(C# UWP/WinRT) 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 Universal Windows Platform (UWP) / WinRT Downloads Chilkat for the Universal Windows Platform (UWP)

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

Chilkat.Rest rest = new Chilkat.Rest();

// Connect to the Amazon AWS REST server.
bool bTls = true;
int port = 443;
bool bAutoReconnect = true;
bool success = await rest.ConnectAsync("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.
Chilkat.AuthAws 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.
Chilkat.FileAccess fac = new Chilkat.FileAccess();
string 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.
int sz = fac.FileSize(localFilepath);
if (sz > 0) {
    Debug.WriteLine("sz = " + Convert.ToString(sz));

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

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

// Read the response header.
int responseStatusCode = await rest.ReadResponseHeaderAsync();
if (responseStatusCode < 0) {
    Debug.WriteLine(rest.LastErrorText);
    return;
}

Debug.WriteLine("Response status code = " + Convert.ToString(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)) {

    Chilkat.Stream 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 = await rest.ReadRespBodyStreamAsync(bodyStream,true);
    if (success != true) {
        Debug.WriteLine(rest.LastErrorText);
        return;
    }

    Debug.WriteLine("Successfully downloaded the file.");

}
else {
    string errResponse = await rest.ReadRespBodyStringAsync();
    if (rest.LastMethodSuccess != true) {
        Debug.WriteLine(rest.LastErrorText);
    }
    else {
        Debug.WriteLine(errResponse);
    }

}