Using client datasets with zlib

I have written a small class to compress and uncompress client data sets. I 
can get the compression TCTableData.Assign method to work but the 
decompression TCTableData.AssignTo method does not work in Delphi 7. Can 
anyone tell me why it does not work? It must work with Delphi 7. I have 
listed the code below:

type TCTableData = class   // Compressed table data class
    fdata : TByteDynArray;

    procedure Assign(ds : TDataSet);
    procedure AssignTo(cds  : TClientDataSet);

    property Data : TByteDynArray read fdata write fdata;

procedure TCTableData.Assign(ds : TDataSet);

// Assigns a dataset to the current compressed table data object

  var mstream  : TMemoryStream;
      cstream  : TCompressionStream;
      cds      : TClientDataSet;
      i        : Integer;

  // Assign input dataset to memory dataset cds
  cds := TClientDataSet.Create(nil);
  while not ds.Eof do
    for i := 0 to ds.FieldCount-1 do
      cds.Fields[i].Value := ds.Fields[i].Value;
  mstream := TMemoryStream.Create;
  cstream := TCompressionStream.Create(clDefault,mstream);
  // Compress and write memory dataset to memory stream
  // Copy compressed data stream to byte array
  mstream.Position := 0;

procedure TCTableData.AssignTo(cds  : TClientDataSet);

// Recreates a client data set from the current compressed table data

  var dstream : TDecompressionStream;
      mstream : TMemoryStream;
      buff    : TByteDynArray;
      size    : Integer;

  mstream := TMemoryStream.Create;
  // Copy compressed table data to memory stream
  mstream.Position := 0;
  dstream := TDecompressionStream.Create(mstream);
  // Uncompress table data and initialize client data set
  size := dstream.Read(buff[1],Length(fdata));;

  mstream := TMemoryStream.Create;
  mstream.Position := 0;

4/10/2015 2:16:59 PM
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