SWE 344
Internet Protocols & Client Server
Programming
Connectionless Sockets
Connectionless Sockets
Because there is no connection between remote hosts, the UDP
application cannot use the standard Send() and Receive() Socket
methods. Instead, two new methods must be used, SendTo() and
ReceiveFrom().
SendTo() The SendTo() method specifies the data to send and the
IPEndpoint of the destination machine.
ReceiveFrom() The ReceiveFrom() method has the same formats
as the SendTo() method, with one important difference: the way
the EndPoint object is declared.
The UDP Server
using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
class SimpleUdpSrvr
{
public static void Main()
{
int recv;
byte[] data = new byte[1024];
IPEndPoint ipep = new IPEndPoint(IPAddress.Any, 9050);
Socket newsock = new Socket(AddressFamily.InterNetwork,
SocketType.Dgram, ProtocolType.Udp);
newsock.Bind(ipep);
Console.WriteLine("Waiting for a client...");
IPEndPoint sender = new IPEndPoint(IPAddress.Any, 0);
EndPoint Remote = (EndPoint)(sender);
recv = newsock.ReceiveFrom(data, ref Remote);
The UDP Server
Console.WriteLine("Message received from {0}:",
Remote.ToString());
Console.WriteLine(Encoding.ASCII.GetString(data, 0, recv));
string welcome = "Welcome to my test server";
data = Encoding.ASCII.GetBytes(welcome);
newsock.SendTo(data, data.Length, SocketFlags.None,
Remote);
while(true)
{
data = new byte[1024];
recv = newsock.ReceiveFrom(data, ref Remote);
}
}
}
Console.WriteLine(Encoding.ASCII.GetString(data, 0, recv));
newsock.SendTo(data, recv, SocketFlags.None, Remote);
The UDP Server
When creating your sample UDP server, be careful that you don’t
choose a UDP port that is already in use by another application on
your machine. You can monitor the arrangement of applications that
are listening on particular UDP ports by using the netstat command at
a command prompt.
C:\>netstat -a
Active Connections
Proto Local Address
Foreign Address State
TCP abednego:epmap
0.0.0.0:0
LISTENING
TCP abednego:microsoft-ds 0.0.0.0:0
LISTENING
TCP abednego:1025
0.0.0.0:0
LISTENING
TCP abednego:1034
0.0.0.0:0
LISTENING
TCP abednego:5000
0.0.0.0:0
LISTENING
UDP abednego:1027
*:*
UDP abednego:1035
*:*
UDP abednego:9050
*:*
UDP abednego:38037
*:*
UDP abednego:38293
*:*
UDP abednego:ntp
*:*
UDP abednego:1036
*:*
UDP abednego:1900
*:*
UDP abednego:12564
*:*
C:\>
A UDP Client
The UDP client program is similar to its partner server program.
Because the client does not need to wait on a specific UDP port for
incoming data, it does not use the Bind() method. Instead, it
employs a random UDP port assigned by the system when the data is
sent, and it uses the same port to receive return messages. If you
are in a production environment, you might want to specify a set
UDP port for the client as well, so that both the server and client
programs use the same port numbers.
using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
class SimpleUdpClient
{
public static void Main()
{
byte[] data = new byte[1024];
string input, stringData;
A UDP Client
IPEndPoint ipep = new IPEndPoint(
IPAddress.Parse("127.0.0.1"), 9050);
Socket server = new
Socket(AddressFamily.InterNetwork,
SocketType.Dgram, ProtocolType.Udp);
string welcome = "Hello, are you there?";
data = Encoding.ASCII.GetBytes(welcome);
server.SendTo(data, data.Length,
SocketFlags.None, ipep);
IPEndPoint sender = new
IPEndPoint(IPAddress.Any, 0);
EndPoint Remote = (EndPoint)sender;
data = new byte[1024];
int recv = server.ReceiveFrom(data, ref Remote);
Console.WriteLine("Message received from {0}:",
Remote.ToString());
Console.WriteLine(Encoding.ASCII.GetString(data,
0, recv));
while(true)
A UDP Client
{
}
input = Console.ReadLine();
if (input == "exit")
break;
server.SendTo(Encoding.ASCII.GetBytes(input), Remote);
data = new byte[1024];
recv = server.ReceiveFrom(data, ref Remote);
stringData = Encoding.ASCII.GetString(data, 0, recv);
Console.WriteLine(stringData);
}
Console.WriteLine("Stopping client");
server.Close();
}
Testing the Client and Server Programs
Start the SimpleUdpSrvr program on the assigned server machine
you will use for your testing. When the server program starts, it
displays a short message:
C:\>SimpleUdpSrvr
Waiting for a client...
C:\>SimpleUdpClient
Message received from
127.0.0.1:9050:
Welcome to my test server
C:\>SimpleUdpSrvr
Waiting for a client...
Message received from 127.0.0.1:1340:
Hello, are you there?
END