TMemoryStream of a file with a string attached to it - delphi

Question

i have a TMemoryStream of a picture but i want to add a String inside that TMemoryStream that defines what that picture is then read them separately.
the TMemoryStream will be sent from IdTCPclient to IdTCPserver and server will read the string then the picture.
id prefer if the string was in the beginning of the stream.
it is my first encounter on dealing with memory stream with multiple date inside it, please enlighten me.
//Edit: adding current code based on MBo Answer
procedure TForm1.Button1Click(Sender: TObject);
var
s: string;
bm: TBitmap;
ms ,ms1: TMemoryStream;
len: Int64;
JPEGImage: TJPEGImage;
begin
IdTCPClient1.Connect;
begin
ms:=TMemoryStream.Create;
ms1:=TMemoryStream.Create;
JPEGImage := TJPEGImage.Create;
s := 'A nice picture';
ms:=CapScreen(100); //function result in memory stream
len := Length(s) * SizeOf(Char);
ms1.Write(len, SizeOf(len));
ms1.Write(PChar(s)^, len);
ms1.copyfrom(ms,ms.Size) ; // <-- stream read error
ms1.Position := 0;
Caption := s;
JPEGImage.LoadFromStream(ms1);
Image1.Picture.Assign(JPEGImage);
end;
IdTCPClient1.IOHandler.Write(ms1, 0, True);
ms.Free;
ms1.Free;
JPEGImage.Free;
end;

Answer 1

Simple example to start from. Picture is loaded from disk here
var
s: string;
bm: TBitmap;
ms: TMemoryStream;
len: Int64;
begin
ms := TMemoryStream.Create;
bm := TBitmap.Create;
try
bm.LoadFromFile('d:\d.bmp');
//write string body size, body itself
s := 'A nice picture';
len := Length(s) * SizeOf(Char);
ms.Write(len, SizeOf(len));
ms.Write(PChar(s)^, len);
//now picture
bm.SaveToStream(ms);
//change string and picture to be sure we load new ones
bm.Canvas.FillRect(rect(0,0,100,100));
s := '';
//now restore and show
ms.Position := 0;
ms.Read(len, sizeof(len));
SetLength(s, len div SizeOf(Char));
ms.Read(PChar(s)^, len);
Caption := s;
bm.LoadFromStream(ms); //reads picture from current position
Canvas.Draw(0, 0, bm);
finally
ms.Free;
bm.Free;
end;
Example for jpeg loaded from another stream:
var
s: string;
ms, jpstream: TMemoryStream;
len: Int64;
jp: TJpegImage;
begin
ms := TMemoryStream.Create;
jpstream := TMemoryStream.Create;
jp := TJpegImage.Create;
try
//write string body size, body itself
s := 'A nice picture';
len := Length(s) * SizeOf(Char);
ms.Write(len, SizeOf(len));
ms.Write(PChar(s)^, len);
jpstream.LoadFromFile('d:\d.jpg');
jpstream.Position := 0;
ms.CopyFrom(jpstream, jpstream.Size);
//now restore ans show
ms.Position := 0;
ms.Read(len, sizeof(len));
SetLength(s, len div SizeOf(Char));
ms.Read(PChar(s)^, len);
Caption := s;
jp.LoadFromStream(ms);
Canvas.Draw(0, 0, jp);
finally
ms.Free;
jp.Free;
jpstream.Free;
end;