Powershell offline WU check

offlinewucheck.ps1

<#
This script performs the 'search' phase of a Windows Update, using the standard WUA API.
It does not download or install updates.
Sole purpose of this script is to find out how long it takes to download the required cabfile,
then process it against a live system and return the list of updates available for that system.
#>
function DownloadFile {
    param (
        [Parameter(Mandatory=$true,Position=0)] $url,
        [Parameter(Mandatory=$true,Position=1)] $file
    )

    $webclient = New-Object System.Net.WebClient
    $webclient.DownloadFile($url, $file)
} 


function OfflineWUCheck {

    param ([Parameter(Mandatory=$true,Position=0)] $file)
    
    #using WU API, as documented at https://goo.gl/E1FKVR

    #get an updateservicemanager interface, https://goo.gl/bltX5q
    #then register our downloaded wsusscn2.cab as an update service, https://goo.gl/g00yVA
    $UpdateServiceManager = New-Object -ComObject 'Microsoft.Update.ServiceManager'
    $UpdateService = $UpdateServiceManager.AddScanPackageService("wsusscn2 file", $file)

    #Setup a searcher, have it use the newly registered updateservice
    $Searcher = New-Object -ComObject Microsoft.Update.Searcher
    $Searcher.ServerSelection = 3
    $Searcher.ServiceID = $UpdateService.ServiceID

    Write-Host "Will search $($UpdateService.Name), $($UpdateService.ServiceID)"
    Write-Host "Beginning search using $($Searcher.ServiceID) $($Searcher.Name)"

    #$SearchResult = $UpdateSearcher.Search("IsInstalled=0 and Type='Software' and IsHidden=0")
    $SearchResult = $Searcher.Search("IsInstalled=0 and IsHidden=0")
    $Updates = $SearchResult.Updates

    Write-Host "$($Updates.Count) outstanding updates"
    if ($Updates.Count -ne 0){
        foreach ($Update in $Updates) {
            $dlsize = $($Update.MaxDownloadSize)/1MB
            $dlsize = "{0:N1}" -f $dlsize
            Write-host "$($Update.KBArticleIDs), $($Update.MSRCSeverity),  $dlsize MB"
        }
    }
}

#--- script start
$url = "http://go.microsoft.com/fwlink/p/?LinkID=74689"
$file = "c:\users\user\downloads\Wsusscn2.cab"

$wuengine = (get-item $env:windir\system32\wuaueng.dll)
$wua = $wuengine.VersionInfo.ProductVersion
Write-Host "WU engine version: $wua"

$dltime = Measure-Command {DownloadFile -url $url -file $file}
$sig = Get-AuthenticodeSignature -FilePath $file

if ($sig.Status -eq "Valid") { 
    Write-Host "Downloaded $file with valid signature in $($dltime.seconds) seconds"
    Write-Host "Beginning offline WU check "
    $checktime = Measure-command {OfflineWUCheck -file $file}
    Write-Host "Offline WU check completed in $($checktime.Minutes) minutes."
}

On a Win7 system freshly installed from SP1 media, the download part takes around 16 seconds; the offline WU check takes around 28 minutes!

Maybe someday (ha ha) I'll try to understand the internals of Wsusscn2.cab ... 2 links:

• 926464
• 927745