CNDS

You may use Visual Basic, Java or Delphi for the implementation of Client/Server programming:

Delphi Client/Server ZIP

how to?

Delphi has a ClientSocket component which supports a client connection to a server. This is contained in the Internet palette. An example of a client socket added to a form is shown in Figure 1.

Figure 1:

In the example in Figure 1 the following code can be used to make a connection to a server:

Connections from client to server

procedure TForm1.Button1Click(Sender: TObject);
var port:integer;
begin
port:=StrToInt(edit4.text);
ClientSocket.Port:=port;
ClientSocket.Host:=edit3.text;
ClientSocket.ClientType:=ctNonBlocking;
ClientSocket.Active:=true;
end;

Initially the properties are set for the socket connection, such as the port, and the server address. Finally the active property is set, which causes the client to connect to the server. When the client detects a connection the Connection event occurs:

Confirmation of the connection on the client

procedure TForm1.ClientSocketConnect(Sender: TObject;
Socket: TCustomWinSocket);
begin
Checkbox1.Checked:=true;
Edit1.Text:=Socket.LocalAddress;
Edit2.Text:=Socket.LocalHost;
Memo2.Lines.Clear;
edit5.Text:='';
end;

The Socket variable contains the information on the connection, such as the LocalAddress, LocalHost, LocalPort, RemoteAddress, RemoteHost and RemoteAddress.

When the code is ready to be send the following can be used to take the text from the Edit text box and send it over the socket.

Sending data form the client to the server

ClientSocket.Socket.SendText(edit5.text + chr(13)+chr(10));

The SendText method is used to send the text over the connected socket. Figure 2 shows an example of some of the properties and routines associated with sockets. Also, in this example, the ASCII characters for Line Feed (10) and Carriage Return (13) are sent to force a new line on the server.

When data arrives over the socket the Read event is called (with the information on the socket passed in the Socket parameter). The ReceiveText property can then be used to read the data from the socket (as illustrated in Figure 3):

Receiving data from the server

procedure TForm1.ClientSocketRead(Sender: TObject;
Socket: TCustomWinSocket);
begin
Memo2.Lines.Add(Socket.ReceiveText);
end;

Figure 2:

Figure 3:

The following code gives an outline of the code:

Client program example

unit client01;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls,
Forms,Dialogs, ScktComp, StdCtrls;

type
TForm1 = class(TForm)
ClientSocket: TClientSocket;
Label1: TLabel;
Label2: TLabel;
GroupBox1: TGroupBox;
Edit3: TEdit;
Label3: TLabel;
Label5: TLabel;
Edit4: TEdit;
Button1: TButton;
Memo2: TMemo;
GroupBox2: TGroupBox;
CheckBox1: TCheckBox;
Label4: TLabel;
Label6: TLabel;
Edit1: TEdit;
Edit2: TEdit;
Label7: TLabel;
Edit5: TEdit;
Button2: TButton;

procedure ClientSocketRead(Sender: TObject;
Socket: TCustomWinSocket);
procedure Button1Click(Sender: TObject);
procedure ClientSocketConnect(Sender: TObject;
Socket: TCustomWinSocket);
procedure Button2Click(Sender: TObject);

private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.ClientSocketRead(Sender: TObject;
Socket: TCustomWinSocket);
begin
Memo2.Lines.Add(Socket.ReceiveText);
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
ClientSocket.Socket.SendText(edit5.text + chr(13)+chr(10));
end;

end.

A sample run is given next.

Figure 4:

Ref: Extract from Chapter 13, Mastering Delphi, W.Buchanan, Palgrave, 2002.