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/*
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 * Licensed to the Apache Software Foundation (ASF) under one
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 * or more contributor license agreements. See the NOTICE file
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 * distributed with this work for additional information
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 * regarding copyright ownership. The ASF licenses this file
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 * to you under the Apache License, Version 2.0 (the
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 * "License"); you may not use this file except in compliance
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 * with the License. You may obtain a copy of the License at
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 *
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 *   http://www.apache.org/licenses/LICENSE-2.0
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 *
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 * Unless required by applicable law or agreed to in writing,
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 * software distributed under the License is distributed on an
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 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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 * KIND, either express or implied. See the License for the
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 * specific language governing permissions and limitations
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 * under the License.
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 */
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package org.apache.thrift.protocol;
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/**
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 * Class for encoding and decoding Base64 data.
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 *
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 * This class is kept at package level because the interface does no input
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 * validation and is therefore too low-level for generalized reuse.
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 *
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 * Note also that the encoding does not pad with equal signs , as discussed in
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 * section 2.2 of the RFC (http://www.faqs.org/rfcs/rfc3548.html). Furthermore,
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 * bad data encountered when decoding is neither rejected or ignored but simply
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 * results in bad decoded data -- this is not in compliance with the RFC but is
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 * done in the interest of performance.
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 *
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 */
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class TBase64Utils {
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  private static final String ENCODE_TABLE =
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    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
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  /**
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   * Encode len bytes of data in src at offset srcOff, storing the result into
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   * dst at offset dstOff. len must be 1, 2, or 3. dst must have at least len+1
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   * bytes of space at dstOff. src and dst should not be the same object. This
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   * method does no validation of the input values in the interest of
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   * performance.
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   *
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   * @param src  the source of bytes to encode
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   * @param srcOff  the offset into the source to read the unencoded bytes
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   * @param len  the number of bytes to encode (must be 1, 2, or 3).
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   * @param dst  the destination for the encoding
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   * @param dstOff  the offset into the destination to place the encoded bytes
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   */
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  static final void encode(byte[] src, int srcOff, int len,  byte[] dst,
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                           int dstOff) {
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    dst[dstOff] = (byte)ENCODE_TABLE.charAt((src[srcOff] >> 2) & 0x3F);
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    if (len == 3) {
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      dst[dstOff + 1] =
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        (byte)ENCODE_TABLE.charAt(
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                         ((src[srcOff] << 4) + (src[srcOff+1] >> 4)) & 0x3F);
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      dst[dstOff + 2] =
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        (byte)ENCODE_TABLE.charAt(
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                         ((src[srcOff+1] << 2) + (src[srcOff+2] >> 6)) & 0x3F);
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      dst[dstOff + 3] =
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        (byte)ENCODE_TABLE.charAt(src[srcOff+2] & 0x3F);
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    }
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    else if (len == 2) {
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      dst[dstOff+1] =
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        (byte)ENCODE_TABLE.charAt(
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                          ((src[srcOff] << 4) + (src[srcOff+1] >> 4)) & 0x3F);
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      dst[dstOff + 2] =
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        (byte)ENCODE_TABLE.charAt((src[srcOff+1] << 2) & 0x3F);
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    }
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    else { // len == 1) {
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      dst[dstOff + 1] =
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        (byte)ENCODE_TABLE.charAt((src[srcOff] << 4) & 0x3F);
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    }
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  }
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  private static final byte[] DECODE_TABLE = {
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    -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
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    -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
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    -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,62,-1,-1,-1,63,
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    52,53,54,55,56,57,58,59,60,61,-1,-1,-1,-1,-1,-1,
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    -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10,11,12,13,14,
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    15,16,17,18,19,20,21,22,23,24,25,-1,-1,-1,-1,-1,
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    -1,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,
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    41,42,43,44,45,46,47,48,49,50,51,-1,-1,-1,-1,-1,
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    -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
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    -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
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    -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
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    -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
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    -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
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    -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
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    -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
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    -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
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  };
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  /**
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   * Decode len bytes of data in src at offset srcOff, storing the result into
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   * dst at offset dstOff. len must be 2, 3, or 4. dst must have at least len-1
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   * bytes of space at dstOff. src and dst may be the same object as long as
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   * dstoff <= srcOff. This method does no validation of the input values in
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   * the interest of performance.
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   *
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   * @param src  the source of bytes to decode
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   * @param srcOff  the offset into the source to read the encoded bytes
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   * @param len  the number of bytes to decode (must be 2, 3, or 4)
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   * @param dst  the destination for the decoding
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   * @param dstOff  the offset into the destination to place the decoded bytes
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   */
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  static final void decode(byte[] src, int srcOff, int len,  byte[] dst,
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                           int dstOff) {
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    dst[dstOff] = (byte)
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      ((DECODE_TABLE[src[srcOff] & 0x0FF] << 2) |
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       (DECODE_TABLE[src[srcOff+1] & 0x0FF] >> 4));
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    if (len > 2) {
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      dst[dstOff+1] = (byte)
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        (((DECODE_TABLE[src[srcOff+1] & 0x0FF] << 4) & 0xF0) |
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         (DECODE_TABLE[src[srcOff+2] & 0x0FF] >> 2));
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      if (len > 3) {
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        dst[dstOff+2] = (byte)
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          (((DECODE_TABLE[src[srcOff+2] & 0x0FF] << 6) & 0xC0) |
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           DECODE_TABLE[src[srcOff+3] & 0x0FF]);
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      }
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    }
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  }
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}