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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

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package jdk.internal.net.http.websocket;

import jdk.internal.net.http.common.Log;

import java.nio.ByteBuffer;

import java.nio.CharBuffer;

import java.nio.charset.CharacterCodingException;

import java.nio.charset.CharsetDecoder;

import java.nio.charset.CoderResult;

import java.nio.charset.CodingErrorAction;

import static java.nio.charset.StandardCharsets.UTF_8;

import static jdk.internal.net.http.common.Utils.EMPTY_BYTEBUFFER;

final class UTF8AccumulatingDecoder {

    private final CharsetDecoder decoder = UTF_8.newDecoder();

    {

        decoder.onMalformedInput(CodingErrorAction.REPORT);

        decoder.onUnmappableCharacter(CodingErrorAction.REPORT);

    }

    private ByteBuffer leftovers = EMPTY_BYTEBUFFER;

    CharBuffer decode(ByteBuffer in, boolean endOfInput)

            throws CharacterCodingException

    {

        ByteBuffer b;

        int rem = leftovers.remaining();

        if (rem != 0) {

            // We won't need this wasteful allocation & copying when JDK-8155222

            // has been resolved

            b = ByteBuffer.allocate(rem + in.remaining());

            b.put(leftovers).put(in).flip();

        } else {

            b = in;

        }

        CharBuffer out = CharBuffer.allocate(b.remaining());

        CoderResult r = decoder.decode(b, out, endOfInput);

        if (r.isError()) {

            r.throwException();

        }

        if (b.hasRemaining()) {

            leftovers = ByteBuffer.allocate(b.remaining()).put(b).flip();

        } else {

            leftovers = EMPTY_BYTEBUFFER;

        }

        // Since it's UTF-8, the assumption is leftovers.remaining() < 4

        // (i.e. small). Otherwise a shared buffer should be used

        if (!(leftovers.remaining() < 4)) {

            Log.logError("The size of decoding leftovers is greater than expected: {0}",

                         leftovers.remaining());

        }

        b.position(b.limit()); // As if we always read to the end

        // Decoder promises that in the case of endOfInput == true:

        // "...any remaining undecoded input will be treated as being

        // malformed"

        assert !(endOfInput && leftovers.hasRemaining()) : endOfInput + ", " + leftovers;

        if (endOfInput) {

            r = decoder.flush(out);

            decoder.reset();

            if (r.isOverflow()) {

                // FIXME: for now I know flush() does nothing. But the

                // implementation of UTF8 decoder might change. And if now

                // flush() is a no-op, it is not guaranteed to remain so in

                // the future

                throw new InternalError("Not yet implemented");

            }

        }

        return out.flip();

    }

}