C# WebClient acting slow the first time

Question

I am using a WebClient to download a string from a website (which just contains plain text, nothing else), so I use the DownloadString method:

WebClient wc = new WebClient();
string str = wc.DownloadString("http://blah");

It works fine, but the problem is that the first time it downloads the string it takes a long time, like 5 seconds. After that it works fast. Why does this happen and how can overcome this problem?

Is this your web service or some one elses? and does this happen every time you start your client? (even if restart directly when the string is downloaded?) — Peter, Feb 08 '11 at 11:39
Also note that this causes the app to freeze, even when using the `async` version of the method. How does shit like this get released!? — BlueRaja - Danny Pflughoeft, Oct 11 '15 at 05:02

score 22 · Accepted Answer · edited Aug 08 '12 at 23:21

22

Setting the Proxy property of your WebClient object to null should eliminate the delays you're seeing. Alternatively if you've configured your system to use a proxy it can be retrieved with WebRequest.GetSystemWebProxy. The second method should eliminate the delay in either case.

edited Aug 08 '12 at 23:21

Drew Noakes

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answered Feb 08 '11 at 12:21

T3hc13h

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Neither `webClient.Proxy = WebRequest.GetSystemWebProxy()` nor `WebRequest.DefaultProxy` fix the problem, the delay still occurs. Setting it to `null` or `GlobalProxySelection.GetEmptyWebProxy()` _does_ work... but then the app can no longer be used on connections that require a proxy! Is there really no solution!? – BlueRaja - Danny Pflughoeft Oct 11 '15 at 04:53

score 6 · Answer 2 · answered Aug 08 '12 at 23:13

6

I noticed the same thing. DotTrace shows it's spending the majority of its time enumerating proxy options:

answered Aug 08 '12 at 23:13

Drew Noakes

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score 4 · Answer 3 · answered Feb 08 '11 at 11:40

Well, the first time it needs to do a DNS lookup and connect to the host - after that, within the same process it may well be reusing the same connection. For the very first request to anywhere, it may well also be trying to detect proxy settings etc.

If you want to see what's really happening at the network level to make it slow, I suggest you grab Wireshark and monitor the traffic with that.

C# WebClient acting slow the first time

3 Answers3

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