Java tutorial
// Copyright 2014 The Bazel Authors. All rights reserved. // // 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 com.google.devtools.build.xcode.zip; import com.google.common.collect.ImmutableMap; import java.io.IOException; import java.nio.ByteBuffer; import java.nio.channels.ReadableByteChannel; import java.nio.channels.SeekableByteChannel; import java.nio.charset.StandardCharsets; import java.nio.file.Files; import java.nio.file.Path; import java.util.Map; /** * Utility code for reading information from zip files. */ public final class ZipFiles { /** Read a little-endian integer comprised of {@code count} bytes from the input channel. */ private static int readBytes(int count, ReadableByteChannel input) throws IOException { ByteBuffer buffer = ByteBuffer.allocate(count); if (input.read(buffer) != count) { throw new IOException("could not read expected number of bytes: " + count); } int result = 0; for (int i = count - 1; i >= 0; i--) { result <<= 8; result |= buffer.get(i) & 0xff; } return result; } /** * Returns the external file attributes of each entry as a mapping from the entry name to the * 32-bit value. As long as the attributes are generated by a Unix host, this includes the POSIX * file permissions in the upper two bytes. Entries not generated by a Unix host are not included * in the result. */ public static Map<String, Integer> unixExternalFileAttributes(Path zipFile) throws IOException { // Field descriptions in comments were taken from this document: // http://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT ImmutableMap.Builder<String, Integer> attributes = new ImmutableMap.Builder<>(); try (SeekableByteChannel input = Files.newByteChannel(zipFile)) { // The data we care about is toward the end of the file, after the compressed data for each // file. We begin by looking for the start of the end of central directory record, which is // marked by the signature 0x06054b50 // // This contains the centralDirectoryStartOffset value, which tells us where to seek to find // the first central directory entry. Each such entry is marked by the signature 0x02014b50 // and appear in sequence, one entry for each file in the .zip. // // The central directory entry contains many values, including the file name, the external // file attributes, and the version made by value. If the version made by indicates a Unix // host (0x03??), we include the external file attributes in the returned map. long offset = input.size() - 4; while (offset >= 0) { input.position(offset); int signature = readBytes(4, input); if (signature == 0x06054b50) { break; } else if (signature == 0x06064b50) { throw new IOException("Zip64 format not supported: " + zipFile); } offset--; } if (offset < 0) { throw new IOException(); } // Read end of central directory structure input.position(input.position() + 2 // number of this disk + 2 // number of the disk with the start of the central directory ); int entryCount = readBytes(2, input); input.position(input.position() + 2 // total number of entries in the central directory ); input.position(input.position() + 4 // size of the central directory ); int centralDirectoryStartOffset = readBytes(4, input); if (0xffffffff == centralDirectoryStartOffset) { throw new IOException("Zip64 format not supported."); } input.position(centralDirectoryStartOffset); int entriesFound = 0; // Read each central directory entry while ((entriesFound < entryCount) && (readBytes(4, input) == 0x02014b50)) { int versionMadeBy = readBytes(2, input); input.position(input.position() + 2 // version needed to extract + 2 // general purpose bit flag + 2 // compression method + 2 // last mod file time + 2 // last mod file date + 4 // crc-32 + 4 // compressed size + 4 // uncompressed size ); int filenameLength = readBytes(2, input); int extraFieldLength = readBytes(2, input); int fileCommentLength = readBytes(2, input); input.position(input.position() + 2 // disk number start + 2 // internal file attributes ); int externalFileAttributes = readBytes(4, input); input.position(input.position() + 4 // relative offset of local header ); ByteBuffer filenameBuffer = ByteBuffer.allocate(filenameLength); if (filenameLength != input.read(filenameBuffer)) { throw new IOException(String.format( "Could not read file name (length %d) in central directory record", filenameLength)); } input.position(input.position() + extraFieldLength + fileCommentLength); entriesFound++; if ((versionMadeBy >> 8) == 3) { // Zip made by a Unix host - the external file attributes are POSIX permissions. String filename = new String(filenameBuffer.array(), StandardCharsets.UTF_8); attributes.put(filename, externalFileAttributes); } } if (entriesFound != entryCount) { System.err.printf( "WARNING: Expected %d entries in central directory record in '%s', but found %d\n", entryCount, zipFile, entriesFound); } } return attributes.build(); } private ZipFiles() { } }