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Remove From My Forums. Answered by:. Smart Device Development. NET Compact Framework. NET Compact Framework 3. Sign in to vote. Hi guys.
I'm facing a problem when I try to download files from Internet. To make the downloads I use a thread pool to download the files. I have the option to cancel the download at any time you want. When I click the cancel button I try to do WebRequest. My question is, how can I can cancel the webrequest without having the error?
Wednesday, June 20, AM. Tuesday, July 24, PM. Does anyone know what's happening? Why I can't abort the request without get an error?
Should I close the webresponse instead? Help me, please.A WebResponse that contains the response from the Internet resource. TransferEncoding is set to a value and SendChunked is false. The ContentLength is greater than zero, but the application does not write all of the promised data. The request cache validator indicated that the response for this request can be served from the cache; however, this request includes data to be sent to the server.
Requests that send data must not use the cache. This exception can occur if you are using a custom cache validator that is incorrectly implemented. Abort was previously called. The GetResponse method returns a WebResponse object that contains the response from the Internet resource.
A ProtocolViolationException is thrown in several cases when the properties set on the HttpWebRequest class are conflicting. This exception occurs if an application tries to send chunked to a server that only supports HTTP 1.
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. You must call the Close method to close the stream and release the connection. Failure to do so may cause your application to run out of connections.
When using the POST method, you must get the request stream, write the data to be posted, and close the stream. This method blocks waiting for content to post; if there is no time-out set and you do not provide content, the calling thread blocks indefinitely. Multiple calls to GetResponse return the same response object; the request is not reissued. Your application cannot mix synchronous and asynchronous methods for a particular request.
If you call the GetRequestStream method, you must use the GetResponse method to retrieve the response. If a WebException is thrown, use the Response and Status properties of the exception to determine the response from the server. This member outputs trace information when you enable network tracing in your application. For more information, see Network Tracing in the. NET Framework. For security reasons, cookies are disabled by default.
Do not use the HttpWebRequest constructor. Use the WebRequest. Create method to initialize new HttpWebRequest objects. The GetResponse method makes a synchronous request to the resource specified in the RequestUri property and returns an HttpWebResponse that contains the response object.
The response data can be received by using the stream returned by GetResponseStream. If the response object or the response stream is closed, remaining data will be forfeited. The remaining data will be drained and the socket will be re-used for subsequent requests when closing the response object or stream if the following conditions hold: it's a keep-alive or pipelined request, only a small amount of data needs to be received, or the remaining data is received in a small time interval.
If none of the mentioned conditions hold or the drain time is exceeded, the socket will be closed. For keep-alive or pipelined connections, we strongly recommend that the application reads the streams until EOF. This ensures that the socket will be re-used for subsequent requests resulting in better performance and less resources used.
When you want to send data to the resource, the GetRequestStream method returns a Stream object to use to send data. For client authentication with HttpWebRequestthe client certificate must be installed in the My certificate store of the current user. The WebException.
Status property contains a WebExceptionStatus value that indicates the source of the error. When WebException. Status is WebExceptionStatus.
HttpWebRequest exposes common HTTP header values sent to the Internet resource as properties, set by methods, or set by the system; the following table contains a complete list.
Note that servers and caches may change or add headers during the request.
The following table lists the HTTP headers that are set either by properties or methods or the system. HttpWebRequest is registered automatically. You do not need to call the RegisterPrefix method to register System. The local computer or application config file may specify that a default proxy be used.
If the Proxy property is specified, then the proxy settings from the Proxy property override the local computer or application config file and the HttpWebRequest instance will use the proxy settings specified. If no proxy is specified in a config file and the Proxy property is unspecified, the HttpWebRequest class uses the proxy settings inherited from Internet Explorer on the local computer.
If there are no proxy settings in Internet Explorer, the request is sent directly to the server. The HttpWebRequest class parses a proxy bypass list with wildcard characters inherited from Internet Explorer differently than the bypass list is parsed directly by Internet Explorer. This differs from the native behavior of Internet Explorer. The Framework caches SSL sessions as they are created and attempts to reuse a cached session for a new request, if possible.
The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. All, I am trying to cancel two concurrent HttpWebRequests using a method similar to the code below shown in pseudo-ish C.
The Main method creates two threads which create HttpWebRequests. If the user wishes to, they may abort the requests by clicking a button which then calls the Abort method. How can I abort both of these requests in a way that the web server knows that the connection has been aborted? As suggested, a good alternative would be to use BeginGetResponse. I have modified the question to show this. Use BeginGetResponse to initiate the call and then use the Abort method on the class to cancel it.
If you have to stick with the synchronous version, to kill the situation, all you can do is abort the thread. To give up waiting, you can specify a timeout:. If you need to kill the process, I would argue launching it inside a new AppDomain and dropping the AppDomain when you want to kill the request; instead of aborting a thread inside your main process.
A ThreadAbortException is highly non-specific. HttpWebRequest already supports a way to cancel the request in a predictable way with the Abort method. I recommend you use it instead. Note that you'll still get a WebException on the thread, designed to tell you that the request got aborted externally.
Be prepared to catch it. This might be because of. NET's connection pooling. Every WebRequest-instance has a ServicePoint that describes the target you want to communicate with server address, port, protocol, These ServicePoints will be reused, so if you create 2 WebRequests with the same server address, port and protocol they will share the same ServicePoint instance.
When you call WebRequest. GetResponse it uses the connection pool provided by the ServicePoint to create connections. If you then kill the thread with Thread. Abort it will NOT return the connection to the ServicePoint's connection pool, so the ServicePoint thinks this connection is still in use. If the connection limit of the ServicePoint is reached default: 2 it will not create any new connections, but instead wait for one of the open connections to be returned.
