(VB.NET) Fetch S3 Object Metadata

Demonstrates how to get the metadata for an S3 object using the REST API.

The HEAD operation retrieves metadata from an object without returning the object itself. This operation is useful if you are interested only in an object's metadata. To use HEAD, you must have READ access to the object.

A HEAD request has the same options as a GET operation on an object. The response is identical to the GET response except that there is no response body.

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' 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 using the correct region (in this example, "us-west-2")
Dim bTls As Boolean = True
Dim port As Integer = 443
Dim bAutoReconnect As Boolean = True
Dim success As Boolean = rest.Connect("s3-us-west-2.amazonaws.com",port,bTls,bAutoReconnect)

' Provide AWS credentials for the REST call.
Dim authAws As New Chilkat.AuthAws
authAws.AccessKey = "AWS_ACCESS_KEY"
authAws.SecretKey = "AWS_SECRET_KEY"
authAws.ServiceName = "s3"
' Make sure the Region agrees with the region in the Connect.
authAws.Region = "us-west-2"
success = rest.SetAuthAws(authAws)

' User-defined metadata are name/value pairs, and are returned in the HTTP response header.
' Metadata header names begin with "x-amz-meta-" to distinguish them from other HTTP headers.
' Note that Amazon S3 stores user-defined metadata keys in lowercase.

' Set the bucket name via the HOST header.
' In this case, the bucket name is "chilkat.ocean".
rest.Host = "chilkat.ocean.s3.amazonaws.com"

' Send the HEAD request.
success = rest.SendReqNoBody("HEAD","/seahorse.jpg")
If (success <> True) Then
    Debug.WriteLine(rest.LastErrorText)
    Exit Sub
End If


' Read the response header.
Dim responseStatusCode As Integer = rest.ReadResponseHeader()
If (responseStatusCode < 0) Then
    Debug.WriteLine(rest.LastErrorText)
    Exit Sub
End If


Debug.WriteLine("Response status code = " & responseStatusCode)
If (responseStatusCode <> 200) Then
    Debug.WriteLine(rest.ResponseHeader)
    Debug.WriteLine("Object does not exist.")
    Exit Sub
End If


' Show the full response header that was received:
Debug.WriteLine("Response header:")
Debug.WriteLine(rest.ResponseHeader)
Debug.WriteLine("--")

' Here is an example response header:

' 	x-amz-id-2: uS4Flff04M8x5YWajU231TP0ClBL19mMhuyfU5ZVQd6NsUHXVhHK+H3b0sjxY98Fujet1ejhyzk=
' 	x-amz-request-id: 27950009AA8E68AA
' 	Date: Mon, 23 Jan 2017 20:12:58 GMT
' 	Last-Modified: Fri, 20 Jan 2017 00:22:57 GMT
' 	ETag: "a8551f0a5437f43a796fca7623ee9232"
' 	x-amz-meta-species: big-belly seahorse
' 	x-amz-meta-genus: Hippocampus
' 	x-amz-meta-habitat: shallow tropical and temperate waters
' 	Accept-Ranges: bytes
' 	Content-Type: image/jpg
' 	Content-Length: 24388
' 	Server: AmazonS3

' Examine particular response headers (the object metadata headers..)
Debug.WriteLine("x-amz-meta-species: " & rest.ResponseHdrByName("x-amz-meta-species"))
Debug.WriteLine("x-amz-meta-genus: " & rest.ResponseHdrByName("x-amz-meta-genus"))
Debug.WriteLine("x-amz-meta-habitat: " & rest.ResponseHdrByName("x-amz-meta-habitat"))
Debug.WriteLine("--")

' It is possible to iterate over the header fields to find all x-amz-meta* headers
Dim i As Integer = 0
Dim numHeaders As Integer = rest.NumResponseHeaders
Dim sbName As New Chilkat.StringBuilder
While i < numHeaders
    sbName.SetString(rest.ResponseHdrName(i))
    If (sbName.StartsWith("x-amz-meta",False) = True) Then
        Debug.WriteLine(sbName.GetAsString() & ": " & rest.ResponseHdrValue(i))
    End If

    i = i + 1
End While

' The output:

' 	x-amz-meta-species: big-belly seahorse
' 	x-amz-meta-genus: Hippocampus
' 	x-amz-meta-habitat: shallow tropical and temperate waters