WCF methods with large result sets - visually tracking transfer progress

Question

I have a WCF services that has to return some data sets that can be as large as 10mb or more, I want some visual feedback for the user on progress, is there a way to track the download progress?

My client is Silverlight 3 and ultimately I would like to be able to bind a progress bar to this; any ideas?

EDIT: After the bounty SO automatically selected the answer with upvotes as the correct answer when this is not the case.

Answer 1

There is an example of this on the code project, see:

http://www.codeproject.com/KB/WCF/WCF%5FFileTransfer%5FProgress.aspx

Answer 2

If you have one giant WCF call, then you only have two states, everything or nothing. Also, WCF has a maximum transaction size, so returning a large dataset runs the risks of going over this limit.

In order to solve these problems in my projects, I split the one big request into many smaller requests. I then check how many responses I have vs. original requests to get an indication of progress.

Edit: added better explanation.

Answer 3

The CodeProject article may be tricky to get working with Silverlight since Silverlight only has access to the BasicHttpBinding -- although it looks like BasicHttpBinding has a TransferMode="Streamed" so perhaps it is possible -- I don't know.

If you can get it to return a Stream, that seems like it would be the best approach.

Still, I thought that I would put forward a random "other" approach.

Perhaps you could serialize the data into a file and use the WebClient to download it. So basically, you would have a WS.GetData() which would save a file on the server and return its filename -- then the Silverlight app would use WebClient to download it (which has a DownloadProgressChanged event).

I know it's not what you're looking for -- just an idea...

Answer 4

EDIT: I answered this thinking you wanted a silverlight uploader, but it actually looks like you want a silverlight downloader. You can do the same thing I suggested for the uploader except use HTTP GET, or Binary WCF, or Sockets.

I have written a Silverlight 2 uploader with a progress bar and I modeled it after this one. It uses HTTP POST to sent the file to the server one piece at a time. The tricky part is that the bigger your POST, the faster the file will be uploaded, but your progress bar only gets updated once per POST. So I wrote an algorithm that dynamically tries to find the biggest POST size that takes less than a second.

If you want to use WCF instead of HTTP POST, that's probably better because Silverlight 3 now supports binary message encoding:

<customBinding> <binding name="MyBinaryBinding" maxBufferSize="2147483647" maxReceivedMessageSize="2147483647"> <binaryMessageEncoding /> <httpTransport /> </binding> </customBinding>

OR you could write a sockets implementation - Silverlight does support this but it can be a little tricky to setup and requires your server to have a port in the range 4502-4532 open, and port 943 open for a policy file.