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.NET Forum / Languages / C# / June 2007

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Socket locking up after inital use

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Pain and headache - 29 Jun 2007 21:22 GMT
Hi,

I am trying to get a webpage using a TcpSocket instead of a standard
Webrequest.  Initial, it works fine but after the 2 or 3 request the
tcpclient I start to get the following error:

A connection attempt failed because the connected party did not properly
respond after a period of time, or established connection failed because
connected host has failed to respond

Here is the code making the call, this is the third iteration after trying
several others with out sucess:

string contents = "GET " + pathQuery + " HTTP/1.1\r\n" +
                             "Host: " + host + ":" + port + "\r\n" +
                             "User-Agent: Mozilla/5.0 (Windows; U; Windows
NT 6.0; en-US; rv:1.8.1.4) Gecko/20070515 Firefox/2.0.0.4\r\n" +
                             "Accept:
text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5\r\n" +
                             "Accept-Language: en-us,en;q=0.5\r\n" +
                             "Accept-Encoding: gzip,deflate\r\n" +
                             "Accept-Charset:
ISO-8859-1,utf-8;q=0.7,*;q=0.7\r\n" +
                             "Keep-Alive: 300\r\n" +
                             "Connection: keep-alive\r\n\r\n";

Byte[] requestObject = Encoding.ASCII.GetBytes(contents.ToCharArray());
           try
           {
               stream = socket.GetStream();

               if (stream.CanWrite)
               {
                   stream.Write(requestObject, 0, contents.Length);
               }

               MemoryStream memoryStream = new MemoryStream();

               if (stream.CanRead)
               {
                   int data = stream.ReadByte();
                   while (data != -1)
                   {
                       memoryStream.WriteByte((byte) data);
                       data = stream.ReadByte();
                   }
                   results =
Encoding.ASCII.GetString(memoryStream.ToArray());
               }

           }
           catch (Exception e)
           {
               
Console.WriteLine(Encoding.ASCII.GetString(memoryStream.ToArray()));
               throw e;
           }
           finally
           {
               stream.Close();
               socket.Close();
           }
Peter Duniho - 29 Jun 2007 21:47 GMT
> I am trying to get a webpage using a TcpSocket instead of a standard
> Webrequest.  Initial, it works fine but after the 2 or 3 request the
[quoted text clipped - 3 lines]
> respond after a period of time, or established connection failed because
> connected host has failed to respond [...]

Some thoughts:

    * You say you get an error trying to make the connection.  But you  
didn't bother to post any code related to creating or connecting your TCP  
socket.

    * As far as I know, there's no such thing as a TcpSocket, nor is there  
a Socket.GetStream() method.  You can create a Socket instance that  
encapsulates a TCP socket, and you can create a NetworkStream instance  
using a Socket instance.  Is that what you did?  If so, why does your post  
and code say something else?  And if not, what _did_ you do?

All that said, assuming your code normally works, you may be running into  
some kind of anti-DoS defense, depending on how you're using the code.  If  
you are repeatedly trying to make the same request to the same HTTP  
server, it may detect that case and stop responding, at least for some  
time.

If you can post a concise-but-complete example of code, client _and_  
server, that reliably reproduces the problem, someone here may be able to  
provide better advice.  Absent that, there's not much in your post to go  
on, and in fact what you posted doesn't make much sense in the context of  
regular .NET/C# programming (since you mention a class and a method that  
are simply not present in the basic .NET Framework).

Pete
Pain and headache - 29 Jun 2007 22:02 GMT
I am very sorry for the confusing.  I was trying to be brief.  Here is the
class, and I renamed the socket to client for easyier reading.  I am using
TCPTrace at the moment to test this, and it gets and sends the proper
responses so I do not believe it is a Dos prevention of some kind.  

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

namespace ReanneCorp.Library.V2.Common.WebUtils
{
   public class PullWebsiteClass
   {
       private Uri websiteUri;
       private TcpClient client = null;
       private string results = "";
       private int port;
       private string host;
       private string pathQuery;

       public Uri WebsiteUri
       {
           get { return websiteUri; }
           set { websiteUri = value; }
       }

       public TcpClient Client
       {
           get { return client; }
           set { client = value; }
       }

       public NetworkStream Stream
       {
           get { return stream; }
           set { stream = value; }
       }

       public string Results
       {
           get { return results; }
           set { results = value; }
       }

       public PullWebsiteClass(Uri websiteUri)
       {
           this.websiteUri = websiteUri;
           InitConnection();
       }
       private void InitConnection()
       {
           port = websiteUri.Port;
           host = websiteUri.Host;
           pathQuery = websiteUri.PathAndQuery;
         
