content: /*
   * Copyright (C) 2016 The Android Open Source Project
   *
   * Licensed 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 android.util.apk;
  
  import android.util.Pair;
  
  import java.io.IOException;
  import java.io.RandomAccessFile;
  import java.nio.ByteBuffer;
  import java.nio.ByteOrder;
  
  /**
   * Assorted ZIP format helpers.
   *
   * <p>NOTE: Most helper methods operating on {@code ByteBuffer} instances expect that the byte
   * order of these buffers is little-endian.
   */
  abstract class ZipUtils {
      private ZipUtils() {}
  
      private static final int ZIP_EOCD_REC_MIN_SIZE = 22;
      private static final int ZIP_EOCD_REC_SIG = 0x06054b50;
      private static final int ZIP_EOCD_CENTRAL_DIR_SIZE_FIELD_OFFSET = 12;
      private static final int ZIP_EOCD_CENTRAL_DIR_OFFSET_FIELD_OFFSET = 16;
      private static final int ZIP_EOCD_COMMENT_LENGTH_FIELD_OFFSET = 20;
  
      private static final int ZIP64_EOCD_LOCATOR_SIZE = 20;
      private static final int ZIP64_EOCD_LOCATOR_SIG_REVERSE_BYTE_ORDER = 0x504b0607;
  
      private static final int UINT16_MAX_VALUE = 0xffff;
  
      /**
       * Returns the ZIP End of Central Directory record of the provided ZIP file.
       *
       * @return contents of the ZIP End of Central Directory record and the record's offset in the
       *         file or {@code null} if the file does not contain the record.
       *
       * @throws IOException if an I/O error occurs while reading the file.
       */
      static Pair<ByteBuffer, Long> findZipEndOfCentralDirectoryRecord(RandomAccessFile zip)
              throws IOException {
          // ZIP End of Central Directory (EOCD) record is located at the very end of the ZIP archive.
          // The record can be identified by its 4-byte signature/magic which is located at the very
          // beginning of the record. A complication is that the record is variable-length because of
          // the comment field.
          // The algorithm for locating the ZIP EOCD record is as follows. We search backwards from
          // end of the buffer for the EOCD record signature. Whenever we find a signature, we check
          // the candidate record's comment length is such that the remainder of the record takes up
          // exactly the remaining bytes in the buffer. The search is bounded because the maximum
          // size of the comment field is 65535 bytes because the field is an unsigned 16-bit number.
  
          long fileSize = zip.length();
          if (fileSize < ZIP_EOCD_REC_MIN_SIZE) {
              return null;
          }
  
          // Optimization: 99.99% of APKs have a zero-length comment field in the EoCD record and thus
          // the EoCD record offset is known in advance. Try that offset first to avoid unnecessarily
          // reading more data.
          Pair<ByteBuffer, Long> result = findZipEndOfCentralDirectoryRecord(zip, 0);
          if (result != null) {
              return result;
          }
  
          // EoCD does not start where we expected it to. Perhaps it contains a non-empty comment
          // field. Expand the search. The maximum size of the comment field in EoCD is 65535 because
          // the comment length field is an unsigned 16-bit number.
          return findZipEndOfCentralDirectoryRecord(zip, UINT16_MAX_VALUE);
      }
  
      /**
       * Returns the ZIP End of Central Directory record of the provided ZIP file.
       *
       * @param maxCommentSize maximum accepted size (in bytes) of EoCD comment field. The permitted
       *        value is from 0 to 65535 inclusive. The smaller the value, the faster this method
       *        locates the record, provided its comment field is no longer than this value.
       *
       * @return contents of the ZIP End of Central Directory record and the record's offset in the
       *         file or {@code null} if the file does not contain the record.
       *
       * @throws IOException if an I/O error occurs while reading the file.
       */
      private static Pair<ByteBuffer, Long> findZipEndOfCentralDirectoryRecord(
              RandomAccessFile zip, int maxCommentSize) throws IOException {
          // ZIP End of Central Directory (EOCD) record is located at the very end of the ZIP archive.
          // The record can be identified by its 4-byte signature/magic which is located at the very
          // beginning of the record. A complication is that the record is variable-length because of
          // the comment field.
          // The algorithm for locating the ZIP EOCD record is as follows. We search backwards from
          // end of the buffer for the EOCD record signature. Whenever we find a signature, we check
          // the candidate record's comment length is such that the remainder of the record takes up
          // exactly the remaining bytes in the buffer. The search is bounded because the maximum
          // size of the comment field is 65535 bytes because the field is an unsigned 16-bit number.
  
