Getting "Missing Data Provider or Data Packet" error - Exhange data as stream within clientdataset

Question

I am using datasnap technology where I got a client a server application. The Server gets the data from database and puts into stream which is then fetched at client side. I keep getting a "Missing Data Provider or Data Packet" error on the client side code.

Server side code:

function GetFiles(ClientID: integer): TStream;
var
  CDS: TClientDataSet;
begin
  try
  Result := TMemoryStream.Create;
  CDS := TClientDataSet.Create(nil);
  with adsFiles do   // ads is adodataset and dspFiles is the dataset provider which has its dataset property set to adsFiles
  begin
    Close;
    Parameters.ParamByName('ClientID').Value := ClientID;
    Open;
    CDS.Data :=  dspFiles.Data;
    CDS.Open; 
    CDS.SaveToStream(Result);
    Result.Position := 0;
  end;
  finally
    CDS.Free;
  end;

Client Side Code:

procedure ExportData;
var
   StreamData: TStream;
begin
    StreamData := SvrMethodClass.GetFiles(AClientID);
    StreamData.Seek(0,soFromBeginning);
    StreamData.Position:= 0;
    cdsClientFiles.LoadFromStream(StreamData); // getting the error message "Missing Data Provider or Data Packet" 
    cdsClientFiles.Open;
end;

Client side I have dropped a clientdataset component and trying to load the data into this dataset where the issue is raised any help pointing me where I am going wrong would be really appreciated. Thanks

similar question: Streaming TClientDataSet using Datasnap in Delphi XE6 checked the solution but it did not work out

Answer 1

I spent a lot of time investigating the problems with returning data as a stream from a datasnap server - see e.g. Can't retrieve TStreams bigger than around 260.000 bytes from a Datasnap Server, but was unable to come up with a satisfactory solution for stream data.

However, experiments revealed that a similar problem does not occur with string data (I tested strings up to several hundred megabytes). So, I would suggest you try sending your binary/blob data from the Datasnap server as a Base64-encoded string.

Of course, if a string representation of your ADO or CDS data is adequate for what you want, one way to achieve that would be to do an adsFile.SaveToFile(..., pfXML) or CDS.SaveToFile(... dfXML) in the server method, then return the resulting file as a string.