Delphi Socket and Indy for Windows

Delphi Socket and Indy

Each TCP connection takes place though a port, which is represented by a 16-bit number. The IP address and the TCP port together specify an Internet connection, or a socket. Different processes running on the same machine can not use the same socket(the same port).

The term Protocol is a set of rules the client and server agree on to determine the communication flow.

Standard Protocol and Port values are as follows:

HTTP (hypertext transfer protocol) -> 80

FTP (file transfer protocol) -> 21

SMTP (simple mail transfer protocol) -> 25

POP3 (post office protocol, version 3) -> 110

Telnet -> 23

Local Domain Name

How does the IP address map to a name ? On the Internet, the client program looks up the values on a domain name server.

But it is also possible to have a local host file, which is a text file you can easily edit to provide local mappings. Look at the HOSTS.SAM file (installed in a subdirectory of the Windows directory or folder. depending on the version of Windows you have) to see a sample

You can eventually rename the file HOSTS with out the extension,

to activate local host mapping.

Foundation of Socket Programming

The heart of the Internet is the Transmission Control Protocol / Internet Protocol (TCP/IP), a combination of two(2) separate protocols that work together to provide connections over the Internet (and that can also provide connection over a private intranet).

In brief, IP is responsible for defining and routing the datagrams (Internet Transmission units) and specifying the addressing scheme.

Specific IP addresses are reserved for unregistered internal networks. Internet routers ignore these address ranges, so you can freely do your tests without interfering with an actual network. For example, the "free" IP address range 192.168.0.0 through 192.168.0.255 can be used for experiments on a network of fewer than 255 machines.

Oh, and the loop back address is 127.0.0.1 by the way...

Indy's TCP component

InterNet Direct, Indy in short is a solution provided by Borland to address the Socket issues for the general users.

To let two(2) programs communicate over a socket(either on a local area network or over the Internet), You can use the IdTCPClient and IdTCPServer components. Place one of them on a program form and the other on another form in a different program; (note there will be two(2) programs a Master Server and a Slave Client) then, make them use the same port, and let the client program refer to the host of the server program, and you'll be able to open a connection between the two(2) applications.

for Example, in the IndySocket project group, below will clearly show the two(2) settings and as follows:

// server program

object IdTCPServer1: TIdTCPServer

DefaultPort = 1050

end

// client program

object IdTCPClient1: TIdTCPClient

Host = 'localhost'

Port = 1050

end

As this point, in the client program you can connect to the server by executing the codes below at the Form Create Event

IdTCPClient1.Connect(-1);

The server program has a list box used to log information. When a client connects or disconnects, the program lists the IP of that client along with the operation, as in the following OnConnect event handler:

procedure TFormServer.IdTCPServer1Connect (AThead: TIdPeerThread);

begin

lbLog.items.add('from: ' + AThead.connection.socket.binding.PeerIP);

end;

The First server command, called test, is the simplest one, because it is fully defined in its properties.

object IdTCPServer1: TIdTCPServer

CommandHandlers = <

item

command = 'test'

name = 'TIdCommandHandler0'

ParseParams = false

ReplyNormal.numericCode = 100

ReplyNormal.Text.Strings = ( 'Hello from your Indy Server')

ReplyNormal.TextCode = '100'

end

The Client code used to execute the command and show it's response is as follows:

procedure TFrmClient.btnTestClick(Sender: TObject);

begin

IdTCPClient1.SendCmd('test');

ShowMessage(IdTCPClient1.lastCmdResult.textcode + ':' + IdTCPClient1.lastCmdResult.text.text);

end;