socket分段传文件问题请教,急!!!

下面的我测试socket分段传文件的代码,文件能传过去,打开时说文件已损坏,但是字节数又没错,请教大家,,急!!!
发送代码-----
implementation
  var filestream:Tfilestream;
      fis,filesize:integer;
     const subsize =2000;
procedure TForm1.Button2Click(Sender: TObject);
begin    filestream:=Tfilestream.Create(edit1.Text,fmopenread);
    filestream.Position:=0;
    filesize:=filestream.Size;
    fis:=filesize;
    //由于测试没有设计协议,这里只能传五位数字节的文件
    clients.Socket.SendText('begin'+inttostr(fis)+'e:\delphi.rar');
    memo1.Lines.Clear;
end;
procedure TForm1.ClientsRead(Sender: TObject; Socket: TCustomWinSocket);
var f:pointer;
    str:string;
begin
    str:=socket.ReceiveText;
    memo1.Lines.Add(str);
    if (trim(str)='ok')  then
    begin
            memo1.Lines.Add('----正在发送数据----');
            getmem(f,subsize);
            while fis>0 do
            begin
                sleep(20);
                if fis>2000 then
                begin
                    filestream.Read(f^,subsize);
                    socket.SendBuf(f^,subsize);
                    fis:=fis-subsize;
                    memo1.Lines.Add('剩余字节数'+inttostr(fis));
                end
                else
                begin
                    filestream.Read(f^,fis);
                    socket.SendBuf(f^,fis);
                    fis:=0;
                    memo1.Lines.Add('剩余字节数'+inttostr(fis));
                    sleep(1000);
                    socket.SendText('over');
                    freemem(f);
                end;
            end;
             memo1.Lines.Add('----发送数据成功----');    end;
end;接收代码--------
type
    fileinfo=record
         filename:string;
         filesize:integer;
         subP:pointer;
         end;
implementation
 var isfile:boolean;
     filestream:Tfilestream;
     fl:fileinfo;
 const subsize=2000;procedure TForm1.ServersClientRead(Sender: TObject;
  Socket: TCustomWinSocket);
  var  substr:string;
begin
    sleep(10);
    substr:=trim(socket.ReceiveText);
    memo1.Lines.Add(substr);
    if copy(substr,1,5)='begin' then
    begin
        fl.filename:=trim(copy(substr,11,20));
        memo1.Lines.Add(fl.filename);
        fl.filesize:=strtoint(trim(copy(substr,6,5)));
        memo1.Lines.Add(inttostr(fl.filesize));
        getmem(fl.subP,2000);
        isfile:=true;
        filestream:=Tfilestream.Create(fl.filename,fmCreate or fmOpenWrite);
        filestream.Position:=0;
        socket.SendText('ok');
    end;    if trim(substr)='over' then
    begin
         isfile:=false;
         filestream.Free;
         freemem(fl.subP);
         exit;
    end;
    if  isfile then
    begin
        if   (fl.filesize>0) then
        if  (fl.filesize>2000) then
        begin
            socket.ReceiveBuf(fl.subP^,2000);
            filestream.Write(fl.subP^,2000);
            fl.filesize:=fl.filesize-2000;
        end
        else
        begin
            socket.ReceiveBuf(fl.subP^,fl.filesize);
            filestream.Write(fl.subP^,fl.filesize);
            fl.filesize:=0;
        end;
    end;
end;