How send/receive a List of elements over socket? - sockets

Question

I have the following code, where I can draw several rectangles and make a hole to each.
How can I send the RectList object over a socket (TServerSocket) and recover (receive in a TClientSocket) this object directly to a variable of same type (var RectList: TList<TRect>)?
type
TForm1 = class(TForm)
ComboBox1: TComboBox;
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
procedure FormMouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
procedure FormMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
procedure FormMouseUp(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
procedure FormPaint(Sender: TObject);
private
{ Private declarations }
Drawing: Boolean;
RectList: TList<TRect>;
Rectangle: TRect;
FormRegion, HoleRegion: HRGN;
function ClientToWindow(const P: TPoint): TPoint;
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
function TForm1.ClientToWindow(const P: TPoint): TPoint;
begin
Result := ClientToScreen(P);
Dec(Result.X, Left);
Dec(Result.Y, Top);
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
RectList := TList<TRect>.Create;
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
RectList.Free;
end;
procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
Rectangle.Left := X;
Rectangle.Top := Y;
Drawing := True;
end;
procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
begin
if Drawing then
begin
Rectangle.Right := X;
Rectangle.Bottom := Y;
Invalidate;
end;
end;
procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
var
I: Integer;
begin
Drawing := false;
Rectangle.Right := X;
Rectangle.Bottom := Y;
Invalidate;
if RectList.Count < StrToInt(ComboBox1.Text) then
begin
Rectangle.NormalizeRect;
if not Rectangle.IsEmpty then
RectList.Add(Rectangle)
else
SetWindowRgn(Handle, 0, True);
end
else
begin
FormRegion := CreateRectRgn(0, 0, Width, Height);
for I := 0 to Pred(RectList.Count) do
begin
HoleRegion := CreateRectRgn(ClientToWindow(RectList.Items[I].TopLeft).X, ClientToWindow(RectList.Items[I].TopLeft).Y, ClientToWindow(RectList.Items[I].BottomRight).X, ClientToWindow(RectList.Items[I].BottomRight).Y);
CombineRgn(FormRegion, FormRegion, HoleRegion, RGN_DIFF);
end;
SetWindowRgn(Handle, FormRegion, True);
RectList.Clear;
end;
end;
procedure TForm1.FormPaint(Sender: TObject);
var
R: TRect;
begin
Canvas.Brush.Style := bsClear;
Canvas.Pen.Style := psSolid;
Canvas.Pen.Color := clRed;
Canvas.Rectangle(Rectangle);
for R in RectList do
Canvas.Rectangle(R);
end;
end.

Answer 1

I made some code to show you how to do it.
In your code, I added a TClientSocketon the form and assigned a few events. Also added a TButton to send the RectList to the other side (server side) thru the TClientSocket.
I designed a new simple server application having a TServerSocket set to listen for client connection and accepting commands from the client. I implemented two commands: rectangle and clear. Obviously clear command is implemented to clear the display on the rectangle list. The rectangle command is used to sent a rectangle (Left, top, right and bottom as coma delimited integers).
Since client and server must understand each other, I designed a very simple communication protocol. Data is exchanged between client and server using ASCII lines. A line is any character collection terminated by a CRLF pair. TCP port 2500 (Almost any other would do) is used.
For example, the command
rectangle 10,20,30,40
will sent a rectangle from client to server (The line above is terminated by CRLF).
If the server receive a valid command, it act on it and then send
OK
The line above is terminated by CRLF. In case of an error, an error message is sent back to the client.
When a client establish a connection, the first thing the server does is to send a welcome banner. That is a line terminated by CRLF.
The client wait to receive the banner before sending any command. Then it send the clear command, wait for OK, then send a rectangle command with first item in RectList and wait for OK, then loop sending all rectangle commands and waiting for OK acknowledge until all RectList has been sent. The the client close the connection.
I'm not completely correct when I say wait for. Actually the socket is event driven. That means everything is done thry events. For example, when a line comes in - sent by the other side - the socket triggers an OnRead event. In the corresponding event handler, you receive the line that is already received.
I used this line oriented protocol because it is really simple, easy to debug and cross platform. Actually, if looks much like the SMTP protocol which is used to send an email! Sending binary data is surely faster but has a lot of difficulties. Binary data format is compiler and platform specific. This result in difficulties. Binary data is diffcult to read for a human and so it is difficult to debug.
Below you'll find your enhanced source code and DFM (This is the client), then the server source code and DFM.
