Question

HttpWebRequest 的 IfModifiedSince 怎么设置才等于 0

抓包得到的数据：

GET /ajax/GetCount.aspx?id=0&nows=1367742955902 HTTP/1.1
Accept: */*
Accept-Language: zh-cn
Referer: http://127.0.0.1/index.aspx
If-Modified-Since: 0
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; Trident/5.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C; .NET4.0E)
Host: 127.0.0.1
Connection: Keep-Alive
Cookie: ASP.NET_SessionId=kzcfqaa3kilah2ejlrkisf45; username=; questionId=

程序代码：

HttpWebRequest request = WebRequest.Create(" http://127.0.0.1/ajax/GetCount.aspx?id=0&nows=1367742955902") as HttpWebRequest;
request.Method = "GET";
request.UserAgent = "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; Trident/5.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C; .NET4.0E)";
request.Accept = "*/*";
request.Headers("Accept-Language") = "zh-cn";
request.Headers("Accept-Encoding") = "gzip, deflate";
request.Referer = " http://127.0.0.1/index.aspx";

request.Headers.Add("If-Modified-Since", "0");
//这里会出现错误：System.ArgumentException: 必须使用适当的属性或方法修改“If-Modified-Since”标头。
//如果写为：request.IfModifiedSince = 这里是 Date类型 不知道怎么写才会等于 0

Answer 1

好像If-Modified-Since只允许在Request.IfModifiedSince属性上设置而且必须是日期类型，如果你要设置其他类型的话可以用反射调用WebHeaderCollection的AddInternal方法跳过Header的验证。

代码如下：

using System.Reflection;

private void button1_Click(object sender, EventArgs e)
{
HttpWebRequest request = WebRequest.Create("http://www.baidu.com/") as HttpWebRequest;
request.Method = "GET";
request.Referer = " http://127.0.0.1/index.aspx";
Type type = request.Headers.GetType();
type.InvokeMember("AddInternal", BindingFlags.Instance | BindingFlags.InvokeMethod | BindingFlags.NonPublic, null, request.Headers, new object[] { "If-Modified-Since", "0" });
type.InvokeMember("AddInternal", BindingFlags.Instance | BindingFlags.InvokeMethod | BindingFlags.NonPublic, null, request.Headers, new object[] { "Test", "123456789" });
WebResponse response = request.GetResponse();
}

Answer 2

DateTime dt1 = DateTime.Parse((DateTime.Now - DateTime.Now).ToString());
DateTime dt2 = DateTime.Parse("00:00:00");
datetime日期类型，需要有个精确的时间值的，一天是24小时，所返回的值最小就是上面两行代码的结果(当天0点)

追问

像你这样写抓到的包：
If-Modified-Since: Mon, 06 May 2013 16:00:00 GMT //注意：我这里要的是 If-Modified-Since: 0