Reader


1   /*
2     Copyright � 2006 Stefano Chizzolini. http://clown.stefanochizzolini.it
3   
4     Contributors:
5       * Stefano Chizzolini (original code developer, info@stefanochizzolini.it):
6         contributed code is Copyright � 2006 by Stefano Chizzolini.
7   
8     This file should be part of the source code distribution of "PDF Clown library"
9     (the Program): see the accompanying README files for more info.
10  
11    This Program is free software; you can redistribute it and/or modify it under
12    the terms of the GNU General Public License as published by the Free Software
13    Foundation; either version 2 of the License, or (at your option) any later version.
14  
15    This Program is distributed in the hope that it will be useful, but WITHOUT ANY
16    WARRANTY, either expressed or implied; without even the implied warranty of
17    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the License for more details.
18  
19    You should have received a copy of the GNU General Public License along with this
20    Program (see README files); if not, go to the GNU website (http://www.gnu.org/).
21  
22    Redistribution and use, with or without modification, are permitted provided that such
23    redistributions retain the above copyright notice, license and disclaimer, along with
24    this list of conditions.
25  */
26  
27  package it.stefanochizzolini.clown.tokens;
28  
29  import it.stefanochizzolini.clown.bytes.IInputStream;
30  import it.stefanochizzolini.clown.files.File;
31  import it.stefanochizzolini.clown.objects.PdfDictionary;
32  import it.stefanochizzolini.clown.objects.PdfInteger;
33  import it.stefanochizzolini.clown.objects.PdfName;
34  import java.io.EOFException  ;
35  
36  /**
37    PDF file reader.
38  */
39  public class Reader
40  {
41    // <class>
42    // <dynamic>
43    // <fields>
44    private Parser parser;
45    // </fields>
46  
47    // <constructors>
48    /**
49      <h3>Remarks</h3>
50      <p>For internal use only.</p>
51    */
52    public Reader(
53      IInputStream stream,
54      File file
55      )
56    {
57      this.parser = new Parser(stream,file);
58    }
59    // </constructors>
60  
61    // <interface>
62    // <public>
63    public int hashCode(
64      )
65    {return parser.hashCode();}
66  
67    public Parser getParser(
68      )
69    {return parser;}
70  
71    public PdfDictionary readTrailer(
72      ) throws FileFormatException
73    {
74      // Get the offset of the last xref-table section!
75      long xrefOffset = parser.retrieveXRefOffset();
76      // Go to the start of the last xref-table section!
77      parser.seek(xrefOffset); parser.moveNext();
78      if(!((String  )parser.getToken()).equals("xref"))
79        throw new FileFormatException("'xref' keyword not found.",parser.getPosition());
80  
81      // Searching the start of the last trailer...
82      while(true)
83      {
84        parser.moveNext();
85        if(parser.getTokenType() == TokenTypeEnum.Keyword)
86          break;
87        parser.moveNext();
88        int count = (Integer  )parser.getToken();
89        parser.skip(count * 20);
90      }
91      if(!((String  )parser.getToken()).equals("trailer"))
92        throw new FileFormatException("'trailer' keyword not found.",parser.getPosition());
93  
94      // Get the last trailer!
95      parser.moveNext();
96      return (PdfDictionary)parser.parsePdfObject();
97    }
98  
99    /**
100     Retrieves the xref-table.
101     @return The xref-table entries array.
102   */
103   public XRefEntry[] readXRefTable(
104     PdfDictionary trailer
105     ) throws FileFormatException
106   {
107     // 1. XRef-table.
108     // Get the xref-table size!
109     PdfInteger xrefTableSize = (PdfInteger)trailer.get(PdfName.Size);
110     // Allocate the xref-table array!
111     XRefEntry[] xrefEntries = new XRefEntry[xrefTableSize.getValue()];
112 
113     // 2. Last xref-table section.
114     // Move to the start of the last xref-table section!
115     parser.seek(parser.retrieveXRefOffset());
116     // Parse the last xref-table section!
