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HttpWebRequest.BeginGetResponse Method

Begins an asynchronous request to an Internet resource.

Namespace: System.Net
Assembly: System (in system.dll)

public override IAsyncResult BeginGetResponse (
	AsyncCallback callback,
	Object state
)
public IAsyncResult BeginGetResponse (
	AsyncCallback callback, 
	Object state
)
public override function BeginGetResponse (
	callback : AsyncCallback, 
	state : Object
) : IAsyncResult

Parameters

callback

The AsyncCallback delegate

state

The state object for this request.

Return Value

An IAsyncResult that references the asynchronous request for a response.
Exception typeCondition

InvalidOperationException

The stream is already in use by a previous call to BeginGetResponse

-or-

TransferEncoding is set to a value and SendChunked is false.

-or-

The thread pool is running out of threads.

ProtocolViolationException

Method is GET or HEAD, and either ContentLength is greater than zero or SendChunked is true.

-or-

KeepAlive is true, AllowWriteStreamBuffering is false, and either ContentLength is -1, SendChunked is false and Method is POST or PUT.

WebException

Abort was previously called.

The BeginGetResponse method starts an asynchronous request for a response from the Internet resource. The asynchronous callback method uses the EndGetResponse method to return the actual WebResponse.

If a WebException is thrown, use the Response and Status properties of the exception to determine the response from the server.

To learn more about the thread pool, see The Managed Thread Pool.

NoteNote

Your application cannot mix synchronous and asynchronous methods for a particular request. If you call the BeginGetRequestStream method, you must use the BeginGetResponse method to retrieve the response.

NoteNote

This member outputs trace information when you enable network tracing in your application. For more information, see Network Tracing.

The following code example uses the BeginGetResponse method to make an asynchronous request for an Internet resource.

NoteNote

In the case of asynchronous requests, it is the responsibility of the client application to implement its own time-out mechanism. The following code example shows how to do it.

using System;
using System.Net;
using System.IO;
using System.Text;
using System.Threading;


public class RequestState
{
  // This class stores the State of the request.
  const int BUFFER_SIZE = 1024;
  public StringBuilder requestData;
  public byte[] BufferRead;
  public HttpWebRequest request;
  public HttpWebResponse response;
  public Stream streamResponse;
  public RequestState()
  {
    BufferRead = new byte[BUFFER_SIZE];
    requestData = new StringBuilder("");
    request = null;
    streamResponse = null;
  }
}

class HttpWebRequest_BeginGetResponse
{
  public static ManualResetEvent allDone= new ManualResetEvent(false);
  const int BUFFER_SIZE = 1024;
  const int DefaultTimeout = 2 * 60 * 1000; // 2 minutes timeout
 
  // Abort the request if the timer fires.
  private static void TimeoutCallback(object state, bool timedOut) { 
      if (timedOut) {
          HttpWebRequest request = state as HttpWebRequest;
          if (request != null) {
              request.Abort();
          }
      }
  }

  static void Main()
  {  
   
    try
    {
      // Create a HttpWebrequest object to the desired URL. 
      HttpWebRequest myHttpWebRequest= (HttpWebRequest)WebRequest.Create("http://www.contoso.com");

    
  /**
    * If you are behind a firewall and you do not have your browser proxy setup
    * you need to use the following proxy creation code.

      // Create a proxy object.
      WebProxy myProxy = new WebProxy();

      // Associate a new Uri object to the _wProxy object, using the proxy address
      // selected by the user.
      myProxy.Address = new Uri("http://myproxy");
       
        
      // Finally, initialize the Web request object proxy property with the _wProxy
      // object.
      myHttpWebRequest.Proxy=myProxy;
    ***/

      // Create an instance of the RequestState and assign the previous myHttpWebRequest
      // object to its request field.  
      RequestState myRequestState = new RequestState();  
      myRequestState.request = myHttpWebRequest;


      // Start the asynchronous request.
      IAsyncResult result=
        (IAsyncResult) myHttpWebRequest.BeginGetResponse(new AsyncCallback(RespCallback),myRequestState);

      // this line implements the timeout, if there is a timeout, the callback fires and the request becomes aborted
      ThreadPool.RegisterWaitForSingleObject (result.AsyncWaitHandle, new WaitOrTimerCallback(TimeoutCallback), myHttpWebRequest, DefaultTimeout, true);

      // The response came in the allowed time. The work processing will happen in the 
      // callback function.
      allDone.WaitOne();
      
