src/log4net/Layout/XmlLayoutBase.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
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//
#endregion

using System.IO;
using System.Xml;

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

namespace log4net.Layout;

/// <summary>
/// Layout that formats the log events as XML elements.
/// </summary>
/// <remarks>
/// <para>
/// This is an abstract class that must be subclassed by an implementation 
/// to conform to a specific schema.
/// </para>
/// <para>
/// Deriving classes must implement the <see cref="FormatXml"/> method.
/// </para>
/// </remarks>
/// <author>Nicko Cadell</author>
/// <author>Gert Driesen</author>
public abstract class XmlLayoutBase : LayoutSkeleton
{
  /// <summary>
  /// Protected constructor to support subclasses
  /// </summary>
  /// <remarks>
  /// <para>
  /// Initializes a new instance of the <see cref="XmlLayoutBase" /> class
  /// with no location info.
  /// </para>
  /// </remarks>
  protected XmlLayoutBase() : this(false) => IgnoresException = false;

  /// <summary>
  /// Protected constructor to support subclasses
  /// </summary>
  /// <remarks>
  /// <para>
  /// The <paramref name="locationInfo" /> parameter determines whether 
  /// location information will be output by the layout. If 
  /// <paramref name="locationInfo" /> is set to <see langword="true"/>, then the 
  /// file name and line number of the statement at the origin of the log 
  /// statement will be output. 
  /// </para>
  /// <para>
  /// If you are embedding this layout within an SMTPAppender
  /// then make sure to set the <b>LocationInfo</b> option of that 
  /// appender as well.
  /// </para>
  /// </remarks>
  protected XmlLayoutBase(bool locationInfo)
  {
    IgnoresException = false;
    LocationInfo = locationInfo;
  }

  /// <summary>
  /// Gets a value indicating whether to include location information in 
  /// the XML events.
  /// </summary>
  /// <value>
  /// <see langword="true"/> if location information should be included in the XML 
  /// events; otherwise, <see langword="false"/>.
  /// </value>
  /// <remarks>
  /// <para>
  /// If <see cref="LocationInfo" /> is set to <see langword="true"/>, then the file 
  /// name and line number of the statement at the origin of the log 
  /// statement will be output. 
  /// </para>
  /// <para>
  /// If you are embedding this layout within an <c>SMTPAppender</c>
  /// then make sure to set the <b>LocationInfo</b> option of that 
  /// appender as well.
  /// </para>
  /// </remarks>
  public bool LocationInfo { get; set; }

  /// <summary>
  /// The string to replace characters that can not be expressed in XML with.
  /// <remarks>
  /// <para>
  /// Not all characters may be expressed in XML. This property contains the
  /// string to replace those that can not with. This defaults to a ?. Set it
  /// to the empty string to simply remove offending characters. For more
  /// details on the allowed character ranges see http://www.w3.org/TR/REC-xml/#charsets
  /// Character replacement will occur in  the log message, the property names 
  /// and the property values.
  /// </para>
  /// </remarks>
  /// </summary>
  public string InvalidCharReplacement { get; set; } = "?";

  /// <summary>
  /// Initialize layout options
  /// </summary>
  /// <remarks>
  /// <para>
  /// This is part of the <see cref="IOptionHandler"/> delayed object
  /// activation scheme. The <see cref="ActivateOptions"/> method must 
  /// be called on this object after the configuration properties have
  /// been set. Until <see cref="ActivateOptions"/> is called this
  /// object is in an undefined state and must not be used. 
  /// </para>
  /// <para>
  /// If any of the configuration properties are modified then 
  /// <see cref="ActivateOptions"/> must be called again.
  /// </para>
  /// </remarks>
  public override void ActivateOptions()
  {
    // nothing to do
  }

  /// <summary>
  /// Gets the content type output by this layout. 
  /// </summary>
  /// <value>
  /// As this is the XML layout, the value is always <c>"text/xml"</c>.
  /// </value>
  /// <remarks>
  /// <para>
  /// As this is the XML layout, the value is always <c>"text/xml"</c>.
  /// </para>
  /// </remarks>
  public override string ContentType => "text/xml";

  /// <summary>
  /// Produces a formatted string.
  /// </summary>
  /// <param name="loggingEvent">The event being logged.</param>
  /// <param name="writer">The TextWriter to write the formatted event to</param>
  /// <remarks>
  /// <para>
  /// Format the <see cref="LoggingEvent"/> and write it to the <see cref="TextWriter"/>.
  /// </para>
  /// <para>
  /// This method creates an <see cref="XmlTextWriter"/> that writes to the
  /// <paramref name="writer"/>. The <see cref="XmlTextWriter"/> is passed 
  /// to the <see cref="FormatXml"/> method. Subclasses should override the
  /// <see cref="FormatXml"/> method rather than this method.
  /// </para>
  /// </remarks>
  public override void Format(TextWriter writer, LoggingEvent loggingEvent)
  {
    loggingEvent.EnsureNotNull();

    using XmlWriter xmlWriter = XmlWriterExtensions.CreateXmlWriter(writer);
    // Write the event to the writer
    FormatXml(xmlWriter, loggingEvent);

    xmlWriter.WriteWhitespace(SystemInfo.NewLine);

    // Close on xmlWriter will ensure xml is flushed
    // the protected writer will ignore the actual close
    // -> Dispose from using var will close & flush
  }

  /// <summary>
  /// Does the actual writing of the XML.
  /// </summary>
  /// <param name="writer">The writer to use to output the event to.</param>
  /// <param name="loggingEvent">The event to write.</param>
  /// <remarks>
  /// <para>
  /// Subclasses should override this method to format the <see cref="LoggingEvent"/> as XML.
  /// </para>
  /// </remarks>
  protected abstract void FormatXml(XmlWriter writer, LoggingEvent loggingEvent);
}