/*
* Copyright 2012-2017 the original author or authors.
*
* 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 org.springframework.boot.loader.jar;
import java.io.IOException;
import org.springframework.boot.loader.data.RandomAccessData;
/**
* A ZIP File "End of central directory record" (EOCD).
*
* @author Phillip Webb
* @author Andy Wilkinson
* @see <a href="http://en.wikipedia.org/wiki/Zip_%28file_format%29">Zip File Format</a>
*/
class CentralDirectoryEndRecord {
private static final int MINIMUM_SIZE = 22;
private static final int MAXIMUM_COMMENT_LENGTH = 0xFFFF;
private static final int MAXIMUM_SIZE = MINIMUM_SIZE + MAXIMUM_COMMENT_LENGTH;
private static final int SIGNATURE = 0x06054b50;
private static final int COMMENT_LENGTH_OFFSET = 20;
private static final int READ_BLOCK_SIZE = 256;
private byte[] block;
private int offset;
private int size;
/**
* Create a new {@link CentralDirectoryEndRecord} instance from the specified
* {@link RandomAccessData}, searching backwards from the end until a valid block is
* located.
* @param data the source data
* @throws IOException in case of I/O errors
*/
CentralDirectoryEndRecord(RandomAccessData data) throws IOException {
this.block = createBlockFromEndOfData(data, READ_BLOCK_SIZE);
this.size = MINIMUM_SIZE;
this.offset = this.block.length - this.size;
while (!isValid()) {
this.size++;
if (this.size > this.block.length) {
if (this.size >= MAXIMUM_SIZE || this.size > data.getSize()) {
throw new IOException("Unable to find ZIP central directory "
+ "records after reading " + this.size + " bytes");
}
this.block = createBlockFromEndOfData(data, this.size + READ_BLOCK_SIZE);
}
this.offset = this.block.length - this.size;
}
}
private byte[] createBlockFromEndOfData(RandomAccessData data, int size)
throws IOException {
int length = (int) Math.min(data.getSize(), size);
return Bytes.get(data.getSubsection(data.getSize() - length, length));
}
private boolean isValid() {
if (this.block.length < MINIMUM_SIZE
|| Bytes.littleEndianValue(this.block, this.offset + 0, 4) != SIGNATURE) {
return false;
}
// Total size must be the structure size + comment
long commentLength = Bytes.littleEndianValue(this.block,
this.offset + COMMENT_LENGTH_OFFSET, 2);
return this.size == MINIMUM_SIZE + commentLength;
}
/**
* Returns the location in the data that the archive actually starts. For most files
* the archive data will start at 0, however, it is possible to have prefixed bytes
* (often used for startup scripts) at the beginning of the data.
* @param data the source data
* @return the offset within the data where the archive begins
*/
public long getStartOfArchive(RandomAccessData data) {
long length = Bytes.littleEndianValue(this.block, this.offset + 12, 4);
long specifiedOffset = Bytes.littleEndianValue(this.block, this.offset + 16, 4);
long actualOffset = data.getSize() - this.size - length;
return actualOffset - specifiedOffset;
}
/**
* Return the bytes of the "Central directory" based on the offset indicated in this
* record.
* @param data the source data
* @return the central directory data
*/
public RandomAccessData getCentralDirectory(RandomAccessData data) {
long offset = Bytes.littleEndianValue(this.block, this.offset + 16, 4);
long length = Bytes.littleEndianValue(this.block, this.offset + 12, 4);
return data.getSubsection(offset, length);
}
/**
* Return the number of ZIP entries in the file.
* @return the number of records in the zip
*/
public int getNumberOfRecords() {
long numberOfRecords = Bytes.littleEndianValue(this.block, this.offset + 10, 2);
if (numberOfRecords == 0xFFFF) {
throw new IllegalStateException("Zip64 archives are not supported");
}
return (int) numberOfRecords;
}
}