src/log4net/Appender/AspNetTraceAppender.cs

#if NET462_OR_GREATER
#region Apache License
//
// Licensed to the Apache Software Foundation (ASF) under one or more 
// contributor license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright ownership. 
// The ASF licenses this file to you under the Apache License, Version 2.0
// (the "License"); you may not use this file except in compliance with 
// the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#endregion

using System.Web;

using log4net.Layout;
using log4net.Core;
using log4net.Util;

namespace log4net.Appender;

/// <summary>
/// <para>
/// Appends log events to the ASP.NET <see cref="TraceContext"/> system.
/// </para>
/// </summary>
/// <remarks>
/// <para>
/// Diagnostic information and tracing messages that you specify are appended to the output 
/// of the page that is sent to the requesting browser. Optionally, you can view this information
/// from a separate trace viewer (Trace.axd) that displays trace information for every page in a 
/// given application.
/// </para>
/// <para>
/// Trace statements are processed and displayed only when tracing is enabled. You can control 
/// whether tracing is displayed to a page, to the trace viewer, or both.
/// </para>
/// <para>
/// The logging event is passed to the <see cref="TraceContext.Write(string)"/> or 
/// <see cref="TraceContext.Warn(string)"/> method depending on the level of the logging event.
/// The event's logger name is the default value for the category parameter of the Write/Warn method. 
/// </para>
/// </remarks>
/// <author>Nicko Cadell</author>
/// <author>Gert Driesen</author>
/// <author>Ron Grabowski</author>
public class AspNetTraceAppender : AppenderSkeleton 
{
  /// <summary>
  /// Write the logging event to the ASP.NET trace <c>HttpContext.Current.Trace</c>.
  /// </summary>
  /// <param name="loggingEvent">the event to log</param>
  protected override void Append(LoggingEvent loggingEvent) 
  {
    // check if log4net is running in the context of an ASP.NET application
    if (HttpContext.Current is not null) 
    {
      // check if tracing is enabled for the current context
      if (HttpContext.Current.Trace.IsEnabled) 
      {
        if (loggingEvent.EnsureNotNull().Level is not null && loggingEvent.Level >= Level.Warn) 
        {
          HttpContext.Current.Trace.Warn(Category.Format(loggingEvent), RenderLoggingEvent(loggingEvent));
        }
        else 
        {
          HttpContext.Current.Trace.Write(Category.Format(loggingEvent), RenderLoggingEvent(loggingEvent));
        }
      }
    }
  }

  /// <summary>
  /// This appender requires a <see cref="Layout"/> to be set.
  /// </summary>
  protected override bool RequiresLayout => true;

  /// <summary>
  /// The category parameter sent to the Trace method.
  /// </summary>
  /// <remarks>
  /// <para>
  /// Defaults to %logger which will use the logger name of the current 
  /// <see cref="LoggingEvent"/> as the category parameter.
  /// </para>
  /// </remarks>
  public PatternLayout Category { get; set; } = new("%logger");
}
#endif