wcf How to: Disable/Enable WCF tracing in C# application code One way: use a custom listener defined in your C# code

Example

It took me a while to get this right, so I decided to share a solution because it might save someone else several days of trial and error.

The problem: I want to be able to enable/disable WCF tracing in my C# .NET application and choose the trace output filename. I don't want users editing the .config file, there's too much room for error there.

Here is one solution.

The application's .config file:

<?xml version="1.0"?>
<configuration>
  <system.diagnostics>
    <trace autoflush="true"/>
    <sources>
      <source name="System.ServiceModel" switchValue="All">
        <listeners>
          <add name="MyListener"/>
        </listeners>
      </source>
      <source name="System.ServiceModel.MessageLogging" switchValue="All">
        <listeners>
          <add name="MyListener"/>
        </listeners>
      </source>
      <source name="System.ServiceModel.Activation" switchValue="All">
        <listeners>
          <add name="MyListener"/>
        </listeners>
      </source>
      <source name="System.IdentityModel" switchValue="All">
        <listeners>
          <add name="MyListener"/>
        </listeners>
      </source>
    </sources>
    <sharedListeners>
      <add name="MyListener" type="MyNamespace.MyXmlListener, MyAssembly"/>
    </sharedListeners>
  </system.diagnostics>
  <system.serviceModel>
    <diagnostics wmiProviderEnabled="true">
      <messageLogging
        logEntireMessage="true"
        logMalformedMessages="true"
        logMessagesAtServiceLevel="true"
        logMessagesAtTransportLevel="true"
        maxMessagesToLog="1000"
        maxSizeOfMessageToLog="8192"/>
    </diagnostics>
  </system.serviceModel>
  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0"/>
  </startup>
</configuration>

And the C# code:

using System;
using System.IO;
using System.Diagnostics;
namespace MyNamespace
{
    public class MyXmlListener : XmlWriterTraceListener
    {
        public static String TraceOutputFilename = String.Empty;

        public static Stream MakeOutputStream()
        {
            if (String.IsNullOrWhiteSpace(TraceOutputFilename))
                return Stream.Null;

            return new FileStream(TraceOutputFilename, FileMode.Create);
        }

        public MyXmlListener ()
            : base(MakeOutputStream())
        { }
    }
}

To enable WCF tracing to a file, set TraceOutputFilename before the WCF object is created:

MyXmlListener.TraceOutputFilename = "trace.svclog";

I've gotten great benefits from this forum, I hope this post pays some of it forward.

Getting the "type" right in the .config file was much more challenging than it should have been, see Specifying Fully Qualified Type Names for setting the "type" correctly in a .config file.