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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 under the License.
 */
package org.apache.catalina.websocket;

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CoderResult;

import org.apache.tomcat.util.buf.B2CConverter;

/**
 * Decodes bytes to UTF-8. Extracted from Apache Harmony and modified to reject
 * code points from U+D800 to U+DFFF as per RFC3629. The standard Java decoder
 * does not reject these.
 */
public class Utf8Decoder extends CharsetDecoder {

    // The next table contains information about UTF-8 charset and
    // correspondence of 1st byte to the length of sequence
    // For information please visit http://www.ietf.org/rfc/rfc3629.txt
    //
    // Please note, o means 0, actually.
    // -------------------------------------------------------------------
    // 0         1         2         3          Value
    // -------------------------------------------------------------------
    // oxxxxxxx                                 00000000 00000000 0xxxxxxx
    // 11oyyyyy  1oxxxxxx                       00000000 00000yyy yyxxxxxx
    // 111ozzzz  1oyyyyyy  1oxxxxxx             00000000 zzzzyyyy yyxxxxxx
    // 1111ouuu  1ouuzzzz  1oyyyyyy  1oxxxxxx   000uuuuu zzzzyyyy yyxxxxxx

    private static final int remainingBytes[] = {
            // 1owwwwww
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            // 11oyyyyy
            1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
            1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
            // 111ozzzz
            2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
            // 1111ouuu
            3, 3, 3, 3, 3, 3, 3, 3,
            // > 11110111
            -1, -1, -1, -1, -1, -1, -1, -1 };

    private static final int remainingNumbers[] = {
                   0, //                0                 1                2           3
                4224, // (01o00000b <<  6)+(1o000000b)
              401536, // (011o0000b << 12)+(1o000000b <<  6)+(1o000000b)
            29892736  // (0111o000b << 18)+(1o000000b << 12)+(1o000000b << 6)+(1o000000b)
    };

    private static final int lowerEncodingLimit[] = { -1, 0x80, 0x800, 0x10000 };

    public Utf8Decoder() {
        super(B2CConverter.UTF_8, 1.0f, 1.0f);
    }

    @Override
    protected CoderResult decodeLoop(ByteBuffer in, CharBuffer out) {
        if (in.hasArray() && out.hasArray()) {
            return decodeHasArray(in, out);
        }
        return decodeNotHasArray(in, out);
    }

    private CoderResult decodeNotHasArray(ByteBuffer in, CharBuffer out) {
        int outRemaining = out.remaining();
        int pos = in.position();
        int limit = in.limit();
        try {
            while (pos < limit) {
                if (outRemaining == 0) {
                    return CoderResult.OVERFLOW;
                }

                int jchar = in.get();
                if (jchar < 0) {
                    jchar = jchar & 0x7F;
                    int tail = remainingBytes[jchar];
                    if (tail == -1) {
                        return CoderResult.malformedForLength(1);
                    }
                    if (limit - pos < 1 + tail) {
                        return CoderResult.UNDERFLOW;
                    }

                    int nextByte;
                    for (int i = 0; i < tail; i++) {
                        nextByte = in.get() & 0xFF;
                        if ((nextByte & 0xC0) != 0x80) {
                            return CoderResult
                                    .malformedForLength(1 + i);
                        }
                        jchar = (jchar << 6) + nextByte;
                    }
                    jchar -= remainingNumbers[tail];
                    if (jchar < lowerEncodingLimit[tail]) {
                        // Should have been encoded in a fewer octets
                        return CoderResult.malformedForLength(1);
                    }
                    pos += tail;
                }
                if (jchar <= 0xffff) {
                  out.put((char) jchar);
                  outRemaining--;
                } else {
                  if (outRemaining < 2) {
                      return CoderResult.OVERFLOW;
                  }
                  out.put((char) ((jchar >> 0xA) + 0xD7C0));
                  out.put((char) ((jchar & 0x3FF) + 0xDC00));
                  outRemaining -= 2;
                }
                pos++;
            }
            return CoderResult.UNDERFLOW;
        } finally {
            in.position(pos);
        }
    }

    private CoderResult decodeHasArray(ByteBuffer in, CharBuffer out) {
        int outRemaining = out.remaining();
        int pos = in.position();
        int limit = in.limit();
        final byte[] bArr = in.array();
        final char[] cArr = out.array();
        final int inIndexLimit = limit + in.arrayOffset();

        int inIndex = pos + in.arrayOffset();
        int outIndex = out.position() + out.arrayOffset();

        // if someone would change the limit in process,
        // he would face consequences
        for (; inIndex < inIndexLimit && outRemaining > 0; inIndex++) {
            int jchar = bArr[inIndex];
            if (jchar < 0) {
                jchar = jchar & 0x7F;
                int tail = remainingBytes[jchar];

                if (tail == -1) {
                    in.position(inIndex - in.arrayOffset());
                    out.position(outIndex - out.arrayOffset());
                    return CoderResult.malformedForLength(1);
                }
                if (inIndexLimit - inIndex < 1 + tail) {
                    break;
                }

                for (int i = 0; i < tail; i++) {
                    int nextByte = bArr[inIndex + i + 1] & 0xFF;
                    if ((nextByte & 0xC0) != 0x80) {
                        in.position(inIndex - in.arrayOffset());
                        out.position(outIndex - out.arrayOffset());
                        return CoderResult.malformedForLength(1 + i);
                    }
                    jchar = (jchar << 6) + nextByte;
                }
                jchar -= remainingNumbers[tail];
                if (jchar < lowerEncodingLimit[tail]) {
                    // Should have been encoded in fewer octets
                    in.position(inIndex - in.arrayOffset());
                    out.position(outIndex - out.arrayOffset());
                    return CoderResult.malformedForLength(1);
                }
                inIndex += tail;
            }
            // Note: This is the additional test added
            if (jchar >= 0xD800 && jchar <=0xDFFF) {
                return CoderResult.unmappableForLength(3);
            }
            if (jchar <= 0xffff) {
              cArr[outIndex++] = (char) jchar;
              outRemaining--;
            } else {
              if (outRemaining < 2) {
                  return CoderResult.OVERFLOW;
              }
              cArr[outIndex++] = (char) ((jchar >> 0xA) + 0xD7C0);
              cArr[outIndex++] = (char) ((jchar & 0x3FF) + 0xDC00);
              outRemaining -= 2;
            }
        }
        in.position(inIndex - in.arrayOffset());
        out.position(outIndex - out.arrayOffset());
        return (outRemaining == 0 && inIndex < inIndexLimit) ?
                CoderResult.OVERFLOW :
                CoderResult.UNDERFLOW;
    }
}




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