Saturday, 20 March 2010

Mmmmm… clean, sweet WCF proxy usage with TidyProxy!

Everyone knows (hopefully) how WCF has made multi-tiered application development easier and cleaner.  You get nicely generated client proxies that reuse common libraries straight out of Visual Studio – no more having to convert between your DTOs and the Web Service DTOs.  They even implement IDisposable - you can just wrap them in using statements and you’re good to go!  How neat is that!
   1: using (var proxy = new TidyProxy<SomeWCFServiceClient>())    
   2: {   
   3:    proxy.Client.DoSomeMagicallyComplexOperation();   
   4: }

But only if nothing goes wrong.

If the service you’re calling throws an exception (or Faults) then the Clients dispose method will throw another exception – masking the actual problem…  There’s an entire MSDN article on the issue.  The suggested fix?  Replace the using block above with something like this:

   1: var client = new SomeWCFServiceClient();
   2: try
   3: {
   4:     client.DoSomeMagicallyComplexOperation();
   5:     client.Close();
   6: }
   7: catch (CommunicationException e)
   8: {
   9:     client.Abort();
  10: }
  11: catch (TimeoutException e)
  12: {
  13:     client.Abort();
  14: }
  15: catch (Exception e)
  16: {
  17:     client.Abort();
  18:     throw;
  19: }

WCF not looking so sweet now, is it?

Now, I’ve got an issue with this type of boilerplate code, it’s verbose and awkward and reeks of having to clean up someone else's mess.  So, what can we do about?  Well, there’s a couple of good ideas out there from replacing the default ClientBase to adding an additional partial class to the generated code.  These are good solutions, but will require modification of the generated code and I’m too lazy to do that for each service I’m consuming. 

So, I want a way to leverage the existing, generated client and keep the implementation as close to the neat using statement as possible.  Thankfully, through the wonders of Generics and the Adapter pattern WCF can be redeemed – here’s TidyProxy:

   1: using System;
   2: using System.ServiceModel;
   3: namespace MartinOnDotNet.Helpers.WCF
   4: {
   5:     /// <summary>
   6:     /// A disposable wrapper that can be used to remove a lot of the WCF boiler plate code
   7:     /// </summary>
   8:     /// <typeparam name="TProxy">The type of the proxy.</typeparam>
   9:     public class TidyProxy<TProxy> : IDisposable where TProxy : ICommunicationObject, new()
  10:     {
  11:         private TProxy _client;
  12:         /// <summary>
  13:         /// Gets or sets the generated client.
  14:         /// </summary>
  15:         /// <value>The client.</value>
  16:         public TProxy Client
  17:         {
  18:             get
  19:             {
  20:                 if (_client == null) _client = new TProxy();
  21:                 return _client;
  22:             }
  23:             set
  24:             {
  25:                 _client = value;
  26:             }
  27:         }
  28:         
  29:         #region IDisposable Members
  30:         /// <summary>
  31:         /// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.
  32:         /// </summary>
  33:         public void Dispose()
  34:         {
  35:             if (_client == null) return;
  36:             try
  37:             {
  38:                 if (_client.State == CommunicationState.Opened)
  39:                 {
  40:                     _client.Close();
  41:                 }
  42:                 else
  43:                 {
  44:                     _client.Abort();
  45:                 }
  46:             }
  47:             catch (Exception ex)
  48:             {
  49:                 try
  50:                 {
  51:                     _client.Abort();
  52:                 }
  53:                 catch 
  54:                 {
  55:                     // Nasty, but this error isn't the problem - 
  56:                     // the one that caused it is!
  57:                 }
  58:                 throw;
  59:             }
  60:             GC.SuppressFinalize(this);
  61:         }
  62:         #endregion
  63:     }
  64: }
So, what does this get me?  Well, to call my magically complex service I now just need to write:
   1: using (var proxy = new TidyProxy<SomeWCFServiceClient>())       
   2: {      
   3:   proxy.Client.DoSomeMagicallyComplexOperation();     
   4: }
Awesome. 

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