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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  package org.apache.commons.fileupload.util.mime;
    18
    19  import java.io.ByteArrayOutputStream;
    20  import java.io.UnsupportedEncodingException;
    21  import java.util.Base64;
    22  import java.util.HashMap;
    23  import java.util.Locale;
    24  import java.util.Map;
    25
    26  /**
    27   * Utility class to decode MIME texts.
    28   *
    29   * @since 1.3
    30   */
    31  public final class MimeUtility {
    32
    33      /**
    34       * The {@code US-ASCII} charset identifier constant.
    35       */
    36      private static final String US_ASCII_CHARSET = "US-ASCII";
    37
    38      /**
    39       * The marker to indicate text is encoded with BASE64 algorithm.
    40       */
    41      private static final String BASE64_ENCODING_MARKER = "B";
    42
    43      /**
    44       * The marker to indicate text is encoded with QuotedPrintable algorithm.
    45       */
    46      private static final String QUOTEDPRINTABLE_ENCODING_MARKER = "Q";
    47
    48      /**
    49       * If the text contains any encoded tokens, those tokens will be marked with "=?".
    50       */
    51      private static final String ENCODED_TOKEN_MARKER = "=?";
    52
    53      /**
    54       * If the text contains any encoded tokens, those tokens will terminate with "=?".
    55       */
    56      private static final String ENCODED_TOKEN_FINISHER = "?=";
    57
    58      /**
    59       * The linear whitespace chars sequence.
    60       */
    61      private static final String LINEAR_WHITESPACE = " \t\r\n";
    62
    63      /**
    64       * Mappings between MIME and Java charset.
    65       */
    66      private static final Map<String, String> MIME2JAVA = new HashMap<>();
    67
    68      static {
    69          MIME2JAVA.put("iso-2022-cn", "ISO2022CN");
    70          MIME2JAVA.put("iso-2022-kr", "ISO2022KR");
    71          MIME2JAVA.put("utf-8", "UTF8");
    72          MIME2JAVA.put("utf8", "UTF8");
    73          MIME2JAVA.put("ja_jp.iso2022-7", "ISO2022JP");
    74          MIME2JAVA.put("ja_jp.eucjp", "EUCJIS");
    75          MIME2JAVA.put("euc-kr", "KSC5601");
    76          MIME2JAVA.put("euckr", "KSC5601");
    77          MIME2JAVA.put("us-ascii", "ISO-8859-1");
    78          MIME2JAVA.put("x-us-ascii", "ISO-8859-1");
    79      }
    80
    81      /**
    82       * Decode a string of text obtained from a mail header into
    83       * its proper form.  The text generally will consist of a
    84       * string of tokens, some of which may be encoded using
    85       * base64 encoding.
    86       *
    87       * @param text   The text to decode.
    88       * @return The decoded text string.
    89       * @throws UnsupportedEncodingException if the detected encoding in the input text is not supported.
    90       */
    91      public static String decodeText(final String text) throws UnsupportedEncodingException {
    92          // if the text contains any encoded tokens, those tokens will be marked with "=?".  If the
    93          // source string doesn't contain that sequent, no decoding is required.
    94          if (!text.contains(ENCODED_TOKEN_MARKER)) {
    95              return text;
    96          }
    97
    98          int offset = 0;
    99          final int endOffset = text.length();
    100
    101         int startWhiteSpace = -1;
    102         int endWhiteSpace = -1;
    103
    104         final StringBuilder decodedText = new StringBuilder(text.length());
    105
    106         boolean previousTokenEncoded = false;
    107
    108         while (offset < endOffset) {
    109             char ch = text.charAt(offset);
    110
    111             // is this a whitespace character?
    112             if (LINEAR_WHITESPACE.indexOf(ch) != -1) { // whitespace found
    113                 startWhiteSpace = offset;
    114                 while (offset < endOffset) {
    115                     // step over the white space characters.
    116                     ch = text.charAt(offset);
    117                     if (LINEAR_WHITESPACE.indexOf(ch) == -1) {
    118                         // record the location of the first non lwsp and drop down to process the
    119                         // token characters.
    120                         endWhiteSpace = offset;
    121                         break;
    122                     }
    123                     offset++;
    124                 }
    125             } else {
    126                 // we have a word token.  We need to scan over the word and then try to parse it.
    127                 final int wordStart = offset;
    128
    129                 while (offset < endOffset) {
    130                     // step over the non white space characters.
    131                     ch = text.charAt(offset);
    132                     if (LINEAR_WHITESPACE.indexOf(ch) != -1) {
    133                         break;
    134                     }
    135                     offset++;
    136
    137                     //NB:  Trailing whitespace on these header strings will just be discarded.
    138                 }
    139                 // pull out the word token.
    140                 final String word = text.substring(wordStart, offset);
    141                 // is the token encoded?  decode the word
    142                 if (word.startsWith(ENCODED_TOKEN_MARKER)) {
    143                     try {
    144                         // if this gives a parsing failure, treat it like a non-encoded word.
    145                         final String decodedWord = decodeWord(word);
    146
    147                         // are any whitespace characters significant?  Append 'em if we've got 'em.
