static {
   List<String> temp = new ArrayList<>(6);
   temp.add(GZIP_ENCODING);
   temp.add(DEFLATE_ENCODING);
   temp.add(COMPRESS_ENCODING);
   temp.add(X_GZIP_ENCODING);
   temp.add(X_COMPRESS_ENCODING);
   temp.add(NO_ENCODING);
   SUPPORTED_ENCODINGS = Collections.unmodifiableList(temp);
 }
 public java.util.List<AirspaceEntry> getEntries() {
   return Collections.unmodifiableList(this.entryList);
 }
/**
 * Implementations of this abstract class can add compression of a particular type to a given {@link
 * OutputStream}. They each return a {@link CompressingOutputStream}, which is just a thin wrapper
 * on top of an {@link OutputStream} that adds the ability to "finish" a stream (see {@link
 * CompressingOutputStream}).
 *
 * <p>
 *
 * <p>This class contains implementations based on several popular compression algorithms, such as
 * gzip. For example, the gzip implementation can decorate an {@link OutputStream} using an instance
 * of {@link GZIPOutputStream} and in that way add gzip compression to the stream.
 *
 * @author Sean Owen
 */
abstract class CompressingStreamFactory {
  /** "No encoding" content type: "identity". */
  static final String NO_ENCODING = "identity";

  private static final Logger LOG = LoggerFactory.getLogger(CompressingStreamFactory.class);
  /** Implementation based on {@link GZIPOutputStream} and {@link GZIPInputStream}. */
  private static final CompressingStreamFactory GZIP_CSF = new GZIPCompressingStreamFactory();
  /** Implementation based on {@link ZipOutputStream} and {@link ZipInputStream}. */
  private static final CompressingStreamFactory ZIP_CSF = new ZipCompressingStreamFactory();
  /** Implementation based on {@link DeflaterOutputStream}. */
  private static final CompressingStreamFactory DEFLATE_CSF = new DeflateCompressingStreamFactory();

  private static final String GZIP_ENCODING = "gzip";
  private static final String X_GZIP_ENCODING = "x-gzip";
  private static final String DEFLATE_ENCODING = "deflate";
  private static final String COMPRESS_ENCODING = "compress";
  private static final String X_COMPRESS_ENCODING = "x-compress";
  static final List<String> ALL_COMPRESSION_ENCODINGS =
      Collections.unmodifiableList(
          Arrays.asList(
              GZIP_ENCODING,
              DEFLATE_ENCODING,
              COMPRESS_ENCODING,
              X_GZIP_ENCODING,
              X_COMPRESS_ENCODING));

  /** "Any encoding" content type: the "*" wildcard. */
  private static final String ANY_ENCODING = "*";

  /** Ordered list of preferred encodings, from most to least preferred */
  private static final List<String> SUPPORTED_ENCODINGS;
  /**
   * Cache mapping previously seen "Accept-Encoding" header Strings to an appropriate instance of
   * {@link CompressingStreamFactory}.
   */
  private static final Map<String, String> BEST_ENCODING_CACHE =
      Collections.synchronizedMap(new HashMap<String, String>(101));
  /** Maps content type String to appropriate implementation of {@link CompressingStreamFactory}. */
  private static final Map<String, CompressingStreamFactory> FACTORY_MAP;

  private static final Pattern COMMA = Pattern.compile(",");

  static {
    List<String> temp = new ArrayList<>(6);
    temp.add(GZIP_ENCODING);
    temp.add(DEFLATE_ENCODING);
    temp.add(COMPRESS_ENCODING);
    temp.add(X_GZIP_ENCODING);
    temp.add(X_COMPRESS_ENCODING);
    temp.add(NO_ENCODING);
    SUPPORTED_ENCODINGS = Collections.unmodifiableList(temp);
  }

  static {
    Map<String, CompressingStreamFactory> temp = new HashMap<>(11);
    temp.put(GZIP_ENCODING, GZIP_CSF);
    temp.put(X_GZIP_ENCODING, GZIP_CSF);
    temp.put(COMPRESS_ENCODING, ZIP_CSF);
    temp.put(X_COMPRESS_ENCODING, ZIP_CSF);
    temp.put(DEFLATE_ENCODING, DEFLATE_CSF);
    FACTORY_MAP = Collections.unmodifiableMap(temp);
  }

