Mike-Ward.Net

C# File Utilities

17 Mar 2007

Since Bloget™ is file based, I needed some file open routines that were robust and tolerant. Das Blog is a popular open source blogging engine that also uses files so I thought I would take a peek at what they did.

As I suspected, Das Blog has some routines that try to open files several times before raising an error. This makes sense since there is a small possibility that the file may be locked for read when you want to write to it or vice versa. I refactored the code to take advantage of delegates which cuts down on the amount of repeated code I found in the original implementation. In addition, since I’m using .NET 2.0, I could take advantage of anonymous delegates which saved and additional few lines of code.

using System ;
using System.IO;
using System.Threading;

namespace BlueOnionSoftware
{
    internal static class FileUtilities
    {
        internal static void WriteFile(string fileName, byte[] buffer)
        {
            if (fileName == null)
            {
                throw new ArgumentNullException("WriteFile(fileName)");
            }

            if (string.IsNullOrEmpty(fileName))
            {
                throw new ArgumentException("WriteFile(fileName)", "fileName string is empty");
            }

            if (buffer == null)
            {
                throw new ArgumentNullException("WriteFile(buffer)");
            }

            CreateBackupFile(fileName);

            using (var fileWriter = OpenForWrite(fileName))
            {
                fileWriter.Write(buffer, 0, buffer.Length);
            }
        }

        internal static FileStream OpenForWrite(string fileName)
        {
            if (fileName == null)
            {
                throw new ArgumentNullException("OpenForWrite(file)");
            }

            if (string.IsNullOrEmpty(fileName))
            {
                throw new ArgumentException("OpenForWrite(file)", "file string is empty");
            }

            return OpenFile(fileName, delegate(string name)
            {
                return new FileStream(name, FileMode.Create, FileAccess.Write, FileShare.None);
            });
        }

        internal static FileStream OpenForRead(string fileName)
        {
            if (fileName == null)
            {
                throw new ArgumentNullException("OpenForRead(file)");
            }

            if (string.IsNullOrEmpty(fileName))
            {
                throw new ArgumentException("OpenForRead(file)", "file string is empty");
            }

            return OpenFile(fileName, delegate(string name)
            {
                return new FileStream(name, FileMode.OpenOrCreate, FileAccess.Read, FileShare.Read);
            });
        }

        internal static FileStream OpenForAppend(string fileName)
        {
            if (fileName == null)
            {
                throw new ArgumentNullException("OpenForAppend(file)");
            }

            if (string.IsNullOrEmpty(fileName))
            {
                throw new ArgumentException("OpenForAppend(file)", "file string is empty");
            }

            return OpenFile(fileName, delegate(string name)
            {
                return new FileStream(name, FileMode.Append, FileAccess.Write, FileShare.None);
            });
        }

        private delegate FileStream OpenFileHandler(string fileName);

        private static FileStream OpenFile(string fileName, OpenFileHandler openFileHandler)
        {
            var retries = 10;
            FileStream file;

            for (;;)
            {
                try
                {
                    file = openFileHandler(fileName);
                    break;
                }

                catch (UnauthorizedAccessException)
                {
                    if (--retries <= 0)
                    {
                        throw;
                    }
                    Thread.Sleep(100);
                }
            }

            return file;
        }

        private static void CreateBackupFile(string file)

        {
            if (File.Exists(file))
            {
                var retries = 10;
                var backupFile = file + ".bak";

                for (;;)
                {
                    try
                    {
                        File.Copy(file, backupFile, true);
                        break;
                    }

                    catch (UnauthorizedAccessException)
                    {
                        if (--retries <= 0)
                        {
                            throw;
                        }
                        Thread.Sleep(100);
                    }
                }
            }
        }
    }
} Download: [fileutilities.cs (4 KB)](/cdn/images/blog/fileutilities.css)

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