(JavaScript) S3 Get Object Metadata, such as ETag

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

Note

This example is intended for running within a Chilkat.Js embedded JavaScript engine. All Chilkat JavaScript examples require Chilkat v11.4.0 or greater.

var success = false;

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

var rest = new CkRest();

// 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 = true;
var port = 443;
var bAutoReconnect = true;
success = rest.Connect("s3-us-west-2.amazonaws.com",port,bTls,bAutoReconnect);

// Provide AWS credentials.
var authAws = new CkAuthAws();
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","/starfish.jpg");
if (success !== true) {
    console.log(rest.LastErrorText);
    return;
}

// Now get the response header.
var statusCode = rest.ReadResponseHeader();
if (statusCode < 0) {
    console.log(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.
    console.log("response status code = " + statusCode);
    console.log("response status text = " + rest.ResponseStatusText);
    console.log("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 = rest.ResponseHdrByName("ETag");
console.log("ETag: " + etag);