(PowerShell) HTTP Download in Parallel with Simultaneous Range Requests

Demonstrates how to download a large file with parallel simultaneous requests, where each request downloads a segment (range) of the remote file.

Chilkat .NET Downloads Chilkat .NET Assemblies

Add-Type -Path "C:\chilkat\ChilkatDotNet47-9.5.0-x64\ChilkatDotNet47.dll"

# This requires the Chilkat API to have been previously unlocked.
# See Global Unlock Sample for sample code.

$http = New-Object Chilkat.Http

# First get the size of the file to be downloaded.
$url = "https://www.chilkatsoft.com/hamlet.xml"

$resp = $http.GetHead($url)
if ($http.LastMethodSuccess -eq $false) {
    $($http.LastErrorText)
    exit
}

$remoteFileSize = $resp.ContentLength

$("Downloading " + $remoteFileSize + " bytes...")

# Let's download in 4 chunks.
# (the last chunk will be whatever remains after the 1st 3 equal sized chunks)
$chunkSize = $remoteFileSize / 4

# The Range header is used to download a range from a resource
# Range: bytes=<range-start>-<range-end>
# or
# Range: bytes=<range-start>-

# We're writing code this way for clarity..
$http1 = New-Object Chilkat.Http
$http2 = New-Object Chilkat.Http
$http3 = New-Object Chilkat.Http
$http4 = New-Object Chilkat.Http

$sbRange = New-Object Chilkat.StringBuilder
$sbRange.SetString("bytes=<range-start>-<range-end>")
$numReplaced = $sbRange.ReplaceI("<range-start>",0)
$numReplaced = $sbRange.ReplaceI("<range-end>",$chunkSize - 1)
$($sbRange.GetAsString())
$http1.SetRequestHeader("Range",$sbRange.GetAsString())

$sbRange.SetString("bytes=<range-start>-<range-end>")
$numReplaced = $sbRange.ReplaceI("<range-start>",$chunkSize)
$numReplaced = $sbRange.ReplaceI("<range-end>",2 * $chunkSize - 1)
$($sbRange.GetAsString())
$http2.SetRequestHeader("Range",$sbRange.GetAsString())

$sbRange.SetString("bytes=<range-start>-<range-end>")
$numReplaced = $sbRange.ReplaceI("<range-start>",2 * $chunkSize)
$numReplaced = $sbRange.ReplaceI("<range-end>",3 * $chunkSize - 1)
$($sbRange.GetAsString())
$http3.SetRequestHeader("Range",$sbRange.GetAsString())

$sbRange.SetString("bytes=<range-start>-")
$numReplaced = $sbRange.ReplaceI("<range-start>",3 * $chunkSize)
$($sbRange.GetAsString())
$http4.SetRequestHeader("Range",$sbRange.GetAsString())

# Start each range download
$task1 = $http1.DownloadAsync($url,"qa_output/chunk1.dat")
$task1.Run()

$task2 = $http2.DownloadAsync($url,"qa_output/chunk2.dat")
$task2.Run()

$task3 = $http3.DownloadAsync($url,"qa_output/chunk3.dat")
$task3.Run()

$task4 = $http4.DownloadAsync($url,"qa_output/chunk4.dat")
$task4.Run()

# Wait for the downloads to complete.
$numLive = 4
while ($numLive -gt 0) {
    $numLive = 0
    if ($task1.Live -eq $true) {
        $numLive = $numLive + 1
    }

    if ($task2.Live -eq $true) {
        $numLive = $numLive + 1
    }

    if ($task3.Live -eq $true) {
        $numLive = $numLive + 1
    }

    if ($task4.Live -eq $true) {
        $numLive = $numLive + 1
    }

    if ($numLive -gt 0) {
        # SleepMs is a convenience method to cause the caller to sleep for N millisec.
        # It does not cause the given task to sleep..
        $task1.SleepMs(10)
    }

}

# All should be downloaded now..
# Examine the result of each Download.
$numErrors = 0
if ($task1.GetResultBool() -eq $false) {
    $($task1.ResultErrorText)
    $numErrors = $numErrors + 1
}

if ($task2.GetResultBool() -eq $false) {
    $($task2.ResultErrorText)
    $numErrors = $numErrors + 1
}

if ($task3.GetResultBool() -eq $false) {
    $($task3.ResultErrorText)
    $numErrors = $numErrors + 1
}

if ($task4.GetResultBool() -eq $false) {
    $($task4.ResultErrorText)
    $numErrors = $numErrors + 1
}

if ($numErrors -gt 0) {

    exit
}

# All downloads were successful.
# Compose the file from the parts.
$fac = New-Object Chilkat.FileAccess
$success = $fac.ReassembleFile("qa_output","chunk","dat","qa_output/hamlet.xml")
if ($success -eq $false) {
    $($fac.LastErrorText)
}
else {
    $("Success.")
}

# Let's download in the regular way, and then compare files..
$success = $http.Download($url,"qa_output/hamletRegular.xml")

# Compare files.
$bSame = $fac.FileContentsEqual("qa_output/hamlet.xml","qa_output/hamletRegular.xml")
$("bSame = " + $bSame)