(PowerShell) S3 Resume Download

Suppose an S3 download of a very large file failed for some reason and you have a partial file on disk. Rather than restart the entire download, you wish to download the remaining portion. This example demonstrates how to finish a previously failed download.

Note: This example requires Chilkat v9.5.0.83 or above.

Chilkat .NET Downloads Chilkat .NET Assemblies

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

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

$rest = New-Object Chilkat.Rest

# Connect to the Amazon AWS REST server.
$bTls = $true
$port = 443
$bAutoReconnect = $true
$success = $rest.Connect("s3.amazonaws.com",$port,$bTls,$bAutoReconnect)

# ---------------------------------------------------------------------------
# Important: For buckets created in regions outside us-east-1,
# there are three important changes that need to be made.
# See Working with S3 Buckets in Non-us-east-1 Regions for the details.
# ---------------------------------------------------------------------------

# Provide AWS credentials for the REST call.
$authAws = New-Object Chilkat.AuthAws
$authAws.AccessKey = "AWS_ACCESS_KEY"
$authAws.SecretKey = "AWS_SECRET_KEY"
$authAws.ServiceName = "s3"
$success = $rest.SetAuthAws($authAws)

# Set the bucket name via the HOST header.
# In this case, the bucket name is "chilkat100".
$rest.Host = "chilkat100.s3.amazonaws.com"

# We want to continue downloading a file.
# The relative local filepath of our previously partially downoaded file is: qa_output/hamlet.xml
# Let's find out how many bytes are already downloaded.
$fac = New-Object Chilkat.FileAccess
$localFilepath = "qa_output/hamlet.xml"
# Note: The FileSize method returns a signed 32-bit integer.  If the file is potentially larger than 2GB, call FileSizeStr instead to return
# the size of the file as a string, then convert to an integer value.
$sz = $fac.FileSize($localFilepath)
if ($sz -gt 0) {
    $("sz = " + $sz)

    # If the sz equals 42375 bytes, then we want to add a Range header that looks like this:
    # Range: bytes=42375-
    $sbRange = New-Object Chilkat.StringBuilder
    $sbRange.Append("bytes=")
    $sbRange.AppendInt($sz)
    $sbRange.Append("-")
    $rest.AddHeader("Range",$sbRange.GetAsString())
    $("Added Range: " + $sbRange.GetAsString())
}

# Send the request to download the remainder of the file.
$success = $rest.SendReqNoBody("GET","/hamlet.xml")
if ($success -ne $true) {
    $($rest.LastErrorText)
    exit
}

# Read the response header.
$responseStatusCode = $rest.ReadResponseHeader()
if ($responseStatusCode -lt 0) {
    $($rest.LastErrorText)
    exit
}

$("Response status code = " + $responseStatusCode)

# We expect a 200 or 206 response status if the file data is coming.
# Otherwise, we'll get a string response body with an error message(or no response body).
if (($responseStatusCode -eq 200) -or ($responseStatusCode -eq 206)) {

    $bodyStream = New-Object Chilkat.Stream

    # The stream's sink will be a file.
    # We will append to the file..
    $bodyStream.SinkFile = $localFilepath

    # Indicate that we wish to append to the output file.
    # The SinkFileAppend property was added in Chilkat v9.50.83
    $bodyStream.SinkFileAppend = $true

    # Read the response body to the stream.  Given that we've
    # set the stream's sink to a file, it will stream directly
    # to the file.
    $success = $rest.ReadRespBodyStream($bodyStream,$true)
    if ($success -ne $true) {
        $($rest.LastErrorText)
        exit
    }

    $("Successfully downloaded the file.")

}
else {
    $errResponse = $rest.ReadRespBodyString()
    if ($rest.LastMethodSuccess -ne $true) {
        $($rest.LastErrorText)
    }
    else {
        $($errResponse)
    }

}