Chunked file download via curl

chunked-download.ps1

param(
    [string]$Url,
    [string]$OutputPath,
    [int]$ChunkSizeMb = 1,
    [int]$MaxRetries = 16
)

$ErrorActionPreference = 'Stop'

if ($ChunkSizeMb -lt 1)
{
    throw 'ChunkSizeMb must be >= 1.'
}

$head = Invoke-WebRequest -Uri $Url -Method Head
$contentLengthHeader = $head.Headers['Content-Length']
if ($contentLengthHeader -is [System.Array])
{
    $contentLengthHeader = $contentLengthHeader[0]
}

$totalBytes = [int64]$contentLengthHeader
if ($totalBytes -le 0)
{
    throw 'Unable to determine Content-Length.'
}

$chunkSizeBytes = [int64]$ChunkSizeMb * 1MB
$partsDir = Join-Path (Get-Location) '.temp\parts'
if (-not (Test-Path -LiteralPath $partsDir))
{
    New-Item -ItemType Directory -Path $partsDir -Force | Out-Null
}

$outputDir = Split-Path -Parent $OutputPath
if (-not (Test-Path -LiteralPath $outputDir))
{
    New-Item -ItemType Directory -Path $outputDir -Force | Out-Null
}

$chunkCount = [int][Math]::Ceiling($totalBytes / [double]$chunkSizeBytes)
$ua = 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/145.0.0.0 Safari/537.36'

Write-Host ("Total bytes: {0}" -f $totalBytes)
Write-Host ("Chunk size:  {0}" -f $chunkSizeBytes)
Write-Host ("Chunk count: {0}" -f $chunkCount)

for ($index = 0; $index -lt $chunkCount; $index++)
{
    $start = [int64]$index * $chunkSizeBytes
    $end = [Math]::Min($start + $chunkSizeBytes - 1, $totalBytes - 1)
    $expectedBytes = $end - $start + 1
    $partPath = Join-Path $partsDir ("part-{0:D5}.bin" -f $index)

    $isValidExistingPart = $false
    if (Test-Path -LiteralPath $partPath)
    {
        $existingLength = (Get-Item -LiteralPath $partPath).Length
        if ($existingLength -eq $expectedBytes)
        {
            $isValidExistingPart = $true
        }
        else
        {
            Remove-Item -LiteralPath $partPath -Force
        }
    }

    if (-not $isValidExistingPart)
    {
        $downloaded = $false
        for ($attempt = 1; $attempt -le $MaxRetries; $attempt++)
        {
            & curl.exe -L --fail --silent --show-error --connect-timeout 10 --max-time 60 `
                -H ("Range: bytes={0}-{1}" -f $start, $end) `
                -H 'Accept-Encoding: identity' `
                -H ("Referer: {0}" -f $Url) `
                -H ("User-Agent: {0}" -f $ua) `
                -o $partPath `
                $Url

            $exitCode = $LASTEXITCODE
            if ($exitCode -eq 0 -and (Test-Path -LiteralPath $partPath))
            {
                $actualLength = (Get-Item -LiteralPath $partPath).Length
                if ($actualLength -eq $expectedBytes)
                {
                    $downloaded = $true
                    break
                }
            }

            if (Test-Path -LiteralPath $partPath)
            {
                Remove-Item -LiteralPath $partPath -Force -ErrorAction SilentlyContinue
            }

            Write-Host ("Retry chunk {0}/{1} range {2}-{3} attempt {4}/{5}" -f ($index + 1), $chunkCount, $start, $end, $attempt, $MaxRetries)
            Start-Sleep -Seconds 1
        }

        if (-not $downloaded)
        {
            throw ("Failed chunk {0}/{1} range {2}-{3}" -f ($index + 1), $chunkCount, $start, $end)
        }
    }

    if ((($index + 1) % 25) -eq 0 -or ($index + 1) -eq $chunkCount)
    {
        $percent = [Math]::Round((($index + 1) * 100.0) / $chunkCount, 2)
        Write-Host ("Downloaded chunks: {0}/{1} ({2}%)" -f ($index + 1), $chunkCount, $percent)
    }
}

$combinedPath = "$OutputPath.download"
if (Test-Path -LiteralPath $combinedPath)
{
    Remove-Item -LiteralPath $combinedPath -Force
}

$outStream = [System.IO.File]::Open($combinedPath, [System.IO.FileMode]::CreateNew, [System.IO.FileAccess]::Write, [System.IO.FileShare]::Read)
try
{
    for ($index = 0; $index -lt $chunkCount; $index++)
    {
        $partPath = Join-Path $partsDir ("part-{0:D5}.bin" -f $index)
        $inStream = [System.IO.File]::Open($partPath, [System.IO.FileMode]::Open, [System.IO.FileAccess]::Read, [System.IO.FileShare]::Read)
        try
        {
            $inStream.CopyTo($outStream)
        }
        finally
        {
            $inStream.Dispose()
        }
    }
}
finally
{
    $outStream.Dispose()
}

$finalSize = (Get-Item -LiteralPath $combinedPath).Length
if ($finalSize -ne $totalBytes)
{
    throw ("Combined file size mismatch. Expected {0}, got {1}" -f $totalBytes, $finalSize)
}

Move-Item -LiteralPath $combinedPath -Destination $OutputPath -Force
Write-Host ("Completed: {0}" -f $OutputPath)
Write-Host ("Size: {0}" -f $finalSize)

usage-example.ps1

chunked-download.ps1 -Url 'https://ndr-progressive.ard-mcdn.de/progressive_geo/2025/1206/TV-20251206-2206-4911.1080.mp4'