117     readXRefSection(xrefEntries);
118 
119     // 3. Previous xref-table sections.
120     while(true)
121     {
122       // 1. Previous xref-table section.
123       // Get the previous xref-table section offset!
124       PdfInteger prevXRefOffset = (PdfInteger)trailer.get(PdfName.Prev);
125       if(prevXRefOffset == null)
126         break;
127       // Move to the start of the previous xref-table section!
128       parser.seek(prevXRefOffset.getValue());
129       // Parse the previous xref-table section!
130       readXRefSection(xrefEntries);
131 
132       // 2. Previous trailer.
133       // Skip 'trailer' keyword!
134       parser.moveNext();
135       // Get the previous trailer!
136       trailer = (PdfDictionary)parser.parsePdfObject();
137     }
138 
139     return xrefEntries;
140   }
141 
142   public String   readVersion(
143     ) throws FileFormatException
144   {
145     return parser.retrieveVersion();
146   }
147   // </public>
148 
149   // <protected>
150   protected void readXRefSection(
151     XRefEntry[] xrefEntries
152     ) throws FileFormatException
153   {
154     // Reach the start of the xref-table section!
155     parser.moveNext();
156     if(!((String  )parser.getToken()).equals("xref"))
157       throw new FileFormatException("'xref' keyword not found.",parser.getPosition());
158 
159     // Loop sequentially across the subsections inside the current xref-table section.
160     while(true)
161     {
162       /*
163         NOTE: Each iteration of this loop block represents the scanning
164         of one subsection.
165         We get its bounds (first and last object numbers within its range)
166         and then collect its entries.
167       */
168       // 1. First object number.
169       parser.moveNext();
170       // Have we reached the end of the xref-table section?
171       if((parser.getTokenType() == TokenTypeEnum.Keyword)
172           && ((String  )parser.getToken()).equals("trailer"))
173         break;
174       // Is the current token type different from the expected one?
175       if(parser.getTokenType() != TokenTypeEnum.Integer)
176         throw new FileFormatException("Neither object number of the first object in this xref subsection nor end of xref section found.",parser.getPosition());
177       // Get the object number of the first object in this xref-table subsection!
178       int startObjectNumber = (Integer  )parser.getToken();
179 
180       // 2. Last object number.
181       parser.moveNext();
182       if(parser.getTokenType() != TokenTypeEnum.Integer)
183         throw new FileFormatException("Number of entries in this xref subsection not found.",parser.getPosition());
184       // Get the object number of the last object in this xref-table subsection!
185       int endObjectNumber = (Integer  )parser.getToken() + startObjectNumber;
186 
187       // 3. xref-table subsection entries.
188       for(
189         int index = startObjectNumber;
190         index < endObjectNumber;
191         index++
192         )
193       {
194         // Is the entry undefined?
195         if(xrefEntries[index] == null) // Undefined entry.
196         {
197           // 1. Get the indirect object offset!
198           parser.moveNext();
199           int offset = (Integer  )parser.getToken();
200           // 2. Get the object generation number!
201           parser.moveNext();
202           int generation = (Integer  )parser.getToken();
203           // 3. Get the usage tag!
204           parser.moveNext();
205           String   usageToken = (String  )parser.getToken();
206           XRefEntryUsageEnum usage;
207           if(usageToken.equals("n"))
208             usage = XRefEntryUsageEnum.InUse;
209           else if(usageToken.equals("f"))
210             usage = XRefEntryUsageEnum.Free;
211           else
212             throw new FileFormatException("Invalid xref entry.",parser.getPosition());
213 
214           // 4. Entry initialization.
215           xrefEntries[index] = new XRefEntry(
216             index,
217             generation,
218             offset,
219             usage
220             );
221         }
222         else // Already-defined entry.
223         {
224           // Skip to the next entry!
225           parser.moveNext(3);
226         }
227       }
228     }
229   }
230   // </protected>
231   // </interface>
232   // </dynamic>
233   // </class>
234 }
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