src/log4net/Layout/Pattern/ExceptionPatternConverter.cs

#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.Diagnostics.CodeAnalysis;
using System.IO;
using log4net.Core;

namespace log4net.Layout.Pattern;

/// <summary>
/// Write the exception text to the output
/// </summary>
/// <remarks>
/// <para>
/// If an exception object is stored in the logging event
/// it will be rendered into the pattern output with a
/// trailing newline.
/// </para>
/// <para>
/// If there is no exception then nothing will be output
/// and no trailing newline will be appended.
/// It is typical to put a newline before the exception
/// and to have the exception as the last data in the pattern.
/// </para>
/// </remarks>
/// <author>Nicko Cadell</author>
[SuppressMessage("Microsoft.Performance", "CA1812:AvoidUninstantiatedInternalClasses", Justification = "Reflection")]
internal sealed class ExceptionPatternConverter : PatternLayoutConverter
{
  /// <summary>
  /// Default constructor
  /// </summary>
  public ExceptionPatternConverter() => IgnoresException = false;

  /// <summary>
  /// Write the exception text to the output
  /// </summary>
  /// <param name="writer"><see cref="TextWriter" /> that will receive the formatted result.</param>
  /// <param name="loggingEvent">the event being logged</param>
  /// <remarks>
  /// <para>
  /// If an exception object is stored in the logging event
  /// it will be rendered into the pattern output with a
  /// trailing newline.
  /// </para>
  /// <para>
  /// If there is no exception or the exception property specified
  /// by the Option value does not exist then nothing will be output
  /// and no trailing newline will be appended.
  /// It is typical to put a newline before the exception
  /// and to have the exception as the last data in the pattern.
  /// </para>
  /// <para>
  /// Recognized values for the Option parameter are:
  /// </para>
  /// <list type="bullet">
  ///    <item>
  ///      <description>Message</description>
  ///    </item>
  ///    <item>
  ///      <description>Source</description>
  ///    </item>
  ///    <item>
  ///      <description>StackTrace</description>
  ///    </item>
  ///    <item>
  ///      <description>TargetSite</description>
  ///    </item>
  ///    <item>
  ///      <description>HelpLink</description>
  ///    </item>    
  /// </list>
  /// </remarks>
  protected override void Convert(TextWriter writer, LoggingEvent loggingEvent)
  {
    if (loggingEvent.ExceptionObject is not null && !string.IsNullOrEmpty(Option))
    {
      switch (Option!.ToLowerInvariant())
      {
        case "message":
          WriteObject(writer, loggingEvent.Repository, loggingEvent.ExceptionObject.Message);
          break;
        case "source":
          WriteObject(writer, loggingEvent.Repository, loggingEvent.ExceptionObject.Source);
          break;
        case "stacktrace":
          WriteObject(writer, loggingEvent.Repository, loggingEvent.ExceptionObject.StackTrace);
          break;
        case "targetsite":
          WriteObject(writer, loggingEvent.Repository, loggingEvent.ExceptionObject.TargetSite);
          break;
        case "helplink":
          WriteObject(writer, loggingEvent.Repository, loggingEvent.ExceptionObject.HelpLink);
          break;
        default:
          // do not output SystemInfo.NotAvailableText
          break;
      }
    }
    else
    {
      string? exceptionString = loggingEvent.GetExceptionString();
      if (!string.IsNullOrEmpty(exceptionString))
      {
        writer.WriteLine(exceptionString);
      }
      else
      {
        // do not output SystemInfo.NotAvailableText
      }
    }
  }
}