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HttpWebRequest.BeginGetResponse Method

Begins an asynchronous request to an Internet resource.

[Visual Basic]
Overrides Public Function BeginGetResponse( _
   ByVal callback As AsyncCallback, _
   ByVal state As Object _
) As IAsyncResult
[C#]
public override IAsyncResult BeginGetResponse(
 AsyncCallback callback,
 object state
);
[C++]
public: IAsyncResult* BeginGetResponse(
 AsyncCallback* callback,
 Object* state
);
[JScript]
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.

Exceptions

Exception Type Condition
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.

Remarks

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.

To learn more about the thread pool, see Thread Pooling.

Example

[Visual Basic, C#, C++] The following example uses the BeginGetResponse method to make an asynchronous request for an internet resource.

[Visual Basic, C#, C++] Note   In the case of asynchronous requests, it is the responsibility of the client application to implement its own timeout mechanism. The following example shows how to do it.
[Visual Basic] 

Imports System
Imports System.Net
Imports System.IO
Imports System.Text
Imports System.Threading
Imports Microsoft.VisualBasic

Public Class RequestState
   ' This class stores the State of the request.
   Private BUFFER_SIZE As Integer = 1024
   Public requestData As StringBuilder
   Public BufferRead() As Byte
   Public request As HttpWebRequest
   Public response As HttpWebResponse
   Public streamResponse As Stream
   
   Public Sub New()
      BufferRead = New Byte(BUFFER_SIZE) {}
      requestData = New StringBuilder("")
      request = Nothing
      streamResponse = Nothing
   End Sub 'New
End Class 'RequestState


Class HttpWebRequest_BeginGetResponse

   Public Shared allDone As New ManualResetEvent(False)
   Private BUFFER_SIZE As Integer = 1024
   Private DefaultTimeout As Integer = 2 * 60 * 1000

    ' 2 minutes timeout
   ' Abort the request if the timer fires.
   Private Shared Sub TimeoutCallback(state As Object, timedOut As Boolean)
      If timedOut Then
         Dim request As HttpWebRequest = state 
        
         If Not (request Is Nothing) Then
            request.Abort()
         End If
      End If
   End Sub 'TimeoutCallback
   
   
   Shared Sub Main()
     
      Try
         ' Create a HttpWebrequest object to the desired URL. 
            Dim myHttpWebRequest As HttpWebRequest = WebRequest.Create("http://www.contoso.com")
         
         ' Create an instance of the RequestState and assign the previous myHttpWebRequest
         ' object to it's request field.  
         
         Dim myRequestState As New RequestState()
         myRequestState.request = myHttpWebRequest

         Dim myResponse As New HttpWebRequest_BeginGetResponse()
         
         ' Start the asynchronous request.
         Dim result As IAsyncResult = CType(myHttpWebRequest.BeginGetResponse(New AsyncCallback(AddressOf RespCallback), myRequestState), IAsyncResult)
         
            ' this line implements the timeout, if there is a timeout, the callback fires and the request aborts.
         ThreadPool.RegisterWaitForSingleObject(result.AsyncWaitHandle, New WaitOrTimerCallback(AddressOf TimeoutCallback), myHttpWebRequest, myResponse.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 e As WebException
         Console.WriteLine(ControlChars.Lf + "Main Exception raised!")
         Console.WriteLine(ControlChars.Lf + "Message:{0}", e.Message)
         Console.WriteLine(ControlChars.Lf + "Status:{0}", e.Status)
         Console.WriteLine("Press any key to continue..........")
      Catch e As Exception
         Console.WriteLine(ControlChars.Lf + "Main Exception raised!")
         Console.WriteLine("Source :{0} ", e.Source)
         Console.WriteLine("Message :{0} ", e.Message)
         Console.WriteLine("Press any key to continue..........")
         Console.Read()
      End Try
   End Sub 'Main
   
   Private Shared Sub RespCallback(asynchronousResult As IAsyncResult)
      Try
         ' State of request is asynchronous.
         Dim myRequestState As RequestState = CType(asynchronousResult.AsyncState, RequestState)
         Dim myHttpWebRequest As HttpWebRequest = myRequestState.request
         myRequestState.response = CType(myHttpWebRequest.EndGetResponse(asynchronousResult), HttpWebResponse)
         
         ' Read the response into a Stream object.
         Dim responseStream As Stream = myRequestState.response.GetResponseStream()
         myRequestState.streamResponse = responseStream
         
         ' Begin the Reading of the contents of the HTML page and print it to the console.
         Dim asynchronousInputRead As IAsyncResult = responseStream.BeginRead(myRequestState.BufferRead, 0, 1024, New AsyncCallback(AddressOf ReadCallBack), myRequestState)
         Return
      Catch e As WebException
         Console.WriteLine(ControlChars.Lf + "RespCallback Exception raised!")
         Console.WriteLine(ControlChars.Lf + "Message:{0}", e.Message)
         Console.WriteLine(ControlChars.Lf + "Status:{0}", e.Status)
      End Try
      allDone.Set()
   End Sub 'RespCallback
   
