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/*
 * Copyright 2015, Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *    * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *    * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *
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 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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package org.glowroot.agent.shaded.grpc;

import static org.glowroot.agent.shaded.google.common.base.Preconditions.checkArgument;
import static org.glowroot.agent.shaded.google.common.base.Preconditions.checkNotNull;

import org.glowroot.agent.shaded.google.common.annotations.VisibleForTesting;

import java.util.Collections;
import java.util.HashSet;
import java.util.Map.Entry;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

import javax.annotation.Nullable;
import javax.annotation.concurrent.ThreadSafe;

/**
 * Encloses classes related to the compression and decompression of messages.
 */
@ExperimentalApi("https://github.com/grpc/grpc-java/issues/492")
@ThreadSafe
public final class DecompressorRegistry {

  private static final DecompressorRegistry DEFAULT_INSTANCE = new DecompressorRegistry(
      new DecompressorInfo(new Codec.Gzip(), true),
      new DecompressorInfo(Codec.Identity.NONE, false));

  public static DecompressorRegistry getDefaultInstance() {
    return DEFAULT_INSTANCE;
  }

  public static DecompressorRegistry newEmptyInstance() {
    return new DecompressorRegistry();
  }

  private final ConcurrentMap decompressors;

  /**
   * Registers a decompressor for both decompression and message encoding negotiation.
   *
   * @param d The decompressor to register
   * @param advertised If true, the message encoding will be listed in the Accept-Encoding header.
   */
  public void register(Decompressor d, boolean advertised) {
    String encoding = d.getMessageEncoding();
    checkArgument(!encoding.contains(","), "Comma is currently not allowed in message encoding");
    decompressors.put(encoding, new DecompressorInfo(d, advertised));
  }

  /**
   * Provides a list of all message encodings that have decompressors available.
   */
  public Set getKnownMessageEncodings() {
    return Collections.unmodifiableSet(decompressors.keySet());
  }

  /**
   * Provides a list of all message encodings that have decompressors available and should be
   * advertised.
   *
   * The specification doesn't say anything about ordering, or preference, so the returned codes
   * can be arbitrary.
   */
  @ExperimentalApi("https://github.com/grpc/grpc-java/issues/492")
  public Set getAdvertisedMessageEncodings() {
    Set advertisedDecompressors = new HashSet(decompressors.size());
    for (Entry entry : decompressors.entrySet()) {
      if (entry.getValue().advertised) {
        advertisedDecompressors.add(entry.getKey());
      }
    }
    return Collections.unmodifiableSet(advertisedDecompressors);
  }

  /**
   * Returns a decompressor for the given message encoding, or {@code null} if none has been
   * registered.
   *
   * This ignores whether the compressor is advertised.  According to the spec, if we know how
   * to process this encoding, we attempt to, regardless of whether or not it is part of the
   * encodings sent to the remote host.
   */
  @Nullable
  public Decompressor lookupDecompressor(String messageEncoding) {
    DecompressorInfo info = decompressors.get(messageEncoding);
    return info != null ? info.decompressor : null;
  }

  @VisibleForTesting
  DecompressorRegistry(DecompressorInfo ...ds) {
    decompressors = new ConcurrentHashMap();
    for (DecompressorInfo d : ds) {
      decompressors.put(d.decompressor.getMessageEncoding(), d);
    }
  }

  /**
   * Information about a decompressor.
   */
  private static final class DecompressorInfo {
    private final Decompressor decompressor;
    private volatile boolean advertised;

    DecompressorInfo(Decompressor decompressor, boolean advertised) {
      this.decompressor = checkNotNull(decompressor);
      this.advertised = advertised;
    }
  }
}