Disable logging on FileConfigurationSourceChanged - LogEnabledFilter

I want Administrators to enable/disable logging at runtime by changing the enabled property of the LogEnabledFilter in the config.

There are several threads on SO that explain workarounds, but I want it this way. I tried to change the Logging Enabled Filter like this:

private static void FileConfigurationSourceChanged(object sender, ConfigurationSourceChangedEventArgs e)
{
    var fcs = sender as FileConfigurationSource;

    System.Diagnostics.Debug.WriteLine("----------- FileConfigurationSourceChanged called --------");

    LoggingSettings currentLogSettings = e.ConfigurationSource.GetSection("loggingConfiguration") as LoggingSettings;
    var fdtl = currentLogSettings.TraceListeners.Where(tld => tld is FormattedDatabaseTraceListenerData).FirstOrDefault();
    var currentLogFileFilter = currentLogSettings.LogFilters.Where(lfd => { return lfd.Name == "Logging Enabled Filter"; }).FirstOrDefault();
    var filterNewValue = (bool)currentLogFileFilter.ElementInformation.Properties["enabled"].Value;

    var runtimeFilter = Logger.Writer.GetFilter<LogEnabledFilter>("Logging Enabled Filter");
    runtimeFilter.Enabled = filterNewValue;

   var test =  Logger.Writer.IsLoggingEnabled();

}

But test reveals always the initially loaded config value, it does not change. I thought, that when changing the value in the config the changes will be propagated automatically to the runtime configuration. But this isn't the case! Setting it programmatically as shown in the code above, doesn't work either.

It's time to rebuild Enterprise Library or shut it down.

Solution

You are right that the code you posted does not work. That code is using a config file (FileConfigurationSource) as the method to configure Enterprise Library.

Let's dig a bit deeper and see if programmatic configuration will work.

We will use the Fluent API since it is the preferred method for programmatic configuration:

var builder = new ConfigurationSourceBuilder();

builder.ConfigureLogging()
    .WithOptions
    .DoNotRevertImpersonation()
    .FilterEnableOrDisable("EnableOrDisable").Enable()
    .LogToCategoryNamed("General")
    .WithOptions.SetAsDefaultCategory()
    .SendTo.FlatFile("FlatFile")
    .ToFile(@"fluent.log");

var configSource = new DictionaryConfigurationSource();
builder.UpdateConfigurationWithReplace(configSource);

var defaultWriter = new LogWriterFactory(configSource).Create();
defaultWriter.Write("Test1", "General");

var filter = defaultWriter.GetFilter<LogEnabledFilter>();
filter.Enabled = false;

defaultWriter.Write("Test2", "General");

If you try this code the filter will not be updated -- so another failure.

Let's try to use the "old school" programmatic configuration by using the classes directly:

var flatFileTraceListener = new FlatFileTraceListener(
    @"program.log", 
    "----------------------------------------", 
    "----------------------------------------"
    );

LogEnabledFilter enabledFilter = new LogEnabledFilter("Logging Enabled Filter", true);
// Build Configuration
var config = new LoggingConfiguration();

config.AddLogSource("General", SourceLevels.All, true)
    .AddTraceListener(flatFileTraceListener);

config.Filters.Add(enabledFilter);

LogWriter defaultWriter = new LogWriter(config);

defaultWriter.Write("Test1", "General");

var filter = defaultWriter.GetFilter<LogEnabledFilter>();
filter.Enabled = false;

defaultWriter.Write("Test2", "General");

Success! The second ("Test2") message was not logged.

So, what is going on here? If we instantiate the filter ourselves and add it to the configuration it works but when relying on the Enterprise Library configuration the filter value is not updated.

This leads to a hypothesis: when using Enterprise Library configuration new filter instances are being returned each time which is why changing the value has no effect on the internal instance being used by Enterprise Library.

If we dig into the Enterprise Library code we (eventually) hit on LoggingSettings class and the BuildLogWriter method. This is used to create the LogWriter. Here's where the filters are created:

var filters = this.LogFilters.Select(tfd => tfd.BuildFilter());

So this line is using the configured LogFilterData and calling the BuildFilter method to instantiate the applicable filter. In this case the BuildFilter method of the configuration class LogEnabledFilterData BuildFilter method returns an instance of the LogEnabledFilter:

return new LogEnabledFilter(this.Name, this.Enabled);

The issue with this code is that this.LogFilters.Select returns a lazy evaluated enumeration that creates LogFilters and this enumeration is passed into the LogWriter to be used for all filter manipulation. Every time the filters are referenced the enumeration is evaluated and a new Filter instance is created! This confirms the original hypothesis.

To make it explicit: every time LogWriter.Write() is called a new LogEnabledFilter is created based on the original configuration. When the filters are queried by calling GetFilter() a new LogEnabledFilter is created based on the original configuration. Any changes to the object returned by GetFilter() have no affect on the internal configuration since it's a new object instance and, anyway, internally Enterprise Library will create another new instance on the next Write() call anyway.

Firstly, this is just plain wrong but it is also inefficient to create new objects on every call to Write() which could be invoked many times..

An easy fix for this issue is to evaluate the LogFilters enumeration by calling ToList():

var filters = this.LogFilters.Select(tfd => tfd.BuildFilter()).ToList();

This evaluates the enumeration only once ensuring that only one filter instance is created. Then the GetFilter() and update filter value approach posted in the question will work.