Node.js

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.

Node.js

NODEJS_PRELUDE

function chilkatExample() {

    var success = false;

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

    var rest = new chilkat.Rest();

    //  Connect to the Amazon AWS REST server.
    var bTls = true;
    var port = 443;
    var 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.
    var authAws = new chilkat.AuthAws();
    authAws.AccessKey = "AWS_ACCESS_KEY";
    authAws.SecretKey = "AWS_SECRET_KEY";
    authAws.ServiceName = "s3";
    success = rest.SetAuthAws(authAws);

    //  Set the bucket name via the HOST header.
    //  In this case, the bucket name is "chilkat100".
    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.
    var fac = new chilkat.FileAccess();
    var 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.
    var sz = fac.FileSize(localFilepath);
    if (sz > 0) {
        console.log("sz = " + sz);

        //  If the sz equals 42375 bytes, then we want to add a Range header that looks like this:
        //  Range: bytes=42375-
        var sbRange = new chilkat.StringBuilder();
        sbRange.Append("bytes=");
        sbRange.AppendInt(sz);
        sbRange.Append("-");
        rest.AddHeader("Range",sbRange.GetAsString());
        console.log("Added Range: " + sbRange.GetAsString());
    }

    //  Send the request to download the remainder of the file.
    success = rest.SendReqNoBody("GET","/hamlet.xml");
    if (success !== true) {
        console.log(rest.LastErrorText);
        return;
    }

    //  Read the response header.
    var responseStatusCode = rest.ReadResponseHeader();
    if (responseStatusCode < 0) {
        console.log(rest.LastErrorText);
        return;
    }

    console.log("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)) {

        var bodyStream = new chilkat.Stream();

        //  The stream's sink will be a file.
        //  We will append to the file..
        bodyStream.SinkFile = localFilepath;

        //  Indicate that we wish to append to the output file.
        //  The SinkFileAppend property was added in Chilkat v9.50.83
        bodyStream.SinkFileAppend = 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) {
            console.log(rest.LastErrorText);
            return;
        }

        console.log("Successfully downloaded the file.");

    }
    else {
        var errResponse = rest.ReadRespBodyString();
        if (rest.LastMethodSuccess !== true) {
            console.log(rest.LastErrorText);
        }
        else {
            console.log(errResponse);
        }

    }


}

chilkatExample();