network programming chapter 4 socket programming in.net

Network Programming

Chapter 4Socket Programming in .NET

Basic Outline

• An Overview of Sockets

• Working with Sockets in .NET

• Asynchronous Programming

• Socket Permissions

An Overview of Sockets

• Definition– A socket is one end of a two-way communication link between two programs running on a

network– Connection can be local or remote– Socket implementation provides the encapsulation of the network and transport level

protocols– A socket, being a resource, is also represented by a descriptor

• Socket Types– Stream Sockets

• Connection-orientated• Consists of a stream of bytes that can be bidirectional• Guarantees error correction, handles delivery and preserves data sequence and guarantees non-

duplicated data• High level of quality using TCP• Suitable for large amounts of data• Large overhead makes it bulky for small amounts of data• Path is formed before communication starts (ensures that both parties are active and participating)• Uses data packets and relies on TCP for delivery of packets

– Datagram Sockets– Raw Sockets

• Sockets and Ports


• Definition• Socket Types

– Stream Sockets– Datagram Sockets

• Also called connectionless sockets (no explicit connections are established)

• Message is just sent without knowledge of the receiver• Uses UDP to pass data from client to server• Message size limitations and no guarantee of delivery• Used when overhead of stream sockets does not warrant the

message (i.e. when the message is too small/insignificant)– Raw Sockets




– Stream Sockets– Datagram Sockets– Raw Sockets

• A socket that takes packets, bypassing the TCP and UDP layers in the TCP/IP stack and sends them directly to the application

• Purpose is to bypass the mechanism by which the computer handles TCP/IP.

• Provides a custom implementation of the TCP/IP stack• It is more efficient than going through the client’s main stack• No processing on the packet (i.e. raw)• The receiving application has to handle the data appropriately and deal with

actions such as stripping off headers and parsing• Used for custom low-level protocol applications




– Stream Sockets– Datagram Sockets– Raw Sockets

• Sockets and Ports– A port is defined to solve the problem of communicating with multiple applications

simultaneously; it basically expands the notion of an IP address– A computer can identify an arriving packet by the port number it is arriving

through– Port numbers are established when connections are made– The socket is composed of the IP address of the machine and the port number

used by the TCP application; this is also called an endpoint.– Endpoints are unique across the entire Internet because IP addresses are unique– Certain services have port numbers reserved for them; these are the well-known

port numbers (FTP = 21)


Server ClientPort

Connection Request

Normally a client/server application using sockets consists of two different applications: a client that initiates the connection with the target (server) and the server, which waits for the connection from the client. For example, on the client side, the client must know the target’s address and the port number. To make the connection request, the client tries to establish the connection with the server.

Server

Client

Port

Port

Startcommunication

PortIf everything goes well, provided that the server is running before the client tries to connect to it, the server accepts the connection. Upon acceptance, the server application create a new socket to deal specifically with the connect client.The client and the server can now communicate with each other by reading from and writing to their respective sockets.

Basic Outline





Classes in the System.Net.Sockets Namespace

Classes DescriptionMulticastOption Contains IPAddress values used to join and drop multicast groups. Sets IP

address values for joining or leaving an IP multicast group.

NetworkStream Provides the underlying stream of data for network access. It is a high-level abstraction representing a connection to a TCP/IP communication channel.

TcpClient Provides client connections for TCP network services. Builds on the socket class to provide TCP services at a higher level. TCPClient provides several methods for sending and receiving data over a network.

TcpListener Listens for connections from TCP network clients. Builds on the low-level Socket class. Its main purpose is in server applications. This class listens for the incoming client connections and notifies the application of any connections.

UdpClient Provides User Datagram Protocol (UDP) network services. Implements UDP services. UDP is a connectionless protocol, therefore a different type of functionality is required to implement UDP services in .NET

SocketException The exception that is thrown when a socket error occurs. The exception thrown when an error occurs in a socket.

Socket Implements the Berkeley sockets interface. Provides the basic functionality of a socket application.

System.Net.Sockets.Socket Properties

AddressFamily Gets the address family of the Socket. The value is from the Socket.AddressFamily enumeration.

Available Gets the amount of data that has been received from the network and is available to be read (returns the amount of available data to read).

Blocking Gets or sets a value that indicates whether the Socket is in blocking mode.

Connected Gets a value that indicates whether a Socket is connected to a remote host as of the last Send or Receive operation.

LocalEndPoint Gets the local endpoint.

System.Net.Sockets.Socket Properties

ProtocolType Gets the protocol type of the Socket.

RemoteEndPoint Gets the remote endpoint of the socket.

SocketType Gets the type of the Socket.

SupportsIPv4 Returns a Boolean value indicating whether IPv4 support is available and enabled on the current host.

