CountingSingleProcessFileAppender.cs

// 
// Copyright (c) 2004-2019 Jaroslaw Kowalski <jaak@jkowalski.net>, Kim Christensen, Julian Verdurmen
// 
// All rights reserved.
// 
// Redistribution and use in source and binary forms, with or without 
// modification, are permitted provided that the following conditions 
// are met:
// 
// * Redistributions of source code must retain the above copyright notice, 
//   this list of conditions and the following disclaimer. 
// 
// * Redistributions in binary form must reproduce the above copyright notice,
//   this list of conditions and the following disclaimer in the documentation
//   and/or other materials provided with the distribution. 
// 
// * Neither the name of Jaroslaw Kowalski nor the names of its 
//   contributors may be used to endorse or promote products derived from this
//   software without specific prior written permission. 
// 
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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namespace NLog.Internal.FileAppenders
{
    using System;
    using System.IO;
    using System.Security;
    using NLog.Common;

    /// <summary>
    /// Implementation of <see cref="BaseFileAppender"/> which caches 
    /// file information.
    /// </summary>
    [SecuritySafeCritical]
    internal class CountingSingleProcessFileAppender : BaseFileAppender
    {
        public static readonly IFileAppenderFactory TheFactory = new Factory();

        private FileStream _file;
        private long _currentFileLength;
        private readonly bool _enableFileDeleteSimpleMonitor;
        private DateTime _lastSimpleMonitorCheckTimeUtc;

        /// <summary>
        /// Initializes a new instance of the <see cref="CountingSingleProcessFileAppender" /> class.
        /// </summary>
        /// <param name="fileName">Name of the file.</param>
        /// <param name="parameters">The parameters.</param>
        public CountingSingleProcessFileAppender(string fileName, ICreateFileParameters parameters)
            : base(fileName, parameters)
        {
            var fileInfo = new FileInfo(fileName);
            _currentFileLength = fileInfo.Exists ? fileInfo.Length : 0;
            _file = CreateFileStream(false);
            _enableFileDeleteSimpleMonitor = parameters.EnableFileDeleteSimpleMonitor;
            _lastSimpleMonitorCheckTimeUtc = OpenTimeUtc;
        }

        /// <summary>
        /// Closes this instance of the appender.
        /// </summary>
        public override void Close()
        {
            if (_file != null)
            {
                InternalLogger.Trace("Closing '{0}'", FileName);

                try
                {
                    _file.Close();
                }
                catch (Exception ex)
                {
                    // Swallow exception as the file-stream now is in final state (broken instead of closed)
                    InternalLogger.Warn(ex, "Failed to close file: '{0}'", FileName);
                    AsyncHelpers.WaitForDelay(TimeSpan.FromMilliseconds(1));    // Artificial delay to avoid hammering a bad file location
                }
                finally
                {
                    _file = null;
                }
            }
        }

        /// <summary>
        /// Flushes this current appender.
        /// </summary>
        public override void Flush()
        {
            if (_file == null)
            {
                return;
            }

            _file.Flush();
        }

        /// <summary>
        /// Gets the creation time for a file associated with the appender. The time returned is in Coordinated Universal 
        /// Time [UTC] standard.
        /// </summary>
        /// <returns>The file creation time.</returns>
        public override DateTime? GetFileCreationTimeUtc()
        {
            return CreationTimeUtc;
        }

        /// <summary>
        /// Gets the length in bytes of the file associated with the appender.
        /// </summary>
        /// <returns>A long value representing the length of the file in bytes.</returns>
        public override long? GetFileLength()
        {
            return _currentFileLength;
        }

        /// <summary>
        /// Writes the specified bytes to a file.
        /// </summary>
        /// <param name="bytes">The bytes array.</param>
        /// <param name="offset">The bytes array offset.</param>
        /// <param name="count">The number of bytes.</param>
        public override void Write(byte[] bytes, int offset, int count)
        {
            if (_file == null)
            {
                return;
            }

            if (_enableFileDeleteSimpleMonitor && MonitorForEnableFileDeleteEvent(FileName, ref _lastSimpleMonitorCheckTimeUtc))
            {
                _file.Dispose();
                _file = CreateFileStream(false);
                _currentFileLength = _file.Length;
            }

            _currentFileLength += count;
            _file.Write(bytes, offset, count);
        }

        /// <summary>
        /// Factory class which creates <see cref="CountingSingleProcessFileAppender"/> objects.
        /// </summary>
        private class Factory : IFileAppenderFactory
        {
            /// <summary>
            /// Opens the appender for given file name and parameters.
            /// </summary>
            /// <param name="fileName">Name of the file.</param>
            /// <param name="parameters">Creation parameters.</param>
            /// <returns>
            /// Instance of <see cref="BaseFileAppender"/> which can be used to write to the file.
            /// </returns>
            BaseFileAppender IFileAppenderFactory.Open(string fileName, ICreateFileParameters parameters)
            {
                return new CountingSingleProcessFileAppender(fileName, parameters);
            }
        }
    }
}