Gre*_*reg 42 http httpwebrequest if-modified-since http-status-code-304
我尝试使用HttpWebRequest访问某些链接的任何想法我得到"远程服务器返回错误:(304)未修改." 在代码中？
我正在使用的代码来自Jeff的帖子(该页面似乎已经消失,请在Wayback Machine上查看归档副本).
注意代码的概念是一个简单的代理服务器,因此我将浏览器指向这个本地运行的代码片段,它获取我的浏览器请求,然后通过创建新的HttpWebRequest代理它,如您所见代码.它适用于大多数网站/链接,但对于一些人来说,这个错误出现了.您将在代码中看到一个关键位,它似乎将http标头设置从浏览器请求复制到它的请求到网站,并在标头属性中复制.不确定问题是否与它如何模仿请求的这个方面有关,然后结果会发生什么？
case "If-Modified-Since":
request.IfModifiedSince = DateTime.Parse(listenerContext.Request.Headers[key]);
break;
我从例如http://en.wikipedia.org/wiki/Main_Page获得了该问题
PS.更新在这里
仍然无法解决这个问题.基本上我可以识别1个有问题的链接,它似乎工作正常,第二次得到错误,第3次OK,第4次得到错误,第5次OK等等好像有一些状态没有被清除或代码中有些东西.我尝试使用"使用"类型语句等来清理代码.
这是代码.如果有人能够发现为什么我每次第二次浏览http://newsimg.bbc.co.uk/css/screen/1_0_16/nol/v4/story.css这样的链接(从第2次开始,而不是第一次)通过这个代理代码,我得到了我想听到的错误.
class Program
{
static void Main(string[] args)
{
Proxy p = new Proxy(8080);
Thread proxythread = new Thread(new ThreadStart(p.Start));
proxythread.Start();
Console.WriteLine("Proxy Started. Press Any Key To Stop...");
Console.ReadKey();
p.Stop();
}
}
public class Proxy
{
private HttpListener _listener;
private int _port;
public Proxy(int port)
{
int defaultport = 8080;
// Setup Thread Pool
System.Threading.ThreadPool.SetMaxThreads(50, 1000);
System.Threading.ThreadPool.SetMinThreads(50, 50);
// Sanitize Port Number
if (port < 1024 || port > 65535)
port = defaultport;
// Create HttpListener Prefix
string prefix = string.Format("http://*:{0}/", port);
_port = port;
// Create HttpListener
_listener = new HttpListener();
_listener.Prefixes.Add(prefix);
}
public void Start()
{
_listener.Start();
while (true)
{
HttpListenerContext request = null;
try
{
request = _listener.GetContext();
// Statistics (by Greg)
int availThreads = -1;
int compPortThreads = -1;
ThreadPool.GetAvailableThreads(out availThreads, out compPortThreads);
log("INFO", request.Request.Url.ToString(), "START - [" + availThreads + "]");
ThreadPool.QueueUserWorkItem(ProcessRequest, request);
}
catch (HttpListenerException ex)
{
log("ERROR", "NA", "INFO: HttpListenerException - " + ex.Message);
break;
}
catch (InvalidOperationException ex)
{
log("ERROR", "NA", "INFO: InvalidOperationException - " + ex.Message);
break;
}
}
}
public void Stop()
{
_listener.Stop();
}
private void log(string sev, string uri, string message)
{
Console.Out.WriteLine(Process.GetCurrentProcess().Id + " - " + sev + " (" + uri + "): " + message);
}
private void ProcessRequest(object _listenerContext)
{
#region local variables
HttpWebRequest psRequest; // Request to send to remote web server
HttpWebResponse psResponse; // Response from remote web server
List<byte> requestBody = new List<byte>(); // Byte array to hold the request's body
List<byte> responseBody = new List<byte>(); // Byte array to hold the response's body
byte[] buffer;
string uri = "";
#endregion
var listenerContext = (HttpListenerContext)_listenerContext;
uri = listenerContext.Request.Url.ToString().Replace(string.Format(":{0}", _port), "");
// Create Interent Request
HttpWebRequest internetRequest = (HttpWebRequest)WebRequest.Create(uri);
#region Build Request Up
internetRequest.Method = listenerContext.Request.HttpMethod;
internetRequest.ProtocolVersion = listenerContext.Request.ProtocolVersion;
internetRequest.UserAgent = listenerContext.Request.UserAgent;
foreach (string key in listenerContext.Request.Headers.AllKeys)
{
try
{
switch (key)
{
case "Proxy-Connection":
case "Connection":
internetRequest.KeepAlive = (listenerContext.Request.Headers[key].ToLower() == "keep-alive") ? true : false;
break;
case "Content-Length":
internetRequest.ContentLength = listenerContext.Request.ContentLength64;
break;
case "Content-Type":
