(Go) 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 Go Downloads Go Package for Windows, MacOS, Linux, Alpine Linux, Solaris

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

    rest := chilkat.NewRest()

    // Connect to the Amazon AWS REST server.
    bTls := true
    port := 443
    bAutoReconnect := true
    success := rest.Connect("s3.amazonaws.com",port,bTls,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.
    authAws := chilkat.NewAuthAws()
    authAws.SetAccessKey("AWS_ACCESS_KEY")
    authAws.SetSecretKey("AWS_SECRET_KEY")
    authAws.SetServiceName("s3")
    success = rest.SetAuthAws(authAws)

    // Set the bucket name via the HOST header.
    // In this case, the bucket name is "chilkat100".
    rest.SetHost("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.
    fac := chilkat.NewFileAccess()
    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.
    sz := fac.FileSize(localFilepath)
    if sz > 0 {
        fmt.Println("sz = ", sz)

        // If the sz equals 42375 bytes, then we want to add a Range header that looks like this:
        // Range: bytes=42375-
        sbRange := chilkat.NewStringBuilder()
        sbRange.Append("bytes=")
        sbRange.AppendInt(sz)
        sbRange.Append("-")
        rest.AddHeader("Range",*sbRange.GetAsString())
        fmt.Println("Added Range: ", *sbRange.GetAsString())
    }

    // Send the request to download the remainder of the file.
    success = rest.SendReqNoBody("GET","/hamlet.xml")
    if success != true {
        fmt.Println(rest.LastErrorText())
        rest.DisposeRest()
        authAws.DisposeAuthAws()
        fac.DisposeFileAccess()
        sbRange.DisposeStringBuilder()
        return
    }

    // Read the response header.
    responseStatusCode := rest.ReadResponseHeader()
    if responseStatusCode < 0 {
        fmt.Println(rest.LastErrorText())
        rest.DisposeRest()
        authAws.DisposeAuthAws()
        fac.DisposeFileAccess()
        sbRange.DisposeStringBuilder()
        return
    }

    fmt.Println("Response status code = ", 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 (responseStatusCode == 200) || (responseStatusCode == 206) {

        bodyStream := chilkat.NewStream()

        // The stream's sink will be a file.
        // We will append to the file..
        bodyStream.SetSinkFile(localFilepath)

        // Indicate that we wish to append to the output file.
        // The SinkFileAppend property was added in Chilkat v9.50.83
        bodyStream.SetSinkFileAppend(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.
        success = rest.ReadRespBodyStream(bodyStream,true)
        if success != true {
            fmt.Println(rest.LastErrorText())
            rest.DisposeRest()
            authAws.DisposeAuthAws()
            fac.DisposeFileAccess()
            sbRange.DisposeStringBuilder()
            bodyStream.DisposeStream()
            return
        }

        fmt.Println("Successfully downloaded the file.")

    }
    else {
        errResponse := rest.ReadRespBodyString()
        if rest.LastMethodSuccess() != true {
            fmt.Println(rest.LastErrorText())
        }
        else {
            fmt.Println(*errResponse)
        }

    }


    rest.DisposeRest()
    authAws.DisposeAuthAws()
    fac.DisposeFileAccess()
    sbRange.DisposeStringBuilder()
    bodyStream.DisposeStream()