Client source code:
unit SktSocketClientDemoMain;
interface
uses
Winapi.Windows, Winapi.Messages,
System.SysUtils, System.Variants, System.Classes,
System.Generics.Collections,
Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls,
System.Win.ScktComp;
type
TSktSocketClientMainForm = class(TForm)
ComboBox1 : TComboBox;
SocketSendButton : TButton;
ClientSocket1 : TClientSocket;
Memo1 : TMemo;
procedure ClientSocket1Connect(
Sender : TObject;
Socket : TCustomWinSocket);
procedure ClientSocket1Connecting(
Sender : TObject;
Socket : TCustomWinSocket);
procedure ClientSocket1Read(
Sender : TObject;
Socket : TCustomWinSocket);
procedure FormCreate(Sender : TObject);
procedure FormDestroy(Sender : TObject);
procedure FormMouseDown(
Sender : TObject;
Button : TMouseButton;
Shift : TShiftState;
X, Y : Integer);
procedure FormMouseMove(
Sender : TObject;
Shift : TShiftState;
X, Y : Integer);
procedure FormMouseUp(
Sender : TObject;
Button : TMouseButton;
Shift : TShiftState;
X, Y : Integer);
procedure FormPaint(Sender : TObject);
procedure SocketSendButtonClick(Sender : TObject);
private
Drawing : Boolean;
RectList : TList<TRect>;
Rectangle : TRect;
FormRegion, HoleRegion : HRGN;
FBanner : string;
FSendIndex : Integer;
function ClientToWindow(const P : TPoint) : TPoint;
end;
var
SktSocketClientMainForm : TSktSocketClientMainForm;
implementation
{$R *.dfm}
function TSktSocketClientMainForm.ClientToWindow(const P : TPoint) : TPoint;
begin
Result := ClientToScreen(P);
Dec(Result.X, Left);
Dec(Result.Y, Top);
end;
procedure TSktSocketClientMainForm.FormCreate(Sender : TObject);
begin
RectList := TList<TRect>.Create;
end;
procedure TSktSocketClientMainForm.FormDestroy(Sender : TObject);
begin
RectList.Free;
end;
procedure TSktSocketClientMainForm.FormMouseDown(
Sender : TObject;
Button : TMouseButton;
Shift : TShiftState;
X, Y : Integer);
begin
Rectangle.Left := X;
Rectangle.Top := Y;
Drawing := True;
end;
procedure TSktSocketClientMainForm.FormMouseMove(
Sender : TObject;
Shift : TShiftState;
X, Y : Integer);
begin
if Drawing then begin
Rectangle.Right := X;
Rectangle.Bottom := Y;
Invalidate;
end;
end;
procedure TSktSocketClientMainForm.FormMouseUp(
Sender : TObject;
Button : TMouseButton;
Shift : TShiftState;
X, Y : Integer);
var
I : Integer;
begin
Drawing := false;
Rectangle.Right := X;
Rectangle.Bottom := Y;
Invalidate;
if RectList.Count < StrToInt(ComboBox1.Text) then begin
Rectangle.NormalizeRect;
if not Rectangle.IsEmpty then
RectList.Add(Rectangle)
else
SetWindowRgn(Handle, 0, True);
end
else begin
FormRegion := CreateRectRgn(0, 0, Width, Height);
for I := 0 to Pred(RectList.Count) do
begin
HoleRegion :=
CreateRectRgn(ClientToWindow(RectList.Items[I].TopLeft).X,
ClientToWindow(RectList.Items[I].TopLeft).Y,
ClientToWindow(RectList.Items[I].BottomRight).X,
ClientToWindow(RectList.Items[I].BottomRight).Y);
CombineRgn(FormRegion, FormRegion, HoleRegion, RGN_DIFF);
end;
SetWindowRgn(Handle, FormRegion, True);
RectList.Clear;
end;
end;
procedure TSktSocketClientMainForm.FormPaint(Sender : TObject);
var
R : TRect;
begin
Canvas.Brush.Style := bsClear;
Canvas.Pen.Style := psSolid;
Canvas.Pen.Color := clRed;
Canvas.Rectangle(Rectangle);
for R in RectList do
Canvas.Rectangle(R);
end;
procedure TSktSocketClientMainForm.SocketSendButtonClick(Sender : TObject);
begin
FBanner := '';
FSendIndex := 0;
ClientSocket1.Port := 2500; // Must be the same as server side
