+ *
+ * There are a set of methods to encode and decode MIME headers as
+ * per RFC 2047. Note that, in general, these methods are
+ * not needed when using methods such as
+ * setSubject and setRecipients; JavaMail
+ * will automatically encode and decode data when using these "higher
+ * level" methods. The methods below are only needed when maniuplating
+ * raw MIME headers using setHeader and getHeader
+ * methods. A brief description on handling such headers is given below:
+ * + * RFC 822 mail headers must contain only US-ASCII + * characters. Headers that contain non US-ASCII characters must be + * encoded so that they contain only US-ASCII characters. Basically, + * this process involves using either BASE64 or QP to encode certain + * characters. RFC 2047 describes this in detail.
+ * + * In Java, Strings contain (16 bit) Unicode characters. ASCII is a + * subset of Unicode (and occupies the range 0 - 127). A String + * that contains only ASCII characters is already mail-safe. If the + * String contains non US-ASCII characters, it must be encoded. An + * additional complexity in this step is that since Unicode is not + * yet a widely used charset, one might want to first charset-encode + * the String into another charset and then do the transfer-encoding. + *
+ * Note that to get the actual bytes of a mail-safe String (say, + * for sending over SMTP), one must do + *
+ *
+ * byte[] bytes = string.getBytes("iso-8859-1");
+ *
+ *
+ *
+ * The setHeader and addHeader methods
+ * on MimeMessage and MimeBodyPart assume that the given header values
+ * are Unicode strings that contain only US-ASCII characters. Hence
+ * the callers of those methods must insure that the values they pass
+ * do not contain non US-ASCII characters. The methods in this class
+ * help do this.
+ *
+ * The getHeader family of methods on MimeMessage and
+ * MimeBodyPart return the raw header value. These might be encoded
+ * as per RFC 2047, and if so, must be decoded into Unicode Strings.
+ * The methods in this class help to do this.
+ * + * Several System properties control strict conformance to the MIME + * spec. Note that these are not session properties but must be set + * globally as System properties.
+ *
+ * The mail.mime.decodetext.strict property controls
+ * decoding of MIME encoded words. The MIME spec requires that encoded
+ * words start at the beginning of a whitespace separated word. Some
+ * mailers incorrectly include encoded words in the middle of a word.
+ * If the mail.mime.decodetext.strict System property is
+ * set to "false", an attempt will be made to decode these
+ * illegal encoded words. The default is true.
+ *
+ * The mail.mime.encodeeol.strict property controls the
+ * choice of Content-Transfer-Encoding for MIME parts that are not of
+ * type "text". Often such parts will contain textual data for which
+ * an encoding that allows normal end of line conventions is appropriate.
+ * In rare cases, such a part will appear to contain entirely textual
+ * data, but will require an encoding that preserves CR and LF characters
+ * without change. If the mail.mime.encodeeol.strict
+ * System property is set to "true", such an encoding will
+ * be used when necessary. The default is false.
+ *
+ * In addition, the mail.mime.charset System property can
+ * be used to specify the default MIME charset to use for encoded words
+ * and text parts that don't otherwise specify a charset. Normally, the
+ * default MIME charset is derived from the default Java charset, as
+ * specified in the file.encoding System property. Most
+ * applications will have no need to explicitly set the default MIME
+ * charset. In cases where the default MIME charset to be used for
+ * mail messages is different than the charset used for files stored on
+ * the system, this property should be set.
+ * + * The current implementation also supports the following System property. + *
+ * The mail.mime.ignoreunknownencoding property controls
+ * whether unknown values in the Content-Transfer-Encoding
+ * header, as passed to the decode method, cause an exception.
+ * If set to "true", unknown values are ignored and 8bit
+ * encoding is assumed. Otherwise, unknown values cause a MessagingException
+ * to be thrown.
+ *
+ * @author John Mani
+ * @author Bill Shannon
+ */
+
+/* FROM mail.jar */
+final class MimeUtility {
+
+ // This class cannot be instantiated
+ private MimeUtility() { }
+
+ private static final boolean ignoreUnknownEncoding =
+ PropUtil.getBooleanSystemProperty(
+ "mail.mime.ignoreunknownencoding", false);
+
+ /**
+ * Decode the given input stream. The Input stream returned is
+ * the decoded input stream. All the encodings defined in RFC 2045
+ * are supported here. They include "base64", "quoted-printable",
+ * "7bit", "8bit", and "binary". In addition, "uuencode" is also
+ * supported.
+ *
+ * In the current implementation, if the
+ * mail.mime.ignoreunknownencoding system property is set to
+ * "true", unknown encoding values are ignored and the
+ * original InputStream is returned.
+ *
+ * @param is input stream
+ * @param encoding the encoding of the stream.
+ * @return decoded input stream.
+ * @exception MessagingException if the encoding is unknown
+ */
+ public static InputStream decode(InputStream is, String encoding)
+ throws DecodingException {
+ if (encoding.equalsIgnoreCase("base64"))
+ return new BASE64DecoderStream(is);
+ else if (encoding.equalsIgnoreCase("quoted-printable"))
+ return new QPDecoderStream(is);
+ else if (encoding.equalsIgnoreCase("uuencode") ||
+ encoding.equalsIgnoreCase("x-uuencode") ||
+ encoding.equalsIgnoreCase("x-uue"))
+ return new UUDecoderStream(is);
+ else if (encoding.equalsIgnoreCase("binary") ||
+ encoding.equalsIgnoreCase("7bit") ||
+ encoding.equalsIgnoreCase("8bit"))
+ return is;
+ else {
+ if (!ignoreUnknownEncoding) {
+ throw new DecodingException("Unknown encoding: " + encoding);
+ }
+ return is;
+ }
+ }
+}