SupportsIPv6 Returns a Boolean value that indicates whether the Framework supports IPv6 for certain obsolete Dns members.

System.Net.Sockets.Socket Methods

Method DescriptionAccept Creates a new Socket for a newly created connection to handle the incoming

connection request.

Bind Associates a Socket with a local endpoint for listening for incoming connections.

Close Overloaded. Closes the Socket connection and releases all associated resources.

Connect Overloaded. Establishes a connection to a remote host.

GetSocketOption Overloaded. Returns the value of a Socket option.

IOControl Overloaded. Sets low-level operating modes for the Socket. This method provides low-level access to the underlying socket instance of the Socket class.

System.Net.Sockets.Socket Methods

Method DescriptionListen Places a Socket in a listening state. This method

is exclusively used to server applications.

Receive Overloaded. Receives data from a bound Socket.

Poll Determines the status of the Socket.

Select Determines the status of one or more sockets.

Send Overloaded. Sends data to a connected Socket.

SetSocketOption Overloaded. Sets a Socket option

Shutdown Disables sends and receives on a Socket.

Working with Sockets in .NET

• Creating a TCP Stream Socket Application– Building a TCP Server– Building a TCP Client

• Managing Exceptions with System.NET Sockets

• Setting and Retrieving Socket Options

Building a TC-based Server

Server

Open a Socket

(Socket)

Name the Socket(Bind)

Listen for incoming Connection(Listen)

Accept client connection(Accept)

Send/Receive Data(Send/Receive)

Close Socket(Close)

using System;using System.Collections.Generic;using System.Text;using System.Net.Sockets;using System.Net;

namespace TestSockets{ class SocketServer { static void Main(string[] args) { //establish the local endpoint for the socket IPHostEntry ipHost = Dns.GetHostEntry("localhost"); IPAddress ipAddr = ipHost.AddressList[0];

IPEndPoint ipEndPoint = new IPEndPoint(ipAddr, 1100);

Establish the local endpoint for the socket.Before opening a socket, you need to establish a local endpoint address.The local endpoint address is the host IP Address and the port number that is going to be used

Note: System.Net & System.Net.Sockets

Returns all network addresses supported

//Create a TCP/IP Socket Socket sListener = new Socket(AddressFamily.InterNetwork,

SocketType.Stream, ProtocolType.Tcp);

//Bind the Socket to the local endpoint and listen to the incoming sockets

try

{

sListener.Bind(ipEndPoint);

sListener.Listen(10);

while (true)

{

Console.WriteLine("Waiting for connection on port {0}.", ipEndPoint);

The Bind method associates a socket with a local endpoint. You must call Bind before any attempt to call Listen or Accept.

The maximum pending connections

//program is suspended while waiting for an incoming connection

Socket handler = sListener.Accept();

string data = null;

//We got the client attempting to connect

while (true)

{

byte[] bytes = new byte[1024];

int bytesRec = handler.Receive(bytes);

data += Encoding.ASCII.GetString(bytes, 0, bytesRec);

if (data.IndexOf("<TheEnd>") > -1)

break;

}//end of while

Accept extracts the first connection in the queue, receives the client connection and creates a new socket to handle it. The Accept method blocks the caller thread until the connection is present.

Accept may open up multiple sockets. Once the client and server are connected with each other, you an send and receive using the Send and Receive methods of the Socket class. The exact protocol definition between the client and server needs to be clearly defined before sockets may send and receive.

//show the data on the console Console.WriteLine("Text Received: {0}", data); string theReply = "Thank you for those " +

data.Length.ToString() + " characters..."; byte[] msg = Encoding.ASCII.GetBytes(theReply); handler.Send(msg); handler.Shutdown(SocketShutdown.Both); handler.Close(); }//end of while Console.WriteLine("press a key"); } //end of try catch(Exception e) { Console.WriteLine(e.ToString()); } finally { sListener.Close(); } Console.ReadLine(); } }}

Building a TC-based Client

Client

Open a Socket

(Socket)

Connect to Remote Host(Connect)

Send/Receive Data(Send/Receive)

Close Socket(Close)


namespace TestSocketClient{ class SocketClient { static void Main(string[] args) { //Data buffer for incoming data byte[] bytes = new byte[1024];

//Connect to a remote device try { //Establish the remote endpoint for the socket IPHostEntry ipHost = Dns.GetHostEntry("127.0.0.1"); IPAddress ipAddr = ipHost.AddressList[0]; IPEndPoint ipEndPoint = new IPEndPoint(ipAddr, 1100); Socket sender = new Socket(AddressFamily.InterNetwork,


//Connect the socket to the remote endpoint sender.Connect(ipEndPoint);

Console.WriteLine("Socket connected to {0}", sender.RemoteEndPoint.ToString());

string theMessage = "This is a test."; byte[] msg = Encoding.ASCII.GetBytes(theMessage + "<TheEnd>");

