forked from MarcoBuster/Magisk
137 lines
5.9 KiB
Java
137 lines
5.9 KiB
Java
package com.topjohnwu.signing;
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import java.nio.ByteBuffer;
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import java.nio.ByteOrder;
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/**
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* Assorted ZIP format helpers.
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*
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* <p>NOTE: Most helper methods operating on {@code ByteBuffer} instances expect that the byte
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* order of these buffers is little-endian.
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*/
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public abstract class ZipUtils {
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private static final int ZIP_EOCD_REC_MIN_SIZE = 22;
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private static final int ZIP_EOCD_REC_SIG = 0x06054b50;
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private static final int ZIP_EOCD_CENTRAL_DIR_SIZE_FIELD_OFFSET = 12;
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private static final int ZIP_EOCD_CENTRAL_DIR_OFFSET_FIELD_OFFSET = 16;
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private static final int ZIP_EOCD_COMMENT_LENGTH_FIELD_OFFSET = 20;
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private static final int ZIP64_EOCD_LOCATOR_SIZE = 20;
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private static final int ZIP64_EOCD_LOCATOR_SIG = 0x07064b50;
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private static final int UINT16_MAX_VALUE = 0xffff;
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private ZipUtils() {
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}
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/**
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* Returns the position at which ZIP End of Central Directory record starts in the provided
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* buffer or {@code -1} if the record is not present.
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*
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* <p>NOTE: Byte order of {@code zipContents} must be little-endian.
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*/
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public static int findZipEndOfCentralDirectoryRecord(ByteBuffer zipContents) {
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assertByteOrderLittleEndian(zipContents);
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// ZIP End of Central Directory (EOCD) record is located at the very end of the ZIP archive.
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// The record can be identified by its 4-byte signature/magic which is located at the very
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// beginning of the record. A complication is that the record is variable-length because of
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// the comment field.
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// The algorithm for locating the ZIP EOCD record is as follows. We search backwards from
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// end of the buffer for the EOCD record signature. Whenever we find a signature, we check
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// the candidate record's comment length is such that the remainder of the record takes up
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// exactly the remaining bytes in the buffer. The search is bounded because the maximum
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// size of the comment field is 65535 bytes because the field is an unsigned 16-bit number.
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int archiveSize = zipContents.capacity();
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if (archiveSize < ZIP_EOCD_REC_MIN_SIZE) {
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return -1;
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}
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int maxCommentLength = Math.min(archiveSize - ZIP_EOCD_REC_MIN_SIZE, UINT16_MAX_VALUE);
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int eocdWithEmptyCommentStartPosition = archiveSize - ZIP_EOCD_REC_MIN_SIZE;
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for (int expectedCommentLength = 0; expectedCommentLength < maxCommentLength; expectedCommentLength++) {
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int eocdStartPos = eocdWithEmptyCommentStartPosition - expectedCommentLength;
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if (zipContents.getInt(eocdStartPos) == ZIP_EOCD_REC_SIG) {
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int actualCommentLength = getUnsignedInt16(zipContents, eocdStartPos + ZIP_EOCD_COMMENT_LENGTH_FIELD_OFFSET);
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if (actualCommentLength == expectedCommentLength) {
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return eocdStartPos;
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}
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}
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}
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return -1;
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}
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/**
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* Returns {@code true} if the provided buffer contains a ZIP64 End of Central Directory
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* Locator.
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*
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* <p>NOTE: Byte order of {@code zipContents} must be little-endian.
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*/
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public static boolean isZip64EndOfCentralDirectoryLocatorPresent(ByteBuffer zipContents, int zipEndOfCentralDirectoryPosition) {
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assertByteOrderLittleEndian(zipContents);
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// ZIP64 End of Central Directory Locator immediately precedes the ZIP End of Central
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// Directory Record.
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int locatorPosition = zipEndOfCentralDirectoryPosition - ZIP64_EOCD_LOCATOR_SIZE;
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if (locatorPosition < 0) {
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return false;
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}
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return zipContents.getInt(locatorPosition) == ZIP64_EOCD_LOCATOR_SIG;
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}
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/**
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* Returns the offset of the start of the ZIP Central Directory in the archive.
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*
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* <p>NOTE: Byte order of {@code zipEndOfCentralDirectory} must be little-endian.
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*/
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public static long getZipEocdCentralDirectoryOffset(ByteBuffer zipEndOfCentralDirectory) {
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assertByteOrderLittleEndian(zipEndOfCentralDirectory);
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return getUnsignedInt32(zipEndOfCentralDirectory, zipEndOfCentralDirectory.position() + ZIP_EOCD_CENTRAL_DIR_OFFSET_FIELD_OFFSET);
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}
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/**
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* Sets the offset of the start of the ZIP Central Directory in the archive.
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*
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* <p>NOTE: Byte order of {@code zipEndOfCentralDirectory} must be little-endian.
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*/
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public static void setZipEocdCentralDirectoryOffset(ByteBuffer zipEndOfCentralDirectory, long offset) {
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assertByteOrderLittleEndian(zipEndOfCentralDirectory);
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setUnsignedInt32(zipEndOfCentralDirectory, zipEndOfCentralDirectory.position() + ZIP_EOCD_CENTRAL_DIR_OFFSET_FIELD_OFFSET, offset);
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}
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/**
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* Returns the size (in bytes) of the ZIP Central Directory.
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*
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* <p>NOTE: Byte order of {@code zipEndOfCentralDirectory} must be little-endian.
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*/
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public static long getZipEocdCentralDirectorySizeBytes(ByteBuffer zipEndOfCentralDirectory) {
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assertByteOrderLittleEndian(zipEndOfCentralDirectory);
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return getUnsignedInt32(zipEndOfCentralDirectory, zipEndOfCentralDirectory.position() + ZIP_EOCD_CENTRAL_DIR_SIZE_FIELD_OFFSET);
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}
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private static void assertByteOrderLittleEndian(ByteBuffer buffer) {
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if (buffer.order() != ByteOrder.LITTLE_ENDIAN) {
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throw new IllegalArgumentException("ByteBuffer byte order must be little endian");
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}
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}
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private static int getUnsignedInt16(ByteBuffer buffer, int offset) {
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return buffer.getShort(offset) & 0xffff;
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}
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private static long getUnsignedInt32(ByteBuffer buffer, int offset) {
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return buffer.getInt(offset) & 0xffffffffL;
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}
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private static void setUnsignedInt32(ByteBuffer buffer, int offset, long value) {
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if ((value < 0) || (value > 0xffffffffL)) {
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throw new IllegalArgumentException("uint32 value of out range: " + value);
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}
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buffer.putInt(buffer.position() + offset, (int) value);
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}
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}
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