Can't retrieve TStreams bigger than around 260.000 bytes from a Datasnap Server

Question

I have a Delphi 10.1 Berlin Datasnap Server, that can\'t return Data packets (through a TStream) bigger than around 260.000 bytes.

I have programmed it following the

Answer 1

@Marc: I think Henrikki meant a single function, not a single function call...
I've modified your code so that only one function is enough and so that projects with different SchemaAdapters/StoredProcedures can be used.
The maximum streamsize is declared as a constant (MaxDataSnapStreamSize) and is set to $F000, wich is the MaxBuffSize a TStream.CopyFrom function handles (see System.Classes).
FComprStream is a private field of type TMemorySTream, taken care of in the constructor and destructor of the servermodule.

On the server side:

const
  MaxDataSnapStreamSize = $F000;

function TServerMethods1.StreamGet(const aFDSchemaAdapter: TFDSchemaAdapter; var aSize: Int64): TStream;
var
  lZIPStream: TZCompressionStream;
  lDataStream: TMemoryStream;
  I: Integer;
  lMinSize: Int64;
begin
if aSize=-1 then
  exit;
lDataStream:=TMemoryStream.Create;
  try
  if aSize=0 then
    begin
    FComprStream.Clear;
    with aFDSchemaAdapter do
      for I := 0 to Count-1 do
        begin
        DataSets[I].Close;
        DataSets[I].Open;
        end;
    lZIPStream := TZCompressionStream.Create(TCompressionLevel.clFastest, FComprStream);
      try
      aFDSchemaAdapter.SaveToStream(lDataStream, TFDStorageFormat.sfBinary);
      lDataStream.Position := 0;
      lZIPStream.CopyFrom(lDataStream, lDataStream.Size);
      finally
      lDataStream.Clear;
      lZIPStream.Free;
      end;
    lMinSize:=Min(FComprStream.Size, MaxDataSnapStreamSize);
    FComprStream.Position:=0;
    end
  else
    lMinSize:=Min(aSize, MaxDataSnapStreamSize);

  lDataStream.CopyFrom(FComprStream, lMinSize);
  lDataStream.Position := 0;
  aSize:=FComprStream.Size-FComprStream.Position;
  Result:=lDataStream;
  if aSize=0 then
    FComprStream.Clear;
  except
  aSize:=-1;
  lDataStream.Free;
  raise;
  end;
end;

On the client side:

procedure TdmClientModuleDS.GetTables(const aStPrGet: TFDStoredProc; const aFDSchemaAdapter: TFDSchemaAdapter);
var
  lSize: Int64;
  lZIPStream: TStringStream;
  lDataStream: TMemoryStream;
  lUNZIPStream:  TZDecompressionStream;
  I: Integer;
begin
  try
  lSize:=0;
  for I := 0 to aFDSchemaAdapter.Count-1 do
    aFDSchemaAdapter.DataSets[I].Close;
  aStPrGet.ParamByName('aSize').AsInteger:=0;
  aStPrGet.ExecProc;
  lZIPStream:=TStringStream.Create(aStPrGet.ParamByName('ReturnValue').AsBlob);
  lSize:=aStPrGet.ParamByName('aSize').AsInteger;
  while lSize>0 do
    with aStPrGet do
      begin
      ParamByName('aSize').AsInteger:=lSize;
      ExecProc;
      lZIPStream.Position:=lZIPStream.Size;
      lZIPStream.WriteBuffer(TBytes(ParamByName('ReturnValue').AsBlob),Length(ParamByName('ReturnValue').AsBlob));
      lSize:=ParamByName('aSize').AsInteger;
      end;
  lZIPStream.Position:=0;
  lDataStream:=TMemoryStream.Create;
  lUNZIPStream:=TZDecompressionStream.Create(lZIPStream);
  lDataStream.CopyFrom(lUNZIPStream, 0);
  lDataStream.Position:=0;
  aFDSchemaAdapter.LoadFromStream(lDataStream,TFDStorageFormat.sfBinary);
  finally
  if Assigned(lZIPStream) then
    FreeAndNil(lZIPStream);
  if Assigned(lDataStream) then
    FreeAndNil(lDataStream);
  if Assigned(lUNZIPStream) then
    FreeAndNil(lUNZIPStream);
  end;
end;