powershell 在异步模式下使用Start-BitsTransfer下载文件

Posted 2021-05-23

function Get-FileBitsTransferAsynchronous{
    param(
        [Parameter(Mandatory=$true)]
        $url, 
        $destinationFolder="$env:USERPROFILE\Downloads",
        [switch]$includeStats
    )
    $start = Get-Date
    $job = Start-BitsTransfer -Source $url -Destination $destinationFolder -DisplayName 'Download' -Asynchronous 
    $destination = Join-Path $destinationFolder ($url | Split-Path -Leaf)

    while (($job.JobState -eq 'Transferring') -or ($job.JobState -eq 'Connecting')){ 
         filter Get-FileSize {
	        "{0:N2} {1}" -f $(
	        if ($_ -lt 1kb) { $_, 'Bytes' }
	        elseif ($_ -lt 1mb) { ($_/1kb), 'KB' }
	        elseif ($_ -lt 1gb) { ($_/1mb), 'MB' }
	        elseif ($_ -lt 1tb) { ($_/1gb), 'GB' }
	        elseif ($_ -lt 1pb) { ($_/1tb), 'TB' }
	        else { ($_/1pb), 'PB' }
	        )
        }
        $elapsed = ((Get-Date) - $start)
        #calculate average speed in Mbps
        $averageSpeed = ($job.BytesTransferred * 8 / 1MB) / $elapsed.TotalSeconds
        $elapsed = $elapsed.ToString('hh\:mm\:ss')
        #calculate remaining time considering average speed
        $remainingSeconds = ($job.BytesTotal - $job.BytesTransferred) * 8 / 1MB / $averageSpeed
        $receivedSize = $job.BytesTransferred | Get-FileSize
        $totalSize = $job.BytesTotal | Get-FileSize 
        $progressPercentage = [int]($job.BytesTransferred / $job.BytesTotal * 100)      
        if ($remainingSeconds -as [int]){
            Write-Progress -Activity (" $url {0:N2} Mbps" -f $averageSpeed) `
                -Status ("{0} of {1} ({2}% in {3})" -f $receivedSize, $totalSize, $progressPercentage, $elapsed) `
                -SecondsRemaining $remainingSeconds `
                -PercentComplete $progressPercentage
        }
    } 
    if ($includeStats.IsPresent){
        ([PSCustomObject]@{Name=$MyInvocation.MyCommand;TotalSize=$totalSize;Time=$elapsed}) | Out-Host
    }
    
    Write-Progress -Activity (" $url {0:N2} Mbps" -f $averageSpeed) `
        -Status 'Done' -Completed
    Switch($job.JobState){
	    'Transferred' {
                        Complete-BitsTransfer -BitsJob $job
                        Get-Item $destination | Unblock-File
                      }
	    'Error'       {
                        Write-Warning "Download of $url failed" 
                        $job | Format-List
                      } 
    }
}