FileInfo returning wrong value?

Question

Okay, so I'm working in VB.NET, manually writing error logs to log files (yes, I know, I didn't make the call). Now, if the files are over an arbitrary size, when the function goes to write out the new error data, it should start a new file with a new file name.

Here's the function:

        Dim listener As New Logging.FileLogTraceListener
        listener.CustomLocation = System.Configuration.ConfigurationManager.AppSettings("LogDir")
        Dim loc As String = DateTime.UtcNow.Year.ToString + DateTime.UtcNow.Month.ToString + DateTime.UtcNow.Day.ToString + DateTime.UtcNow.Hour.ToString + DateTime.UtcNow.Minute.ToString

        listener.BaseFileName = loc

        Dim logFolder As String
        Dim source As String

        logFolder = ConfigurationManager.AppSettings("LogDir")
        If ex.Data.Item("Source") Is Nothing Then
            source = ex.Source
        Else
            source = ex.Data.Item("Source").ToString
        End If

        Dim errorFileInfo As New FileInfo(listener.FullLogFileName)

        Dim errorLengthInBytes As Long = errorFileInfo.Length


        If (errorLengthInBytes > CType(System.Configuration.ConfigurationManager.AppSettings("maxFileSizeInBytes"), Long)) Then

            listener.BaseFileName = listener.BaseFileName + "1"

        End If


        Dim msg As New System.Text.StringBuilder
        If String.IsNullOrEmpty(logFolder) Then logFolder = ConfigurationManager.AppSettings("LogDir")

        msg.Append(vbCrLf & "Exception" & vbCrLf)
        msg.Append(vbTab & String.Concat("App: AppMonitor | Time: ", Date.Now.ToString) & vbCrLf)
        msg.Append(vbTab & String.Concat("Source: ", source, " | Message: ", ex.Message) & vbCrLf)
        msg.Append(vbTab & "Stack: " & ex.StackTrace & vbCrLf)


        listener.Write(msg.ToString())
        listener.Flush()

        listener.Close()

I have this executing in a loop for testing purposes, so I can see what happens when it gets (say) 10000 errors in all at once. Again, I know there are better ways to handle this systemically, but this was the code I was told to implement.

How can I reliably get the size of the log file before writing to it, as I try to do above?

Answer 1

Well, as with many things, the answer to this turned out to be "did you read your own code closely" with a side order of "eat something, you need to fix your blood sugar."

On review, I saw that I was always checking BaseFileName and, if it was over the arbitrary limit, appending a character and writing to that file. What I didn't do was check to see if that file or, indeed, other more recent files existed. I've solved the issue be grabbing a directory list of all the files matching the "BaseFileName*" argument in Directory.GetFiles and selecting the most recently accessed one. That ensures that the logger will always select the more current file to write to or -if necessary- use as the base-name for another appended character.

Here's that code:

        Dim directoryFiles() As String = Directory.GetFiles(listener.Location.ToString(), listener.BaseFileName + "*")

        Dim targetFile As String = directoryFiles(0)

        For j As Integer = 1 To directoryFiles.Count - 1 Step 1
            Dim targetFileInfo As New FileInfo(targetFile)
            Dim compareInfo As New FileInfo(directoryFiles(j))

            If (targetFileInfo.LastAccessTimeUtc < compareInfo.LastAccessTimeUtc) Then
                targetFile = directoryFiles(j)
            End If
        Next


        Dim errorFileInfo As New FileInfo(listener.Location.ToString() + targetFile)
        Dim errorLengthInBytes As Long = errorFileInfo.Length