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   /*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project 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:
    *
    *   https://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 io.netty.handler.codec.http.websocketx;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.Unpooled;
  import io.netty.handler.codec.base64.Base64;
  import io.netty.util.CharsetUtil;
  import io.netty.util.concurrent.FastThreadLocal;
  import io.netty.util.internal.PlatformDependent;
  import io.netty.util.internal.SuppressJava6Requirement;
  
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  
  /**
   * A utility class mainly for use by web sockets
   */
  final class WebSocketUtil {
  
      private static final FastThreadLocal<MessageDigest> MD5 = new FastThreadLocal<MessageDigest>() {
          @Override
          protected MessageDigest initialValue() throws Exception {
              try {
                  //Try to get a MessageDigest that uses MD5
                  //Suppress a warning about weak hash algorithm
                  //since it's defined in draft-ietf-hybi-thewebsocketprotocol-00
                  return MessageDigest.getInstance("MD5");
              } catch (NoSuchAlgorithmException e) {
                  //This shouldn't happen! How old is the computer?
                  throw new InternalError("MD5 not supported on this platform - Outdated?");
              }
          }
      };
  
      private static final FastThreadLocal<MessageDigest> SHA1 = new FastThreadLocal<MessageDigest>() {
          @Override
          protected MessageDigest initialValue() throws Exception {
              try {
                  //Try to get a MessageDigest that uses SHA1
                  //Suppress a warning about weak hash algorithm
                  //since it's defined in draft-ietf-hybi-thewebsocketprotocol-00
                  return MessageDigest.getInstance("SHA1");
              } catch (NoSuchAlgorithmException e) {
                  //This shouldn't happen! How old is the computer?
                  throw new InternalError("SHA-1 not supported on this platform - Outdated?");
              }
          }
      };
  
      /**
       * Performs a MD5 hash on the specified data
       *
       * @param data The data to hash
       * @return The hashed data
       */
      static byte[] md5(byte[] data) {
          // TODO(normanmaurer): Create md5 method that not need MessageDigest.
          return digest(MD5, data);
      }
  
      /**
       * Performs a SHA-1 hash on the specified data
       *
       * @param data The data to hash
       * @return The hashed data
       */
      static byte[] sha1(byte[] data) {
          // TODO(normanmaurer): Create sha1 method that not need MessageDigest.
          return digest(SHA1, data);
      }
  
      private static byte[] digest(FastThreadLocal<MessageDigest> digestFastThreadLocal, byte[] data) {
          MessageDigest digest = digestFastThreadLocal.get();
          digest.reset();
          return digest.digest(data);
      }
  
      /**
       * Performs base64 encoding on the specified data
       *
       * @param data The data to encode
       * @return An encoded string containing the data
       */
      @SuppressJava6Requirement(reason = "Guarded with java version check")
      static String base64(byte[] data) {
         if (PlatformDependent.javaVersion() >= 8) {
             return java.util.Base64.getEncoder().encodeToString(data);
         }
         String encodedString;
         ByteBuf encodedData = Unpooled.wrappedBuffer(data);
         try {
             ByteBuf encoded = Base64.encode(encodedData);
             try {
                 encodedString = encoded.toString(CharsetUtil.UTF_8);
             } finally {
                 encoded.release();
             }
         } finally {
             encodedData.release();
         }
         return encodedString;
     }
 
     /**
      * Creates an arbitrary number of random bytes
      *
      * @param size the number of random bytes to create
      * @return An array of random bytes
      */
     static byte[] randomBytes(int size) {
         byte[] bytes = new byte[size];
         PlatformDependent.threadLocalRandom().nextBytes(bytes);
         return bytes;
     }
 
     /**
      * Generates a pseudo-random number
      *
      * @param minimum The minimum allowable value
      * @param maximum The maximum allowable value
      * @return A pseudo-random number
      */
     static int randomNumber(int minimum, int maximum) {
         assert minimum < maximum;
         double fraction = PlatformDependent.threadLocalRandom().nextDouble();
 
         // the idea here is that nextDouble gives us a random value
         //
         //              0 <= fraction <= 1
         //
         // the distance from min to max declared as
         //
         //              dist = max - min
         //
         // satisfies the following
         //
         //              min + dist = max
         //
         // taking into account
         //
         //         0 <= fraction * dist <= dist
         //
         // we've got
         //
         //       min <= min + fraction * dist <= max
         return (int) (minimum + fraction * (maximum - minimum));
     }
 
     static int byteAtIndex(int mask, int index) {
         return (mask >> 8 * (3 - index)) & 0xFF;
     }
 
     /**
      * A private constructor to ensure that instances of this class cannot be made
      */
     private WebSocketUtil() {
         // Unused
     }
 }