(Lianja) 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.

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// 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.
loCrypt = createobject("CkCrypt2")
loCrypt.EncodingMode = "hex"
loCrypt.HashAlgorithm = "sha-256"
lcFileToUploadPath = "qa_data/xml/hamlet.xml"
lcHashStr = loCrypt.HashFileENC(lcFileToUploadPath)

loRest = createobject("CkRest")

// Connect to the Amazon AWS REST server.
llBTls = .T.
lnPort = 443
llBAutoReconnect = .T.
llSuccess = loRest.Connect("s3.amazonaws.com",lnPort,llBTls,llBAutoReconnect)

// ----------------------------------------------------------------------------
// 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.
loAuthAws = createobject("CkAuthAws")
loAuthAws.AccessKey = "AWS_ACCESS_KEY"
loAuthAws.SecretKey = "AWS_SECRET_KEY"
loAuthAws.ServiceName = "s3"
// Provide the pre-computed SHA-256 here:
loAuthAws.PrecomputedSha256 = lcHashStr

llSuccess = 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"

loFileStream = createobject("CkStream")
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 <> .T.) then
    ? loRest.LastErrorText
    release loCrypt
    release loRest
    release loAuthAws
    release loFileStream
    return
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