final Iterable source,
      CallStreamObserver target) {
    Preconditions.checkNotNull(source, "source");
    copyWithFlowControl(source.iterator(), target);
  }
}