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   * Licensed to the Apache Software Foundation (ASF) under one
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   * 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
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   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
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   * See the License for the specific language governing permissions and
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  package org.apache.beam.sdk.fn.channel;
  
  import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkArgument;
  
  import org.apache.beam.vendor.grpc.v1p69p0.io.grpc.ClientInterceptor;
  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.stub.MetadataUtils;
  
  /** A {@link ClientInterceptor} that attaches a provided SDK Harness ID to outgoing messages. */
  public class AddHarnessIdInterceptor {
    private static final Key<String> ID_KEY = Key.of("worker_id", Metadata.ASCII_STRING_MARSHALLER);
  
    public static ClientInterceptor create(String harnessId) {
      checkArgument(harnessId != null, "harnessId must not be null");
      Metadata md = new Metadata();
      md.put(ID_KEY, harnessId);
      return MetadataUtils.newAttachHeadersInterceptor(md);
    }
  
    // This is implemented via MetadataUtils, so we never actually create an instance of this class
    private AddHarnessIdInterceptor() {}
  }
  