   Private Shared Sub ReadCallBack(asyncResult As IAsyncResult)
      Try
         
         Dim myRequestState As RequestState = CType(asyncResult.AsyncState, RequestState)
         Dim responseStream As Stream = myRequestState.streamResponse
         Dim read As Integer = responseStream.EndRead(asyncResult)
         ' Read the HTML page and then print it to the console.
         If read > 0 Then
            myRequestState.requestData.Append(Encoding.ASCII.GetString(myRequestState.BufferRead, 0, read))
            Dim asynchronousResult As IAsyncResult = responseStream.BeginRead(myRequestState.BufferRead, 0, 1024, New AsyncCallback(AddressOf ReadCallBack), myRequestState)
            Return
         Else
            Console.WriteLine(ControlChars.Lf + "The contents of the Html page are : ")
            If myRequestState.requestData.Length > 1 Then
               Dim stringContent As String
               stringContent = myRequestState.requestData.ToString()
               Console.WriteLine(stringContent)
            End If
            Console.WriteLine("Press any key to continue..........")
            Console.ReadLine()
            
            responseStream.Close()
         End If
      
      Catch e As WebException
         Console.WriteLine(ControlChars.Lf + "ReadCallBack Exception raised!")
         Console.WriteLine(ControlChars.Lf + "Message:{0}", e.Message)
         Console.WriteLine(ControlChars.Lf + "Status:{0}", e.Status)
      End Try
      allDone.Set()
   End Sub 'ReadCallBack 
End Class 'HttpWebRequest_BeginGetResponse


[C#] 
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 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.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();

  }

[C++] 
#using <mscorlib.dll>
#using <System.dll>
using namespace System;
using namespace System::Net;
using namespace System::IO;
using namespace System::Text;
using namespace System::Threading;

public __gc class RequestState {
   // This class stores the State of the request.
   const int BUFFER_SIZE;
public:
   StringBuilder* requestData;
   Byte BufferRead[];
   HttpWebRequest* request;
   HttpWebResponse* response;
   Stream* streamResponse;

   RequestState() : BUFFER_SIZE(1024){
      BufferRead = new Byte[BUFFER_SIZE];
      requestData = new StringBuilder(S"");
      request = 0;
      streamResponse = 0;
   }
};

__gc class HttpWebRequest_BeginGetResponse {
public:
   static ManualResetEvent* allDone = new ManualResetEvent(false);
   static const int BUFFER_SIZE = 1024;
   static const int DefaultTimeOut = 120000;   // 2 minute timeout 

   // Abort the request if the timer fires.
   static void TimeoutCallback(Object* state, bool timedOut) {
      if (timedOut) {
         HttpWebRequest* request = dynamic_cast<HttpWebRequest*>(state);
         if (request != 0) {
            request->Abort();
         }
      }
   }

   static void RespCallback(IAsyncResult* asynchronousResult) {
      try {
         // State of request is asynchronous.
         RequestState* myRequestState=dynamic_cast<RequestState*> (asynchronousResult->AsyncState);
         HttpWebRequest*  myHttpWebRequest=myRequestState->request;
         myRequestState->response = dynamic_cast<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(0, ReadCallBack),
            myRequestState);
         return;
      } catch (WebException* e) {
         Console::WriteLine(S"\nRespCallback Exception raised!");
         Console::WriteLine(S"\nMessage: {0}", e->Message);
         Console::WriteLine(S"\nStatus: {0}", __box(e->Status));
      }
      allDone->Set();
   }

   static  void ReadCallBack(IAsyncResult* asyncResult) {
      try {

         RequestState * myRequestState = dynamic_cast<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(0, ReadCallBack),
               myRequestState);
            return;
         } else {
            Console::WriteLine(S"\nThe contents of the Html page are : ");
            if (myRequestState->requestData->Length>1) {
               String* stringContent;
               stringContent = myRequestState->requestData->ToString();
               Console::WriteLine(stringContent);
            }
            Console::WriteLine(S"Press any key to continue..........");
            Console::ReadLine();

            responseStream->Close();
         }

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

int main() {

   try {
      // Create a HttpWebrequest object to the desired URL.
      HttpWebRequest * myHttpWebRequest= dynamic_cast<HttpWebRequest*>
         (WebRequest::Create(S"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(S"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= dynamic_cast<IAsyncResult*>(myHttpWebRequest->BeginGetResponse(
         new AsyncCallback(0, HttpWebRequest_BeginGetResponse::RespCallback),
         myRequestState));

      // this line impliments the timeout, if there is a timeout, the callback fires and the request becomes aborted
      ThreadPool::RegisterWaitForSingleObject (
         result->AsyncWaitHandle,
         new WaitOrTimerCallback(0, HttpWebRequest_BeginGetResponse::TimeoutCallback),
         myHttpWebRequest,
         HttpWebRequest_BeginGetResponse::DefaultTimeOut,
         true);

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

      // Release the HttpWebResponse resource.
      myRequestState->response->Close();
   } catch (WebException* e) {
      Console::WriteLine(S"\nMain Exception raised!");
      Console::WriteLine(S"\nMessage: {0}", e->Message);
      Console::WriteLine(S"\nStatus: {0}", __box(e->Status));
      Console::WriteLine(S"Press any key to continue..........");
   } catch (Exception* e) {
      Console::WriteLine(S"\nMain Exception raised!");
      Console::WriteLine(S"Source : {0} " , e->Source);
      Console::WriteLine(S"Message : {0} " , e->Message);
      Console::WriteLine(S"Press any key to continue..........");
      Console::Read();
   }
}

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework, Common Language Infrastructure (CLI) Standard

See Also

HttpWebRequest Class | HttpWebRequest Members | System.Net Namespace

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