DataFlex

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.

DataFlex

Use ChilkatAx-win32.pkg

Procedure Test
    Boolean iSuccess
    Handle hoRest
    Boolean iBTls
    Integer iPort
    Boolean iBAutoReconnect
    Variant vAuthAws
    Handle hoAuthAws
    Handle hoFac
    String sLocalFilepath
    Integer iSz
    Handle hoSbRange
    Integer iResponseStatusCode
    Variant vBodyStream
    Handle hoBodyStream
    String sErrResponse
    String sTemp1
    Boolean bTemp1

    Move False To iSuccess

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

    Get Create (RefClass(cComChilkatRest)) To hoRest
    If (Not(IsComObjectCreated(hoRest))) Begin
        Send CreateComObject of hoRest
    End

    // Connect to the Amazon AWS REST server.
    Move True To iBTls
    Move 443 To iPort
    Move True To iBAutoReconnect
    Get ComConnect Of hoRest "s3.amazonaws.com" iPort iBTls iBAutoReconnect To iSuccess

    // ---------------------------------------------------------------------------
    // 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.
    Get Create (RefClass(cComChilkatAuthAws)) To hoAuthAws
    If (Not(IsComObjectCreated(hoAuthAws))) Begin
        Send CreateComObject of hoAuthAws
    End
    Set ComAccessKey Of hoAuthAws To "AWS_ACCESS_KEY"
    Set ComSecretKey Of hoAuthAws To "AWS_SECRET_KEY"
    Set ComServiceName Of hoAuthAws To "s3"
    Get pvComObject of hoAuthAws to vAuthAws
    Get ComSetAuthAws Of hoRest vAuthAws To iSuccess

    // Set the bucket name via the HOST header.
    // In this case, the bucket name is "chilkat100".
    Set ComHost Of hoRest To "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.
    Get Create (RefClass(cComCkFileAccess)) To hoFac
    If (Not(IsComObjectCreated(hoFac))) Begin
        Send CreateComObject of hoFac
    End
    Move "qa_output/hamlet.xml" To sLocalFilepath
    // 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.
    Get ComFileSize Of hoFac sLocalFilepath To iSz
    If (iSz > 0) Begin
        Showln "sz = " iSz

        // If the sz equals 42375 bytes, then we want to add a Range header that looks like this:
        // Range: bytes=42375-
        Get Create (RefClass(cComChilkatStringBuilder)) To hoSbRange
        If (Not(IsComObjectCreated(hoSbRange))) Begin
            Send CreateComObject of hoSbRange
        End
        Get ComAppend Of hoSbRange "bytes=" To iSuccess
        Get ComAppendInt Of hoSbRange iSz To iSuccess
        Get ComAppend Of hoSbRange "-" To iSuccess
        Get ComGetAsString Of hoSbRange To sTemp1
        Get ComAddHeader Of hoRest "Range" sTemp1 To iSuccess
        Get ComGetAsString Of hoSbRange To sTemp1
        Showln "Added Range: " sTemp1
    End

    // Send the request to download the remainder of the file.
    Get ComSendReqNoBody Of hoRest "GET" "/hamlet.xml" To iSuccess
    If (iSuccess <> True) Begin
        Get ComLastErrorText Of hoRest To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Read the response header.
    Get ComReadResponseHeader Of hoRest To iResponseStatusCode
    If (iResponseStatusCode < 0) Begin
        Get ComLastErrorText Of hoRest To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Showln "Response status code = " iResponseStatusCode

    // 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)) Begin

        Get Create (RefClass(cComChilkatStream)) To hoBodyStream
        If (Not(IsComObjectCreated(hoBodyStream))) Begin
            Send CreateComObject of hoBodyStream
        End

        // The stream's sink will be a file.
        // We will append to the file..
        Set ComSinkFile Of hoBodyStream To sLocalFilepath

        // Indicate that we wish to append to the output file.
        // The SinkFileAppend property was added in Chilkat v9.50.83
        Set ComSinkFileAppend Of hoBodyStream To 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.
        Get pvComObject of hoBodyStream to vBodyStream
        Get ComReadRespBodyStream Of hoRest vBodyStream True To iSuccess
        If (iSuccess <> True) Begin
            Get ComLastErrorText Of hoRest To sTemp1
            Showln sTemp1
            Procedure_Return
        End

        Showln "Successfully downloaded the file."

    End
    Else Begin
        Get ComReadRespBodyString Of hoRest To sErrResponse
        Get ComLastMethodSuccess Of hoRest To bTemp1
        If (bTemp1 <> True) Begin
            Get ComLastErrorText Of hoRest To sTemp1
            Showln sTemp1
        End
        Else Begin
            Showln sErrResponse
        End

    End



End_Procedure