problems sending picture from client to server

Question

i am trying to send a picture from 'C:\picture.bmp' to 'c:\temp\picture.bmp' using server and client socket clients onconnect event handler is as follow:

procedure TForm2.ClientSocket1Connect(Sender: TObject;
  Socket: TCustomWinSocket);
 var
  fs : tfilestream;
  begin
     fs := TFileStream.create('C:\picture.bmp', fmOpenRead);//picture allready exists
     socket.SendStream(fs);
     fs.free;             
end;

and servers onclientread as :

procedure TForm2.ServerSocket1ClientRead(Sender: TObject;
  Socket: TCustomWinSocket);
var
  fmm : tfilestream;
  iLen: Integer;
    Bfr: Pointer;
  begin

     iLen := Socket.ReceiveLength;
  GetMem(Bfr, iLen);
  fmm := TFileStream.Create('c:\temp\picture.bmp', fmCreate or 

fmShareDenyWrite);
  try
    Socket.ReceiveBuf(Bfr^, iLen);
    fmm.Write(Bfr^, iLen);
  finally
    FreeMem(Bfr);
    fmm.Free;
  end;

end;

picture is recieved/created but is either corrupt on was never recieved i.e created because of tfilestream.create method? please help!what am i doing wrong?

Answer 1

I don't know what's wrong, but I'd try troubleshooting a simpler problem. i.e. can you even transfer somethign simple? See if you can transfer c:\hello.txt containing just "Hello" and have it arrive in the right order. It should be easier to examine the stream and resulting file, to see if/where things are getting garbled. If you don't receive "Hello" on the server, then you know it's got nothing to do with the size or complexity of the data.

Answer 2

Despite its name, SendStream() is NOT guaranteed to send the entire stream (especially if you are using a non-blocking socket). Its return value returns how many bytes are actually sent. If less than the full size of the stream are sent in one call, you have to call SendStream() again, potentially many times, to finish sending the entire stream (the same problems exists with SendText() as well).

On the other side, ReceiveLength() only reports how many bytes are available on the socket AT THAT MOMENT. That is likely to be less than the full stream being sent (likewise, ReceiveText() may not receive a full sent string either because it uses ReceiveLength() internally).

The best way to send a stream (or any arbitrary data in general) is to send the data's size first, then send the actual data afterwards. Keep calling SendBuf/Stream/Text() until that size is reached (if -1 is returned by a non-blocking socket without raising an exception, you have to wait for the socket's OnWrite event to trigger before the socket can accept more data again). On the receiving end, read the size first, then keep reading until the specified size is reached. You may have to read in multiple triggering of the OnRead event before you get all of the data.

Go to http://www.deja.com and http://forums.embarcadero.com to search the Borland/CodeGear/Embarcadero newsgroup/forum archives. I have posted example code many times before.