content: /*
   * 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.
   */
  /* Apache Harmony HEADER because the code in this class comes mostly from ZipFile, ZipEntry and
   * ZipConstants from android libcore.
   */
  
  package android.support.multidex;
  
  import java.io.File;
  import java.io.IOException;
  import java.io.RandomAccessFile;
  import java.util.zip.CRC32;
  import java.util.zip.ZipException;
  
  /**
   * Tools to build a quick partial crc of zip files.
   */
  final class ZipUtil {
      static class CentralDirectory {
          long offset;
          long size;
      }
  
      /* redefine those constant here because of bug 13721174 preventing to compile using the
       * constants defined in ZipFile */
      private static final int ENDHDR = 22;
      private static final int ENDSIG = 0x6054b50;
  
      /**
       * Size of reading buffers.
       */
      private static final int BUFFER_SIZE = 0x4000;
  
      /**
       * Compute crc32 of the central directory of an apk. The central directory contains
       * the crc32 of each entries in the zip so the computed result is considered valid for the whole
       * zip file. Does not support zip64 nor multidisk but it should be OK for now since ZipFile does
       * not either.
       */
      static long getZipCrc(File apk) throws IOException {
          RandomAccessFile raf = new RandomAccessFile(apk, "r");
          try {
              CentralDirectory dir = findCentralDirectory(raf);
  
              return computeCrcOfCentralDir(raf, dir);
          } finally {
              raf.close();
          }
      }
  
      /* Package visible for testing */
      static CentralDirectory findCentralDirectory(RandomAccessFile raf) throws IOException,
              ZipException {
          long scanOffset = raf.length() - ENDHDR;
          if (scanOffset < 0) {
              throw new ZipException("File too short to be a zip file: " + raf.length());
          }
  
          long stopOffset = scanOffset - 0x10000 /* ".ZIP file comment"'s max length */;
          if (stopOffset < 0) {
              stopOffset = 0;
          }
  
          int endSig = Integer.reverseBytes(ENDSIG);
          while (true) {
              raf.seek(scanOffset);
              if (raf.readInt() == endSig) {
                  break;
              }
  
              scanOffset--;
              if (scanOffset < stopOffset) {
                  throw new ZipException("End Of Central Directory signature not found");
              }
          }
          // Read the End Of Central Directory. ENDHDR includes the signature
          // bytes,
          // which we've already read.
  
          // Pull out the information we need.
          raf.skipBytes(2); // diskNumber
          raf.skipBytes(2); // diskWithCentralDir
          raf.skipBytes(2); // numEntries
          raf.skipBytes(2); // totalNumEntries
          CentralDirectory dir = new CentralDirectory();
          dir.size = Integer.reverseBytes(raf.readInt()) & 0xFFFFFFFFL;
          dir.offset = Integer.reverseBytes(raf.readInt()) & 0xFFFFFFFFL;
          return dir;
      }
  
      /* Package visible for testing */
      static long computeCrcOfCentralDir(RandomAccessFile raf, CentralDirectory dir)
              throws IOException {
          CRC32 crc = new CRC32();
          long stillToRead = dir.size;
          raf.seek(dir.offset);
          int length = (int) Math.min(BUFFER_SIZE, stillToRead);
          byte[] buffer = new byte[BUFFER_SIZE];
          length = raf.read(buffer, 0, length);
          while (length != -1) {
              crc.update(buffer, 0, length);
              stillToRead -= length;
              if (stillToRead == 0) {
                  break;
              }
              length = (int) Math.min(BUFFER_SIZE, stillToRead);
              length = raf.read(buffer, 0, length);
          }
          return crc.getValue();
      }
  }
  