Utf8Validator

/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project 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
 * under the License.
 */
/*
 * Adaptation of http://bjoern.hoehrmann.de/utf-8/decoder/dfa/
 *
 * Copyright (c) 2008-2009 Bjoern Hoehrmann <[email protected]>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
 * and associated documentation files (the "Software"), to deal in the Software without restriction,
 * including without limitation the rights to use, copy, modify, merge, publish, distribute,
 * sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies or
 * substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING
 * BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
package org.jboss.netty.handler.codec.http.websocketx;

import org.jboss.netty.handler.codec.frame.CorruptedFrameException;

/**
 * Checks UTF8 bytes for validity before converting it into a string
 */
final class Utf8Validator {
    private static final int UTF8_ACCEPT = 0;
    private static final int UTF8_REJECT = 12;

    private static final byte[] TYPES = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1,
            1, 1, 1, 1, 1, 1, 1, 1, 1, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 7, 7, 7, 7,
            7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 8,
            8, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
            2, 2, 10, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 3, 3, 11, 6, 6, 6, 5, 8, 8, 8, 8, 8,
            8, 8, 8, 8, 8, 8 };

    private static final byte[] STATES = { 0, 12, 24, 36, 60, 96, 84, 12, 12, 12, 48, 72, 12, 12,
            12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 0, 12, 12, 12, 12, 12, 0, 12, 0, 12, 12,
            12, 24, 12, 12, 12, 12, 12, 24, 12, 24, 12, 12, 12, 12, 12, 12, 12, 12, 12, 24, 12, 12,
            12, 12, 12, 24, 12, 12, 12, 12, 12, 12, 12, 24, 12, 12, 12, 12, 12, 12, 12, 12, 12, 36,
            12, 36, 12, 12, 12, 36, 12, 12, 12, 12, 12, 36, 12, 36, 12, 12, 12, 36, 12, 12, 12, 12,
            12, 12, 12, 12, 12, 12 };

    @SuppressWarnings("RedundantFieldInitialization")
    private int state = UTF8_ACCEPT;
    private int codep;
    private boolean checking;

    public void check(byte[] bytes) throws CorruptedFrameException {
        checking = true;
        for (byte b : bytes) {
            write(b);
        }
    }

    private void write(int b) throws CorruptedFrameException {
        byte type = TYPES[b & 0xFF];

        codep = state != UTF8_ACCEPT ? b & 0x3f | codep << 6 : 0xff >> type & b;

        state = STATES[state + type];

        if (state == UTF8_REJECT) {
            throw new CorruptedFrameException("bytes are not UTF-8");
        }
    }

    public void finish() throws CorruptedFrameException {
        checking = false;
        codep = 0;
        if (state != UTF8_ACCEPT) {
            state = UTF8_ACCEPT;
            throw new CorruptedFrameException("bytes are not UTF-8");
        }
    }

    public boolean isChecking() {
        return checking;
    }
}