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/*
 * Copyright 2014, 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 io.grpc;

import com.google.common.base.Preconditions;

import java.util.Arrays;
import java.util.List;

/**
 * Utility methods for working with {@link ClientInterceptor}s.
 */
public class ClientInterceptors {

  // Prevent instantiation
  private ClientInterceptors() {}

  /**
   * Create a new {@link Channel} that will call {@code interceptors} before starting a call on the
   * given channel. The last interceptor will have its {@link ClientInterceptor#interceptCall}
   * called first.
   *
   * @param channel the underlying channel to intercept.
   * @param interceptors array of interceptors to bind to {@code channel}.
   * @return a new channel instance with the interceptors applied.
   */
  public static Channel intercept(Channel channel, ClientInterceptor... interceptors) {
    return intercept(channel, Arrays.asList(interceptors));
  }

  /**
   * Create a new {@link Channel} that will call {@code interceptors} before starting a call on the
   * given channel. The last interceptor will have its {@link ClientInterceptor#interceptCall}
   * called first.
   *
   * @param channel the underlying channel to intercept.
   * @param interceptors a list of interceptors to bind to {@code channel}.
   * @return a new channel instance with the interceptors applied.
   */
  public static Channel intercept(Channel channel, List interceptors) {
    Preconditions.checkNotNull(channel);
    for (ClientInterceptor interceptor : interceptors) {
      channel = new InterceptorChannel(channel, interceptor);
    }
    return channel;
  }

  private static class InterceptorChannel extends Channel {
    private final Channel channel;
    private final ClientInterceptor interceptor;

    private InterceptorChannel(Channel channel, ClientInterceptor interceptor) {
      this.channel = channel;
      this.interceptor = Preconditions.checkNotNull(interceptor, "interceptor");
    }

    @Override
    public  ClientCall newCall(
        MethodDescriptor method, CallOptions callOptions) {
      return interceptor.interceptCall(method, callOptions, channel);
    }
  }

  private static final ClientCall NOOP_CALL = new ClientCall() {
    @Override
    public void start(Listener responseListener, Metadata.Headers headers) {}

    @Override
    public void request(int numMessages) {}

    @Override
    public void cancel() {}

    @Override
    public void halfClose() {}

    @Override
    public void sendMessage(Object message) {}

    /**
     * Always returns {@code false}, since this is only used when the startup of the {@link
     * ClientCall} fails (i.e. the {@link ClientCall} is closed).
     */
    @Override
    public boolean isReady() {
      return false;
    }
  };

  /**
   * A {@link io.grpc.ForwardingClientCall} that delivers exceptions from its start logic to the
   * call listener.
   *
   * 
{@link ClientCall#start(ClientCall.Listener, Metadata.Headers)} should not throw any
   * exception other than those caused by misuse, e.g., {@link IllegalStateException}.  {@code
   * CheckedForwardingClientCall} provides {@code checkedStart()} in which throwing exceptions is
   * allowed.
   */
  public abstract static class CheckedForwardingClientCall
      extends io.grpc.ForwardingClientCall {

    private ClientCall delegate;

    /**
     * Subclasses implement the start logic here that would normally belong to {@code start()}.
     *
     * 
Implementation should call {@code this.delegate().start()} in the normal path. Exceptions
     * may safely be thrown prior to calling {@code this.delegate().start()}. Such exceptions will
     * be handled by {@code CheckedForwardingClientCall} and be delivered to {@code
     * responseListener}.  Exceptions must not be thrown after calling {@code
     * this.delegate().start()}, as this can result in {@link ClientCall.Listener#onClose} being
     * called multiple times.
     */
    protected abstract void checkedStart(Listener responseListener, Metadata.Headers headers)
        throws Exception;

    protected CheckedForwardingClientCall(ClientCall delegate) {
      this.delegate = delegate;
    }

    @Override
    protected final ClientCall delegate() {
      return delegate;
    }

    @Override
    @SuppressWarnings("unchecked")
    public final void start(Listener responseListener, Metadata.Headers headers) {
      try {
        checkedStart(responseListener, headers);
      } catch (Exception e) {
        // Because start() doesn't throw, the caller may still try to call other methods on this
        // call object. Passing these invocations to the original delegate will cause
        // IllegalStateException because delegate().start() was not called. We switch the delegate
        // to a NO-OP one to prevent the IllegalStateException. The user will finally get notified
        // about the error through the listener.
        delegate = (ClientCall) NOOP_CALL;
        responseListener.onClose(Status.fromThrowable(e), new Metadata.Trailers());
      }
    }
  }
}
 















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