Powershell try block doesn't release file handle for catch block - powershell

Question

I'm writing a script that tries to download a file with two file-download methods.
I'm not going to go into great details, but the resulting function looks something like this:
function Download-FileRobust($url, $targetFile) {
try {
Download-File $url $targetFile
}
catch {
Download-FileWget $url $targetFile
}
}
When the Download-File function fails, PowerShell doesn't loosen the handle on the created file at location $targetFile, and Download-FileWget can't write to that location.
I'm used to Python, so it took me quite a while to figure out the problem.
The source-code for the other two functions are as follows:
function Download-FileWget($url, $targetFile){
$wgetDir = (Get-ChildItem -Path "$env:userprofile\Downloads\wget*win32").FullName
if($env:Path -notlike "*$wgetDir*"){
$env:Path = "$wgetDir;$env:Path"
}
Invoke-Expression "wget '$url' -O '$targetFile'"
}
function Download-File($url, $targetFile){
$uri = New-Object "System.Uri" "$url"
$request = [System.Net.HttpWebRequest]::Create($uri)
$request.set_Timeout(15000) #15 second timeout
$response = $request.GetResponse()
$totalLength = [System.Math]::Floor($response.get_ContentLength()/1024)
$responseStream = $response.GetResponseStream()
$targetStream = New-Object -TypeName System.IO.FileStream -ArgumentList $targetFile, Create
$buffer = new-object byte[] 10KB
$count = $responseStream.Read($buffer,0,$buffer.length)
$downloadedBytes = $count
while ($count -gt 0){
$targetStream.Write($buffer, 0, $count)
$count = $responseStream.Read($buffer,0,$buffer.length)
$downloadedBytes = $downloadedBytes + $count
Write-Progress -activity "Downloading file '$($url.split('/') | Select -Last 1)'" -status "Downloaded ($([System.Math]::Floor($downloadedBytes/1024))K of $($totalLength)K): " -PercentComplete ((([System.Math]::Floor($downloadedBytes/1024)) / $totalLength) * 100)
}
Write-Progress -activity "Finished downloading file '$($url.split('/') | Select -Last 1)'"
$targetStream.Flush()
$targetStream.Close()
$targetStream.Dispose()
$responseStream.Dispose()
}

Answer 1

Inside the Download-File function you never actually do anything to ensure the $targetStream is properly flushed and disposed of. You need to wrap the streams in a try/catch/finally blocks:
function Download-File {
param([string]$url, [string]$targetFile)
$uri = New-Object "System.Uri" "$url"
$request = [System.Net.HttpWebRequest]::Create($uri)
$request.set_Timeout(15000) #15 second timeout
$response = $request.GetResponse()
$totalLength = [System.Math]::Floor($response.get_ContentLength()/1024)
$responseStream = $response.GetResponseStream()
try {
$targetStream = New-Object -TypeName System.IO.FileStream -ArgumentList $targetFile, Create
try {
$buffer = new-object byte[] 10KB
$count = $responseStream.Read($buffer,0,$buffer.length)
$downloadedBytes = $count
while ($count -gt 0){
$targetStream.Write($buffer, 0, $count)
$count = $responseStream.Read($buffer,0,$buffer.length)
$downloadedBytes = $downloadedBytes + $count
Write-Progress -activity "Downloading file '$($url.split('/') | Select -Last 1)'" -status "Downloaded ($([System.Math]::Floor($downloadedBytes/1024))K of $($totalLength)K): " -PercentComplete ((([System.Math]::Floor($downloadedBytes/1024)) / $totalLength) * 100)
}
Write-Progress -activity "Finished downloading file '$($url.split('/') | Select -Last 1)'"
}
catch {
throw
}
finally {
if($targetStream){
$targetStream.Flush()
$targetStream.Close()
$targetStream.Dispose()
}
}
}
catch {
throw
}
finally {
$responseStream.Dispose()
}
}