      // Release the HttpWebResponse resource.
      myRequestState.response.Close();
    }
    catch(WebException e)
    {
      Console.WriteLine("\nMain Exception raised!");
      Console.WriteLine("\nMessage:{0}",e.Message);
      Console.WriteLine("\nStatus:{0}",e.Status);
      Console.WriteLine("Press any key to continue..........");
    }
    catch(Exception e)
    {
      Console.WriteLine("\nMain Exception raised!");
      Console.WriteLine("Source :{0} " , e.Source);
      Console.WriteLine("Message :{0} " , e.Message);
      Console.WriteLine("Press any key to continue..........");
      Console.Read();
    }
  }
  private static void RespCallback(IAsyncResult asynchronousResult)
  {  
    try
    {
      // State of request is asynchronous.
      RequestState myRequestState=(RequestState) asynchronousResult.AsyncState;
      HttpWebRequest  myHttpWebRequest=myRequestState.request;
      myRequestState.response = (HttpWebResponse) myHttpWebRequest.EndGetResponse(asynchronousResult);
      
      // Read the response into a Stream object.
      Stream responseStream = myRequestState.response.GetResponseStream();
      myRequestState.streamResponse=responseStream;
      
      // Begin the Reading of the contents of the HTML page and print it to the console.
      IAsyncResult asynchronousInputRead = responseStream.BeginRead(myRequestState.BufferRead, 0, BUFFER_SIZE, new AsyncCallback(ReadCallBack), myRequestState);
      return;
    }
    catch(WebException e)
    {
      Console.WriteLine("\nRespCallback Exception raised!");
      Console.WriteLine("\nMessage:{0}",e.Message);
      Console.WriteLine("\nStatus:{0}",e.Status);
    }
    allDone.Set();
  }
  private static  void ReadCallBack(IAsyncResult asyncResult)
  {
    try
    {

    RequestState myRequestState = (RequestState)asyncResult.AsyncState;
    Stream responseStream = myRequestState.streamResponse;
    int read = responseStream.EndRead( asyncResult );
    // Read the HTML page and then print it to the console.
    if (read > 0)
    {
      myRequestState.requestData.Append(Encoding.ASCII.GetString(myRequestState.BufferRead, 0, read));
      IAsyncResult asynchronousResult = responseStream.BeginRead( myRequestState.BufferRead, 0, BUFFER_SIZE, new AsyncCallback(ReadCallBack), myRequestState);
      return;
    }
    else
    {
      Console.WriteLine("\nThe contents of the Html page are : ");
      if(myRequestState.requestData.Length>1)
      {
        string stringContent;
        stringContent = myRequestState.requestData.ToString();
        Console.WriteLine(stringContent);
      }
      Console.WriteLine("Press any key to continue..........");
      Console.ReadLine();
      
      responseStream.Close();
    }

    }
    catch(WebException e)
    {
      Console.WriteLine("\nReadCallBack Exception raised!");
      Console.WriteLine("\nMessage:{0}",e.Message);
      Console.WriteLine("\nStatus:{0}",e.Status);
    }
    allDone.Set();

  }

import System.*;
import System.Net.*;
import System.IO.*;
import System.Text.*;
import System.Threading.*;

public class RequestState
{
    // This class stores the State of the request.
    private final int BUFFER_SIZE = 1024;
    public StringBuilder requestData;
    public ubyte bufferRead[];
    public HttpWebRequest request;
    public HttpWebResponse response;
    public Stream streamResponse;
   
    public RequestState() 
    {
        bufferRead = new ubyte[BUFFER_SIZE];
        requestData = new StringBuilder("");
        request = null;
        streamResponse = null;
    } //RequestState
} //RequestState

class HttpWebRequest_BeginGetResponse
{
    public static ManualResetEvent allDone = new ManualResetEvent(false);
    private static final int BUFFER_SIZE = 1024;
    private static int defaultTimeout = 2 * 60 * 1000; // 2 minutes timeout
    
    // Abort the request if the timer fires.
    private static void TimeoutCallback(Object state, boolean timedOut)
    {
        if (timedOut ) {
            HttpWebRequest request = (HttpWebRequest)state;
            if (request  != null) {
                request.Abort();
            }
        }
    } //TimeoutCallback
   
       public static void main(String[] args)
    {
        try {
            // Create a HttpWebrequest object to the desired URL. 
            HttpWebRequest myHttpWebRequest =((HttpWebRequest)
                (WebRequest.Create("http://www.contoso.com")));
            /**
                 If you are behind a firewall and you do not have your browser 
                 proxy setup you need to use the following proxy creation code.