//Send the data through the socket int bytesSent = sender.Send(msg);

//Recieve the response from the remote device int bytesRec = sender.Receive(bytes);

Console.WriteLine("The Server says : {0}", Encoding.ASCII.GetString(bytes, 0, bytesRec));

//Release the Socket sender.Shutdown(SocketShutdown.Both); sender.Close();

} //end of try catch (Exception e) { Console.WriteLine("Exception: {0}", e.ToString()); } //end of catch Console.ReadLine(); } //end of Main }}

Constructing a Port Scanner

• Scans for open ports (sees who is listening)

• Makes a connection with each port specified in the loop

• Socket Exceptions have an integer value associated with it


namespace PortScanner{ class Program { static void Main(string[] args) { IPAddress address = IPAddress.Parse("127.0.0.1"); int[] listeningPorts = new int[50]; int count = -1; Socket sSocket = new Socket(AddressFamily.InterNetwork,


//Loop through ports 1 to 1024 for (int i = 1; i <= 1024; i++) { Console.WriteLine("Checking port {0}", i.ToString()); try { //Establish the remote endpoint for the socket IPEndPoint endPoint = new IPEndPoint(address, i); sSocket = new Socket(AddressFamily.InterNetwork,


//Connect the socket to the remote endpointsSocket.Connect(endPoint);

Console.WriteLine("Port {0} is listening.", i.ToString()); ++count; listeningPorts[count] = i;

} //end of try catch (SocketException ignored) { if (ignored.ErrorCode != 10061) Console.WriteLine(ignored.Message); } //end of catch finally { if (sSocket.Connected) { sSocket.Shutdown(SocketShutdown.Both); sSocket.Close(); } //end of if } //end of finally } //end of for loop

Console.WriteLine("There are {0} ports listening.", count + 1); for (int j = 0; j <= count; ++j) Console.WriteLine("Port {0} is listening.",

listeningPorts[j].ToString()); Console.ReadLine(); } }}

Managing Exceptions with System.Net.Sockets

• Socket class generally throws the SocketException

• SocketException thrown when– Mismatch or incompatibility in AddressFamily, SocketType or ProtocolType

– Possible places: construct new socket or connect method

Socket Exception EnumerationsMember name Description

AccessDenied An attempt was made to access a Socket in a way that is forbidden by its access permissions.

AddressAlreadyInUse Only one use of an address is normally permitted.

AddressFamilyNotSupported The address is incompatible with the requested protocol.

AddressNotAvailable The selected address is valid in this context.

AlreadyInProgress The nonblocking Socket already has an operation in progress.

ConnectionAborted The connection was aborted by the .NET Framework or the underlying socket provider.

ConnectionRefused The remote host is actively refusing a connection.

ConnectionReset The connection was reset by the remote peer.

DestinationAddressRequired A required address was omitted from an operation on a Socket.

Disconnecting A graceful shutdown is in progress.

Fault An invalid pointer address was detected by the underlying socket provider.

HostDown The operation failed because the remote host is down.

HostNotFound No such host is known. The name is not an official host name or alias.


HostUnreachable There is no network route to the specified host.

InProgress A blocking operation is in progress.

Interrupted A blocking Socket call was cancelled.

InvalidArgument An invalid argument was supplied to a Socket member.

IOPending The application has initiated an overlapped operation that cannot be completed immediately.

IsConnected The Socket is already connected.

MessageSize The datagram is too long.

NetworkDown The network is not available.

NetworkReset The application tried to set KeepAlive on a connection that has already timed out.

NetworkUnreachable No route to the remote host exists.

NoBufferSpaceAvailable No free buffer space is available for a Socket operation.

NoData The requested name or IP address was not found on the name server.

NoRecovery The error is unrecoverable or the requested database cannot be located.

http://msdn2.microsoft.com/en-us/library/system.net.sockets.socketoptionname.aspx


NotConnected The application tried to send or receive data, and the Socket is not connected.

NotInitialized The underlying socket provider has not been initialized.

NotSocket A Socket operation was attempted on a non-socket.

OperationAborted The overlapped operation was aborted due to the closure of the Socket.

OperationNotSupported The address family is not supported by the protocol family.

ProcessLimit Too many processes are using the underlying socket provider.

ProtocolFamilyNotSupported The protocol family is not implemented or has not been configured.

ProtocolNotSupported The protocol is not implemented or has not been configured.

ProtocolOption An unknown, invalid, or unsupported option or level was used with a Socket.

ProtocolType The protocol type is incorrect for this Socket.

Shutdown A request to send or receive data was disallowed because the Socket has already been closed.

SocketError An unspecified Socket error has occurred.


SocketNotSupported The support for the specified socket type does not exist in this address family.

