B4X

Read S3 Object Metadata of File Already Uploaded to S3

See more Amazon S3 Examples

Demonstrates how to retrieve the metadata from an S3 object.

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.

B4X

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

Dim http As ChilkatHttp
http.Initialize("http")

'  Insert your AWS keys here:
http.AwsAccessKey = "AWS_ACCESS_KEY"
http.AwsSecretKey = "AWS_SECRET_KEY"

Dim bucketName As String = "chilkat.ocean"
Dim objectName As String = "seahorse.jpg"

'  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.

'  A HEAD request can be sent to return the response header without the response body.
'  The S3_FileExists method sends a HEAD request.
'  It can be used to get the response header.
Dim retval As Int = http.S3_FileExists(bucketName, objectName)
If retval < 0 Then
    Log("Failed to check for the S3 object existence")
    Log(http.LastErrorText)
    Return
End If

If retval = 0 Then
    Log("The S3 object does not exist.")
    Return
End If


'  The response header is available in the LastResponseHeader property.
Dim responseHeader As String = http.LastResponseHeader
Log("Response header:")
Log(responseHeader)
Log("--")

'  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

'  HTTP requests and responses are MIME.  For easy parsing, the response header
'  can be loaded into a Chilkat MIME object
Dim mime As ChilkatMime
mime.Initialize

mime.LoadMime(responseHeader)

'  Examine the metadata values:
Log("x-amz-meta-species: " & mime.GetHeaderField("x-amz-meta-species"))
Log("x-amz-meta-genus: " & mime.GetHeaderField("x-amz-meta-genus"))
Log("x-amz-meta-habitat: " & mime.GetHeaderField("x-amz-meta-habitat"))
Log("--")

'  It is possible to iterate over the header fields to find all x-amz-meta* headers
Dim i As Int = 0
Dim numHeaders As Int = mime.NumHeaderFields
Dim sbName As ChilkatStringBuilder
sbName.Initialize
Do While i < numHeaders
    sbName.SetString(mime.GetHeaderFieldName(i))
    If sbName.StartsWith("x-amz-meta", False) = True Then
        Log(sbName.GetAsString & ": " & mime.GetHeaderFieldValue(i))
    End If

    i = i + 1
Loop

'  The output:

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