B4X

S3 Get Object Metadata, such as ETag

See more Amazon S3 (new) Examples

Demonstrates how to get an S3 object's metadata using a HEAD request. B4X

Dim success As Boolean = False

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

Dim rest As ChilkatRest
rest.Initialize("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 = True
Dim port As Int = 443
Dim bAutoReconnect As Boolean = True
success = rest.Connect("s3-us-west-2.amazonaws.com", port, bTls, bAutoReconnect)

'  Provide AWS credentials.
Dim authAws As ChilkatAuthAws
authAws.Initialize
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
    Log(rest.LastErrorText)
    Return
End If


'  Now get the response header.
Dim statusCode As Int = rest.ReadResponseHeader
If statusCode < 0 Then
    Log(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.
    Log("response status code = " & statusCode)
    Log("response status text = " & rest.ResponseStatusText)
    Log("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 = rest.ResponseHdrByName("ETag")
Log("ETag: " & etag)