如何解决绑定IP地址只是第一次使用
| 我想从服务器上的可用IP地址之一发出Web请求，所以我使用了此类：public class UseIP
{
public string IP { get; private set; }
public UseIP(string IP)
{
this.IP = IP;
}
public HttpWebRequest CreateWebRequest(Uri uri)
{
ServicePoint servicePoint = ServicePointManager.FindServicePoint(uri);
servicePoint.BindIPEndPointDelegate = new BindIPEndPoint(Bind);
return WebRequest.Create(uri) as HttpWebRequest;
}
private IPEndPoint Bind(ServicePoint servicePoint,IPEndPoint remoteEndPoint,int retryCount)
{
IPAddress address = IPAddress.Parse(this.IP);
return new IPEndPoint(address,0);
}
}
UseIP useIP = new UseIP(\"Valid IP address here...\");
Uri uri = new Uri(\"http://ip.nefsc.noaa.gov\");
HttpWebRequest request = useIP.CreateWebRequest(uri);
// Then make the request with the specified IP address
解决方法
理论：
HttpWebRequest依赖于基础ServicePoint。 ServicePoint代表与URL的实际连接。与您的浏览器保持与请求之间打开的URL的连接并重用该连接（以消除打开和关闭每个请求的连接的开销）非常相似，ServicePoint对HttpWebRequest执行相同的功能。
我认为每次使用HttpWebRequest时都不会调用您为ServicePoint设置的BindIPEndPointDelegate，因为ServicePoint正在重新使用连接。如果您可以强制关闭连接，则下一次对该URL的调用将导致ServicePoint需要再次调用BindIPEndPointDelegate。
不幸的是，似乎没有ServicePoint接口使您能够直接强制关闭连接。
两种解决方案（每种解决方案的结果略有不同）
1）对于每个请求，设置HttpWebRequest.KeepAlive = false。在我的测试中，这导致Bind委托在每个请求中被一对一调用。
2）将ServicePoint ConnectionLeaseTimeout属性设置为零或某个较小的值。这将具有定期强制调用Bind委托的效果（不是每个请求都一对一）。
从文档中：
您可以使用此属性来确保ServicePoint对象的
活动连接不会无限期保持打开状态。该属性是
适用于应该断开连接并
定期重新建立，例如负载平衡方案。
默认情况下，当请求的KeepAlive为true时，MaxIdleTime
属性设置由于以下原因而关闭ServicePoint连接的超时
不活动。如果ServicePoint具有活动连接，则MaxIdleTime
无效，连接将无限期保持打开状态。
当ConnectionLeaseTimeout属性设置为其他值时
-1，并且在经过指定的时间后，通过将KeepAlive设置为来服务请求后，将关闭活动的ServicePoint连接
在该请求中为假。
设置此值会影响ServicePoint对象管理的所有连接。
public class UseIP
{
public string IP { get; private set; }
public UseIP(string IP)
{
this.IP = IP;
}
public HttpWebRequest CreateWebRequest(Uri uri)
{
ServicePoint servicePoint = ServicePointManager.FindServicePoint(uri);
servicePoint.BindIPEndPointDelegate = (servicePoint,remoteEndPoint,retryCount) =>
{
IPAddress address = IPAddress.Parse(this.IP);
return new IPEndPoint(address,0);
};
//Will cause bind to be called periodically
servicePoint.ConnectionLeaseTimeout = 0;
HttpWebRequest req = (HttpWebRequest)WebRequest.Create(uri);
//will cause bind to be called for each request (as long as the consumer of the request doesn\'t set it back to true!
req.KeepAlive = false;
return req;
}
}
static void Main(string[] args)
{
//Note,I don\'t have a multihomed machine,so I\'m not using the IP in my test implementation. The bind delegate increments a counter and returns IPAddress.Any.
UseIP ip = new UseIP(\"111.111.111.111\");
for (int i = 0; i < 100; ++i)
{
HttpWebRequest req = ip.CreateWebRequest(new Uri(\"http://www.yahoo.com\"));
using (WebResponse response = req.GetResponse())
{
}
}
Console.WriteLine(string.Format(\"Req: {0}\",UseIP.RequestCount));
Console.WriteLine(string.Format(\"Bind: {0}\",UseIP.BindCount));
}
//servicePoint.BindIPEndPointDelegate = null; // Clears all delegates first,for testing
servicePoint.BindIPEndPointDelegate += delegate
{
var address = IPAddress.Parse(this.IP);
return new IPEndPoint(address,0);
};
public HttpWebRequest CreateWebRequest(Uri uri)
{
HttpWebRequest wr = WebRequest.Create(uri) as HttpWebRequest;
wr.ServicePoint.BindIPEndPointDelegate = new BindIPEndPoint(Bind);
return wr;
}
FindServicePoint
ServicePointManager
private IPEndPoint Bind(ServicePoint servicePoint,IPEndPoint remoteEndPoint,int retryCount)
{
if ((null != IP) && (IP.AddressFamily == remoteEndPoint.AddressFamily))
return new IPEndPoint(this.IP,0);
if (AddressFamily.InterNetworkV6 == remoteEndPoint.AddressFamily)
return new IPEndPoint(IPAddress.IPv6Any,0);
return new IPEndPoint(IPAddress.Any,0);
}
ServicePoint servicePoint = ServicePointManager.FindServicePoint(uri);
servicePoint.BindIPEndPointDelegate -= this.Bind; // avoid duplicate calls to Bind
servicePoint.BindIPEndPointDelegate += this.Bind;
private static Dictionary<IPAddress,UseIP> _eachNIC = new Dictionary<IPAddress,UseIP>();
public static UseIP ForNIC(IPAddress nic)
{
lock (_eachNIC)
{
UseIP useIP = null;
if (!_eachNIC.TryGetValue(nic,out useIP))
{
useIP = new UseIP(nic);
_eachNIC.Add(nic,useIP);
}
return useIP;
}
}
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