          if ((maxCommentSize < 0) || (maxCommentSize > UINT16_MAX_VALUE)) {
              throw new IllegalArgumentException("maxCommentSize: " + maxCommentSize);
          }
  
          long fileSize = zip.length();
          if (fileSize < ZIP_EOCD_REC_MIN_SIZE) {
              // No space for EoCD record in the file.
              return null;
          }
          // Lower maxCommentSize if the file is too small.
          maxCommentSize = (int) Math.min(maxCommentSize, fileSize - ZIP_EOCD_REC_MIN_SIZE);
  
          ByteBuffer buf = ByteBuffer.allocate(ZIP_EOCD_REC_MIN_SIZE + maxCommentSize);
          buf.order(ByteOrder.LITTLE_ENDIAN);
          long bufOffsetInFile = fileSize - buf.capacity();
          zip.seek(bufOffsetInFile);
          zip.readFully(buf.array(), buf.arrayOffset(), buf.capacity());
          int eocdOffsetInBuf = findZipEndOfCentralDirectoryRecord(buf);
          if (eocdOffsetInBuf == -1) {
              // No EoCD record found in the buffer
              return null;
          }
          // EoCD found
          buf.position(eocdOffsetInBuf);
          ByteBuffer eocd = buf.slice();
          eocd.order(ByteOrder.LITTLE_ENDIAN);
          return Pair.create(eocd, bufOffsetInFile + eocdOffsetInBuf);
      }
  
      /**
       * Returns the position at which ZIP End of Central Directory record starts in the provided
       * buffer or {@code -1} if the record is not present.
       *
       * <p>NOTE: Byte order of {@code zipContents} must be little-endian.
       */
      private static int findZipEndOfCentralDirectoryRecord(ByteBuffer zipContents) {
          assertByteOrderLittleEndian(zipContents);
  
          // ZIP End of Central Directory (EOCD) record is located at the very end of the ZIP archive.
          // The record can be identified by its 4-byte signature/magic which is located at the very
          // beginning of the record. A complication is that the record is variable-length because of
          // the comment field.
          // The algorithm for locating the ZIP EOCD record is as follows. We search backwards from
          // end of the buffer for the EOCD record signature. Whenever we find a signature, we check
          // the candidate record's comment length is such that the remainder of the record takes up
          // exactly the remaining bytes in the buffer. The search is bounded because the maximum
          // size of the comment field is 65535 bytes because the field is an unsigned 16-bit number.
  
          int archiveSize = zipContents.capacity();
          if (archiveSize < ZIP_EOCD_REC_MIN_SIZE) {
              return -1;
          }
          int maxCommentLength = Math.min(archiveSize - ZIP_EOCD_REC_MIN_SIZE, UINT16_MAX_VALUE);
          int eocdWithEmptyCommentStartPosition = archiveSize - ZIP_EOCD_REC_MIN_SIZE;
          for (int expectedCommentLength = 0; expectedCommentLength <= maxCommentLength;
                  expectedCommentLength++) {
              int eocdStartPos = eocdWithEmptyCommentStartPosition - expectedCommentLength;
              if (zipContents.getInt(eocdStartPos) == ZIP_EOCD_REC_SIG) {
                  int actualCommentLength =
                          getUnsignedInt16(
                                  zipContents, eocdStartPos + ZIP_EOCD_COMMENT_LENGTH_FIELD_OFFSET);
                  if (actualCommentLength == expectedCommentLength) {
                      return eocdStartPos;
                  }
              }
          }
  
