(DataFlex) 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.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

Use ChilkatAx-win32.pkg

Procedure Test
    Handle hoRest
    Boolean iBTls
    Integer iPort
    Boolean iBAutoReconnect
    Boolean iSuccess
    Variant vAuthAws
    Handle hoAuthAws
    Integer iResponseStatusCode
    Integer i
    Integer iNumHeaders
    Handle hoSbName
    String sTemp1
    String sTemp2
    Boolean bTemp1

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

    Get Create (RefClass(cComChilkatRest)) To hoRest
    If (Not(IsComObjectCreated(hoRest))) Begin
        Send CreateComObject of hoRest
    End

    // Connect to the Amazon AWS REST server using the correct region (in this example, "us-west-2")
    Move True To iBTls
    Move 443 To iPort
    Move True To iBAutoReconnect
    Get ComConnect Of hoRest "s3-us-west-2.amazonaws.com" iPort iBTls iBAutoReconnect To iSuccess

    // Provide AWS credentials for the REST call.
    Get Create (RefClass(cComChilkatAuthAws)) To hoAuthAws
    If (Not(IsComObjectCreated(hoAuthAws))) Begin
        Send CreateComObject of hoAuthAws
    End
    Set ComAccessKey Of hoAuthAws To "AWS_ACCESS_KEY"
    Set ComSecretKey Of hoAuthAws To "AWS_SECRET_KEY"
    Set ComServiceName Of hoAuthAws To "s3"
    // Make sure the Region agrees with the region in the Connect.
    Set ComRegion Of hoAuthAws To "us-west-2"
    Get pvComObject of hoAuthAws to vAuthAws
    Get ComSetAuthAws Of hoRest vAuthAws To iSuccess

    // 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".
    Set ComHost Of hoRest To "chilkat.ocean.s3.amazonaws.com"

    // Send the HEAD request.
    Get ComSendReqNoBody Of hoRest "HEAD" "/seahorse.jpg" To iSuccess
    If (iSuccess <> True) Begin
        Get ComLastErrorText Of hoRest To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Read the response header.
    Get ComReadResponseHeader Of hoRest To iResponseStatusCode
    If (iResponseStatusCode < 0) Begin
        Get ComLastErrorText Of hoRest To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Showln "Response status code = " iResponseStatusCode
    If (iResponseStatusCode <> 200) Begin
        Get ComResponseHeader Of hoRest To sTemp1
        Showln sTemp1
        Showln "Object does not exist."
        Procedure_Return
    End

    // Show the full response header that was received:
    Showln "Response header:"
    Get ComResponseHeader Of hoRest To sTemp1
    Showln sTemp1
    Showln "--"

    // 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..)
    Get ComResponseHdrByName Of hoRest "x-amz-meta-species" To sTemp1
    Showln "x-amz-meta-species: " sTemp1
    Get ComResponseHdrByName Of hoRest "x-amz-meta-genus" To sTemp1
    Showln "x-amz-meta-genus: " sTemp1
    Get ComResponseHdrByName Of hoRest "x-amz-meta-habitat" To sTemp1
    Showln "x-amz-meta-habitat: " sTemp1
    Showln "--"

    // It is possible to iterate over the header fields to find all x-amz-meta* headers
    Move 0 To i
    Get ComNumResponseHeaders Of hoRest To iNumHeaders
    Get Create (RefClass(cComChilkatStringBuilder)) To hoSbName
    If (Not(IsComObjectCreated(hoSbName))) Begin
        Send CreateComObject of hoSbName
    End
    While (i < iNumHeaders)
        Get ComResponseHdrName Of hoRest i To sTemp1
        Get ComSetString Of hoSbName sTemp1 To iSuccess
        Get ComStartsWith Of hoSbName "x-amz-meta" False To bTemp1
        If (bTemp1 = True) Begin
            Get ComGetAsString Of hoSbName To sTemp1
            Get ComResponseHdrValue Of hoRest i To sTemp2
            Showln sTemp1 ": " sTemp2
        End

        Move (i + 1) To i
    Loop

    // The output:

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


End_Procedure