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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); 
   3:   
   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.

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