internetRequest.ContentType = listenerContext.Request.ContentType;
break;
case "Accept":
internetRequest.Accept = listenerContext.Request.Headers[key];
break;
case "Host":
break;
case "Referer":
internetRequest.Referer = listenerContext.Request.Headers[key];
break;
case "If-Modified-Since":
internetRequest.IfModifiedSince = DateTime.Parse(listenerContext.Request.Headers[key]);
break;
default:
internetRequest.Headers.Add(key, listenerContext.Request.Headers[key]);
break;
}
}
catch (Exception ex)
{
Console.WriteLine("Error settup up psRequest object. Error = " + ex.Message + "\n" + ex.StackTrace);
}
}
#endregion
#region Copy content into request
buffer = new byte[1024];
using (Stream instream = listenerContext.Request.InputStream)
{
int incount = instream.Read(buffer, 0, buffer.Length);
while (incount > 0)
{
internetRequest.GetRequestStream().Write(buffer, 0, incount);
incount = instream.Read(buffer, 0, buffer.Length);
}
}
#endregion
// Get Internet Response
HttpWebResponse internetResponse = null;
try
{
using (internetResponse = (HttpWebResponse)internetRequest.GetResponse())
{
#region Configure Local Response Header Keys
foreach (string key in internetResponse.Headers.Keys)
{
try
{
switch (key)
{
case "Transfer-Encoding":
listenerContext.Response.SendChunked = (internetResponse.Headers[key].ToLower() == "chunked") ? true : false;
break;
case "Content-Length":
listenerContext.Response.ContentLength64 = internetResponse.ContentLength;
break;
case "Content-Type":
listenerContext.Response.ContentType = internetResponse.Headers[key];
break;
case "Keep-Alive":
listenerContext.Response.KeepAlive = true;
break;
default:
listenerContext.Response.Headers.Add(key, internetResponse.Headers[key]);
break;
}
}
catch (Exception ex)
{
log("ERROR", uri, "Error settup up listenerContext.Response objects. Error = " + ex.Message + "\n" + ex.StackTrace);
}
}
#endregion
try
{
// Transfer the body data from Internet Response to Internal Response
buffer = new byte[1024];
using (Stream inputStream = internetResponse.GetResponseStream())
{
int outcount = inputStream.Read(buffer, 0, buffer.Length);
while (outcount > 0)
{
listenerContext.Response.OutputStream.Write(buffer, 0, outcount);
outcount = inputStream.Read(buffer, 0, buffer.Length);
}
}
}
catch (Exception ex)
{
log("ERROR", uri, "Could not obtain response from URI: " + ex.Message);
}
finally
{
listenerContext.Response.OutputStream.Close();
}
}
}
catch (Exception ex)
{
//if (ex is InvalidOperationException ||
// ex is ProtocolViolationException ||
// ex is WebException)
//{
// log(uri, "Could not successfully get response: " + ex.GetType() + " - " + ex.Message);
// listenerContext.Response.Close();
// return;
//}
//else { throw; }
log("ERROR", uri, "Could not successfully get response: " + ex.GetType() + " - " + ex.Message);
listenerContext.Response.Close();
}
}
}
这是我看到的一个例子 - 第一次打击是好的,第二次有错误...
Proxy Started. Press Any Key To Stop...
2080 - INFO (http://newsimg.bbc.co.uk:8080/css/screen/1_0_16/nol/v4/story.css): START - [50]
2080 - INFO (http://newsimg.bbc.co.uk:8080/css/screen/1_0_16/nol/v4/story.css): START - [50]
2080 - ERROR (http://newsimg.bbc.co.uk/css/screen/1_0_16/nol/v4/story.css): Could not successfully get response: System.Net.WebException - The remote server returned an error: (304) Not Modified.
Bal*_*usC 83
首先,这不是错误.该3xx表示重定向.真正的错误是4xx(客户端错误)和5xx(服务器错误).
如果客户获得a 304 Not Modified,则客户有责任从其自己的缓存中显示有问题的资源.通常,代理不应该担心这一点.这只是信使.
Ash*_*ada 15
只是按下F5并不总是有效.
为什么？
因为您的ISP也在为您缓存Web数据.
解决方案:强制刷新.
强制刷新浏览器,方法是在Firefox或Chrome中按CTRL+ F5清除ISP缓存,而不是仅按F5
然后,您可以在浏览器F12开发人员工具网络选项卡中看到200响应而不是304响应.
另一个技巧是?在请求页面的URL字符串末尾添加问号:
http://localhost:52199/Customers/Create?
问号将确保浏览器刷新请求而不缓存任何先前的请求.