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1   /************************************************************************
2    * Copyright (c) 1999-2006 The Apache Software Foundation.             *
3    * All rights reserved.                                                *
4    * ------------------------------------------------------------------- *
5    * Licensed under the Apache License, Version 2.0 (the "License"); you *
6    * may not use this file except in compliance with the License. You    *
7    * may obtain a copy of the License at:                                *
8    *                                                                     *
9    *     http://www.apache.org/licenses/LICENSE-2.0                      *
10   *                                                                     *
11   * Unless required by applicable law or agreed to in writing, software *
12   * distributed under the License is distributed on an "AS IS" BASIS,   *
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or     *
14   * implied.  See the License for the specific language governing       *
15   * permissions and limitations under the License.                      *
16   ***********************************************************************/
17  
18  package org.apache.james.util;
19  
20  import java.io.IOException;
21  import java.io.InputStream;
22  
23  /***
24   * An InputStream class that terminates the stream when it encounters a
25   * particular byte sequence.
26   *
27   * @version 1.0.0, 24/04/1999
28   */
29  public class CharTerminatedInputStream
30      extends InputStream {
31  
32      /***
33       * The wrapped input stream
34       */
35      private InputStream in;
36  
37      /***
38       * The terminating character array
39       */
40      private int match[];
41  
42      /***
43       * An array containing the last N characters read from the stream, where
44       * N is the length of the terminating character array
45       */
46      private int buffer[];
47  
48      /***
49       * The number of bytes that have been read that have not been placed
50       * in the internal buffer.
51       */
52      private int pos = 0;
53  
54      /***
55       * Whether the terminating sequence has been read from the stream
56       */
57      private boolean endFound = false;
58  
59      /***
60       * A constructor for this object that takes a stream to be wrapped
61       * and a terminating character sequence.
62       *
63       * @param in the <code>InputStream</code> to be wrapped
64       * @param terminator the array of characters that will terminate the stream.
65       *
66       * @throws IllegalArgumentException if the terminator array is null or empty
67       */
68      public CharTerminatedInputStream(InputStream in, char[] terminator) {
69          if (terminator == null) {
70              throw new IllegalArgumentException("The terminating character array cannot be null.");
71          }
72          if (terminator.length == 0) {
73              throw new IllegalArgumentException("The terminating character array cannot be of zero length.");
74          }
75          match = new int[terminator.length];
76          buffer = new int[terminator.length];
77          for (int i = 0; i < terminator.length; i++) {
78              match[i] = (int)terminator[i];
79              buffer[i] = (int)terminator[i];
80          }
81          this.in = in;
82      }
83  
84      /***
85       * Read a byte off this stream.
86       *
87       * @return the byte read off the stream
88       * @throws IOException if an IOException is encountered while reading off the stream
89       * @throws ProtocolException if the underlying stream returns -1 before the terminator is seen.
90       */
91      public int read() throws IOException {
92          if (endFound) {
93              //We've found the match to the terminator
94              return -1;
95          }
96          if (pos == 0) {
97              //We have no data... read in a record
98              int b = in.read();
99              if (b == -1) {
100                 //End of stream reached without seeing the terminator
101                 throw new java.net.ProtocolException("pre-mature end of data");
102             }
103             if (b != match[0]) {
104                 //this char is not the first char of the match
105                 return b;
106             }
107             //this is a match...put this in the first byte of the buffer,
108             // and fall through to matching logic
109             buffer[0] = b;
110             pos++;
111         } else {
112             if (buffer[0] != match[0]) {
113                 //Maybe from a previous scan, there is existing data,
114                 // and the first available char does not match the
115                 // beginning of the terminating string.
116                 return topChar();
117             }
118             //we have a match... fall through to matching logic.
119         }
120         //MATCHING LOGIC
121 
122         //The first character is a match... scan for complete match,
123         // reading extra chars as needed, until complete match is found
124         for (int i = 0; i < match.length; i++) {
125             if (i >= pos) {
126                 int b = in.read();
127                 if (b == -1) {
128                     //end of stream found, so match cannot be fulfilled.
129                     // note we don't set endFound, because otherwise
130                     // remaining part of buffer won't be returned.
131                     return topChar();
132                 }
133                 //put the read char in the buffer
134                 buffer[pos] = b;
135                 pos++;
136             }
137             if (buffer[i] != match[i]) {
138                 //we did not find a match... return the top char
139                 return topChar();
140             }
141         }
142         //A complete match was made...
143         endFound = true;
144         return -1;
145     }
146 
147     /***
148      * Private helper method to update the internal buffer of last read characters
149      *
150      * @return the byte that was previously at the front of the internal buffer
151      */
152     private int topChar() {
153         int b = buffer[0];
154         if (pos > 1) {
155             //copy down the buffer to keep the fresh data at top
156             System.arraycopy(buffer, 1, buffer, 0, pos - 1);
157         }
158         pos--;
159         return b;
160     }
161 }
162