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JDBC Driver for Google Cloud Spanner
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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
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 *
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 * 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
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 */

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

import nl.topicus.jdbc.shaded.javax.annotation.concurrent.ThreadSafe;

/**
 * Interface for intercepting outgoing calls before they are dispatched by a {@link Channel}.
 *
 * Implementers use this mechanism to add cross-cutting behavior to {@link Channel} and
 * stub implementations. Common examples of such behavior include:
 * 

 * Adding credentials to header metadata
 * Logging and monitoring call behavior
 * Request and response rewriting
 * 
 */
@ThreadSafe
public interface ClientInterceptor {
  /**
   * Intercept {@link ClientCall} creation by the {@code next} {@link Channel}.
   *
   * Many variations of interception are possible. Complex implementations may return a wrapper
   * around the result of {@code next.newCall()}, whereas a simpler implementation may just modify
   * the header metadata prior to returning the result of {@code next.newCall()}.
   *
   * {@code next.newCall()} must not be called under a different {@link Context}
   * other than the current {@code Context}. The outcome of such usage is undefined and may cause
   * memory leak due to unbounded chain of {@code Context}s.
   *
   * @param method the remote method to be called.
   * @param callOptions the runtime options to be applied to this call.
   * @param next the channel which is being intercepted.
   * @return the call object for the remote operation, never {@code null}.
   */
   ClientCall interceptCall(
      MethodDescriptor method, CallOptions callOptions, Channel next);
}