----------------------------------------------------------------

-- ZLib for Ada thick binding. --

-- --

-- Copyright (C) 2002-2004 Dmitriy Anisimkov --

-- --

-- Open source license information is in the zlib.ads file. --

----------------------------------------------------------------

--

-- $Id: buffer_demo.adb,v 1.3 2004/09/06 06:55:35 vagul Exp $

-- This demo program provided by Dr Steve Sangwine <sjs@essex.ac.uk>

--

-- Demonstration of a problem with Zlib-Ada (already fixed) when a buffer

-- of exactly the correct size is used for decompressed data, and the last

-- few bytes passed in to Zlib are checksum bytes.

-- This program compresses a string of text, and then decompresses the

-- compressed text into a buffer of the same size as the original text.

with Ada.Streams; use Ada.Streams;

with Ada.Text_IO;

with ZLib; use ZLib;

procedure Buffer_Demo is

EOL : Character renames ASCII.LF;

Text : constant String

:= "Four score and seven years ago our fathers brought forth," & EOL &

"upon this continent, a new nation, conceived in liberty," & EOL &

"and dedicated to the proposition that `all men are created equal'.";

Source : Stream_Element_Array (1 .. Text'Length);

for Source'Address use Text'Address;

begin

Ada.Text_IO.Put (Text);

Ada.Text_IO.New_Line;

Ada.Text_IO.Put_Line

("Uncompressed size : " & Positive'Image (Text'Length) & " bytes");

declare

Compressed_Data : Stream_Element_Array (1 .. Text'Length);

L : Stream_Element_Offset;

begin

Compress : declare

Compressor : Filter_Type;

I : Stream_Element_Offset;

begin

Deflate_Init (Compressor);

-- Compress the whole of T at once.

Translate (Compressor, Source, I, Compressed_Data, L, Finish);

pragma Assert (I = Source'Last);

Close (Compressor);

Ada.Text_IO.Put_Line

("Compressed size : "

& Stream_Element_Offset'Image (L) & " bytes");

end Compress;

-- Now we decompress the data, passing short blocks of data to Zlib

-- (because this demonstrates the problem - the last block passed will

-- contain checksum information and there will be no output, only a

-- check inside Zlib that the checksum is correct).

Decompress : declare

Decompressor : Filter_Type;

Uncompressed_Data : Stream_Element_Array (1 .. Text'Length);

Block_Size : constant := 4;

-- This makes sure that the last block contains

-- only Adler checksum data.

P : Stream_Element_Offset := Compressed_Data'First - 1;

O : Stream_Element_Offset;

begin

Inflate_Init (Decompressor);

loop

Translate

(Decompressor,

Compressed_Data

(P + 1 .. Stream_Element_Offset'Min (P + Block_Size, L)),

P,

Uncompressed_Data

(Total_Out (Decompressor) + 1 .. Uncompressed_Data'Last),

O,

No_Flush);

Ada.Text_IO.Put_Line

("Total in : " & Count'Image (Total_In (Decompressor)) &

", out : " & Count'Image (Total_Out (Decompressor)));

exit when P = L;

end loop;

Ada.Text_IO.New_Line;

Ada.Text_IO.Put_Line

("Decompressed text matches original text : "

& Boolean'Image (Uncompressed_Data = Source));

end Decompress;

end;

end Buffer_Demo;