[SOLVED] Stream newb - simple question

[BigChimp]

Hi all,

Trying to decompress .bz2 files, but getting a stream read error.
(Note: I know there's an error in the Pascal bzip2 decompressor on i386; see bug 21242; I'm trying this with a x64 Linux compiler)

I've tried to chain the input file stream to the decompression stream, but I'm probably doing something wrong there. The code errors at the marked point.

Code:

Code: [Select]

var
  InFile:TFileStream;
  Decompressed:TDecompressBzip2Stream;
  OutFile:TFileStream;
begin
  result:=false;
  InFile:=TFileStream.Create(SourceFile, fmOpenRead);
  try
    Decompressed:=TDecompressBzip2Stream.Create(InFile);
    OutFile:=TFileStream.Create(TargetFile, fmCreate);
    try
      Decompressed.CopyFrom(InFile, InFile.Size); //error occurs here.
      OutFile.CopyFrom(Decompressed, Decompressed.Size);
      result:=true;
    finally
      Decompressed.Free;
      OutFile.Free;
    end;
  finally
    InFile.Free;
  end;

Entire Lazarus program attached.

Thanks!

[User137]

I don't know about these streams, but doesn't the program logic feel odd? I mean, you give TDecompressBzip2Stream 2 references to InFile.

I'd try with like:

Code: [Select]

...
  try
    Decompressed:=TDecompressBzip2Stream.Create(InFile);
    OutFile:=TFileStream.Create(TargetFile, fmCreate);
    try
      //Decompressed.CopyFrom(InFile, InFile.Size); //error occurs here. (Just comment it out)
      // Possibly here is some method from TDecompressBzip2Stream, don't know, maybe not needed
      OutFile.CopyFrom(Decompressed, Decompressed.Size);
...

[BigChimp]

Thanks, user137.

Yes, I am giving 2 references, but I had thought that I had to instruct the TDecompressBzip2Stream to actually get its data from the other stream, therefore the copyfrom method.

If I try your code, I get

TDecompressBzip2Stream.Seek not implemented

(running on a patched x86 Windows compiler that has the bunzip2 i386 asm code disabled, so should not error there)

TDecompressBzip2Stream has just these public methods/functions:

Code: [Select]

Constructor Create(ASource : TStream);
Destructor Destroy; override;
function Read(var Buffer; Count: Longint): Longint; override;


[ludob]

If I try your code, I get

TDecompressBzip2Stream.Seek not implemented

And since the decompressed size is not known before decompressing, stream copy isn't possible. You'll need to use buffer reads:

Code: [Select]

function Decompress(SourceFile, TargetFile: string; out ErrorLog: string): boolean;
var
  InFile:TFileStream;
  Decompressed:TDecompressBzip2Stream;
  OutFile:TFileStream;
  Buffer: Pointer;
  i:integer;
const buffersize=$2000;
begin
  result:=false;
  InFile:=TFileStream.Create(SourceFile, fmOpenRead);
  try
    Decompressed:=TDecompressBzip2Stream.Create(InFile);
    OutFile:=TFileStream.Create(TargetFile, fmCreate);
    try
      GetMem(Buffer,BufferSize);
      repeat
        i:=Decompressed.Read(buffer^,BufferSize);
        if i>0 then
          OutFile.WriteBuffer(buffer^,i);
      until i<BufferSize;
      result:=true;
    finally
      Decompressed.Free;
      OutFile.Free;
    end;
  finally
    InFile.Free;
  end;
end;



[BigChimp]

Thanks, that solved it!

[User137]

Lastly:

Code: [Select]

free(buffer);Or there will be a memory leak 

[BigChimp]

 

Thanks; used FreeMem(Buffer, BufferSize) though...

That's why nobody should let me near pointers and raw memory until I have my adult teeth.. I mean need a walking frame 

[ludob]

Lastly:

Code: [Select]

free(buffer);Or there will be a memory leak 

That was left as an exercise for the OP   

[BigChimp]

Hi Ludo,

Have you had your coffee already