socket server

using System;
using System.Threading;
using System.Net.Sockets;
using System.Net;

// Implements the connection logic for the socket server.
// After accepting a connection, all data read from the client
// is sent back to the client. The read and echo back to the client pattern
// is continued until the client disconnects.
class Server
{
private int m_numConnections; // the maximum number of connections the sample is designed to handle simultaneously
private int m_receiveBufferSize;// buffer size to use for each socket I/O operation
BufferManager m_bufferManager; // represents a large reusable set of buffers for all socket operations
const int opsToPreAlloc = 2; // read, write (don't alloc buffer space for accepts)
Socket listenSocket; // the socket used to listen for incoming connection requests
// pool of reusable SocketAsyncEventArgs objects for write, read and accept socket operations
SocketAsyncEventArgsPool m_readWritePool;
int m_totalBytesRead; // counter of the total # bytes received by the server
int m_numConnectedSockets; // the total number of clients connected to the server
Semaphore m_maxNumberAcceptedClients;

// Create an uninitialized server instance.
// To start the server listening for connection requests
// call the Init method followed by Start method
//
// <param name="numConnections">the maximum number of connections the sample is designed to handle simultaneously</param>
// <param name="receiveBufferSize">buffer size to use for each socket I/O operation</param>
public Server(int numConnections, int receiveBufferSize)
{
m_totalBytesRead = 0;
m_numConnectedSockets = 0;
m_numConnections = numConnections;
m_receiveBufferSize = receiveBufferSize;
// allocate buffers such that the maximum number of sockets can have one outstanding read and
//write posted to the socket simultaneously
m_bufferManager = new BufferManager(receiveBufferSize * numConnections * opsToPreAlloc,
receiveBufferSize);

m_readWritePool = new SocketAsyncEventArgsPool(numConnections);
m_maxNumberAcceptedClients = new Semaphore(numConnections, numConnections);
}

// Initializes the server by preallocating reusable buffers and
// context objects. These objects do not need to be preallocated
// or reused, but it is done this way to illustrate how the API can
// easily be used to create reusable objects to increase server performance.
//
public void Init()
{
// Allocates one large byte buffer which all I/O operations use a piece of. This gaurds
// against memory fragmentation
m_bufferManager.InitBuffer();

// preallocate pool of SocketAsyncEventArgs objects
SocketAsyncEventArgs readWriteEventArg;

for (int i = 0; i < m_numConnections; i++)
{
//Pre-allocate a set of reusable SocketAsyncEventArgs
readWriteEventArg = new SocketAsyncEventArgs();
readWriteEventArg.Completed += new EventHandler<SocketAsyncEventArgs>(IO_Completed);
readWriteEventArg.UserToken = new AsyncUserToken();

// assign a byte buffer from the buffer pool to the SocketAsyncEventArg object
m_bufferManager.SetBuffer(readWriteEventArg);

// add SocketAsyncEventArg to the pool
m_readWritePool.Push(readWriteEventArg);
}

}

// Starts the server such that it is listening for
// incoming connection requests.
//
// <param name="localEndPoint">The endpoint which the server will listening
// for connection requests on</param>
public void Start(IPEndPoint localEndPoint)
{
// create the socket which listens for incoming connections
listenSocket = new Socket(localEndPoint.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
listenSocket.Bind(localEndPoint);
// start the server with a listen backlog of 100 connections
listenSocket.Listen(100);

// post accepts on the listening socket
StartAccept(null);

//Console.WriteLine("{0} connected sockets with one outstanding receive posted to each....press any key", m_outstandingReadCount);
Console.WriteLine("Press any key to terminate the server process....");
Console.ReadKey();
}

// Begins an operation to accept a connection request from the client
//
// <param name="acceptEventArg">The context object to use when issuing
// the accept operation on the server's listening socket</param>
public void StartAccept(SocketAsyncEventArgs acceptEventArg)
{
if (acceptEventArg == null)
{
acceptEventArg = new SocketAsyncEventArgs();
acceptEventArg.Completed += new EventHandler<SocketAsyncEventArgs>(AcceptEventArg_Completed);
}
else
{
// socket must be cleared since the context object is being reused
acceptEventArg.AcceptSocket = null;
}

m_maxNumberAcceptedClients.WaitOne();
bool willRaiseEvent = listenSocket.AcceptAsync(acceptEventArg);
if (!willRaiseEvent)
{
ProcessAccept(acceptEventArg);
}
}

