Custom Parsers

When learning to create custom parsers for LogViewPlus it is helpful to begin with the sample code projects.  This tutorial will assume that you have downloaded and run the sample projects successfully. Please see running the samples for more information.

Custom parsers are helpful when your log files are stored as text data, but the text data cannot be parsed easily by one of the installed LogViewPlus parsers. For example, if your log files used a proprietary text-based data format.

Our custom parser implementation will be responsible for parsing a very simple log file which should be written in the format %d{yyyy-MM-dd HH:mm:ss,fff} - %m%n.  Note that LogViewPlus is already capable of parsing log files in this format. Therefore our custom parser will provide no functional benefit. However, it would likely have a performance benefit - although this is not been tested.

If we look at the code included in the CustomParser project and remove of the comments, we can see the custom parser implementation is straightforward.

public class MyParser : ILogParser
{
     public string Arguments { get; private set; }

     public bool AcceptsConfiguration()
     {
          return true;
     }

     public void Initialize(string arguments)
     {
          Arguments = arguments;
     }

     public List<string> GetWarnings()
     {
          return new List<string>();
     }

     public bool IsLogEntry(string logLine)
     {
          if (string.IsNullOrEmpty(logLine))
               return false;

          return logLine.IndexOf(" - ", StringComparison.Ordinal) >= 0;
     }

     public ParseResult Parse(string logLine, LogEntry newEntry)
     {
          int pos = logLine.IndexOf(" - ", StringComparison.Ordinal);
          if(pos <= 0)
               return ParseResult.Fail;

          var date = logLine.Substring(0, pos);
          var msg = logLine.Substring(pos + 3);

          newEntry.Date = DateTime.ParseExact(date, "yyyy-MM-dd HH:mm:ss,fff", CultureInfo.CurrentCulture);
          newEntry.Message = msg;
          return ParseResult.Success;
     }
}

Note that MyParser is a sample implementation of the ILogParser interface:

public interface ILogParser
{
     string Arguments { get; }
     bool AcceptsConfiguration();
     void Initialize(string arguments);
     List<string> GetWarnings();
     bool IsLogEntry(string logLine);
     ParseResult Parse(string logLine, LogEntry newEntry);
}

public enum ParseResult
{
     Success,
     Fail,
     ContinueRead,
     EndRead
}

This interface has four parts:

GetDescription - This method will return a description for our parser. This description will be displayed to the user in the tooltip that is displayed when the user hovers over a log file.

Initialize - A custom parser is initialized with a string that is provided by the user when creating the parser. Providing a initialization string to a custom filter is optional as some parsers may not need initialization.  Initialization arguments can use Argument Templates. 

If your parser implements ICustomConfiguration, the Parser Arguments will be shown with a configuration command which calls back into your code to display a configuration dialog.  Please see Custom Configuration for more information.

IsLogEntry - Given a line of text, this method is responsible for determining whether or not the line is the beginning of a new log entry.  Our (overly simplistic) example simply checks whether the line has the text " - " in it.  While this is fine for our example it probably wouldn't work in a production system because a long line may have the text " - " unexpectedly as part of its log message.  It would be better to check both the date and the static text.

Parse - This method is responsible for parsing the given log line and saving the result into the provided log entry. Note the log entry may span multiple lines.  You can control the way the log entry is parsed by managing your parse result.  A parse result could have one of four values:

As you can see, creating a custom parser for LogViewPlus is relatively simple. If you have any questions or comments please feel free to contact us.