          return -1;
      }
  
      /**
       * Returns {@code true} if the provided file contains a ZIP64 End of Central Directory
       * Locator.
       *
       * @param zipEndOfCentralDirectoryPosition offset of the ZIP End of Central Directory record
       *        in the file.
       *
       * @throws IOException if an I/O error occurs while reading the file.
       */
      public static final boolean isZip64EndOfCentralDirectoryLocatorPresent(
              RandomAccessFile zip, long zipEndOfCentralDirectoryPosition) throws IOException {
  
          // ZIP64 End of Central Directory Locator immediately precedes the ZIP End of Central
          // Directory Record.
          long locatorPosition = zipEndOfCentralDirectoryPosition - ZIP64_EOCD_LOCATOR_SIZE;
          if (locatorPosition < 0) {
              return false;
          }
  
          zip.seek(locatorPosition);
          // RandomAccessFile.readInt assumes big-endian byte order, but ZIP format uses
          // little-endian.
          return zip.readInt() == ZIP64_EOCD_LOCATOR_SIG_REVERSE_BYTE_ORDER;
      }
  
      /**
       * Returns the offset of the start of the ZIP Central Directory in the archive.
       *
       * <p>NOTE: Byte order of {@code zipEndOfCentralDirectory} must be little-endian.
       */
      public static long getZipEocdCentralDirectoryOffset(ByteBuffer zipEndOfCentralDirectory) {
          assertByteOrderLittleEndian(zipEndOfCentralDirectory);
          return getUnsignedInt32(
                  zipEndOfCentralDirectory,
                  zipEndOfCentralDirectory.position() + ZIP_EOCD_CENTRAL_DIR_OFFSET_FIELD_OFFSET);
      }
  
      /**
       * Sets the offset of the start of the ZIP Central Directory in the archive.
       *
       * <p>NOTE: Byte order of {@code zipEndOfCentralDirectory} must be little-endian.
       */
      public static void setZipEocdCentralDirectoryOffset(
              ByteBuffer zipEndOfCentralDirectory, long offset) {
          assertByteOrderLittleEndian(zipEndOfCentralDirectory);
          setUnsignedInt32(
                  zipEndOfCentralDirectory,
                  zipEndOfCentralDirectory.position() + ZIP_EOCD_CENTRAL_DIR_OFFSET_FIELD_OFFSET,
                  offset);
      }
  
      /**
       * Returns the size (in bytes) of the ZIP Central Directory.
       *
       * <p>NOTE: Byte order of {@code zipEndOfCentralDirectory} must be little-endian.
       */
      public static long getZipEocdCentralDirectorySizeBytes(ByteBuffer zipEndOfCentralDirectory) {
          assertByteOrderLittleEndian(zipEndOfCentralDirectory);
          return getUnsignedInt32(
                  zipEndOfCentralDirectory,
                  zipEndOfCentralDirectory.position() + ZIP_EOCD_CENTRAL_DIR_SIZE_FIELD_OFFSET);
      }
  
      private static void assertByteOrderLittleEndian(ByteBuffer buffer) {
          if (buffer.order() != ByteOrder.LITTLE_ENDIAN) {
              throw new IllegalArgumentException("ByteBuffer byte order must be little endian");
          }
      }
  
      private static int getUnsignedInt16(ByteBuffer buffer, int offset) {
          return buffer.getShort(offset) & 0xffff;
      }
  
      private static long getUnsignedInt32(ByteBuffer buffer, int offset) {
          return buffer.getInt(offset) & 0xffffffffL;
      }
  
      private static void setUnsignedInt32(ByteBuffer buffer, int offset, long value) {
          if ((value < 0) || (value > 0xffffffffL)) {
              throw new IllegalArgumentException("uint32 value of out range: " + value);
          }
          buffer.putInt(buffer.position() + offset, (int) value);
      }
  }
  