Unable to gather error info from halting Powershell script - powershell

Question

I'm writing a script that will watch a directory for any new mp4 files, then convert the file using HandBrake's CLI tool. The logic that watches the directory for changes works by itself, but if I drop a large video into the "watched" directory the conversion fails since it kicks off as soon as it sees a new file, before the file has time to finish copying.
I'm using a do until loop to check if the file is locked/downloading and then continues once the file is unlocked/writable. The loop works as a stand-alone script, but when used inside the filesystem watcher the script it will halt without any errors on this line:
[System.IO.FileStream] $fs = $convertingFile.OpenWrite();
This occurs regardless if $ErrorActionPreference = "SilentlyContinue" is commented out. I've been unable to gather any log output to see why the script is halting using Start-Transcript or Out-File.
How should I best gather error info about why the script halts once it hits this line?
Bonus: Why might this script not provide error information?
$ErrorActionPreference = "SilentlyContinue"
function Start-FileSystemWatcher {
[CmdletBinding()]
param(
[Parameter()]
[string]$Path,
[Parameter()]
[ValidateSet('Changed','Created','Deleted','Renamed')]
[string[]]$EventName,
[Parameter()]
[string]$Filter,
[Parameter()]
[System.IO.NotifyFilters]$NotifyFilter,
[Parameter()]
[switch]$Recurse,
[Parameter()]
[scriptblock]$Action
)
#region Build FileSystemWatcher
$FileSystemWatcher = New-Object System.IO.FileSystemWatcher
if (-not $PSBoundParameters.ContainsKey('Path')) {
$Path = $PWD
}
$FileSystemWatcher.Path = $Path
if ($PSBoundParameters.ContainsKey('Filter')) {
$FileSystemWatcher.Filter = $Filter
}
if ($PSBoundParameters.ContainsKey('NotifyFilter')) {
$FileSystemWatcher.NotifyFilter = $NotifyFilter
}
if ($PSBoundParameters.ContainsKey('Recurse')) {
$FileSystemWatcher.IncludeSubdirectories = $True
}
if (-not $PSBoundParameters.ContainsKey('EventName')) {
$EventName = 'Changed','Created','Deleted','Renamed'
}
if (-not $PSBoundParameters.ContainsKey('Action')) {
$Action = {
switch ($Event.SourceEventArgs.ChangeType) {
'Renamed' {
$Object = "{0} was {1} to {2} at {3}" -f $Event.SourceArgs[-1].OldFullPath,
$Event.SourceEventArgs.ChangeType,
$Event.SourceArgs[-1].FullPath,
$Event.TimeGenerated
}
Default {
$Object = "{0} was {1} at {2}" -f $Event.SourceEventArgs.FullPath,
$Event.SourceEventArgs.ChangeType,
$Event.TimeGenerated
}
}
$WriteHostParams = #{
ForegroundColor = 'Green'
BackgroundColor = 'Black'
Object = $Object
}
Write-Host #WriteHostParams
}
}
$ObjectEventParams = #{
InputObject = $FileSystemWatcher
Action = $Action
}
foreach ($Item in $EventName) {
$ObjectEventParams.EventName = $Item
$ObjectEventParams.SourceIdentifier = "File.$($Item)"
Write-Verbose "Starting watcher for Event: $($Item)"
$Null = Register-ObjectEvent #ObjectEventParams
}
}
$FileSystemWatcherParams = #{
Path = 'X:\share\scripts\ps\converter\input'
Recurse = $True
NotifyFilter = 'FileName'
Verbose = $True
Action = {
$Item = Get-Item $Event.SourceEventArgs.FullPath
$WriteHostParams = #{
ForegroundColor = 'Green'
BackgroundColor = 'Black'
}
$inputFile = "${PWD}\input\$($Item.Name)".trim()
$outputFile = "${PWD}\output\$($Item.Name)".trim()
$logFile = "${PWD}\log\$($Item.Name).txt"
$testLogFile = "${PWD}\log\$($Item.Name)(t).txt"
function mp4-Func {
Start-Transcript -path $logFile
Write-Host "New mp4 file detected..."
$convertingFile = New-Object -TypeName System.IO.FileInfo -ArgumentList $inputFile
$locked = 1
do {
[System.IO.FileStream] $fs = $convertingFile.OpenWrite();
if (!$?) {
Write-Host "Can't convert yet, file appears to be loading..."
sleep 2
}
else {
$fs.Dispose()
$locked = 0
}
} until ($locked -eq 0)
Write-Host "File unlocked and ready for conversion."
HandBrake
Stop-Transcript
$WriteHostParams.Object = "Finished converting: $($Item.Name)"
}
function HandBrake {
.\HandBrakeCLI.exe --input "$inputFile" `
--output "$outputFile" `
--format av_mp4 `
--encoder x264 `
--vb 1700 `
--two-pass `
--aencoder copy:aac `
--ab 320 `
--arate 48 `
--mixdown stereo
}
switch -regex ($Item.Extension) {
'\.mp4' { mp4-Func }
}
Write-Host #WriteHostParams
}
}
#( 'Created') | ForEach-Object {
$FileSystemWatcherParams.EventName = $_
Start-FileSystemWatcher #FileSystemWatcherParams
}

Answer 1

I think you'll find that $ErrorActionPreference only impact errors at the level of cmdlets, while you hitting a problem in non-cmdlet code. For that, you'll probably need a try/catch construct.

Answer 2

Based on Burt_Harris' answer (please upvote his answer over this one), I changed the "do while" loop so that it would use try/catch rather than an if/else statement. By using $.Exception.Message and $.Exception.ItemName I was able to better understand why the script was halting at that particular line.
Working code:
Do {
Try {
[System.IO.FileStream] $fs = $convertingFile.OpenWrite()
$fs.Dispose()
$locked = 0
}
Catch {
$ErrorMessage = $_.Exception.Message
$FailedItem = $_.Exception.ItemName
Write-Host $ErrorMessage
Write-Host $FailedItem
Write-Host "Can't convert yet, file appears to be loading..."
sleep 5
continue
}
} until ($locked -eq 0)