Success The Socket operation succeeded.

SystemNotReady The network subsystem is unavailable.

TimedOut The connection attempt timed out, or the connected host has failed to respond.

TooManyOpenSockets There are too many open sockets in the underlying socket provider.

TryAgain The name of the host could not be resolved. Try again later.

TypeNotFound The specified class was not found.

VersionNotSupported The version of the underlying socket provider is out of range.

WouldBlock An operation on a non-blocking socket cannot be completed immediately.

Setting and Retrieving Socket Options

• SetSocketOption– Customise socket– SocketOptionLevel– SocketOptionName– Value to set for the socket option

• GetSocketOption

SetSocketOptionName Description

Socket.SetSocketOption (SocketOptionLevel, SocketOptionName, Boolean)

Sets the specified Socket option to the specified Boolean value.

Socket.SetSocketOption (SocketOptionLevel, SocketOptionName, Byte[])

Sets the specified Socket option to the specified value, represented as a byte array. Supported by the .NET Compact Framework.

Socket.SetSocketOption (SocketOptionLevel, SocketOptionName, Int32)

Sets the specified Socket option to the specified integer value. Supported by the .NET Compact Framework.

Socket.SetSocketOption (SocketOptionLevel, SocketOptionName, Object)

Sets the specified Socket option to the specified value, represented as an object. Supported by the .NET Compact Framework.

http://msdn2.microsoft.com/en-us/library/e160993d.aspx






http://msdn2.microsoft.com/en-us/library/system.boolean.aspx

http://msdn2.microsoft.com/en-us/library/w8h0abdk.aspx






Socket Option Levels

• Enumeration

• Used to specify at which level of the OSI model the option is applied

SocketOptionLevel

Member name Description

IP Socket options apply only to IP sockets.

IPv6 Socket options apply only to IPv6 sockets.

Socket Socket options apply to all sockets.

Tcp Socket options apply only to TCP sockets.

Udp Socket options apply only to UDP sockets.

Socket Option Names

• Defines the name of the parameter whose value is being set

• Examples– ReuseAddress– Linger

SocketOptionNameMember name Description

AcceptConnection The socket is listening.

AddMembership Add an IP group membership.

AddSourceMembership Join a source group.

BlockSource Block data from a source.

Broadcast Permit sending broadcast messages on the socket.

BsdUrgent Use urgent data as defined in RFC-1222. This option can be set only once; after it is set, it cannot be turned off.

ChecksumCoverage Set or get the UDP checksum coverage.

Debug Record debugging information.

DontFragment Do not fragment IP datagrams.

DontLinger Close the socket gracefully without lingering.

DontRoute Do not route; send the packet directly to the interface addresses.

DropMembership Drop an IP group membership.

DropSourceMembership Drop a source group.

Error Get the error status and clear.

SocketOptionName


ExclusiveAddressUse Enables a socket to be bound for exclusive access.

Expedited Use expedited data as defined in RFC-1222. This option can be set only once; after it is set, it cannot be turned off.

HeaderIncluded Indicates that the application provides the IP header for outgoing datagrams.

HopLimit Specifies the maximum number of router hops for an Internet Protocol version 6 (IPv6) packet. This is similar to Time to Live (TTL) for Internet Protocol version 4.

IPOptions Specifies the IP options to be inserted into outgoing datagrams.

IpTimeToLive Set the IP header Time-to-Live field.

KeepAlive Use keep-alives.

Linger Linger on close if unsent data is present.

MaxConnections Not supported; will throw a SocketException if used.

MulticastInterface Set the interface for outgoing multicast packets.

SocketOptionName


MulticastLoopback An IP multicast loopback.

MulticastTimeToLive An IP multicast Time to Live.

NoChecksum Send UDP datagrams with checksum set to zero.

NoDelay Disables the Nagle algorithm for send coalescing.

OutOfBandInline Receives out-of-band data in the normal data stream.

PacketInformation Return information about received packets.

ReceiveBuffer Specifies the total per-socket buffer space reserved for receives. This is unrelated to the maximum message size or the size of a TCP window.

ReceiveLowWater Specifies the low water mark for Receive operations.

ReceiveTimeout Receive a time-out. This option applies only to synchronous methods; it has no effect on asynchronous methods such as the BeginSend method.

SocketOptionNameMember name Description

ReuseAddress Allows the socket to be bound to an address that is already in use.

SendBuffer Specifies the total per-socket buffer space reserved for sends. This is unrelated to the maximum message size or the size of a TCP window.

SendLowWater Specifies the low water mark for Send operations.

SendTimeout Send a time-out. This option applies only to synchronous methods; it has no effect on asynchronous methods such as the BeginSend method.

Type Get the socket type.

TypeOfService Change the IP header type of the service field.

UnblockSource Unblock a previously blocked source.

