Biff8EncryptionKey.java

/* ====================================================================
   Licensed to the Apache Software Foundation (ASF) under one or more
   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You 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

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   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
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package org.apache.poi.hssf.record.crypto;

import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.util.ThreadLocalUtil;

public final class Biff8EncryptionKey {
    /**
     * Stores the BIFF8 encryption/decryption password for the current thread.  This has been done
     * using a {@link ThreadLocal} in order to avoid further overloading the various public APIs
     * (e.g. {@link HSSFWorkbook}) that need this functionality.
     */
    private static final ThreadLocal<String> _userPasswordTLS = new ThreadLocal<>();
    static {
        // allow to clear all thread-locals via ThreadLocalUtil
        ThreadLocalUtil.registerCleaner(_userPasswordTLS::remove);
    }

    /**
     * Sets the BIFF8 encryption/decryption password for the current thread.
     * <p>
     *     It is strongly recommended that you call `setCurrentUserPassword(null)` as
     *     soon as you are finished with the calls that need the password. One option is
     *     to use a try block with a `finally` clause that calls `setCurrentUserPassword(null)`.
     * </p>
     * <p>
     *     The POI APIs for newer OOXML based file formats like xlsx, docx and pptx have never used
     *     this Biff8EncryptionKey support. Passwords are passed using dedicated parameters in the
     *     relevant APIs, and are not stored in thread-locals.
     * </p>
     * <p>
     *     POI 6.0.0 introduces alternatives API methods for HSSF and other H**F classes that take an
     *     explicit password parameter, and do not rely on this thread-local. It is recommended to use
     *     those APIs instead of the ones that rely on this thread-local.
     * </p>
     *
     * @param password pass <code>null</code> to clear user password (and use default)
     */
    public static void setCurrentUserPassword(String password) {
        if (password == null) {
            _userPasswordTLS.remove();
        } else {
            _userPasswordTLS.set(password);
        }
    }

    /**
     * @return the BIFF8 encryption/decryption password for the current thread.
     * <code>null</code> if it is currently unset.
     */
    public static String getCurrentUserPassword() {
        return _userPasswordTLS.get();
    }
}