           client = new TcpClient();
           client.ReceiveTimeout = 10000;
           try
           {
               client.Connect(host, port);
           }
           catch(SocketException ex)
           {
               throw ex;
           }
       }
       public void MakePageRequest()
       {
           string contents = "GET " + pathQuery + " HTTP/1.1\r\n" +
                             "Host: " + host + ":" + port + "\r\n" +
                             "User-Agent: Mozilla/5.0 (Windows; U; Windows
NT 6.0; en-US; rv:1.8.1.4) Gecko/20070515 Firefox/2.0.0.4\r\n" +
                             "Accept:
text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5\r\n" +
                             "Accept-Language: en-us,en;q=0.5\r\n" +
                             "Accept-Encoding: gzip,deflate\r\n" +
                             "Accept-Charset:
ISO-8859-1,utf-8;q=0.7,*;q=0.7\r\n" +
                             "Keep-Alive: 300\r\n" +
                             "Connection: keep-alive\r\n\r\n";
           MemoryStream memoryStream = new MemoryStream();

           Byte[] requestObject =
Encoding.ASCII.GetBytes(contents.ToCharArray());
           try
           {
               stream = client.GetStream();

               if (stream.CanWrite)
               {
                   stream.Write(requestObject, 0, contents.Length);
               }
               if (stream.CanRead)
               {
                   int data = stream.ReadByte();
                   while (data != -1)
                   {
                       memoryStream.WriteByte((byte) data);
                       data = stream.ReadByte();
                   }
                   results =
Encoding.ASCII.GetString(memoryStream.ToArray());
               }

               if (results.Contains("HTTP/1.1 302 Moved Temporarily"))
               {
                   client.Close();
                   string redirect = results.Remove(0,
results.IndexOf("Location: ") + 10);

                   redirect = redirect.Substring(0,
                                             
redirect.IndexOf("Content-Length:") - 1).Trim();

                   PullWebsiteClass newRequest = new PullWebsiteClass(new
Uri(redirect));
                   newRequest.MakePageRequest();
                   results = newRequest.Results;
               }
           }
           catch (Exception e)
           {
               throw e
           }
           finally
           {
               memoryStream.Close();
               client.Close();
           }
       }
   }
}

Here is the calling code:

[Test]
       public void CheckHeaders()
       {
           
           PullWebsiteClass getPage = new PullWebsiteClass(new
Uri("http://localhost:8081/test.aspx"));
           getPage.MakePageRequest();
           string page = getPage.Results;
           Console.WriteLine(page);
           Assert.AreNotEqual(page.Length, 0);        
}

> > I am trying to get a webpage using a TcpSocket instead of a standard
> > Webrequest.  Initial, it works fine but after the 2 or 3 request the
[quoted text clipped - 30 lines]
>
> Pete
Peter Duniho - 29 Jun 2007 22:49 GMT
> I am very sorry for the confusing.  I was trying to be brief.  Here is  
> the
> class, and I renamed the socket to client for easyier reading.  I am  
> using
> TCPTrace at the moment to test this, and it gets and sends the proper
> responses so I do not believe it is a Dos prevention of some kind.

Well, I don't see anything obvious.  As I mentioned, you really need to  
post a _complete_ sample of code that reliably reproduces the problem if  
anyone is to actually try to look at your specific problem.  You've only  
posted the client side of things.

There do happen to be some odd things in your code, even without me  
inspecting each line carefully (which I didn't do).  Nothing that seems  
like it would be causing the issue, but which are to me a sign of  
less-than-perfect code:

    -- When you write to the NetworkStream, you use the length of the  
original string, not the byte array you're passing.  In this case, they  
should be the same, but there are potential situations in which they  
wouldn't be.  You should pass the length of the actual data you expect to  
send, not some other length that is related but not necessarily identical.

    -- You check the CanWrite and CanRead properties of the stream, but  
don't do anything sensible if they aren't what you expect.  One particular  
issue is that if CanWrite is false but CanRead is true, you skip trying to  
write but go ahead and try to read a response to something you never  
sent.  That makes no sense.  Presumably, both CanWrite and CanRead are  
true in this situation, so the oddity shouldn't affect you.  But the code  
is wrong, nevertheless.

    -- You are catching exceptions that you then do nothing with other  
than to throw them again.  What's the point?

Have you tried not setting the timeout?  It's not supposed to affect  
connecting, but maybe it does, or maybe having a timeout on a previous  
connection somehow interferes with the subsequent one.  I admit, I'm just  
making wild guesses here...I don't see anything obvious.  Even more reason  
for you to construct self-contained server/client sample code that  
reliably reproduces the problem.  Just looking at the code doesn't suggest  
anything obvious, at least not to me.

Pete

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