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模拟IIS向Silverlight输出策略文件

作者: Leon Weng  来源: 博客园  发布时间: 2010-09-17 07:56  阅读: 1067 次  推荐: 0   原文链接   [收藏]  

  问题

  最近的Silverlight开发中,由于部分需求对实时性和数据量下载速度有要求,部分WCF服务配置成了netTcpBinding,这种方式跟普通的service.svc寄宿IIS不同的是,Silverlight需要的策略文件需要放置在本机IIS的根下,也就是wwwroot文件夹下,以满足Silverlight在以TCP协议调用本机WCF服务时请求策略文件。(注:Silverlight通过TCP协议调用WCF服务时,会以http方式请求主机的一个策略文件,地址是http://localhost/clientaccesspolicy.xml)

  这其实是个不太好的选择,程序运行的所需的环境被分成了两部分,同事的机器上并未安装IIS,为了大家开发简便,不用在额外安装IIS,也为了让程序更加独立,我就想能不能写代码监控80端口模拟IIS向Silverlight输出这个策略文件。

  解决方法

  有了这个想法之后,首先想到的是通过Socket进行监听,因为此前在MSDN上看到过这种方式,但很无奈,将代码转移过来之后,并未成功。相信做过Silverlight在Socket方面应用的朋友对下面这个PolicyServer类很熟悉吧。

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

namespace PolicyServer
{
// Encapsulate and manage state for a single connection from a client
class PolicyConnection
{
private Socket m_connection;

// buffer to receive the request from the client
private byte[] m_buffer;
private int m_received;

// the policy to return to the client
private byte[] m_policy;

// the request that we're expecting from the client
private static string s_policyRequestString = "<policy-file-request/>";



public PolicyConnection(Socket client, byte[] policy)
{
m_connection
= client;
m_policy
= policy;

m_buffer
= new byte[s_policyRequestString.Length];
m_received
= 0;

try
{
// receive the request from the client
m_connection.BeginReceive(m_buffer, 0, s_policyRequestString.Length, SocketFlags.None, new AsyncCallback(OnReceive), null);
}
catch (SocketException)
{
m_connection.Close();
}
}

// Called when we receive data from the client
private void OnReceive(IAsyncResult res)
{
try
{
m_received
+= m_connection.EndReceive(res);

// if we haven't gotten enough for a full request yet, receive again
if (m_received < s_policyRequestString.Length)
{
m_connection.BeginReceive(m_buffer, m_received, s_policyRequestString.Length
- m_received, SocketFlags.None, new AsyncCallback(OnReceive), null);
return;
}

// make sure the request is valid
string request = System.Text.Encoding.UTF8.GetString(m_buffer, 0, m_received);
if (StringComparer.InvariantCultureIgnoreCase.Compare(request, s_policyRequestString) != 0)
{
m_connection.Close();
return;
}

// send the policy
m_connection.BeginSend(m_policy, 0, m_policy.Length, SocketFlags.None, new AsyncCallback(OnSend), null);
}
catch (SocketException)
{
m_connection.Close();
}
}

// called after sending the policy to the client; close the connection.
public void OnSend(IAsyncResult res)
{
try
{
m_connection.EndSend(res);
}
finally
{
m_connection.Close();
}
}
}

// Listens for connections on port 943 and dispatches requests to a PolicyConnection
class PolicyServer
{
private Socket m_listener;
private byte[] m_policy;

// pass in the path of an XML file containing the socket policy
public PolicyServer(string policyFile)
{
// Load the policy file
FileStream policyStream = new FileStream(policyFile, FileMode.Open);

m_policy
= new byte[policyStream.Length];
policyStream.Read(m_policy,
0, m_policy.Length);

policyStream.Close();

m_listener
= new Socket(AddressFamily.InterNetworkV6, SocketType.Stream, ProtocolType.Tcp);

m_listener.SetSocketOption(SocketOptionLevel.IPv6, (SocketOptionName)
27, 0);

m_listener.Bind(
new IPEndPoint(IPAddress.IPv6Any, 943));
m_listener.Listen(
10);

m_listener.BeginAccept(
new AsyncCallback(OnConnection), null);
}

public void OnConnection(IAsyncResult res)
{
Socket client
= null;

try
{
client
= m_listener.EndAccept(res);
}
catch (SocketException)
{
return;
}

// handle this policy request with a PolicyConnection
PolicyConnection pc = new PolicyConnection(client, m_policy);

// look for more connections
m_listener.BeginAccept(new AsyncCallback(OnConnection), null);
}

public void Close()
{
m_listener.Close();
}
}
public class Program
{
static void Main(string[] args)
{
if (args.Length == 0)
{
Console.WriteLine(
"usage: PolicyServer.exe PolicyFile.xml");
return;
}

PolicyServer ps
= new PolicyServer(args[0]);
System.Threading.Thread.Sleep(System.Threading.Timeout.Infinite);
}
}
}

  此路不通之后,又想起使用HttpListener类,看看是否能够监听http请求,果然能够截获HTTP的请求。

HttpListener listener = new HttpListener();
listener.Prefixes.Add(http:
//localhost/);

listener.Start();Console.WriteLine(
"开始监听…");

HttpListenerContext context
= listener.GetContext();
HttpListenerRequest request
= context.Request;
HttpListenerResponse response
= context.Response;

  但是这种方式有个明显的缺点,就是线程是阻塞的。于是,又想到使用线程池。

System.Threading.ThreadPool.QueueUserWorkItem(new System.Threading.WaitCallback(Listen));
private static void Listen(object state)
{
while (httpListener.IsListening)
{
httpListener.BeginGetContext(
new AsyncCallback(ListenerCallback), httpListener);
listenForNextRequest.WaitOne();
}
}

  这样的话,每接收一个请求便会异步处理这个请求。在请求的处理上,接收请求后需要向外输出策略文件流,供silverlight端接收验证。

using (System.Net.HttpListenerResponse response = context.Response)
{
System.Threading.Thread.Sleep(
1000);

string responseString = "<?xml version=\"1.0\" encoding=\"utf-8\"?> "
+ " <access-policy> "
+ " <cross-domain-access> "
+ " <policy> "
+ " <allow-from http-request-headers=\"*\">"
+ " <domain uri=\"*\" /> "
+ " </allow-from> "
+ " <grant-to> "
+ " <socket-resource port=\"4502-4534\" protocol=\"tcp\" /> "
+ " </grant-to> "
+ " </policy> "
+ " </cross-domain-access>"
+ " </access-policy>";
byte[] buffer = System.Text.Encoding.UTF8.GetBytes(responseString);
response.ContentLength64
= buffer.LongLength;
response.OutputStream.Write(buffer,
0, buffer.Length);
}

  启动这个模拟服务,将clientaccesspolicy从wwwroot中移除后再运行一下程序,OK,我们不再需要将策略文件放到IIS下了。

  提醒 

  如果你的机器装了IIS,请还是放一个策略文件到wwwroot吧,否则就停掉IIS再使用这个类,因为IIS和这个类只能有一方监听80端口。

  本文中的这个类参考了:http://forums.silverlight.net/forums/p/113106/255614.aspx

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