WCF Tracing FAQs

Table of Contents

• Introduction and Goal
• WCF Basic Questions and Answers
• Can You Explain the Concept of Trace Listener?
• What are the Readymade Trace Events and They Are Available for Which WCF Objects?
• How Can We Enable Tracing on the Readymade Tracing WCF Objects?
• What is the Concept of tracelevel in Trace Listeners?
• What is a Service Level Message and Transport Level Message? 

Introduction and Goal

In this article, we will look at how we can trace and debug information in WCF services. There are some ready made tracelisteners provided by WCF. The base of these ready made trace listeners is .NET trace listener. So we will first understand the basic concept of trace listener and then go through the ready made tracelisteners provided by WCF.

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WCF Basic Questions and Answers

If you are new to WCF, I will recommend that you give one read to my WCF FAQs before reading this article. It will help you to understand WCF fundamentals so that you can understand this article much better.

Can You Explain the Concept of Trace Listener?

Tracelisteners are objects that get tracing information from the trace class and they output the data to some medium. For instance, you can see from the figure TraceListener how it listens to the trace object and outputs the same to UI, File or a Windows event log. There are three different types of tracelisteners, the first is the defaulttracelistener (this outputs the data to UI), the second is textwritertracelistener (this outputs to a file) and the final one is ‘Eventlogtracelistener’ which outputs the same to a Windows event log.

Below is a code snippet for textwritertracelistener and eventlogtracelistener. Using textwritertracelistener, we have forwarded the traces to ErrorLog.txt file and in the second snippet, we have used the Eventlogtracelistener to forward the traces to Windows event log.

What are the Readymade Trace Events and They Are Available for Which WCF Objects ?

You can always use the core Tracelistener events provided by .NET, but WCF has readymade trace listeners for the core WCF objects.

How Can We Enable Tracing on the Readymade Tracing WCF Objects?

We will enable tracing on System.ServiceModel tracing object. To enable tracing, we need to enable the system.diagnostics XML node in the web.config file of the WCF service. We need to also define the type of listeners for the System.ServiceModel listener object. So we add the listeners tag with the type as System.Diagnostics.XmlWriterTraceListener. We need to also define the file and path where the file is created. For the current scenario, we have defined the file as Traces.svclog and the folder as c:\ drive.

<system.diagnostics>
<sources>
<source name="System.ServiceModel"
switchValue="Information, ActivityTracing">
<listeners>
<add name="log"
type="System.Diagnostics.XmlWriterTraceListener"
initializeData="c:\Traces.svclog" />
</listeners>
</source>
</sources>
</system.diagnostics>

Now if you run the WCF service, you can see an XML file created as shown below:

#<E2ETraceEvent xmlns="http://schemas.microsoft.com/2004/06/E2ETraceEvent">
<System xmlns="http://schemas.microsoft.com/2004/06/windows/eventlog/system">
<EventID>0</EventID>
<Type>3</Type>
<SubType Name="Transfer">0</SubType>
<Level>255</Level>
<TimeCreated SystemTime="2009-04-30T03:21:09.5625000Z" />
<Source Name="System.ServiceModel" />
<Correlation ActivityID="{00000000-0000-0000-0000-000000000000}" 
	RelatedActivityID="{d11829b7-d2db-46d5-a4ac-49a37a56376e}" />
<Execution ProcessName="WebDev.WebServer" ProcessID="2660" ThreadID="8" />
<Channel/>
<Computer>COMPAQ-JZP37MD0</Computer>
</System>
<ApplicationData></ApplicationData>
</E2ETraceEvent>

What is the Concept of tracelevel in Trace Listeners?

In the previous question, we have specified switch value as information. This value indicates what type and level of tracing information you want to record. Below is the list of the same.

Trace level value is specified in source tag in switch value. For instance the below web.config snippet indicates the trace type as Information.

<system.diagnostics>
<sources>
<source name="System.ServiceModel"
switchValue="Information, ActivityTracing">
............
............
............
............

What is a Service Level Message and Transport Level Message?

You can log WCF messages at two levels, one is service level and the other is transport level. Service level: In this, the messages are logged as they enter the user code or leave the user code.
Transport level: In this, the messages are logged as they are ready to be encoded / decoded. All transport level, infrastructure messages and also reliable messaging is logged. You specify the message levels in the diagnostics node as shown in the below code snippet.

<system.serviceModel> 
<diagnostics>
<messageLogging
logEntireMessage="true"
logMalformedMessages="false"
logMessagesAtServiceLevel="false"
logMessagesAtTransportLevel="true"
maxMessagesToLog="3000"
maxSizeOfMessageToLog="10000"/>
</diagnostics>
</system.serviceModel>

Messagelogging also has other attributes. Below is the short description about the same.

History

• 30^th April, 2009: Initial post