4.4. The Policy Server
The policy server is
similarly implemented as a console program that listens on all available
IP addresses, bound to a well-known port 943. Listing 7 shows the code for the policy server.
Listing 7. Implementation for the PolicyServer type in PolicyListener.cs
using System;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Text;
namespace Recipe7_5.PolicyServer
{
internal class PolicyListener
{
Socket ListenerSocket { get; set; }
SocketAsyncEventArgs sockEvtArgs = null;
//valid policy request string
public static string ValidPolicyRequest = "<policy-file-request/>";
public PolicyListener()
{
//bind to all available addresses and port 943
IPEndPoint ListenerEndPoint =
new IPEndPoint(IPAddress.Any, 943);
ListenerSocket =
new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
ListenerSocket.Bind(ListenerEndPoint);
ListenerSocket.Listen(20);
}
internal void ListenForPolicyRequest()
{
sockEvtArgs = new SocketAsyncEventArgs();
sockEvtArgs.Completed += new EventHandler<SocketAsyncEventArgs>(
delegate(object Sender, SocketAsyncEventArgs e)
{
//process this request
ReadPolicyRequest(e.AcceptSocket);
//go back to listening
ListenForPolicyRequest();
});
ListenerSocket.AcceptAsync(sockEvtArgs);
}
private bool ReadPolicyRequest(Socket ClientSocket)
{
SocketAsyncEventArgs sockEvtArgs =
new SocketAsyncEventArgs { UserToken = ClientSocket };
sockEvtArgs.SetBuffer(
new byte[ValidPolicyRequest.Length], 0, ValidPolicyRequest.Length);
sockEvtArgs.Completed += new EventHandler<SocketAsyncEventArgs>(
delegate(object Sender, SocketAsyncEventArgs e)
{
if (e.SocketError == SocketError.Success)
{
//get policy request string
string PolicyRequest = new UTF8Encoding().
GetString(e.Buffer, 0, e.BytesTransferred);
//check for valid format
if (PolicyRequest.CompareTo(ValidPolicyRequest) == 0)
//valid request-send policy
SendPolicy(e.UserToken as Socket);
}
});
return ClientSocket.ReceiveAsync(sockEvtArgs);
}
private void SendPolicy(Socket ClientSocket)
{
//read the policy file
FileStream fs = new FileStream("clientaccesspolicy.xml", FileMode.Open);
byte[] PolicyBuffer = new byte[(int)fs.Length];
fs.Read(PolicyBuffer, 0, (int)fs.Length);
fs.Close();
SocketAsyncEventArgs sockEvtArgs =
new SocketAsyncEventArgs { UserToken = ClientSocket };
//send the policy
sockEvtArgs.SetBuffer(PolicyBuffer, 0, PolicyBuffer.Length);
sockEvtArgs.Completed += new EventHandler<SocketAsyncEventArgs>(
delegate(object Sender, SocketAsyncEventArgs e)
{
//close this connection
if (e.SocketError == SocketError.Success)
(e.UserToken as Socket).Close();
});
ClientSocket.SendAsync(sockEvtArgs);
}
}
}
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After a connection request is
accepted by the policy server, it attempts to receive a policy request
from the client and checks it for validity by comparing it to the string
literal <policy-file-request/>. If
valid, the policy file is read into memory and sent back to the client
through the connected client socket. When the send is completed, the
socket connection is closed, and the policy server keeps listening for
more policy requests.
