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TrueZIP is a Java based Virtual File System (VFS) to enable transparent, multi-threaded read/write access to archive files (ZIP, TAR etc.) as if they were directories. Archive files may be arbitrarily nested and the nesting level is only limited by heap and file system size.

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/*
 * Copyright (C) 2005-2010 Schlichtherle IT Services
 *
 * 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 de.schlichtherle.io.rof;

import java.io.*;

/**
 * A base class for any class which wants to decorate a {@link ReadOnlyFile}.
 * 
 * Note that subclasses of this class often implement their own virtual file
 * pointer.
 * Thus, if you would like to access the underlying {@code ReadOnlyFile}
 * again after you have finished working with the
 * {@code FilteredReadOnlyFile}, you should synchronize their file
 * pointers a'la:
 * 
 *     ReadOnlyFile rof = new SimpleReadOnlyFile(new File("HelloWorld.java"));
 *     try {
 *         ReadOnlyFile frof = new FilteredReadOnlyFile(rof);
 *         try {
 *             // Do any file input on brof here...
 *             frof.seek(1);
 *         } finally {
 *             // Synchronize the file pointers.
 *             rof.seek(frof.getFilePointer());
 *         }
 *         // This assertion would fail if we hadn't done the file pointer
 *         // synchronization!
 *         assert rof.getFilePointer() == 1;
 *     } finally {
 *         rof.close();
 *     }
 * 
 * This does not apply to this base class, however.
 * 
 * Subclasses implemententing their own virtual file pointer should add a note
 * referring to this classes Javadoc like this:
 * 

 * Note: This class implements its own virtual file pointer.
 * Thus, if you would like to access the underlying {@code ReadOnlyFile}
 * again after you have finished working with an instance of this class,
 * you should synchronize their file pointers using the pattern as described
 * in {@link FilterReadOnlyFile}.
 * 
 *
 * @author Christian Schlichtherle
 * @version $Id: FilterReadOnlyFile.java,v 1.4 2010/08/20 13:09:47 christian_schlichtherle Exp $
 */
public class FilterReadOnlyFile extends AbstractReadOnlyFile {

    /** The read only file to be filtered. */
    protected ReadOnlyFile rof;
    
    /**
     * Creates a new instance of {@code FilterReadOnlyFile},
     * which filters the given read only file.
     */
    public FilterReadOnlyFile(ReadOnlyFile rof) {
        this.rof = rof;
    }

    public long length() throws IOException {
        return rof.length();
    }

    public long getFilePointer() throws IOException {
        return rof.getFilePointer();
    }

    public void seek(long pos) throws IOException {
        rof.seek(pos);
    }

    public int read() throws IOException {
        return rof.read();
    }

    public int read(byte[] b, int off, int len) throws IOException {
        return rof.read(b, off, len);
    }

    public void close() throws IOException {
        rof.close();
    }
}