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package org.ietf.ldap.util;

/** Implements a plaintext -> Base64 encoder.
 */
public final class MimeBase64Decoder extends MimeEncoder {

    static final long serialVersionUID = 797397585345375903L;
    private byte token[] = new byte[4];      // input buffer
    private byte bytes[] = new byte[3];      // output buffer
    private int token_length = 0;            // input buffer length

    static private final byte NUL = 127;     // must be out of range 0-64
    static private final byte EOF = 126;     // must be out of range 0-64

    static private final byte map[] = {
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   000-007
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   010-017
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   020-027
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   030-037
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   040-047   !"#$%&'
      NUL, NUL, NUL,  62, NUL, NUL, NUL,  63,      //   050-057  ()*+,-./
       52,  53,  54,  55,  56,  57,  58,  59,      //   060-067  01234567
       60,  61, NUL, NUL, NUL, EOF, NUL, NUL,      //   070-077  89:;<=>?

      NUL,   0,   1,   2,   3,   4,   5,   6,      //   100-107  @ABCDEFG
        7,   8,   9,  10,  11,  12,  13,  14,      //   110-117  HIJKLMNO
       15,  16,  17,  18,  19,  20,  21,  22,      //   120-127  PQRSTUVW
       23,  24,  25, NUL, NUL, NUL, NUL, NUL,      //   130-137  XYZ[\]^_
      NUL,  26,  27,  28,  29,  30,  31,  32,      //   140-147  `abcdefg
       33,  34,  35,  36,  37,  38,  39,  40,      //   150-157  hijklmno
       41,  42,  43,  44,  45,  46,  47,  48,      //   160-167  pqrstuvw
       49,  50,  51, NUL, NUL, NUL, NUL, NUL,      //   170-177  xyz{|}~

      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   200-207
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   210-217
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   220-227
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   230-237
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   240-247
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   250-257
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   260-267
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   270-277

      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   300-307
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   310-317
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   320-327
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   330-337
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   340-347
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   350-357
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   360-367
      NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   370-377
    };


    // Fast routine that assumes full 4-char tokens with no '=' in them.
    //
    private final void decode_token(ByteBuf out) {
        int num = ((map[token[0]] << 18) |
                   (map[token[1]] << 12) |
                   (map[token[2]] << 6) |
                   (map[token[3]]));

        bytes[0] = (byte) (0xFF & (num >> 16));
        bytes[1] = (byte) (0xFF & (num >> 8));
        bytes[2] = (byte) (0xFF & num);

        out.append(bytes);
    }


    // Hairier routine that deals with the final token, which can have fewer
    // than four characters, and that might be padded with '='.
    //
    private final void decode_final_token(ByteBuf out) {

        byte b0 = map[token[0]];
        byte b1 = map[token[1]];
        byte b2 = map[token[2]];
        byte b3 = map[token[3]];

        int eq_count = 0;

        if (b0 == EOF) { b0 = 0; eq_count++; }
        if (b1 == EOF) { b1 = 0; eq_count++; }
        if (b2 == EOF) { b2 = 0; eq_count++; }
        if (b3 == EOF) { b3 = 0; eq_count++; }

        int num = ((b0 << 18) | (b1 << 12) | (b2 << 6) | (b3));

        // eq_count will be 0, 1, or 2.
        // No "=" padding means 4 bytes mapped to 3, the normal case,
        //        not handled in this routine.
        // "xxx=" means 3 bytes mapped to 2.
        // "xx==" means 2 bytes mapped to 1.
        // "x===" can't happen, because "x" would then be encoding
        //        only 6 bits, not 8, the minimum possible.

        out.append((byte) (num >> 16));             // byte 1, count = 0 or 1 or 2
        if (eq_count <= 1) {
            out.append((byte) ((num >> 8) & 0xFF)); // byte 2, count = 0 or 1
            if (eq_count == 0) {
                out.append((byte) (num & 0xFF));    // byte 3, count = 0
            }
        }
    }


    /** Given a sequence of input bytes using the Base64 encoding, produces a
        sequence of unencoded output bytes.  Note that some (small) amount of
        buffering may be necessary, if the input byte stream didn't fall on an
        appropriate boundary.  If there are bytes in `out' already, the new
        bytes are appended, so the caller should do `out.setLength(0)' first
        if that's desired.
     */
    public final void translate(ByteBuf in, ByteBuf out) {

        if (token == null) // already saw eof marker?
            return;

        byte inb[] = in.toBytes();
        int in_length = in.length();

        for (int i = 0; i < in_length; i++) {
            byte b = inb[i];
                  int x=(b&0xff);
            byte t = map[x];

            if (t != NUL)
                token[token_length++] = b;

            if (t == EOF) {
                eof(out);
                return;
            } else if (token_length == 4) {
                decode_token(out);
                token_length = 0;
            }
        }
    }


    /** Tell the Base64 decoder that no more input data will be forthcoming.
        This may result in output, as a result of flushing the internal buffer.
        This object must not be used again after calling eof().  If there are
        bytes in `out' already, the new bytes are appended, so the caller should
        do `out.setLength(0)' first if that's desired.
     */
    public final void eof(ByteBuf out) {
        if (token != null && token_length != 0) {
            while (token_length < 4)
                token[token_length++] = (byte)'=';
            decode_final_token(out);
        }
        token_length = 0;
        token = new byte[4];
        bytes = new byte[3];
    }
}
