nosuchblogger

Problem: I wanted a simple way of configuring log4net so I can view the log details via a url - not having to log into the server to view a log file, or having to query a table in a database. I wanted a simple setup, and I was inspired by ELMAH - incredibly easy to configure and get up and running.

My solution: Create an in-memory appender to log to a fixed-length buffer and an http handler to view the buffer.

So, to start off, the appender. Couldn't be easier, create a class thus:

public class InMemoryAppender : IAppender

And the append implementation:

public void DoAppend(LoggingEvent loggingEvent)
{
  InMemoryBuffer.Instance.AppendEvent(loggingEvent);
}

That's the appender, now for the InMemoryBuffer - some snippets from this class:

public class InMemoryBuffer
{
  public static readonly InMemoryBuffer Instance = new InMemoryBuffer();
  private readonly LinkedList<LogEventInfo> logBuffer = new LinkedList<LogEventInfo>();

  public void AsyncAppendEvent(LoggingEvent loggingEvent)
  {
    var timestamp = loggingEvent.TimeStamp;
    var loggingLevel = loggingEvent.Level;
    var name = loggingEvent.LoggerName;
    var message = loggingEvent.RenderedMessage;
    this.logBuffer.AddLast(new LogEventInfo(timestamp, loggingLevel.DisplayName, name, message));
    while (this.logBuffer.Count > InMemoryBuffer.MaxBufferSize) this.logBuffer.RemoveFirst();
  }
}

And for the HttpHandler to enable viewing the log messages via a url:

public class Log4NetDisplayHttpHandler : IHttpHandler
{
  public void ProcessRequest(HttpContext context)
  {
    var templateFile = Resources.Template;
    var rows = new StringBuilder();
    foreach (var logEventInfo in InMemoryBuffer.Instance.LogEvents)
      rows.AppendFormat(@"
        <tr>
          <td>{0}</td>
          <td>{1}</td>
          <td>{2}</td>
          <td>{3}</td>
        </tr>",
        logEventInfo.Timestamp.ToString("u"), logEventInfo.Level,
        logEventInfo.Class, logEventInfo.Message);

      var replaced = templateFile.Replace("${LOGGINGROWS}", rows.ToString());
      context.Response.Write(replaced);
  }
}

The project contains the Template resource which contains the html page into which the logging rows are inserted. I then use jquery-based flexigrid to turn the table into a fancy grid!

Finally, the web.config configuration. Add the appender to the log4net section:

<appender name="InMemory" type="InMemoryAppender, MyLog4Net" />

And to the httpHandler section:

<add verb="POST,GET,HEAD" path="inmemorylogging.axd" type="Log4NetDisplayHttpHandler, MyLog4Net" />