Delphi :Transferring Image

Question

Delphi 2010

I'm Transferring Image via custom TCP Socket control uses UTF-8

Client Side

var
TSS: TStringStream;
STR :String;
JPG:TJPEGImage;
BMP:TBitmap;
begin
Try
BMP.LoadFromFile('C:\1.bmp');

JPG.Assign(BMP);
JPG.CompressionQuality:=80;
JPG.Compress;

TSS:=TStringStream.Create;
JPG.SaveToStream(TSS);

STR:=TSS.DataString;

MyTCPSocket.SendString(STR);


finally
BMP.free;
JPG.free;
TSS.free;
end;
end;

Server Side

Var
TSS: TStringStream;

TSS:=TStringStream.Create;
TSS.WriteString(STR);
TSS.SaveToFile('C:\2.jpg');

This code working on the same pc great.

The problem when I send the image to other pc that uses different encoding it receive the image but I see many wrong characters in the data "?????"

I think when TStringStream writes the bytes to the file it fails to convert the unicode characters to bytes so it appears like "?"

Any idea is much appreciated

Answer 1

You are trying to send binary data as if it were UTF-8 encoded text. It is not, so do not try to do that! Send the binary data in its original binary form, eg:

var
  MS: TMemoryStream;
  JPG: TJPEGImage;
  BMP: TBitmap;
begin
  MS := TMemoryStream.Create;
  try
    JPG := TJPEGImage.Create;
    try
      BMP := TBitmap.Create;
      try
        BMP.LoadFromFile('C:\1.bmp');
        JPG.Assign(BMP);
      finally
        BMP.Free;
      end;
      JPG.CompressionQuality := 80;
      JPG.Compress;
      JPG.SaveToStream(MS);
    finally
      JPG.Free;
    end;
    MS.Position := 0;
    MyTCPSocket.SendStream(MS);
  finally
    MS.free;
  end;
end;

var
  MS: TMemoryStream;
begin
  MS := TMemoryStream.Create;
  try
    MyTCPSocket.ReadStream(MS);
    MS.Position := 0;
    MS.SaveToFile('C:\2.jpg');
  finally
    MS.Free;
  end;
end;

If you must send binary data as text, you need to encode the data using a real binary-to-text encoding algorithm, such as base64 or yEnc, not UTF-8 (which is designed for only encoding Unicode text, not binary data), eg:

// TIdEncoderMIME and TIdDecoderMIME are part of Indy,
// which ships with Delphi, but you can use whatever
// you want...

uses
  ..., IdCoderMIME;

var
  S: String;
  MS: TMemoryStream;
  JPG: TJPEGImage;
  BMP: TBitmap;
begin
  MS := TMemoryStream.Create;
  try
    JPG := TJPEGImage.Create;
    try
      BMP := TBitmap.Create;
      try
        BMP.LoadFromFile('C:\1.bmp');
        JPG.Assign(BMP);
      finally
        BMP.Free;
      end;
      JPG.CompressionQuality := 80;
      JPG.Compress;
      JPG.SaveToStream(MS);
    finally
      JPG.Free;
    end;
    MS.Position := 0;
    S := TIdEncoderMIME.EncodeStream(MS);
  finally
    MS.free;
  end;
  MyTCPSocket.SendString(S);
end;

uses
  ..., IdCoderMIME;

var
  S: string;
  MS: TMemoryStream;
begin
  S := MyTCPSocket.ReadString;
  MS := TMemoryStream.Create;
  try
    TIdDecoderMIME.DecodeStream(S, MS);
    MS.Position := 0;
    MS.SaveToFile('C:\2.jpg');
  finally
    MS.Free;
  end;
end;