Visual FoxPro

S3 Resume Download

See more Amazon S3 (new) Examples

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.

Visual FoxPro

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

lnSuccess = 0

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

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.
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.
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-
    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

    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