(Swift 3,4,5...) S3 Get Object Metadata, such as ETag

Demonstrates how to get an S3 object's metadata using a HEAD request.

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

    let rest = CkoRest()!

    // Connect to the Amazon AWS REST server in the desired region.
    // In this case we connect to S3 in the "us-west-2" region.
    var bTls: Bool = true
    var port: Int = 443
    var bAutoReconnect: Bool = true
    var success: Bool = rest.connect("s3-us-west-2.amazonaws.com", port: port, tls: bTls, autoReconnect: bAutoReconnect)

    // Provide AWS credentials.
    let authAws = CkoAuthAws()!
    authAws.accessKey = "AWS_ACCESS_KEY"
    authAws.secretKey = "AWS_SECRET_KEY"
    authAws.serviceName = "s3"

    // This particular bucket is in the Oregon region, as opposed to the US Standard,
    // therefore the Region must be set appropriately.
    // Also note that we connected to "s3-us-west-2.amazonaws.com".
    authAws.region = "us-west-2"

    success = rest.setAuthAws(authAws)

    // Note: The above REST connection and setup of the AWS credentials
    // can be done once.  After connecting, any number of REST calls can be made.
    // The "auto reconnect" property passed to rest.Connect indicates that if
    // the connection is lost, a REST method call will automatically reconnect
    // if needed.
    // --------------------------------------------------------------------------

    // Set the bucket name via the HOST header.
    // In this case, the bucket name is "chilkat.ocean".
    // Note that the Host header should use "bucketName.s3.amazonaws.com", not "bucketName.s3-us-west-2.amazonaws.com"
    rest.host = "chilkat.ocean.s3.amazonaws.com"

    // Our object is "starfish.jpg".
    // Get the metadata.
    // Since we are sending a HEAD request, we shouldn't use any of the Full* methods.
    // Instead, send the request, then just read the response header.
    success = rest.sendReqNoBody("HEAD", uriPath: "/starfish.jpg")
    if success != true {
        print("\(rest.lastErrorText!)")
        return
    }

    // Now get the response header.
    var statusCode: Int = rest.readResponseHeader().intValue
    if statusCode < 0 {
        print("\(rest.lastErrorText!)")
        return
    }

    // When successful, the S3 Storage service will respond with a 200 response code,
    // with an XML body.  
    if statusCode != 200 {
        // Examine the request/response to see what happened.
        print("response status code = \(statusCode)")
        print("response status text = \(rest.responseStatusText!)")
        print("response header: \(rest.responseHeader!)")
        return
    }

    // The response header contains information about the S3 object.
    // For example:

    // 	HTTP/1.1 200 OK
    // 	x-amz-id-2: GrV/hrB2EUkBlWc0h3JDdmVIrYDXfPC7CGvo/qSVRmYRPwilAOry8+4r2YWl4xJfa1HRYXrP808=
    // 	x-amz-request-id: 4BDC6D6AEA0BDEF3
    // 	Date: Mon, 13 May 2019 22:03:13 GMT
    // 	Last-Modified: Mon, 10 Nov 2014 16:10:23 GMT
    // 	ETag: "2e9c59dbf2662367dc97dfdda85da048"
    // 	Accept-Ranges: bytes
    // 	Content-Type: image/jpg
    // 	Content-Length: 6229
    // 	Server: AmazonS3

    // Get the ETag response header value:
    var etag: String? = rest.responseHdr(byName: "ETag")
    print("ETag: \(etag!)")

}