com.facebook.buck.cxx.ArchiveScrubberStep.java Source code

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Here is the source code for com.facebook.buck.cxx.ArchiveScrubberStep.java

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/*
 * Copyright 2014-present Facebook, Inc.
 *
 * 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.facebook.buck.cxx;

import com.facebook.buck.step.ExecutionContext;
import com.facebook.buck.step.Step;
import com.google.common.base.Charsets;
import com.google.common.base.Preconditions;
import com.google.common.base.Strings;

import java.io.IOException;
import java.nio.BufferUnderflowException;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.ReadOnlyBufferException;
import java.nio.channels.FileChannel;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;
import java.util.Arrays;

/**
 * Scrub any non-deterministic meta-data from the given archive (e.g. timestamp, UID, GID).
 */
public class ArchiveScrubberStep implements Step {

    private static final byte[] GLOBAL_HEADER = String.format("!<arch>%s", System.lineSeparator())
            .getBytes(Charsets.US_ASCII);
    private static final byte[] FILE_MAGIC = { 0x60, 0x0A };

    private final Path archive;

    public ArchiveScrubberStep(Path archive) {
        this.archive = archive;
    }

    private byte[] getBytes(ByteBuffer buffer, int len) {
        byte[] bytes = new byte[len];
        buffer.get(bytes);
        return bytes;
    }

    private int getDecimalStringAsInt(ByteBuffer buffer, int len) {
        byte[] bytes = getBytes(buffer, len);
        String str = new String(bytes, Charsets.US_ASCII);
        return Integer.parseInt(str.trim());
    }

    private void putIntAsDecimalString(ByteBuffer buffer, int len, int value) {
        String val = String.format("%d", value);
        Preconditions.checkState(val.length() <= len);
        val = Strings.repeat(" ", len - val.length()) + val;
        buffer.put(val.getBytes(Charsets.US_ASCII));
    }

    private void checkArchive(boolean expression, String msg) throws ArchiveException {
        if (!expression) {
            throw new ArchiveException(msg);
        }
    }

    /**
     * Efficiently modifies the archive backed by the given buffer to remove any non-deterministic
     * meta-data such as timestamps, UIDs, and GIDs.
     * @param archive a {@link ByteBuffer} wrapping the contents of the archive.
     */
    private void scrubArchive(ByteBuffer archive) throws ArchiveException {
        try {

            // Grab the global header chunk and verify it's accurate.
            byte[] globalHeader = getBytes(archive, GLOBAL_HEADER.length);
            checkArchive(Arrays.equals(GLOBAL_HEADER, globalHeader), "invalid global header");

            // Iterate over all the file meta-data entries, injecting zero's for timestamp,
            // UID, and GID.
            while (archive.hasRemaining()) {
                /* File name */ getBytes(archive, 16);

                // Inject 0's for the non-deterministic meta-data entries.
                /* File modification timestamp */ putIntAsDecimalString(archive, 12, 0);
                /* Owner ID */ putIntAsDecimalString(archive, 6, 0);
                /* Group ID */ putIntAsDecimalString(archive, 6, 0);

                /* File mode */ getBytes(archive, 8);
                int fileSize = getDecimalStringAsInt(archive, 10);

                // Lastly, grab the file magic entry and verify it's accurate.
                byte[] fileMagic = getBytes(archive, 2);
                checkArchive(Arrays.equals(FILE_MAGIC, fileMagic), "invalid file magic");

                // Skip the file data.
                archive.position(archive.position() + fileSize + fileSize % 2);
            }

            // Convert any low-level exceptions to `ArchiveExceptions`s.
        } catch (BufferUnderflowException | ReadOnlyBufferException e) {
            throw new ArchiveException(e.getMessage());
        }
    }

    private FileChannel readWriteChannel(Path path) throws IOException {
        return FileChannel.open(path, StandardOpenOption.READ, StandardOpenOption.WRITE);
    }

    @Override
    public int execute(ExecutionContext context) throws InterruptedException {
        Path archivePath = context.getProjectFilesystem().resolve(archive);
        try {
            try (FileChannel channel = readWriteChannel(archivePath)) {
                MappedByteBuffer map = channel.map(FileChannel.MapMode.READ_WRITE, 0, channel.size());
                scrubArchive(map);
            }
        } catch (IOException | ArchiveException e) {
            context.logError(e, "Error scrubbing non-deterministic metadata from %s", archivePath);
            return 1;
        }
        return 0;
    }

    @Override
    public String getShortName() {
        return "archive-scrub";
    }

    @Override
    public String getDescription(ExecutionContext context) {
        return "archive-scrub";
    }

    @SuppressWarnings("serial")
    public static class ArchiveException extends Exception {
        public ArchiveException(String msg) {
            super(msg);
        }
    }

}