content: /*
   * 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 org.apache.commons.codec.DecoderException;
  import org.apache.commons.codec.EncoderException;
  import org.apache.commons.codec.binary.StringUtils;
  
  /**
   * <p>
   * Implements methods common to all codecs defined in RFC 1522.
   * </p>
   * 
   * <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>
  
   * @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>
   * </p>
   * 
   * @author Apache Software Foundation
   * @since 1.3
   * @version $Id: RFC1522Codec.java 798428 2009-07-28 07:32:49Z ggregory $
   */
  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. 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 enconding.
       * 
       * @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 conidition during the Encoding 
       *  process.
       * @throws UnsupportedEncodingException thrown if charset is not supported 
       * 
       * @see <a href="http://java.sun.com/j2se/1.4.2/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
       */
      protected String encodeText(final String text, final String charset)
       throws EncoderException, UnsupportedEncodingException  
      {
          if (text == null) {
              return null;
          }
          StringBuffer buffer = new StringBuffer();
          buffer.append(PREFIX); 
          buffer.append(charset);
          buffer.append(SEP);
          buffer.append(getEncoding());
          buffer.append(SEP);
          byte [] rawdata = doEncoding(text.getBytes(charset)); 
          buffer.append(StringUtils.newStringUsAscii(rawdata));
          buffer.append(POSTFIX); 
          return buffer.toString();
      }
      
      /**
       * Applies an RFC 1522 compliant decoding scheme to the given string of text. 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 deconding.
       * 
       * @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 conidition 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");
          }
          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");
          }
          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");
          }
          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;
  }
  