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    1   /*
    2    * Licensed to the Apache Software Foundation (ASF) under one or more
    3    * contributor license agreements.  See the NOTICE file distributed with
    4    * this work for additional information regarding copyright ownership.
    5    * The ASF licenses this file to You under the Apache License, Version 2.0
    6    * (the "License"); you may not use this file except in compliance with
    7    * the License.  You may obtain a copy of the License at
    8    *
    9    *      http://www.apache.org/licenses/LICENSE-2.0
    10   *
    11   * Unless required by applicable law or agreed to in writing, software
    12   * distributed under the License is distributed on an "AS IS" BASIS,
    13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    14   * See the License for the specific language governing permissions and
    15   * limitations under the License.
    16   */
    17
    18  package org.apache.commons.fileupload;
    19
    20  import java.io.ByteArrayOutputStream;
    21  import java.io.UnsupportedEncodingException;
    22
    23  /**
    24   * Utility class to decode/encode character set on HTTP Header fields based on RFC 2231. This implementation adheres to RFC 5987 in particular, which was
    25   * defined for HTTP headers.
    26   * <p>
    27   * RFC 5987 builds on RFC 2231, but has lesser scope like <a href="https://tools.ietf.org/html/rfc5987#section-3.2">mandatory charset definition</a> and
    28   * <a href="https://tools.ietf.org/html/rfc5987#section-4">no parameter continuation</a>
    29   * </p>
    30   *
    31   * @see <a href="https://tools.ietf.org/html/rfc2231">RFC 2231</a>
    32   * @see <a href="https://tools.ietf.org/html/rfc5987">RFC 5987</a>
    33   */
    34  final class RFC2231Utility {
    35
    36      /**
    37       * Percent character '{@value}'.
    38       */
    39      private static final char PERCENT = '%';
    40      /**
    41       * The Hexadecimal values char array.
    42       */
    43      private static final char[] HEX_DIGITS = "0123456789ABCDEF".toCharArray();
    44      /**
    45       * The Hexadecimal representation of 127.
    46       */
    47      private static final byte MASK = 0x7f;
    48      /**
    49       * The Hexadecimal representation of 128.
    50       */
    51      private static final int MASK_128 = 0x80;
    52      /**
    53       * The Hexadecimal decode value.
    54       */
    55      private static final byte[] HEX_DECODE = new byte[MASK_128];
    56      // create a ASCII decoded array of Hexadecimal values
    57      static {
    58          for (int i = 0; i < HEX_DIGITS.length; i++) {
    59              HEX_DECODE[HEX_DIGITS[i]] = (byte) i;
    60              HEX_DECODE[Character.toLowerCase(HEX_DIGITS[i])] = (byte) i;
    61          }
    62      }
    63
    64      /**
    65       * Decodes a string of text obtained from a HTTP header as per RFC 2231
    66       * <p>
    67       * <strong>Eg 1.</strong> {@code us-ascii'en-us'This%20is%20%2A%2A%2Afun%2A%2A%2A} will be decoded to {@code This is ***fun***}
    68       * </p>
    69       * <p>
    70       * <strong>Eg 2.</strong> {@code iso-8859-1'en'%A3%20rate} will be decoded to {@code £ rate}
    71       * </p>
    72       * <p>
    73       * <strong>Eg 3.</strong> {@code UTF-8''%c2%a3%20and%20%e2%82%ac%20rates} will be decoded to {@code £ and € rates}
    74       * </p>
    75       *
    76       * @param encodedText Text to be decoded has a format of {@code <charset>'<language>'<encoded_value>} and ASCII only
    77       * @return Decoded text based on charset encoding
    78       * @throws UnsupportedEncodingException The requested character set wasn't found.
    79       */
    80      static String decodeText(final String encodedText) throws UnsupportedEncodingException {
    81          final int langDelimitStart = encodedText.indexOf('\'');
    82          if (langDelimitStart == -1) {
    83              // missing charset
    84              return encodedText;
    85          }
    86          final String mimeCharset = encodedText.substring(0, langDelimitStart);
    87          final int langDelimitEnd = encodedText.indexOf('\'', langDelimitStart + 1);
    88          if (langDelimitEnd == -1) {
    89              // missing language
    90              return encodedText;
    91          }
    92          final byte[] bytes = fromHex(encodedText.substring(langDelimitEnd + 1));
    93          return new String(bytes, getJavaCharset(mimeCharset));
    94      }
    95
    96      /**
    97       * Converts {@code text} to their corresponding Hex value.
    98       *
    99       * @param text ASCII text input
    100      * @return Byte array of characters decoded from ASCII table
    101      */
    102     private static byte[] fromHex(final String text) {
    103         final int shift = 4;
    104         final ByteArrayOutputStream out = new ByteArrayOutputStream(text.length());
    105         for (int i = 0; i < text.length();) {
    106             final char c = text.charAt(i++);
    107             if (c == PERCENT) {
    108                 if (i > text.length() - 2) {
    109                     break; // unterminated sequence
    110                 }
    111                 final byte b1 = HEX_DECODE[text.charAt(i++) & MASK];
    112                 final byte b2 = HEX_DECODE[text.charAt(i++) & MASK];
    113                 out.write(b1 << shift | b2);
    114             } else {
    115                 out.write((byte) c);
    116             }
    117         }
    118         return out.toByteArray();
    119     }
    120
    121     private static String getJavaCharset(final String mimeCharset) {
    122         // good enough for standard values
    123         return mimeCharset;
    124     }
    125
    126     /**
    127      * Checks if Asterisk (*) at the end of parameter name to indicate, if it has charset and language information to decode the value.
    128      *
    129      * @param paramName The parameter, which is being checked.
    130      * @return {@code true}, if encoded as per RFC 2231, {@code false} otherwise
    131      */
    132     static boolean hasEncodedValue(final String paramName) {
    133         if (paramName != null) {
    134             return paramName.lastIndexOf('*') == paramName.length() - 1;
    135         }
    136         return false;
    137     }
    138
    139     /**
    140      * If {@code paramName} has Asterisk (*) at the end, it will be stripped off, else the passed value will be returned.
    141      *
    142      * @param paramName The parameter, which is being inspected.
    143      * @return stripped {@code paramName} of Asterisk (*), if RFC2231 encoded
    144      */
    145     static String stripDelimiter(final String paramName) {
    146         if (hasEncodedValue(paramName)) {
    147             final StringBuilder paramBuilder = new StringBuilder(paramName);
    148             paramBuilder.deleteCharAt(paramName.lastIndexOf('*'));
    149             return paramBuilder.toString();
    150         }
    151         return paramName;
    152     }
    153
    154     /**
    155      * Private constructor so that no instances can be created. This class contains only static utility methods.
    156      */
    157     private RFC2231Utility() {
    158     }
    159 }