MimeUtils.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.fileupload2.core;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.nio.charset.StandardCharsets;
import java.text.ParseException;
import java.util.Base64;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;
/**
* Utility class to decode MIME texts.
*/
final class MimeUtils {
/**
* The marker to indicate text is encoded with BASE64 algorithm.
*/
private static final String BASE64_ENCODING_MARKER = "B";
/**
* The marker to indicate text is encoded with QuotedPrintable algorithm.
*/
private static final String QUOTEDPRINTABLE_ENCODING_MARKER = "Q";
/**
* If the text contains any encoded tokens, those tokens will be marked with "=?".
*/
private static final String ENCODED_TOKEN_MARKER = "=?";
/**
* If the text contains any encoded tokens, those tokens will terminate with "=?".
*/
private static final String ENCODED_TOKEN_FINISHER = "?=";
/**
* The linear whitespace chars sequence.
*/
private static final String LINEAR_WHITESPACE = " \t\r\n";
/**
* Mappings between MIME and Java charset.
*/
private static final Map<String, String> MIME2JAVA = new HashMap<>();
static {
MIME2JAVA.put("iso-2022-cn", "ISO2022CN");
MIME2JAVA.put("iso-2022-kr", "ISO2022KR");
MIME2JAVA.put("utf-8", "UTF8");
MIME2JAVA.put("utf8", "UTF8");
MIME2JAVA.put("ja_jp.iso2022-7", "ISO2022JP");
MIME2JAVA.put("ja_jp.eucjp", "EUCJIS");
MIME2JAVA.put("euc-kr", "KSC5601");
MIME2JAVA.put("euckr", "KSC5601");
MIME2JAVA.put("us-ascii", StandardCharsets.ISO_8859_1.name());
MIME2JAVA.put("x-us-ascii", StandardCharsets.ISO_8859_1.name());
}
/**
* Decodes a string of text obtained from a mail header into its proper form. The text generally will consist of a string of tokens, some of which may be
* encoded using base64 encoding.
*
* @param text The text to decode.
* @return The decoded text string.
* @throws UnsupportedEncodingException if the detected encoding in the input text is not supported.
*/
static String decodeText(final String text) throws UnsupportedEncodingException {
// if the text contains any encoded tokens, those tokens will be marked with "=?". If the
// source string doesn't contain that sequent, no decoding is required.
if (!text.contains(ENCODED_TOKEN_MARKER)) {
return text;
}
var offset = 0;
final var endOffset = text.length();
var startWhiteSpace = -1;
var endWhiteSpace = -1;
final var decodedText = new StringBuilder(text.length());
var previousTokenEncoded = false;
while (offset < endOffset) {
var ch = text.charAt(offset);
// is this a whitespace character?
if (LINEAR_WHITESPACE.indexOf(ch) != -1) { // whitespace found
startWhiteSpace = offset;
while (offset < endOffset) {
// step over the white space characters.
ch = text.charAt(offset);
if (LINEAR_WHITESPACE.indexOf(ch) == -1) {
// record the location of the first non lwsp and drop down to process the
// token characters.
endWhiteSpace = offset;
break;
}
offset++;
}
} else {
// we have a word token. We need to scan over the word and then try to parse it.
final var wordStart = offset;
while (offset < endOffset) {
// step over the non white space characters.
ch = text.charAt(offset);
if (LINEAR_WHITESPACE.indexOf(ch) != -1) {
break;
}
offset++;
// NB: Trailing whitespace on these header strings will just be discarded.
