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HttpWebRequest.BeginGetResponse Method

Begins an asynchronous request to an Internet resource.

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

[<HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)>]
abstract BeginGetResponse : 
        callback:AsyncCallback * 
        state:Object -> IAsyncResult 
[<HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)>]
override BeginGetResponse : 
        callback:AsyncCallback * 
        state:Object -> IAsyncResult 

Parameters

callback
Type: System.AsyncCallback
The AsyncCallback delegate
state
Type: System.Object
The state object for this request.

Return Value

Type: System.IAsyncResult
An IAsyncResult that references the asynchronous request for a response.

ExceptionCondition
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.

-or-

The HttpWebRequest has an entity body but the BeginGetResponse method is called without calling the BeginGetRequestStream method.

-or-

The ContentLength is greater than zero, but the application does not write all of the promised data.

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.

A ProtocolViolationException is thrown in several cases when the properties set on the HttpWebRequest class are conflicting. This exception occurs if an application sets the ContentLength property and the SendChunked property to true, and then sends an HTTP GET request. This exception occurs if an application tries to send chunked to a server that only supports HTTP 1.0 protocol, where this is not supported. This exception occurs if an application tries to send data without setting the ContentLength property or the SendChunked is false when buffering is disabled and on a keepalive connection (the KeepAlive property is true).

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

The BeginGetResponse method requires some synchronous setup tasks to complete (DNS resolution, proxy detection, and TCP socket connection, for example) before this method becomes asynchronous. As a result, this method should never be called on a user interface (UI) thread because it might take some time, typically several seconds. In some environments where the webproxy scripts are not configured properly, this can take 60 seconds or more. The default value for the downloadTime attribute on the <webProxyScipt> config file element is one minute which accounts for most of the potential time delay.

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.

NoteNote

The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

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.

No code example is currently available or this language may not be supported.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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

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