(Visual Basic 6.0) Refresh Access Token on 401 Unauthorized and Retry (Service Account)

See more Google Cloud Storage Examples

Demonstrates how to handle an expired access token error, refresh the token, and retry the request. (In this case, the request is to download an object from Google Cloud Storage.)

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

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

' This example uses a previously obtained access token having permission for the 
' scope "https://www.googleapis.com/auth/cloud-platform"

' In this example, Get Google Cloud Storage OAuth2 Access Token, 
' the service account access token was saved to a text file.  This example fetches the access token from the file..
Dim sbToken As New ChilkatStringBuilder
Dim success As Long
success = sbToken.LoadFile("qa_data/tokens/googleCloudStorageAccessToken.txt","utf-8")
If (success = 0) Then
    Debug.Print "Failed to load access token."
    Exit Sub
End If

Dim http As New ChilkatHttp

http.AuthToken = sbToken.GetAsString()

' Construct a URL to download an object named "starfish.jpg" from the "chilkat-ocean" bucket.
success = http.SetUrlVar("bucket_name","chilkat-ocean")
success = http.SetUrlVar("object_name","starfish.jpg")
Dim url As String
url = "https://www.googleapis.com/storage/v1/b/{$bucket_name}/o/{$object_name}?alt=media"

' If there is an error response, then we didn't actually download the file data,
' but instead we downloaded an error response..
Dim fileData As New ChilkatBinData
success = http.DownloadBd(url,fileData)
Dim responseCode As Long
responseCode = http.LastStatus
If ((success = 0) And (responseCode <> 401)) Then
    Debug.Print http.LastErrorText
    Exit Sub
End If

If (responseCode = 401) Then
    Debug.Print "Received 401 Unauthorized response. Attempting to refresh the access token..."

    ' May be that the access token expired.
    ' Load our JSON key and request a new access token, then retry the original request.
    Dim fac As New CkFileAccess
    Dim jsonKey As String
    jsonKey = fac.ReadEntireTextFile("qa_data/googleApi/ChilkatCloud-13a07a2e8b3f.json","utf-8")
    If (fac.LastMethodSuccess <> 1) Then
        Debug.Print fac.LastErrorText
        Exit Sub
    End If

    Dim gAuth As New ChilkatAuthGoogle
    gAuth.JsonKey = jsonKey
    gAuth.Scope = "https://www.googleapis.com/auth/cloud-platform"
    gAuth.ExpireNumSeconds = 3600
    gAuth.SubEmailAddress = ""

    Dim tlsSock As New ChilkatSocket
    success = tlsSock.Connect("www.googleapis.com",443,1,5000)
    If (success <> 1) Then
        Debug.Print tlsSock.LastErrorText
        Exit Sub
    End If

    success = gAuth.ObtainAccessToken(tlsSock)
    If (success <> 1) Then
        Debug.Print gAuth.LastErrorText
        Exit Sub
    End If

    success = fac.WriteEntireTextFile("qa_data/tokens/googleCloudStorageAccessToken.txt",gAuth.AccessToken,"utf-8",0)

    ' Retry the original request.
    http.AuthToken = gAuth.AccessToken
    success = http.DownloadBd(url,fileData)
    If (success = 0) Then
        Debug.Print http.LastErrorText
        Exit Sub
    End If

End If

If (responseCode <> 200) Then
    ' Get the error response
    Dim sbErrorResponse As New ChilkatStringBuilder
    success = sbErrorResponse.AppendBd(fileData,"utf-8",0,0)
    Debug.Print "Error response code = " & responseCode
    Debug.Print "Error:"
    Debug.Print sbErrorResponse.GetAsString()
    Exit Sub
End If

Debug.Print "Success."

' Save the downloaded data to a file.
success = fileData.WriteFile("qa_output/starfish.jpg")