Entlib6 SLAB - Custom IEventTextFormatter Implementation

We have seen how we can use IEventTextFormatter to further format the data from the source sinks using Semantic Application Block. SLAB provides three implementations of the interface and we discussed all three of them. You might be wondering what if we want to format this differently to be consumed by a certain stakeholder. So the main question is if we can introduce and utilize custom implementation of IEventTextFormatter. This post is a continuation of previous post discussing the custom event text formatter.

Let's create a simple class library project and install EnterpriseLibrary.SemanticLogging nuget package to the project. Let's name the project as EventSourceCustomizations. We add the following implementation of IEventTextFormatter to the project.


This is a very simple implementation of the interface. Here the formatter is just formatting the event entry data in CSV format and writes using the TextWriter passed as method argument. This is enough to define a custom event text formatter.

In-Proc Usage of Custom IEventTextFormatter implementation
In order to use the IEventTextFormatter in-process where the ETW events are originating, we need to add the assembly reference of the library to the source project. As discussed before, we can use ObservableEventListener to in-process consume the events. SLAB provides extension methods to the type to log to console which specifies the IEventTextFormatter as one of the parameter. Here we can use our custom implementation of IEventTextFormatter.


Running the above code with our sample ApplicationEventSource shows the data being pushed to the console as follows:



Semantic Logging Service - Custom IEventTextFormatter
We can appreciate the custom IEventTextFormatter more if we are able to use it out-proc. In this case, we need to make no change in the source application. It is possible that during the life time of the application, we realize that we need to format the event data in a different format. We don't need to make a single line of code change to the source application in this case. Semantic Logging Service configuration completely supports this change. We can add the new custom IEventTextFormatter to the SemanticLoggingSvc configuration as follows:


When the application logs the ETW events using the same source, Semantic Logging Service uses the new custom event text formatter and writes the data to the console as follows:



Just make sure that you have copied the assembly containing the custom IEventTextFormatter to the service folder:



Please note that this can be further improved by incorporating the intellisense support. That requires the schema definition for the custom IEventTextFormatter. We also need to provide an implemenation of IFormatterElement for the element. But we should be able to use the type directly instead of through CustomEventTextFormatter. Please refer development guide for Enterprise Library 6 for such an example.

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