Find the docker image from Docker Hub, for the current Windows Server OS

Get-ImageFromHub.ps1

function Get-ImageFromHub {
<#
.SYNOPSIS
    Find the docker image for the current Windows Server OS from Docker Hub.
    Additionally it can also inspect the image and get its size (from all of its layers)

    NOTE: This function does not download the docker image, just its metadata.
          The -ShowSize switch requires the docker tool.
.EXAMPLE
    Get-ImageFromHub -ShowSize
    
    Find the image from Docker Hub along with its layers.
.EXAMPLE
    $img = Get-ImageFromHub
    docker pull $img

    Find the image for the current OS and then pull it from docker hub
#>
[OutputType([string],[psobject])]  # <-- default is [string], and [psobject] with ShowSize switch
[cmdletbinding()]
param (    
    [ValidateSet('Release','Insider')]
    [string]$Channel = 'Release',

    [ValidateSet('Base','Core','Nano')]
    [string]$Type = 'Core',

    [switch]$ShowSize
)

$list = @(
    [pscustomobject] @{
        Type = 'Base'
        Chan = 'Release'
        Img  = 'mcr.microsoft.com/windows'
        Tag  = 'https://mcr.microsoft.com/v2/windows/tags/list'
        Url  = 'https://hub.docker.com/r/microsoft-windows'
    }
    [pscustomobject] @{
        Type = 'Base'
        Chan = 'Insider'
        Img  = 'mcr.microsoft.com/windows/insider'
        Tag  = 'https://mcr.microsoft.com/v2/windows/insider/tags/list'
        Url  = 'https://hub.docker.com/r/microsoft-windows-insider'
    }
    [pscustomobject] @{
        Type = 'Core'
        Chan = 'Release'
        Img  = 'mcr.microsoft.com/windows/servercore'
        Tag  = 'https://mcr.microsoft.com/v2/windows/servercore/tags/list'
        Url  = 'https://hub.docker.com/r/microsoft-windows-servercore'
    }
    [pscustomobject] @{
        Type = 'Core'
        Chan = 'Insider'
        Img  = 'mcr.microsoft.com/windows/servercore/insider'
        Tag  = 'https://mcr.microsoft.com/v2/windows/servercore/insider/tags/list'
        Url  = 'https://hub.docker.com/r/microsoft-windows-servercore-insider'
    }
    [pscustomobject] @{
        Type = 'Nano'
        Chan = 'Release'
        Img  = 'mcr.microsoft.com/windows/nanoserver'
        Tag  = 'https://mcr.microsoft.com/v2/windows/nanoserver/tags/list'
        Url  = 'https://hub.docker.com/r/microsoft-windows-nanoserver'
    }
    [pscustomobject] @{
        Type = 'Nano'
        Chan = 'Insider'
        Img  = 'mcr.microsoft.com/windows/nanoserver/insider'
        Tag  = 'https://mcr.microsoft.com/v2/windows/nanoserver/insider/tags/list'
        Url  = 'https://hub.docker.com/r/microsoft-nanoserver-insider'
    }
)
$obj = $list | where {$_.Type -eq $Type -and $_.Chan -eq $Channel}

$ProgressPreference = 'SilentlyContinue'  # <-- makes Invoke-RestMethod faster

# find appropriate version for your OS
try {
    Write-Verbose "Find docker image from: $($obj.Url)"
    $all = (Invoke-RestMethod $obj.Tag -Verbose:$false).tags
    $ver = [System.Environment]::OSVersion.Version.ToString(3)   # <-- ex. 10.0.20348
    $reg = 'HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion'
    $rev = (Get-ItemProperty $reg -Name 'UBR').UBR               # <-- ex. 4106
    $tag = '{0}.{1}' -f $ver,$rev
    $t2  = $all | where {$_ -like "$tag*"} | select -First 1
    $t3a = $all | where {$_ -match "^$ver\.\d+$"} | foreach {[version]$_} | Sort-Object
    $less= $t3a | where {$_.Revision -lt $rev} | select -Last 1
    $more= $t3a | where {$_.Revision -gt $rev} | select -First 1
    $Blu = '{0}[38;2;{1};{2};{3}m' -f [char]27,  61, 148, 243  # Blue
    $Ita = '{0}[3m'                -f [char]27                 # Italic
    $Def = '{0}[0m'                -f [char]27                 # Default

    if ([bool]$t2) {
        $img = '{0}:{1}' -f $obj.img,$t2
    }
    elseif ([bool]$less -or [bool]$more){
        $msg = $Blu + $Ita + "Could not find the exact tag $tag. Will fetch closest tags as fallback" + $Def
        Write-Information $msg -InformationAction Continue
        $img = @(
            '{0}:{1}' -f $obj.img,$less.ToString()
            '{0}:{1}' -f $obj.img,$more.ToString()
        )
    }    
    else {
        $msg1 = "Could not find tag $tag in URL $($obj.Tag)"
        $msg2 = "Make sure the Channel ($Channel) param aligns with your OS"
        $msg3 = "Or that your OS version ($tag) actually has a docker image of $Type type"
        $msg1,$msg2,$msg3 | foreach {Write-Warning $_}
        return
    }
}
catch {throw $_}

if ($ShowSize.IsPresent) {
    try {
        docker.exe -v *>$null
        $HasDocker = $true
    }
    catch {
        $HasDocker = $false
    }
}

# helper function that shows human-readable sizes (which returns a string not a number)
function Get-PrettyCapacity ([uint64]$Size) {
    $SzId = ('b', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB')
    $Ord  = [Math]::Floor( [Math]::Log($Size, 1000) )
    $Num  = $Size/([Math]::Pow(1000,$Ord))
    $Flo  = if ($Num -ge 100) {0} elseif ($Num -ge 10) {1} else {2}
    $Rnd  = [Math]::Round($Num,$Flo)
    [String]($Rnd) + $SzId[$Ord]
}

if (-not $ShowSize.IsPresent) {
    $out = $img
}
elseif ($ShowSize.IsPresent -and -not $HasDocker) {
    $msg = $Blu + $Ita + 'Docker tool was not found, could not fetch the image size.' + $Def
    Write-Information $msg -InformationAction Continue
    $out = $img
}
elseif ($ShowSize -and $HasDocker) {
    try {
        $out = foreach ($image in $img) {
            $man = docker manifest inspect --verbose $image 2>&1  # <-- the manifest from docker hub
            if ($man -is [System.Management.Automation.ErrorRecord]) {throw $man}
        
            $json = $man | ConvertFrom-Json -ErrorAction Stop
            $Size = ($json.SchemaV2Manifest.layers | Measure-Object size -Sum).Sum

            $i = 1 ; $Layers = [ordered]@{}
            $json.SchemaV2Manifest.layers | foreach {$Layers.Add($i++,$_.size)}

            [PSCustomObject] @{
                Image    = $image
                Size     = Get-PrettyCapacity $Size
                SizeByte = $Size -as [uint64]
                Layers   = $Layers
            }
        } #foreach image
    }
    catch {throw $_}
} #elseif showsize

# return the results
Write-Output $out
}