(Visual FoxPro) AWS S3 File Streaming Upload

Demonstrates how to do a streaming upload from a file to the AWS S3 storage service. The AWS authorization presents some difficulties when the REST request body is to be streamed from a file (or from some other source). The issue is that the SHA-256 hash of the file data must be calculated. There are only two possible ways to do this: (1) stream the file into memory in its entirety and calculate the SHA-256 hash prior to uploading, or (2) pre-calculate the SHA-256 in a streaming fashion, and then provide it to the AWS authentication object.

If the application does NOT pre-compute the SHA-256, then Chilkat (internally) is forced to stream into memory, calculate the SHA-256, and then upload from the in-memory copy of the file.

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

LOCAL loCrypt
LOCAL lcFileToUploadPath
LOCAL lcHashStr
LOCAL loRest
LOCAL lnBTls
LOCAL lnPort
LOCAL lnBAutoReconnect
LOCAL lnSuccess
LOCAL loAuthAws
LOCAL loFileStream
LOCAL lcResponseStr

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

* This first part is optional.  AWS authentication requires
* the SHA-256 hash of the request body (i.e. the contents of the file
* to be uploaded).  We can choose to pre-calculate the SHA-256 in a streaming fashion
* and then provide it to the authenticator object.  This way, if the file is
* extremely large, it never needs to completely reside in memory.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Crypt2')
loCrypt = CreateObject('Chilkat.Crypt2')
loCrypt.EncodingMode = "hex"
loCrypt.HashAlgorithm = "sha-256"
lcFileToUploadPath = "qa_data/xml/hamlet.xml"
lcHashStr = loCrypt.HashFileENC(lcFileToUploadPath)

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Rest')
loRest = CreateObject('Chilkat.Rest')

* Connect to the Amazon AWS REST server.
lnBTls = 1
lnPort = 443
lnBAutoReconnect = 1
lnSuccess = loRest.Connect("s3.amazonaws.com",lnPort,lnBTls,lnBAutoReconnect)

* ----------------------------------------------------------------------------
* Important: For buckets created in regions outside us-east-1,
* there are three important changes that need to be made.
* See Working with S3 Buckets in Non-us-east-1 Regions for the details.
* ----------------------------------------------------------------------------

* Provide AWS credentials for the REST call.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.AuthAws')
loAuthAws = CreateObject('Chilkat.AuthAws')
loAuthAws.AccessKey = "AWS_ACCESS_KEY"
loAuthAws.SecretKey = "AWS_SECRET_KEY"
loAuthAws.ServiceName = "s3"
* Provide the pre-computed SHA-256 here:
loAuthAws.PrecomputedSha256 = lcHashStr

lnSuccess = loRest.SetAuthAws(loAuthAws)

* Set the bucket name via the HOST header.
* In this case, the bucket name is "chilkat100".
loRest.Host = "chilkat100.s3.amazonaws.com"

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Stream')
loFileStream = CreateObject('Chilkat.Stream')
loFileStream.SourceFile = lcFileToUploadPath

* Upload to the S3 Storage service.
* If the application provided the SHA-256 hash of the file contents (as shown above)
* then file is streamed and never has to completely reside in memory.
* If the application did NOT provide the SHA-256, then Chilkat will (internally) 
* load the entire file into memory, calculate the SHA-256, and then upload.
lcResponseStr = loRest.FullRequestStream("PUT","/hamlet.xml",loFileStream)
IF (loRest.LastMethodSuccess <> 1) THEN
    ? loRest.LastErrorText
    RELEASE loCrypt
    RELEASE loRest
    RELEASE loAuthAws
    RELEASE loFileStream
    CANCEL
ENDIF

* When successful, the S3 Storage service will respond with a 200 response code,
* with an XML body.  
IF (loRest.ResponseStatusCode = 200) THEN
    ? lcResponseStr
    ? "File uploaded."
ELSE
    * Examine the request/response to see what happened.
    ? "response status code = " + STR(loRest.ResponseStatusCode)
    ? "response status text = " + loRest.ResponseStatusText
    ? "response header: " + loRest.ResponseHeader
    ? "response body: " + lcResponseStr
    ? "---"
    ? "LastRequestStartLine: " + loRest.LastRequestStartLine
    ? "LastRequestHeader: " + loRest.LastRequestHeader
ENDIF

RELEASE loCrypt
RELEASE loRest
RELEASE loAuthAws
RELEASE loFileStream