/*

  * Copyright 1999,2004 The Apache Software Foundation.

  * 

  * Licensed 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.feedparser.tools;

 /**

  *

  * Given an XML document pull out the encoding or the default (UTF-8) if not

  * specified.

  *

  * @author <a href="mailto:burton@openprivacy.org">Kevin A. Burton</a>

  */

 public class XMLEncodingParser {

     public static final String ENCODING = "encoding=\"";

     /**

      *

      * 

      */

     public static String parse( byte[] content ) throws Exception {

         //this isn't really pretty but it is fast.

         //just use the first 100 bytes

         String str;

         if ( content.length > 100 ) {

             str = new String( content, 0, 100 );

         } else {

             str = new String( content );

         }

         String result = getEncodingFromBOM( content );

         if ( result != null )

             return result;

         int end = str.indexOf( ">" );

         if ( end == -1 )

             return "UTF-8";

         String decl = str.substring( 0, end );

         int index = decl.indexOf( ENCODING );

         if ( index != -1 ) {

             String encoding = decl.substring( index + ENCODING.length(),

                                               decl.length() );

             end = encoding.indexOf( "\"" );

             if ( end == -1 )

                 return "UTF-8";

             encoding = encoding.substring( 0, end);

             encoding = encoding.toUpperCase();

             if ( "UTF8".equals( encoding ) )

                 encoding = "UTF-8";

             return encoding;

         }

         return "UTF-8";

     }

     private static String getEncodingFromBOM( byte[] content ) {

         // Technically speaking if we see a BOM is specified we're supposed to

         // return UTF-16 or UTF-32 but because we only care about anything UTF

         // returning UTF-8 is incorrect but acceptable.

         //

         // http://www.unicode.org/faq/utf_bom.html#BOM

         if ( content.length > 2 ) {

             //perform UTF-16 tests

             if ( content[0] == -1 &&

                  content[1] == -2 ) 

                 return "UTF-16";

             if ( content[0] == -2 &&

                  content[1] == -1 ) 

                 return "UTF-16";

         }

         if ( content.length > 4 ) {

             //perform UTF-16 tests

             if ( content[0] == 0 &&

                  content[1] == 0 &&

                  content[2] == -2 &&

                  content[3] == -1 ) 

                 return "UTF-32";

             if ( content[0] == -1 &&

                  content[1] == -2 &&

                  content[2] == 0 &&

                  content[3] == 0 ) 

                 return "UTF-32";

         }

         return null;

     }

     public static void main( String[] args ) throws Exception {

         System.out.println( parse( "<?xml encoding=\"utf-8\"?>".getBytes() ) );

         System.out.println( parse( "<?xml encoding=\"UTF-8\"?>".getBytes() ) );

         System.out.println( parse( "<?xml encoding=\"utf8\"?>".getBytes() ) );

     }

 }