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1   /*
2    * $Id: XmlMessageProtocol.java 7976 2007-08-21 14:26:13Z dirk.olmes $
3    * --------------------------------------------------------------------------------------
4    * Copyright (c) MuleSource, Inc.  All rights reserved.  http://www.mulesource.com
5    *
6    * The software in this package is published under the terms of the CPAL v1.0
7    * license, a copy of which has been included with this distribution in the
8    * LICENSE.txt file.
9    */
10  
11  package org.mule.providers.tcp.protocols;
12  
13  import java.io.IOException;
14  import java.io.InputStream;
15  import java.io.PushbackInputStream;
16  
17  import edu.emory.mathcs.backport.java.util.concurrent.ConcurrentHashMap;
18  
19  /**
20   * <p>
21   * The XmlMessageProtocol is an application level tcp protocol that can be used to
22   * read streaming xml documents. The only requirement is that each document include
23   * an xml declaration at the beginning of the document of the form "<?xml...". In
24   * section 2.8, the xml 1.0 standard contains "Definition: XML documents
25   * <strong>SHOULD</strong> begin with an XML declaration which specifies the version
26   * of XML being used" while the xml 1.1 standard contains "Definition: XML 1.1
27   * documents <strong>MUST</strong> begin with an XML declaration which specifies the
28   * version of XML being used". The SHOULD indicates a recommendation that, if not
29   * followed, needs to be carefully checked for unintended consequences. MUST
30   * indicates a mandatory requirement for a well-formed document. Please make sure
31   * that the xml documents being streamed begin with an xml declaration when using
32   * this class.
33   * </p>
34   * <p>
35   * Data are read until a new document is found or there are no more data
36   * (momentarily).  For slower networks,
37   * {@link org.mule.providers.tcp.protocols.XmlMessageEOFProtocol} may be more reliable.
38   * </p>
39   * <p>
40   * Also, the default character encoding for the platform is used to decode the
41   * message bytes when looking for the XML declaration. Some caution with message
42   * character encodings is warranted.
43   * </p>
44   * <p>
45   * Finally, this class uses a PushbackInputStream to enable parsing of individual
46   * messages. The stream stores any pushed-back bytes into it's own internal buffer
47   * and not the original stream. Therefore, the read buffer size is intentionally
48   * limited to insure that unread characters remain on the stream so that all data may
49   * be read later.
50   * </p>
51   */
52  public class XmlMessageProtocol extends ByteProtocol
53  {
54      private static final String XML_PATTERN = "<?xml";
55  
56      private static final int READ_BUFFER_SIZE = 4096;
57      private static final int PUSHBACK_BUFFER_SIZE = READ_BUFFER_SIZE * 2;
58  
59      private ConcurrentHashMap pbMap = new ConcurrentHashMap();
60  
61      public XmlMessageProtocol()
62      {
63          super(STREAM_OK);
64      }
65  
66      public Object read(InputStream is) throws IOException
67      {
68          PushbackInputStream pbis = (PushbackInputStream) pbMap.get(is);
69          if (null == pbis)
70          {
71              pbis = new PushbackInputStream(is, PUSHBACK_BUFFER_SIZE);
72              PushbackInputStream prev = (PushbackInputStream) pbMap.putIfAbsent(is, pbis);
73              pbis = null == prev ? pbis : prev;
74          }
75  
76          int len = -1;
77          try
78          {
79              // read until xml pattern is seen (and then pushed back) or no more data
80              // to read. return all data as message
81              byte[] buffer = new byte[READ_BUFFER_SIZE];
82              StringBuffer message = new StringBuffer(READ_BUFFER_SIZE);
83              int patternIndex = -1;
84              boolean repeat;
85              do
86              {
87                  len = safeRead(pbis, buffer);
88                  if (len >= 0)
89                  {
90                      // TODO take encoding into account, ideally from the incoming XML
91                      message.append(new String(buffer, 0, len));
92                      // start search at 2nd character in buffer (index=1) to
93                      // indicate whether we have reached a new document.
94                      patternIndex = message.toString().indexOf(XML_PATTERN, 1);
95                      repeat = isRepeat(patternIndex, len, pbis.available());
96                  }
97                  else
98                  {
99                      // never repeat on closed stream (and avoid calling available)
100                     repeat = false;
101                 }
102 
103             }
104             while (repeat);
105 
106             if (patternIndex > 0)
107             {
108                 // push back the start of the next message and
109                 // ignore the pushed-back characters in the return buffer
110                 pbis.unread(message.substring(patternIndex, message.length()).getBytes());
111                 message.setLength(patternIndex);
112             }
113 
114             // TODO encoding here, too...
115             return nullEmptyArray(message.toString().getBytes());
116 
117         }
118         finally
119         {
120             // TODO - this doesn't seem very reliable, since loop above can end
121             // without EOF.  On the other hand, what else can we do?  Entire logic
122             // is not very dependable, IMHO.  XmlMessageEOFProtocol is more likely
123             // to be correct here, I think.
124 
125             // clear from map if stream has ended
126             if (len < 0)
127             {
128                 pbMap.remove(is);
129             }
130         }
131     }
132 
133     /**
134      * Show we continue reading?  This class, following previous implementations, only
135      * reads while input is saturated.
136      * @see XmlMessageEOFProtocol
137      *
138      * @param patternIndex The index of the xml tag (or -1 if the next message not found)
139      * @param len The amount of data read this loop (or -1 if EOF)
140      * @param available The amount of data available to read
141      * @return true if the read should continue
142      */
143     protected boolean isRepeat(int patternIndex, int len, int available)
144     {
145         return patternIndex < 0 && len == READ_BUFFER_SIZE && available > 0;
146     }
147 
148 }