UpdateAcceptContext Updates an accepted socket's properties by using those of an existing socket. This is equivalent to using the Winsock2 SO_UPDATE_ACCEPT_CONTEXT socket option and is supported only on connection-oriented sockets.

UpdateConnectContext Updates a connected socket's properties by using those of an existing socket. This is equivalent to using the Winsock2 SO_UPDATE_CONNECT_CONTEXT socket option and is supported only on connection-oriented sockets.

UseLoopback Bypass hardware when possible.

ReuseAddress

• By default only one socket may be bound to a local address that is already in use. However, you may want to bind more than one socket to a local address

• The solution is the ReuseAddress

ReuseAddress (throws error)

using System;using System.Collections.Generic;using System.Text;using System.Net;using System.Net.Sockets;

namespace SocketReuseAddress{ class Program { static void Main(string[] args) { try { //Establish the local endpoint for the socket IPEndPoint ipEndPoint = new IPEndPoint(Dns.GetHostEntry(Dns.GetHostName()).AddressList[0], 11000);

//Create a TCP/IP Socket Socket sListener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

//Bind the socket to the local endpoint and listen to incoming sockets sListener.Bind(ipEndPoint); sListener.Listen(10);

//Create a new socket Socket sListener2 = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

//Bind the socket to the local endpoint and listen to the incoming sockets

sListener2.Bind(ipEndPoint); sListener2.Listen(10); } catch (Exception e) { Console.WriteLine(e.Message); }

//Stop console from closing Console.ReadLine(); } }}

ReuseAddress (fixed)

using System;using System.Collections.Generic;using System.Text;using System.Net;using System.Net.Sockets;

namespace SocketReuseAddress{ class Program { static void Main(string[] args) { try { //Establish the local endpoint for the socket IPEndPoint ipEndPoint = new IPEndPoint(Dns.GetHostEntry(Dns.GetHostName()).AddressList[0], 11000);

//Create a TCP/IP Socket Socket sListener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

//Bind the socket to the local endpoint and listen to incoming sockets sListener.Bind(ipEndPoint); sListener.Listen(10);

//Create a new socket Socket sListener2 = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

//Adding ReuseAddress option to prevent error message sListener2.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, 1);

//Bind the socket to the local endpoint and listen to the incoming sockets

sListener2.Bind(ipEndPoint); sListener2.Listen(10); Console.WriteLine("Sockets successfully bound."); } catch (Exception e) { Console.WriteLine(e.Message); }

//Stop console from closing Console.ReadLine(); } }}

Linger

• Linger (from dictionary.com)– v. lin·gered, lin·ger·ing, lin·gers

v. intr.– To be slow in leaving, especially out of reluctance; tarry. See

Synonyms at stay1. – To remain feebly alive for some time before dying. – To persist: an aftertaste that lingers. – To proceed slowly; saunter. – To be tardy in acting; procrastinate. –

v. tr.• To pass (a period of time) in a leisurely or aimless manner.

• Linger has an enumeration, called LingerOption

Linger

// Send operations will time-out if //confirmation is not received within 1000 //milliseconds.s.SetSocketOption (SocketOptionLevel.Socket, SocketOptionName.SendTimeout, 1000);

// The socket will linger for 10 seconds //after Socket.Close is called.LingerOption lingerOption = new LingerOption (true, 10);

s.SetSocketOption (SocketOptionLevel.Socket, SocketOptionName.Linger, lingerOption);

Basic Outline





Asynchronous Programming

• Introduction

• Creating an Asynchronous Client Application

• Creating an Asynchronous Server Application


• Most socket functions– Indefinite time to complete– Blocked

• Asynchronous programming– Functions that “can’t afford to hang around”– A connection does not block an application– Events can be..

• Signalled• Non-signalled


• Two event types– Automatic (set themselves back to non-signalled state

when they are signalled)– Manual (stay signalled until manually reset to non-

signalled state)

• ManualResetEvent – use to indicate that you want your program to continue

• The .NET Framework provides a delegate class for asynchronous operations.

• The class is called AsyncCallback


• Introduction



The flow of an asynchronous client application

Original Thread

Create Socket

Waiting

Waiting

Waiting and further processing

Close Socket

Initialise Connection Request: BeginConnect

ConnectCallBack()

Initialise Sending Request: BeginSend

SendCallBack()

Initialise Receiving Request: BeginReceive

Secondary Thread

ReceiveCallback()

Asynchronous Clientusing System;using System.Net;using System.Net.Sockets;using System.Text;using System.Threading;

namespace AsyncClientExample{

/// <summary>/// Summary description for Class1./// </summary>public class AsyncClient{

public static ManualResetEvent connectDone = new ManualResetEvent( false );public static ManualResetEvent sendDone = new ManualResetEvent( false );public static ManualResetEvent receiveDone = new ManualResetEvent( false );

public static string response = string.Empty;public static string sb = string.Empty;

public static byte[] buffer = new byte[8192];

