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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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.incubator.http.internal.websocket;

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.lang.System.Logger.Level.WARNING;
import static java.nio.charset.StandardCharsets.UTF_8;
import static jdk.incubator.http.internal.common.Utils.EMPTY_BYTEBUFFER;
import static jdk.incubator.http.internal.websocket.WebSocketImpl.logger;

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)) {
            logger.log(WARNING,
                       "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();
    }
}