zlib 1.2.1.2v1.2.1.2

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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;