ByteCursor.java

/*
 * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
 * 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.
 *
 * 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.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

class ByteCursor {
    private int offset;
    private byte[] data;

    public ByteCursor(byte[] data) {
        this.offset = 0;
        this.data = data;
    }

    public int getOffset() {
        return offset;
    }

    public void skipBytes(int n) {
        offset += n;
    }

    public int readUnsignedByte() {
        int val = readUnsignedByteAt(offset);
        offset += 1;
        return val;
    }

    public int readUnsignedByteAt(int offset) {
        return data[offset++] & 0xff;
    }

    public int readUnsignedShort() {
        int val = readUnsignedShortAt(offset);
        offset += 2;
        return val;
    }

    public int readInt() {
        int val = readIntAt(offset);
        offset += 4;
        return val;
    }

    public int readUnsignedShortAt(int offset) {
        int b1 = data[offset++] & 0xff;
        int b2 = data[offset] & 0xff;

        return (b1 << 8) + b2;
    }

    public int readIntAt(int offset) {
        int s1 = readUnsignedShortAt(offset);
        int s2 = readUnsignedShortAt(offset + 2);
        return (s1 << 16) + s2;
    }

    public String readUtf8(int length) throws IllegalStateException {
        char str[] = new char[length];
        int count = 0;
        int pos = 0;
        while (count < length) {
            int c = readUnsignedByte();
            switch (c >> 4) {
                case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7: {
                    // 0xxxxxxx
                    count++;
                    if(c == '/') {
                        str[pos++] = '.';
                    } else {
                        str[pos++] = (char) c;
                    }
                    break;
                } case 12: case 13: {
                    // 110x xxxx   10xx xxxx
                    count += 2;
                    int c2 = readUnsignedByte();
                    if ((c2 & 0xC0) != 0x80) {
                        throw new IllegalStateException();
                    }
                    str[pos++] = (char) (((c & 0x1F) << 6) | (c2 & 0x3F));
                    break;
                } case 14: {
                    // 1110 xxxx  10xx xxxx  10xx xxxx
                    count += 3;
                    int c2 = readUnsignedByte();
                    int c3 = readUnsignedByte();
                    if ((c2 & 0xC0) != 0x80 || (c3 & 0xC0) != 0x80) {
                        throw new IllegalStateException();
                    }
                    str[pos++] = (char)(((c  & 0x0F) << 12) |
                                        ((c2 & 0x3F) << 6)  |
                                        ((c3 & 0x3F) << 0));
                    break;
                } default:
                    // 10xx xxxx,  1111 xxxx
                    throw new IllegalStateException();
            }
        }
        return new String(str);
    }
}