(Visual FoxPro) 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 ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

LOCAL loRest
LOCAL lnBTls
LOCAL lnPort
LOCAL lnBAutoReconnect
LOCAL lnSuccess
LOCAL loAuthAws
LOCAL loFac
LOCAL lcLocalFilepath
LOCAL lnSz
LOCAL loSbRange
LOCAL lnResponseStatusCode
LOCAL loBodyStream
LOCAL lcErrResponse

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

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Rest')
loRest = CreateObject('Chilkat.Rest')

* Connect to the Amazon AWS REST server.
lnBTls = 1
lnPort = 443
lnBAutoReconnect = 1
lnSuccess = loRest.Connect("s3.amazonaws.com",lnPort,lnBTls,lnBAutoReconnect)

* ---------------------------------------------------------------------------
* 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.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.AuthAws')
loAuthAws = CreateObject('Chilkat.AuthAws')
loAuthAws.AccessKey = "AWS_ACCESS_KEY"
loAuthAws.SecretKey = "AWS_SECRET_KEY"
loAuthAws.ServiceName = "s3"
lnSuccess = loRest.SetAuthAws(loAuthAws)

* Set the bucket name via the HOST header.
* In this case, the bucket name is "chilkat100".
loRest.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.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.FileAccess')
loFac = CreateObject('Chilkat.FileAccess')
lcLocalFilepath = "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.
lnSz = loFac.FileSize(lcLocalFilepath)
IF (lnSz > 0) THEN
    ? "sz = " + STR(lnSz)

    * If the sz equals 42375 bytes, then we want to add a Range header that looks like this:
    * Range: bytes=42375-
    * For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.StringBuilder')
    loSbRange = CreateObject('Chilkat.StringBuilder')
    loSbRange.Append("bytes=")
    loSbRange.AppendInt(lnSz)
    loSbRange.Append("-")
    loRest.AddHeader("Range",loSbRange.GetAsString())
    ? "Added Range: " + loSbRange.GetAsString()
ENDIF

* Send the request to download the remainder of the file.
lnSuccess = loRest.SendReqNoBody("GET","/hamlet.xml")
IF (lnSuccess <> 1) THEN
    ? loRest.LastErrorText
    RELEASE loRest
    RELEASE loAuthAws
    RELEASE loFac
    RELEASE loSbRange
    CANCEL
ENDIF

* Read the response header.
lnResponseStatusCode = loRest.ReadResponseHeader()
IF (lnResponseStatusCode < 0) THEN
    ? loRest.LastErrorText
    RELEASE loRest
    RELEASE loAuthAws
    RELEASE loFac
    RELEASE loSbRange
    CANCEL
ENDIF

? "Response status code = " + STR(lnResponseStatusCode)

* 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 ((lnResponseStatusCode = 200) OR (lnResponseStatusCode = 206)) THEN

    * For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Stream')
    loBodyStream = CreateObject('Chilkat.Stream')

    * The stream's sink will be a file.
    * We will append to the file..
    loBodyStream.SinkFile = lcLocalFilepath

    * Indicate that we wish to append to the output file.
    * The SinkFileAppend property was added in Chilkat v9.50.83
    loBodyStream.SinkFileAppend = 1

    * 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.
    lnSuccess = loRest.ReadRespBodyStream(loBodyStream,1)
    IF (lnSuccess <> 1) THEN
        ? loRest.LastErrorText
        RELEASE loRest
        RELEASE loAuthAws
        RELEASE loFac
        RELEASE loSbRange
        RELEASE loBodyStream
        CANCEL
    ENDIF

    ? "Successfully downloaded the file."

ELSE
    lcErrResponse = loRest.ReadRespBodyString()
    IF (loRest.LastMethodSuccess <> 1) THEN
        ? loRest.LastErrorText
    ELSE
        ? lcErrResponse
    ENDIF

ENDIF

RELEASE loRest
RELEASE loAuthAws
RELEASE loFac
RELEASE loSbRange
RELEASE loBodyStream