有没有想法为什么我使用HttpWebRequest访问某些链接时，代码中会出现"The remote server returned an error: (304) Not Modified."？
我使用的代码来自Jeff在这里的帖子（该页面似乎已经消失，请参见Wayback Machine的存档副本）。
请注意，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本地运行的代码，它获取我的浏览器请求，然后通过创建新的HttpWebRequest进行代理传递，正如您在代码中看到的那样。它对大多数站点/链接都有效，但对于某些站点/链接，会出现此错误。您将在代码中看到一个关键部分，它似乎从浏览器请求中复制http标头设置到其发送到站点的请求中，并且复制了标头属性。不确定问题是否与它模拟请求的这个方面以及结果返回时发生的情况有关？
我使用的代码来自Jeff在这里的帖子（该页面似乎已经消失，请参见Wayback Machine的存档副本）。
请注意，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本地运行的代码，它获取我的浏览器请求，然后通过创建新的HttpWebRequest进行代理传递，正如您在代码中看到的那样。它对大多数站点/链接都有效，但对于某些站点/链接，会出现此错误。您将在代码中看到一个关键部分，它似乎从浏览器请求中复制http标头设置到其发送到站点的请求中，并且复制了标头属性。不确定问题是否与它模拟请求的这个方面以及结果返回时发生的情况有关？
case "If-Modified-Since":
request.IfModifiedSince = DateTime.Parse(listenerContext.Request.Headers[key]);
break;
我从http://en.wikipedia.org/wiki/Main_Page获取了一个示例问题。
提示：此处进行更新
仍然无法解决。基本上我可以确定有一个链接有问题，第一次它似乎工作正常，第二次出现错误，第三次正常，第四次出现错误，第五次正常等等。好像代码中有某些状态没有清除或者其他的东西。我尝试使用“using”类型语句等来清理代码。
下面是代码。如果有人能找出为什么每隔一次浏览到像http://newsimg.bbc.co.uk/css/screen/1_0_16/nol/v4/story.css（从第二次开始，而不是第一次）的链接时，通过这个代理代码会出现错误，我会很高兴听到你的意见。
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();
}
}
}
以下是我看到的一个例子 - 第一个结果很好，第二个出现了错误...
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.
