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DataFlex Examples

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(DataFlex) Read S3 Object Metadata of File Already Uploaded to S3

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.

Chilkat ActiveX Downloads

ActiveX for 32-bit and 64-bit Windows

Use ChilkatAx-9.5.0-win32.pkg

Procedure Test
    Handle hoHttp
    String sBucketName
    String sObjectName
    Integer iRetval
    String sResponseHeader
    Handle hoMime
    Integer i
    Integer iNumHeaders
    Handle hoSbName
    String sTemp1
    String sTemp2
    Boolean bTemp1

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

    Get Create (RefClass(cComChilkatHttp)) To hoHttp
    If (Not(IsComObjectCreated(hoHttp))) Begin
        Send CreateComObject of hoHttp
    End

    //  Insert your AWS keys here:
    Set ComAwsAccessKey Of hoHttp To "AWS_ACCESS_KEY"
    Set ComAwsSecretKey Of hoHttp To "AWS_SECRET_KEY"

    Move "chilkat.ocean" To sBucketName
    Move "seahorse.jpg" To sObjectName

    //  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.
    Get ComS3_FileExists Of hoHttp sBucketName sObjectName To iRetval
    If (iRetval < 0) Begin
        Showln "Failed to check for the S3 object existence"
        Get ComLastErrorText Of hoHttp To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    If (iRetval = 0) Begin
        Showln "The S3 object does not exist."
        Procedure_Return
    End

    //  The response header is available in the LastResponseHeader property.
    Get ComLastResponseHeader Of hoHttp To sResponseHeader
    Showln "Response header:"
    Showln sResponseHeader
    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

    //  HTTP requests and responses are MIME.  For easy parsing, the response header
    //  can be loaded into a Chilkat MIME object
    Get Create (RefClass(cComChilkatMime)) To hoMime
    If (Not(IsComObjectCreated(hoMime))) Begin
        Send CreateComObject of hoMime
    End

    Get ComLoadMime Of hoMime sResponseHeader To iSuccess

    //  Examine the metadata values:
    Get ComGetHeaderField Of hoMime "x-amz-meta-species" To sTemp1
    Showln "x-amz-meta-species: " sTemp1
    Get ComGetHeaderField Of hoMime "x-amz-meta-genus" To sTemp1
    Showln "x-amz-meta-genus: " sTemp1
    Get ComGetHeaderField Of hoMime "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 ComNumHeaderFields Of hoMime To iNumHeaders
    Get Create (RefClass(cComChilkatStringBuilder)) To hoSbName
    If (Not(IsComObjectCreated(hoSbName))) Begin
        Send CreateComObject of hoSbName
    End
    While (i < iNumHeaders)
        Get ComGetHeaderFieldName Of hoMime 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 ComGetHeaderFieldValue Of hoMime 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

 

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