1 /* 2 * Copyright 2014 The gRPC Authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package io.grpc; 18 19 import javax.annotation.concurrent.ThreadSafe; 20 21 /** 22 * Interface for intercepting outgoing calls before they are dispatched by a {@link Channel}. 23 * 24 * <p>Implementers use this mechanism to add cross-cutting behavior to {@link Channel} and 25 * stub implementations. Common examples of such behavior include: 26 * <ul> 27 * <li>Logging and monitoring call behavior</li> 28 * <li>Adding metadata for proxies to observe</li> 29 * <li>Request and response rewriting</li> 30 * </ul> 31 * 32 * <p>Providing authentication credentials is better served by {@link 33 * CallCredentials}. But a {@code ClientInterceptor} could set the {@code 34 * CallCredentials} within the {@link CallOptions}. 35 * 36 * <p>The interceptor may be called for multiple {@link ClientCall calls} by one or more threads 37 * without completing the previous ones first. Refer to the 38 * {@link io.grpc.ClientCall.Listener ClientCall.Listener} docs for more details regarding thread 39 * safety of the returned listener. 40 */ 41 @ThreadSafe 42 public interface ClientInterceptor { 43 /** 44 * Intercept {@link ClientCall} creation by the {@code next} {@link Channel}. 45 * 46 * <p>Many variations of interception are possible. Complex implementations may return a wrapper 47 * around the result of {@code next.newCall()}, whereas a simpler implementation may just modify 48 * the header metadata prior to returning the result of {@code next.newCall()}. 49 * 50 * <p>{@code next.newCall()} <strong>must not</strong> be called under a different {@link Context} 51 * other than the current {@code Context}. The outcome of such usage is undefined and may cause 52 * memory leak due to unbounded chain of {@code Context}s. 53 * 54 * @param method the remote method to be called. 55 * @param callOptions the runtime options to be applied to this call. 56 * @param next the channel which is being intercepted. 57 * @return the call object for the remote operation, never {@code null}. 58 */ interceptCall( MethodDescriptor<ReqT, RespT> method, CallOptions callOptions, Channel next)59 <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall( 60 MethodDescriptor<ReqT, RespT> method, CallOptions callOptions, Channel next); 61 } 62