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/*
 * Copyright (c) 2011, 2020 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

package org.glassfish.grizzly.websockets;

import java.io.IOException;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.CharacterCodingException;
import java.nio.charset.Charset;
import java.nio.charset.CharsetEncoder;
import java.nio.charset.CoderResult;

import org.glassfish.grizzly.utils.Charsets;

public class Utf8Utils {
    private static final byte[] EMPTY_ARRAY = new byte[0];

    public static byte[] encode(Charset charset, String string) {
        if (string.length() == 0) {
            return EMPTY_ARRAY;
        }

        CharsetEncoder ce = Charsets.getCharsetEncoder(charset);

        int en = scale(string.length(), ce.maxBytesPerChar());
        byte[] ba = new byte[en];

        ce.reset();
        ByteBuffer bb = ByteBuffer.wrap(ba);
        CharBuffer cb = CharBuffer.wrap(string);
        try {
            CoderResult cr = ce.encode(cb, bb, true);
            if (!cr.isUnderflow()) {
                cr.throwException();
            }
            cr = ce.flush(bb);
            if (!cr.isUnderflow()) {
                cr.throwException();
            }
        } catch (CharacterCodingException x) {
            // Substitution is always enabled,
            // so this shouldn't happen
            throw new Error(x);
        }
        return safeTrim(ba, bb.position());
    }

    public static void encode(Charset charset, String string, OutputStream os) throws IOException {

        if (string.length() == 0) {
            return;
        }

        final CharsetEncoder ce = Charsets.getCharsetEncoder(charset);
        int en = scale(string.length(), ce.maxBytesPerChar());
        byte[] ba = new byte[en];

        ce.reset();
        ByteBuffer bb = ByteBuffer.wrap(ba);
        CharBuffer cb = CharBuffer.wrap(string);
        try {
            CoderResult cr = ce.encode(cb, bb, true);
            if (!cr.isUnderflow()) {
                cr.throwException();
            }
            cr = ce.flush(bb);
            if (!cr.isUnderflow()) {
                cr.throwException();
            }
        } catch (CharacterCodingException x) {
            // Substitution is always enabled,
            // so this shouldn't happen
            throw new Error(x);
        }

        os.write(ba, 0, bb.position());
    }

    private static int scale(int len, float expansionFactor) {
        // We need to perform double, not float, arithmetic; otherwise
        // we lose low order bits when len is larger than 2**24.
        return (int) (len * (double) expansionFactor);
    }

    // Trim the given byte array to the given length
    //
    private static byte[] safeTrim(byte[] ba, int len) {
        if (len == ba.length && System.getSecurityManager() == null) {
            return ba;
        } else {
            return copyOf(ba, len);
        }
    }

    private static byte[] copyOf(byte[] original, int newLength) {
        byte[] copy = new byte[newLength];
        System.arraycopy(original, 0, copy, 0, Math.min(original.length, newLength));
        return copy;
    }

}