  private static OutputStream maybeWrapStatsOutputStream(
      OutputStream outputStream,
      CompressingFilterContext context,
      CompressingFilterStats.StatsField field) {
    assert outputStream != null;
    OutputStream result;
    if (context.isStatsEnabled()) {
      CompressingFilterStats stats = context.getStats();
      CompressingFilterStats.OutputStatsCallback callbackOutput =
          stats.getOutputStatsCallback(field);
      result = new StatsOutputStream(outputStream, callbackOutput);
    } else {
      result = outputStream;
    }
    return result;
  }

  private static InputStream maybeWrapStatsInputStream(
      InputStream inputStream,
      CompressingFilterContext context,
      CompressingFilterStats.StatsField field) {
    assert inputStream != null;
    InputStream result;
    if (context.isStatsEnabled()) {
      CompressingFilterStats stats = context.getStats();
      CompressingFilterStats.InputStatsCallback callbackInput = stats.getInputStatsCallback(field);
      result = new StatsInputStream(inputStream, callbackInput);
    } else {
      result = inputStream;
    }
    return result;
  }

  private static boolean isSupportedResponseContentEncoding(String contentEncoding) {
    return NO_ENCODING.equals(contentEncoding) || FACTORY_MAP.containsKey(contentEncoding);
  }

  static boolean isSupportedRequestContentEncoding(String contentEncoding) {
    return NO_ENCODING.equals(contentEncoding) || FACTORY_MAP.containsKey(contentEncoding);
  }

  /**
   * Returns the instance associated to the given content encoding.
   *
   * @param contentEncoding content encoding (e.g. "gzip")
   * @return instance for content encoding
   */
  static CompressingStreamFactory getFactoryForContentEncoding(String contentEncoding) {
    assert FACTORY_MAP.containsKey(contentEncoding);
    return FACTORY_MAP.get(contentEncoding);
  }

  /**
   * Determines best content encoding for the response, based on the request -- in particular, based
   * on its "Accept-Encoding" header.
   *
   * @param httpRequest request
   * @return best content encoding
   */
  static String getBestContentEncoding(HttpServletRequest httpRequest) {

    String forcedEncoding = (String) httpRequest.getAttribute(CompressingFilter.FORCE_ENCODING_KEY);
    String bestEncoding;
    if (forcedEncoding != null) {

      bestEncoding = forcedEncoding;

    } else {

      String acceptEncodingHeader =
          httpRequest.getHeader(CompressingHttpServletResponse.ACCEPT_ENCODING_HEADER);
      if (acceptEncodingHeader == null) {

        bestEncoding = NO_ENCODING;

      } else {

        bestEncoding = BEST_ENCODING_CACHE.get(acceptEncodingHeader);

        if (bestEncoding == null) {

          // No cached value; must parse header to determine best encoding
          // I don't synchronize on bestEncodingCache; it's not worth it to avoid the rare case
          // where
          // two thread get in here and both parse the header. It's only a tiny bit of extra work,
          // and
          // avoids the synchronization overhead.

          if (acceptEncodingHeader.indexOf((int) ',') >= 0) {
            // multiple encodings are accepted
            bestEncoding = selectBestEncoding(acceptEncodingHeader);
          } else {
            // one encoding is accepted
            bestEncoding = parseBestEncoding(acceptEncodingHeader);
          }

          BEST_ENCODING_CACHE.put(acceptEncodingHeader, bestEncoding);
        }
      }
    }

    // User-specified encoding might not be supported
    if (!isSupportedResponseContentEncoding(bestEncoding)) {
      bestEncoding = NO_ENCODING;
    }

    return bestEncoding;
  }

  private static String parseBestEncoding(String acceptEncodingHeader) {
    ContentEncodingQ contentEncodingQ = parseContentEncodingQ(acceptEncodingHeader);
    String contentEncoding = contentEncodingQ.getContentEncoding();
    if (contentEncodingQ.getQ() > 0.0) {
      if (ANY_ENCODING.equals(contentEncoding)) {
        return SUPPORTED_ENCODINGS.get(0);
      } else if (SUPPORTED_ENCODINGS.contains(contentEncoding)) {
        return contentEncoding;
      }
    }
    return NO_ENCODING;
  }