ClientSocket1.Address := '127.0.0.1';
ClientSocket1.Active := True;
end;
procedure TSktSocketClientMainForm.ClientSocket1Connect(
Sender : TObject;
Socket :
TCustomWinSocket);
begin
Memo1.Lines.Add('Connected');
end;
procedure TSktSocketClientMainForm.ClientSocket1Connecting(
Sender : TObject;
Socket : TCustomWinSocket);
begin
Memo1.Lines.Add('Connecting...');
end;
procedure TSktSocketClientMainForm.ClientSocket1Read(
Sender : TObject;
Socket : TCustomWinSocket);
var
Line : string;
CmdLine : string;
R : TRect;
begin
Line := Trim(string(Socket.ReceiveText));
Memo1.Lines.Add('Rcvd: "' + Line + '"');
if FBanner = '' then begin
FBanner := Line;
Socket.SendText('Clear' + #13#10);
Exit;
end;
if Line <> 'OK' then begin
Memo1.Lines.Add('Expected "OK", received "' + Line + '"');
Socket.Close;
Exit;
end;
if FSendIndex >= RectList.Count then begin
// We have sent everything in RectList
Memo1.Lines.Add('Send completed OK');
Socket.Close;
Exit;
end;
// Send next item in RectList
R := RectList[FSendIndex];
CmdLine := Format('Rectangle %d,%d,%d,%d' + #13#10,
[R.Left, R.Top, R.Right, R.Bottom]);
Inc(FSendIndex);
Socket.SendText(AnsiString(CmdLine));
end;
end.
Client DFM:
object SktSocketClientMainForm: TSktSocketClientMainForm
Left = 0
Top = 0
Caption = 'SktSocketClientMainForm'
ClientHeight = 299
ClientWidth = 635
Color = clBtnFace
Font.Charset = DEFAULT_CHARSET
Font.Color = clWindowText
Font.Height = -11
Font.Name = 'Tahoma'
Font.Style = []
OldCreateOrder = False
OnCreate = FormCreate
OnDestroy = FormDestroy
OnMouseDown = FormMouseDown
OnMouseMove = FormMouseMove
OnMouseUp = FormMouseUp
OnPaint = FormPaint
DesignSize = (
635
299)
PixelsPerInch = 96
TextHeight = 13
object ComboBox1: TComboBox
Left = 24
Top = 12
Width = 145
Height = 21
Style = csDropDownList
ItemIndex = 4
TabOrder = 0
Text = '5'
Items.Strings = (
'1'
'2'
'3'
'4'
'5'
'6'
'7'
'8'
'9')
end
object SocketSendButton: TButton
Left = 188
Top = 8
Width = 75
Height = 25
Caption = 'Send'
TabOrder = 1
OnClick = SocketSendButtonClick
end
object Memo1: TMemo
Left = 8
Top = 192
Width = 621
Height = 101
Anchors = [akLeft, akTop, akRight, akBottom]
Lines.Strings = (
'Memo1')
TabOrder = 2
end
object ClientSocket1: TClientSocket
Active = False
ClientType = ctNonBlocking
Port = 0
OnConnecting = ClientSocket1Connecting
OnConnect = ClientSocket1Connect
OnRead = ClientSocket1Read
Left = 44
Top = 148
end
end
Server source code:
unit SktSocketServerDemoMain;
interface
uses
Winapi.Windows, Winapi.Messages,
System.SysUtils, System.Variants, System.Classes,
System.Generics.Collections,
Vcl.Graphics,
Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, System.Win.ScktComp,
Vcl.ExtCtrls;
type
TCmdProc = procedure (Socket : TCustomWinSocket;
const Params : String) of object;
TCmdItem = record
Cmd : String;
Proc : TCmdProc;
constructor Create(const ACmd : String; AProc : TCmdProc);
end;
TServerMainForm = class(TForm)
ServerSocket1 : TServerSocket;
Memo1 : TMemo;
ServerStartButton : TButton;
PaintBox1 : TPaintBox;
ServerStopButton : TButton;
procedure PaintBox1Paint(Sender : TObject);
procedure ServerSocket1ClientConnect(
Sender : TObject;
Socket : TCustomWinSocket);
procedure ServerSocket1ClientDisconnect(
Sender : TObject;
Socket :
TCustomWinSocket);
procedure ServerSocket1ClientRead(
Sender : TObject;
Socket : TCustomWinSocket);
procedure ServerSocket1Listen(
