---------------------------------------------------------------- -- 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 1.1.1.2 2016/07/28 12:20:05 christos Exp $ -- This demo program provided by Dr Steve Sangwine -- -- 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;