Martin Melka
Martin Melka

Reputation: 7799

Sending and receiving a TMemoryStream using IdTCPClient and IdTCPServer

I found Remy Lebeau's chat demo of IdTCP components in XE2 and I wanted to play with it a little bit. (It can be found here) I would like to send a picture using these components and the best approach seems to be using TMemoryStream. If I send strings, the connection works fine, the strings are transmitted successfully, however when I change it to Stream instead, it doesn't work. Here is the code:

Server

procedure TMainForm.IdTCPServerExecute(AContext: TIdContext);
var rcvdMsg: string;
  ms:TMemoryStream;
begin
// This commented code is working, it receives and sends strings.
//  rcvdMsg:=AContext.Connection.IOHandler.ReadLn;
//  LogMessage('<ServerExec> '+rcvdMsg);
//
//  TResponseSync.SendResponse(AContext, rcvdMsg);
  try
    ms:=TMemoryStream.Create;
    AContext.Connection.IOHandler.ReadStream(ms);

    ms.SaveToFile('c:\networked.bmp');
  except
    LogMessage('Failed to receive',clred);
  end;
end;

Client

procedure TfrmMain.Button1Click(Sender: TObject);
var ms: TMemoryStream;
    bmp: TBitmap;
    pic: TPicture;
    s: string;
begin
  // Again, this code is working for sending strings.
  // s:=edMsg.Text;
  // Client.IOHandler.WriteLn(s);
  ms:=TMemoryStream.Create;

  pic:=TPicture.Create;
  pic.LoadFromFile('c:\Back.png');

  bmp:=TBitmap.Create;
  bmp.Width:=pic.Width;
  bmp.Height:=pic.Height;
  bmp.Canvas.Draw(0,0,pic.Graphic);

  bmp.SaveToStream(ms);
  ms.Position:=0;
  Client.IOHandler.Write(ms);
  ms.Free;
end;

When I try to send the stream from the client, nothing observable happens (breakpoint in the OnExecute doesn't fire). However, when closing the programs(after sending the MemoryStream), two things happen:

Note: The server uses IdSchedulerOfThreadDefault and IdAntiFreeze, if that matters.

As I can't find any reliable source of help for the revamped Indy 10 (it all appears to apply for the older Indy 10, or even Indy 9), I hope you can tell me what is wrong. Thanks


- ANSWER -

SERVER

procedure TMainForm.IdTCPServerExecute(AContext: TIdContext);
var size: integer;
    ms:TMemoryStream;
begin
  try
    ms:=TMemoryStream.Create;
    size:=AContext.Connection.IOHandler.ReadLongInt;
    AContext.Connection.IOHandler.ReadStream(ms, size);

    ms.SaveToFile('c:\networked.bmp');
  except
    LogMessage('Failed to receive',clred);
  end;
end;

CLIENT

procedure TfrmMain.Button1Click(Sender: TObject);
var ms: TMemoryStream;
    bmp: TBitmap;
    pic: TPicture;
begin
  ms:=TMemoryStream.Create;

  pic:=TPicture.Create;
  pic.LoadFromFile('c:\Back.png');

  bmp:=TBitmap.Create;
  bmp.Width:=pic.Width;
  bmp.Height:=pic.Height;
  bmp.Canvas.Draw(0,0,pic.Graphic);

  bmp.SaveToStream(ms);
  ms.Position:=0;
  Client.IOHandler.Write(ms, 0, True);
  ms.Free;
end;

Upvotes: 4

Views: 14409

Answers (2)

whosrdaddy
whosrdaddy

Reputation: 11860

Send the size of the stream upfront so that the server knows how many bytes it must read.

Server:

procedure TMainForm.IdTCPServerExecute(AContext: TIdContext);
var rcvdMsg: string;
  ms:TMemoryStream;
  size : integer;
begin
// This commented code is working, it receives and sends strings.
//  rcvdMsg:=AContext.Connection.IOHandler.ReadLn;
//  LogMessage('<ServerExec> '+rcvdMsg);
//
//  TResponseSync.SendResponse(AContext, rcvdMsg);
  try
    ms:=TMemoryStream.Create;
    try 
     size := AContext.Connection.IOHandler.ReadLongint; 
     AContext.Connection.IOHandler.ReadStream(ms, size, false);
     ms.SaveToFile('c:\networked.bmp');
    finally
     ms.Free;
    end;        
  except
    LogMessage('Failed to receive',clred);
  end;
end;

Client (Fixed resource handling)

procedure TfrmMain.Button1Click(Sender: TObject);
var ms: TMemoryStream;
    bmp: TBitmap;
    pic: TPicture;
    s: string;
begin
  // Again, this code is working for sending strings.
  // s:=edMsg.Text;
  // Client.IOHandler.WriteLn(s);
  ms:=TMemoryStream.Create;
  pic:=TPicture.Create;
  bmp:=TBitmap.Create;
  try
   pic.LoadFromFile('c:\Back.png');   
   bmp.Width:=pic.Width;
   bmp.Height:=pic.Height;
   bmp.Canvas.Draw(0,0,pic.Graphic);
   bmp.SaveToStream(ms);
   ms.Position:=0;
   Client.IOHandler.Write(ms.Size);
   Client.IOHandler.Write(ms);
  finally
   ms.Free;
   bmp.Free;
   pic.Free;
  end;
end;

Upvotes: 3

markus_ja
markus_ja

Reputation: 2951

Just use the proper parameters:

.IOHandler.Write(ms, 0, true); //true ... indicates WriteByteCount

.IOHandler.ReadStream(ms, -1); //-1 ... use ByteCount

Upvotes: 6

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