Sender : TObject;
Socket : TCustomWinSocket);
procedure ServerStartButtonClick(Sender : TObject);
procedure ServerStopButtonClick(Sender : TObject);
private
RectList : TList<TRect>;
CmdList : TList<TCmdItem>;
procedure ProcessCmd(
Socket : TCustomWinSocket;
const CmdLine : string);
procedure CmdNoop(
Socket : TCustomWinSocket;
const Params : string);
procedure CmdClear(
Socket : TCustomWinSocket;
const Params : string);
procedure CmdRectangle(
Socket : TCustomWinSocket;
const Params : string);
public
constructor Create(AOwner : TComponent); override;
destructor Destroy; override;
end;
var
ServerMainForm: TServerMainForm;
implementation
{$R *.dfm}
function SkipOverWhiteSpaces(const CmdLine : String; Index : Integer) : Integer;
var
I : Integer;
begin
I := Index;
while (I <= Length(CmdLine)) and
CharInSet(CmdLine[I], [' ', #13, #10, #9]) do
Inc(I);
Result := I;
end;
function SkipToNextWhiteSpace(const CmdLine : String; Index : Integer) : Integer;
var
I : Integer;
begin
I := Index;
while (I <= Length(CmdLine)) and
(not CharInSet(CmdLine[I], [' ', #13, #10, #9])) do
Inc(I);
Result := I;
end;
function SkipToNextDelimiter(
const CmdLine : String;
Index : Integer;
Delimiters : array of const) : Integer;
var
I : Integer;
nArg : Integer;
V : TVarRec;
begin
I := Index;
while I <= Length(CmdLine) do begin
nArg := 0;
while nArg <= High(Delimiters) do begin
V := Delimiters[nArg];
case (V.VType and varTypeMask) of
vtWideChar:
begin
if CmdLine[I] = V.VWideChar then begin
Result := I;
Exit;
end;
end;
end;
Inc(nArg);
end;
Inc(I);
end;
Result := I;
end;
function GetInteger(
const CmdLine : String;
Index : Integer;
out Value : Integer) : Integer;
var
I : Integer;
begin
Value := 0;
I := SkipOverWhiteSpaces(CmdLine, Index);
while (I <= Length(CmdLine)) and
CharInSet(CmdLine[I], ['0'..'9']) do begin
Value := Value * 10 + Ord(CmdLine[I]) - Ord('0');
Inc(I);
end;
Result := I;
end;
procedure TServerMainForm.CmdClear(Socket: TCustomWinSocket; const Params: String);
begin
RectList.Clear;
PaintBox1.Invalidate;
Socket.SendText('OK' + #13#10);
end;
procedure TServerMainForm.CmdNoop(Socket: TCustomWinSocket; const Params: String);
begin
Socket.SendText('OK' + #13#10);
end;
procedure TServerMainForm.CmdRectangle(Socket: TCustomWinSocket; const Params: String);
var
Param : array [0..3] of Integer;
I, J, K : Integer;
begin
// Clear all parameters
for K := Low(Param) to High(Param) do
Param[K] := 0;
// Parse all parameters
J := 1;
K := Low(Param);
while K <= High(Param) do begin
I := GetInteger(Params, J, Param[K]);
J := SkipOverWhiteSpaces(Params, I);
if J > Length(Params) then
break;
if K = High(Param) then // Check if we got all
break;
if Params[J] <> ',' then // Check for coma delimiter
break;
Inc(J); // Skip over coma
Inc(K);
end;
if K <> High(Param) then begin
Socket.SendText('Rectangle requires 4 parameters.'#13#10);
Exit;
end;
RectList.Add(TRect.Create(Param[0], Param[1], Param[2], Param[3]));
PaintBox1.Invalidate;
Socket.SendText('OK'#13#10);
end;
constructor TServerMainForm.Create(AOwner: TComponent);
begin
inherited Create(AOwner);
RectList := TList<TRect>.Create;
RectList.Add(TRect.Create(10, 10, 50, 50));
RectList.Add(TRect.Create(20, 30, 80, 100));
CmdList := TList<TCmdItem>.Create;
CmdList.Add(TCmdItem.Create('', CmdNoop));
CmdList.Add(TCmdItem.Create('Clear', CmdClear));
CmdList.Add(TCmdItem.Create('Rectangle', CmdRectangle));
end;
