(Lianja) S3 Get Object Metadata, such as ETag

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

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

loRest = createobject("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.
llBTls = .T.
lnPort = 443
llBAutoReconnect = .T.
llSuccess = loRest.Connect("s3-us-west-2.amazonaws.com",lnPort,llBTls,llBAutoReconnect)

// Provide AWS credentials.
loAuthAws = createobject("CkAuthAws")
loAuthAws.AccessKey = "AWS_ACCESS_KEY"
loAuthAws.SecretKey = "AWS_SECRET_KEY"
loAuthAws.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".
loAuthAws.Region = "us-west-2"

llSuccess = loRest.SetAuthAws(loAuthAws)

// 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"
loRest.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.
llSuccess = loRest.SendReqNoBody("HEAD","/starfish.jpg")
if (llSuccess <> .T.) then
    ? loRest.LastErrorText
    release loRest
    release loAuthAws
    return
endif

// Now get the response header.
lnStatusCode = loRest.ReadResponseHeader()
if (lnStatusCode < 0) then
    ? loRest.LastErrorText
    release loRest
    release loAuthAws
    return
endif

// When successful, the S3 Storage service will respond with a 200 response code,
// with an XML body.  
if (lnStatusCode <> 200) then
    // Examine the request/response to see what happened.
    ? "response status code = " + str(lnStatusCode)
    ? "response status text = " + loRest.ResponseStatusText
    ? "response header: " + loRest.ResponseHeader
    release loRest
    release loAuthAws
    return
endif

// 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:
lcEtag = loRest.ResponseHdrByName("ETag")
? "ETag: " + lcEtag


release loRest
release loAuthAws