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 *   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
 *
 *  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
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package org.apache.cayenne.crypto.transformer.bytes;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.security.Key;
import java.util.Arrays;
import java.util.zip.GZIPInputStream;

import org.apache.cayenne.crypto.CayenneCryptoException;

/**
 * @since 4.0
 */
class GzipDecryptor implements BytesDecryptor {

    private BytesDecryptor delegate;

    public GzipDecryptor(BytesDecryptor delegate) {
        this.delegate = delegate;
    }

    @Override
    public byte[] decrypt(byte[] input, int inputOffset, Key key) {

        byte[] decrypted = delegate.decrypt(input, inputOffset, key);
        try {
            return gunzip(decrypted);
        } catch (IOException e) {
            // really not expecting an error here...
            throw new CayenneCryptoException("Error uncompressing input", e);
        }
    }

    static byte[] gunzip(byte[] input) throws IOException {

        ByteArrayInputStream zipBytes = new ByteArrayInputStream(input);
        GZIPInputStream in = new GZIPInputStream(zipBytes);

        // duplicating ByteArrayOutputStream logic here... too much overhead and
        // inefficiency using ByteArrayOutputStream directly

        byte[] out = new byte[input.length * 2];

        int totalRead = 0;
        int read;
        int resizeBy = input.length;

        while ((read = in.read(out, totalRead, out.length - totalRead - 1)) > 0) {

            totalRead += read;
            if (totalRead + 1 == out.length) {
                out = Arrays.copyOf(out, out.length + resizeBy);
            }
        }

        if (totalRead < out.length) {
            out = Arrays.copyOf(out, totalRead);
        }

        return out;
    }
}