VB.NET

Streaming Download Large File to the Local Filesystem

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

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 New Chilkat.Rest

' Connect to the Azure Storage Blob Service
Dim bTls As Boolean = True
Dim port As Integer = 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
    Debug.WriteLine(rest.LastErrorText)
    Exit Sub
End If


' Provide Azure Cloud credentials for the REST calls.
Dim azAuth As New Chilkat.AuthAzureStorage
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
    Debug.WriteLine(rest.LastErrorText)
    Exit Sub
End If


' Read the response header.
Dim responseStatusCode As Integer = rest.ReadResponseHeader()
If (responseStatusCode < 0) Then
    Debug.WriteLine(rest.LastErrorText)
    Exit Sub
End If


Debug.WriteLine("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 New Chilkat.Stream

    ' 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
        Debug.WriteLine(rest.LastErrorText)
        Exit Sub
    End If


    Debug.WriteLine("Successfully received the large file.")

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

End If