Friday, June 11, 2010

Uploading file streams over HTTP using WCF

Although WCF is really great, for some scenario’s it can be really hard to get everything up and running correctly. One of these scenario’s is uploading files.

Some important considerations:

Choose wisely between the streamed and buffered option

You have two main options for uploading files in WCF:

  • streamed
  • buffered/chunked

If you want to have reliable data transfer you’ll have to use the buffered/chunked option. Reliable messaging cannot be used with streaming as the WS-RM mechanism requires processing the data as a unity to apply checksums, etc. If you do not need the robustness of reliable messaging, streaming lets you transfer large amount of data using small message buffers without the overhead of implementing chuncking.

Secure your streams

Streaming over HTTP requires you to use basicHttpBinding; thus you will need SSL to encrypt the transferred data. Buffered transfer, on the other hand, can use wsHttpBinding, which by default provides integrity and confidentiality for your messages; thus there is no need for SSL then.

Use message headers for meta-data

   1:  [OperationContract(Action = "UploadFile", IsOneWay = true)] 
   2:  void UploadFile(UploadMessage request); 
   4:  [MessageContract] 
   5:  public class UploadMessage 
   6:  { 
   7:     [MessageHeader]
   8:     public string MetaData{get;set;}  
   9:     [MessageBodyMember]
  10:     public System.IO.Stream File{get;set;}
  11:  } 

WCF requires that the stream object is the only item in the message body for a streamed operation. Therefore headers are the recommended way for sending meta-data when streaming.

Configure the transferMode on the client

The setting for transferMode does not propagate to clients when using a HTTP binding. You must manually edit the client config file to set transferMode = "Streamed" after using 'Add service reference' or running SVCUTIL.EXE.

ASP.NET Developer Server limitations

If you try to run your streaming webservice, expect a big failure. Cassini support neither streamed transfers/MTOM encoding neither SSL.

So configure your service to be hosted in IIS.

Uploading large data streams over HTTP

WCF streaming is not only limited by the maxReceivedMessageSize settingb but also by IIS/ASP.NET who has a limit on the size of a HTTP request to prevent denial-of-service attacks. So for WCF streaming in IIS to work properly, you need to update your web.config and add following line:

   1:  <!-- maxRequestLength (in KB) max size: 2048MB --> 
   2:  <httpRuntime maxRequestLength="2000000" /> 

After that you are finally streaming large amounts of data over HTTPS.


sukumar said...

Our company has providing .Net application development. Thanks for sharing your experience. ASP.Net developers India

dEA said...

I did what you described but I wasn't able to run my upload when hosted in IIS (while it works perfectly hosted in Console application).

The server trace shows: System.ServiceModel.ProtocolException:
"There is a problem with the XML that was received from the network. See inner exception for more details."
"The body of the message cannot be read because it is empty."

Only changing client config to StreamedResponse make it works, but obviously in this way it uses buffering when sending.

Could you please post your VS sample ? Thanks a lot

Psycho Mantis said...

Note that file streaming in iis over https doesn't work, I had this confirmed by Microsoft. It will be fixed in .NET 4.5.