(PureBasic) S3 Resume Download

Suppose an S3 download of a very large file failed for some reason and you have a partial file on disk. Rather than restart the entire download, you wish to download the remaining portion. This example demonstrates how to finish a previously failed download.

Note: This example requires Chilkat v9.5.0.83 or above.

Chilkat PureBasic Module Download Chilkat PureBasic Module

IncludeFile "CkStringBuilder.pb"
IncludeFile "CkAuthAws.pb"
IncludeFile "CkRest.pb"
IncludeFile "CkFileAccess.pb"
IncludeFile "CkStream.pb"

Procedure ChilkatExample()

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

    rest.i = CkRest::ckCreate()
    If rest.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; Connect to the Amazon AWS REST server.
    bTls.i = 1
    port.i = 443
    bAutoReconnect.i = 1
    success.i = CkRest::ckConnect(rest,"s3.amazonaws.com",port,bTls,bAutoReconnect)

    ; ---------------------------------------------------------------------------
    ; 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.
    authAws.i = CkAuthAws::ckCreate()
    If authAws.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkAuthAws::setCkAccessKey(authAws, "AWS_ACCESS_KEY")
    CkAuthAws::setCkSecretKey(authAws, "AWS_SECRET_KEY")
    CkAuthAws::setCkServiceName(authAws, "s3")
    success = CkRest::ckSetAuthAws(rest,authAws)

    ; Set the bucket name via the HOST header.
    ; In this case, the bucket name is "chilkat100".
    CkRest::setCkHost(rest, "chilkat100.s3.amazonaws.com")

    ; We want to continue downloading a file.
    ; The relative local filepath of our previously partially downoaded file is: qa_output/hamlet.xml
    ; Let's find out how many bytes are already downloaded.
    fac.i = CkFileAccess::ckCreate()
    If fac.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    localFilepath.s = "qa_output/hamlet.xml"
    ; Note: The FileSize method returns a signed 32-bit integer.  If the file is potentially larger than 2GB, call FileSizeStr instead to return
    ; the size of the file as a string, then convert to an integer value.
    sz.i = CkFileAccess::ckFileSize(fac,localFilepath)
    If sz > 0
        Debug "sz = " + Str(sz)

        ; If the sz equals 42375 bytes, then we want to add a Range header that looks like this:
        ; Range: bytes=42375-
        sbRange.i = CkStringBuilder::ckCreate()
        If sbRange.i = 0
            Debug "Failed to create object."
            ProcedureReturn
        EndIf

        CkStringBuilder::ckAppend(sbRange,"bytes=")
        CkStringBuilder::ckAppendInt(sbRange,sz)
        CkStringBuilder::ckAppend(sbRange,"-")
        CkRest::ckAddHeader(rest,"Range",CkStringBuilder::ckGetAsString(sbRange))
        Debug "Added Range: " + CkStringBuilder::ckGetAsString(sbRange)
    EndIf

    ; Send the request to download the remainder of the file.
    success = CkRest::ckSendReqNoBody(rest,"GET","/hamlet.xml")
    If success <> 1
        Debug CkRest::ckLastErrorText(rest)
        CkRest::ckDispose(rest)
        CkAuthAws::ckDispose(authAws)
        CkFileAccess::ckDispose(fac)
        CkStringBuilder::ckDispose(sbRange)
        ProcedureReturn
    EndIf

    ; Read the response header.
    responseStatusCode.i = CkRest::ckReadResponseHeader(rest)
    If responseStatusCode < 0
        Debug CkRest::ckLastErrorText(rest)
        CkRest::ckDispose(rest)
        CkAuthAws::ckDispose(authAws)
        CkFileAccess::ckDispose(fac)
        CkStringBuilder::ckDispose(sbRange)
        ProcedureReturn
    EndIf

    Debug "Response status code = " + Str(responseStatusCode)

    ; We expect a 200 or 206 response status if the file data is coming.
    ; Otherwise, we'll get a string response body with an error message(or no response body).
    If (responseStatusCode = 200) OR (responseStatusCode = 206)

        bodyStream.i = CkStream::ckCreate()
        If bodyStream.i = 0
            Debug "Failed to create object."
            ProcedureReturn
        EndIf

        ; The stream's sink will be a file.
        ; We will append to the file..
        CkStream::setCkSinkFile(bodyStream, localFilepath)

        ; Indicate that we wish to append to the output file.
        ; The SinkFileAppend property was added in Chilkat v9.50.83
        CkStream::setCkSinkFileAppend(bodyStream, 1)

        ; Read the response body to the stream.  Given that we've
        ; set the stream's sink to a file, it will stream directly
        ; to the file.
        success = CkRest::ckReadRespBodyStream(rest,bodyStream,1)
        If success <> 1
            Debug CkRest::ckLastErrorText(rest)
            CkRest::ckDispose(rest)
            CkAuthAws::ckDispose(authAws)
            CkFileAccess::ckDispose(fac)
            CkStringBuilder::ckDispose(sbRange)
            CkStream::ckDispose(bodyStream)
            ProcedureReturn
        EndIf

        Debug "Successfully downloaded the file."

    Else
        errResponse.s = CkRest::ckReadRespBodyString(rest)
        If CkRest::ckLastMethodSuccess(rest) <> 1
            Debug CkRest::ckLastErrorText(rest)
        Else
            Debug errResponse
        EndIf

    EndIf



    CkRest::ckDispose(rest)
    CkAuthAws::ckDispose(authAws)
    CkFileAccess::ckDispose(fac)
    CkStringBuilder::ckDispose(sbRange)
    CkStream::ckDispose(bodyStream)


    ProcedureReturn
EndProcedure