Asynchronous Client//ConnectCallback is called when connection is readypublic static void ConnectCallback( IAsyncResult a ){

Thread thr = Thread.CurrentThread;Console.WriteLine( "ConnectCallback Thread State: " + thr.ThreadState );

Socket sktClient = (Socket) a.AsyncState;sktClient.EndConnect( a );Console.WriteLine("Socket connected to {0}", sktClient.RemoteEndPoint.ToString() );

//Signal connectDone event to inform other thread//that connection is ready for useconnectDone.Set();} //End public static void ConnectCallback( IAsyncResult a )

Asynchronous Client//SendCallback is called when sending is completepublic static void SendCallback( IAsyncResult a ){

Thread thr = Thread.CurrentThread;Console.WriteLine( "SendCallback Thread State: " + thr.ThreadState );

Socket sktClient = (Socket) a.AsyncState;int bytesSent = sktClient.EndSend( a );

Console.WriteLine( "Sent {0} bytes to server", bytesSent );

//Signal sentDone event sendDone.Set();

} //End public static void SendCallback( IAsyncResult a )

Asynchronous Client//ReceiveCallback is called when receiving is completepublic static void ReceiveCallback( IAsyncResult a ){

Thread thr = Thread.CurrentThread;Console.WriteLine( "ReceiveCallback Thread State: " + thr.ThreadState );Socket sktClient = (Socket) a.AsyncState;int bytesRead = sktClient.EndReceive( a );

if( bytesRead > 0 ){

sb += Encoding.ASCII.GetString(buffer,0, bytesRead);sktClient.BeginReceive( buffer, 0, buffer.Length, 0, new AsyncCallback( ReceiveCallback), sktClient );

}else{

//Signal receiveDone eventreceiveDone.Set();

}} //End public static void receiveCallback( IAsyncResult a )

Asynchronous Client[STAThread]static void Main(string[] args){

try{

Thread thr = Thread.CurrentThread;Console.WriteLine( "Main Thread State: " +

thr.ThreadState );IPHostEntry ipHost = Dns.Resolve( "127.0.0.1" );IPAddress ipAddr = ipHost.AddressList[0];IPEndPoint endPoint = new IPEndPoint( ipAddr,

11000 );

Socket sktClient = new Socket( AddressFamily.InterNetwork,

SocketType.Stream,ProtocolType.Tcp );

Asynchronous Client//Create new thread to initiate the connection to //the serversktClient.BeginConnect( endPoint, new AsyncCallback( ConnectCallback ), sktClient );

connectDone.WaitOne();

string data = "This is a test";

for( int i = 0; i < 72; i++ ){

data += i.ToString() + ":" + (new string( '=', i ));}byte[] byteData = Encoding.ASCII.GetBytes( data + "." );

//Send data in a separate threadsktClient.BeginSend( byteData, 0, byteData.Length, SocketFlags.None, new AsyncCallback( SendCallback ), sktClient );

Asynchronous Client//Do something in the main threadbyte[] byteData = Encoding.ASCII.GetBytes( data + "." );

//Send data in a separate threadsktClient.BeginSend( byteData, 0, byteData.Length, SocketFlags.None,

new AsyncCallback( SendCallback ), sktClient );

//Do something in the main threadfor( int i = 0; i < 10; i++ ){

Console.WriteLine( i );Thread.Sleep( 10 );

}//Wait until all sending is donesendDone.WaitOne();

Asynchronous Client//Start receiving data in a separate threadsktClient.BeginReceive( buffer, 0, buffer.Length,

SocketFlags.None,new AsyncCallback( ReceiveCallback ), sktClient );

receiveDone.WaitOne();

Console.WriteLine( "Response received: {0} ", sb );sktClient.Shutdown( SocketShutdown.Both );sktClient.Close();

}catch( Exception e ){

Console.WriteLine( e.ToString() );}

Console.ReadLine();

} //End Main} //End Class} //End Namespace


• Introduction



Asynchronous Serverusing System;using System.Net;using System.Net.Sockets;using System.Text;using System.Threading;

namespace AsyncServerExample{

/// <summary>/// Summary description for Class1./// </summary>class AsyncServer{

//Buffer to send and receive datapublic static byte[] buffer = new byte[8192];

//Event class to support synchronizationpublic static ManualResetEvent socketEvent = new

ManualResetEvent( false );

[STAThread]static void Main(string[] args){

Console.WriteLine( "Main Thread ID: " + AppDomain.GetCurrentThreadId() );

byte[] bytes = new byte[8192];IPHostEntry ipHost = Dns.Resolve( Dns.GetHostName() );IPAddress ipAddr = ipHost.AddressList[0];IPEndPoint localEnd = new IPEndPoint( ipAddr, 11000 );Socket sListener = new