  @SuppressWarnings("squid:S1244")
  private static String selectBestEncoding(String acceptEncodingHeader) {
    // multiple encodings are accepted; determine best one

    Collection<String> bestEncodings = new HashSet<>(3);
    double bestQ = 0.0;
    Collection<String> unacceptableEncodings = new HashSet<>(3);
    boolean willAcceptAnything = false;

    for (String token : COMMA.split(acceptEncodingHeader)) {
      ContentEncodingQ contentEncodingQ = parseContentEncodingQ(token);
      String contentEncoding = contentEncodingQ.getContentEncoding();
      double q = contentEncodingQ.getQ();
      if (ANY_ENCODING.equals(contentEncoding)) {
        willAcceptAnything = q > 0.0;
      } else if (SUPPORTED_ENCODINGS.contains(contentEncoding)) {
        if (q > 0.0) {
          // This is a header quality comparison.
          // So it is safe to suppress warning squid:S1244
          if (q == bestQ) {
            bestEncodings.add(contentEncoding);
          } else if (q > bestQ) {
            bestQ = q;
            bestEncodings.clear();
            bestEncodings.add(contentEncoding);
          }
        } else {
          unacceptableEncodings.add(contentEncoding);
        }
      }
    }

    if (bestEncodings.isEmpty()) {
      // nothing was acceptable to us
      if (willAcceptAnything) {
        if (unacceptableEncodings.isEmpty()) {
          return SUPPORTED_ENCODINGS.get(0);
        } else {
          for (String encoding : SUPPORTED_ENCODINGS) {
            if (!unacceptableEncodings.contains(encoding)) {
              return encoding;
            }
          }
        }
      }
    } else {
      for (String encoding : SUPPORTED_ENCODINGS) {
        if (bestEncodings.contains(encoding)) {
          return encoding;
        }
      }
    }

    return NO_ENCODING;
  }

  private static ContentEncodingQ parseContentEncodingQ(String contentEncodingString) {

    double q = 1.0;

    int qvalueStartIndex = contentEncodingString.indexOf((int) ';');
    String contentEncoding;
    if (qvalueStartIndex >= 0) {
      contentEncoding = contentEncodingString.substring(0, qvalueStartIndex).trim();
      String qvalueString = contentEncodingString.substring(qvalueStartIndex + 1).trim();
      if (qvalueString.startsWith("q=")) {
        try {
          q = Double.parseDouble(qvalueString.substring(2));
        } catch (NumberFormatException ignored) {
          // That's bad -- browser sent an invalid number. All we can do is ignore it, and
          // pretend that no q value was specified, so that it effectively defaults to 1.0
          LOG.trace("Couldn't parse a Double from {}.", qvalueString.substring(2), ignored);
        }
      }
    } else {
      contentEncoding = contentEncodingString.trim();
    }

    return new ContentEncodingQ(contentEncoding, q);
  }

  abstract CompressingOutputStream getCompressingStream(
      OutputStream servletOutputStream, CompressingFilterContext context) throws IOException;

  abstract CompressingInputStream getCompressingStream(
      InputStream servletInputStream, CompressingFilterContext context) throws IOException;

  private static final class ContentEncodingQ {

    private final String contentEncoding;
    private final double q;

    private ContentEncodingQ(String contentEncoding, double q) {
      assert contentEncoding != null && contentEncoding.length() > 0;
      this.contentEncoding = contentEncoding;
      this.q = q;
    }

    String getContentEncoding() {
      return contentEncoding;
    }

    double getQ() {
      return q;
    }

    @Override
    public String toString() {
      return contentEncoding + ";q=" + q;
    }
  }

  private static class GZIPCompressingStreamFactory extends CompressingStreamFactory {
    @Override
    CompressingOutputStream getCompressingStream(
        final OutputStream outputStream, final CompressingFilterContext context)
        throws IOException {
      return new CompressingOutputStream() {
        private final DeflaterOutputStream gzipOutputStream =
            new GZIPOutputStream(
                CompressingStreamFactory.maybeWrapStatsOutputStream(
                    outputStream,
                    context,
                    CompressingFilterStats.StatsField.RESPONSE_COMPRESSED_BYTES));
        private final OutputStream statsOutputStream =
            CompressingStreamFactory.maybeWrapStatsOutputStream(
                gzipOutputStream, context, CompressingFilterStats.StatsField.RESPONSE_INPUT_BYTES);