destructor TServerMainForm.Destroy;
begin
FreeAndNil(CmdList);
FreeAndNil(RectList);
inherited Destroy;
end;
procedure TServerMainForm.PaintBox1Paint(Sender: TObject);
var
R: TRect;
ACanvas : TCanvas;
begin
ACanvas := (Sender as TPaintBox).Canvas;
ACanvas.Brush.Style := bsClear;
ACanvas.Pen.Style := psSolid;
ACanvas.Pen.Color := clRed;
for R in RectList do
ACanvas.Rectangle(R);
end;
procedure TServerMainForm.ServerSocket1ClientConnect(
Sender: TObject;
Socket: TCustomWinSocket);
begin
Memo1.Lines.Add('Client connected');
Socket.SendText('Welcome to myServer' + #13#10);
end;
procedure TServerMainForm.ServerSocket1ClientRead(Sender: TObject; Socket:
TCustomWinSocket);
var
CmdLine : String;
begin
CmdLine := String(Socket.ReceiveText);
Memo1.Lines.Add('Rcvd: "' + CmdLine + '"');
ProcessCmd(Socket, CmdLine);
end;
procedure TServerMainForm.ProcessCmd(
Socket : TCustomWinSocket;
const CmdLine : String);
var
Cmd : String;
Params : String;
I, J : Integer;
begin
I := SkipOverWhiteSpaces(CmdLine, 1);
J := SkipToNextWhiteSpace(CmdLine, I);
// Split command and parameters
Cmd := UpperCase(Copy(CmdLine, I, J - I));
Params := Copy(CmdLine, J, MAXINT);
Memo1.Lines.Add(Format('Cmd="%s" Params="%s"', [Cmd, Params]));
for I := 0 to CmdList.Count - 1 do begin
if CmdList[I].Cmd = Cmd then begin
CmdList[I].Proc(Socket, Params);
Exit;
end;
end;
Socket.SendText('Unknown command' + #13#10);
end;
procedure TServerMainForm.ServerSocket1ClientDisconnect(Sender: TObject; Socket:
TCustomWinSocket);
begin
Memo1.Lines.Add('Client disconnected');
end;
procedure TServerMainForm.ServerSocket1Listen(Sender: TObject; Socket: TCustomWinSocket);
begin
Memo1.Lines.Add('Waiting for client connection');
end;
procedure TServerMainForm.ServerStartButtonClick(Sender: TObject);
begin
ServerSocket1.Port := 2500; // Almost any (free) port is OK
ServerSocket1.Open; // Start listening for clients
end;
procedure TServerMainForm.ServerStopButtonClick(Sender: TObject);
begin
ServerSocket1.Close;
Memo1.Lines.Add('Server stopped');
end;
{ TCmdItem }
constructor TCmdItem.Create(const ACmd: String; AProc: TCmdProc);
begin
Cmd := UpperCase(ACmd);
Proc := AProc;
end;
end.
Server DFM:
object ServerMainForm: TServerMainForm
Left = 0
Top = 0
Caption = 'ServerMainForm'
ClientHeight = 498
ClientWidth = 635
Color = clBtnFace
Font.Charset = DEFAULT_CHARSET
Font.Color = clWindowText
Font.Height = -11
Font.Name = 'Tahoma'
Font.Style = []
OldCreateOrder = False
DesignSize = (
635
498)
PixelsPerInch = 96
TextHeight = 13
object PaintBox1: TPaintBox
Left = 8
Top = 48
Width = 617
Height = 273
Anchors = [akLeft, akTop, akRight, akBottom]
OnPaint = PaintBox1Paint
end
object Memo1: TMemo
Left = 8
Top = 329
Width = 617
Height = 161
Anchors = [akLeft, akTop, akRight, akBottom]
Lines.Strings = (
'Memo1')
TabOrder = 0
end
object ServerStartButton: TButton
Left = 12
Top = 8
Width = 75
Height = 25
Caption = 'Server Start'
TabOrder = 1
OnClick = ServerStartButtonClick
end
object ServerStopButton: TButton
Left = 93
Top = 8
Width = 75
Height = 25
Caption = 'Server Stop'
TabOrder = 2
OnClick = ServerStopButtonClick
end
object ServerSocket1: TServerSocket
Active = False
Port = 0
ServerType = stNonBlocking
OnListen = ServerSocket1Listen
OnClientConnect = ServerSocket1ClientConnect
OnClientDisconnect = ServerSocket1ClientDisconnect
OnClientRead = ServerSocket1ClientRead
Left = 64
Top = 196
end
end