                // Create a proxy object.
                WebProxy myProxy = new WebProxy();

                // Associate a new Uri object to the _wProxy object, using the 
                // proxy address selected by the user.
                myProxy.set_Address(new Uri("http://myproxy"));

                // Finally, initialize the Web request object proxy property
                // with the _wProxy object.
                myHttpWebRequest.set_Proxy(myProxy);
             */

            // Create an instance of the RequestState and assign the previous 
            // myHttpWebRequest object to it's request field.  
            RequestState myRequestState = new RequestState();
            myRequestState.request = myHttpWebRequest;

            // Start the asynchronous request.
            IAsyncResult result = 
                ((IAsyncResult)(myHttpWebRequest.BeginGetResponse(
                new AsyncCallback(RespCallback), myRequestState)));

            // this line impliments the timeout, if there is a timeout, 
            // the callback fires and the request becomes aborted
            ThreadPool.RegisterWaitForSingleObject(
                result.get_AsyncWaitHandle(), 
                new WaitOrTimerCallback(TimeoutCallback), 
                myHttpWebRequest, defaultTimeout, true);

            // The response came in the allowed time. 
            // The work processing will happen in the callback function.
            allDone.WaitOne();

            // Release the HttpWebResponse resource.
            myRequestState.response.Close();
        }
        catch(WebException e) {
            Console.WriteLine("\nMain Exception raised!");
            Console.WriteLine("\nMessage:{0}", e.get_Message());
            Console.WriteLine("\nStatus:{0}", e.get_Status());
            Console.WriteLine("Press any key to continue..........");
        }
        catch(System.Exception  e) {
            Console.WriteLine("\nMain Exception raised!");
            Console.WriteLine("Source :{0} ", e.get_Source());
            Console.WriteLine("Message :{0} ", e.get_Message());
            Console.WriteLine("Press any key to continue..........");
            Console.Read();
        }
    } //main
   
    private static void RespCallback(IAsyncResult asynchronousResult)
    {
        try {
            // State of request is asynchronous.
            RequestState myRequestState = 
                ((RequestState)(asynchronousResult.get_AsyncState()));
            HttpWebRequest myHttpWebRequest = myRequestState.request;
            myRequestState.response =
                ((HttpWebResponse)(myHttpWebRequest.EndGetResponse(
                    asynchronousResult)));

            // Read the response into a Stream object.
            Stream responseStream = 
                myRequestState.response.GetResponseStream();
            myRequestState.streamResponse = responseStream;

            // Begin the Reading of the contents of the HTML page and 
            // print it to the console.
            IAsyncResult asynchronousInputRead = 
                responseStream.BeginRead(myRequestState.bufferRead, 0, 
                BUFFER_SIZE, new AsyncCallback(ReadCallBack), myRequestState);
            return;
        }
        catch(WebException e) {
            Console.WriteLine("\nRespCallback Exception raised!");
            Console.WriteLine("\nMessage:{0}", e.get_Message());
            Console.WriteLine("\nStatus:{0}", e.get_Status());
        }
        allDone.Set();
    } //RespCallback
   
    private static void ReadCallBack(IAsyncResult asyncResult) 
    {
        try {
            RequestState myRequestState = 
                ((RequestState)(asyncResult.get_AsyncState()));
            Stream responseStream = myRequestState.streamResponse;
            int read = responseStream.EndRead(asyncResult);
            // Read the HTML page and then print it to the console.
            if ( read > 0  ) {
                myRequestState.requestData.Append(
                    Encoding.get_ASCII().GetString(
                    myRequestState.bufferRead, 0, read));
                IAsyncResult asynchronousResult = 
                    responseStream.BeginRead(myRequestState.bufferRead, 0, 
                    BUFFER_SIZE, new AsyncCallback(ReadCallBack), 
                    myRequestState);
                return ;
            }
            else {
                Console.WriteLine("\nThe contents of the Html page are : ");
                if ( myRequestState.requestData.get_Length() > 1  ) {
                    String stringContent;
                    stringContent = myRequestState.requestData.ToString();
                    Console.WriteLine(stringContent);
                }
                Console.WriteLine("Press any key to continue..........");
                Console.ReadLine();
                responseStream.Close();
            }
        } 
        catch(WebException e) {
            Console.WriteLine("\nReadCallBack Exception raised!");
            Console.WriteLine("\nMessage:{0}", e.get_Message());
            Console.WriteLine("\nStatus:{0}", e.get_Status());
        }
        allDone.Set();
    } //ReadCallBack 

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

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