PowerBuilder

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.

PowerBuilder

integer li_rc
long li_Success
oleobject loo_Rest
long li_BTls
long li_Port
long li_BAutoReconnect
oleobject loo_AuthAws
oleobject loo_Fac
string ls_LocalFilepath
long li_Sz
oleobject loo_SbRange
long li_ResponseStatusCode
oleobject loo_BodyStream
string ls_ErrResponse

li_Success = 0

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

loo_Rest = create oleobject
li_rc = loo_Rest.ConnectToNewObject("Chilkat.Rest")
if li_rc < 0 then
    destroy loo_Rest
    MessageBox("Error","Connecting to COM object failed")
    return
end if

//  Connect to the Amazon AWS REST server.
li_BTls = 1
li_Port = 443
li_BAutoReconnect = 1
li_Success = loo_Rest.Connect("s3.amazonaws.com",li_Port,li_BTls,li_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.
loo_AuthAws = create oleobject
li_rc = loo_AuthAws.ConnectToNewObject("Chilkat.AuthAws")

loo_AuthAws.AccessKey = "AWS_ACCESS_KEY"
loo_AuthAws.SecretKey = "AWS_SECRET_KEY"
loo_AuthAws.ServiceName = "s3"
li_Success = loo_Rest.SetAuthAws(loo_AuthAws)

//  Set the bucket name via the HOST header.
//  In this case, the bucket name is "chilkat100".
loo_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.
loo_Fac = create oleobject
li_rc = loo_Fac.ConnectToNewObject("Chilkat.FileAccess")

ls_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.
li_Sz = loo_Fac.FileSize(ls_LocalFilepath)
if li_Sz > 0 then
    Write-Debug "sz = " + string(li_Sz)

    //  If the sz equals 42375 bytes, then we want to add a Range header that looks like this:
    //  Range: bytes=42375-
    loo_SbRange = create oleobject
    li_rc = loo_SbRange.ConnectToNewObject("Chilkat.StringBuilder")

    loo_SbRange.Append("bytes=")
    loo_SbRange.AppendInt(li_Sz)
    loo_SbRange.Append("-")
    loo_Rest.AddHeader("Range",loo_SbRange.GetAsString())
    Write-Debug "Added Range: " + loo_SbRange.GetAsString()
end if

//  Send the request to download the remainder of the file.
li_Success = loo_Rest.SendReqNoBody("GET","/hamlet.xml")
if li_Success <> 1 then
    Write-Debug loo_Rest.LastErrorText
    destroy loo_Rest
    destroy loo_AuthAws
    destroy loo_Fac
    destroy loo_SbRange
    return
end if

//  Read the response header.
li_ResponseStatusCode = loo_Rest.ReadResponseHeader()
if li_ResponseStatusCode < 0 then
    Write-Debug loo_Rest.LastErrorText
    destroy loo_Rest
    destroy loo_AuthAws
    destroy loo_Fac
    destroy loo_SbRange
    return
end if

Write-Debug "Response status code = " + string(li_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 (li_ResponseStatusCode = 200) OR (li_ResponseStatusCode = 206) then

    loo_BodyStream = create oleobject
    li_rc = loo_BodyStream.ConnectToNewObject("Chilkat.Stream")

    //  The stream's sink will be a file.
    //  We will append to the file..
    loo_BodyStream.SinkFile = ls_LocalFilepath

    //  Indicate that we wish to append to the output file.
    //  The SinkFileAppend property was added in Chilkat v9.50.83
    loo_BodyStream.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.
    li_Success = loo_Rest.ReadRespBodyStream(loo_BodyStream,1)
    if li_Success <> 1 then
        Write-Debug loo_Rest.LastErrorText
        destroy loo_Rest
        destroy loo_AuthAws
        destroy loo_Fac
        destroy loo_SbRange
        destroy loo_BodyStream
        return
    end if

    Write-Debug "Successfully downloaded the file."

else
    ls_ErrResponse = loo_Rest.ReadRespBodyString()
    if loo_Rest.LastMethodSuccess <> 1 then
        Write-Debug loo_Rest.LastErrorText
    else
        Write-Debug ls_ErrResponse
    end if

end if



destroy loo_Rest
destroy loo_AuthAws
destroy loo_Fac
destroy loo_SbRange
destroy loo_BodyStream