src/log4net/Util/OnlyOnceErrorHandler.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;

using log4net.Core;

namespace log4net.Util;

/// <summary>
/// Implements log4net's default error handling policy which consists 
/// of emitting a message for the first error in an appender and 
/// ignoring all subsequent errors.
/// </summary>
/// <remarks>
/// <para>
/// The error message is processed using the LogLog sub-system by default.
/// </para>
/// <para>
/// This policy aims at protecting an otherwise working application
/// from being flooded with error messages when logging fails.
/// </para>
/// </remarks>
/// <author>Nicko Cadell</author>
/// <author>Gert Driesen</author>
/// <author>Ron Grabowski</author>
public class OnlyOnceErrorHandler : IErrorHandler
{
  /// <summary>
  /// Default Constructor
  /// </summary>
  /// <remarks>
  /// <para>
  /// Initializes a new instance of the <see cref="OnlyOnceErrorHandler" /> class.
  /// </para>
  /// </remarks>
  public OnlyOnceErrorHandler() => _prefix = string.Empty;

  /// <summary>
  /// Constructor
  /// </summary>
  /// <param name="prefix">The prefix to use for each message.</param>
  /// <remarks>
  /// <para>
  /// Initializes a new instance of the <see cref="OnlyOnceErrorHandler" /> class
  /// with the specified prefix.
  /// </para>
  /// </remarks>
  public OnlyOnceErrorHandler(string prefix) => this._prefix = prefix;

  /// <summary>
  /// Reset the error handler back to its initial disabled state.
  /// </summary>
  public void Reset()
  {
    EnabledDateUtc = DateTime.MinValue;
    ErrorCode = ErrorCode.GenericFailure;
    Exception = null;
    ErrorMessage = null;
    IsEnabled = true;
  }

  /// <summary>
  /// Log an Error
  /// </summary>
  /// <param name="message">The error message.</param>
  /// <param name="e">The exception.</param>
  /// <param name="errorCode">The internal error code.</param>
  /// <remarks>
  /// <para>
  /// Invokes <see cref="FirstError"/> if and only if this is the first error or the first error after <see cref="Reset"/> has been called.
  /// </para>
  /// </remarks>
  public void Error(string message, Exception? e, ErrorCode errorCode)
  {
    if (IsEnabled)
    {
      FirstError(message, e, errorCode);
    }
  }

  /// <summary>
  /// Log the very first error
  /// </summary>
  /// <param name="message">The error message.</param>
  /// <param name="e">The exception.</param>
  /// <param name="errorCode">The internal error code.</param>
  /// <remarks>
  /// <para>
  /// Sends the error information to <see cref="LogLog"/>'s Error method.
  /// </para>
  /// </remarks>
  public virtual void FirstError(string message, Exception? e, ErrorCode errorCode)
  {
    EnabledDateUtc = DateTime.UtcNow;
    ErrorCode = errorCode;
    Exception = e;
    ErrorMessage = message;
    IsEnabled = false;

    if (LogLog.InternalDebugging && !LogLog.QuietMode)
    {
      LogLog.Error(_declaringType, "[" + _prefix + "] ErrorCode: " + errorCode.ToString() + ". " + message, e);
    }
  }

  /// <summary>
  /// Log an Error
  /// </summary>
  /// <param name="message">The error message.</param>
  /// <param name="e">The exception.</param>
  /// <remarks>
  /// <para>
  /// Invokes <see cref="FirstError"/> if and only if this is the first error or the first error after <see cref="Reset"/> has been called.
  /// </para>
  /// </remarks>
  public void Error(string message, Exception e) => Error(message, e, ErrorCode.GenericFailure);

  /// <summary>
  /// Log an error
  /// </summary>
  /// <param name="message">The error message.</param>
  /// <remarks>
  /// <para>
  /// Invokes <see cref="FirstError"/> if and only if this is the first error or the first error after <see cref="Reset"/> has been called.
  /// </para>
  /// </remarks>
  public void Error(string message) => Error(message, null, ErrorCode.GenericFailure);

  /// <summary>
  /// Is error logging enabled
  /// </summary>
  /// <remarks>
  /// <para>
  /// Logging is only enabled for the first error delivered to the <see cref="OnlyOnceErrorHandler"/>.
  /// </para>
  /// </remarks>
  public bool IsEnabled { get; private set; } = true;

  /// <summary>
  /// The date the first error that triggered this error handler occurred, or <see cref="DateTime.MinValue"/> if it has not been triggered.
  /// </summary>
  public DateTime EnabledDate
  {
    get
    {
      if (EnabledDateUtc == DateTime.MinValue)
      {
        return DateTime.MinValue;
      }

      return EnabledDateUtc.ToLocalTime();
    }
  }

  /// <summary>
  /// The UTC date the first error that triggered this error handler occured, or <see cref="DateTime.MinValue"/> if it has not been triggered.
  /// </summary>
  public DateTime EnabledDateUtc { get; private set; }

  /// <summary>
  /// The message from the first error that triggered this error handler.
  /// </summary>
  public string? ErrorMessage { get; private set; }

  /// <summary>
  /// The exception from the first error that triggered this error handler.
  /// </summary>
  /// <remarks>
  /// May be <see langword="null" />.
  /// </remarks>
  public Exception? Exception { get; private set; }

  /// <summary>
  /// The error code from the first error that triggered this error handler.
  /// </summary>
  /// <remarks>
  /// Defaults to <see cref="log4net.Core.ErrorCode.GenericFailure"/>
  /// </remarks>
  public ErrorCode ErrorCode { get; private set; } = ErrorCode.GenericFailure;

  /// <summary>
  /// String to prefix each message with
  /// </summary>
  private readonly string _prefix;

  /// <summary>
  /// The fully qualified type of the OnlyOnceErrorHandler class.
  /// </summary>
  /// <remarks>
  /// Used by the internal logger to record the Type of the
  /// log message.
  /// </remarks>
  private static readonly Type _declaringType = typeof(OnlyOnceErrorHandler);
}