ClientInterceptor.java

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package io.grpc;

import javax.annotation.concurrent.ThreadSafe;

/**
 * Interface for intercepting outgoing calls before they are dispatched by a {@link Channel}.
 *
 * <p>Implementers use this mechanism to add cross-cutting behavior to {@link Channel} and
 * stub implementations. Common examples of such behavior include:
 * <ul>
 * <li>Adding credentials to header metadata</li>
 * <li>Logging and monitoring call behavior</li>
 * <li>Request and response rewriting</li>
 * </ul>
 */
@ThreadSafe
public interface ClientInterceptor {
  /**
   * Intercept {@link ClientCall} creation by the {@code next} {@link Channel}.
   *
   * <p>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()}.
   *
   * <p>{@code next.newCall()} <strong>must not</strong> 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}.
   */
  <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(
      MethodDescriptor<ReqT, RespT> method, CallOptions callOptions, Channel next);
}