WebClient::DownloadFileAsync() Throttling

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Mark Olbert - 11 Mar 2006 20:59 GMT

I have a situation where I would like to manage how fast an http download occurs from a server (basically, the server risks crashing
itself if it goes full bore).

I know there's no download rate paramter for the DownloadFile() methods in WebClient. I was wondering if some other class offers
that capability. Or, failing that, is the DownloadProgressChanged event a blocking call? If it is, I could insert some logic to
delay executing the event handler, thereby slowing down the data transfer rate.

- Mark

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Joerg Jooss - 12 Mar 2006 10:07 GMT

Thus wrote Mark,

> I have a situation where I would like to manage how fast an http
> download occurs from a server (basically, the server risks crashing
[quoted text clipped - 9 lines]
> delay executing the event handler, thereby slowing down the data
> transfer rate.

Whether a .NET method call is blocking or not doesn't affect a remote server
sending data. What you would need to do is throttle the traffic at TCP level.
But fixing this on the client side is a doomed approach anyway...

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Joerg Jooss
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Steven Cheng[MSFT] - 13 Mar 2006 08:29 GMT

Hi Mark,

Glad to see you. As for the WebClient class, when we use asynchronous
downloading, the download work is done in a background thread pool thread,
and the DownloadProgressChanged just work like a one way notification to
inform us the status(the underlying download work continue no matter what
we do in the event handler).

Also, for the data transfering rate control, generally it is done at raw
TCP/ IP protocol level through some specific component or APIs , it is
beyond the ability of the .NET network components (Like webclient or
httpwebrequest...).

BTW, if the server-side application is also developed by you, you can
consider controling the rate your server application flush data into the
response stream. For example, in ASP.NET's page or handler code, we can
manually use a loop to write out a file stream into page's response stream.

Anyway, for standard networking transfer rate control, you may have a look
at some general networking programming reference.

Regards,

Steven Cheng
Microsoft Online Support

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Mark Olbert - 13 Mar 2006 16:41 GMT

Thanks for the quick reply, Steven.

- Mark

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Steven Cheng[MSFT] - 14 Mar 2006 06:40 GMT

You're welcome Mark,

Please feel free to post here when there is anything else we can help.

Regards,

Steven Cheng
Microsoft Online Support

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