/*
* 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.codec.net;
import java.io.UnsupportedEncodingException;
import java.nio.charset.Charset;
import org.apache.commons.codec.DecoderException;
import org.apache.commons.codec.EncoderException;
import org.apache.commons.codec.binary.StringUtils;
/**
* Implements methods common to all codecs defined in RFC 1522.
* <p>
* <a href="http://www.ietf.org/rfc/rfc1522.txt">RFC 1522</a> describes techniques to allow the
* encoding of non-ASCII text in various portions of a RFC 822 [2] message header, in a manner which
* is unlikely to confuse existing message handling software.
* <p>
* This class is immutable and thread-safe.
*
* @see <a href="http://www.ietf.org/rfc/rfc1522.txt">MIME (Multipurpose Internet Mail Extensions) Part Two:
* Message Header Extensions for Non-ASCII Text</a>
*
* @since 1.3
* @version $Id$
*/
abstract class RFC1522Codec {
/** Separator. */
protected static final char SEP = '?';
/** Prefix. */
protected static final String POSTFIX = "?=";
/** Postfix. */
protected static final String PREFIX = "=?";
/**
* Applies an RFC 1522 compliant encoding scheme to the given string of text with the given charset.
* <p>
* This method constructs the "encoded-word" header common to all the RFC 1522 codecs and then invokes
* {@link #doEncoding(byte [])} method of a concrete class to perform the specific encoding.
*
* @param text
* a string to encode
* @param charset
* a charset to be used
* @return RFC 1522 compliant "encoded-word"
* @throws EncoderException
* thrown if there is an error condition during the Encoding process.
* @see <a href="http://download.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
*/
protected String encodeText(final String text, final Charset charset) throws EncoderException {
if (text == null) {
return null;
}
final StringBuilder buffer = new StringBuilder();
buffer.append(PREFIX);
buffer.append(charset);
buffer.append(SEP);
buffer.append(this.getEncoding());
buffer.append(SEP);
final byte [] rawData = this.doEncoding(text.getBytes(charset));
buffer.append(StringUtils.newStringUsAscii(rawData));
buffer.append(POSTFIX);
return buffer.toString();
}
/**
* Applies an RFC 1522 compliant encoding scheme to the given string of text with the given charset.
* <p>
* This method constructs the "encoded-word" header common to all the RFC 1522 codecs and then invokes
* {@link #doEncoding(byte [])} method of a concrete class to perform the specific encoding.
*
* @param text
* a string to encode
* @param charsetName
* the charset to use
* @return RFC 1522 compliant "encoded-word"
* @throws EncoderException
* thrown if there is an error condition during the Encoding process.
* @throws UnsupportedEncodingException
* if charset is not available
*
* @see <a href="http://download.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
*/
protected String encodeText(final String text, final String charsetName)
throws EncoderException, UnsupportedEncodingException {
if (text == null) {
return null;
}
return this.encodeText(text, Charset.forName(charsetName));
}
/**
* Applies an RFC 1522 compliant decoding scheme to the given string of text.
* <p>
* This method processes the "encoded-word" header common to all the RFC 1522 codecs and then invokes
* {@link #doEncoding(byte [])} method of a concrete class to perform the specific decoding.
*
* @param text
* a string to decode
* @return A new decoded String or <code>null</code> if the input is <code>null</code>.
* @throws DecoderException
* thrown if there is an error condition during the decoding process.
* @throws UnsupportedEncodingException
* thrown if charset specified in the "encoded-word" header is not supported
*/
protected String decodeText(final String text)
throws DecoderException, UnsupportedEncodingException {
if (text == null) {
return null;
}
if (!text.startsWith(PREFIX) || !text.endsWith(POSTFIX)) {
throw new DecoderException("RFC 1522 violation: malformed encoded content");
}
final int terminator = text.length() - 2;
int from = 2;
int to = text.indexOf(SEP, from);
if (to == terminator) {
throw new DecoderException("RFC 1522 violation: charset token not found");
}
final String charset = text.substring(from, to);
if (charset.equals("")) {
throw new DecoderException("RFC 1522 violation: charset not specified");
}
from = to + 1;
to = text.indexOf(SEP, from);
if (to == terminator) {
throw new DecoderException("RFC 1522 violation: encoding token not found");
}
final String encoding = text.substring(from, to);
if (!getEncoding().equalsIgnoreCase(encoding)) {
throw new DecoderException("This codec cannot decode " + encoding + " encoded content");
}
from = to + 1;
to = text.indexOf(SEP, from);
byte[] data = StringUtils.getBytesUsAscii(text.substring(from, to));
data = doDecoding(data);
return new String(data, charset);
}
/**
* Returns the codec name (referred to as encoding in the RFC 1522).
*
* @return name of the codec
*/
protected abstract String getEncoding();
/**
* Encodes an array of bytes using the defined encoding scheme.
*
* @param bytes
* Data to be encoded
* @return A byte array containing the encoded data
* @throws EncoderException
* thrown if the Encoder encounters a failure condition during the encoding process.
*/
protected abstract byte[] doEncoding(byte[] bytes) throws EncoderException;
/**
* Decodes an array of bytes using the defined encoding scheme.
*
* @param bytes
* Data to be decoded
* @return a byte array that contains decoded data
* @throws DecoderException
* A decoder exception is thrown if a Decoder encounters a failure condition during the decode process.
*/
protected abstract byte[] doDecoding(byte[] bytes) throws DecoderException;
}