    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.fileupload.util.mime;
    018
    019import java.io.ByteArrayOutputStream;
    020import java.io.UnsupportedEncodingException;
    021import java.util.Base64;
    022import java.util.HashMap;
    023import java.util.Locale;
    024import java.util.Map;
    025
    026/**
    027 * Utility class to decode MIME texts.
    028 *
    029 * @since 1.3
    030 */
    031public final class MimeUtility {
    032
    033    /**
    034     * The {@code US-ASCII} charset identifier constant.
    035     */
    036    private static final String US_ASCII_CHARSET = "US-ASCII";
    037
    038    /**
    039     * The marker to indicate text is encoded with BASE64 algorithm.
    040     */
    041    private static final String BASE64_ENCODING_MARKER = "B";
    042
    043    /**
    044     * The marker to indicate text is encoded with QuotedPrintable algorithm.
    045     */
    046    private static final String QUOTEDPRINTABLE_ENCODING_MARKER = "Q";
    047
    048    /**
    049     * If the text contains any encoded tokens, those tokens will be marked with "=?".
    050     */
    051    private static final String ENCODED_TOKEN_MARKER = "=?";
    052
    053    /**
    054     * If the text contains any encoded tokens, those tokens will terminate with "=?".
    055     */
    056    private static final String ENCODED_TOKEN_FINISHER = "?=";
    057
    058    /**
    059     * The linear whitespace chars sequence.
    060     */
    061    private static final String LINEAR_WHITESPACE = " \t\r\n";
    062
    063    /**
    064     * Mappings between MIME and Java charset.
    065     */
    066    private static final Map<String, String> MIME2JAVA = new HashMap<>();
    067
    068    static {
    069        MIME2JAVA.put("iso-2022-cn", "ISO2022CN");
    070        MIME2JAVA.put("iso-2022-kr", "ISO2022KR");
    071        MIME2JAVA.put("utf-8", "UTF8");
    072        MIME2JAVA.put("utf8", "UTF8");
    073        MIME2JAVA.put("ja_jp.iso2022-7", "ISO2022JP");
    074        MIME2JAVA.put("ja_jp.eucjp", "EUCJIS");
    075        MIME2JAVA.put("euc-kr", "KSC5601");
    076        MIME2JAVA.put("euckr", "KSC5601");
    077        MIME2JAVA.put("us-ascii", "ISO-8859-1");
    078        MIME2JAVA.put("x-us-ascii", "ISO-8859-1");
    079    }
    080
    081    /**
    082     * Decode a string of text obtained from a mail header into
    083     * its proper form.  The text generally will consist of a
    084     * string of tokens, some of which may be encoded using
    085     * base64 encoding.
    086     *
    087     * @param text   The text to decode.
    088     * @return The decoded text string.
    089     * @throws UnsupportedEncodingException if the detected encoding in the input text is not supported.
    090     */
    091    public static String decodeText(final String text) throws UnsupportedEncodingException {
    092        // if the text contains any encoded tokens, those tokens will be marked with "=?".  If the
    093        // source string doesn't contain that sequent, no decoding is required.
    094        if (!text.contains(ENCODED_TOKEN_MARKER)) {
    095            return text;
    096        }
    097
    098        int offset = 0;
    099        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}