Download Docker Image powershell

download-docker-image.ps1

param(
    [Parameter(Mandatory = $true)]
    [string]$ImageName,
    [string]$Tag = 'latest',
    [ValidateSet(
        'DockerIO',
        'Microsoft'
    )]
    [string]$Registry = 'DockerIO'
)

switch ($Registry) {
    'DockerIO' {
        $LocalImageName = $ImageName
        if (! $ImageName.Contains('/')) {
            $LocalImageName = "library/$ImageName"
        }
        $Response = Invoke-RestMethod "https://auth.docker.io/token?service=registry.docker.io&scope=repository:$($LocalImageName):pull"
        $Headers = @{
            Authorization = "Bearer $($Response.token)";
            Accept        = 'application/vnd.docker.distribution.manifest.v2+json';
        }           
    }
    Default {
        $Headers = @{ }
    }
}

switch ($Registry) {
    'DockerIO' {
        $LocalImageName = $ImageName
        if (! $ImageName.Contains('/')) {
            $LocalImageName = "library/$ImageName"
        } 
        $DownloadMetadata = "https://registry-1.docker.io/v2/$LocalImageName/manifests/$Tag"
        $DownloadLayer = "https://registry-1.docker.io/v2/$LocalImageName/blobs/"
    }
    'Microsoft' { 
        $DownloadMetadata = "https://mcr.microsoft.com/v2/$ImageName/manifests/$Tag"
        $DownloadLayer = "https://mcr.microsoft.com/v2/$ImageName/blobs/"
    }
}

Write-Host "Downloading url($DownloadMetadata) $($ImageName):$Tag from $Registry" -ForegroundColor DarkGray
$Response = Invoke-RestMethod $DownloadMetadata -Headers $Headers

$Layers = $Response.layers;
if (! $Layers) {
    $Layers = $Response.manifests
}
if (! $Layers) {
    $Layers = $Response.fsLayers
}

foreach ($Layer in $Layers) {
    $LayerDigest = $Layer.digest ?? $Layer.blobSum
    $LayerUrl = $DownloadLayer + $LayerDigest
    
    $NormalizedName = $ImageName.Replace('/','_') + '__' + $LayerDigest.Replace(':', '_') + '.tar.gz'

    Write-Host "Downloading $LayerDigest from $LayerUrl" -ForegroundColor DarkGray
    Invoke-WebRequest $LayerUrl -Headers $Headers -OutFile $NormalizedName
    Write-Host "Downloaded $LayerDigest"
}