Socket( AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp );

//Bind socketsListener.Bind( localEnd);//Start listeningsListener.Listen( 10 );Console.WriteLine( "Waiting for a connection....." );AsyncCallback aCallback = new

AsyncCallback( AcceptCallback );//Asynchronous method for accepting connectionssListener.BeginAccept( aCallback, sListener );//Waiting for other threads to finishsocketEvent.WaitOne();Console.Read();

} //End Main()

Method AcceptCallBackpublic static void AcceptCallback( IAsyncResult ar ){

Console.WriteLine( "AcceptCallback Thread ID: " + AppDomain.GetCurrentThreadId() );

//Retrieved the socketSocket listener = (Socket) ar.AsyncState;//New socketSocket handler = listener.EndAccept( ar );

handler.BeginReceive( buffer, 0, buffer.Length, 0,new AsyncCallback( ReceivCallback),

handler );} //End public static void

AcceptCallback( IAsyncResult ar )

public static void ReceiveCallback( IAsyncResult ar ){

Console.WriteLine( "ReceiveCallback Thread ID: "+ AppDomain.GetCurrentThreadId() );string content = string.Empty;Socket handler = (Socket) ar.AsyncState;int bytesRead = handler.EndReceive( ar );

//check for dataif( bytesRead > 0 ){

//Append data to main stringcontent += Encoding.ASCII.GetString( buffer, 0, bytesRead );

//If end of message character is encounteredif( content.IndexOf( "." ) > -1 ){

Console.WriteLine( "Read {0} bytes from socket. \n Data: {1}",content.Length, content );

byte[] byteData = Encoding.ASCII.GetBytes( content );//Send data back to the clienthandler.BeginSend( byteData, 0, byteData.Length, 0, new

AsyncCallback( SendCallback ), handler );}else {

//Otherwise receive remaining datahandler.BeginReceive( buffer, 0, buffer.Length, 0, new

AsyncCallback( ReceiveCallback), handler );}

}} //End public static void ReceiveCallback( IAsyncResult ar )

public static void SendCallback( IAsyncResult ar ){

Console.WriteLine( "SendCallback Thread ID: " + AppDomain.GetCurrentThreadId() );

Socket handler = (Socket) ar.AsyncState;

//Send Data back to clientint bytesSent = handler.EndSend( ar );

Console.WriteLine( "Sent {0} bytes to Client. ", bytesSent );

handler.Shutdown( SocketShutdown.Send );handler.Close();

//Set main thread eventsocketEvent.Set();

} //End public static void SendCallback( IAsyncResult ar )} //End class AsyncServer

} //End namespace AsyncServerExample

Basic Outline





Socket Permissions

• Introduction

• Using Imperative Security

• Using Declarative Security

Socket Permissions• Help develop secure code• Only the code that has permission to run in the current context can

be executed• Each code-access permission demonstrates one of the following

rights:– The right to access protected resources such as files– The right to perform a protected operation such as accessing managed

code• SocketPermission class

– enforces code-access permissions– Used to control rights to make or accept connections (control

connections via sockets)– Consists of host specification and a set of “actions” specifying ways to

connect to the host– Enforces secure code by monitoring the values of the host name, IP

address and transport protocol

Socket Permissions

• There are two ways to enforce security permission in C# sockets:– Imperatively

• Implements permissions by creating a new instance of the SocketPermission class to demand a particular permission when the code is executed, such as the right to make a TCP connection. It is generally used when the security setting are changed at runtime.

– Declaratively• Declarative syntax uses attributes to place security

information into the metadata of your code, so that the client calls your code can use reflection to see what permissions are required by the code.

Imperative Security

• Creates a new instance of the SocketPermission class to enforce security

• Use imperative security syntax to perform demands and overrides, but not requests

• Before calling the corresponding security measure, it is necessary to initialise the state of the SocketPermission class through the constructor so that it represents the particular form of permission that you want to use.

• This kind of security is only useful when you have some information needed for security that is available only at runtime; for example; if you want to secure some host over a port but don’t know the host name and port number until the program executes

Imperative Security

using System;using System.Collections.Generic;using System.Text;using System.Net;using System.Net.Sockets;using System.Security;using System.Security.Permissions;

namespace SocketsImperativeSecurity{ class Program { static void Main(string[] args) { //Option could be either Assert or Deny passed on the command line //If option is Assert, then the program executes successfully //Otherwise, it triggers a SecurityException string option = null;

if (args.Length > 0) { option = args[0]; } else { option = "assert"; } //end of if-else Console.WriteLine("option: " + option); MethodA(option); Console.WriteLine("Done"); }

public static void MethodA(string option) { Console.WriteLine("Method A"); IPHostEntry ipHost = Dns.GetHostEntry("127.0.0.1"); IPAddress ipAddress = ipHost.AddressList[0]; IPEndPoint ipEndPoint = new IPEndPoint(ipAddress, 11000); Socket sender = new Socket(AddressFamily.InterNetwork,