// This method is the callback method associated with Socket.AcceptAsync
// operations and is invoked when an accept operation is complete
//
void AcceptEventArg_Completed(object sender, SocketAsyncEventArgs e)
{
ProcessAccept(e);
}

private void ProcessAccept(SocketAsyncEventArgs e)
{
Interlocked.Increment(ref m_numConnectedSockets);
Console.WriteLine("Client connection accepted. There are {0} clients connected to the server",
m_numConnectedSockets);

// Get the socket for the accepted client connection and put it into the
//ReadEventArg object user token
SocketAsyncEventArgs readEventArgs = m_readWritePool.Pop();
((AsyncUserToken)readEventArgs.UserToken).Socket = e.AcceptSocket;

// As soon as the client is connected, post a receive to the connection
bool willRaiseEvent = e.AcceptSocket.ReceiveAsync(readEventArgs);
if (!willRaiseEvent)
{
ProcessReceive(readEventArgs);
}

// Accept the next connection request
StartAccept(e);
}

// This method is called whenever a receive or send operation is completed on a socket
//
// <param name="e">SocketAsyncEventArg associated with the completed receive operation</param>
void IO_Completed(object sender, SocketAsyncEventArgs e)
{
// determine which type of operation just completed and call the associated handler
switch (e.LastOperation)
{
case SocketAsyncOperation.Receive:
ProcessReceive(e);
break;
case SocketAsyncOperation.Send:
ProcessSend(e);
break;
default:
throw new ArgumentException("The last operation completed on the socket was not a receive or send");
}

}

// This method is invoked when an asynchronous receive operation completes.
// If the remote host closed the connection, then the socket is closed.
// If data was received then the data is echoed back to the client.
//
private void ProcessReceive(SocketAsyncEventArgs e)
{
// check if the remote host closed the connection
AsyncUserToken token = (AsyncUserToken)e.UserToken;
if (e.BytesTransferred > 0 && e.SocketError == SocketError.Success)
{
//increment the count of the total bytes receive by the server
Interlocked.Add(ref m_totalBytesRead, e.BytesTransferred);
Console.WriteLine("The server has read a total of {0} bytes", m_totalBytesRead);

//echo the data received back to the client
e.SetBuffer(e.Offset, e.BytesTransferred);
bool willRaiseEvent = token.Socket.SendAsync(e);
if (!willRaiseEvent)
{
ProcessSend(e);
}

}
else
{
CloseClientSocket(e);
}
}

// This method is invoked when an asynchronous send operation completes.
// The method issues another receive on the socket to read any additional
// data sent from the client
//
// <param name="e"></param>
private void ProcessSend(SocketAsyncEventArgs e)
{
if (e.SocketError == SocketError.Success)
{
// done echoing data back to the client
AsyncUserToken token = (AsyncUserToken)e.UserToken;
// read the next block of data send from the client
bool willRaiseEvent = token.Socket.ReceiveAsync(e);
if (!willRaiseEvent)
{
ProcessReceive(e);
}
}
else
{
CloseClientSocket(e);
}
}

private void CloseClientSocket(SocketAsyncEventArgs e)
{
AsyncUserToken token = e.UserToken as AsyncUserToken;

// close the socket associated with the client
try
{
token.Socket.Shutdown(SocketShutdown.Send);
}
// throws if client process has already closed
catch (Exception) { }
token.Socket.Close();

// decrement the counter keeping track of the total number of clients connected to the server
Interlocked.Decrement(ref m_numConnectedSockets);
m_maxNumberAcceptedClients.Release();
Console.WriteLine("A client has been disconnected from the server. There are {0} clients connected to the server", m_numConnectedSockets);

// Free the SocketAsyncEventArg so they can be reused by another client
m_readWritePool.Push(e);
}

}