The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. The essential structure for making an asynchronous web request is to call BeginGetResponse and start a timer at the same time.
If the response doesn't timeout, BeginGetResponse will call a callback method that will call EndGetResponse and read the response. If the response does timeout, a different callback method to the timer gets called and WebRequest. Abort is invoked. This structure hinges on the fact that Abort and EndGetResponse are exclusive.
Calling Abort after EndGetResponse has basically no effect and calling EndGetResponse after Abort causes EndGetResponse to throw an exception which can then be caught and handled however you want to handle timeouts. My problem is when I need to make several hundred requests per second to several services and one service starts becoming very, very latent.
The Timeout callback might get called after ms and calls Abort and my program continues happily. But because the service still hasn't returned 10 seconds later, the first thread started by BeginGetResponse is still waiting and the network connection resource is unavailable for use by any future requests.
Is there any way to have a timeout free up the resources of the thread that is supposedly timing out? If not, is there something like a Web. Learn more. Asked 7 years, 9 months ago.
Active 7 years, 9 months ago. Viewed times. Here's what I understand about using HttpWebRequest to make a request asyncronously: The essential structure for making an asynchronous web request is to call BeginGetResponse and start a timer at the same time. We eventually came up with a solution that worked. We started our own threads, one for each HttpWebReqest, and then within those threads we called the synchronous GetResponse rather than the asynchronous BeginGetResponse.
From what we can tell so far, the HttpWebRequest Timeout property that causes a WebException to be thrown seems to handle closing the connection and no longer waiting for a response from the server. I'm not sure about this, but it appears that HttpWebRequest should not be used asynchronously in cases where lots of connections to potentially really slow servers are needed.
Active Oldest Votes. Travis J Travis J BeginGetResponse starts its own thread that I don't control. If I did, I could implement a destructor to the thread that frees the network connection.
The problem appears to be that there is no way to end the thread until the response comes from the server which could potentially be an infinite amount of time.The AsyncCallback delegate.
An IAsyncResult that references the asynchronous request for a response. TransferEncoding is set to a value and SendChunked is false. The ContentLength is greater than zero, but the application does not write all of the promised data. Abort was previously called. The following code example uses the BeginGetResponse method to make an asynchronous request for an Internet resource.
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.
The BeginGetResponse method starts an asynchronous request for a response from the Internet resource. A ProtocolViolationException is thrown in several cases when the properties set on the HttpWebRequest class are conflicting. This exception occurs if an application tries to send chunked to a server that only supports HTTP 1. 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 considerable time up to several minutes depending on network settings to complete the initial synchronous setup tasks before an exception for an error is thrown or the method succeeds. To learn more about the thread pool, see The managed thread pool. Your application cannot mix synchronous and asynchronous methods for a particular request.
This member outputs trace information when you enable network tracing in your application. For more information, see Network Tracing in the.
NET Framework. Skip to main content. Exit focus mode. Http Web Request. Net Assembly: System. Begins an asynchronous request to an Internet resource.
Note In the case of asynchronous requests, it is the responsibility of the client application to implement its own time-out mechanism. Note Your application cannot mix synchronous and asynchronous methods for a particular request. Note This member outputs trace information when you enable network tracing in your application.
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Any additional feedback? Skip Submit.I literally spent days poring over our app's code to figure out what was going wrong. Eventually I gave up and blamed our failure on the Compact Framework code, and it seems I was correct. It appears that in CF 2. Abort is broken in some cases and causes very difficult-to-detect incorrectness in subsequent requests.
It's obvious what this code is supposed to do, and the API also clearly states what is supposed to happen — the request is cancelled. However, due to a CF bug, that doesn't always work correctly. In this case, the Abort call actually fails to abort the connection.
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In fact, the HttpWebRequest will appear to have been aborted, but its underlying Connection object and its Socket object will still be sitting around. Since the Connection objects used by HttpWebRequest are pooled, this is very bad. It leaves the Connection object in an unaborted state while its owning HttpWebRequest has been aborted — meaning when the Connection object is reused by a different request, it still has old state and will behave in unexpected ways.
So you end up with random data corruption. Not only that, but it's silent: it's very difficult to detect this condition, and most of the time the data looks legitimate. For example if you're downloading images and image 50 actually contains the data that was supposed to go into image 49, well, tough luck because it looks like a legitimate image.
I spent forever trying to come up with solutions to this, but could only come up with ones that don't work:. The problem is that Abort is the only way to kill the request, and it may not be possible for your app to completely avoid aborting requests.
In addition, since the Connection objects are pooled and there are very few of them in the pool, you can't leave these requests hanging around or your app will quickly run out of connections.
If Abort is called and this bug is triggered, the Connection will be returned to the pool and not block subsequent requests; it will just have unpredictable behavior next time. When an HttpWebRequest returns data, check to see whether it came from a broken Connection ; if so disregard the data and retry. This would work Inherit from HttpWebRequest. Tag each one with a unique ID, and when the response comes back check to see the ID is what you expect. Since HttpWebRequest s aren't pooled this doesn't work.
It's the underlying Connection which is pooled and left in an invalid state, not the request itself. Set a timeout on the underlying Connection or the Socket that it owns so they can dispose themselves. HttpWebRequest has a timeout but it is useless as it simply calls Abort when the timer rings, so will still exhibit the buggy behavior.
Tags: cfhttpwebrequest. Depinder Bharti on Sunday, April 25, at