带有Datasnap Rest和Close-session的TStream

Question

I build a datasnap REST application and I can't close the session.

For example if I call my URL 4 times in my web browser: http://127.0.0.1:4445/REST/image?json=false

There is 4 sessions opened.

Here is my function:

function TV1.TestImage:TStream;
var
ContentType : String;
FileStream : TFileStream;
begin
    FileStream := TFileStream.Create('C:\santiago.jpg', fmOpenRead or fmShareDenyNone);
    ContentType := 'image/jpg';

    GetInvocationMetadata.ResponseContentType := ContentType;
    ContentTypeHeaderToUse := ContentType;
    GetInvocationMetadata().ResponseCode := 200;

    result := FileStream;

    //Can't call CloseSession with TStream, pointer exception
    //GetInvocationMetaData.CloseSession := True;

end;

And I use the WebModuleAfterDispatch like that:

  procedure TWebModule2.WebModuleAfterDispatch(Sender: TObject;
  Request: TWebRequest; Response: TWebResponse; var Handled: Boolean);
  var session : TDSSession;
  begin
      response.FreeContentStream := true;

      if ContentTypeHeaderToUse<>'' then begin
          Response.ContentType := ContentTypeHeaderToUse;
          ContentTypeHeaderToUse := ''; // Reset global variable
      end;

  end;

As you can see, GetInvocationMetaData.CloseSession := True; can't be used here.

Do you know how to close session after sending the TStream?

Answer 1

On a REST server I prefer to return a base64 string, it's easier to deal for the client app than the JSON representation of a Delphi TStream (an array of bytes).

The EncodeBase64 function on the Soap.EncdDecd unit does the transformation very easily :

function TV1.TestImage:string;
var MemoryStream: TMemoryStream;
begin
  MemoryStream := TMemoryStream.Create;
  MemoryStream.LoadFromFile('C:\santiago.jpg');
  Result := EncodeBase64(MemoryStream.Memory, MemoryStream.Size);
  MemoryStream.Free; // Now you can free the Stream yourself
end;

An additional benefit is that you can now release your Stream and not depend on Datasnap doing it. So you should be able to manually close your connection without that pointer exception and solve the problem of multiple sessions remaining open.

You can directly use that base64 image string on your web application. You only need to add their type at the start of an < img > tag.

Example :

<img src="data:image/jpeg;base64,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">