Chapter 54: Networking

Section 54.1: Basic TCP chat (TcpListener, TcpClient, NetworkStream)

using System; using System.IO; using System.Net;

using System.Net.Sockets; using System.Text;

class TcpChat

{

static void Main(string[] args)

{

if(args.Length == 0)

{

Console.WriteLine("Basic TCP chat"); Console.WriteLine(); Console.WriteLine("Usage:"); Console.WriteLine("tcpchat server <port>"); Console.WriteLine("tcpchat client <url> <port>"); return;

}

try

{

Run(args);

}

catch(IOException)

{

Console.WriteLine("--- Connection lost");

}

catch(SocketException ex)

{

Console.WriteLine("--- Can't connect: " + ex.Message);

}

}

static void Run(string[] args)

{

TcpClient client; NetworkStream stream;

byte[] buffer = new byte[256]; var encoding = Encoding.ASCII;

if(args[0].StartsWith("s", StringComparison.InvariantCultureIgnoreCase))

{

var port = int.Parse(args[1]);

var listener = new TcpListener(IPAddress.Any, port); listener.Start();

Console.WriteLine("--- Waiting for a connection..."); client = listener.AcceptTcpClient();

}

else

{

var hostName = args[1];

var port = int.Parse(args[2]); client = new TcpClient(); client.Connect(hostName, port);

}

stream = client.GetStream();

Console.WriteLine("--- Connected. Start typing! (exit with Ctrl-C)");

while(true)

{

if(Console.KeyAvailable)

{

var lineToSend = Console.ReadLine();

var bytesToSend = encoding.GetBytes(lineToSend + "\r\n"); stream.Write(bytesToSend, 0, bytesToSend.Length); stream.Flush();

}

if (stream.DataAvailable)

{

var receivedBytesCount = stream.Read(buffer, 0, buffer.Length);

var receivedString = encoding.GetString(buffer, 0, receivedBytesCount); Console.Write(receivedString);

}

}

}

}

Section 54.2: Basic SNTP client (UdpClient)

See RFC 2030 for details on the SNTP protocol.

using System;

using System.Globalization; using System.Linq;

using System.Net;

using System.Net.Sockets;

class SntpClient

{

const int SntpPort = 123;

static DateTime BaseDate = new DateTime(1900, 1, 1);

static void Main(string[] args)

{

if(args.Length == 0) { Console.WriteLine("Simple SNTP client"); Console.WriteLine();

Console.WriteLine("Usage: sntpclient <sntp server url> [<local timezone>]"); Console.WriteLine();

Console.WriteLine("<local timezone>: a number between -12 and 12 as hours from UTC"); Console.WriteLine("(append .5 for an extra half an hour)");

return;

}

double localTimeZoneInHours = 0; if(args.Length > 1)

localTimeZoneInHours = double.Parse(args[1], CultureInfo.InvariantCulture);

var udpClient = new UdpClient(); udpClient.Client.ReceiveTimeout = 5000;

var sntpRequest = new byte[48];

sntpRequest[0] = 0x23; //LI=0 (no warning), VN=4, Mode=3 (client)

udpClient.Send(

dgram: sntpRequest, bytes: sntpRequest.Length, hostname: args[0],

port: SntpPort);

byte[] sntpResponse; try

{

IPEndPoint remoteEndpoint = null;

sntpResponse = udpClient.Receive(ref remoteEndpoint);

}

catch(SocketException)

{

Console.WriteLine("*** No response received from the server"); return;

}

uint numberOfSeconds; if(BitConverter.IsLittleEndian)

numberOfSeconds = BitConverter.ToUInt32( sntpResponse.Skip(40).Take(4).Reverse().ToArray() ,0);

else

numberOfSeconds = BitConverter.ToUInt32(sntpResponse, 40);

var date = BaseDate.AddSeconds(numberOfSeconds).AddHours(localTimeZoneInHours);

Console.WriteLine(

$"Current date in server: {date:yyyy-MM-dd HH:mm:ss} UTC{localTimeZoneInHours:+0.#;-0.#;.}");

}

}