    148                         if (!previousTokenEncoded && startWhiteSpace != -1) {
    149                             decodedText.append(text, startWhiteSpace, endWhiteSpace);
    150                             startWhiteSpace = -1;
    151                         }
    152                         // this is definitely a decoded token.
    153                         previousTokenEncoded = true;
    154                         // and add this to the text.
    155                         decodedText.append(decodedWord);
    156                         // we continue parsing from here...we allow parsing errors to fall through
    157                         // and get handled as normal text.
    158                         continue;
    159
    160                     } catch (final ParseException e) {
    161                         // just ignore it, skip to next word
    162                     }
    163                 }
    164                 // this is a normal token, so it doesn't matter what the previous token was.  Add the white space
    165                 // if we have it.
    166                 if (startWhiteSpace != -1) {
    167                     decodedText.append(text, startWhiteSpace, endWhiteSpace);
    168                     startWhiteSpace = -1;
    169                 }
    170                 // this is not a decoded token.
    171                 previousTokenEncoded = false;
    172                 decodedText.append(word);
    173             }
    174         }
    175
    176         return decodedText.toString();
    177     }
    178
    179     /**
    180      * Parse a string using the RFC 2047 rules for an "encoded-word"
    181      * type.  This encoding has the syntax:
    182      *
    183      * encoded-word = "=?" charset "?" encoding "?" encoded-text "?="
    184      *
    185      * @param word   The possibly encoded word value.
    186      * @return The decoded word.
    187      * @throws ParseException in case of a parse error of the RFC 2047
    188      * @throws UnsupportedEncodingException Thrown when Invalid RFC 2047 encoding was found
    189      */
    190     private static String decodeWord(final String word) throws ParseException, UnsupportedEncodingException {
    191         // encoded words start with the characters "=?".  If this not an encoded word, we throw a
    192         // ParseException for the caller.
    193
    194         if (!word.startsWith(ENCODED_TOKEN_MARKER)) {
    195             throw new ParseException("Invalid RFC 2047 encoded-word: " + word);
    196         }
    197
    198         final int charsetPos = word.indexOf('?', 2);
    199         if (charsetPos == -1) {
    200             throw new ParseException("Missing charset in RFC 2047 encoded-word: " + word);
    201         }
    202
    203         // pull out the character set information (this is the MIME name at this point).
    204         final String charset = word.substring(2, charsetPos).toLowerCase(Locale.ROOT);
    205
    206         // now pull out the encoding token the same way.
    207         final int encodingPos = word.indexOf('?', charsetPos + 1);
    208         if (encodingPos == -1) {
    209             throw new ParseException("Missing encoding in RFC 2047 encoded-word: " + word);
    210         }
    211
    212         final String encoding = word.substring(charsetPos + 1, encodingPos);
    213
    214         // and finally the encoded text.
    215         final int encodedTextPos = word.indexOf(ENCODED_TOKEN_FINISHER, encodingPos + 1);
    216         if (encodedTextPos == -1) {
    217             throw new ParseException("Missing encoded text in RFC 2047 encoded-word: " + word);
    218         }
    219
    220         final String encodedText = word.substring(encodingPos + 1, encodedTextPos);
    221
    222         // seems a bit silly to encode a null string, but easy to deal with.
    223         if (encodedText.isEmpty()) {
    224             return "";
    225         }
    226
    227         try {
    228             // the decoder writes directly to an output stream.
    229             final ByteArrayOutputStream out = new ByteArrayOutputStream(encodedText.length());
    230
    231             final byte[] encodedData = encodedText.getBytes(US_ASCII_CHARSET);
    232
    233             // Base64 encoded?
    234             if (encoding.equals(BASE64_ENCODING_MARKER)) {
    235                 out.write(Base64.getDecoder().decode(encodedData));
    236             } else if (encoding.equals(QUOTEDPRINTABLE_ENCODING_MARKER)) { // maybe quoted printable.
    237                 QuotedPrintableDecoder.decode(encodedData, out);
    238             } else {
    239                 throw new UnsupportedEncodingException("Unknown RFC 2047 encoding: " + encoding);
    240             }
    241             // get the decoded byte data and convert into a string.
    242             final byte[] decodedData = out.toByteArray();
    243             return new String(decodedData, javaCharset(charset));
    244         } catch (final Exception e) {
    245             throw new UnsupportedEncodingException("Invalid RFC 2047 encoding");
    246         }
    247     }
    248
    249     /**
    250      * Translate a MIME standard character set name into the Java
    251      * equivalent.
    252      *
    253      * @param charset The MIME standard name.
    254      * @return The Java equivalent for this name.
    255      */
    256     private static String javaCharset(final String charset) {
    257         // nothing in, nothing out.
    258         if (charset == null) {
    259             return null;
    260         }
    261
    262         final String mappedCharset = MIME2JAVA.get(charset.toLowerCase(Locale.ROOT));
    263         // if there is no mapping, then the original name is used.  Many of the MIME character set
    264         // names map directly back into Java.  The reverse isn't necessarily true.
    265         if (mappedCharset == null) {
    266             return charset;
    267         }
    268         return mappedCharset;
    269     }
    270
    271     /**
    272      * Hidden constructor, this class must not be instantiated.
    273      */
    274     private MimeUtility() {
    275         // do nothing
    276     }
    277
    278 }