}
// pull out the word token.
final var word = text.substring(wordStart, offset);
// is the token encoded? decode the word
if (word.startsWith(ENCODED_TOKEN_MARKER)) {
try {
// if this gives a parsing failure, treat it like a non-encoded word.
final var decodedWord = decodeWord(word);
// are any whitespace characters significant? Append 'em if we've got 'em.
if (!previousTokenEncoded && startWhiteSpace != -1) {
decodedText.append(text, startWhiteSpace, endWhiteSpace);
startWhiteSpace = -1;
}
// this is definitely a decoded token.
previousTokenEncoded = true;
// and add this to the text.
decodedText.append(decodedWord);
// we continue parsing from here...we allow parsing errors to fall through
// and get handled as normal text.
continue;
} catch (final ParseException ignored) {
// just ignore it, skip to next word
}
}
// this is a normal token, so it doesn't matter what the previous token was. Add the white space
// if we have it.
if (startWhiteSpace != -1) {
decodedText.append(text, startWhiteSpace, endWhiteSpace);
startWhiteSpace = -1;
}
// this is not a decoded token.
previousTokenEncoded = false;
decodedText.append(word);
}
}
return decodedText.toString();
}
/**
* Decodes a string using the RFC 2047 rules for an "encoded-word" type. This encoding has the syntax:
*
* encoded-word = "=?" charset "?" encoding "?" encoded-text "?="
*
* @param word The possibly encoded word value.
* @return The decoded word.
* @throws ParseException in case of a parse error of the RFC 2047.
* @throws UnsupportedEncodingException Thrown when Invalid RFC 2047 encoding was found.
*/
private static String decodeWord(final String word) throws ParseException, UnsupportedEncodingException {
// encoded words start with the characters "=?". If this not an encoded word, we throw a
// ParseException for the caller.
final var etmPos = word.indexOf(ENCODED_TOKEN_MARKER);
if (etmPos != 0) {
throw new ParseException("Invalid RFC 2047 encoded-word: " + word, etmPos);
}
final var charsetPos = word.indexOf('?', 2);
if (charsetPos == -1) {
throw new ParseException("Missing charset in RFC 2047 encoded-word: " + word, charsetPos);
}
// pull out the character set information (this is the MIME name at this point).
final var charset = word.substring(2, charsetPos).toLowerCase(Locale.ROOT);
// now pull out the encoding token the same way.
final var encodingPos = word.indexOf('?', charsetPos + 1);
if (encodingPos == -1) {
throw new ParseException("Missing encoding in RFC 2047 encoded-word: " + word, encodingPos);
}
final var encoding = word.substring(charsetPos + 1, encodingPos);
// and finally the encoded text.
final var encodedTextPos = word.indexOf(ENCODED_TOKEN_FINISHER, encodingPos + 1);
if (encodedTextPos == -1) {
throw new ParseException("Missing encoded text in RFC 2047 encoded-word: " + word, encodedTextPos);
}
final var encodedText = word.substring(encodingPos + 1, encodedTextPos);
// seems a bit silly to encode a null string, but easy to deal with.
if (encodedText.isEmpty()) {
return "";
}
try {
// the decoder writes directly to an output stream.
final var out = new ByteArrayOutputStream(encodedText.length());
final var encodedData = encodedText.getBytes(StandardCharsets.US_ASCII);
// Base64 encoded?
if (encoding.equals(BASE64_ENCODING_MARKER)) {
out.write(Base64.getMimeDecoder().decode(encodedData));
} else if (encoding.equals(QUOTEDPRINTABLE_ENCODING_MARKER)) { // maybe quoted printable.
QuotedPrintableDecoder.decode(encodedData, out);
} else {
throw new UnsupportedEncodingException("Unknown RFC 2047 encoding: " + encoding);
}
// get the decoded byte data and convert into a string.
final var decodedData = out.toByteArray();
return new String(decodedData, javaCharset(charset));
} catch (final IOException e) {
throw new UnsupportedEncodingException("Invalid RFC 2047 encoding");
}
}
/**
* Translate a MIME standard character set name into the Java equivalent.
*
* @param charset The MIME standard name.
* @return The Java equivalent for this name.
*/
private static String javaCharset(final String charset) {
// nothing in, nothing out.
if (charset == null) {
return null;
}
final var mappedCharset = MIME2JAVA.get(charset.toLowerCase(Locale.ROOT));
// if there is no mapping, then the original name is used. Many of the MIME character set
// names map directly back into Java. The reverse isn't necessarily true.
return mappedCharset == null ? charset : mappedCharset;
}
/**
* Hidden constructor, this class must not be instantiated.
*/
private MimeUtils() {
// do nothing
}
}