(PureBasic) S3 Get Object Metadata, such as ETag

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

Chilkat PureBasic Module Download Chilkat PureBasic Module

IncludeFile "CkRest.pb"
IncludeFile "CkAuthAws.pb"

Procedure ChilkatExample()

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

    rest.i = CkRest::ckCreate()
    If rest.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; Connect to the Amazon AWS REST server in the desired region.
    ; In this case we connect to S3 in the "us-west-2" region.
    bTls.i = 1
    port.i = 443
    bAutoReconnect.i = 1
    success.i = CkRest::ckConnect(rest,"s3-us-west-2.amazonaws.com",port,bTls,bAutoReconnect)

    ; Provide AWS credentials.
    authAws.i = CkAuthAws::ckCreate()
    If authAws.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkAuthAws::setCkAccessKey(authAws, "AWS_ACCESS_KEY")
    CkAuthAws::setCkSecretKey(authAws, "AWS_SECRET_KEY")
    CkAuthAws::setCkServiceName(authAws, "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".
    CkAuthAws::setCkRegion(authAws, "us-west-2")

    success = CkRest::ckSetAuthAws(rest,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"
    CkRest::setCkHost(rest, "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 = CkRest::ckSendReqNoBody(rest,"HEAD","/starfish.jpg")
    If success <> 1
        Debug CkRest::ckLastErrorText(rest)
        CkRest::ckDispose(rest)
        CkAuthAws::ckDispose(authAws)
        ProcedureReturn
    EndIf

    ; Now get the response header.
    statusCode.i = CkRest::ckReadResponseHeader(rest)
    If statusCode < 0
        Debug CkRest::ckLastErrorText(rest)
        CkRest::ckDispose(rest)
        CkAuthAws::ckDispose(authAws)
        ProcedureReturn
    EndIf

    ; 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.
        Debug "response status code = " + Str(statusCode)
        Debug "response status text = " + CkRest::ckResponseStatusText(rest)
        Debug "response header: " + CkRest::ckResponseHeader(rest)
        CkRest::ckDispose(rest)
        CkAuthAws::ckDispose(authAws)
        ProcedureReturn
    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:
    etag.s = CkRest::ckResponseHdrByName(rest,"ETag")
    Debug "ETag: " + etag


    CkRest::ckDispose(rest)
    CkAuthAws::ckDispose(authAws)


    ProcedureReturn
EndProcedure