SocketType.Stream, ProtocolType.Tcp); SocketPermission permitSocket = new

SocketPermission(NetworkAccess.Connect, TransportType.Tcp, "127.0.0.1", SocketPermission.AllPorts);

//Select assert or deny on the basis of paramter passed if (option.Equals("deny")) permitSocket.Deny(); else permitSocket.Assert(); try { //Connect the socket to the romote endpoint. Catch an errors sender.Connect(ipEndPoint); Console.WriteLine("Socket connected to {0}.",

sender.RemoteEndPoint.ToString()); byte[] bytes = new byte[1024]; byte[] msg = Encoding.ASCII.GetBytes("This is a test.<EOF>");

//send the data through the socket int bytesSent = sender.Send(msg);

//receive the response from the remote device int bytesRec = sender.Receive(bytes);

Console.WriteLine("Echoed Test = {0}", Encoding.ASCII.GetString(bytes, 0, bytesRec));

} catch (SocketException s) { Console.WriteLine("Socket Exception: " + s.ToString()); } catch (SecurityException se) { Console.WriteLine("Socket Exception: " + se.ToString()); } //end of catch finally { if (sender.Connected) { //Release the socket sender.Shutdown(SocketShutdown.Both); sender.Close(); } } Console.WriteLine("Closing method A."); Console.ReadLine(); } //end of MethodA }}

Declarative Security

• Uses .NET attributes to place security information inside the metadata of the code

• Attributes can be placed at the assembly, class or member level to indicate the type of request, demand, or override that is needed.

• In order to use this security syntax, the state of the data must be initialised first for the SocketPermissionAttribute object through the declarative syntax, so that it represents the form of permission that is being enforced on the code.

Declarative Securityusing System;using System.Collections.Generic;using System.Text;using System.Net;using System.Net.Sockets;using System.Security;using System.Security.Permissions;

namespace SocketDeclarativeSecurity{ class Program { static void Main(string[] args) { LegalMethod(); IllegalMethod(); Console.Write("Press a key to continue."); Console.ReadLine(); }

Legal Method

[SocketPermission (SecurityAction.Assert, Access = "Connect", Host = "127.0.0.1", Port = "All", Transport = "Tcp")]public static void LegalMethod(){

Console.WriteLine("Legal Method");IPHostEntry ipHost = Dns.GetHostEntry("127.0.0.1");IPAddress ipAddr = ipHost.AddressList[0];IPEndPoint ipEndPoint = new IPEndPoint(ipAddr, 11000);Socket sender = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);try{

//Connect the socket to the remote endpoint. Catch any errors sender.Connect(ipEndPoint); Console.WriteLine("Socket connected to {0}", sender.RemoteEndPoint.ToString());

} //end of trycatch (SecurityException se){

Console.WriteLine("Security Exception: " + se); } //end of catch catch (SocketException se) { Console.WriteLine("Socket Exception: " + se);

} //end of catchfinally

{ if (sender.Connected) { //release the socket sender.Shutdown(SocketShutdown.Both); sender.Close(); } } //end of finally } // end of legalMethod

Illegal Method

[SocketPermission(SecurityAction.Deny, Access = "Connect", Host = "127.0.0.1", Port = "All", Transport = "Tcp")] public static void IllegalMethod() { Console.WriteLine("Illegal Method"); IPHostEntry ipHost = Dns.GetHostEntry("127.0.0.1"); IPAddress ipAddr = ipHost.AddressList[0]; IPEndPoint ipEndPoint = new IPEndPoint(ipAddr, 11000); Socket sender = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); try { //Connect the socket to the remote endpoint. Catch any errors sender.Connect(ipEndPoint); Console.WriteLine("Socket connected to {0}", sender.RemoteEndPoint.ToString()); } //end of try catch (SecurityException se) { Console.WriteLine("Security Exception: " + se); } //end of catch catch (SocketException se) { Console.WriteLine("Socket Exception: " + se); } //end of catch finally { if (sender.Connected) { //release the socket sender.Shutdown(SocketShutdown.Both); sender.Close(); } } //end of finally } }}

Summary• Socket class• Two main socket types

– Stream sockets– Datagram sockets

• System.Net.Sockets namespace• SocketException Class

– Finally block should contain Close and Shutdown methods• Basic socket options• Asynchronous programming model• Security

– Imperative• Permissions known only at runtime

– Declarative• Permissions needed are known at compile-time

network programming chapter 4 socket programming in.net

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