SharePoint 2010 supports writing custom messages to ULS log. A blog post by Waldek Mastykarz of Mavention provides a good example of how to do this. UPDATE 02/24/2011: Andrew Connell's article on MSDN from December 2010 provides essential information on diagnostics logging.
Ability to send messages from System.Diagnostics.Trace.Write() and Trace.Fail() method overloads to ULS is yet another “logging novelty” I will be focusing on in this post.
There is a new type in Microsoft.SharePoint assembly, which was not there in version 12 – Microsoft.SharePoint.SPULSTraceListener. As its name suggests it allows sending trace messages to ULS.
If you are instrumenting your custom SharePoint code and need to write diagnostic traces to ULS then you can wire up SPULSTraceListener type in your web.config and use tracing infrastructure available in System.Diagnostics.Trace. Here are the steps:
1. Add a trace listener element to web.config. For more information see description of system.diagnostics element on MSDN.
type="Microsoft.SharePoint.SPULSTraceListener, Microsoft.SharePoint, version=188.8.131.52, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
In this XML snippet note the <remove name=”Default”>. This is done to remove default trace listener, which is wired up by default and displays a pop-up window with the message when Trace.Fail() is called.
2. In central administration site configure diagnostic logging (Central Administration >> Diagnostic Logging). If you are using Trace.Write() method calls then they are logged as Verbose and so in order to actually see them in ULS logs you need to make sure that throttling level is set to Verbose for SharePoint Foundation > Service Connections category. If you use Trace.Fail() overloaded methods then the message will be written as a High level, which by default is on, so the message will normally end up being written to a log file. And yes, all messages will be written to the log under Service Connections category.
What About TraceContext.Write()?
UserControl, Page and HttpContext classes have a property named Trace of type System.Web.TraceContext. It allows tracing messages using ASP.NET trace infrastructure, for example: HttpContext.Current.Trace.Write(string message);. You can send ASP.NET trace messages to ULS using standard technique but with a caveat:
Add trace configuration element under system.web element in your web.config as follows:
<trace enabled="true" requestLimit="1000" mostRecent="true" writeToDiagnosticsTrace="true"/>
SharePoint Foundation General b9y3 High Failed to open the file 'C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\Resources\wss.resx'.
SharePoint Foundation General b9y4 High #20015: Cannot open "": no such file or folder.
SharePoint Foundation General b9y4 High (#2: Cannot open "": no such file or folder.)
SharePoint Foundation General b9y9 High Failed to read resource file "C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\Resources\wss.resx" from feature id "(null)".
UPDATE (01-16-2011): There is yet another issue caused by turning on trace that I ran into today: SharePoint designer cannot open a site in a web application for which tracing is enabled, and keeps prompting for credentials. If you check out traffic with Fiddler, you will find that SPD makes requests to http://devserver2010/_vti_bin/shtml.dll/_vti_rpc, which return a 401 UNAUTHORIZED. Not even verbose logging reveals anything useful. Well, commenting out <trace> element in web.config restores normal functionality.