        @Override
        public OutputStream getCompressingOutputStream() {
          return statsOutputStream;
        }

        @Override
        public void finish() throws IOException {
          gzipOutputStream.finish();
        }
      };
    }

    @Override
    CompressingInputStream getCompressingStream(
        final InputStream inputStream, final CompressingFilterContext context) {
      return new CompressingInputStream() {
        @Override
        public InputStream getCompressingInputStream() throws IOException {
          return CompressingStreamFactory.maybeWrapStatsInputStream(
              new GZIPInputStream(
                  CompressingStreamFactory.maybeWrapStatsInputStream(
                      inputStream,
                      context,
                      CompressingFilterStats.StatsField.REQUEST_COMPRESSED_BYTES)),
              context,
              CompressingFilterStats.StatsField.REQUEST_INPUT_BYTES);
        }
      };
    }
  }

  private static class ZipCompressingStreamFactory extends CompressingStreamFactory {
    @Override
    CompressingOutputStream getCompressingStream(
        final OutputStream outputStream, final CompressingFilterContext context) {
      return new CompressingOutputStream() {
        private final DeflaterOutputStream zipOutputStream =
            new ZipOutputStream(
                CompressingStreamFactory.maybeWrapStatsOutputStream(
                    outputStream,
                    context,
                    CompressingFilterStats.StatsField.RESPONSE_COMPRESSED_BYTES));
        private final OutputStream statsOutputStream =
            CompressingStreamFactory.maybeWrapStatsOutputStream(
                zipOutputStream, context, CompressingFilterStats.StatsField.RESPONSE_INPUT_BYTES);

        @Override
        public OutputStream getCompressingOutputStream() {
          return statsOutputStream;
        }

        @Override
        public void finish() throws IOException {
          zipOutputStream.finish();
        }
      };
    }

    @Override
    CompressingInputStream getCompressingStream(
        final InputStream inputStream, final CompressingFilterContext context) {
      return new CompressingInputStream() {
        @Override
        public InputStream getCompressingInputStream() {
          return CompressingStreamFactory.maybeWrapStatsInputStream(
              new ZipInputStream(
                  CompressingStreamFactory.maybeWrapStatsInputStream(
                      inputStream,
                      context,
                      CompressingFilterStats.StatsField.REQUEST_COMPRESSED_BYTES)),
              context,
              CompressingFilterStats.StatsField.REQUEST_INPUT_BYTES);
        }
      };
    }
  }

  private static class DeflateCompressingStreamFactory extends CompressingStreamFactory {
    @Override
    CompressingOutputStream getCompressingStream(
        final OutputStream outputStream, final CompressingFilterContext context) {
      return new CompressingOutputStream() {
        private final DeflaterOutputStream deflaterOutputStream =
            new DeflaterOutputStream(
                CompressingStreamFactory.maybeWrapStatsOutputStream(
                    outputStream,
                    context,
                    CompressingFilterStats.StatsField.RESPONSE_COMPRESSED_BYTES));
        private final OutputStream statsOutputStream =
            CompressingStreamFactory.maybeWrapStatsOutputStream(
                deflaterOutputStream,
                context,
                CompressingFilterStats.StatsField.RESPONSE_INPUT_BYTES);

        @Override
        public OutputStream getCompressingOutputStream() {
          return statsOutputStream;
        }

        @Override
        public void finish() throws IOException {
          deflaterOutputStream.finish();
        }
      };
    }

    @Override
    CompressingInputStream getCompressingStream(
        final InputStream inputStream, final CompressingFilterContext context) {
      return new CompressingInputStream() {
        @Override
        public InputStream getCompressingInputStream() {
          return CompressingStreamFactory.maybeWrapStatsInputStream(
              new InflaterInputStream(
                  CompressingStreamFactory.maybeWrapStatsInputStream(
                      inputStream,
                      context,
                      CompressingFilterStats.StatsField.REQUEST_COMPRESSED_BYTES)),
              context,
              CompressingFilterStats.StatsField.REQUEST_INPUT_BYTES);
        }
      };
    }
  }
}