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POWhy is WCF reading input stream to EOF on Close()?
 

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    <p>We're using WCF to build a simple web service which our product uses to upload large files over a WAN link. It's supposed to be a simple HTTP PUT, and it's working fine for the most part.</p> <p>Here's a simplified version of the service contract:</p> <pre><code>[ServiceContract, XmlSerializerFormat] public interface IReplicationWebService { [OperationContract] [WebInvoke(Method = "PUT", UriTemplate = "agents/{sourceName}/epoch/{guid}/{number}/{type}")] ReplayResult PutEpochFile(string sourceName, string guid, string number, string type, Stream stream); } </code></pre> <p>In the implementation of this contract, we read data from <code>stream</code> and write it out to a file. This works great, so we added some error handling for cases when there's not enough disk space to store the file. Here's roughly what it looks like:</p> <pre><code> public ReplayResult PutEpochFile(string sourceName, string guid, string number, string type, Stream inStream) { //Stuff snipped try { //Read from the stream and write to the file } catch (IOException ioe) { //IOException may mean no disk space try { inStream.Close(); } // if instream caused the IOException, close may throw catch { } _logger.Debug(ioe.ToString()); throw new FaultException&lt;IOException&gt;(ioe, new FaultReason(ioe.Message), new FaultCode("IO")); } } </code></pre> <p>To test this, I'm sending a 100GB file to a server that doesn't have enough space for the file. As expected this throws an exception, but the call to <code>inStream.Close()</code> appeared to hang. I checked into it, and what's actually happening is that the call to <code>Close()</code> made its way through the WCF plumbing until it reached <code>System.ServiceModel.Channels.DrainOnCloseStream.Close()</code>, which according to Reflector allocates a <code>Byte[]</code> buffer and keeps reading from the stream until it's at EOF.</p> <p>In other words, the <code>Close</code> call is reading the entire 100GB of test data from the stream before returning!</p> <p>Now it may be that I don't need to call <code>Close()</code> on this stream. If that's the case I'd like an explanation as to why. But more importantly, I'd appreciate it if anyone could explain to me why <code>Close()</code> is behaving this way, why it's not considered a bug, and how to reconfigure WCF so that doesn't happen.</p>
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