/*
* 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);
}
}