B4X

Streaming Download Large File to the Local Filesystem

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Downloads a large file in a streaming fashion to the local filesystem. B4X

Dim success As Boolean = False

'  Azure File Service Example: Downloads a large file to the local filesystem using a Chilkat stream.
'  See:  https://docs.microsoft.com/en-us/rest/api/storageservices/get-file

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

Dim rest As ChilkatRest
rest.Initialize("rest")

'  Connect to the Azure Storage Blob Service
Dim bTls As Boolean = True
Dim port As Int = 443
Dim bAutoReconnect As Boolean = True
'  In this example, the storage account name is "chilkat".
success = rest.Connect("chilkat.file.core.windows.net", port, bTls, bAutoReconnect)
If success <> True Then
    Log(rest.LastErrorText)
    Return
End If


'  Provide Azure Cloud credentials for the REST calls.
Dim azAuth As ChilkatAuthAzureStorage
azAuth.Initialize
azAuth.AccessKey = "AZURE_ACCESS_KEY"
'  The account name used here should match the 1st part of the domain passed in the call to Connect (above).
azAuth.Account = "chilkat"
azAuth.Scheme = "SharedKey"
azAuth.Service = "File"
'  This causes the "x-ms-version: 2021-08-06" header to be automatically added.
azAuth.XMsVersion = "2021-08-06"
success = rest.SetAuthAzureStorage(azAuth)

'  Note: The application does not need to explicitly set the following
'  headers: x-ms-date, Authorization.  These headers
'  are automatically set by Chilkat.

'  When streaming a download to the local filesystem or directed elsewhere,
'  the complete HTTP GET operation must be broken into parts.
'  For example, an HTTP GET consists of sending the request, followed by reading the response header,
'  and then finally the response body.  We'll want to read the response header, and then based
'  on the information received (such as success or failure), either read the response body
'  as an error message, or as the file data.

'  Send the HTTP GET request to download the file.
'  The share is named "pip".
success = rest.SendReqNoBody("GET", "/pip/somethingBig.zip")
If success <> True Then
    Log(rest.LastErrorText)
    Return
End If


'  Read the response header.
Dim responseStatusCode As Int = rest.ReadResponseHeader
If responseStatusCode < 0 Then
    Log(rest.LastErrorText)
    Return
End If


Log("Response status code = " & responseStatusCode)

'  We expect a 200 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 Then

    Dim bodyStream As ChilkatStream
    bodyStream.Initialize("bodyStream")

    '  The stream's sink will be a file.
    bodyStream.SinkFile = "qa_output/somethingBig.zip"

    '  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 = rest.ReadRespBodyStream(bodyStream, True)
    If success <> True Then
        Log(rest.LastErrorText)
        Return
    End If


    Log("Successfully received the large file.")

Else
    Dim errResponse As String = rest.ReadRespBodyString
    If rest.LastMethodSuccess <> True Then
        Log(rest.LastErrorText)
    Else
        Log(errResponse)
    End If

End If