Fix problem with PnP.PowerShell log file locked for writing by Set-PnPTraceLog

If you use PnP.PowerShell then most probably you are familiar with Set-PnPTraceLog cmdlet which allows to enable logging from PnP cmdlets. This is useful feature which simplifies troubleshooting especially if error got reproduced only on customer's environment. However there is one unpleasant side effect: Set-PnPTraceLog locks log file for writing. I.e. it is not possible to reuse the same file for other purposes and write there from anoter sources. Let's see why it happens.

Internally Set-PnPTraceLog uses TextWriterTraceListener (thanks Gautam Sheth for sharing it):

If we will decompile code of TextWriterTraceListener (which is quite easy in VS2022) we will find that it opens FileStream with FileShare.Read option:

And that's exactly the reason why it is not possible to write anything else to this log file until PowerShell session where Set-PnPTraceLog was called will be closed.

In order to solve this problem we need to use our own FileStream and inject it to PnP logging system. It can be done by the following PowerShell code:

# enable logging
Set-PnPTraceLog -On -LogFile $logFilePath -Level Debug
# close default file stream
[System.Diagnostics.Trace]::Listeners[1].Writer.Close()
# open new file stream with FileShare.ReadWrite
$fileStream = New-Object System.IO.FileStream($logFilePath, [System.IO.FileMode]::Append, [System.IO.FileAccess]::Write, [System.IO.FileShare]::ReadWrite, 4096)
# inject new file stream to PnP
[System.Diagnostics.Trace]::Listeners[1].Writer = New-Object System.IO.StreamWriter($fileStream, [System.Text.Encoding]::UTF8, 4096, $false)

Here we first enable PnP logging Set-PnPTraceLog. Every process by default already has trace listener called DefaultTraceListener which is accessible from Trace.Listeners[0]. In order to access listener added by Set-PnPTraceLog we need access Trace.Listeners[1]. So after that we open new FileStream with FileShare.ReadWrite and then use it for StreamWriter which we inject to PnP. As result PnP will use our own FileStream and it will be possible to write to the same log from another sources.