Overview

In MediaPortal 2, log output can be written by using our logging service (service interface ILogger ). That service is automatically installed by the main MP2 applications and provides a simple logging interface.

Details

Supported features are:

• Log levels (Critical, Error, Warning, Information, Debug)
• Logging of exceptions
• Logging to the console
• Logging to a file
• Support of multiple opened log files from different MP2 applications at the same logfile path
• Logging to multiple loggers at the same time

What should be logged and how

Logging has multiple jobs:

• Error debugging
• Tracing a user's action to reproduce an error

There are some elementary guidelines which should be followed when a log output is written from code

Write enough information into the log message

This sounds trivial but is sometimes done wrong. When logging an exception in a catch block, please write enough , sensible and informative information into the message. Avoid writing useless messages:

Bad log message:

An exception has occured

Good log message:

Error unmarshalling data from IR service 'localhost'

The exception object should be passed to the logger if it brings more information about the error:

try
{
  ...
}
catch (XxxException e)
{
  ServiceRegistration.Get<ILogger>().Warn("Error unmarshalling data from IR service '{0}'", e, irServiceHost);
}

Write actual data into the log message

To make log message helpful, all necessary data should be provided to understand what happened. For example, a log message can be made much more useful by giving the user more information about the data which caused the exception.

Bad log message:

Illegal character encountered

Better you tell the reader WHICH character was illegal at what position:
Message with more information:

Illegal character 'X' (#88) encountered in document at position 7

Quote logged data

When actual data is logged, please quote strings. A log message

Illegal user Mr. X

is harder to read than

Illegal user 'Mr. X'

Furthermore, if a string is empty or contains leading or trailing spaces, it is very hard to find the problem in a message like

// Do you see the trailing spaces?
Illegal user  

or

// Do you see the trailing space?
Illegal user Mr. X 

Better would be

Illegal user ' '

or

Illegal user 'Mr. X '

where the reader can see that maybe a space is the problem.