Xbase++

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.

Xbase++

LOCAL nSuccess
LOCAL oRest
LOCAL nBTls
LOCAL nPort
LOCAL nBAutoReconnect
LOCAL oAuthAws
LOCAL oFac
LOCAL cLocalFilepath
LOCAL nSz
LOCAL oSbRange
LOCAL nResponseStatusCode
LOCAL oBodyStream
LOCAL cErrResponse

nSuccess := 0

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

oRest := CreateObject("Chilkat.Rest")

//  Connect to the Amazon AWS REST server.
nBTls := 1
nPort := 443
nBAutoReconnect := 1
nSuccess := oRest:Connect("s3.amazonaws.com", nPort, nBTls, nBAutoReconnect)

//  ---------------------------------------------------------------------------
//  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 := CreateObject("Chilkat.AuthAws")
oAuthAws:AccessKey := "AWS_ACCESS_KEY"
oAuthAws:SecretKey := "AWS_SECRET_KEY"
oAuthAws:ServiceName := "s3"
nSuccess := 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 := CreateObject("Chilkat.FileAccess")
cLocalFilepath := "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.
nSz := oFac:FileSize(cLocalFilepath)
IF (nSz > 0)
    ? "sz = " + Str(nSz)

    //  If the sz equals 42375 bytes, then we want to add a Range header that looks like this:
    //  Range: bytes=42375-
    oSbRange := CreateObject("Chilkat.StringBuilder")
    oSbRange:Append("bytes=")
    oSbRange:AppendInt(nSz)
    oSbRange:Append("-")
    oRest:AddHeader("Range", oSbRange:GetAsString())
    ? "Added Range: " + oSbRange:GetAsString()
ENDIF

//  Send the request to download the remainder of the file.
nSuccess := oRest:SendReqNoBody("GET", "/hamlet.xml")
IF (nSuccess != 1)
    ? oRest:LastErrorText
    oRest:destroy()
    oAuthAws:destroy()
    oFac:destroy()
    oSbRange:destroy()
    RETURN
ENDIF

//  Read the response header.
nResponseStatusCode := oRest:ReadResponseHeader()
IF (nResponseStatusCode < 0)
    ? oRest:LastErrorText
    oRest:destroy()
    oAuthAws:destroy()
    oFac:destroy()
    oSbRange:destroy()
    RETURN
ENDIF

? "Response status code = " + Str(nResponseStatusCode)

//  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 ((nResponseStatusCode == 200) .OR. (nResponseStatusCode == 206))

    oBodyStream := CreateObject("Chilkat.Stream")

    //  The stream's sink will be a file.
    //  We will append to the file..
    oBodyStream:SinkFile := cLocalFilepath

    //  Indicate that we wish to append to the output file.
    //  The SinkFileAppend property was added in Chilkat v9.50.83
    oBodyStream: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.
    nSuccess := oRest:ReadRespBodyStream(oBodyStream, 1)
    IF (nSuccess != 1)
        ? oRest:LastErrorText
        oRest:destroy()
        oAuthAws:destroy()
        oFac:destroy()
        oSbRange:destroy()
        oBodyStream:destroy()
        RETURN
    ENDIF

    ? "Successfully downloaded the file."

ELSE
    cErrResponse := oRest:ReadRespBodyString()
    IF (oRest:LastMethodSuccess != 1)
        ? oRest:LastErrorText
    ELSE
        ? cErrResponse
    ENDIF

ENDIF

oRest:destroy()
oAuthAws:destroy()
oFac:destroy()
oSbRange:destroy()
oBodyStream:destroy()