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+----------------------------------------------------------------
+-- 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;