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S3 Resume Download

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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.

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Local $bSuccess = False

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

$oRest = ObjCreate("Chilkat.Rest")

;  Connect to the Amazon AWS REST server.
Local $bTls = True
Local $iPort = 443
Local $bAutoReconnect = True
$bSuccess = $oRest.Connect("s3.amazonaws.com",$iPort,$bTls,$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.
$oAuthAws = ObjCreate("Chilkat.AuthAws")
$oAuthAws.AccessKey = "AWS_ACCESS_KEY"
$oAuthAws.SecretKey = "AWS_SECRET_KEY"
$oAuthAws.ServiceName = "s3"
$bSuccess = $oRest.SetAuthAws($oAuthAws)

;  Set the bucket name via the HOST header.
;  In this case, the bucket name is "chilkat100".
$oRest.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.
$oFac = ObjCreate("Chilkat.FileAccess")
Local $sLocalFilepath = "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.
Local $iSz = $oFac.FileSize($sLocalFilepath)
If ($iSz > 0) Then
    ConsoleWrite("sz = " & $iSz & @CRLF)

    ;  If the sz equals 42375 bytes, then we want to add a Range header that looks like this:
    ;  Range: bytes=42375-
    $oSbRange = ObjCreate("Chilkat.StringBuilder")
    $oSbRange.Append("bytes=")
    $oSbRange.AppendInt($iSz)
    $oSbRange.Append("-")
    $oRest.AddHeader("Range",$oSbRange.GetAsString())
    ConsoleWrite("Added Range: " & $oSbRange.GetAsString() & @CRLF)
EndIf

;  Send the request to download the remainder of the file.
$bSuccess = $oRest.SendReqNoBody("GET","/hamlet.xml")
If ($bSuccess <> True) Then
    ConsoleWrite($oRest.LastErrorText & @CRLF)
    Exit
EndIf

;  Read the response header.
Local $iResponseStatusCode = $oRest.ReadResponseHeader()
If ($iResponseStatusCode < 0) Then
    ConsoleWrite($oRest.LastErrorText & @CRLF)
    Exit
EndIf

ConsoleWrite("Response status code = " & $iResponseStatusCode & @CRLF)

;  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 (($iResponseStatusCode = 200) Or ($iResponseStatusCode = 206)) Then

    $oBodyStream = ObjCreate("Chilkat.Stream")

    ;  The stream's sink will be a file.
    ;  We will append to the file..
    $oBodyStream.SinkFile = $sLocalFilepath

    ;  Indicate that we wish to append to the output file.
    ;  The SinkFileAppend property was added in Chilkat v9.50.83
    $oBodyStream.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.
    $bSuccess = $oRest.ReadRespBodyStream($oBodyStream,True)
    If ($bSuccess <> True) Then
        ConsoleWrite($oRest.LastErrorText & @CRLF)
        Exit
    EndIf

    ConsoleWrite("Successfully downloaded the file." & @CRLF)

Else
Local $sErrResponse = $oRest.ReadRespBodyString()
    If ($oRest.LastMethodSuccess <> True) Then
        ConsoleWrite($oRest.LastErrorText & @CRLF)
    Else
        ConsoleWrite($sErrResponse & @CRLF)
    EndIf

EndIf