Using TIdCompressorLib to Decompress gzip file - delphi

Question

I am using Delphi 2007 with Indy 10. I have a gzip file. I have verified it can be decompressed with this Online Decompression Tool.
I am trying to use the TIdCompressorZlib component to decompress using Delphi. Here is my code:
procedure TForm2.Button9Click(Sender: TObject);
var
lCompressor : TIdCompressorZLib;
FileStream : TFileStream;
memorystream: TMemoryStream;
begin
lCompressor := TIdCompressorZLib.create(self);
FileStream := TFileStream.Create('c:\temp\test.gz', fmOpenRead);
filestream.position := 0;
memorystream:= TMemoryStream.create;
memorystream.position := 0;
lcompressor.DecompressGZipStream(FileStream,MemoryStream);
filestream.free;
showmessage('done');
end;
I cannot get it to work. If I pass fmOpenReadWrite in the constructor I get a zlib error (-5) when DecompressGZipStream is called.
If I pass fmOpenRead in the constructor I get a OS System Error Code 5 Access Denied when DecompressGZipStream is called.
Update David Hefferan suggested it is a file reading issue. So I am zeroing in on that. I am able to copy the file using this procedure:
Procedure FileCopy( Const sourcefilename, targetfilename: String );
Var
S, T: TFileStream;
Begin
S := TFileStream.Create( sourcefilename, fmOpenRead );
try
T := TFileStream.Create( targetfilename,
fmOpenWrite or fmCreate );
try
T.CopyFrom(S, S.Size ) ;
finally
T.Free;
end;
finally
S.Free;
end;
showmessage('done');
End;
UPD Per David Heffernan, I have verified I can Read the data. I successfully ran the file through the following function. It returns the proper number of characters (bytes):
function GetTextFromFile(AFile: string; var Returnstring: string): Boolean;
var
FileStream: TFileStream;
begin
Result := False;
if not FileExists(AFile) then Exit;
FileStream := TFileStream.Create(AFile, fmOpenRead);
try
if FileStream.Size <> 0 then
begin
SetLength(Returnstring, FileStream.Size);
FileStream.Read(Returnstring[1], FileStream.Size);
Result := True;
end;
finally
FileStream.Free;
end;
end;

Answer 1

You can try to use Delphi zlib unit to decompress gzip.
Sample code:
procedure TForm2.Button9Click(Sender: TObject);
var
DecompressionStream : TDecompressionStream;
FileStream : TFileStream;
dest: TFileStream;
byteCount: Integer;
buffer: array [0..65535] of Byte;
begin
FileStream := TFileStream.Create('c:\temp\test.gz', fmOpenRead);
try
//no need to set FileStream position to 0, it's there already
DecompressionStream:=TDecompressionStream.Create(FileStream, 15+16);
//16 is flag that gzip stream used, not zlib.
//15 is maximum memory usage, to speed-up decompression.
try
dest:=TFileStream.Create('c:\temp\test.txt', fmCreate);
try
dest.CopyFrom(DecompressionStream,0);
finally
dest.free;
end;
finally
DecompressionStream.free;
end;
finally
filestream.free;
end;
showmessage('done');
end;
UPD: this code doesn't work for D2007 or earlier versions, no overloaded constructor with WindowBits argument...