1----------------------------------------------------------------
2--  ZLib for Ada thick binding.                               --
3--                                                            --
4--  Copyright (C) 2002-2004 Dmitriy Anisimkov                 --
5--                                                            --
6--  Open source license information is in the zlib.ads file.  --
7----------------------------------------------------------------
8--
9--  $Id: buffer_demo.adb,v 1.3 2004/09/06 06:55:35 vagul Exp $
10
11--  This demo program provided by Dr Steve Sangwine <sjs@essex.ac.uk>
12--
13--  Demonstration of a problem with Zlib-Ada (already fixed) when a buffer
14--  of exactly the correct size is used for decompressed data, and the last
15--  few bytes passed in to Zlib are checksum bytes.
16
17--  This program compresses a string of text, and then decompresses the
18--  compressed text into a buffer of the same size as the original text.
19
20with Ada.Streams; use Ada.Streams;
21with Ada.Text_IO;
22
23with ZLib; use ZLib;
24
25procedure Buffer_Demo is
26   EOL  : Character renames ASCII.LF;
27   Text : constant String
28     := "Four score and seven years ago our fathers brought forth," & EOL &
29        "upon this continent, a new nation, conceived in liberty," & EOL &
30        "and dedicated to the proposition that `all men are created equal'.";
31
32   Source : Stream_Element_Array (1 .. Text'Length);
33   for Source'Address use Text'Address;
34
35begin
36   Ada.Text_IO.Put (Text);
37   Ada.Text_IO.New_Line;
38   Ada.Text_IO.Put_Line
39     ("Uncompressed size : " & Positive'Image (Text'Length) & " bytes");
40
41   declare
42      Compressed_Data : Stream_Element_Array (1 .. Text'Length);
43      L               : Stream_Element_Offset;
44   begin
45      Compress : declare
46         Compressor : Filter_Type;
47         I : Stream_Element_Offset;
48      begin
49         Deflate_Init (Compressor);
50
51         --  Compress the whole of T at once.
52
53         Translate (Compressor, Source, I, Compressed_Data, L, Finish);
54         pragma Assert (I = Source'Last);
55
56         Close (Compressor);
57
58         Ada.Text_IO.Put_Line
59           ("Compressed size :   "
60            & Stream_Element_Offset'Image (L) & " bytes");
61      end Compress;
62
63      --  Now we decompress the data, passing short blocks of data to Zlib
64      --  (because this demonstrates the problem - the last block passed will
65      --  contain checksum information and there will be no output, only a
66      --  check inside Zlib that the checksum is correct).
67
68      Decompress : declare
69         Decompressor : Filter_Type;
70
71         Uncompressed_Data : Stream_Element_Array (1 .. Text'Length);
72
73         Block_Size : constant := 4;
74         --  This makes sure that the last block contains
75         --  only Adler checksum data.
76
77         P : Stream_Element_Offset := Compressed_Data'First - 1;
78         O : Stream_Element_Offset;
79      begin
80         Inflate_Init (Decompressor);
81
82         loop
83            Translate
84              (Decompressor,
85               Compressed_Data
86                 (P + 1 .. Stream_Element_Offset'Min (P + Block_Size, L)),
87               P,
88               Uncompressed_Data
89                 (Total_Out (Decompressor) + 1 .. Uncompressed_Data'Last),
90               O,
91               No_Flush);
92
93               Ada.Text_IO.Put_Line
94                 ("Total in : " & Count'Image (Total_In (Decompressor)) &
95                  ", out : " & Count'Image (Total_Out (Decompressor)));
96
97               exit when P = L;
98         end loop;
99
100         Ada.Text_IO.New_Line;
101         Ada.Text_IO.Put_Line
102           ("Decompressed text matches original text : "
103             & Boolean'Image (Uncompressed_Data = Source));
104      end Decompress;
105   end;
106end Buffer_Demo;
107