indy tcpclient发送和接收

下面的代码是实现从客户端发送一个命令给服务端,
服务端接收到命令后截取屏幕并发送给客户端,客户端接收保存显示
客户端:
    var
    ftmpStream : TFileStream;
    bitmap:Tbitmap;
begin
try
with IdTCPClient do
    begin
    if connected then DisConnect;
    Host := edtServerHost.text;
    Port := StrToInt(edtServerPort.text);
    Connect;
    WriteLn('SRN');
    // delete if exists
    // in production situation you might store binary downloads like this in a cache folder
    if FileExists(ExtractFileDir(ParamStr(0)) + '\ServerScreen.bmp') then
        DeleteFile(ExtractFileDir(ParamStr(0)) + '\ServerScreen.bmp');
    ftmpStream := TFileStream.Create(ExtractFileDir(ParamStr(0)) + '\ServerScreen.bmp',fmCreate);
//   bmpstream.Clear;
//   bitmap:=Tbitmap.Create;
    while connected do
//      ReadStream(bmpStream,-1,true);
        ReadStream(fTmpStream,-1,true);
    FreeAndNil(fTmpStream);
    Disconnect;
    imgMain.Picture.LoadFromFile(ExtractFileDir(ParamStr(0)) + '\ServerScreen.bmp');
//      bitmap.LoadFromStream(bmpStream);
//      imgMain.Picture.Bitmap:=bitmap;
    end;
except
on E : Exception do
    ShowMessage(E.Message);
end;

服务端:
procedure TFMain.IdTCPServerExecute(AThread: TIdPeerThread);
var
    s, sCommand, sAction : string;
    fStream : TFileStream;
    tBM : tbitmap;
begin
CS.Enter;
try
s := uppercase(AThread.Connection.ReadLn);
sCommand := copy(s,1,3);
sAction := copy(s,5,100);
if sCommand = 'SRN' then
    begin
    // in production version you would use a unique file name such as one generated
    // from a tickcount plus clint IP / id etc.
    // take snapshot
    GetBitMap();
    // copy file stream to write stream
    AThread.Connection.OpenWriteBuffer;
    AThread.Connection.WriteStream(bmpStream);
    AThread.Connection.CloseWriteBuffer;
    // free the file stream
    bmpstream.Clear;

    AThread.Connection.Disconnect;
    End
else
if (sCommand <> 'LST') and (sCommand <> 'PIC') and (sCommand <> 'SRN') then
    Begin
    AThread.Connection.WriteLn('ERR : Unknown command / action');
    AThread.Connection.Disconnect;
    end;
except
on E : Exception do
ShowMessage(E.Message);
End;
CS.Leave;
end;