sdks/java/harness/src/main/java/org/apache/beam/fn/harness/control/AddHarnessIdInterceptor.java

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 * 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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package org.apache.beam.fn.harness.control;

import static org.apache.beam.vendor.guava.v20_0.com.google.common.base.Preconditions.checkArgument;

import org.apache.beam.vendor.grpc.v1p13p1.io.grpc.ClientInterceptor;
import org.apache.beam.vendor.grpc.v1p13p1.io.grpc.Metadata;
import org.apache.beam.vendor.grpc.v1p13p1.io.grpc.Metadata.Key;
import org.apache.beam.vendor.grpc.v1p13p1.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() {}
}