content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you under the Apache License, Version 2.0 (the
   * "License"); you may not use this file except in compliance
   * with the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.beam.sdk.fn.server;
  
  import org.apache.beam.vendor.grpc.v1p69p0.io.grpc.Context;
  import org.apache.beam.vendor.grpc.v1p69p0.io.grpc.Contexts;
  import org.apache.beam.vendor.grpc.v1p69p0.io.grpc.Metadata;
  import org.apache.beam.vendor.grpc.v1p69p0.io.grpc.Metadata.Key;
  import org.apache.beam.vendor.grpc.v1p69p0.io.grpc.ServerCall;
  import org.apache.beam.vendor.grpc.v1p69p0.io.grpc.ServerCall.Listener;
  import org.apache.beam.vendor.grpc.v1p69p0.io.grpc.ServerCallHandler;
  import org.apache.beam.vendor.grpc.v1p69p0.io.grpc.ServerInterceptor;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions;
  
  /**
   * A HeaderAccessorProvider which intercept the header in a GRPC request and expose the relevant
   * fields.
   */
  @SuppressWarnings({
    "nullness" // TODO(https://github.com/apache/beam/issues/20497)
  })
  public class GrpcContextHeaderAccessorProvider {
  
    private static final Key<String> WORKER_ID_KEY =
        Key.of("worker_id", Metadata.ASCII_STRING_MARSHALLER);
    private static final Context.Key<String> SDK_WORKER_CONTEXT_KEY = Context.key("worker_id");
    private static final GrpcHeaderAccessor HEADER_ACCESSOR = new GrpcHeaderAccessor();
  
    @SuppressWarnings("UnnecessaryAnonymousClass")
    private static final ServerInterceptor INTERCEPTOR =
        new ServerInterceptor() {
          @Override
          public <ReqT, RespT> Listener<ReqT> interceptCall(
              ServerCall<ReqT, RespT> call,
              Metadata requestHeaders,
              ServerCallHandler<ReqT, RespT> next) {
            String workerId = requestHeaders.get(WORKER_ID_KEY);
            Context context = Context.current().withValue(SDK_WORKER_CONTEXT_KEY, workerId);
            return Contexts.interceptCall(context, call, requestHeaders, next);
          }
        };
  
    public static ServerInterceptor interceptor() {
      return INTERCEPTOR;
    }
  
    public static HeaderAccessor getHeaderAccessor() {
      return HEADER_ACCESSOR;
    }
  
    private static class GrpcHeaderAccessor implements HeaderAccessor {
  
      @Override
      // This method should be called from the request method.
      public String getSdkWorkerId() {
        return Preconditions.checkNotNull(
            SDK_WORKER_CONTEXT_KEY.get(), "No worker_id header provided in client headers.");
      }
    }
  }
  