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/**
 * 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.hadoop.ipc;

import org.apache.commons.lang.builder.EqualsBuilder;
import org.apache.commons.lang.builder.HashCodeBuilder;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;

import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;

/**
 * A class defining the caller context for auditing coarse granularity
 * operations.
 *
 * This class is immutable.
 */
@InterfaceAudience.LimitedPrivate({"HBase", "HDFS", "Hive", "MapReduce",
    "Pig", "Spark", "YARN"})
@InterfaceStability.Evolving
public final class CallerContext {
  public static final Charset SIGNATURE_ENCODING = StandardCharsets.UTF_8;
  /** The caller context.
   *
   * It will be truncated if it exceeds the maximum allowed length in
   * server. The default length limit is
   * {@link org.apache.hadoop.fs.CommonConfigurationKeysPublic#HADOOP_CALLER_CONTEXT_MAX_SIZE_DEFAULT}
   */
  private final String context;

  /** The caller's signature for validation.
   *
   * The signature is optional. The null or empty signature will be abandoned.
   * If the signature exceeds the maximum allowed length in server, the caller
   * context will be abandoned. The default length limit is
   * {@link org.apache.hadoop.fs.CommonConfigurationKeysPublic#HADOOP_CALLER_CONTEXT_SIGNATURE_MAX_SIZE_DEFAULT}
   */
  private final byte[] signature;

  private CallerContext(Builder builder) {
    this.context = builder.context;
    this.signature = builder.signature;
  }

  public String getContext() {
    return context;
  }

  public byte[] getSignature() {
    return signature == null ?
        null : Arrays.copyOf(signature, signature.length);
  }

  @InterfaceAudience.Private
  public boolean isContextValid() {
    return context != null && !context.isEmpty();
  }

  @Override
  public int hashCode() {
    return new HashCodeBuilder().append(context).toHashCode();
  }

  @Override
  public boolean equals(Object obj) {
    if (obj == null) {
      return false;
    } else if (obj == this) {
      return true;
    } else if (obj.getClass() != getClass()) {
      return false;
    } else {
      CallerContext rhs = (CallerContext) obj;
      return new EqualsBuilder()
          .append(context, rhs.context)
          .append(signature, rhs.signature)
          .isEquals();
    }
  }

  @Override
  public String toString() {
    if (!isContextValid()) {
      return "";
    }
    String str = context;
    if (signature != null) {
      str += ":";
      str += new String(signature, SIGNATURE_ENCODING);
    }
    return str;
  }

  /** The caller context builder. */
  public static final class Builder {
    private final String context;
    private byte[] signature;

    public Builder(String context) {
      this.context = context;
    }

    public Builder setSignature(byte[] signature) {
      if (signature != null && signature.length > 0) {
        this.signature = Arrays.copyOf(signature, signature.length);
      }
      return this;
    }

    public CallerContext build() {
      return new CallerContext(this);
    }
  }

  /**
   * The thread local current caller context.
   * 
   * Internal class for defered singleton idiom.
   * https://en.wikipedia.org/wiki/Initialization_on_demand_holder_idiom
   */
  private static final class CurrentCallerContextHolder {
    static final ThreadLocal CALLER_CONTEXT =
        new InheritableThreadLocal<>();
  }

  public static CallerContext getCurrent() {
    return CurrentCallerContextHolder.CALLER_CONTEXT.get();
  }

  public static void setCurrent(CallerContext callerContext) {
    CurrentCallerContextHolder.CALLER_CONTEXT.set(callerContext);
  }
}