(Xojo Plugin) S3 Get Object Metadata, such as ETag

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

Chilkat Xojo Plugin Download Xojo Plugin for Windows, Linux, Mac OS X, and ARM, ARM64

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

Dim rest As New Chilkat.Rest

// Connect to the Amazon AWS REST server in the desired region.
// In this case we connect to S3 in the "us-west-2" region.
Dim bTls As Boolean
bTls = True
Dim port As Int32
port = 443
Dim bAutoReconnect As Boolean
bAutoReconnect = True
Dim success As Boolean
success = rest.Connect("s3-us-west-2.amazonaws.com",port,bTls,bAutoReconnect)

// Provide AWS credentials.
Dim authAws As New Chilkat.AuthAws
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) Then
    System.DebugLog(rest.LastErrorText)
    Return
End If

// Now get the response header.
Dim statusCode As Int32
statusCode = rest.ReadResponseHeader()
If (statusCode < 0) Then
    System.DebugLog(rest.LastErrorText)
    Return
End If

// When successful, the S3 Storage service will respond with a 200 response code,
// with an XML body.  
If (statusCode <> 200) Then
    // Examine the request/response to see what happened.
    System.DebugLog("response status code = " + Str(statusCode))
    System.DebugLog("response status text = " + rest.ResponseStatusText)
    System.DebugLog("response header: " + rest.ResponseHeader)
    Return
End If

// 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:
Dim etag As String
etag = rest.ResponseHdrByName("ETag")
System.DebugLog("ETag: " + etag)